Aquifer Recharge Rates and Septic System Density

August 9, 2017

Chazen worked with Dutchess County to identify calibrated aquifer recharge rates, useful for aquifer safe-yield budgets and municipal planning. Chazen also recommended minimum sustainable parcel sizes using individual septic systems and domestic wells.

Recharge rate analysis included baseflow separation of stream flows to identify flow coming from watershed aquifers. These groundwater outflows were calibrated to the distribution of soil types and long-term rainfall records across three adjoining watersheds to identify average annual recharge rates by hydrologic soil group and rainfall value. The resulting recharge rates, specified by hydrologic soil group and annual rainfall value, allow development of site specific or regional aquifer recharge budgets useful to local or regional groundwater allocation and planning efforts.

Chazen then modified an existing nitrate loading model to recommend minimum sustainable septic densities allowing successful rural area uses of domestic wells and septic systems. These recommendations allow identification of density thresholds where central water or sewer service may be needed, and suggests minimum average parcel sizes suitable for rural zoning where central services are not anticipated.

The study was funded by Dutchess County to provide a technical basis for planning and zoning decisions made by Towns throughout Dutchess County. The results have been used to identify areas where existing settled parcel sizes may be too small to ensure reliable groundwater well quality, and to specify large enough rural zoning in areas where Towns hope not to extend central water or wastewater service in the future. The recharge rates have been used in many water budget evaluations.