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==Recommended credits for impervious surface disconnection== | ==Recommended credits for impervious surface disconnection== |
Impervious surface disconnection is the redirection of stormwater runoff from impervious surfaces (e.g., sidewalks, parking lots, rooftops, etc.) to vegetated areas instead of the runoff being discharged offsite via a storm sewer system or other conveyance methods. Redirection of impervious surface runoff to properly maintained vegetated areas promotes increased infiltration and reduces overall site runoff. The reduction in site runoff from impervious surface disconnection can vary considerably, depending on many factors, including the size of the contributing drainage area, size and infiltration capacity of the vegetated area receiving the additional stormwater, and numerous other site conditions such as slope and site grading.
To estimate the runoff reduction from impervious surface disconnection, two variables were examined:
A modeling analysis was performed to quantify the runoff reduction achieved from redirecting runoff from impervious areas to pervious areas of varying size and soil type. The long-term, 35-year continuous simulation XP-SWMM model developed in support of the MIDS performance goal development (Barr, 2011) was modified to represent watersheds with I/P ratios ranging from 0.2:1 to 50:1 and hydrologic soil types of A, B, C, and D. See the Assessment of MIDS Performance Goal Alternatives: Runoff Volumes, Runoff Rates, and Pollutant Removal Efficiencies report for additional information on the hydrologic model input parameters utilized for this model. As described in the report, all soil types were assumed to be frozen and impervious to infiltration each year from December 6 to April 7. Hydrologic soil type and I/P ratio are therefore assumed to have no effect on runoff volume during the frozen ground period.
The figures to the right show the average annual runoff depths for all modeled I/P ratios and soil types and the average annual runoff reductions for all modeled I/P ratios and soil types. Note that the annual runoff depths are based on the assumption that runoff from the frozen ground period is 4.0 inches for all I/P ratios and soil types. The runoff reduction is greatest from the sites with the smallest I/P ratio of 0.2:1 (for example, 100 square feet of impervious surface redirected to 500 square feet of pervious area) and decreases as the I/P ratio increases. For a given I/P ratio, the runoff reduction is greatest for A soils and least for D soils, as would be expected.
Impervious surface disconnection spreads runoff generated from parking lots, driveways, rooftops, sidewalks and other impervious surfaces onto adjacent pervious areas where it can be infiltrated. The larger the pervious area is in comparison to the redirected impervious area, the greater the runoff reduction achieved. However, when applying the modeling results it is important to recognize that the “effective” pervious area on a site may be less than the available pervious area, as redirected flows will tend to channelize at flow lengths greater than 100 feet (WinTR-55, 2009) and prevent runoff from being distributed over the entire available area. To prevent overestimating the effectiveness of impervious surface disconnection, we suggest that the “effective” pervious area be limited to a flow length of 100 feet beyond the impervious surface runoff discharge point and have less than a 5 percent slope.
For new developments that create more than one acre of new impervious surface on sites without restrictions, the MIDS performance goal is that stormwater runoff volumes will be controlled and the post-construction runoff volume shall be retained on site for 1.1 inches of runoff from impervious surfaces statewide. Our suggested approach for quantifying the volume reduction benefit achieved from impervious surface disconnection in terms of the MIDS performance goal is summarized below. An example calculation is included below.
\(Pre-disconnection RO = (Area_{p})(RD_{p}) + (Area_{i})(RD_{i})\)
where:
\(I/P Ratio = (Area_{i redirect})/(Area_{p eff})\)
where:
\(Post-disconnection RO = (Area_{i redirect} + Area_{p eff})(RD_{redirect}) + (Area_{p noneff})(RD_p) + (Area_{i nonredirect})(RD_i)\)
where:
\(Adjusted impervious RO = (Post-disconnection RO) - (Area_p)(RD_p)\)
where:
\(Area_{i,adj} = (Adjusted impervious RO) / (RD_i)\)
where:
\(BMP volume credit = 0.092 (Area_i - Area_{i, adj})\)
where:
The approach described in the steps above results in an equivalent BMP volume credit that can be used to evaluate conformance with the MIDS performance goal. To estimate the annual runoff volume reduction that is achieved by implementation of impervious surface disconnection, we recommend applying the performance curves developed for assessing annual performance of bioretention basins. These performance curves, which were developed for sites ranging from 10 to 90 percent imperviousness and hydrologic soils groups A, B, and C, allow for estimation of the average annual runoff volume reduction based on an equivalent BMP volume per tributary drainage area.
The MIDS calculator estimates the average annual removal of total phosphorus (TP), dissolved phosphorus (DP), and total suspended solids (TSS) from stormwater runoff as a result of BMP implementation. For runoff that is infiltrated as a result of the impervious surface disconnection, 100 percent pollutant removal is suggested. For runoff that is not infiltrated, but conveyed across the effective pervious area, pollutant removal consistent with that of a filter strip is suggested (current draft of MIDS calculator uses 68 percent annual TSS removal and 0 percent TP and DP removal). If pollutant removal credit is included in the calculator for runoff conveyed over the effective pervious area, additional definition of effective pervious area may be warranted to ensure that the pervious flow length is sufficient to achieve the sedimentation expected to occur during flow through a filter strip. For pervious areas that extend beyond the effective pervious area, a treatment train approach could be used in the MIDS calculator by treating the additional pervious area as a filter strip.
The amount of runoff from pervious surfaces is dependent on many characteristics, with a primary factor being the infiltration capacity of the soil. While the infiltration capacity and runoff potential vary among soil types, other factors such as compaction or soil loosening can result in more or less runoff for a given soil type or texture. Maintaining and/or amending soils in vegetated areas to increase infiltration, termed “Soil Improvements” in this memorandum, is a method of reducing runoff from pervious areas. Soil maintenance and amendment includes loosening or ripping of existing soils to decrease the soil density or modifying or replacing existing soil to achieve increased infiltration.
Barr conducted a modeling analysis to estimate the runoff reduction from maintaining and/or amending soils in vegetated areas using the long-term, 35-year continuous simulation XP-SWMM model developed in support of the MIDS performance goal development (Barr, 2011). To assess the difference in average annual runoff depths under compacted, average, and loosened soil conditions, the saturated hydraulic conductivity (Ksat) values in the XP-SWMM model were adjusted. “Average” values represent the mean Ksat values for each soil texture based on a national database of over 1,000 observed saturated hydraulic conductivities (Rawls, 1998). “Compacted” and “loosened” values represent the geometric mean Ksat values for soils within the national database developed by Rawls that have bulk densities higher and lower than the NRCS recommended value for the soil texture class, respectively (Rawls, 1998). The figure to the right shows the average annual runoff depths under compacted, average, and loosened soil conditions for A, B, and C hydrologic soil groups, as well as average conditions for D soils.
.
Saturated hydraulic conductivity values used in long-term continuous simulation modeling analysis
Link to this table.
Hydrologic soil group | Representative soil texture | Saturated hydraulic conductivity (in/hr) | ||
---|---|---|---|---|
Compacted | Average1 | Loosened2 | ||
A | sandy loam | 0.50 | 0.90 | 2.20 |
B | loam | 0.15 | 0.205 | 0.24 |
C | sandy clay loam | 0.11 | 0.14 | 0.30 |
D | silty clay | N/A | 0.06 | N/A |
1
The Ksat values termed “average” for the modeling analysis represent the mean Ksat values for each soil texture based on a national database of over 1,000 observed saturated hydraulic conductivities (Rawls, 1998).
2The Ksat values termed “compacted” and “loosened” for the modeling analysis represent the geometric mean Ksat values for soils within the national database developed by Rawls that have bulk densities higher and lower than the NRCS recommended value for the given soil texture class, respectively (Rawls, 1998).
For new developments that create more than one acre of new impervious surface on sites without restrictions, the MIDS performance goal is that stormwater runoff volumes will be controlled and the post-construction runoff volume shall be retained on site for 1.1 inches of runoff from impervious surfaces statewide. Our suggested approach to quantifying the volume reduction benefit achieved from maintaining and/or amending soils in vegetated areas in terms of the MIDS performance goal is summarized below. Note that the determination of appropriate soil conditions prior to and following soil improvements will be site dependent.
\(Pre-soil improvement RO = (Area_p)(RD_{po}) + (Area_i)(RD_i)\)
where:
\(Post-soil improvement RO = (Area_{p imp})(RD_{p imp}) + (Area_{p unimp})(RD_{po}) + (Area_i))(RD_i)\)
where:
\(Adjusted impervious RO = post-soil improvement RO - (Area_p)(RD_{po})\)
where:
\(Area_{i adj} = (Adjusted impervious RO) / RD_i\)
where:
\(BMP volume credit = 0.092 (Area_i - Area_{i adj})\)
where:
Areai adj = adjusted impervious area (square feet) for calculation of of performance goal conformance.
The approach described in the steps above results in an equivalent BMP volume credit that can be used to evaluate conformance with the MIDS performance goal. To estimate the annual runoff volume reduction that is achieved by implementation of soil improvements, we recommend applying the performance curves developed for assessing the annual performance of bioretention basins. These performance curves, which were developed for sites ranging from 10 to 90 percent imperviousness and hydrologic soils groups A, B, and C, allow for estimation of the average annual runoff volume reduction based on an equivalent BMP volume per tributary drainage area.
The MIDS calculator estimates the average annual removal of total phosphorus, dissolved phosphorus, and total suspended solids from stormwater runoff as a result of BMP implementation. For runoff that is infiltrated as a result of soil improvements in the vegetated pervious areas, 100 percent pollutant removal is suggested. For runoff that is not infiltrated, 0 percent pollutant removal is suggested. For example, if a 5 percent annual runoff volume reduction is estimated as a result of soil improvements, the average annual total phosphorus, dissolved phosphorus, and total suspended sediment reductions will be 5 percent. For the 95 percent of annual runoff discharged from a site, no additional pollutant removal will be credited.
Three example calculations are presented below. The 1st two examples are for disconnected impervious surfaces (A and B soils, respectively) and the 3rd is for improved soil.
To perform the calculations to determine volume credits for improved turf, runoff depth must be known for the three soil conditions (compacted, average, loosened) and the three soil types being considered (A, B, C. Note that D soils are not considered for this credit.). These values were determined from continuous simulation modeling using XP-SWMM and they are summarized below:
The runoff depth from impervious surfaces is 22.5 inches.
The figure at the right summarizes BMP volume credits for a range of site conditions (20, 50, and 80% impervious) and soil types (A, B, and C soils).
Compost is the product resulting from the controlled biological decomposition of organic materials that has been sanitized through the generation of heat and stabilized to the point that it is beneficial to plant growth. It is an organic matter resource that has the unique ability to improve the chemical, physical, and biological characteristics of soil.
Healthy, undisturbed soils provide important stormwater management functions including efficient water infiltration and storage, adsorption of excess nutrients, filtration of sediments, biological decomposition of pollutants, and moderation of peak stream flows and temperatures. In addition, healthy soils support vigorous plant growth that intercepts rainfall, returning much of it to the sky through evaporation and transpiration. Common development practices include removal of topsoil during grading and clearing, compaction of remaining soil, and planting into unimproved soil or shallow depths of poor quality imported topsoil. These conditions typically produce unhealthy plants that require excessive water, fertilizers and pesticides, further contaminating runoff.
To maintain the natural soil qualities, impacts to undisturbed soils should be avoided and minimized during the construction process. When impacts are unavoidable and soils have been compacted or otherwise disturbed, compost can be used as an amendment to regain some of the characteristics of undisturbed soils.
Compaction of soils significantly affects infiltration of water into sandy and clay soils. Uncompacted sandy soils will infiltrate up to 12 inches of water per hour. When compacted, the infiltration rate decreases to 1 inch or less per hour or a 90 percent reduction in the infiltration of water. Uncompacted clay soils are able to infiltrate up to 9 inches per hour. However, when compacted, the infiltration rate drops to less than ½ inch per hour or a 95 percent reduction in the infiltration of water. This illustrates how compacted soils contribute a significantly greater volume of runoff to the storm water system. Later discussion shows how compost can help to off-set the effect of compaction.
Establishing soil quality and depth regains greater stormwater function in the post development landscape, provides increased treatment of pollutants and sediments that result from development and habitation, and minimizes the need for some landscaping chemicals, thus reducing pollution through prevention. Establishing a minimum soil quality and depth is not the same as preservation of naturally occurring soil and vegetation. However, establishing a minimum soil quality and depth will provide improved onsite management of stormwater flow and water quality.
Compost can be used as a soil amendment to
When amending disturbed soils with compost, it is important to use a compost product that fits the specific situation. In Minnesota, compost is made from a variety of feed-stocks, including yard and leaf debris, residential or commercial food residuals, and animal manure. Each type of feedstock produces a slightly different compost. Examples would be, a yard and leaf compost is low in nutrients (N-P-K or nitrogen-phosphorus-potassium) and the particle size is generally a little more coarse than a manure compost which is higher in N-P-K and has a finer, more uniform particle size. These are important factors, as a yard - leaf compost would be more appropriately used when applying compost to a project site that is close to a water source. In addition, yard – leaf compost is more coarse and is a better choice for a blanket, filter sox or berm to control erosion.
Both yard – leaf compost and the manure compost could be used for turf applications. However, if using manure compost, the fertilizer application may need to be adjusted downward so as to not over fertilize the turf and inadvertently create nutrient runoff.
Compost maturity is another important factor. Using compost that has been properly aged as a post-construction soil amendment promotes healthy root and plant growth and will prevent damage to turf and plantings. When immature compost is applied to soils it continues to decompose and the process of decomposition robs nitrogen from the plants and stunts plant growth, possibly even killing the plant. To facilitate the creation of consistent compost products throughout the United States, the U.S. Composting Council (USCC) created the Seal of Testing Assurance Program (STA). This voluntary program requires participating compost facilities to perform a uniform set of tests on their compost products. Composters who are STA participants are required to furnish test information to compost buyers. This gives the purchaser of the compost the agronomic information needed (such as pH, particle size and test results from a number of other parameters) to successfully use the compost.
When purchasing compost to be used for turf establishment or incorporation into soil as a post-construction soil amendment, look for the specifications listed in the table below.
The goal in amending compacted soils with compost is to reach or exceed the stormwater management benefits of naturally occurring soil and vegetation. Compost amended soils will improve on-site stormwater management and reduce long term operation and maintenance costs for off-site water treatment best management practices. Developing a Soil Management Plan is an important first step in minimizing and mitigating impacts to native soils and maximizing onsite stormwater management benefits.
Step 1 - Determine soil conditions
Step 2: Develop site and grading plans, which:
Step 3 – Develop soil management plan that determines
Step 4: Identify available material source
Step 5: Select amendment options & application
Step 6: Calculate application volumes
Step 7: Specify as-built testing procedures
In areas where remaining topsoil or subsoil will be amended in place, it is important that, at a minimum, certain soil quality and depth improvements are achieved, as follows:
When leaching of nutrients could be harmful to a receiving water, is it important to take the compost source into consideration. Because compost made from biosolids or animal manure tends to be higher in nutrients, there is the possibility of nutrient leaching. In general, adequately composted tree and grass material presents less of a problem than animal waste or mixed municipal compost. These types of compost are less appropriate for certain uses in areas in close proximity to water bodies. Peat (Glader, 2013) and coir (Lucas 2012) compost are lowest in phosphorus and do not typically leach phosphorus. Avoid compost high in phosphorus in projects aiming to minimize phosphorus in runoff from bioretention.
Note that the use of potential nutrient leaching compost as a filter material in such things as compost socks or filter bags should be avoided whenever excess nutrient (see material specifications) content of water flowing through the filter and into a receiving water would cause a problem. Specification of compost without extractable phosphorus is recommended in cases when nutrients are a receiving water concern.
In addition to improving the stormwater management functions of compacted soils, compost has several other beneficial uses. The first part of this Fact Sheet addressed soil compost for uses as a post-construction BMP. Because there are so many benefits for compost, its use in construction runoff control is also discussed in the following paragraphs. Many of the uses of compost certainly overlap and can serve both construction and post-construction purposes.
When purchasing compost to be used for turf establishment or incorporation into soil as a postconstruction soil amendment, look for these specifications.
Link to this table
Parameter | Parameter Definition | Range (Provided by G. Black, MPCA, 2007) |
---|---|---|
Source Material/Nutrient Content | Compost typically comes from biosolids/animal manure or yard wastes. Compost made from biosolids and animal manure typically contains more nutrients.1 |
|
Maturity | Maturity refers to the level of completeness of the composting process. Composts that have not progressed far enough along the decomposition process may contain phytotoxic compounds that inhibit plant growth.2 | Seed emergence and seed vigor = minimum 80% relative to positive control |
Stability | Compost stability refers to the biological activity in the composted material. Unstable composts may use available nitrogen in the soil and stunt plant growth. | CO2 Evolution rate: < 8 mg CO2-C/g-OM/day |
pH | pH is a measure of acidity/alkalinity. Amending soil with compost can alter soil pH, which in turn can improve plant growth. | 5.5 – 8.5 |
Soluble salts | The term “soluble salts” refers to the amount of soluble ions in a solution of compost and water. Because most plant nutrients are supplied in soluble form, excess non-nutrient soluble salts can inhibit plant growth. | Varies widely according to source materials for compost, but should be < 10 dS/m (mmhos/cm) |
Organic matter | Organic matter is a measure of the amount of carbon-based materials in compost. There is no ideal range of organic matter for compost, but knowing the amount of organic matter in compost may help determine application rates for specific applications. | 30-65% dry weight basis |
Particle size | It is helpful to know the size of particles in a compost product. There is no ideal range, but particle size does influence the usability of a compost product for a specific application. | Pass through 1-inch screen or less; 3/4 inch is preferable per MnDOR Specification 3890 |
Biological contaminants (weed seeds and pathogens) | Biological contaminants consist of pathogens (disease causing organisms) and weed seeds. High temperatures will inactivate both types of biological contaminants. Minnesota State composting rules require commercial composting operations to hold temperatures over 55 degrees C over an extended period of time to destroy pathogens. In addition, compost operations must monitor the process to prove that these conditions have been met. | Meet or exceed US EPA Class A standards, 40 CFR §503.32(a) levels |
Physical contaminants (inerts)* | Inerts are man-made materials (like pieces of plastic or glass) that do not decompose. There is no ideal range but they may be aesthetically unpleasing and add no value to the compost. | < 1% dry weight basis3 |
Trace metals | Trace metals are elements that can be toxic to humans, animals, or plants at elevated concentrations | Meet or exceed US EPA Class A standards, 40 CFR §503.32(a) levels |
* Inert material should not be present in adequately screened, vegetated waste compost. Caution should be used when the compost originates as mixed municipal or unscreened compost. |
1 MnDOT Grade 1 compost is derived from animal material; Grade 2 compost is derived from leaves and yard wastes. See MnDOT Specification 3890
2MnDOT Specification 3890 states: "Considered mature and useable when 60 percent decomposition has been achieved as determined by an ignition-loss analysis test method and any one additional test method including the Solvita test value of equal to or greater than 5. This means that the compost product has no offensive smell, no identifiable organic materials, and will not reheat to more than 20 °F [11 °C] above the ambient temperature."
3 MnDOT Specification 3890 states: "< 3% at 0.15 in [4 mm]"
Application guidelines for compost.
Link to this table
Planting areas | Turf areas | |
---|---|---|
High-traffic areas | (18 inch uncompacted depth) Incorporate 3 inches of compost into the top 5 inches of compacted soil to create a topsoil layer with a minimum depth of 8 inches. Soils below the top soil layer should be scarified to at least 10 inches. | Incorporate 1.75 inches of compost into the top 6.25 inches of compacted soil to create a topsoil layer with a minimum depth of 8 inches. Soils below the top soil layer should be scarified to at least 10 inches |
Construction limits | (12 inch uncompacted depth) Incorporate 3 inches of compost into the top 5 inches of compacted soil to create a topsoil layer with a minimum depth of 8 inches. Soils below the top soil layer should be scarified to at least 4 inches | Incorporate 1.75 inches of compost into the top 6.25 inches of compacted soil to create a topsoil layer with a minimum depth of 8 inches. Soils below the top soil layer should be scarified to at least 4 inches |
If you are considering using compost as a “blanket” to reduce or prevent erosion the soil blanket should be a composted, weed free organic matter source derived from: agricultural, food, or industrial residuals; yard trimmings; or source-separated or mixed solid waste. Particle size shall be as described below in the product parameters table. The compost shall possess no objectionable odors, will be reasonably free (less than 1 percent by dry weight) of foreign matter and will meet the product parameters outlined below.
Well-composted product will provide the best planting medium for grass, wildflower, legume seeding or ornamental planting. Very coarse composts may need to be avoided if the slope is to be landscaped or seeded, as it will make planting and crop establishment more difficult. Composts containing fibrous particles that range in size produce a more stable mat.
Product parameters for compost blanket
Link to this table
Parameters1,4 | Reported as (units of measure) | Blanket Media to be Vegetated | Blanket media to be left Unvegetated |
---|---|---|---|
pH2 | pH units | 6.0 - 8.5 | N/A |
Soluble Salt Concentration2 (electrical conductivity) | dS/m (mmhos/cm) | Maximum 5 | Maximum 5 |
Moisture Content | %, wet weight basis | 30 – 60 | 30 – 60 |
Organic Matter Content | %, dry weight basis | 25 – 65 | 25-100 |
Particle Size | % passing a selected mesh size, dry weight basis |
|
|
Stability3 Carbon Dioxide Evolution Rate | mg CO2-C per g OM per day | < 8 | N/A |
Physical Contaminants (man-made inerts) | %, dry weight basis | < 1 | < 1 |
1 Recommended test methodologies are provided in Test Methods for the Examination of Composting and Compost (TMECC, The US Composting Council)
2 Each specific plant species requires a specific pH range. Each plant also has a salinity tolerance rating, and maximum tolerable quantities are known. When specifying the establishment of any plant or turf species, it is important to understand their pH and soluble salt requirements, and how they relate to the compost in use.
3 Stability/Maturity rating is an area of compost science that is still evolving, and as such, other various test methods could be considered. Also, never base compost quality conclusions on the result of a single stability/maturity test.
4 Landscape architects, plant specialists and project (field) engineers may modify the allowable compost specification ranges based on specific field conditions and plant requirements.
A. Construction Requirements:
Compost mulch shall be uniformly applied to a depth described below. Areas receiving greater precipitation, possessing a higher erosivity index, or which will remain unvegetated, will require greater application rates.
The compost should be spread uniformly on up to 1:2 slopes, then track (compact) the compost layer using a bulldozer or other appropriate equipment, if possible. Alternatively, apply compost using a pneumatic (blower) or slinger type spreader unit. Project compost directly at soil surface, thereby preventing water from moving between the soil-compost interface. Apply compost layer approximately 3 feet beyond the top of the slope or overlap it into existing vegetation. On highly unstable soils, use compost in conjunction with appropriate structural, stabilization and diversion measures. Follow by seeding or ornamental planting if desired.
Summary of construction requirements: Compost blanket application.
Link to this table
Annual Rainfall/Flow Rate | Total Precipitation & Rainfall Erosivity Index | Application Rate For Vegetated1 Compost Surface Mulch | Application Rate For Unvegetated Compost Surface Mulch |
---|---|---|---|
Low | 1-25”, 20-90 | ½ - ¾ ” (12.5 mm – 19 mm) | 1” – 1 ½” (25 mm – 37.5mm) |
Average | 26-50”, 91-200 | ¾ - 1” (19 mm – 25 mm) | 1 ½” – 2” (37 mm – 50 mm) |
High | 51” and above, 201 and above | 1-2” (25 mm – 50 mm) | 2-4” (50mm – 100mm) |
1These lower application rates should only be used in conjunction with seeding, and for compost blankets applied during the prescribed planting season for the particular region.
A. Description:
This work consists of constructing a raised berm of compost on a soil surface to contain soil erosion, control the movement of sediment off site, and to filter storm water.
B. Materials: Filter berm media should be a composted, weed free organic matter source derived from: agricultural, food, or industrial residuals; yard trimmings; source-separated or mixed solid waste. Particle size may vary widely. The compost shall possess no objectionable odors, will be reasonably free (less than 1 percent by dry weight) of man-made foreign matter and will meet the product parameters outlined below.
Where seeding of the berm is planned, use only well composted product that contains no substances toxic to plants. Avoid coarse composts if the berm is to be seeded, as it will make establishment more difficult.
The Landscape Architect/Designer shall specify the berm dimensions depending upon specific site (e.g., soil characteristics, existing vegetation) and climatic conditions, as well as particular project related requirements. The severity of slope grade, as well as slope length, will also influence compost application.
Construction requirements for compost blanket application
Link to this table
Parameters1,4 | Reported as (units of measure) | Filter Berm to be Vegetated | Filter Berm to be left Un-vegetated |
---|---|---|---|
pH2 | pH units | 6.0 - 8.5 | N/A |
Soluble Salt Concentration2 (electrical conductivity) | dS/m (mmhos/cm) | Maximum 5 | N/A |
Moisture Content | %, wet weight basis | 30 – 60 | 30 – 60 |
Organic Matter Content | %, dry weight basis | 25 – 65 | 25-100 |
Particle Size | % passing a selected mesh size, dry weight basis |
|
|
Stability3 Carbon Dioxide Evolution Rate | mg CO2-C per g OM per day | < 8 | N/A |
Physical Contaminants (man-made inerts) | %, dry weight basis | < 1 | < 1 |
1Recommended test methodologies are provided in Test Methods for the Examination of Composting and Compost (TMECC, The US Composting Council)
2Each specific plant species requires a specific pH range. Each plant also has a salinity tolerance rating, and maximum tolerable quantities are known. When specifying the establishment of any plant or turf species, it is important to understand their pH and soluble salt requirements, and how they relate to the compost in use.
3Stability/Maturity rating is an area of compost science that is still evolving, and as such, other various test methods could be considered. Also, never base compost quality conclusions on the result of a single stability/maturity test.
4Landscape architects, plant specialists and project (field) engineers may modify the allowable compost specification ranges based on specific field conditions and plant requirements.
C. Construction Requirements: Parallel to the base of the slope or other affected areas, construct a berm of compost to size specifications.
In extreme conditions and where specified by the Landscape Architect/Designer, a second berm shall be constructed at the top of the slope or silt fencing shall be installed in conjunction with the compost berm. Where the berm deteriorates, it shall be reconstructed. Do not use filter berms in any runoff channels (concentrated flows).
Construction requirements for compost filter berm.
Link to this table
Annual Rainfall/Flow Rate | Total Precipitation & Rainfall Erosivity Index | Dimensions for the Compost Filter Berm (height x width) |
---|---|---|
Low | 1-25”, 20-90 | 1’x 2’ – 1.5’ x 3’ (30 cm x 60 cm – 45 cm x 90 cm) |
Average | 51” and above, 201 and above | 1’x 2’ - 1.5’ x 3’ (30 cm x 60 cm – 45 cm x 90 cm) |
High | 51” and above, 201 and above | 1.5’x 3’ – 2’ x 4’ (45 cm x 90 cm – 60cm x 120 cm) |
In addition to improving the stormwater management functions of compacted soils, compost has several other beneficial uses.
Compost can be used to reclaim highly disturbed and low quality soils on sites of old factories, landfills, and brownfields. Application rates in such situations often range from 25 to 175 tons per acre, much higher than typical compost application rates. Benefits include improved soil quality and enhanced plant establishment (Alexander, 1999).
Due to its similar physical and chemical properties to certain wetland soils, compost is being used to mimic hydrology, soil properties and plant community composition wetland functions.
Compost has been shown to be effective in degrading or immobilizing several types of contaminants, including hydrocarbons, solvents, and heavy metals (Alexander, 1999).
Compost has been included as a component of biofilters and bioswales to treat contaminated air and water with great success (Alexander, 1999). Compost treated areas have also be shown to be effective at reducing erosion and stormwater runoff (Glanville, et. al., 2003). Because contaminants adhere to soil particles, this limits the amount of sediment and contaminants reaching water bodies.