PROPOSED BACTERIA TMDL FOR THE SHAWSHEEN RIVER, MASSACHUSETTS

The National Wildlife Federation (NWF) sponsored development of a case study TMDL for ultimate inclusion in a NWF publication highlighting citizen involvement in the TMDL process. This paper highlights development of a pathogen TMDL for the Shawsheen River, Massachusetts, and demonstrates: 1) real world TMDL development constrained by deadlines and data limitations; 2) the importance of volunteer data.The Shawsheen River flows north from its source, located approximately 12 miles northwest of Boston, Massachusetts, to its confluence with the Merrimack River in Lawrence. The 78 mi2 watershed is primarily developed with suburban residential land use. High levels of fecal coliform bacteria have been recorded throughout the Shawsheen River watershed. As a result, the Shawsheen River, along with three tributaries, were placed on the 1998 Final Massachusetts Section 303(d) list due to pathogen violations.Current bacterial loads were estimated from available information and attributed to four source categories: 1) illicit sewer connections; 2) sewer line leaks; 3) septic systems; and 4) urban stormwater runoff. Illicit sewer connections and sewer line breaks were determined to be the source components of greatest significance during dry weather, low flow conditions. Urban stormwater runoff was determined to be the source component of greatest significance during high flow conditions. Much of the data used in this analysis were collected and provided by the Merrimack River Watershed Council (MRWC).A mass balance model was applied to the Shawsheen River to define the maximum allowable bacteria load that will achieve compliance with water quality. Allocation of allowable loads was divided into two categories: 1) load reductions that should be pursued immediately (i.e. dry weather); and 2) load reductions that may be deferred until more data can be collected on origin and controllability (primarily wet weather).Reductions from sewer breaks and illicit sewer connections will be required in order to achieve compliance with water quality standards during dry weather. Reductions from urban stormwater runoff and illicit connections to storm sewer lines will be required in order to achieve compliance with water quality standards during wet weather. Immediate efforts should be devoted to eliminating continuous sources that have the greatest impact during dry weather.