Page 5 - USDA Compost sock use

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Utilization of Compost Filter Socks

(Agronomy Technical Note 4, January 2011)

should be used in conjunction with other integrated stormwater management practices. Finally, if installa-tion guidelines are not followed or maintenance is not conducted, the compost flter sock may not perform at an optimum level.

Effectiveness

Compost flter socks have been extensively researched and evaluated at the USDA Agricultural Research Service (ARS) and universities. Research literature has shown that this management practice can physi-cally flter fne and coarse sediment and chemically flter soluble pollutants from stormwater. A USDA ARS study showed that compost flter socks can remove 65 percent of clay and 66 percent of silt particulates; 74 percent of total coliform bacteria and 75 percent of E. coli; 37 percent to 72 percent of Cd, Cr, Cu, Ni, Pb, and Zn; 99 percent of diesel fuel; 84 percent of motor oil; 43 percent of gasoline; 17 percent of ammonium-N; and 11 percent of nitrate-N from stormwater runoff (Faucette et al. 2009a).

Another USDA ARS study reported that compost flter socks removed 59 percent to 65 percent of total P, 14 percent to 27 percent of soluble P, 62 percent to 90 per-cent of total suspended solids (TSS), and 53 percent to 78 percent of turbidity in stormwater runoff (Faucette et al. 2008). A study published in the Journal of Soil and Water Conservation, conducted at the University of Georgia, compared the performance of compost flter socks, straw bales, and mulch berms, on feld test plots. Compost flter socks reduced runoff TSS and tur-bidity by 76 percent and 29 percent, straw bales by 54 percent and 12 percent, and mulch berms by 51 percent and 8 percent, respectively (Faucette et al. 2009a).

An Ohio State University study evaluated the hydrau-lic fow-though rate for compost flter socks and silt fence. It was determined that compost flter socks have a 50 percent greater fow-through rate than silt fence without a reduction in sediment removal eff-ciency performance (Keener, Faucette, and Klingman 2007). Field evaluation of compost flter socks by the City of Chattanooga Water Quality Program reported that use of this management practice reduced parking lot stormwater TSS by 99 percent, chemical oxygen demand (COD) by 92 percent, and oil/grease by 74 percent (Faucette, Minkara, and Cardoso 2009).

Compost quality

Compost quality is extremely important for the function and performance of compost flter socks. Adherence to parameter range limits presented in table 1 will ensure compost material used for com-post flter sock applications will meet associated design criteria and the unique advantages attributed to this management practice. It is recommended that compost is analyzed for these parameters using Test Methods for the Examination of Composting and Compost (TMECC) guidelines, test methods uniquely designed for evaluating compost quality. Furthermore, compost that has the U.S. Composting Council Seal of Testing Assurance (STA) label or third party testing and certifcation is preferred.

All compost should be odor free and have no recogniz-able original feedstock materials. Composts should adhere to Title 40 Code of Federal Regulations (CFR) Part 503, which ensures safe standards for pathogen reduction and heavy metals contents (table 1).

Table 1 Compost quality guidelines

Parameters Units of measure Compost

pH pH units 6.0–8.0 Soluble salt concentration (electrical con-ductivity)

dS/m (mmhos/cm) Maximum 5

Moisture content percent, wet weight

basis

30–60

Organic matter content

percent , dry weight basis

25–65

Particle size percent passing a

selected mesh size, dry weight basis

2 in (51 mm), 100% passing –0.375 in (10 mm), 10% –30% passing Biological stabil-ity

Carbon dioxide evolution rate

mg CO

2

–C per gram of organic matter per day

<8

Physical contami-nants (human-made inerts)

percent, dry weight basis

<1

Source: U.S. Environmental Protection Agency (2006)