Hydrologic Monitoring in the Three Bays Watershed in Support of Nutrient Management Activities, Cape Cod, Massachusetts
In 2019 the USGS began a partnership with the U.S. Environmental Protection Agency (EPA) Office of Research and Development (ORD), EPA Region 1 Southeast New England Program for Coastal Watershed Restoration (SNEP), Barnstable Clean Water Coalition (BCWC), and other stakeholders to conduct hydrologic monitoring and assessment in support of multifaceted nutrient-management activities in the Three Bays watershed on Cape Cod. USGS is conducting hydrologic monitoring to evaluate the effectiveness of non-traditional wastewater-disposal technologies such as innovative and alternative (I/A) septic systems that reduce nitrogen inputs to groundwater and to monitor surface-water nitrogen export during cranberry bog restoration.
The Three Bays watershed (fig. 1) has been selected by EPA ORD as a location to conduct solutions-driven nutrient research in a southern New England coastal setting. Similar to other areas on Cape Cod, Three Bays is a groundwater dominated watershed in which substantial fractions of the total nitrogen load to surface-water bodies are delivered by groundwater. Consequently, understanding groundwater and surface water as a single interconnected resource is important. Although the groundwater-flow system in the watershed is generally understood from regional modeling studies, assessments of local groundwater conditions (for example, flow directions and rates, depth to groundwater, subsurface geologic conditions, and water quality) is needed for most of the technology demonstration projects in the watershed.
The first phase of the study, completed in 2019, focused on identifying sites in the watershed that were potentially favorable for demonstrations of I/A septic systems. Preliminary site assessments were conducted at four sites in the watershed, identified from a screening process based on hydrologic and land-use characteristics, to determine local hydrologic and water-quality conditions. Based on the hydrologic results from these assessments and other considerations, a neighborhood adjacent to Shubael Pond in the northeastern part of the watershed was selected for the I/A system demonstration. The effectiveness of new I/A systems is being evaluated for individual systems (for example, measurement of influent and effluent nitrogen concentrations for individual systems) and a group of 10-20 systems clustered in the neighborhood. The groundwater-monitoring goals of the neighborhood-scale demonstration are to determine cumulative changes in groundwater quality, primarily concentrations of nitrate, and quantify changes in groundwater nitrogen loading in response to installation of the I/A systems. More information about I/A systems is available at the Massachusetts Alternative Septic System Test Center (MASSTC) (https://www.masstc.org/) web site.
Since the selection of the neighborhood near Shubael Pond for the demonstration, USGS completed multiple additional phases of on-site work to characterize local hydrologic and water-quality conditions and install a groundwater monitoring network capable of detecting changes in water quality resulting from installation of a limited number of I/A septic systems. USGS site-characterization work consisted of well and multilevel sampler (MLS) installation, Shubael Pond shoreline temperature profiling, groundwater and pond-level measurements, and groundwater sample collection to determine concentration of nitrogen and other constituents.
Site characterization and installation of the groundwater-monitoring network were completed in 2021 and to date (August 2022) twelve I/A septic systems have been installed in the Shubael Pond neighborhood. A subset of the groundwater monitoring network consisting of 21 monitoring wells and 3 MLSs (fig. 2) is sampled quarterly to document and quantify changes in groundwater quality in response to installation of the I/A systems. Improved groundwater quality will be indicated by key constituents such as specific conductance, nitrate, and dissolved oxygen. Examples of vertical profiles of groundwater constituents are shown in figure 3. Periodic sampling of the monitoring network is expected to continue for several years to account for the relatively slow movement of groundwater and associated response to I/A system installation.
In addition to the I/A system demonstration, USGS is providing support for other nutrient management activities in the watershed. In 2021, USGS installed a streamgage on the Marstons Mills River (site 0110588332) downstream from an abandoned cranberry bog complex (fig. 1) being restored back to wetlands. Since June 2021, USGS has also been collecting and managing discrete and continuous nitrogen-concentration data at the streamgage site. Currently (2022) pre-restoration baseline conditions are being monitored. Streamflow and nitrogen data will be used primarily to monitor changes in streamflow and nitrogen export (as nitrogen concentrations and loads) from the bog complex as the restoration proceeds.
In 2019 the USGS began a partnership with the U.S. Environmental Protection Agency (EPA) Office of Research and Development (ORD), EPA Region 1 Southeast New England Program for Coastal Watershed Restoration (SNEP), Barnstable Clean Water Coalition (BCWC), and other stakeholders to conduct hydrologic monitoring and assessment in support of multifaceted nutrient-management activities in the Three Bays watershed on Cape Cod. USGS is conducting hydrologic monitoring to evaluate the effectiveness of non-traditional wastewater-disposal technologies such as innovative and alternative (I/A) septic systems that reduce nitrogen inputs to groundwater and to monitor surface-water nitrogen export during cranberry bog restoration.
The Three Bays watershed (fig. 1) has been selected by EPA ORD as a location to conduct solutions-driven nutrient research in a southern New England coastal setting. Similar to other areas on Cape Cod, Three Bays is a groundwater dominated watershed in which substantial fractions of the total nitrogen load to surface-water bodies are delivered by groundwater. Consequently, understanding groundwater and surface water as a single interconnected resource is important. Although the groundwater-flow system in the watershed is generally understood from regional modeling studies, assessments of local groundwater conditions (for example, flow directions and rates, depth to groundwater, subsurface geologic conditions, and water quality) is needed for most of the technology demonstration projects in the watershed.
The first phase of the study, completed in 2019, focused on identifying sites in the watershed that were potentially favorable for demonstrations of I/A septic systems. Preliminary site assessments were conducted at four sites in the watershed, identified from a screening process based on hydrologic and land-use characteristics, to determine local hydrologic and water-quality conditions. Based on the hydrologic results from these assessments and other considerations, a neighborhood adjacent to Shubael Pond in the northeastern part of the watershed was selected for the I/A system demonstration. The effectiveness of new I/A systems is being evaluated for individual systems (for example, measurement of influent and effluent nitrogen concentrations for individual systems) and a group of 10-20 systems clustered in the neighborhood. The groundwater-monitoring goals of the neighborhood-scale demonstration are to determine cumulative changes in groundwater quality, primarily concentrations of nitrate, and quantify changes in groundwater nitrogen loading in response to installation of the I/A systems. More information about I/A systems is available at the Massachusetts Alternative Septic System Test Center (MASSTC) (https://www.masstc.org/) web site.
Since the selection of the neighborhood near Shubael Pond for the demonstration, USGS completed multiple additional phases of on-site work to characterize local hydrologic and water-quality conditions and install a groundwater monitoring network capable of detecting changes in water quality resulting from installation of a limited number of I/A septic systems. USGS site-characterization work consisted of well and multilevel sampler (MLS) installation, Shubael Pond shoreline temperature profiling, groundwater and pond-level measurements, and groundwater sample collection to determine concentration of nitrogen and other constituents.
Site characterization and installation of the groundwater-monitoring network were completed in 2021 and to date (August 2022) twelve I/A septic systems have been installed in the Shubael Pond neighborhood. A subset of the groundwater monitoring network consisting of 21 monitoring wells and 3 MLSs (fig. 2) is sampled quarterly to document and quantify changes in groundwater quality in response to installation of the I/A systems. Improved groundwater quality will be indicated by key constituents such as specific conductance, nitrate, and dissolved oxygen. Examples of vertical profiles of groundwater constituents are shown in figure 3. Periodic sampling of the monitoring network is expected to continue for several years to account for the relatively slow movement of groundwater and associated response to I/A system installation.
In addition to the I/A system demonstration, USGS is providing support for other nutrient management activities in the watershed. In 2021, USGS installed a streamgage on the Marstons Mills River (site 0110588332) downstream from an abandoned cranberry bog complex (fig. 1) being restored back to wetlands. Since June 2021, USGS has also been collecting and managing discrete and continuous nitrogen-concentration data at the streamgage site. Currently (2022) pre-restoration baseline conditions are being monitored. Streamflow and nitrogen data will be used primarily to monitor changes in streamflow and nitrogen export (as nitrogen concentrations and loads) from the bog complex as the restoration proceeds.