Watershed Characterization and Planning for Pathogen Source Reduction in the U.S. Virgin Islands

Working with EPA to perform a comprehensive assessment and develop recommendations

Over the past decade, ambient monitoring of coastal waters of the U.S. Virgin Islands (USVI) has shown episodic violations of water quality standards for bacteria, which pose a threat to the health of the island’s permanent residents and create the potential for loss of tourism dollars. Additionally, many of these coastal waters contain rare and sensitive ecosystems such as coral reefs and mangrove forests. While previous efforts to identify the causes of bacteria impairments have pointed to a variety of sources, further investigation was needed to better understand sources of bacteria pollution and implications for watershed management.

Cadmus was retained by the U.S. Environmental Protection Agency (EPA) to perform a comprehensive assessment of sources of bacteria, including sanitary discharges from marine vessels, failing septic systems, and urban stormwater discharges, as well as to develop tools to support efforts to reduce bacteria loading.

In the course of its assessment, Cadmus:

• Identified priority areas for sanitary sewer expansion based on land suitability for, and failure analysis of, septic systems.
• Evaluated changes in land use and associated bacteria loading over time to inform land-use planning.
• Reviewed the relative importance of drivers of coastal bacteria impairments through statistical analysis of historical water quality data to guide targeted monitoring and assessment activities.
• Configured and calibrated a time-variable model of storm runoff and fecal coliform/sediment loading from USVI’s subwatersheds using the System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN) model. SUSTAIN uses a modified version of EPA’s Storm Water Management Model (SWMM) structure for runoff and water quality simulation. The calibrated SWMM was used to highlight subwatersheds requiring stormwater best management practices (BMP) and serves as a baseline model for evaluating specific BMP and green infrastructure treatments using SUSTAIN’s BMP simulation and optimization features.

Cadmus also developed the Virgin Islands Stormwater Analysis Tool (VI-STAT), a customized Excel tool for performing screening-level analysis of storm runoff and pollutant loading under existing conditions and user-defined BMP-implementation scenarios.

Lastly, Cadmus’ final report included recommendations on strengthening policy and planning for USVI’s watershed and water quality management programs.