Funding Acknowledgment
This report was prepared by the Clean Washington Center, with funding from the state of Washington and the U.S. Commerce Department's National Institute of Standards and Technology (NIST). The Clean Washington Center is the Managing Partner of the Recycling Technology Assistance Partnership (ReTAP), an affiliate of NIST's Manufacturing Extension Partnership (MEP).
Disclaimer
ReTAP and the Clean Washington Center disclaim all warranties to this report, including mechanics, data contained within and all other aspects, whether expressed or implied, without limitation on warranties of merchantability, fitness for a particular purpose, functionality, data integrity, or accuracy of results.
This report was designed for a wide range of commercial, industrial and institutional facilities and a range of complexity and levels of data input. Carefully review the results of this report prior to using them as the basis for decisions or investments.
Copyright
This report is copyrighted by the Clean Washington Center. All rights reserved. Federal copyright laws prohibit reproduction, in whole or in part, in any printed, mechanical, electronic, film or other distribution and storage media, without the written consent of the Clean Washington Center. To write or call for permission: Clean Washington Center, 2200 Alaskan Way, Suite 460, Seattle, Washington 98121. (206) 443-7746. TABLE
OF CONTENTS ACKNOWLEDGMENT EXECUTIVE SUMMARY 1. INITIAL SITE ASSESSMENT AND DESCRIPTION 1.1 TREATMENT DESCRIPTION 1.2 SITE CONDITIONS 1.3 PHOTOGRAPHIC RECORD 1.4 BIOSWALE DESIGN BASIS
2. EXPERIMENTAL PLAN DESIGN 3. PERFORMANCE MONITORING 3.1 STORM 1 DATA
3.2 STORM 2 DATA
3.3 STORM 3 DATA
3.4 STORM 4 DATA
3.5 STORM 5 DATA
3.6 STORM 6 DATA
3.7 STORM 7 DATA
3.8 AVERAGE
GRASS HEIGHT COMPARISON
3.9 AVERAGE PERCENT COVERAGE COMPARISON
3.10 FLOW RATE COMPARISON
3.11 AVERAGE REMOVAL PERCENTAGE COMPARISON
4. RECOMMENDATIONS
Appendices
Appendix A: Photographic Record (Not included in this electronic file but available upon request Appendix B: Laboratory Data (Not included in this electronic file but available upon request Appendix C: Graphs of Individual Parameters by Storm (Not included in this electronic file but available upon request) Appendix D: King County Surface Water Design Manual - Bioswale Section (Not included in this electronic file but available upon request)
List of Tables
Table l Proposed Protection Technologies Table 2 Nutrient Needs of Several Grass Types Table 3 Compost Characteristics Table 4 Nutrient Needs and Loading for Bioswale Table 5 Seeding Needs For Bioswale Design Table 6 Initial Testing Analyses Table 7 Testing Results for Each Storm Event Table 8 Testing Results for Storm 1 Table 9 Testing Results for Storm 2 Table 10 Testing Results for Storm 3 Table 11 Testing Results for Storm 4 Table 12 Testing Results for Storm 5 Table 13 Testing Results for Storm 6 Table 14 Testing Results for Storm 7
List of Figures
Figure l Storm 1 Treatment Comparison for Compost Amended Bioswale and Control Figure 2 Storm 2 Treatment Comparison for Compost Amended Bioswale and Control Figure 3 Storm 3 Treatment Comparison for Compost Amended Bioswale and Control Figure 4 Storm 4 Treatment Comparison for Compost Amended Bioswale and Control Figure 5 Storm 5 Treatment Comparison for Compost Amended Bioswale and Control Figure 6 Storm 6 Treatment Comparison for Compost Amended Bioswale and Control Figure 7 Storm 7 Treatment Comparison for Compost Amended Bioswale and Control Figure 8 Comparison of Grass Height for Compost and Control Figure 9 Grass Coverage Comparison Figure 10 Flow Rate Comparison Figure 11 Comparison of Average Removal Efficiency ACKNOWLEDGMENT
ReTAP is a venture of the Clean Washington Center, Washington State's lead agency for the market development of recycled materials, and a Division of the Department of Community Trade and Economic Development. 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.
Executive Summary
This report discusses the design, testing procedure, and results from a project that examined the effects of using compost in bioswales for the treatment of storm water runoff. Bioswales are narrow, shallow, grass lined ditches, which are considered appropriate technology for treating contaminated runoff for sediment, hydrocarbon, color, and BOD5 removal. Design guidelines for bioswales call for a substrate of rich, organic soil suitable for moisture retention and promotion of thick grass growth. Compost, mixed at the appropriate rate to avoid overloading of nutrient and subsequent nutrient rich runoff, is well suited for a bioswale substrate.
The results of testing from several storm events indicated that the use of compost promotes better treatment of the runoff sent through the swale. A test swale 200 feet long was split in half length-wise with a flow divider. One half was built and seeded according to traditional practices, and the other half used compost in the substrate. Identical seeding practices were used on both sides, and equal flow was sent down the two halves.
The compost side showed faster growth, thicker coverage, and higher removal efficiency than the control side (no compost). The compost helped the grass endure poor weather conditions such as dry spells and heavy flow. The thicker growth helped prevent erosion of the soil, and therefore provided more even and slower flow through the swale. Slow flow is needed to ensure that the sediment settles out of the flow, and the control side had erosion problems, in the form of rivulets, where all of the seed and soil was washed out, allowing the water to flow through quickly. The compost side did not erode, and provided the proper flow speed to treat the runoff. In almost every case for all seven of the storms, the compost side outperformed the control side in terms of pollutant contaminant removal.
The report also provides design guidelines for the design of bioswales and the use of compost. Although there are some site specific conditions, bioswales should have a:
· Minimum length of 200 feet. · Maximum velocity of 1.5 ft/sec. · Maximum depth of flow of 1 inch (urban). · Maximum depth of flow of 4 inches (rural). · Minimum contact time of 2.5 minute. · Maximum width of 50 feet. · Maximum grass height of 6 inches of dense growth.
For the compost used in this test, the nutrient needs of the grass were met with a two inch layer tilled in to a depth of six inches. This is approximately what should be used on most swale situations, but the nutrient content of the compost will dictate the exact loading rate, and should be calculated on a site-by-site basis. The calculation methodology is shown in the report.
1. INITIAL SITE ASSESSMENT AND DESCRIPTION1.1 TREATMENT DESCRIPTION
A biofiltration swale is a vegetated channel which is sloped similarly to a standard storm drain. Stormwater runoff from a given physical area is collected and directed to the swale for water quality treatment. Stormwater enters the swale at one end and exits from the other, with treatment provided as the runoff passes through the channel. Bioswales treat runoff through both physical and microbiological principles.
Bioswale is a term with roots in the words biofiltration and swale. Biofiltration is a general term which refers to physical ability of vegetation to remove pollutants from water. Swales are shallow, wide ditches in which a dense growth of grass is established. Bioswales are broad, shallow ditches specifically designed to direct flow through at a rate and depth which will allow for control of pollution from urban and rural runoff. Bioswales have somewhat recently been recognized as an innovative method of reducing pollutant flow to the surface waters of an area.
Pollutant removal in a bioswale depends on the time the water spends in the swale (residence time) and the contact with the soil and vegetation. As a result, minimum swale lengths along with maximum flow speeds and water depth have been established as part of the design criteria for a bioswale. Residence time depends upon swale length, volume of runoff, and flow velocity. Flow velocity depends upon vegetation, and cross sectional dimension. Performance depends upon proper design of all of these factors.
Treatment is achieved through simultaneous processes of filtration, infiltration, absorption and biological uptake of pollutants in stormwater, which take place as stormwater runs over the vegetated areas of the swale. Vegetation acts as a physical filter which slows flow and causes gravity-settling of particulates; it also acts as a biological sink when direct uptake of dissolved pollutants occur. Another means of pollutant removal occurs as stormwater comes in contact with the soil surface and infiltrates the underlying soil. Soil filtration acts as an important removal mechanism for both dissolved heavy metals and phosphorus. These contaminants are reduced/removed by undergoing ion exchange with elements in the soil. In addition, biological activity in the soil can metabolize organic contaminants. In cases where porous soils are present, general limits for infiltration must be met, or a liner must be put in place to ensure that the runoff receives treatment along the entire length of the swale.
When considering the parameters stated above, it makes intuitive sense that a swale which establishes thick, dense, grass growth is likely to show superior treatment of the runoff directed through it over one with a weaker growth of grass. Therefore, a method of establishing this growth sooner and stronger would be a beneficial addition to a bioswale project. Compost should provide this positive addition, if added at the proper loading rate to ensure that nutrients do no exceed the needs of the grass.
The King County Surface Water Management Division is revising their Surface Water Design Manual, and is proposing new levels of treatment for the protection of sensitive surface water. The four levels of treatment including their target goals are shown in Table 1. Table 1: Proposed Protection Technologies
1.2 SITE CONDITIONS
The bioswale used for this experiment is located at the Land Recovery, Inc. (LRI) landfill in Puyallup, Pierce County, Washington. The swale is designed to handle and treat runoff from the yard debris receiving and processing area. This area is approximately 1 acre in size and is paved with an impervious surface. Flow from this area consists of leachate from truck loads of yard debris and runoff from rainfall (the site is uncovered). The runoff comes in contact with both unchipped and ground materials, and is directed to a catch basin located at the lowest point of the paved surface. The water flows to a lined holding pond, designed to contain large storm flow and regulate discharge to the bioswale. Level sensors trip pumps at the bottom of the pond, which pump the water approximately 1000’ to the bioswale. 1.3 PHOTOGRAPHIC RECORD
A photographic record of site conditions is available in Appendix A. These photos show the site before construction began and during each of the storm sampling events. In addition, there are photos of the pipe discharge (entrance to the bioswale), growth differences, and bioswale discharge. The photos are intended to provide a visual context to the reader. 1.4 BIOSWALE DESIGN BASIS
The bioswale design specifications were derived from two documents. These documents are: · The King County Surface Water Design Manual, January 1990. · The Storm Water Management Manual for the Puget Sound Area, DOE, February 1992.
The pertinent chapters of these two documents can be found in Appendix D at the end of this report. In addition to the design guidelines, a sample worksheet for calculating bioswale specifications is included. The design guidelines outline several parameters and list minimums or maximums for each. These include:
· Minimum length 200 feet · Maximum velocity 1.5 ft/sec · Maximum depth of flow (urban) 1 inch · Maximum depth of flow (rural) 4 inches · Minimum contact time (approximate) 2.5 minutes · Maximum width 50 feet · Maximum grass height 6 inches, dense growth
The bioswale designed for the LRI site has been tested for all of the above parameters, and is well within all of the criteria. The swale measured 260 feet long and 10 feet wide, and its hydraulic performance was quite good. The performance comparison for the two sides of the bioswale is addressed in Section 3 of this report.
A flow splitter was designed to split the swale lengthwise and allow for a roughly equal distribution of the flow between the two sides of the swale. The splitter was two feet high and was buried to a depth of one foot, leaving one foot above the ground. It was constructed with wood and had a plastic liner draped over its top. This liner was buried and served as the liner of the swale, as well. Covering the splitter with a liner served to protect the experiment from any danger of cross flow between sides and subsequent skewing of results. The splitter worked well for the duration of the experiment.
2. EXPERIMENTAL PLAN DESIGNThis section defines the compost and seeding application rates used in the experimental design plan for the study of the use of compost in bioswales. Bioswales are used for the treatment of surface runoff from roads, parking lots, and other impervious surfaces. The runoff is polished (cleaned) in a grassy swale through physical and biological removal of contaminants in order to render the water suitable for discharge into the surface water of the surrounding area. The purpose of the study is to determine if the addition of compost to bioswales can increase their effectiveness in treating the runoff for nutrient and contaminant removal.
The experiment used the King County Surface Water Design Manual for the design of the bioswale with modifications in the fertilization recommendations only. The analysis of the compost to be used established what level of nutrients were available in the compost, and therefore what amount of fertilizer could be omitted from the recommendation. The use of compost adds valuable nutrients and organic material for the promotion of target plant survival and growth density. This improvement in soil structure and organic base should, in turn, promote a better polishing effect in a bioswale. There is the possibility that the compost will release nitrogen into the water stream for a period of time. This phenomenon was monitored closely in the bioswale, which was split in two identical halves (side by side), one with compost amendment, and one without.
Supplement Needs (per 1000 square feet, as per King County Surface water
Design Manual)
If hydro-seeding - 5 lb. seed mix* 50 lb. mulch product (native mulch compost, 2 cubic feet) If broadcast seeding - 5 lb. seed mix* 70 lb. mulch product (native mulch compost, 2.5 cubic feet) *Seed mixes are described in detail in Table 5. Nutrient needs for the grass seed mix were modified from the King County Surface Water Design Manual to take into consideration the nutrients already present in the compost and the organic nature of the material. The nutrient needs described in Table 2 are based upon actual data from uptake studies on the listed grasses.
Table 2:
Nutrient Needs of Several Grass Types
The bioswale designed at the LRI landfill at 10’ wide and 260’ long, had a total surface area of 2600 square feet. Half of the bioswale area, or 1300 square feet, was treated with compost, while the other half was treated as described in the King County Surface Water Design Manual.
Pounds of Nutrients Required As stated, the area of the bioswale which was amended with compost was approximately 1300 square feet. The nutrient needs in lb/1000 ft2 can be converted to lb/1300 ft2 by multiplying by 1.3. The nutrients available in the compost can be expressed in dry lbs./cy. From this, an application rate can be calculated in cubic yards/1300 ft2 with the following equation:
cubic yards of compost/1300 ft2 = lb nutrients/1300 ft 2 lb available nutrients/cy
The compost will be applied in a quantity to satisfy the lower of the two demands for nitrogen and phosphorus, in an effort not to over apply either. In this case, the compost is applied to supply all of the nitrogen needs of the grasses. Table 3 shows the characteristics of the compost used to amend the bioswale.
Table 3: Compost Characteristics
Table 4 details the calculation process for determining the compost application rate for the bioswale. As can be seen in Table 4, there is sufficient nitrogen in the 7.9 cubic yards of compost designed to meet the plant needs. Nitrogen and phosphorus were chosen as limiting factors since they both pose a threat to the area surface waters.
Table 4: - Nutrient Needs and Loading for Bioswale
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