Wastewater Planning and Permitting Services for Development on Undeveloped/Agricultural Land
Weston & Sampson was retained by the largest landholder in southeastern Massachusetts to provide wastewater planning and permitting services for a 1,175-unit development on 1,500 acres of undeveloped/agricultural land. To permit development in this watershed, the client was required to provide a no-net nitrogen solution to wastewater disposal.
Analysis. Due to the complexity of the water quality constraints and the groundwater/surface water flow regime in Southeastern Massachusetts, a multi-tiered evaluation effort was conducted. First, an environmental site screening analysis was conducted over the entire area. The screening process included the development of a list of environmental criteria to assign to current geographic regions. Overlay maps were then developed defining setback distances to sensitive environmental conditions, such as wetland resource areas, endangered species habitat, Zone II wellhead protection areas, surface water setbacks, local resource protection overlay maps, and Areas of Critical Environmental Concern. A summary map was linked to a matrix allowing discrete land parcels to be scored and ranked relative to the number and severity of the environmental concerns. Further analysis was conducted to identify site development constraints including depth to groundwater, presence of bedrock or ledge, soil types, degree of vegetative cover, topographic relief, etc. From this screening effort appropriate field data collection efforts could be designed for the area based on the ranking or priority assigned.
Once favorable sites for wastewater discharge were determined and prioritized, Weston & Sampson used the USGS Regional Plymouth-Carver Aquifer groundwater model to assess flow patterns in both the surface water bodies and the groundwater in the basins. This analysis determined the fate of the treated effluent and nitrate in the groundwater at various discharge locations.
Following the groundwater modeling, field testing was conducted to verify model findings. Once the model was calibrated, wastewater disposal impacts were assessed with a mass-balance nitrogen-mixing model constructed using USGS methodologies. The model required estimating recharge rates for current land use activities with respect to impervious surface, stormwater practices, agricultural activities, wastewater discharges, and any other commercial or industrial input. The nitrogen loading approach provided a method for estimating potential nutrient loads from all cumulative nitrogen inputs created or removed by the development. Once the model was constructed, development techniques (as-of-right, mixed-use) were compared to develop appropriate offset strategies (mitigation) for potential nutrient impacts within the watershed resulting from the project.
Permitting. Based on the analyses, Weston & Sampson applied for and received a groundwater discharge permit for discharge of 395,000 gallons per day of treated effluent in the Agawam River Basin in Plymouth. The project was designed to minimize nutrient loading and to maximize attenuation and uptake of nutrient loads within the area. More than 1,600 acres of open space, including habitats for rare and endangered species, are to be permanently protected and maintained.
The location of the wastewater treatment facility and effluent disposal field was chosen to maintain significant separation from surface water bodies, maximize nutrient attenuation within the upper reaches of the watershed, and maximize return flow to the Agawam River basin upstream of the proposed drinking water well site, providing an excellent water mass-balance.
Future changes in agricultural practices for cranberry bogs will eliminate the use of phosphorous or nitrogen-based fertilizers, thereby eliminating a source of both within the basin.