r,. ;cr ,,^v.eos'-... -l_4d SDMS DocID 449095 I .c? UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 1 1 Congress Street, Suite 1100 BOSTON. MA 02114-2023 To; Nyanza Chemical Waste Dump Site File - Sudbury River From; Bart Hoskins, EPA Ecological Risk Assessor Thru; Daniel Keefe, EPA Remedial Project Man Subject; Suitability ofthe Sudbury Reservoir as a reference area for Nyanza OUIV Sudbury River studies Date: December 4, 2009 The purpose of this memorandum is to evaluate the suitability ofthe Sudbury Reservoir as a "reference" area for the on-going Nyanza OU4 (Sudbury River) Feasibility Study (FS). As part ofthe FS, EPA is preparing a mercury fate and transport computer model to assist with the evaluation of different remedial alternatives. In the course of gathering hydrologic data for the model, information was identified regarding water management practices within the Sudbury Reservoir which suggests that the Sudbury Reservoir is likely not a suitable reference location. The Sudbury Reservoir was initially selected as one [of three] reference areas unaffected by Nyanza mercury with similar atmospheric (background) sources of mercury because it was located within the same watershed. Subsequently, EPA contacted the Massachusetts Department of Conservation and Recreation (DCR) and the Massachusetts Water Resources Authority (MWRA), owners and operators respectively, ofthe Sudbury Reservoir. EPA was informed that the Sudbury Reservoir receives periodic additions of water (over 100 million gallons per day) from the Wachussett Reservoir. Further, the Wachussett Reservoir is itself fed in part by water from the Quabbin Reservoir in western Massachusetts. These occasional large volumes of water from other watersheds make it less suitable for use as a reference location. In addition, management practices around the Sudbury Reservoir (and active secondary/emergency water supply) are substantially different than Reservoirs 1 and 2 (which are located along the main stem ofthe Sudbury River). Specifically, access to and development around the Sudbury Reservoir is significantly different than Reservoirs 1 and 2 which are largely surround by residences, roads, and railroad tracks. Based on water inputs from different watersheds as well as fundamental differences in land use (i.e., development) surrounding the Sudbury Reservoir, EPA recommends that the other two remaining reference area (Charles River and upstream portions ofthe Sudbury River) be used to document background concentration of methylmercury. .