Groundwater Modeling to Support Comprehensive Wastewater Managment Planning
Guidance Document and and Case Study Report
Sterns and Wheler GHD
Watershed Hydrogerlogic Inc
June 2009
This document has been prepared to assist the Towns of Falmouth and Mashpee
Massachusetts (and other Cape Cod communities with similar wastewater and nutrient
management problems) on the best ways to utilize groundwater modeling and evaluate
wastewater nitrogen management alternatives to meet nitrogen Total Maximum Daily Loads
(TMDLs). The procedures presented in this document can be an integral part of wastewater
management planning efforts, and are typically used as the basis for recommended
Comprehensive Wastewater Management Plans (CWMP) and Environmental Impact Reports.
The same procedures can be used to evaluate phosphorus management alternatives for the
watersheds of freshwater lakes and ponds.
Groundwater modeling is needed as part of a CWMP project to determine if potential recharge
locations can accommodate the recharge flow without causing flooding of neighboring
properties. Groundwater modeling is also needed to accurately predict the location (which
portion of the estuary, pond, stream, or bay) where the treated water will surface. This
knowledge allows the development of a nitrogen balance to meet the nitrogen TMDLs as well
as a hydraulic balance to meet water resource management goals.
Part 1 of this document describes the United States Geological Survey (USGS) regional model
that has been developed for Cape Cod. Additionally, Part 1 describes typical steps that are
taken to create a sub-regional model (at a smaller grid size) that is needed for the more
detailed site specific modeling for wastewater planning.
Part 2 of this document provides a case study of the application of groundwater modeling in
the towns of Falmouth and Mashpee to evaluate potential treated water recharge sites and the
ability of alternative nitrogen (wastewater) management scenarios to meet nitrogen TMDLs.
Coastal estuaries in the two towns along the south coast of Cape Cod have new nitrogen
TMDLs and need large wastewater nitrogen removals to meet the TMDLs.