Characterizing Effluent Flows From Biosolids Stockpiles
For the past 3 years, over 90% of the sewage sludge generated in Maine has been utilized, after either being composted or lime-stabilized. Sewage sludge is the by-product of making clean water, so it is generated year-round. However, it is only needed as a fertilizer during narrow windows in the crop cycle, so it has to be stored. The most cost effective and convenient method of storage is to stack the sludge in the field. Sludge is stacked for up to 8 months, before use.
While field stacking is a standard agricultural practice, the Maine Department of Environmental Protection (ME DEP) is concerned about the impacts to groundwater that the practice creates. In particular, the ME DEP is concerned that nitrate-N leached from the pile may have significant adverse impacts to area groundwater users.
Maine regulations will phase in much stricter siting standards for field stacking in October of 2002. This will mean that most of the 50 POTWs that currently apply sludge to land will need to build permanent storage facilities, at a rough total cost of $10M. It is prudent to evaluate the potential for pollution of field stacking before expending this kind of money.
The primary contaminant of concern for the study is nitrate-nitrogen (nitrate-N) and other forms of nitrogen that may change to Nitrate in the environment. The nitrate-N is a concern for groundwater contamination. The nitrogen and other characteristic data collected for this study will be used in groundwater and vadose zone models to look at the attenuation of any nitrogen that enters the soils below stockpiles. Since this is the primary use for the data collected, the quality of the data must be such that it is representative of what can occur in field stockpiling situations. Movement of nutrients from the biosolids into the soil below is strongly dependent on weather conditions, so data collected will be highly variable from sample set to sample set and will be dependent on the weather conditions that create the sampling event.