Considerations Regarding Nutrient Pathways and Loads into Surface-Water Resulting from Subsurface Discharges of Wastewater Effluent

This paper addresses the nature of contamination that may enter surface water bodies from the subsurface, with particular consideration to effluent discharges of nutrients from treated wastewater disposal systems. The pathways and transport mechanisms are addressed by considering the transport of phosphorous and other constituents from a sewage-contaminated aquifer into Ashumet Pond, a kettle pond located adjacent to the Massachusetts Military Reservation (MMR) in Cape Cod, MA. For this paper, some previous ground-water data are analyzed and additional surface-water and ground-water samples are collected to characterize the nature of the exchange processes. As such, these results are intended to complement previous analyses being completed by the USGS. Ground-water samples were collected during the summer months of 2005 from multi-level samplers (MLSs) located adjacent to the pond. Results for ground-water samples were found to match the previous results well, confirming that significant loads of phosphorous enter the pond from ground-water. Results also indicated that the phosphorous transport might be affected by phosphorous associated with solids. Trends in surface-water samples collected from a number of locations at varying distances from the banks of the pond revealed that phosphorous distributions may be affected by presence of a geochemical barrier and also by variability of ground-water entering the pond. Additional results, including chlorophyll-a analyses and in vivo chlorophyll-a estimates obtained with fluorometer, also provided insight into the nature of phosphorous discharge in the vicinity of the geochemical barrier. The results illustrate the near-shore trends in nutrient discharge from ground-water into surface-water, and also illustrate the importance of the pathways that nutrients follow as they enter a lake.