Management of stormwater runoff at open windrow composting sites

Abstract

Composting of yard waste and other organic material is an effective means of diverting solid wastes from landfill sites (Wilson 2002). However, there is some concern about the potential adverse environmental effects that open windrow composting sites might have on nearby surface water. Since windrow composting is open to the elements, combined runoff (stormwater and leachate) might be high in BOD, COD, suspended solids and other nutrients. Hence, runoff from composting sites is usually unsuitable for discharge into receiving water bodies and should be treated prior to release. The purpose of this research was to develop guidelines for sizing stormwater detention ponds at open windrow composting sites. Laboratory experiments were conducted on cow manure compost to measure the runoff produced by different intensities of rainfall. A lab setup was created to depict a slice of half of a windrow. Water was sprayed onto the compost and the runoff volume was measured 20 minutes and 24 hours after the water was added. Moisture contents were also measured, and verified that some of the water was leaching out from the bottom of the piles. Using the runoff volumes collected during the laboratory experiments, a compost runoff coefficient of 0.7 was calculated. Field data on precipitation and water levels in a detention pond were collected at the Atlantic Topsoil and Compost facility in South Branch, New Brunswick. This data was used to verify the accuracy of the compost runoff coefficient. The true pond levels were compared to predicted pond levels calculated using both the rational equation (Q=CIA) and the compost runoff coefficient of 0.7. It was concluded that the results showed a strong relationship between the true runoff generated and the runoff calculated using the rational equation. Hence, the compost runoff coefficient can be used along with a stormwater drainage model like the SUDS 3.1 software package to determine the reservoir storage and the controlled outflow rate. Also, modeling using SUDS or some other program is an improvement over current practices, since there a currently no guidelines to size stormwater detention ponds. Further studies are needed in the areas of precipitation and pond level data collection, laboratory testing and modeling to improve the accuracy of the results.