Preliminary TMDL and Nonpoint Source Pollution Assessment of Coastal Areas in Southern Massachusetts
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Section 303(d) of the Clean Water Act requires states to list water bodies as "impaired" if they do not meet one or more of a defined list of water quality standards. It also requires the states to determine Total Maximum Daily Loads (TMDLs) for the pollutant(s) in each impaired water body that are contributing to the impairment. TMDLs determine the amount of a pollutant that a water body can safely handle without violating water quality standards.

In 2001, the Massachusetts Department of Environmental Protection (MassDEP) classified 32 ponds and stream segments as "impaired" under Section 303(d) in the towns of Plymouth, Kingston, and Pembroke in southeastern Massachusetts. These towns fall within the state's South Coastal watershed. Many of these water bodies were impaired due to noxious aquatic plants, but other pollutants included metals, turbidity, bacteria, and nutrients.

The regional watershed coordinator with the MassDEP for the South Coastal watershed identified the need to conduct a further investigation of the 32 listed water bodies to assess the nature of the pollution problems and to identify which water bodies were in most need of attention.

Geosyntec's Scope of Services

MassDEP retained Geosyntec to conduct a nonpoint source pollution assessment for the South Coastal watershed, as well as a preliminary TMDL assessment for all of the watershed's 32 impaired water bodies. MassDEP selected this area because it contained the highest number of water bodies listed as impaired in the state.

Geosyntec conducted an inventory and mapping of each of the 32 water bodies' stormwater, drainage, and erosion features. The information was organized into a relational database to generate a field data report and into GIS layers for display and management purposes. We also gathered existing water quality and hydrology information from available databases, reports, and agency files to evaluate these water bodies, and conducted field reconnaissance surveys to map stormwater outfalls and identify any other sources of pollution.

Geosyntec established a water quality task force/public awareness panel to supply us with local firsthand knowledge of the watershed. This panel was comprised of representatives from each of the three towns and the local watershed association. We acquired and updated land use and orthophoto maps, identified stormwater structures and impervious areas that discharge to water bodies in the towns, evaluated local water quality protection measures, and prepared a summary report and updated maps.

Notable Accomplishments

Geosyntec's TMDL assessment and nonpoint source pollution assessment serves as an easy-to-read data repository for the South Coastal watershed, and provides, in a single location, a variety of electronic maps, land use determinations, and pollutant loading and water quality data. We found that much of the water quality problem in the South Coastal watershed arose from streambank and shoreline erosion and various stormwater and cranberry bog outfalls. MassDEP used our information to help them prioritize and rank the listed water bodies as to which needed the most attention.

Geosyntec created a technical report and an interactive map that runs on both CD and the internet to provide state officials with a tool to manage the impaired water bodies in this watershed, as well as a public outreach mechanism to the three communities. The web-based document provides watershed managers with the ability to review the report online, and to obtain facts and recommendations for each water body.

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Project Summary

  • Location: South Coastal Watershed, Massachusetts, USA
  • Client: Massachusetts Department of Environmental Protection
  • Project Practice Areas: Water and Natural Resources
  • Type of Facility: Watershed
  • Services Provided: GIS Infrastructure Mapping; Field Data Collection; Water Quality and Hydraulic Modeling; Database Construction and Web Mapping; Public Outreach
  • Type of Work: Pollution Assessment
  • Governing Regulation: Clean Water Act (CWA)