Records of water quantity, water quality, and meteorological parameters were continuously collected from three reservoirs, two primary streams, and four subbasin tributaries in the Cambridge, Massachusetts, drinking-water source area during water year 2005 (October 2004 through September 2005). Water samples were collected during base-flow conditions and storms in the subbasins of the Cambridge Reservoir and Stony Brook Reservoir drainage areas and analyzed for selected elements, organic constituents, suspended sediment, and Escherichia coli bacteria. These data were collected to assist watershed administrators in managing the drinking-water source area and to identify potential sources of contaminants and trends in contaminant loading to the water supply.
Monthly reservoir capacities for the Cambridge Reservoir varied from about 59 to 98 percent during water year 2005, while monthly reservoir capacities for the Stony Brook Reservoir and the Fresh Pond Reservoir were maintained at capacities greater than 84 and 96 percent, respectively. Assuming a water demand of 15 million gallons per day by the city of Cambridge, the volume of water released from the Stony Brook Reservoir to the Charles River during the 2005 water year is equivalent to an annual water surplus of about 119 percent. Recorded precipitation in the source area for the 2005 water year was within 2 inches of the total annual precipitation for the previous 2 water years.
The monthly mean specific conductances for the outflow of the Cambridge Reservoir were similar to historical monthly mean values. However, monthly mean specific conductances for Stony Brook near Route 20, in Waltham (U.S. Geological Survey station 01104460), which is the principal tributary feeding the Stony Brook Reservoir, were generally higher than the medians of the monthly mean specific conductances for the period of record. Similarly, monthly mean specific conductances for a small tributary to Stony Brook (U.S. Geological Survey station 01104455) were generally higher than the medians of the monthly mean specific conductances for the period of record. The annual mean specific conductance for Fresh Pond Reservoir increased from 514 microsiemens per centimeter (?S/cm) in the 2004 water year to 553 ?S/cm for the 2005 water year.
Water samples were collected from four tributaries during base-flow and stormflow conditions in December 2004, and July, August, and September 2005 and analyzed for suspended sediment, 6 major dissolved ions, total nitrogen, total phosphorus, 8 total metals, 18 polyaromatic hydrocarbons (PAHs), 61 pesticides and metabolites, and Escherichia coli bacteria. Concentrations for most dissolved constituents in samples of stormwater were generally lower than the concentrations observed in samples collected during base flow; however, concentrations of total phosphorus, PAHs, suspended sediment, and some total recoverable metals were substantially greater in stormwater samples.
Concentrations of dissolved chloride and total recoverable manganese in water samples collected during base-flow conditions from three tributaries exceeded the U.S. Environmental Protection Agency (USEPA) secondary drinking water standards of 250 and 0.05 milligrams per liter (mg/L), respectively. Concentrations of total recoverable manganese exceeded the secondary drinking water standard in samples of stormwater from each tributary. Concentrations of total recoverable iron in water samples exceeded the (USEPA) secondary drinking water standard of 0.3 mg/L periodically in water samples collected at (USEPA) stations 01104415, 01104455, and 01104475, and consistently in all water samples collected at USGS station 01104433.
Concentrations of Escherichia coli bacteria in water samples collected during base flow ranged from 4 to 1,400 colony-forming units per 100 milliliters (col/100mL). Concentrations of Escherichia coli bacteria in composite samples of stormwater ranged between 1,700 to 43,000 c