Reprocessing and

Reuse of Street Waste Solids


Report No. IBP-97-5


Table of Contents

 

Executive Summary                                                                                                   1

 

1.      Introduction                                                                                                          4

1.1 Project Overview                                                                                                   4

1.2 Problem Statement                                                                                     4

1.3 Reuse Alternatives                                                                                      4

1.4 Proposed Solution                                                                                                  6

1.5 Project Objectives                                                                                                  6

1.6 Previous Studies                                                                                                     6

 

2.     Street Waste Characterization                                                                            9

2.1 Preliminary Testing of Street Waste Solids                                                   9

2.2 Conclusions                                                                                                            9

 

3.   Separation Alternatives                                                                                       10

3.1 Introduction                                                                                                            10

3.2 Liquid Separation                                                                                                   10

3.3 Vibratory Separation                                                                                              11

3.4 Air Separation                                                                                                        12

3.5 Mechanical Screening                                                                                             13

3.6 Combustion                                                                                                            15

3.7 Component Equipment for Material Separation                                                       15

3.7.1    Log Washer                                                                                                     15

3.7.2    Fine Material Screw Washer                                                                             16

3.7.3    Dairy Manure/Sand Separator                                                                          17

3.7.4    Vibratory Air Knife Separator                                                               18

3.8 Further Discussion of Separation Alternatives                                                          19

3.8.1 Mechanical Screening                                                                                          19

3.8.2 Wet System Separation                                                                                       20

3.8.3 Dry System Separation                                                                                        21

3.8.4 Combustion                                                                                                         22

3.9 Conclusions                                                                                                            23

3.10 Recommendations                                                                                                25

4.     Economic Evaluation                                                                                           27

4.1 Basis for Economic Evaluation                                                                                27

4.2 Discussion of Processing Costs                                                                               28

4.2.1 Existing Aggregate Wash Plant and Concrete Batch Plant                         28

4.2.2 Dedicated, Private Receiving and Processing Site                                     29

4.2.3 Dedicated Generator Processing Site                                                                   30

4.2.4 Mobile, Private Processing Equipment                                                                  32

4.2.5 Existing Asphalt Plant to Burn Organics and Hydrocarbons                                   32

4.3 Conclusions                                                                                                            32

 

5.   Full Scale Materials Separation Test                                                                 34

5.1 Overview                                                                                                               34

5.2 Pre-Screening                                                                                                         35

5.3 Screen and Wash Separation Process                                                                     35

5.4 Soil and Water Sampling                                                                                         37

5.5 Observations and Conclusions                                                                                38

 

6.   Full Scale Test - Analytical Test Results                                                           40

6.1 Soil Samples                                                                                                           40

6.2 Water Samples                                                                                                       41

6.3 Conclusions                                                                                                            42

 

7.     Summary of Conclusions                                                                         43

7.1 Previous Studies                                                                                               43

7.2 Street Waste Characterization                                                                           43

7.3 Separation Alternatives                                                                         44

7.4 Economic Evaluation                                                                                         45

7.5 Full Scale Materials Separation Test                                                                  46

7.6 Full Scale Test - Analytical Test Results                                                            47

 

8.   Acknowledgments                                                                                                48

 

List of Tables

Table 1 - Existing Aggregate Wash Plant, Tip Fee Estimates

Table 2 - Dedicated, Private Receiving and Processing Site, Tip Fee Estimates

Table 3 - Dedicated Generator Processing Site, New and Used Equipment Prices Table 4

Table 4 - Dedicated Generator Processing Site, Operating Cost Estimates

Table 5 - Mobile, Private Processing Cost Estimates

Table 6 - Summary Cost Estimates

Table 7 - Estimated Proportion of Separated Materials

Table 8 - Soil Sample Description

Table 9 - Water Sample Description

Table 10 - Summary Cost Estimates

 

Appendices

 

Appendix A - Snohomish Health District Policy Statement Regarding Street Waste Solids          Recycling and Disposal.

 

Appendix B - Summary and Conclusions (Section 5) and the List of References

                       (Section 6), from Snohomish County Street Waste Characterization        (Landau Associates, December 1995).

 

Appendix C - Snohomish County Public Works, Road Maintenance Division, Laboratory Test Results and Sweepings Testing Interim Report.

 

Appendix D - Eco-Block Manufacturing as an Alternative Catch Basin Waste Disposal Method, Kitsap County Public Works, Surface and Stormwater Management Program, November 13, 1996

 

Appendix E - General Kinematics Conceptual Drawing of Prototype Street Solids         Separation Equipment, “Vibratory Air Knife Separator”.

 

Appendix F - Land Technologies, Inc. Schematic Drawing of Prototype Street Solids    Separation Equipment.

 

 

 


Executive Summary

 

In 1993, the Washington State Department of Ecology (Ecology) defined street sweepings and vactor grit as municipal solid wastes.  This action has resulted in severe economic impact on public jurisdictions responsible for collection and disposal of these materials.

 

Solids collected during the cleaning of storm sewers, streets and drainage ditches (collectively referred to as “Street Waste Solids”) fall into the state definition of solid waste established under RCW 70.95.030.  Street Waste Solids typically fail Model Toxics Control Act standards for total petroleum hydrocarbon levels.  A significant problem in determining the contaminant concentrations of the street waste solids is the presence of vegetative matter, which causes false positive analytical test results.  As such, both public and private generators of these materials are disposing of this material in landfills at considerable expense to the tax payer and private industry.

 

The Snohomish Health District (SHD), in accordance with the Department of Ecology’s waste reduction and recycling objectives, is promoting recycling options for street waste solids which protect both public health and the environment.  In January 1995, the SHD issued a Policy Statement Regarding Street Waste Solids Recycling and Disposal (Policy), in which they define classes of materials, and reuse options for each class. The Policy states that all potential end uses “would first require the removal of litter and vegetative matter”.

 

The solution to this significant waste disposal / resource utilization problem is to economically process these materials to remove contaminating litter and organics, and to separate the mineral constituents into specified size fractions (i.e., fine sand, coarse sand and gravel) to produce useable and/or marketable end products.  The solution also includes selecting a processing technology that is economical and environmentally compatible for this approach to be viable.

 

This report discusses five alternative methods of material separation, including liquid, vibratory, and air separation, mechanical screening, and combustion. 

 

Considering the available technologies, five alternative approaches for separating and utilizing the street waste solids are recommended.  These are discussed in their order of preference.

 

The first recommendation is to haul street wastes to existing aggregate wash plants equipped with wood removal equipment, and blend these materials with daily process materials for use as aggregate in concrete.

 

The second is to seek an interested party (public or private) to develop a dedicated processing site for the street waste solids.  The separation process may be a closed wash system for all the street waste or a dry system with facilities to condition the vactor waste before processing.

 

The third alternative would be for individual generators to purchase equipment to process street waste for re-use at their facility.

 

The fourth would be to seek an interested party to develop a mobile processing plant.  This option would reduce handling and hauling costs and leave sand and aggregate products for re-use by the waste generator.  The waste generator would also be responsible for disposal of unsuitable materials.

 

The fifth and final option would be to haul the street waste solids to an asphalt plant retro-fitted to burn organics and hydrocarbons.

 

For the five alternatives considered in the economic evaluation, the range of costs to process the street waste solids materials are summarized in the following table.

 

Alternative Description

 

Low cost/ton

High cost/ton

Existing Aggregate Wash Plant and Concrete Batch Plant

$5

$45

Dedicated, Private Receiving and Processing Site

25

60

Dedicated Generator Processing Site

17

25

Mobile, Private Processing Equipment

25

50

Existing Asphalt Plant to Burn Organics and Hydrocarbons

45

75

 

 

A full scale separation test was conducted at the Smokey Point Concrete plant in Arlington, Washington.  This test successfully demonstrated that organics and fines can be effectively removed from the mineral sand and gravel fraction.

The breakdown of the constituents were visually estimated as follows:

 

Plus 1-inch                                                                   10 percent of total pile.

Of the remaining 90 percent that passed the 1” screen:

1 to 5/8-inch                                                                 10 percent

5/8 to ¼-inch                                                                15 percent

Coarse Sand                                                                35 percent

Fine Sand                                                                     35 percent

Organics (sticks, pine needles & leaves) and Silt              5 percent

Because of the heavy load of organics in the street solids materials, it would be more effective to combine these materials with other source materials prior to screening and washing.  In this way, the percentage of organics would be reduced in the process materials, and the efficiency of the total system would be increased.

 

The concentrations of heavy oil in the soil samples ranged from 230 ppm to 380 ppm, which characterizes this material as a Class B soil, in accordance with the SHD Policy.  Concentrations of diesel in all liquid samples were well below reportable levels.


1.  Introduction

 

1.1       Project Overview

 

In 1993, the Washington State Department of Ecology (Ecology) defined street sweepings and vactor grit as municipal solid wastes.  This action has resulted in severe economic impact on public jurisdictions responsible for collection and disposal of these materials. 

 

1.2       Problem Statement

 

 Solids collected during the cleaning of storm sewers, streets and drainage ditches (collectively referred to as “Street Waste Solids”) fall into the state definition of solid waste established under RCW 70.95.030.  Street Waste Solids typically fail Model Toxics Control Act (MTCA) standards for total petroleum hydrocarbon levels.  A significant problem in determining the contaminant concentrations of the street waste solids is the presence of vegetative matter, which causes false positive analytical test results.  As such, both public and private generators of these materials are disposing of this material in landfills at considerable expense to the tax payer and private industry.  The cost for landfill disposal of Snohomish County street sweepings and vactor grit waste is $89 per ton.  As of January 1996, Snohomish County had accumulated an estimated 1,600 cubic yards (~2,500 tons) of street sweepings, representing a total potential liability of $222,500.  In addition to street sweepings, the cost for disposal of vactor grit exceeded $66,500 in 1995.

 

1.3       Reuse Alternatives

 

The Snohomish Health District (SHD), in accordance with the Department of Ecology’s waste reduction and recycling objectives, is promoting recycling options for street waste solids which protect both public health and the environment.  In January 1995, the SHD issued a Policy Statement Regarding Street Waste Solids Recycling and Disposal (Policy), presented as Appendix A. 

 

In the Policy, Street Waste Solids are divided into two categories, including Class A and Class B materials, which are determined by maximum contaminant levels.  The two material classes have identified potential end uses, including:

 

Class A

 

·        Encapsulated soil fills and pipe bedding which are not likely to result in contamination of ground or surface water or lead to other potential environmental or public health problems.

·        Reuse as street traction sand.

 

Class B

 

·        Pre-fabricated concrete manufacturing, Portland cement manufacturing and asphalt manufacturing, provided a recycling permit application is submitted and approved by the SHD.

·        Treatment at a contaminated soil treatment facility.

·        Daily cover of fill in a permitted municipal solid waste landfill.

 

The Policy states that all potential end uses “would first require the removal of litter and vegetative matter”.  In addition, “all recycling end-uses must be conducted in compliance with specifications required by federal, state or local regulations, or specifications required by a facility, manufacturer or vendor accepting the street solids for processing or recycling”.

 


1.4       Proposed Solution

 

The solution to this significant waste disposal / resource utilization problem is to economically process these materials to remove contaminating litter and organics, and to separate the mineral constituents into specified size fractions (i.e., fine sand, coarse sand and gravel) to produce useable and/or marketable end products.  The solution also includes selecting a processing technology that is economical and environmentally compatible, for this approach to be viable.  As part of the solution, a sampling and laboratory testing program was implemented to establish whether the processed materials meet the SHD’s Class A or Class B criteria. 

 

1.5       Project Objectives

 

The objectives of this project were three-fold:

 

·        Evaluate existing, cost effective technologies for physically separating street sweepings and vactor grit constituents (sand and gravel, from organics, silt, and litter);

·        Determine the level of contamination of the separated mineral fraction, with regard to the SHD reuse criteria; and

·        Evaluate viable reuse alternatives for the sand and gravel components which contribute to protection of human health and the environment, and reduce landfill quantities and costs.

 

1.6       Previous Studies

 

Numerous studies have been completed by Ecology and local municipalities to evaluate the character of street waste solids, and to develop analytical methods for resolving the problems associated with false positive laboratory test results. 

 

Of these studies, the most recent was conducted by Landau Associates, Inc. for Snohomish County and the City of Everett.  The final report for this study, entitled Snohomish County Street Waste Characterization (December 1995), provides the following conclusions:

 

·        Organic (plant) material contributed to a false positive result with each of the three total petroleum hydrocarbon (TPH) analysis methods used;

·        Sources likely to contribute to TPH concentrations in street waste include organic (plant) material, automobile and truck tires, asphalt paving materials, and motor oil and lubricants from cars and trucks.  Relative amounts of contribution to the TPH concentration were not identified.

·        Street waste is a solid waste and is typically not a dangerous waste, and Ecology and the SHD regulations support reuse of street waste.

·        Chemical analysis results for metals do not exceed MTCA Method A soil cleanup levels or SHD threshold criteria, and do not limit reuse options.

·        Chemical test results for CPAH exceed SHD threshold criteria and may limit management options to those associated with Class B material.

 

The Summary and Conclusions (Section 5) and the List of References (Section 6) from the Landau Associates report are presented as Appendix B.

 

Prior to this project, samples of street sweepings and vactor grit were tested by Snohomish County to determine the presence of contaminants and classify material for reuse.  Handling, storage and processing evaluations were done to classify the street sweepings using the criteria in the SHD Policy.  Six samples were evaluated for gradation by sieve analysis and twenty three samples were selected for analytical testing.  In all cases, the test results indicated that total metals, PAH’s, PCB’s and BTEX were below detection limits.  TPH results showed concentrations from 85 - 620 parts per million, after silica gel and acid cleanup step on the extracts.  Summary tables of these test results are presented in Appendix C.

 

Vactor grit land use classification study of 15 locations defined a baseline for classification using the TPH 418.1 test, however that test has subsequently been replaced with the TPHDx with cleanup, due to the false positives in samples from organics.  ICP metals tests were run on these samples for the seven basic reference metals with only two of the 115 analytical results exceeding the acceptable Petroleum Contaminated Soils (PCS) threshold.  No PAH results exceeded the thresholds.

 

The WTPH-D extended method with Silica Gel and Acid Wash modification, per Washington Ecology Laboratory, is the current preferred method for testing street wastes.  Multiple test sample results have substantiated that this procedure eliminated about 85 percent of the false positives caused by organics in the samples.

 

Three other prototype tests have been evaluated by Snohomish County Road Maintenance using screened and tested street sweepings.

 

1.     Composting of high organic content material is currently being evaluated.

2.     Use of street sweeping solids for top dressing on reclamation slopes, as described in the Snohomish County Public Works Road Maintenance Division Sweepings Testing Interim Report, presented as Appendix C.

3.     Encapsulation of material in precast concrete products, even with fine organics achieves satisfactory results.  Eco-Block manufacturing by Kitsap County Public Works has been successful, as discussed in a paper by this title, presented in
Appendix D.

 

 

 


2.  Street Waste Characterization

 

2.1       Preliminary Testing of Street Waste Solids

 

At the outset of this project, preliminary laboratory tests were conducted on one composite sample of dry street sweeping material.  The sample was first screened into size fractions using US Standard sieves, and then each size range was further separated into mineral and organic fractions using a vacuum line to pull off the lighter organic materials.  The organic material (Sample SS-9 in Table 1) showed values for heavy oil that exceeded the reportable level.  These results may in part be indicative of the false positives derived when testing organic materials.

 

Of the mineral components, the initial acid clean-up test results also showed that the 3/8-inch plus fraction (Sample SS-10) slightly exceeded the heavy oil limit while the fine sand (Sample SS-11) was under the reportable level.  Retesting of the 3/8-inch fraction (Sample SS-10A) showed that this material was also under the reportable level.

 

2.2 Conclusions

 

Given these preliminary test results, the separated mineral fraction could be used for any of the Class A and Class B applications.  In the event that future samples showed heavy oil concentrations exceeding the 200 ppm criteria, then these materials would be restricted to Class B reuse alternatives.

 

 


3.  Separation Alternatives

 

3.1       Introduction

 

There are a wide array of material separation and handling technologies available in heavy industry for processing highly variable solid materials. Street waste solids consist of comparatively dry street sweepings and wet vactor grit, each with seasonally variable quantities of organics.  Separation of these highly variable waste materials could be accomplished by a combination of mechanical separation by size and density with effective use of a liquid (water), vibration, air flow, and mechanical screening.  Another method of separation is by use of heat, which generally causes a conversion of at least one of the components. In practice, combinations of the above technologies are often used to process and separate common waste products.  Each of these basic methods, along with the several specific technologies, are discussed in the following sections.

 

3.2       Liquid Separation

 

Historically, liquid separation was the first method commonly used for separating combined materials where individual components have varying particle density.  Natural geologic processes demonstrate the power and effectiveness of liquid separation.  For example, in a marine environment, where water motion often ranges from highly turbulent to quiescent, a well graded mix of materials can be effectively separated into the separate constituents, including boulders, cobbles, gravel, sand, silt and clay materials that settle, and organics which float.

 

Numerous mechanical systems have been developed that perform the same function as natural liquid separation processes to separate a wide range of materials.  For example, water has been used in numerous types of float tanks designed to separate rock used in log handling operations from bark and wood that falls off the logs and intermixes with the rock.  By theory, the rock will sink to the bottom of the tank and the wood should float off the top.  Complications arise when saturated wood sinks along with the rock.  Various methods have been devised to increase the “floatability” of the wood, usually by use of upstream currents or jets.  These “float tanks” work well when the wood is dry and floatable.

 

3.3       Vibratory Separation

 

Material on a vibrating conveyor is said to be “alive” and moves independently of the conveying medium, unlike other types of conveyors where the material is static and the conveying medium moves.  This characteristic provides a solution to many difficult materials handling and processing applications with highly varied materials, including street waste solids.

 

The separation equipment can provide a range of motion, from an aggressive tossing action to a gentle sliding motion.  This range is determined by the adjustable combination of amplitude, total movement of the material carrying deck, frequency, and the number of cycles of motion for a given time period, together with the angle at which the resulting force is applied. 

 

In addition to conveying materials, the vibratory action has the effect of stratifying the materials into layers, wherein the materials with greater density “sift” to the bottom and the lighter density materials “float” to the top.  To a lesser degree, the vibratory action also sorts by size, wherein two materials with roughly the same density will sort out with the finer material beneath the coarser. 

 

Vibratory conveyance and sorting systems are often used in conjunction with air separation systems.  Common in agriculture, is the use of slanted vibratory tables.  The particles will stratify horizontally, a mechanical split can be made along the light/heavy line sending each classification a different direction.  More effective is to use an airstream to blow away the lighter fraction after it has been separated from the bulk of the heavier fraction.

 

3.4             Air Separation

 

Air separation systems take advantage of differences in material density, particle size and aerodynamic characteristics to separate mixed materials into component parts.  For example, it would be an easy matter to separate lead shot from feathers using a stream of air.  Similarly, rock, sand and wood can also be separated because each component responds differently to a stream of high pressure air. 

 

A steady stream of air, combined with vibration, has been used to stratify the material in preparation for separation.  This is often followed by a high pressure, linear stream of air from a device known commonly as an air knife.  This type of vibrating / pneumatic classification equipment is used extensively in waste recovery industries to process various materials including bio-mass fuels, auto shredder fluff, construction/demolition waste, scrap processing and tire recycling.

 

The above described air separation equipment is very specialized and is generally used on materials with a size range varying from ½ inch to 8 inches.  Cyclones are commonly used in gas/solid separation of small “dust” like particles from an air stream.  Basically, a particulate-laden air stream is mechanically forced into a cone shaped cylinder, specifically designed for each type of gas/solid mixture, the airstream forms a high velocity vortex and centrifugal force hurls the denser particles toward the cyclone walls. The denser particles spiral downward into a collection receptacle and the lighter fraction, generally the gas, is exhausted from the cyclone’s outlet.  A properly designed  cyclone can remove up to 99.9% of the solids from an air stream.  Cyclones can be used in sets and designed to separate multiple particles in a gas stream by density and size before exhausting a clean gas stream.

 

3.5       Mechanical Screening

 

Mechanical screening is another common method of classifying materials, primarily by size.  Screening systems rely on gravity for the flow of material, and can consist of single screens or sets of multiple screens with varying opening sizes.  In all cases, coarser material is retained on the screen as finer material passes through the screen.  The separated material typically exits the screen at different points and is conveyed away from the equipment for separate discharge and handling.

 

There are numerous types and configurations of screens, with the three predominant types being the vibratory deck screen, the trommel screen, and the disc screen.  The vibratory deck screen typically consists of a feed hopper that meters the material onto a conveyor that in turn feeds a uniform stream of material onto the vibrating set of screens.  The feed hopper is commonly equipped with a “grizzly” or multiple set of parallel bars designed to separate the very large material.  A vibratory deck screen commonly separates materials into three or four size components.

 

Vibrating deck screens that use “cascading fingers” are somewhat more effective than a grid screen but still will not remove adhered fines effectively nor will they break up agglomerated particles.  The fingers will collect organic strings at the ends of the runs and need to be shut down and cleaned periodically as these strings build up.  This cleaning has to be done by hand and the shut down stops production

 

A trommel screen consists of a gently sloping, cylindrical screen that rotates.  The material is fed into the trommel screen using a metering feed hopper and conveyor, similar to that of the vibratory deck screen.  As the material is tossed across the screen surface, the fines pass through onto a return conveyor for side discharge, and the coarse materials (“overs”) exit the end of the screen.   Some trommels have two screen sizes, with the larger screen located near the discharge end.  In this case, the two screened materials are generally allowed to fall into separate bins beneath the screen for removal using a front end loader.

 

The trommel is probably the most effective piece of screening equipment that can process and condition wet material for further separation. With lifting flights installed in the screen, material will be lifted, turned and dropped onto the effective screen surface, breaking agglomerated chunks and jarring free adhered particles.  Chains have been installed in the screening chamber to further breakup and break free agglomerated and adhered particles into free particulates for clean size separation.  The trommel slope can be easily adjusted so as to increase retention and exposure to the screen surface, thus cleaning the oversize waste material.  The trommel is the recommended sizing and preconditioning screen for use with the street solids, especially vactor waste.

 

Disc screens, or “star” screens, are also effective for separating organic laden and somewhat cohesive materials.  Rapidly rotating discs lift and drop materials with an aggressive rolling action that breaks up cemented or adhered materials.  This violent action exposes more surface to the screening aspect, and since every disc is rotating, it is self cleaning.

 

The primary disadvantage with the vibratory deck screen is a tendency for the screen decks to clog up, or blind, with fine and damp material that adheres to the screen.  Several attempts have been made to equip these screens with a self-cleaning mechanism, but short of stopping the process and brushing the screen clean, none have worked with organic or cohesive materials. The flat deck vibratory screen is not very effective on materials with a high organic content or on particles that have high cohesiveness. 

 

This problem is somewhat overcome with the trommel screen. As a rotating cylinder, brushes can be placed on the high side of the screen and the brushes rotate as the trommel rotates. The bristles penetrate the screen openings and remove the fines thereby maintaining the full screen-opening dimension as it passes under the material in the effective screen area.

 

The disk screen is commonly used in the waste industry, as it has better production rates than a trommel.  The oversize, which is usually the waste, is cleaner with little lost “product”. The star screen is usually equipped with polyurethane discs that would be subject to excessive wear with the aggregate materials.  The star screen is very effective with organic materials where the medium is not as abrasive.  The disc screen is not as simple mechanically as the trommel, therefore maintenance can be considerably higher.

 

3.6       Combustion

 

When components of a mixed particle stream have different combustion temperatures, with the desired “product” having the highest, the undesired product can be burnt off leaving the desired product.  Specific to the street waste material, both the undesired hydrocarbons and the organics can be vaporized, leaving a relatively clean aggregate material. 

 

Several asphalt plants have retrofitted their plants to receive hydrocarbon laden materials.  With the street wastes, this type of processing could fit, since the aggregate product left after processing is ready for use in asphalt.  The limiting factor with this separation process is the cost.  Facilities actively receiving this type of material are charging about $40 to $50 per ton.  In addition, the hot embers from the organic fraction have been reported to cause problems with the bag houses which are susceptible to fire.

 

3.7       Component Equipment for Material Separation

 

3.7.1    Log Washer

 

A log washer is a liquid separation device that operates with sets of rotating paddles mounted on a shaft, combined with high-pressure water jets.  The name of this equipment is a carry over from late nineteenth century practices when paddles were affixed to logs that rotated, thereby causing the desired agitation of the water and materials to be separated.  The technology has advanced significantly since the turn of the century, and is used widely for washing gravel, cemented aggregates, limestone, phosphate and various ores.  Nevertheless, the shaft to which the paddles are bolted is still referred to as “the log”.

 

Log washers commonly provide from 80 to 125 tons per hour capacity when washing average natural gravel up to 4-inches in size.  Capacities are reduced for washing material that is crushed or angular since this material does not move as freely as round or natural aggregate.  In general, the capacity also varies with the percent and tenacity of fines to be removed.

 

Log washers range in size from small units measuring 36-inches by 25-feet to larger units measuring 46-inches by 35-feet.  Water requirements range from 75 to 150 gallons per minute (gpm) for the smaller units up to 300 gpm for the larger units.  In all cases, the water jet pressure is on the order of 75 pounds per square inch (psi).  Horsepower (HP) requirements range from 60 to 75 HP for the smaller units up to 150 to 200 HP for the larger units.

 

3.7.2    Fine Material Screw Washer

 

A screw washer consists of a gently sloping, continuous helical screw, partially submerged in an elongated tank, or “washer box”.  A feed hopper is located at the low end of the device and receives a liquid slurry of silty and fine granular material.  This method of separation relies on low energy ( i.e., minimal turbulence) to allow the mineral fraction to settle to the bottom of the washer box.  The curvature of the rotating screw flights conforms to the curved section of the washer box to efficiently convey, wash the sand particles, and direct the water away from the sand to the opposite side of the washer box where a drainage channel is designed for quick removal of water from the dry deck area. 

 

Water manifolds and adjusting weirs in the large pool area at the feed end of the screw washer enable the operator to adjust the amount of fine sand required in the end product.  The classification of fines in this manner may be sufficient to meet product specifications without prior classification in a sand classifying tank.

 

The principal working component of the fine material screw washer is an extra heavy steel pipe shaft with continuous spiral steel screw flights welded to the pipe shaft.  The flights are typically equipped with renewable, wear-resistant polyurethane shoes.  At the drive end, a flange on the screw shaft is bolted to a mating flange on the stub shaft.  The screw shaft at the feed end is attached to the submerged bearing shaft.  These flanges permit easy removal of the entire screw from the washer box.

 

Screw washers come in single and double screw configuration.  A single screw model ranges in size from 36-inches by 24-feet up to 72-inches by 36-feet.  The double screw ranges from 36-inches by 24-feet, to 72-inches by 38-feet.  The capacity of this equipment ranges from 35 to 475 tons per hour (tph) for the single screw washer and 210 to 950 tph for the double screw washer.   Horsepower requirements range from 5 to 75 HP for the single screw and from 2 times 15 HP to 2 times 75 HP for the double screw.

 

3.7.3    Dairy Manure/Sand Separator

 

The McLanahan Sand/Manure Separator removes bedding sand from dairy manure prior to long term storage of the manure fraction. Sand / manure separation is a liquid (manure slurry) based process that relies on turbulent water action to “flush” the organic materials out of the sand matrix, and allow the clean sand to be removed from the apparatus with a screw conveyor.  Dilution water is used with this system, however the water is recycled.  The amount of organic manure solids remaining in the recovered sand is reported to be minimal, and the manure fraction contains a minute amount of only the finest sand particles.

 

This separation technology is new, with the first of the full scale proto-type models only recently installed at a large dairy in Michigan.  While there are bench scale models available for testing, there is no long term operational experience with the full scale equipment. 

 

McLanahan Corporation, of Holidaysburg, Pennsylvania, was provided samples of both the Snohomish County street sweeping solids and the vactor grit for bench scale testing.  Based on preliminary sieve analyses, they felt that the sand separation equipment would work for the intended purpose, however not as well as their fine material screw separation equipment.  For this reason, the sand / manure separator was dropped from further consideration.

 

3.7. 4   Vibratory Air Knife Separator

 

General Kinematics (GK), of Barrington, Illinois has prepared a design for a prototype separation device, specifically intended to separate street sweeping and vactor grit materials.  This device, with the working name “Vibratory Air Knife Separator”, combines mechanical screening, vibratory and air separation technologies from their other existing classification equipment.  GK plans to construct the prototype in 1997 to 1998, and conduct extensive full scale field tests for municipalities throughout the northwest United States and western Canada.  A copy of the GK preliminary design drawing is presented in Appendix E.

 

The flow of materials with this equipment would include screening and removal of the coarse materials, air and vibratory stratification and air knife separation.  Being a dry system, dust and litter control would consist of a cyclone and possibly a small bag house device.  Depending on the flow through requirements, the equipment may be small and portable for mobile operations or larger for stationary centralized operations.

 

Product specifications, including size, weight, capacity, motor horsepower, etc. are not available at this time.

 

3.8       Further Discussion of Separation Alternatives.

 

Street waste solids consist of both wet and dry materials,  made up of several components varying in size, density and combustion temperatures.  With these characteristics, several alternatives are available to process this waste into viable products acceptable for reuse by the regulating agencies.  Three categories of separation are feasible for this material 1) a wet separation using water, 2) dry separation using an air stream combined with vibration, and 3) combustion.  Each of these alternatives will use mechanical screening to remove litter and oversized material as a precursor to further separation by other physical characteristics, and therefore screening alternatives are evaluated with these other choices.

 

3.8.1    Mechanical Screening

 

Street waste solids come in two primary states; one is as a primarily dry material from street sweepings and the other is as a generally very wet vactor waste which has been wet vacuumed from catch basins.  The dry street sweepings can be screened effectively over any industrial screening equipment, however, the wet vactor waste can only be effectively separated using a trommel or disc screen, each of which has the  means of de-blinding itself.  Using either of these methods, the oversize material will still have a relatively small percentage of fines or product mixed with it.  The off-size material is the waste material that may have to be hauled to a landfill.  Economically, it is important to clean this waste material as effectively as possible. 


3.8.2    Wet System Separation

 

Wet separation in western Washington is an attractive process alternative.  While the street sweepings can be easily dry separated, the vactor waste would need extensive pre-conditioning.  Wet separation eliminates the need to dry the vactor waste.  Use of the water medium does have a water quality aspect that needs to be addressed.  Physical separation by use of water is effective in yielding good quality products of sand and rock.  Several commercial concrete plants have existing equipment that can be used in their everyday processing to produce aggregate that meets industry specification for concrete products.  A full scale test was done at Smokey Point Concrete, in north Snohomish County, and is described in Section 5 of this report.  This test demonstrated that four suitable aggregates could be produced for use in concrete, including fine sand, coarse sand, pea gravel, and a #5 rock.

 

The downfall of a wet system separation system is the water required.  Significant volumes of water are used in any flow through wash system.  Static float tanks require less water but are not very effective in washing the product clean.  A “live system” (using flowing water) would use at least 50 gallons a minute for the smaller system and up to 200 gallons per minute for larger systems.  Recycling of the water with some makeup (replacement water) supply is most reasonable.  Several clarifying systems have been used in the waste industry and the aggregate industry.  Most water recycling systems deal primarily with solids in water, and utilize clarifying tanks for removal of sediment prior to reuse of the water.  These systems are used by the aggregate industry at sites that have a limited water source.  Clarifying tanks have a low volume of water when compared to lagoon type systems, and with the large rate of use these systems need polymers to help settle out solids.  The polymers leave the system with the silts that are usually drag-chained from the bottom of the clarifying tank.  An additional requirement of this type of water clarification, specific to street waste, may be a treatment system for removal of hydrocarbons from the wash water. 


3.8.3    Dry System Separation

 

The great advantage of separating materials with an air stream is not having to contend with the wash water.  The disadvantage is the need to dry the vactor waste before processing.  In most cases, this would mean stockpiling until the summer sun could be used to adequately dry the material or stockpiling out of the weather until the material is dry.  The vactor waste could be dried with forced heat through a pile (undercover) or in a rotary drier.  This would eliminate the storage aspect, but would increase the processing cost significantly (however it would still be significantly cheaper than disposal at a landfill).

 

Unlike the wet separation process, there is no ready-made equipment that can be bought off the shelf to set-up a dry separation system.  A system would have to be specifically designed for the street waste material.  Land Technologies, Inc. of Arlington, Washington has previously designed and built a prototype air separation system that was used to separate log yard debris, a waste stream that is far more difficult to handle than the street waste. The design included a vibratory screen for preliminary material segregation and a cyclone to further separate the fines from the air stream.  This prototype design would be very effective for street wastes.  A schematic of this equipment is presented in Appendix F.

 

General Kinematics makes several air separators called “de-stoners” that are used in the waste recovery industry, and are currently working on the design of a system that could be used for dry street wastes.  This system uses vibratory screen and air knife to separate the light fraction from the heavier fraction. A cyclone would have to be added to this system, for fine material recovery and air quality (dust) control.

 

A dry separation system could be made the most portable and versatile of all the options available; it would be the least expensive of the options when building a new system specific to street waste separation.  For municipalities or private companies that wanted to process their own waste materials, dry system separation equipment would be the best choice.

 

The product produced by the air separation process would not be as finished as the wash system, but would be a good usable aggregate. The product out of the air system would be a clean pit run gravel.  Screening could produce sand for re-use on the roads and an un-washed rock aggregate.  The organic fraction would not be “lost” to the process and could be used in compost or soil mixes.  These uses would be conditioned on the levels of total petroleum hydrocarbons found in each of the components, in accordance with the Snohomish Health District Policy (refer to Section 2).

 

3.8.4    Combustion

 

Combustion removes some of the residual problems left by the other options discussed, namely, the hydrocarbons are volatilized and are not re-circulated back into the environment.  Except for ash residue, the organic fraction is removed, leaving only the aggregate which, if prescreened to the specified size, could be used directly in asphalt.  Several asphalt producers have fitted their plants so as to be able to receive hydrocarbon contaminated soils.  In addition, special precautions would need to be taken to avoid fire resulting from hot embers produced by the burned organic materials.

 

Asphalt generally uses a ¾ inch minus stone and for the Class B specifications, that is usually a 5/8 inch fractured rock.  The street waste aggregate would be used in Asphalt Treated Base (ATB), which is a lower quality asphalt, usually placed in 4 inch lifts under a Class B wearing course.  If a one-inch aggregate is not acceptable, this process would generate more waste material for disposal.

 

Two options are viable with combustion: 1) process the whole waste fraction through the burner, and 2) Prescreen and deliver only the asphalt usable fraction to the burner for direct use in ATB.  The first option is a one-stop means of disposing of all the street waste with little extra handling.  The results would be a clean bank run gravel that could be used in any application currently used for gravel, and could be processed with any end use goal.  There may be fewer options as to who could accept and process the “raw” street wastes, and therefore hauling costs and tipping fees would be higher. 

 

The second option, that of prescreening to meet an ATB aggregate size specification, would increase the number of asphalt plants that could accept and use the material.  Prescreened, the street waste could be used directly.  Perhaps it could be blended with other aggregate, in the production of ATB.  With direct use, the asphalt producer could charge a smaller tipping fee.  Prescreening to ¾ inch would leave more waste requiring disposal.

 

3.9       Conclusions

 

For generators of street waste solids, the easiest option to implement would be to haul the street wastes to an existing facility that could utilized the aggregate fraction of this waste. Alternatives would consist of either a concrete plant that has equipment in line for removing wood contaminants from the aggregate, or an asphalt plant retrofitted to burn hydrocarbon soil. 

 

A concrete plant could be the least expensive option if the street waste, after pre-screening, could be blended into their regular bank run aggregate prior to processing through the wash plant.  This would cause little disruption in the daily process and would provide another source of aggregate for the concrete producer.  If the generator prescreened the street wastes so there was no waste handling required of the concrete plant, tipping fees would be minimal.  If the street wastes could not be pre-screened by the generator, tipping fees would have to cover screening and waste disposal.  While this approach is technically desirable, special approvals would need to be obtained from the jurisdictional Health District to mix street waste solids with regular bank run material.

 

If regulating agencies would not approve the blending of materials at an existing wash plant, and a dedicated process had to be implemented, cost would increase dramatically.  Nevertheless, the cost of processing would still be considerably less than landfilling.  If a concrete plant was willing to retrofit their process to process the street waste as a dedicated operation, it would still be viable and the preferred option.  Wash water quality would still be the primary issue that would limit the concrete plant’s ability to handle the material, and a water treatment process would likely have to be incorporated upstream of the point of discharge to the water supply pond. 

 

There are several resource recovery yards that currently handle CDL (Construction, Demolition and Land Clearing debris) waste.  One of these sites could set up a dedicated separation process using a closed wet separation system or an air separator.  As mentioned earlier, the wet system would produce the highest quality end product, but has a water quality issue that would need resolution.  The air separator means pre-conditioning (drying) the vactor waste before separation.  If storage space is not a problem, this could be done by waiting for dry weather and then “land farming” the material to dry and precondition the material before processing.  Street sweepings are generally dry enough to air separate without further drying, especially during the summer.

 

Development of a portable system that could go the generator’s stockpiles would be a desirable solution.  To accomplish this, enough generators would need to cooperate on a long term contract basis, either through an interlocal agreement or with private industry, to provide enough revenue to capitalize and operate a system.

 

A portable air separation system would eliminate the water quality issues associated with wet separation systems and would be the easiest to design and build for portability.  Generators could consider an air separation system for recovery of sand from their street sweepings.  For onsite application, this option would be the least costly.  In all cases, the vactor waste would need drying prior to processing by air.

With  street sweepings only to consider, air separation is the most viable solution to recovery and reuse.  When vactor waste is included, more complexity develops.  At issue is the water in the vactor waste and its cost of removal, either by active dewatering and the use of energy, or by passive dewatering and the cost of storage until dry weather farming can condition the waste to air separation.

 

Alternatively, to facilitate processing the vactor waste materials, the 3/8-inch minus material could be mechanically screened, and the sand fraction could be cleaned and further separated using a fine material sand screw.  This would process approximately 65 to 70 percent of the total volume of vactor waste.  The remaining material, without the fine fraction, would dry relatively quickly under cover or in dry weather, and could then be further processed using a selected dry separation technology.

 

Combustion is a solution that is currently available at about one half the cost of land filling. If water quality issues prevent washing the street waste at a concrete plant, the vactor waste could be processed at an asphalt plant and the street sweepings could be air separated. 

 

3.10     Recommendations

 

Several viable recommendations for processing street wastes are discussed below, in order of preference.

 

The first recommendation is to haul street wastes to existing aggregate wash plants equipped with wood removal equipment, and to blend these materials with daily process materials for use as aggregate in concrete.  To accomplish this, it would be necessary to resolve regulatory issues with the Jurisdictional Health Districts and Ecology regarding: 1) blending street waste solids with bank run materials to facilitate separation, and 2) wash water quality.

 

Second, seek an interested party to develop a dedicated processing site for the street waste solids.  The separation process may be a closed wash system for all the street waste or a dry system with facilities to condition the vactor waste before processing.

 

A centralized processing facility could be set up at one of the sites currently permitted to take construction and land clearing debris.  To warrant the capitalization expense, multiple generators would have to contract with possible a receiver as no single source has enough material to create a large enough income stream.

 

Third, individual generators could purchase equipment to process street waste for re-use at their facility.  Because of the relatively small quantities produced by each jurisdiction, small production rates would be acceptable and therefore small, less expensive equipment would be required.  Since the equipment would not have to be mobile, its cost could be further reduced. 

 

Fourth, seek an interested party to develop a mobile processing plant.  This option would reduce handling and hauling costs and leave sand and aggregate product for re-use by the Public Works Department.  A dry system would be the easiest and most versatile equipment to move from facility to facility, but would require pre-drying of the vactor waste or an alternate disposal option.  Street sweepings could be easily processed in the dry months without any conditioning.  A portable wet system would be more cumbersome to move-in for small quantities.  While it would produce a higher quality product, the wash water treatment issues may make a portable wet system impractical, especially in dealing with the small quantities in yearly stockpile at most generator sites.

 

Last, the generator could screen the street waste solids, and the screened material could be hauled to an asphalt plant retro-fitted to burn hydrocarbons.  All the pre-screened street waste solids could be processed at an asphalt plant, although at significantly higher cost.

 


4.  Economic Evaluation

 

4.1       Basis for Economic Evaluation

 

The previous section of this report discusses alternative methods of separating street waste solids into usable components, and provides recommendations for preferred processing systems.  This economic evaluation considers the following five processing systems:

 

1.                  Existing aggregate wash plant and concrete batch plant;

2.                  Dedicated, private receiving and processing site;

3.                  Dedicated, municipal receiving and processing site;

4.                  Mobile, private processing equipment; and

5.                  Existing asphalt plant to burn organics and hydrocarbons.

 

For each of these alternatives, the generator (i.e., municipality or private sweeper or vactor company) may also have the choice of pre-screening the street waste solids at their own holding facility, and transporting the finer material to the processing plant, and disposing of the overs at their cost.  Alternatively, the generator could deliver the entire mix of materials, and let the processor (either private or public) separate and dispose of the overs materials.  The latter alternative will certainly cost the generator more and would likely have additional regulatory compliance issues and/or permit conditions.

 

The economics for each of the five recommended processing alternatives also depend on the volume of material to be processed.  There is limited information available on the actual amount of street waste solids generated state wide, however two examples provide a basis for this economic analysis.  First, the Snohomish County Road Maintenance Division estimates that 4,500 tons of street sweeping material and 1,000 tons of vactor waste were generated in 1996.  This amount of material is generated in unincorporated Snohomish County.  Second, the City of Bellingham, Washington advertised for bids to receive and process street solids waste in September 1996.  The bid document indicates that for all of Whatcom County, the estimated quantity of street sweepings is 3,000 tons annually and vactor waste is 4,500  tons annually.  The street sweepings will vary considerably seasonally, with much of the material consisting of vegetative matter (leaves) during the fall season.  Therefore the actual tonnage of street sweepings requiring reprocessing would be somewhat less.

 

The equipment and site requirements for this evaluation were selected to accommodate this range of material processing quantities.

 

4.2       Discussion of Processing Costs

 

Each of the alternatives will necessitate a County Health District materials recycling permit, either existing with revised conditions or newly obtained.  In the event that a Conditional Use Permit is needed, the cost of obtaining such a permit could easily range between $40,000 to $50,000, and could take between 12 and 24 months to complete, depending on zoning, jurisdiction and public support or opposition. 

 

In addition, each alternative will have different investment requirements resulting from the purchase of land and new equipment or the use of existing sites and equipment in other material processing industries.  Some of the alternatives will also require the generator to pay a tip fee, while others assume the generator will pay capital and operating expenses.  For these reasons, a direct cost comparison is not possible between the five alternatives.  The costs for each alternative are discussed in the following sections, and the range of costs for each alternative are summarized in Section 4.3.

 

4.2.1    Existing Aggregate Wash Plant and Concrete Batch Plant

 

Four approaches have been considered for using an existing aggregate wash plant.  These are listed in Table 1, along with an estimated tip fee cost.

 

 

 

Table 1 - Existing Aggregate Wash Plant, Tip Fee Estimates

 

Description

Tip Fee

(cost/ton)

Materials pre-screened by generator, blended with bank run material, and without process water treatment.

 

$5 – 10

Materials pre-screened by generator, blended with bank run material, with process water treatment.

 

15 – 20

Materials pre-screened by generator, not blended with bank run material, with process water treatment.

 

30 – 35

Materials not pre-screened by generator, not blended with bank run material, with process water treatment.

 

40 - 45

 

 

4.2.2    Dedicated Private Receiving and Processing Site

 

This second alternative assumes that an existing site currently used for recycling various municipal solid waste materials (e.g., construction, demolition and land clearing debris) could be used.  The street waste solids would be separated using either wet or dry technologies.  Table 2 estimates the tip fee for four alternative approaches.

 

 

Table 2 - Dedicated Private Receiving and Processing Site, Tip Fee Estimates

 

Description

Tip Fee

(cost/ton)

Materials pre-screened by generator, separated using an air classification equipment

$25 – 30

Materials pre-screened by generator, separated using a water based classification system.

30 – 35

Materials not pre-screened by generator, separated using an air classification system.

40 – 45

Materials not pre-screened by generator, separated using a water based classification system.

50 - 60

 

 

4.2.3    Dedicated Generator Processing Site

 

Should a generator consider doing their own dry processing, they will need a large enough facility to stockpile their yearly supply of street waste solids to allow for drying during the dry season.  With wet separation technologies, long term storage would not be necessary, however some means of treating the process water would likely be required.  The equipment needed for processing could be new or used.

 

Typical costs for equipment components for both wet and dry separation systems are provided Table 3 (based on prices quoted in heavy equipment catalogs).  For the purposes of this analysis, it is assumed that the generator already owns a front-end loader.

 

 

Table 3 - Dedicated Generator Processing Site, New and Used Equipment Prices

 

 

Description

 

Used Equipment

New Equipment

Trommel Screen equipped with feed hopper, flights and chains, and material out conveyors.

$40,000

$115,000

Small air separator for processing post-screened street sweeping solids (dry) for light air separation.

20,000

35,000

Full scale air separator de-stoner to process fine and coarse debris, for heavy air separation.

70,000

110,000

Fine material sand screw for wet separation of 3/8-inch minus material, plus discharge water clarifier

10,000

30,000

Hydrobelt type log washer, plus discharge water clarifier

25,000

85,000

Flat deck screen for separating coarse and fine aggregate

15,000

50,000

Stacking conveyors (2)

 

5,000

15,000

 

 

The following costs for processing the materials assumes that a total of 5,000 tons of street waste solids would be produced annually, and that the equipment would have a life expectancy of 4 years for used equipment and 8 years for new equipment.  The cost per ton to process the materials does not include the cost of the processing site, as this would be variable between public and private generators. 

 

In Table 4, heavy waste separation refers to recovery of all aggregate materials, including cobbles and boulders which could be crushed and used as aggregate.  Recovery of these heavy materials would offset the cost of disposal of these materials.  Conversely, light waste separation refers to aggregate recovery from the 1-inch minus materials, and substantially increased cost for overs disposal.

 

 

Table 4 - Dedicated Generator Processing Site, Operating Cost Estimates

 

 

Description

 

Used Eq. Operating Cost/ton

New Eq. Operating Cost/ton

Dry, Heavy Waste Separation

$17

$19

Dry, Light Waste Separation

18

20

Wet Waste Separation, with Process Water Treatment

22

25

 

 

These operating costs could be somewhat offset by revenues or savings generated for the finished processed materials.  In addition, the actual cost per ton would increase with quantities less than the 5,000 tons assumed, and similarly would decrease with quantities greater than those assumed.

 

 


4.2.4    Mobile Private Processing Equipment

 

The fourth alternative consists of the same basic operations as described in the previous alternative, with the exception that all of the equipment would be privately owned and mobile.  In this case, the equipment would be more costly to produce and the service offered would consist solely of separation of materials, such that all separated materials and overs materials would be left on site for the owner to utilize and dispose, respectively.  The anticipated range of costs are presented in Table 5.

 

 

Table 5 - Mobile Private Processing Cost Estimates

 

 

Description

 

 

Low Cost/ton

 

High Cost/ton

Dry, Heavy Waste Separation

$30

$45

Dry, Light Waste Separation

25

35

Wet Waste Separation, with Process Water Treatment

35

50

 

4.2.5    Existing Asphalt Plant to Burn Organics and Hydrocarbons

 

The cost of using an existing asphalt plant to burn organics and hydrocarbons is currently $45 to $55 per ton of material processed, for 1-inch minus soil.  The cost to process the unscreened material, and dispose of litter and other reject materials would range between $60 and $75 per ton.

 

4.3 Conclusions

 

For the five alternatives considered in this economic evaluation, the range of costs to process the street waste solids materials are summarized in Table 6.


 

 

Table 6 - Summary Cost Estimates

 

 

Alternative Description

 

 

Low cost/ton

 

High cost/ton

Existing Aggregate Wash Plant and Concrete Batch Plant

5

45

Dedicated Private Receiving and Processing Site

25

60

Dedicated Generator Processing Site

17

25

Mobile Private Processing Equipment

25

50

Existing Asphalt Plant to Burn Organics and Hydrocarbons

45

75

 

 


5.  Full Scale Materials Separation Test

 

5.1       Overview

 

To validate the premise that street waste solids can be separated into constituent materials using a combination of separation technologies,  a full scale test was conducted on Wednesday, May 14th, 1997, at Smokey Point Concrete, in Arlington, Washington.  The objectives of this test were to:

 

·        remove litter, oversized material, organics and silt from the sand and gravel fractions;

·        estimate relative quantities of reusable and discard materials;

·        evaluate methods to improve the efficiency of the respective separation technologies;

·        determine the level of contamination of the clean aggregate materials, in accordance with the SHD Interim Policy.

 

Beginning in late April, 1997, the Snohomish County Roads Maintenance Division coordinated the delivery of approximately 200 cubic yards of street sweeping and vactor grit materials from a variety of municipalities located throughout the western area of the County.  These materials, when stockpiled, formed a heterogeneous mix with varying quantities of litter, vegetative matter, construction debris, large rock, and other discard materials.  In most cases the material was wet, however no free water was observed.

 

Prior to and during the test, photographs and video footage were taken to document the event.  The test lasted approximately 4 hours, which provided sufficient time to refine the method of operation and optimize the flow of materials through the separation process.

 


5.2       Pre-Screening

 

The combined street waste solids were prescreened to remove the 1-inch plus material.  A vibratory deck screen (Powerscreen) was used, and included a 4-inch grizzly for separating the oversized contaminants and large rock, and a 1-inch deck screen to separate the middle fraction.  A Cat 988 Front End Loader was used to feed the material into the screen hopper.

 

At the outset of the pre-screening phase, a Snohomish County 5-cubic yard dump truck was situated beneath the middle fraction, side-discharge conveyor.  During the first hour of operation, it was observed that a moderate to high percentage of reusable granular materials were being discharged along with the discard material.  When the first truck load of discard materials were taken to the Arlington transfer station, approximately 4 cubic yards of the middle fraction was allowed to accumulate on the ground.  This material was then re-screened, which reduced the discard pile size by approximately one-third.  The remainder of the pre-screened material was processed twice to minimize the quantity of discard materials.

 

The 1-inch minus material was discharged by the end conveyor and allowed to accumulate in a large pile.  This material was dark brownish-black in color, moist and well graded.  Organics consisted primarily of dark fines, small sticks and pine needles.  Composite samples of this material were taken during the early, middle and late stages of pile development, in accordance with the procedures specified in the project sampling plan (as discussed in Section 5.4, below).  The prescreening operation continued after the start of the wash and separation phase of the test.

 

5.3       Screen and Wash Separation Process

 

The 1-inch minus material was transported to the feed hopper of the aggregate screen and wash plant using the Cat 988 Front End Loader.  The hopper metered the material onto a conveyor which then delivered it to a wet screen located at the top of the separation plant.  The wet screen accomplished a second stage separation into two size fractions, including a coarse fraction consisting of 1-inch to ¼-inch, and a fine fraction consisting of minus ¼-inch.  The coarse fraction was then directed to the log washer, and the fine fraction was directed to a double sand screw separator.

 

The coarse fraction was introduced into the log washer along a sloping, vibrating chute.  The method of separation in the log washer consisted of a set of sloping conveyor-type screens rotating in the uphill direction and a set of 24 high pressure nozzles pointed mostly in the downhill direction.  The screens separated the coarser material into two components, including the 1-inch to 5/8-inch fraction (“concrete rock”) and the 5/8-inch to ¼-inch fraction (“pea gravel”).  The water jets were very effective at removing the organics in the log washer, most of which consisted of small sticks and bark. The organics remained in the wash water that was returned to the settling pond.  The clean concrete rock and pea gravel were discharged onto separate stacking conveyors.

 

The fine fraction from the second stage separation, consisted of well graded sand and fine organics.  This material was then further processed in a flow density separator and a double sand screw separator.  The flow density separator generally operates with a sand and water slurry flowing horizontally in a basin, with the flow passing over a vertical baffle.  With this arrangement, the coarser sand falls out of suspension quickly and is trapped on the leading side of the baffle and directed to a vertical discharge.  Similarly, the finer sand carries over the baffle and is directed to a separate discharge.  The two gradations of material are then directed into one side or the other of the double screw separator.  The flow of liquid also serves to remove a large portion of the remaining fine organics, and is returned to the wash water settling pond.

 

The double sand screw separator consists of a two parallel, gently sloping, continuous helical screws, partially submerged in an elongated tank or “washer box”.  A feed hopper is located at the low end of the device and receives a liquid slurry of silty and fine granular material.  A water jet is located in the washer box to further remove residual fines.  Each of the screws discharged onto stacking conveyors.

 

5.4       Soil and Water Sampling

 

Samples of each of the unseparated and separated soils were obtained during the test, in a manner that was consistent with procedures used by Snohomish County Road Maintenance Division for their analytical studies.  The procedures for preparing composite laboratory soil samples are summarized below.

 

1.     Obtain three equal quantities of material from separate areas and depths of the pile of material to be tested, and place in a mixing container or on a durable plastic tarp.

2.     Stir the mixture thoroughly, and remove sticks, organics, trash and rocks over 1/8-inch in diameter.

3.     Fill laboratory prepared sample jars, tapping for compaction, and topping off to minimize air space above the sample.  Seal the jars with an air tight lid, label completely and place in a cooler with frozen cold blocks or ice.  Follow laboratory instructions for maximum holding times.

4.     Prepare the Chain of Custody form immediately after each sampling.

 

Liquid samples were also taken; four on the day preceding the test and three more on the day of the test.  Three of the samples on the first day were taken from points of discharge on the screen and wash separation equipment.  The three samples on the day of the test were taken from the same locations.  The fourth sample taken on the first day was obtained from the wash water sediment pond.

 


All of these samples were obtained using the following procedures:

 

1.      Fill laboratory prepared sample jars directly at the point of discharge, topping off to                       minimize air space above the sample.

2.      Seal the jars with an air tight lid, label completely and place in a cooler with frozen cold blocks or ice.

3.      Follow laboratory instructions for maximum holding times.

4.      Prepare the Chain of Custody form immediately after each sampling.

 

5.5       Observations and Conclusions

 

The breakdown of the constituents were visually estimated as indicated in Table 7:

 

 

Table 7 - Estimated Proportion of Separated Materials

 

Plus 1-inch                                          

10 percent of total pile.

 

Of the remaining 90 percent that passed the 1” screen:

 

 

1 to 5/8-inch                                        

            10 percent

5/8 to ¼-inch                                       

15 percent

Coarse Sand                                       

            35 percent

Fine Sand                                            

            35 percent

Organics (sticks & leaves) and Silt       

              5 percent

 

 

The following observations were made during the course of the full scale materials separation test:

 

·        The full scale test was successful at demonstrating that organics and fines can be effectively removed from the mineral sand and gravel fraction.

·        Pre-screening of the street sweeping and vactor grit materials is essential to the overall separation process.  However, it would likely be more efficient to use a self cleaning trommel screen instead of a vibratory deck screen.

·        The deck screen used during the test had a tendency to blind, resulting in production delays.
 

Because of the heavy load of organics in the street waste solids materials, it would be more effective to combine these materials with other source materials prior to screening and washing.  In this way, the percentage of organics would be reduced in the process materials, and the efficiency of the total system would be increased.  While some sticks made it through the process to both the concrete rock and pea gravel piles, it is believed that virtually all of the sticks would be removed if the organic loading was decreased.  Combining street waste solids with bank run material would require special approval by the jurisdictional health districts and Ecology.

The wash water separates the organics and fines from the sand and gravel fraction, and returns this material to the sediment pond.  Because of this and concerns over TPH constituents accumulating in the pond, it would be appropriate to provide a separate liquid post-processing system to remove the organics and TPH products.  This would also be a reason to conduct additional field tests using dry separation technologies, including vibratory and airflow separation in combination with mechanical screening.  These tests were not conducted as part of this project because of time and resource limitations.

 

 

 


6. Full Scale Test - Analytical Test Results

 

Samples of each of the pre-screened and clean, separated soils were obtained during the full scale field test, as described in Section 5.4 of this report.  The analytical test results for these samples are discussed below.

 

6.1 Soil Samples

 

Five soil samples were obtained at the time of the full scale separation test, as described in Table 8.

 

 

Table 8 - Soil Sample Description

 

 

Sample No.

 

Sample Description

 

 

23S

Minus 1-inch screened, not separated by wash plant

24S

Minus 1-inch to 5/8-inch, separated concrete rock

25S

Minus 5/8-inch to ¼-inch, separated pea gravel

26S

Separated coarse sand

27S

Separated fine sand

 

The analytical test results for these samples are presented on Table 2, and discussed below.

 

For all five samples, total metals, PAH’s and PCB’s were either non-detectable or well below reportable levels. 

 

As with the preliminary test results for the laboratory separated sample, total petroleum hydrocarbons did exceed the reportable level (200 ppm) in all five samples for heavy oil, using the WTPH with acid cleanup method..   The concentrations of heavy oil in the samples ranged from 230 ppm to 380 ppm, which characterizes this material as a Class B soil, in accordance with the SHD Policy, (i.e., Ecology - Class 3 soil).

 

Diesel was detected in both of the sand samples, at concentrations below the reportable level (200 ppm).  These concentrations were 41 ppm for the coarse sand and 74 ppm for the fine sand.

 

6.2 Water Samples

 

Seven water samples were obtained of process water at intake and discharge points in the processing equipment.  These samples are described in Table 9

.

 

 

Table 9 - Water Sample Description

 

 

Sample No.

 

Sample Description

 

19L

Log Washer (1)

20L

Fines material sand screw (1)

21L

Inlet water (1).

22L

Sedimentation / Process Water Pond (1)

28L

Wet sand density separator, that fed the fine material sand screw (2)

29L

Fine material sand screw(2)

30L

Log washer(2)

 

(1) Preceding the full scale field test

(2) During the full scale field test

 

 

The analytical tests for these seven samples consisted of TPH’s only, as these were the only constituents previously found in any of the samples tested.  For five of the seven samples, both diesel and heavy oil were non-detected, and the remaining two samples, diesel and heavy oil were very low, less than 3 percent of the reportable levels.

 

6.3       Conclusions

 

The concentrations of heavy oil in the soil samples ranged from 230 ppm to 380 ppm, which characterizes this material as a Class B soil, in accordance with the SHD Policy.  Concentrations of diesel in all liquid samples were well below reportable levels.


7.     Summary of Conclusions

 

7.1       Previous Studies

 

Numerous studies have been completed by Ecology and local municipalities to evaluate the character of street waste solids, and to develop analytical methods for resolving the problems associated with false positive laboratory test results.  Previous studies concluded:

 

·        Organic (plant) material contributed to a false positive result with each of the three total petroleum hydrocarbon (TPH) analysis methods used;

·        Sources likely to contribute to TPH concentrations in street waste include organic (plant) material, automobile and truck tires, asphalt paving materials, and motor oil and lubricants from cars and trucks.  Relative amounts of contribution to the TPH concentration were not identified.

·        Street waste is a solid waste and is typically not a dangerous waste, and Ecology and the SHD regulations support reuse of street waste.

·        Chemical analysis results for metals do not exceed MTCA Method A soil cleanup levels or SHD threshold criteria, and do not limit reuse options.

·        Chemical test results for CPAH exceed SHD threshold criteria and may limit management options to those associated with Class B material.

 

7.2       Street Waste Characterization

 

Preliminary tests conducted on one sample of street sweeping material suggested  that organic materials could be separated from mineral constituents, and that the mineral fraction was contaminated with total petroleum hydrocarbons, confined to heavy oil, in concentrations below the reportable limits. Given these preliminary test results, the separated mineral fraction could be used for any of the Class A and Class B applications, as defined by the Snohomish Health District Policy Statement regarding Street Waste Solids Recycling and Disposal.  In the event that future samples showed heavy oil concentrations exceeding the 200 ppm criteria, then these materials would be restricted to Class B reuse alternatives, which consist primarily of encapsulation in concrete and asphalt products.

 

7.3       Separation Alternatives

 

Five alternative methods of material separation were discussed, including the use of liquid, vibratory, and air separation, mechanical screening, and combustion. 

 

Considering the available technologies, five alternative approaches for separating and utilizing the street waste solids are recommended.  The first recommendation is to haul street wastes to existing aggregate wash plants equipped with wood removal equipment, and blend these materials with daily process materials for use as aggregate in concrete.  To accomplish this, it would be necessary to resolve regulatory issues with the Jurisdictional Health Districts and Ecology regarding: 1) blending street waste solids with bank run materials to facilitate separation; and 2) wash water quality.

 

Second, seek an interested party to develop a dedicated processing site for the street waste solids.  The separation process may be a closed wash system for all the street waste or a dry system with facilities to condition the vactor waste before processing.  A centralized processing facility could be set up at one of the sites currently permitted to take construction and land clearing debris.  To warrant the capitalization expense, multiple generators would have to contract with a possible receiver as no single source has enough material to create a large enough income stream.

 

Third, individual generators could purchase equipment to process street waste for re-use at their facility.  Because of the relatively small quantities produced by each jurisdiction, small production rates would work and therefore small, less expensive equipment would be required.  Since the equipment would not have to be mobile, its cost could be further reduced. 

 

Fourth, seek an interested party to develop a mobile processing plant.  This option would reduce handling and hauling costs and leave sand and aggregate product for re-use by the waste generator.  A dry system would be the easiest and most versatile equipment to move from facility to facility, but would require pre-drying of the vactor waste or an alternate disposal option.  Street sweepings could be easily processed in the dry months without any conditioning.  A portable wet system would be more cumbersome to move-in for small quantities.  While it would produce a higher quality product, the wash water treatment issues may make a portable wet system impractical, especially in dealing with the small quantities in yearly stockpiles at most generator sites.

 

Last, the generator could screen the street waste solids, and the screened material could be hauled to an asphalt plant retro-fitted to burn hydrocarbons.  All the pre-screened street waste solids could be processed at an asphalt plant, although at significantly higher cost.

 

7.4       Economic Evaluation

 

For the five alternatives considered in this economic evaluation, the range of costs to process the street waste solids materials are summarized in the following table.

 

 

Table 10 - Summary Cost Estimates

 

 

Alternative Description

 

 

Low cost/ton

 

High cost/ton

Existing Aggregate Wash Plant and Concrete Batch Plant

$5

     $45

Dedicated Private Receiving and Processing Site

25

60

Dedicated Generator Processing Site

17

25

Mobile Private Processing Equipment

25

50

Existing Asphalt Plant to Burn Organics and Hydrocarbons

45

75

 

7.5 Full Scale Materials Separation Test

 

The full scale test was successful at demonstrating that organics and fines can be effectively removed from the mineral sand and gravel fraction.

The breakdown of the constituents were visually estimated as follows:

 

Plus 1-inch                                                                   10 percent of total pile.

 

Of the remaining 90 percent that passed the 1” screen:

 

1 to 5/8-inch                                                                 10 percent

5/8 to ¼-inch                                                                15 percent

Coarse Sand                                                                35 percent

Fine Sand                                                                     35 percent

Organics (sticks & leaves) and Silt                                  5 percent

Pre-screening of the street sweeping and vactor grit materials is essential to the overall separation process.  However, it would be more efficient to use a self-cleaning trommel screen instead of a vibratory deck screen.  The deck screen used during the test had a tendency to blind, resulting in production delays.
 

Because of the heavy load of organics in the street solids materials, it would be more effective to combine these materials with other source materials prior to screening and washing.  In this way, the percentage of organics would be reduced in the process materials, and the efficiency of the total system would be increased.  While some sticks made it through the process to both the concrete rock and pea gravel piles, it is believed that virtually all of the sticks would be removed if the organic loading was decreased.  Combining street waste solids with bank run material would require special approval by the jurisdictional health districts and Ecology.

The wash water separates the organics and fines from the sand and gravel fraction, and returns this material to the sediment pond.  Because of this and concerns over TPH/PAH constituents accumulating in the pond, it would be appropriate to provide a separate liquid post-processing system to remove the organics and contaminant products.  This would also be a reason to conduct additional field tests using dry separation technologies, including vibratory and airflow separation in combination with mechanical screening.

 

7.6       Full Scale Test - Analytical Test Results

 

The concentrations of heavy oil in the soil samples ranged from 230 ppm to 380 ppm, which characterizes this material as a Class B soil, in accordance with the SHD Policy.  Concentrations of diesel in all liquid samples were well below reportable levels.

 


8.  Acknowledgments

 

This Report was funded by the Recycling Technology Assistance Partnership (ReTAP).  ReTAP is a program of the Clean Washington Center, Washington State’s lead agency for the market development of recycled materials.  ReTAP is an affiliate of the national Manufacturing Extension Partnership (MEP), a program of the U.S. Commerce Department’s National Institute of Standards and Technology.  The MEP is a growing nationwide network of extension services to help smaller U.S. manufacturers improve their performance and become more competitive.  ReTAP is also sponsored by the U.S. Environmental Protection Agency and the American Plastics Council.

 

The following organizations contributed their time, effort, and support during the conduct of this project:

 

Snohomish County Roads Maintenance Department, Snohomish, Washington

Land Technologies, Inc. of Arlington, Washington

Price-Moon Enterprises of Snohomish, Washington

 

In addition, special thanks are extended to the following companies for the time and resources that they so graciously donated to this project:

 

Smokey Point Concrete, Arlington, Washington for providing equipment and manpower to conduct the full scale separation test.

McClanahan Corporation for providing information on fine material screws, log washers and for conducting preliminary laboratory separation tests of street sweeping and vactor grit materials.

 

General Kinematics Corporation for providing information and a prototype design for a “Vibratory Air Knife Separator”.

Cities of Arlington, Everett, and Mount Lake Terrace, Washington for providing street sweepings for the full scale separation test.


Appendix A

 

Snohomish Health District Policy Statement

Regarding Street Waste Solids Recycling and Disposal


SNOHOHOM!SH     

                                                                          HEALTH  

                                     DISTRICT

SNOHOMISH HEALTH DISTRICT                                                                                                           95-11

RESOLUTION OF THE BOARD OF HEALTH

RESOLUTION NUMBER:                        95-11

RESOLUTION SUBJECT:                   STREET WASTE SOLIDS RECYCLING

                                                              AND DISPOSAL GUIDANCE

 

WHEREAS the Board of Health of the Snohomish Health District serves to promote the public health of the residents of Snohomish County, and

 

WHEREAS the Board of Health recognizes the need, as outlined in the Snohomish County Moderate Risk Waste Management Plan, for local best management practices concerning recycling and disposal alternatives for street sweepings, vactor grit solids and ditch cleanings (collectively referred to as "street waste solids"), and

 

WHEREAS the Snohomish Health District has written and adopted a widely accepted countywide policy addressing this issue, but recognizes that uniform statewide implementation of best management practices concerning recycling and disposal alternatives for street waste solids is needed, and

 

WHEREAS the Washington Department of Ecology is the most appropriate agency to develop an effective statewide policy, and

 

WHEREAS such a policy should take into consideration the need for refined laboratory test methods for these wastes which can accurately quantify petroleum contamination levels without interference from naturally occurring vegetative debris, and

 

WHEREAS the Washington Department of Ecology has also recognized the need for revised test methods and a statewide street waste solids recycling and disposal policy,

 

NOW THEREFORE the Board of Health hereby adopts this resolution encouraging the Washington Department of Ecology to continue to give priority to the research of laboratory test methods that could be used to accurately detect petroleum contamination in street waste solids, and the associated development of statewide best management practices concerning recycling and disposal alternatives for street waste solids.

 

ADOPTED this 11th day of April. 1995.


 

                                    SNOHOMISH                                     POLICY STATEMENT REGARDING

                           HEALTH                                         Street Waste Solids

                           DISTRICT                                       Recyci mg and Disposal

                           3020 Rucker                                    Environmental Health Division

                           Everett, WA           98201               Solid Waste and Toxics Section

                                                                                    (206) 339-5250

 

 

BACKGROUND

 

Solids collected during the cleaning of storm sewers, streets and drainage ditches (collectively referred to as "street waste solids") have often been used in the past by generators as general purpose fill material. However, street waste solids fall within the state definition of solid waste established under RCW 70.95.030, and typically fail Model Toxics Control Act standards for total petroleum hydrocarbon (WTPH 418.1 Modified) levels. As such, many generators are now disposing of this material in landfills at considerable (and many believe unjustifiable) expense.

 

The State's Solid Waste Management Act, Chapter 70.95 RCW, promotes waste recycling (rather than landfill disposal) among its highest waste management priorities. The Snohomish Health District (Health District), in accordance with the Department of Ecology's (Ecology) waste reduction and recycling objectives, is therefore promoting recycling options for street waste solids which protect both public health and the environment.

 

POLICY STATEMENT

 

It is not the intent of this policy to establish a Health District program for formally regulating this type of material through a permit or routine inspection program.  However, this interim policy will serve to guide Health District staff in assessing and directing street waste solids disposal and/or recycling situations, on a complaint basis or when a request for assistance is received from a generator. This policy will remain in effect until a statewide guidance policy is promulgated by the Department of Ecology or until the policy is rescinded by the Health District.

 

It should be noted that this policy has not been formally adopted or endorsed by the Department of Ecology. However, this interim policy was developed in cooperation with Ecology personnel responsible for solid waste policy development, and the contamination levels and end-uses for street waste solids outlined in this document were originally drafted by Ecology staff.  The Health District believes the criteria contained in this interim policy meet with the Department of Ecology's approval.

 

It should also be noted that the Health District recognizes concerns expressed by many street waste solids generators regarding possible interferences (i.e. "false positives" resulting from the presence of vegetative matter) when using test method WTPH 418.1 Modified. The Health District supports the generators efforts, through the work of the Snohomish County Vactor Grit Task Force, to resolve this issue to the satisfaction of both the generators and the Department of Ecology.   Resolution of this question, and reliance upon a different test method for characterizing street waste solids, may allow additional recycling opportunities for this material that are not currently outlined in this policy.

 

 

 

WASTE CHARACTERIZATION

 

Test data indicate that most street waste solids are typically not dangerous (hazardous) waste as defined by the State Dangerous Waste Regulations, Chapter 173-303 WAC. Therefore, routine testing of street waste solids for dangerous waste criteria is not typically necessary. However, if the waste collector finds upon visual inspection that the waste exhibits unusual characteristics that would indicate excessive pollution, that waste should be handled by following accepted spill response protocol, or appropriate precautions should be taken to segregate the contaminated materials until they can be properly characterized and disposed of as a dangerous waste. Indications that a street waste solid may be a dangerous waste include an obvious odor of gasoline or other volatile solvents; obvious pooling or accumulation of petroleum products upon visual inspection; suspicion of the presence of extremely acidic or alkaline materials; signs of chemical reaction, etc.

 

Testing of street waste solids for other constituents not necessarily specified in the State Dangerous Waste Regulations is necessary in order to determine contamination levels and identify appropriate end-uses as outlined in this policy.  Sampling plans can be developed following guidelines for collecting samples from piles of contaminated soils, as outlined in the Department of Ecology's, Guidance for Remediation of Petroleum Contaminated Soils. 91-30, or sampling plans can be individually developed with assistance from the Health District. Unless there is reason to suspect that other contaminants may be present, samples should be analyzed for TPH (using WTPH 418.1 Modified), plus the following metals: arsenic, cadmium, chromium, lead, and inorganic mercury (using "total metals" analysis).  If test results -consistently show the same outcome, the Health District will consider a reduction in the frequency, constituents or number of samples analyzed, as proposed by the generator.

 

STORAGE

 

Piles of contaminated street waste solids must be placed on a liner, such as asphalt, concrete, or other impervious material, to collect and control any liquids associated with the pile. Surface water run-on and run-off from the piles must be controlled and managed as required by State Water Quality Regulations to prevent surface and groundwater quality degradation. Generally this will be accomplished by covering the piles with plastic tarps during rainy periods, to prevent water infiltration and the possible production of contaminated run-off from the piles. Piles established on an impervious surface which drains to a sanitary sewer (i.e. sewage treatment plant) need not be covered. Appropriate steps must also be taken to contain and dispose of liffer or other garbage associated with the street waste solids.

 

It is recommended that street sweepings and vactor solids be stored in separate piles, due to the potential for differing levels of contamination.  If vactor solids are being stored in conjunction with an operating vactor decant station, the dewatered solids should be stored as described above to prevent surface or groundwater quality degradation.

 

EXCLUSION

 

Street waste solids may be excluded from regulation as solid waste by the Snohomish Health

District if it can be shown that:

 

1 ) The collected or processed solids consist only of soils, sands, gravels or sediments, and garbage, refuse, vegetative debris and other solids contaminants have been removed; and

 

2 ) Free liquids have been removed and appropriately treated and/or disposed of and

 

3 ) Concentrations of chemical contaminants do not exceed cleanup values identified in Table 2, Method A Cleanup Levels - Soil, of the Model Toxics Control Act Cleanup Regulation (MTCA), WAC 173-340-740.  (See Table 2 of this policy for partial list of contaminants.)

 

Street waste solids must be handled as solid waste until it is determined that this exclusion applies.  Such solids that have been excluded from solid waste regulation by the Snohomish Health District may be used in any manner that would not cause a threat to human health or the environment.  In keeping with established Ecology guidelines, the Health District recommends that these solids not be used in or adjacent to wetlands, surface water, groundwater, drinking water wells, or plastic pipes carrying drinking water.  The Health District also recommends that they not be used near food crop growing areas, as residential topsoil or for other residential uses.

 

In addition, the Health District recognizes that street sweepings collected at certain times of the year may be nearly or entirely vegetative matter (e.g. fallen leaves, needles and branches), as opposed to potentially contaminated soil, rock and grit. Likewise, some jurisdictions may have the equipment to separate out vegetative matter from mineral constituents. In instances when segregated or collected street waste solids contain little soil (i.e. less than 10% by volume), these wastes may be managed as yard debris and would not be subject to the sampling and testing requirements of this interim policy  The material managed as yard debris must be taken to a permitted or approved composting facility, composted by the municipality according to a plan of operation acceptable to the Health District, or otherwise properly managed as yard waste.

 

Furthermore, it is the Health District's understanding that roadside ditch cleanings are unlikely to be contaminated unless such material is associated with a stormwater retention/detention system, a "biofilter" system or has been contaminated by a spill or other release.  As such, ditching material not associated with one of these systems and presumed to be uncontaminated is excluded from this policy. Typically, clean ditching material can be segregated into vegetative and soil fractions, and recycled as yard waste (the sod fraction) and "clean" soil.  Ditching material that may be contaminated must be stored, tested and handled in the same manner as other street waste solids covered under this policy.  It is the generator's responsibility to visually inspect and otherwise determine whether the ditching material may be contaminated.

 

RECYCLING

 

The State's solid waste statute, Chapter 7O~95 RCW, prioritizes the need to recycle rather than dispose of waste. When considering recycling options for street waste solids, contaminant levels must be considered to insure that the final end-use does not compromise the health of the public or the environment.  Until such waste is recycled, it continues to be regulated as solid waste. The following are options for street waste solids recycling:

 

 

 

 

 CLASS "A" STREET WASTE SOLIDS

 

Class "A" street waste solids are those solids whose contaminants do not exceed levels established in Table 1 of this interim policy, and (for contaminants not identified in Table 1) whose levels do not exceed cleanup levels identified in Table 2, Method A Cleanup Levels - Soil, of the Model Toxics Control Act Cleanup Regulation, WAC 173-340-740. Street waste solids must be tested to determine a baseline for levels of regulated contaminants. (Refer to the Waste Characterization section of this policy for information concerning testing.)

 

POTENTIAL END USES - CLASS "A" STREET WASTE SOLIDS:

 

·   Road subgrade, parking lot subgrade, or other road construction fill. Must be used under or incorporated into asphalt or concrete paving, and the road must have a design which meets standards and specifications of the local jurisdictional authority (1)

 

·   Reuse as street traction sand (1)

 

·   Pipe bedding - excluding bedding around plastic (e.g. PVC, polyethytene) pipe used to convey drinking water (1) (2).

 

·   Utility trench backfill - excluding backfill around plastic (e.g. PVC, polyethylene) pipe used to convey drinking water (1) (2).

 

·   Controlled density fill - utilizing a design which meets standards and specifications of the local jurisdictional authority (1) (2).

 

Fill in commercial or industrial zones (1) (2) (3).

 

·   Any option approved for recycling of Class "B" street waste solids.

 

·   Other end-use as approved by the Snohomish Health District.

 

Class "A" street waste solids cannot be reused for the end-uses listed above if they would be placed in an area which is likely to result in the contamination of ground or surface water, or lead to other potential environmental or public health problems (for example, a roadside ditch likely to convey water).

 

 

1)   Would first require removal of litter and vegetative matter.

 

2)   The end-use should take into consideration potential human contact exposure both at the time of use and in the future.

 

3)      This end-use requires the following actions be taken:

 

(a)     Completed fill must be "encapsulated" with two (2) feet or more of uncontaminated, relatively impervious soil.

 

 

      (b)    Completed fill site must be recorded on Deed with Snohomish County Auditor's Office, to

 

include the following information:

 

·  Tax l.D. Number(s) for fill area.

 

·  General description of fill location on tax lot, attach map.

 

·  Certification Statement regarding contaminant levels, for example:

 

"I certify that the Class A street waste solids disposed here meet contaminant levels specified by Snohomish Health District's Interim Policy Concerning Street Waste Solids Recycling and Disposal. This determination has been made under my direction and supervision in accordance with the system designed to ensure that qualified personnel properly gather and evaluate the information used to determine that the Class A Street Waste Solids contaminant levels have been met."

 

NOTE:       All  recycling end-uses must be conducted in  compliance with specifications required by federal, state or local regulations, or specifications  required  by  a  facility,  manufacturer  or  vendor accepting the street waste solids for processing or recycling.

 

Although use of Class "A" street waste solids in the manners outlined above is accepted as a prudent end-use by the Health District, certain end-uses may not be consistent with the Model Toxics Control Act Cleanup Regulation.  Generators interested in pursuing these options are therefore advised to seek independent legal counsel before proceeding.

 

CLASS "B" STREET WASTE SOLIDS

 

Class "B" street waste solids are solids whose contaminant levels exceed Class "A" street waste solids contaminant levels, but do not designate as dangerous waste under Chapter 173-303

WAC.

 

POTENTIAL END-USES - CLASS "B" STREET WASTE SOLIDS:

 

·   Pre-fab concrete manufacturing. NOTE:  Facility manufacturing concrete must, in most instances, submit recycling permit application to the Health District for review and approval.

 

· Portland cement manufacturing.  NOTE:  Facility manufacturing cement must, in most instances, submit recycling permit application to the Health District for review and approval.

 

·    Asphalt manufacturing.  NOTE:  Facility manufacturing asphalt must, in most instances, submit recycling permit application to the Health District for review and approval.

 

·   Treatment at a contaminated soil treatment facility. NOTE: Facility treating contaminated soil must, in most instances, submit an application to the Health District for review and approval.

 

·   Daily cover or fill in permitted municipal solid waste landfills, provided that the street waste solids have been dewatered. Class "B" street waste solids cannot be used for final cover during a landfill closure.

 

·   Other end-use as approved by the Snohomish Health District.

 

INAPPROPRIATE END-USES - CLASS "A" and CLASS "B" SOLIDS:

 

·   Department of Natural Resources surface mining reclamation (for example, gravel pit

reclamations   not specifically permitted as solid waste disposal sites).

 

·   On-site sewage disposal sand filter and/or mound system construction.

 

·    Cover or fill in an inert-demolition waste landfill.

 

DISPOSAL

 

Untreated street waste solids destined for final disposal may only be disposed in a permitted municipal solid waste landfill, provided that they have passed the visual insp~ction for dangerous waste identification, and have been dewatered.

 

 

 

 

 

Robert A. Pekich,  Director

Environmental Health Division

 

Effective Date:      January 1, 1995

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TABLE 1

 

MAXIMUM END-USE CONTAMINANT LEVELS FOR

VACTOR AND STREET SWEEPING SOLIDS

 

ANALYTE                       ANALYTICAL METHOD                              MAXIMUM LEVEL

                                                                                                                                (ppm)

 

HeavyFuel                                    WTPH 418.1*                                                        2000

Hydrocarbons                                Modified

(C24-C30)

 

Diesel                                           WTPH-D                                                                 500

(Cl 2-C24)

 

Gasoline                                        WTPH-G                                                                 250

(C6-C1 2)

 

Benzene                                          8020                                                                     0.5

 

Ethylbenzene                                   8020                                                                     20

 

Toluene                                           8020                                                                     40

 

Xylenes (total)                                 8020                                                                     20

 

 

 

Contaminants not identified in Table 1 must meet levels established in MTCA Method A Cleanup Levels - Soil (Refer to Table 2 of this document).

 

To support the accuracy of test results, alternative testing protocols may be substituted upon approval by the Snohomish Health District.

 

*   The Health District recognizes concerns expressed by many street waste solids generators regarding possible interferences (i.e. "false positives" resulting from the presence of vegetative matter) when using test method WTPH 418.1 Modified.

 

 

 

 

TABLE 2

 

MODEL TOXICS CONTROL ACT (CHAPTER 173-340 WAC)

METHOD A CLEANUP LEVELS - SOIL

 

ANALYTE                       ANALYTICAL METHOD                              MAXIMUM LEVEL

                                                                                                                              (ppm)

Arsenic                                    Total Metals Analysis                                                 20

Cadmium                                 Total Metals Analysis                                                 2.0

 

Chromium                                Total Metals Analysis                                                 100

 

Lead                                        Total Metals Analysis                                                 250

 

Mercury                                   Total Metals Analysis                                                1.0

(Inorganic)

 

PAHs                                       8270                                                                         1.0

(Carcinogenic)

 

PCB Mixtures                                       8080                                                                                                   1.0

TPH (Heavy                            WTPH 418.1                                                              200

Fuel Hydrocarbons)                  Modified

TPH (Diesel)                           WTPH-D                                                                   200

 

TPH (Gasoline)                         WTPH-G                                                                          100

 

 

NOTE:    Refer to Table 2, Method A Cleanup Levels - Soil, of the Model Toxics Control Act Cleanup Regulation, Chapter 173-340-740, for complete listing of substances.

 

 

 

 

 

121 394/dmb

 

 

 

 


Appendix B

 

Summary and Conclusions (Section 5) and the

List of References (Section 6) from

Snohomish County Street Waste Characterization


5.0   SUMMARY AND CONCLUSIONS

 

 

Samples of street waste (street sweeping and vactor solids) were obtained from three routes, two from the City of Everett and one from County Roads, during winter, summer, and autumn 1995. Samples were collected from material staged at City of Everett and Snohomish County both before and after processing of street waste to remove debris. The samples were tested for metals, 'PH, and PAL' to evaluate potential contaminants. The effect of composting or decomposition was evaluated by using concentrations before and after processing. Samples of reference materials such as asphalt, automobile tires, and organic material were analyzed and compared to actual street waste samples. Regulations from solid waste, toxics cleanup, and water quality areas were reviewed for potential application to street waste.

 

Conclusions are organized to address the objectives identified in Section 1.0. Conclusions associated with the chemical characterization information objective include:

 

·   Metals, TPH, and CPAH were detected in street waste samples.

 

·   No seasonal differences were identified.

 

·   No consistent route differences were identified.

 

·   Organic (plant) material contributed to a false positive result with each of the three TPH analysis methods used.

 

·   Method WTPH-D (extended) with a sulfuric acid cleanup step typically provided the lowest TPH result and was the best of the three evaluated methods for minimizing the false positive contribution to the TPH result.

 

·   Method WTPHAI8.1 typically provided the highest TPH result of the three methods.

 

·   WTPH-D (extended) chromatograms show a single broad peak that was interpreted to be associated with a refined or processed hydrocarbon material. The similarity of the street waste peak with the used automobile tire reference material peak suggested a significant contribution from tires to street waste.

 

·   WTPH-D (extended) chromatograms show that the reported diesel range TPH results were not diesel fuel.

 

·   Sources likely to contribute to TPH concentrations in street waste include organic (plant) material, automobile and truck fires, asphalt paving materials, and motor oil and lubricants from cars and trucks. Relative amounts of contribution to the TPH concentration were not identified.

 

·   Sources likely to contribute PAH and CPAH to street waste include automobile and truck tires, heavy oils, and asphalt paving materials.

 

Conclusions associated with the regulatory framework applicable to test results include:

 

·     Street waste is a solid waste and is typically not a dangerous waste, and Ecology and SHD regulations support reuse of street waste.

 

·     Chemical analysis results for metals do not exceed MTCA Method A soil cleanup levels, SLID threshold criteria, and do not limit reuse options.

 

·     Chemical test results for CPAH exceed SHD threshold criteria and may limit management options to those associated with Class B material such as disposal at a solid waste landfill.

 

·     Chemical analysis results for TPH in all samples (including organic material) using each of the three methods exceed MTCA Method A cleanup levels for TPH (diesel and other) referenced by SHD (1995).

 

·     WTPH-D (extended) oil range hydrocarbon results (95 percent UCL on mean) are less than the SLID (1995) heavy hydrocarbon level.

 

·     Without the acid cleanup TPH analysis method, TPH results would exceed the SLID threshold criteria and may limit management options to those associated with a Class B material.

 

·     MTCA regulations do not apply directly to management of street waste. Risk-based exposure estimates (using an approach such as that in the MTCA regulations) allow possible future cleanup liability to be considered if material were placed in selected hypothetical exposure settings.

 

·     Risk-based exposure estimates and comparison with MTCA residential and industrial soil cleanup levels show that CPAH concentrations in street waste material may not be acceptable for residential settings but may be acceptable for reuse in settings such as recreational, commercial, and industrial.

 

Conclusions associated with the management (and reuse) alternative information objective include:

·        Composting contributes to a decrease in detected TPH concentration.  Greater TPH concentration reductions are anticipated if more time for composting is

allowed before samples are collected and if larger organic material is retained and not removed by screening until composting has been completed.

 

 

·     Risk-based analysis may be useful in evaluating possible settings for reuse of street waste material (as alternatives to more expensive landfill disposal).

 

In addition to these conclusions, several issues were identified which were beyond the scope of the present project. These issues include the effect of composting duration on 'PH and CPAH concentrations, urban soil background levels, and regulation of diesel range hydrocarbons that are not diesel fuel.

 

We trust that this information meets your needs. We appreciate the opportunity to provide environmental consultation to Snohomish County Solid Waste Management Division. Please contact us if you have questions.

 

 

LANDAU ASSOCIATES, NC.

 

By:

                               

Brian F. Butler, Project Manager

 

and

 

Nancy B. Ball,  Ph.D.

Senior Chemist


6.0     REFERENCES

 

Carrell, R. 3 May and 25 July 1995. Personal communication (conversation with B. Butler, Landau Associates, Edmonds, WA regarding WTPH analytical method change). Washington State Department of Ecology.

 

Ecology. 1995. Best Management Practices (BMPs) for Management and Disposal of Street Wastes. Draft. Washington State Department of Ecology1 Water Quality Program. July.

 

Ecology. 1994. Guidance for Remediation of Petroleum Contaminated Soils. Washington State Department of Ecology.

 

Ecology. 1993a. MTCA-STAT. July.

 

Ecology. 1993b.  The Model Toxics Control Act Cleanup Relations. Chapter 173-340 WAC.

Washington State Department of Ecology, Toxics Cleanup Program. Publication No. 9&06.

Amended December.

 

Ecology. 199la. Total Petroleum Hydrocarbons Analytical Methods for Soil and Water. Guidance for

Remediation of Releases from Underground Storage Tanks. Appendix L. Washington State

Department of Ecology. April.

 

Ecology. 1992b. Statistical Guidance for Ecology Site Managers. Washington State Department of Ecology, Toxics Cleanup Program. August.

 

EPA. 1991. Human Health Evaluation Manual, Supplemental Guidance: "Standard Default Exposure Factors." Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency, Washington, D.C. OSWER Directive 9285.64)3. March.

 

EPA. 1990. National Oil and Hazardous Substances Pollution Contingency Plan. Final Plan. U.S. Environmental Protection Agency. Federal Register 55(46): 8665-8865.

 

EPA. 1989. Risk Assessment Guidance for Superfund. Volume 1: Human Health Evaluation Manual

(Part A). Interim Final. Office of Emergency and Remedial Response, U.S. Environmental

Protection Agency, Washington, D.C. EPA/540/1-89/002. July

 

EPA. 1986. Test Methods for Evaluating Solid Waste. SW-846, third edition with updates. U.S. Environmental Protection Agency.

 

Calvin, David V. and Richard K Moore. 1982. Toxicants in Urban Runoff - Metro Toxicant

Program Report #2, Toxicant Control Planning Section, U.S. Environmental Protection Agency.

December.

 

Hepp, M. 8 December 1995. Personal communication (conversation with B. Butler, Landau Associates, Edmonds, WA).

 

IRIS. 1995. Integrated Risk Information System, National Library of Medicine. Bethesda, MD. December Landau Associates, Inc. 1995a. Letter from B. Butler to M. Perla (Snohomish County) regarding project scope. February 1.

 

Landau Associates, Inc. 1995b. Street Waste Characterization Project, Report of Winter 1995 Chemical Analysis Results. Landau Associates, Inc. Edmonds, Washington. May 12.

 

Landau Associates, Inc. 1995c. Street Waste Characterization Project, Report of Summer 1995 Chemical Analysis Results. Landau Associates, Inc. Edmonds, Washington. October 27.

 

Landau Associates, Inc. 1995d. Street Waste Characterization Project, Transmittal of Autumn 199 Chemical Laboratory Data Sheets. Landau Associates, Inc. Edmonds, Washington. December 11

 

San Juan, C. 1994. Natural Background Soil Metals Concentrations in Washington State. Washington State Department of Ecology 9&115.

 

Shaheen, D. 1975. Contributions of Urban Roadway Usage to Water Pollution. Washington, D.C.

U.S. Environmental Protection Agency, Office of Research and Development (EPA-60O/2-754)04~

346 pp.

 

SHD. 1995. Policy Statement Regarding Street Waste Solids, Recycling and Disposal. Snohomish

Health District, Environmental Health Division, Solid Waste and Toxics Section, Everett, WA

January 1.

 

SWMD. 1995a. Memorandum from M. Perla to S. Johnson (Snohomish County Council regarding VGTF study update July 31.

 

SWMD. 199Sb. Letter from M. Perla (Snohomish County Solid Waste Management Division to B. Butler ~andau Associates) regarding additional chemical analyses. August.

 

W & H Pacific. 1994. Final Report: Vactor and Street Sweeping Treatment, Recycling and Disposa Options, Snohomish County, WA. February 16.

 

Zemo, D.A., J.E. Bruya, and T.E. Graf. 1995. The Application of Petroleum Hydrocarbor

Fingerprint Characterization in Site Investigation and Remediation. Ground Water Monitoring

Review. pp.147-156. Spring.


Appendix C

 

Snohomish County Public Works, Road Maintenance Division

Laboratory Test Results and Sweeping Testing

Interim Report



 









    



 






        
Snohomish County Public Works

Road Maintenance Division

Sweepings Testing Interim Report   June 26, 1996

 

Background

 

Pursuant to the issuance of Snohomish County Health District (SHD) Policy on Street Waste Solids Recycling and Disposal, in January, 1995, we have constructed containment facilities, treated and tested 2,600 CY of street sweepings. In the spring of 1995, existing sheds at three locations were modified to accommodate storage of this material on asphalt pads, under roofs and with controlled drainage. The volume soon exceeded this capacity, due to lack of viable reuse options, and the sweepings were stockpiled in open yard space. This report will address three phases of the program which has been pursued to determine how this material can be reused.

 

 

Initial Characterization

 

The 1,600 CY of sweepings accumulated from January to June, 1995, were screened and stored in inside and outside stockpiles. In August, 1995, base line samples were taken for laboratory analysis from pre and post screened material. Six samples were taken for sieve analysis and % organic content as shown on Sheet 2. Results of this initial testing eliminated the potential for reusing the screenings incorporated with feed stock for asphalt production; due to excessive organic content, which ranged from 4.2% to 13.4%. Laboratory testing using the criteria in Table 2, MTCA Method A Soils Cleanup, SHD Policy, showed NO contamination other than Heavy Oil (C24-C34) hydrocarbons, after using the acid cleanup step with the WTPH-D Extended method.

 

Efforts were initiated to find a way to physically separate the screened material by particle size and separate fractions. After researching national sources and talking to five vendors/consultants with environmental expertise, it was apparent that no current technology was available to perform the separation. In October, 1995, samples were taken for experimental bench testing of the physical separation concept, with encouraging results; both physically and chemically. In January, 1996, a Clean Washington Center Technology Validation Project Grant proposal was submitted for a development project.

 

The outside pile of 835 CY was screened in 33.2 machine hours, 58 man-hours, at a rate of 23 CY/IHr. That effort produced 80 CY of trash or 10% trash. The screenings are fairly uniform

in composition and particle size, however still contain excessive organics, plainly visible, as well as trash particles and chips of the yellow chromate rpm's.

 

The inside pile of 765 CY was screened in 25.2 machine hours, 44 man-hours, at a rate of 33 CY/IHr. That effort produced 30 CY of trash or 4% trash. Screening the dry materials went through the screen quicker than the wet; however, it seems that protection from the weather aided the decomposition of the inside pile, since the composition of the original materials had to be fairly uniform.

 

 

 

Followup Testing

 

      Twenty three samples have been taken for laboratory analysis; before and after screening some of the material, from material which has been stockpiled uncovered and covered, over months of time and that which was recently screened. Sheets 1, 3, 4 & 7 show the test results. The quantifying analysis, which I did on the initial completion of screening the sweepings from early in 1995, showed that the decomposition of covered piles is accelerated over the uncovered piles. The stockpile which had been under roof produced 4% trash off the screen, by volume. The uncovered stockpile produced 10% trash by volume. Seven samples taken from the covered piles, over eight months, average 46 ppm diesel and 357 ppm heavy oil after the WTPH-D ext Cleanup testing. These appear to be residual contamination since the diesel deviation is only ±7 ppm and the heavy oil is + 143 and - 167 ppm. Although there is no laboratory test available to prove it; I am fully convinced that any lingering heavy oil result is mostly asphalt particles. Charts #2 & 3 show the graphic results of the diesel and heavy oils values. The graphics demonstrate the difference between the D-ext test and the Cleanup for both products; however there are still false positives in the latter, proven by lab testing of 100% organic samples.

 

The remaining analytes identified in Table 2 of the reference follow:

 

WTPH-G was not run on these samples as no volitles were suspected.

 

PAH test results were well below the reportable 1.0 ppm range. The maximum value of the eighteen compounds in the test parameters of 0.37 was defined from sample #16 as pyrene.

The majority of the mini spikes, shown on chart #1, are pyrene. Over half of the samples show less than 0.15 ppm.

 

PCB testing was included in twenty one samples and no detects were identiied for any of the seven compounds per sample.

 

Metals testing for the five elements had some random values detected, however none of the results exceeded the reportable limits for the respective elements, shown on chart #4.

 

          The results of the above testing should demonstrate that a baseline program has been established in Snohomish County for street sweepings, which defines that this material, when screened, can be used for general purpose fill in industrial and commercial sites as described in the reference.

 

 

Composting

 

We have a test pile of mixed material; 25% each of screened sweepings, screenings from log yard, sawdust and chicken manure, which has been composting since early November, 1995. The test is ongoing at this time. Six samples have been taken, two each at 60 day intervals. Samples # 12, 13, 18, 19, 28 & 29 on the tables and graphics are from this high organic mixture. At this time, after six months decomposition and pile rotation eight times, the current testing methods and standards will not allow rich organic compost to achieve the 65 PPM "Clean" threshold.

 

 

 

 

 

Summary

 

Working closely with the SEID, we have been successful in reusing sweepings for two specific projects; building a berm and top dressing on reclamation slopes, both of which were encapsulated by hydroseeding.

 

We have been successful in achieving the CWC grant assistance to conduct the Street Wastes Reprocessing and Reuse Project (SWRRP) which will include vactor grit and sweepings. The one year contracted performance period started on June 24, 1995.

 

win6/datalswwaste~swtstrpUbc/hd


 

Appendix D

 

Eco-Block Manufacturing as an Alternative Catch Basin

Waste Disposal Method


Eco-Block Manufacturing

as an alternative

Catch Basin Waste Disposal Method

November 13, 1996

 

                          In late 1994 we began to investigate methods of disposal for waste material removed from stormwater catch basins and control structures throughout Kitsap County. Study revealed the cost of disposal at the local landfill to be $39.95 per ton. At this tonnage rate, the tipping fees for the contaminated material would be approximately $6,800.00 per 100 cubic yards. $9,000.00 includes truck time and driver wages for a total of$15,800.00. It was decided at that time that further analysis was in order to find a less expensive means of disposal.

 

Since the fall of 1994, an experimental method of disposal has been introduced with notable success, both logistically and financially. The material removed from catch basins and control structures is being cast into concrete Ecology Blocks. A surplus concrete mixing machine purchased from the U.S. military was brought to the Central Kitsap Treatment Plant. Repairs and refinements were made to the machine, for total outlay of $1,000.00. Concrete forms were constructed with steel and materials purchased at auction for $1,000 and production was begun.

 

In the first eleven months of 1996 seventy-nine stormwater control structures and 1254 catch basins were cleaned. This maintenance operation generated 417 tons of waste material. Two hundred sixty blocks were produced, using 390 tons of the waste. Each block uses 3,000 lbs. of the catch basin waste and 5 sacks of cement at $5.00 per sack. Total expenditure for cement at that point was $6,500.00. After a few initial castings, it was found necessary to add some washed rock to the casting mix to achieve a suitable strength. Approximately 1/10 cubic yard of rock is added to each block, which increased the cost per block by 70 cents. The cost outlay for block production as of November '96 was $25.70, or approximately $26.00 per block. Labor for block production is offset by the labor saved for hauling time to landfill, the labor that would be used to haul blocks purchased from outside vendors, and truck rental fees. The difference in cost between our "Bob-Blocks" and those locally available from private manufacturers is approximately $8.00 per block, ours being the more expensive. The tipping fee at the landfill for the waste put into one block is $60.00, and would have been $15,580.50 for the 390 tons we have already disposed of. (For under $8,500, $2,000 of which is one-time outlay for equipment.)

 

One hundred fifty blocks were used on one bank stabilization project by the Surface and Stormwater team. The Berger Street Detention Pond had one to one slopes on the sides of the pond in sandy material, which had become increasingly difficult to hold in place. The concrete blocks were placed on two sides in a three tiered wall, which produced a stable, attractive, no maintenance bank control. Another 50 blocks have been utilized by the Road Department for

 

 

 

614 Division Street, MS-26, Port Orchard, WA 98366 (360) 876-7124

 

A cooperative effort by Kitap County Departments of Public Works and Community Development, Bremerton-Kitsap County Health District and Kitsap Conservation District

various construction projects, and they have recently ordered more. Some remain in stock at this time.

 

Interest in using more of our "Bob-Blocks" from the Road Department has been strong, and the Surface and Storinwater Management Program intends to utilize them yearly for various bank stabilization and erosion control projects. As of June 1997 the Kitsap County Road Department continues to use our blocks on their bank stabilization tasks. Our department drew the attention of the Kitsap County Board of Commissioners last year ('95) and was issued a Waste Prevention Award for our progress in reducing wastes sent to the landfill.

 

Latex paint from the 1995 Household Hazardous Waste Round-up has been added to the concrete mixture with satisfactory results. The latex does not change the color of the block, and does not noticeably affect strength. This will eliminate another disposal expense to Kitsap County, and further reduces the volume of waste sent to the landfill. Many blocks that have had the latex added to them are doing well in service around the county.

 

In conclusion:

The block manufacturing test has proven itself to be cost effective, environmentally sound and very productive.

 

 

Bob Mills

SSWM Operations & Maintenance Supervisor

Kitsap County Public Works

4117 Kitsap Way

Bremerton, WA 98312

(360) 895-8990 or 8996


Appendix E

 

General Kinematics Drawing of Prototype Street

Solids Separation Equipment




Appendix F

 


Schematic Drawing of Prototype Street Solids

Separation Equipment