foghp-logo
DONATE

Septic Systems

DEM Considers Green Hill Pond Significantly Impaired

In their most recent nitrogen assessment, Rhode Island Department of Environmental Management found that mean total nitrogen (TN) concentrations to be on average 0.61 milligrams per liter (mg/L). This corresponds to “Significant Impairment” according to standard guidelines for TN and environmental health.

nitrogen-assessment

Source: RIDEM 2006, Determination of Nitrogen Thresholds and Nitrogen Load Reductions for Green Hill and Ninigret Ponds, page 12.

Total Nitrogen Has Continued to Remain High for Years

Although there are year to year fluctuations, the nitrogen situation in Green Hill Pond overall has continued to remain in the significantly impaired range for at least the last decade.

total-nitrogen-green-hill-pond

Source: URI Watershed Watch

Septic Systems are By Far the Major Source of Nitrogen Loading

Multiple models show that wastewater from septic systems is the largest source of nitrogen loading to the salt ponds. For Green Hill Pond, nitrogen from septic systems accounts for nearly three-quarters of nitrogen loading. Wastewater nitrogen from septic systems enters the groundwater below the drainage field and eventually the pond. Nitrogen is not significantly reduced in concentration by passing through the sandy soil in our area. So, any mitigation of nitrogen has to take place at the septic system.

nitrogen-loading-green-hill-pond

Source: Horsley Witten Group, 2007, Final Watershed Management Plan, page 19