Denitrification as a means of addressing nitrate-contaminated groundwater on Cape Cod, Massachusetts

Abstract

The residents of Cape Cod face a problem of nitrate contamination of their groundwater (their primary source of drinking water) and their coastal and aquatic environments. Groundwater is the only source of drinking water on Cape Cod and the aquifer is defined as a "sole source aquifer" by the Safe Drinking Water Act. While many activities contribute nitrate (NO₃-) contamination to groundwater, nitrate contamination from land application poses the greatest threat on Cape Cod. Only a few small areas on Cape Cod are sewered, and the majority of homes and businesses rely on septic systems. Increased urban development has increased the frequency of installation of septic systems. In many locations, the density of septic systems is greater than the natural ability of the subsurface environment to receive and purify system effluents prior to their movement into groundwater. Many of Cape Cod's environmental resources, including coastal receiving waters, marine embayments threatened with eutrophication, endangered wetlands, and Areas of Critical Environmental Concern (ACECs), are also threatened by nitrate-contaminated groundwater flowing into the coastal waters of Cape Cod, which are extremely sensitive to eutrophication from excess nitrogen loading. In order to address nitrate-contaminated groundwater on Cape Cod, solutions based on biological denitrification should be considered. In this work, these solutions are discussed and explored. First, the major sources of contamination and possible health and environmental effects are discussed. Second, the fate and transport of nitrate in the subsurface environment is analyzed, with a detailed discussion of the factors governing biological denitrification. Third, the current status of groundwater nitrate contamination on Cape Cod is detailed. Fourth, possible options, alternative septic systems and in-situ remedial schemes, which all use biological denitrification as a means of attenuating nitrate in septic system effluent, are presented. Lastly, a proposal for action to deal with nitrate contamination on Cape Cod and suggestions for future study and long-term action for domestic sewage are given, based on my opinion of the scientific and engineering aspects of the circumstances of the contamination.