Information: This section focuses on conformance with the Minimal Impact Design Standards performance goal of 1.1 inches. However, the methodology can be applied to other performance goals by adjusting the conversion factor in Step 6.
Caution: Turf are not included in the Minimal Impact Design Standards (MIDS) calculator because design, construction and maintenance criteria and specifications have not been developed yet.

This page includes discussion of volume and associated phosphorus and total suspended sediment reduction credits for disconnection of existing impervious surfaces and for soil improvements to enhance infiltration.

## Recommended credits for impervious surface disconnection

Warning: Impervious surface disconnection does not meet the requirement of the Construction Stormwater permit (Part III.D.1.e) that the water quality volume be calculated as an instantaneous volume.

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.

### Modeling analysis and results

Average annual runoff depth from 35 years (1972-2006) of continuous simulation modeling using XP-SWMM. The plots show results for varying ratios of impervious area to pervious area (I/P ratio) for A, B, C, and D soils.
Average annual runoff depth reduction from 35 years (1972-2006) of continuous simulation modeling using XP-SWMM. The plots show results for varying ratios of impervious area to pervious area (I/P ratio) for A, B, C, and D soils.
Illustration showing the recommended effective pervious flow length of 100 feet. This is due to the tendency for flow to channelize beyond 100 feet. In this schematic, the effective pervious area equals 100 feet times the length of parking area adjacent to the pervious surface. The I/P ratio will be the area of parking area redirected to the effective pervious area divided by the effective pervious area.

To estimate the runoff reduction from impervious surface disconnection, two variables were examined:

1. ratio of impervious area to pervious area (I/P Ratio); and
2. infiltration capacity of the vegetated area.

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.

### Suggested credit calculations

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.

### Conformance with the MIDS performance goal

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.

#### Step 1

$$Pre-disconnection RO = (Area_{p})(RD_{p}) + (Area_{i})(RD_{i})$$

where:

Pre-disconnection RO = runoff volume (cubic feet) from site if impervious surface is not redirected to pervious area;
Areap = total pervious area (square feet);
RDp = runoff depth (feet) from pervious area (4.4 inches for A soil, 5.7 inches for B soil, 6.1 inches for C soil, 7.2 inches for D soil);
Areai = impervious area (square feet); and
RDi = runoff depth (feet) from impervious area (22.5 inches).

#### Step 2

$$I/P Ratio = (Area_{i redirect})/(Area_{p eff})$$

where:

I/P Ratio = ratio of redirected impervious area to "effective" pervious area;
Areai redirect = impervious area (square feet) redirected to pervious area; and
Areap eff = “effective” pervious area (square feet) receiving redirected impervious runoff.

The "effective" pervious area is the area over which infiltration of redirected water occurs. In calculating the effective pervious area, the maximum width should be 100 feet. See the discussion of effective pervious and the schematic to the right.

#### Step 3

$$Post-disconnection RO = (Area_{i redirect} + Area_{p eff})(RD_{redirect}) + (Area_{p noneff})(RD_p) + (Area_{i nonredirect})(RD_i)$$

where:

Post-disconnection RO = post-disconnection runoff volume (cubic feet) from entire site;
RDredirect = runoff depth (feet) from redirected impervious area and effective pervious area (determined from modeling results based on soil type and I/P ratio);
Areap noneff = pervious area (square feet) not considered “effective” for receiving redirected impervious runoff;
RDp = runoff depth (feet) from pervious area (4.4 inches for A soil, 5.7 inches for B soil, 6.1 inches for C soil, 7.2 inches for D soil);
Areai nonredirect = impervious area (square feet) not redirected to pervious area; and
RDi = runoff depth (feet) from non-redirected impervious area (22.5 inches).
Average annual runoff depth from 35 years (1972-2006) of continuous simulation modeling using XP-SWMM. The plots show results for varying ratios of impervious area to pervious area (I/P ratio) for A, B, C, and D soils.

To calculate RDredirect, use the figure on the right. For example, a B soil with an I/P ratio of 2:1 has an RDSubscript text of 10.1 inches.

#### Step 4

$$Adjusted impervious RO = (Post-disconnection RO) - (Area_p)(RD_p)$$

where:

Adjusted impervious RO = adjusted runoff volume (cubic feet) from impervious area as a result of redirection to pervious area;
Post-disconnection RO = post-disconnection runoff volume (cubic feet) from entire site;
Areap = total pervious area (square feet); and
RDp = runoff depth (feet) from pervious area (determined from model results based on soil type).

#### Step 5

$$Area_{i,adj} = (Adjusted impervious RO) / (RD_i)$$

where:

Areai,adj = adjusted impervious area (square feet) for calculation of performance goal conformance;
Adjusted impervious RO = adjusted runoff volume (cubic feet) from impervious area as a result of redirection to pervious area; and
RDi = runoff depth (feet) from impervious area (determined from model results).

#### Step 6

$$BMP volume credit = 0.092 (Area_i - Area_{i, adj})$$

where:

Areai = impervious area (square feet);
Areai, adj = adjusted impervious area (square feet) for calculation of performance goal conformance; and
0.092 is a conversion factor. Note this conversion factor is for the 1.1 inch performance goal.

### Annual volume reduction

Bioretention basin volume reduction performance curves for A, B, and C soil types on a 50 percent impervious site

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.

### Annual pollutant removal

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.

## Recommended credits for soil improvement

Information: This section focuses on conformance with the Minimal Impact Design Standards performance goal of 1.1 inches. However, the methodology can be applied to other performance goals by adjusting the conversion factor in Step 5.
Caution: Turf is not included in the Minimal Impact Design Standards (MIDS) calculator because design, construction and maintenance criteria and specifications have not been developed yet.

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.

### Modeling analysis and results

Comparison of average annual runoff grouped by soil type and soil condition.

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.

Caution: It should be noted that due to the empirical methodology used to define the Ksat values, loosened C soils have a higher Ksat than loosened B soils, and thus a lower runoff depth. Given this, it is suggested that the runoff depth from “loosened” C soils be approximated as equivalent to the runoff from “average” B soils for credit calculations

Saturated hydraulic conductivity values used in long-term continuous simulation modeling analysis

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).

### Suggested credit calculations

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.

#### Step 1

$$Pre-soil improvement RO = (Area_p)(RD_{po}) + (Area_i)(RD_i)$$

where:

Pre-Soil Improvement RO = runoff volume (cubic feet) from site if soils not improved;
Areap = total pervious area (square feet);
RDpo = runoff depth (feet) from pervious area reflecting pre-project soil conditions, typically compacted or average (determined from model results);
Area i = impervious area (square feet); and
RDi = runoff depth from impervious area (1.875 feet (22.5 inches)).

#### Step 2

$$Post-soil improvement RO = (Area_{p imp})(RD_{p imp}) + (Area_{p unimp})(RD_{po}) + (Area_i))(RD_i)$$

where:

Post-Soil Improvement RO = runoff volume (cubic feet) from site following soil improvements;
Areap imp = pervious area (square feet) with improved soils;
RDP imp = runoff depth (feet) from pervious area reflecting improved soil conditions, typically average or loosened (determined from model results);
Areap unimp = pervious area (square feet) without improved soils;
RDpo = runoff depth (feet) from pervious areas with unimproved soil conditions, typically compacted or average (determined from model results);
Areai = impervious area (square feet); and
RDi = runoff depth from impervious area (1.875 feet (22.5 inches), based on impervious surface disconnection modeling).

#### Step 3

$$Adjusted impervious RO = post-soil improvement RO - (Area_p)(RD_{po})$$

where:

Adjusted impervious RO = adjusted impervious runoff volume (cubic feet) to represent equivalent runoff reduction from pervious soil improvements;
Post-soil improvement RO = runoff volume (cubic feet) from site following soil improvements;
Areap = total pervious area (square feet); and
RDpo = runoff depth (feet) from pervious areas with unimproved soil conditions, typically compacted or average (determined from model results).

#### Step 4

$$Area_{i adj} = (Adjusted impervious RO) / RD_i$$

where:

Areai adj = adjusted impervious area (square feet) for calculation of performance goal conformance;
Adjusted impervious RO = adjusted impervious runoff volume to represent equivalent runoff reduction from pervious soil improvements; and
RDi = runoff depth from impervious area (1.875 feet (22.5 inches)).

#### Step 5

$$BMP volume credit = 0.092 (Area_i - Area_{i adj})$$

where:

Areai = impervious area (square feet); and

Areai adj = adjusted impervious area (square feet) for calculation of of performance goal conformance.

### Annual volume reduction

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.

### Annual pollutant removal

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.

### Example calculations

Schematic used for the example calculations
Bioretention basin volume reduction performance curves for A, B, and C soil types on a 50 percent impervious site

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.

#### Scenario 1

• 3 acres consisting of 1.5 acres of impervious parking lot and 1.5 acres of pervious turf
• 50 percent impervious
• A soils, with all of the impervious area draining to the pervious area next to a parking lot. The length of the impervious area is 350 feet.
Calculate conformance with the performance goal (1.1 inches)
• Calculate the effective pervious area: Effective pervious area = (100 feet)(350 feet) = 35,000 square feet or 0.8 acres
• The runoff depth from impervious area (RDi = 22.5 inches (from model results))
• Step 1: Pre-disconnection site runoff = ((1.5 acres)(4.4 inches) + (1.5 acres)(22.5 inches))(43560 square feet per acre)(1 foot/12 inches) = 146471 cubic feet
• Step 2: I/Peff ratio = (1.5 acres)/(0.8 acres) = 1.9
• Step 3: Post-disconnection site runoff volume = ((1.5 acre + 0.8 acre)(6.55 inches)+(1.5 acre – 0.8 acre)(4.4 inches))(43560 square feet/acre)(1 foot/12 inches) = 65866 cubic feet
• Step 4: Adjusted impervious runoff = (65866 cubic feet)-(1.5 acre)(4.4 inches)(43560 square feet/acre)(1 foot/12inches) = 41908 cubic feet
• Step 5: Adjusted impervious area = (41908 cubic feet)/((22.5 inches)(1 foot/12 inches)) = 22351 square feet
• Step 6: BMP volume credit = (1.5 acre - 0.51 acre)(1.1 inches)(43560 square feet/acre)(1 foot/12 inches)) = 3941 cubic feet
Calculate annual volume reduction using performance curve for 50 percent impervious site.
• BMP Volume /Drainage Area = (3941 cubic feet)/(43560 aquare feet/acre)/(3 acres) = 0.03
• Corresponding annual volume removal (from performance curve, for A soils, 50% impervious site) = 91 percent
• Annual TP removal = annual volume removal = 91 percent
• Annual TSS removal = (91 percent)(100 percent) + (9 percent)(68 percent) = 97 percent

#### Scenario 2

• 3 acres consisting of 1.5 acres of impervious parking lot and 1.5 acres of pervious turf
• 50 percent impervious
• B soils, with all of the impervious area draining to the pervious area next to a parking lot. The length of the impervious area is 350 feet.

Calculate conformance with the performance goal (1.1 inches)
• Calculate the effective pervious area: Effective pervious area = (100 feet)(350 feet) = 35,000 square feet or 0.8 acres
• The runoff depth from impervious area (RDi = 22.5 inches (from model results)
• Step 1: Pre-disconnection site runoff = ((1.5 acres)(5.7 inches) + (1.5 acres)(22.5 inches))(43560 square feet per acre)(1 foot/12 inches) = 153549 cubic feet
• Step 2: I/Peff ratio = (1.5 acres)/(0.8 acres) = 1.9
• Step 3: Post-disconnection site runoff volume = ((1.5 acre + 0.8 acre)(9.84 inches)+(1.5 acre – 0.8 acre)(5.7 inches))(43560 square feet/acre)(1 foot/12 inches) = 65601 cubic feet
• Step 4: Adjusted impervious runoff = (96638 cubic feet)-(1.5 acre)(5.7 inches)(43560 square feet/acre)(1 foot/12inches) = 65601 cubic feet
• Step 5: Adjusted impervious area = (65601 cubic feet)/((22.5 inches)(1 foot/12 inches) = 34987 square feet
• Step 6: BMP volume credit = (1.5 acre - 0.8 acre)(1.1 inches)(43560 square feet/acre)(1 foot/12 inches)) = 2795 cubic feet
Calculate annual volume reduction using performance curve for 50 percent impervious site.
• BMP Volume /Drainage Area = (2795 cubic feet)/(43560 aquare feet/acre)/(3 acres) = 0.02
• Corresponding annual volume removal (from performance curve, for B soils, 50% impervious site) = 68 percent
• Annual TP removal = annual volume removal = 68 percent
• Annual TSS removal = (68 percent)(100 percent) + (32 percent)(68 percent) = 90 percent

#### Scenario 3

• 10-acre, 50% impervious site
• B soils, with all of the impervious area being "improved" from "compacted" to "average".

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:

A soil
Compacted soil = 4.4 inches
Average soil = 4.1 inches
loosened soil = 4.0 inches
B soil
Compacted soil = 5.2 inches
Average soil = 4.9 inches
loosened soil = 4.7 inches
C soil
Compacted soil = 5.5 inches
Average soil = 5.2 inches
loosened soil = 4.9 inches

Summary of BMP volume credits for range of sites (20%, 50%, 80% impervious) and soil types (A, B, C). The data assume a 10 acre site. For example, on a site that is 50% impervious and having B soils, improving the soil from compacted to loosened provides 0.024 equivalent inches off impervious surface.

The runoff depth from impervious surfaces is 22.5 inches.

Calculate conformance with performance goal
• Treatment volume required to meet 1.1-inch performance goal = (10 acres)(0.50)(43560 square feet/acre)(1.1 inches)(1 foot/12 inches) = 19965 cubic feet
• Step 1: Calculate site runoff prior to soil improvements = (Areap)(RDpo) + (Areai)(RDi) = (5 acres)(5.2 inches)(43560 square feet/acre)(1 foot/inch) = 502755 cubic feet
• Step 2: Calculate site runoff following improvements = (Areap imp)(RDp imp) + (Areap unimp)((RDpo) + (Areai)(RDi) = (5 acres)(43560 square feet/acre)(4.9 inches)(1 foot/inch) + (5 acres)(43560 square feet/acre)(22.5 inches)(1 foot/acre) = 497310 cubic feet
• Step 3: Calculate adjusted impervious runoff to determine credit = (Post-soil improvement runoff) - ((Areap)(RDpo)) = 497310 - (5 acres(43560 acres/square feet)(5.2 inches)(1 foot/12 inches) = 402930 square feet
• Step 4: Calculate ajusted impervious area = (Adjusted impervious runoff)/(RDi) = (402930)/((22.5inches)(1 foot/12 inches)) = 214896 square feet
• Step 5: Calculate performance goal credit = (217800 - 214896)(1.1 inches)(1 foot/12 inches) = 266.2 cubic feet
• BMP volume credit in inches off impervious surface = (performance goal credit)/(performance goal volume) = 266.2/19965 = 0.013 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).

## Spreadsheet for calculating disconnection credit

Schematic illustrating the terms used to calculate the impervious surface disconnection. Note that the maximum flowpath length for the effective pervious area (the area receiving runoff from the redirected impervious surface) is 100 feet.
Average annual runoff depth from 35 years (1972-2006) of continuous simulation modeling using XP-SWMM. The plots show results for varying ratios of impervious area to pervious area (I/P ratio) for A, B, C, and D soils.

A simple calculator allows you to calculate the credit for impervious surface disconnection (File:Disconnection credit calculator.xlsx). You will need the following information to use the calculator:

• soil type;
• area of non-redirected impervious surface (the impervious area that does not run off to the pervious area);
• area of redirected impervious surface (the impervious area that runs off to the pervious area);
• effective pervious area (the pervious area that receives runoff from the redirected impervious); and
• ineffective impervious area.

Another input in the spreadsheet, the I/P ratio, is the area of redirected impervious surface to effective pervious area. Using the I/P ratio for the appropriate soil in the figure to the right allows determination of the runoff depth, which is input into the spreadsheet.

Note that the spreadsheet generates a volume credit for disconnection. It does not calculate the percent credit toward the performance goal. The performance goal includes runoff from both the non-redirected and redirected impervious areas. Thus, the greater the percent of redirected impervious area relative to total impervious area at a site, the greater the volume credit as a percent of the performance goal.

## Compost

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. It can be derived, for example, from composted yard waste, food waste, manure, leaves, grass clippings, straw, or biosolids. Minnesota’s stormwater manual currently calls for organic leaf compost, MnDOT Type 2 compost, to be used in bioretention media (See Specification 3890).

### Key considerations

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.

Figure of Comparison of Soil Infiltration after Compaction (from John Barten, Three Rivers Park District)

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.

Example of dormant seeding - a compost blanket at a Two Harbors site in late November.
The Two Harbors site in early spring. Compost blanket on left, seeded straw mat on right
The Two Harbors site in late summer shows the relative success of the two methods
County Road 41 roadside in Carver County after application of compost blanket.
Compost grouting on Highway 61.
Highway 61 roadside after application of compost grouting.

#### Benefits

Compost can be used as a soil amendment to

• improve soil aggregation;
• increase infiltration;
• reduce runoff;
• improve soil porosity;
• increase soil moisture holding capacity (reduce water demand of lawns and landscaping);
• reduce erosion;
• absorb or aids in degradation of certain pollutants, including hydrocarbons, solvents and heavy metals (due to increased cation exchange capacity);
• reduce fertilizer needs by improving soil nutrient golding capacity;
• reduce pesticide and herbicide needs;
• low cost; and
• does not increase maintenance needs.

### Material specifications

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.

### Turf establishment or incorporation in soil as an amendment

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.

#### Application guidelines

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.

##### Guide to developing a soil management plan

Step 1 - Determine soil conditions

• Soil type
• Organic and moisture content
• Degree of compaction

Step 2: Develop site and grading plans, which:

• Minimize construction limits
• Minimize compaction and construction disturbance
• Minimize soil cut and filling
• Maximize green space
• Maximize preservation of soils with high infiltration rates

Step 3 – Develop soil management plan that determines

• Areas where native soil and/or vegetation will be retained in place;
• Areas where topsoil or subsoil will be amended in place;
• Areas where topsoil will be stripped and stockpiled prior to grading for reapplication; and
• Areas where imported topsoil will be applied.

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:

Soil Quality: For soils in planting areas, a minimum dry weight organic matter content of 10 percent is recommended. For soils in turf areas, a minimum dry weight organic matter content of 5 percent is recommended. Soil pH should range from 6.0 to 8.0 or match the pH of the original topsoil (WDOE, 2005).
Depth: Within the construction limits, a minimum, uncompacted depth of 12 inches is recommended (Kunz and Jurries, 2001, WDOE, 2005). In high traffic areas, a minimum uncompacted depth of 18 inches is recommended.
Warning: Immature compost will not provide the benefits of mature compost. When immature compost is applied to soils it will continue to decompose and the process of decomposition and the by-products it creates and nutrients it demands may be harmful to plants growing in the soil (Garland and Grist, 1995). These effects may be eliminated by adding additional fertilizer, thereby supplying the nitrogen needed for the continued decomposition of the compost and plant needs.

#### Nutrient precaution

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.

### Other benefits and emerging uses of compost

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.

### Erosion control and stormwater management uses of compost

When purchasing compost to be used for turf establishment or incorporation into soil as a postconstruction soil amendment, look for these specifications.

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
• N: 0.5 – 3 (mg/kg)
• P: 0.5 - 1.5 (mg/kg)
• K: 0.5 - 1 (mg/kg)
• NPK ratio: 2:2:1 - 4:4:2
• C:N ratio: 6:1 - 20:1
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, page 685
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.

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

#### Compost blanket application

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

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
• 3” (75 mm), 100% passing
• 1” (25mm), 90% to 100% passing
• 3/4” (19mm), 65% to 100%passing
• 1/4” (6.4 mm), 0% to 75% passing
• Maximum particle length of 6” (152mm)
• 3” (75 mm), 100% passing
• 1” (25mm), 90% to 100% passing
• 3/4” (19mm), 65% to 100%passing
• 1/4” (6.4 mm), 0% to 75% passing
• Maximum particle length of 6” (152mm)
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.

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.

### Compost filter berm application or sediment control

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

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
• 3” (75 mm), 100% passing
• 1” (25mm), 90% to 100% passing
• 3/4” (19mm), 70% to 100% passing
• 1/4” (6.4 mm), 0% to 75% passing Maximum:
• particle size length of 6” (152mm) (no more than 60% passing 1/4” (6.4 mm) in high rainfall/flow rate situations)
• 3” (75 mm), 100% passing
• 1” (25mm), 90% to 100% passing
• 3/4” (19mm), 70% to 100% passing
• 1/4” (6.4 mm), 0% to 75% passing Maximum:
• particle size length of 6” (152mm) (no more than 60% passing 1/4” (6.4 mm) in high rainfall/flow rate situations)
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.

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)

#### Other uses

In addition to improving the stormwater management functions of compacted soils, compost has several other beneficial uses.

#### Soil reclamation

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).

#### Wetland construction

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.

#### Pollution remediation

Compost has been shown to be effective in degrading or immobilizing several types of contaminants, including hydrocarbons, solvents, and heavy metals (Alexander, 1999).

#### Pollution prevention

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.

### References

• Glanville, T., Richard, T., and Persyn, R. 2003. Impacts of Compost Blankets on Erosion Control, Revegetation, and Water Quality at Highway Construction Sites in Iowa. Iowa State University.
• Kunz, D. and D. Jurries. 2001. Restoring Soil Health. Oregon Department of Environmental Quality.
• Lucas, W. C. and M. Greenway. 2011.Phosphorus Retention by Bioretention Mecocosms Using MediaFormulated for Phosphorus Sorption: Response to Accelerated Loads. Journal of Irrigation and Drainage Engineering 137(3): 144-152.
• McDonald, D. 2005. Soil Restoration with Organics Enters Mainstream of Storm Water Practices. BioCycle. Vol. 46, No. 4, pp. 20-22.
• Rawls, W.J., D. Gimenez, and R. Grossman. Use of Soil Texture, Bulk Density, and Slope of the Water Retention Curve to Predict Saturated Hydraulic Conductivity. 1998. Transactions of the ASAE. Vol. 41(4):983-988.
• U.S. Department of Agriculture, Natural Resources Conservation Service. 2009. Small Watershed Hydrology WinTR-55 User Guide.
• Washington Department of Ecology. 2005. Guidelines and Resources for Implementing Soil Quality and Depth BMP T5.13.

### Literature review

• Alexander, R. 1999. Compost markets grow with environmental applications. BioCycle 40(4): 43- 48. Summarizes uses of compost: erosion control, revegetation and reclamation of marginal and low quality soils, biofilters and bioswales, bioremediation, wetlands construction. The benefits of amending soil with compost include improved soil quality, reduced erosion, enhanced plant establishment, immobilization of toxic metals and supplying microbes.
• Alexander, R. 2003. Landscape Architect Specifications for Compost Utilization. The LASCU, developed for the Clean Washington Center and the US Composting Council is a guide that give specifications for specific uses of compost. Topics include turf establishment (page 40-41), planting bed establishment, backfill mix, mulch, compost blanket for erosion control (pages 48-19), and compost filter berms for sediment control (pages 40-51).
• Composting Council Research and Education Foundation. 2001. Compost Use on State Highway Applications. CCREF/USCC. Document focuses on compost use on state and local ‘roadside’ applications. Defines compost as “the product resulting from the controlled biological decomposition of organic material that has been sanitized through the generation of heat and stabilized to the point that it is beneficial to plant growth. Compost bears little physical resemblance to the raw material from which it originated. Compost is an organic matter resource that has the unique ability to improve the chemical, physical, and biological characteristics of soils or growing media” (p. 2) The addition of compost to soil provides the following benefits: improved structure, moisture management, modifies and stabilizes ph,increases cation exchange capacity, provides nutrients, provides soil biota, suppresses plant diseases, binds contaminants (p. 3). Includes info on State DOT compost specifications and a “Model DOT Compost Specification. Common specification parameters include pH, particle size, soluble salts, organic matter, moisture content, stability/maturity, pathogens, heavy metals, inerts (p. 55).The importance of each parameter is discussed on p. 61-62.
• Garland, G. and Grist, T.1995. The compost story: From soil enrichment to pollution remediation. Bio-Cycle 36(10): 53-56.
• Defines compost as “a recycled product made from the organic portion of municipal solid waste” (p. 2). Compost is NOT peat or mulch. As organic wood mulch decays it tends to use the nitrogen already in the soil, reducing the amount available for plants. This lack of available nitrogen can retard the growth of young plants. Immature compost is nothing more than an organic mulch and does not provide the benefits of mature compost.</p>
• Beneficial uses of compost: soil enrichment (adds organic bulk, increases earthworm populations, humus, and cation exchange capacity), pollution prevention, and pollution reduction.
• Ge, B., McCartney, D., and Zeb, J. 2006. Compost Environmental Protection standards in Canada. Journal of Environmental Engineering Science 5: 221-234.
• Canadian standards typically consider maturity, trace element (heavy metals), time-temperature requirements, microbial pathogens, and foreign matter.
• Defines stability as “the rate or degree of organic matter decomposition” (p. 223). Stability can be determined by microbial activity and/or substrate availability (examples include microbial respiration and energy release).
• Defines maturity as “the degree of decomposition of phytotoxic organic substances produced during decomposition” (p. 223). Can be determined by a plant biotest.
• Maturity and stability are important considerations because “immature compost applied to the soil will continue to decompose and may produce odorous products and are often toxic to plants.
• A trace element is a chemical element present in compost at a very low concentration (p. 224). States that there are three approaches to developing trace element standards: no net degradation, risk-based, and best achievable technology.
• Microbial pathogens: Four major categories of pathogens: bacteria, enteric viruses, protozoa, and helminthes. Some pathogens may survive in finished compost if the compost is immature or if thermophilic conditions are not achieved throughout the composting mass.
• Foreign matter: Defined as “any matter over 2 mm in dimension that results from human intervention and has organic or inorganic components such as metal, glass, synthetic polymers” (p. 230). Excludes mineral soil, woody material, and pieces of rock.
• Glanville, T., Richard, T., and Persyn, R. 2003. Impacts of Compost Blankets on Erosion Control, Revegetation, and Water Quality at Highway Construction Sites in Iowa. Iowa State University.
• The primary objective of this research project is to compare the performance of compost treated and conventionally treated roadway embankments. Performance was measured using the following parameters: runoff quantity, runoff quality, rill and interrill erosion, and seasonal growth of planted species and weeds.
• Study tested 3 types of compost: fine-textured biosolids compost, a coarse-textured mulch-like yard waste compost, and a medium-textured bio-industrial compost derived from paper mill and grain processing sludge (selected because of wide-spread availability in Iowa). Compost types were spread as blankets at 2 depths (5 cm and 10 cm) and were not incorporated into the underlying soil.
• Results:
• Compost treated areas produced equal amounts of plant material when compared to topsoil or compacted subsoils
• Compost treated areas produced 1/3 of the weed biomass found on conventionally treated areas
• Compost treated areas produced 0.2 millimeters of runoff or less during the first ½ hour of intense rainfall (compared to 0.15 millimeters runoff from conventionally treated areas)
• Blanket depth had a significant affect on the amount of runoff – areas treated with 5 centimeters of compost had 1.5 times the runoff of areas treated with 10 cm of compost
• Total mass of eroded material in runoff from composted plots was less than 0.02 percent of that in runoff from conventionally treated plots
• Kunz, D. and Jurries, D. 2001. Restoring Soil Health. Oregon Department of Environmental Quality.
• This document explains the link between land use planning, and building and road construction, and degraded surface water. It summarizes current research on the benefits of amending soil with compost and provides information on technical specifications for using and applying compost to building and road construction projects.
• Suggests “tilling in about 4” of compost is a simple, cost-effective way to restore organic health to a site” (p. 5). Construction activities can increase stormwater runoff by compacting soil (p. 8). Discusses impacts of human activity on soils including compaction and degraded soils and suggests compost amendments to be a solution to the problems associated with compact and degraded soils. Compost amendments can increase the porosity of the soil and add beneficial organisms and nutrients back to the soil. Recommend applying four inches of compost on the surface and tilling it in to a depth of eight inches of compacted soil for a total depth of twelve inches (p. 13).
• McDonald, D. 2005. Soil Restoration with Organics Enters Mainstream of Storm Water Practices. Bio-Cycle 46 (4): 20-22. Features the Soils for Salmon project. The project promotes BMPs for protecting native soil and vegetation where possible, and for restoring soil functions on disturbed sites through the incorporation of organic amendments. Amending the soil with compost provides the following benefits: “increases stormwater infiltration, reducing damaging runoff, and also helps filter out urban pollutants (oils and metals from roads, pesticides and fertilizers from landscapes) while creating more successful landscapes that need less chemicals and less summer irrigation” (p. 20).
• Musick M, and Stenn, H. 2004. Best Management Practices for Post-Construction Soils. BioCycle 45 (2): 29. Summarizes new guidelines for soil quality and depth BMPs in Washington State Stormwater Manual. Benefits of undisturbed soils include: water infiltration and storage, nutrient and sediment adsorption, and pollutant biofiltration. Top priority is given to preservation of existing soils. For sites that must be cleared and graded, guidelines require that all disturbed and compacted soils shall be amended to mitigate for lost moisture infiltration and moisture holding capacity. Guidelines call for a minimum of 8 inches of topsoil over subsoil scarified to a depth of 4 inches.
• Noble, R., and Coventry, E. 2005. Suppression of soil-borne plant diseases with composts: A review. Biocontrol Science and Technology 15(1): 3-20. Reviews several studies that show the suppressive effect of compost on soil-borne diseases.
• Pitt, R., et al.1999. Infiltration Through Disturbed Urban Soils and Compost-Amended Soil Effects on Runoff Quality and Quantity. US EPA. Article examines the effects of urbanization on soil structure and how compaction affects infiltration of rainwater. Also looks at the effectiveness of using compost as a soil amendment to increase infiltration and reduce runoff. Found a “generally beneficial effect of the compost amendment in regards to nutrient content as well as soil physical properties known to affect water relations in soils” (p. 4-1). Found that “the use of compost amended soil resulted in significantly increase infiltration rates compared to soil alone” (p. 4-2). Found that “the growth rates of turf were also greater for the amended sites” (p. 4-4).
• Risse, M. and Faucette, B. 2001. Compost Utilization for Erosion Control. Cooperative Extension Service, The University of Georgia college of Agricultural and Environmental Science.
• Defines composting as “the controlled biological process of decomposition and recycling of organic material into a humus rich soil amendment known as compost. Mixed organic materials (Example: manure, yard trimmings, food waste, biosolids) must go through a controlled heat process before they can be used as high quality, biologically stable and mature compost (otherwise it is just mulch, manure or byproduct)” (p. 1). Focuses on benefits of compost for erosion control such as increasing water infiltration, reducing runoff and soil particle transport in runoff, increasing plant growth and soil cover, reducing soil particle dislodging, increasing water holding capacity of soil, which reduces runoff, buffering soil ph which can increase vegetation establishment and growth, alleviates soil compaction by increasing soil structure, new vegetation can be established directly into compost (p. 3)
• Includes recommended compost specifications for several parameters including particle size, moisture content, soluble salt, organic matter, ph, nitrogen content, human made inerts, application rate/size, maturity
• Russell, S. and Best, L. 2006. Setting the Standards for Compost. BioCycle 47(6): 53-56. Summarizes UK standards for compost (feedstocks, stability tests, monitoring procedures, and certification methods). Includes guidelines for pathogens, potentially toxic elements, stability/maturity, plant response, weed seeds and propagules, physical contaminants, stones (see page 55).
• Zabinski, C., et al. 2002. Restoration of Highly Impacted Subalpine Campsites in the Eagle Cap Wilderness, Oregon. Restoration Ecology 10(2): 275-281. Tested the use of compost in the restoration of highly impacted campsites in the Eagle Cap Wilderness. Plotes as four campsites were scarified, amended with compost, and planted to native species. Assessed the degree to which campsite activity altered soil chemical and microbial properties relative to undisturbed soils and the degree of recovery after compost application. Found that three years after compost amendments were applied, levels of total carbon, PMN, and microbial carbon utilization profiles on campsites were equivalent to those under vegetation on undisturbed sites. Compost amendments also supplied “a slow release of macro and micronutrients, improved water-holding capacity, reduced albedo, and increased heat absorption in the spring” (p. 279).