Risk Characterization of Biosolids Land Application Practices Using EPA's Multimedia, Multi-pathway, Multi-receptor Exposure and Risk Assessment (3MRA) Technology

All biosolids land application activities must comply with Title 40 of the Code of Federal Regulations (40 CFR) Part 503 - “Standards for the Use or Disposal of Biosolids” rule (Part 503). During Part 503 development, the US Environmental Protection Agency (EPA) evaluated a number of human exposure pathways including: 1) pollutant exposure through public consumption of well water impacted by pollutants from biosolids and 2) pollutant exposure through public consumption of surface water impacted by surface runoff or though impaired groundwater. While neither of these pathways was originally found by EPA to limit pollutant concentrations in land applied biosolids, recent improvements in EPA risk assessment methodology has generated regulatory and public interest in reevaluating the underlying assumptions from the groundwater exposure pathway risk assessment.An important risk assessment tool recently released by EPA is the Multimedia, Multi-pathway, Multi-receptor Exposure and Risk Assessment (3MRA) technology. A risk characterization screening tool (RCST) based on the 3MRA framework has been developed to evaluate the potential impact of biosolids land application practices on groundwater quality. Based on general site specific parameters, the RCST computes a hazard quotient (HQ) for each pollutant selected by the user.Results from RCST application to biosolids land application sites located in the states of Georgia, Virginia and Washington demonstrate that Part 503 concentration limits are protective of groundwater quality when application rates are as high as 45 metric tons per hectare (mt/ha). Moreover, when the biosolids land application rate is limited to 18 mt/ha, regulated pollutant concentrations can be as high as 2X the ceiling concentration limits without any significant impact to groundwater quality. Based on simulation results, facilities that restrict their regulated biosolids pollutant concentrations to Part 503 pollutant concentration limits and land apply their biosolids at rates that are equal to or less than the agronomic rate will significantly reduce the risk to groundwater quality impairment.