Open-File Report 2008–1175
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 2006 (October 2005 through September 2006). 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 dissolved calcium, sodium, chloride, and sulfate; total nitrogen and phosphorus; and polar pesticides and metabolites. 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 contents for the Cambridge Reservoir varied from about 59 to 98 percent of capacity during water year 2006, while monthly reservoir contents for the Stony Brook Reservoir and the Fresh Pond Reservoir was maintained at greater than 83 and 94 percent of capacity, respectively. If water demand is assumed to be 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 2006 water year is equivalent to an annual water surplus of about 127 percent. Recorded precipitation in the source area was about 16 percent greater for the 2006 water year than for the previous water year and was between 12 and 73 percent greater than for any recorded amount since water year 2002.
The monthly mean specific-conductance values for all continuously monitored stations within the drinking-water source area were generally within the range of historical data collected since water year 1997, and in many cases were less than the historical medians. The annual mean specific conductance of 738 µS/cm (microsiemens per centimeter) for water discharged from the Cambridge Reservoir was nearly identical to the annual mean specific conductance for water year 2005 which was 737 µS/cm. However, the annual mean specific conductance at Stony Brook near Route 20 in Waltham (U.S. Geological Survey (USGS) station 01104460), on the principal tributary to the Stony Brook Reservoir, and at USGS station 01104475 on a smaller tributary to the Stony Brook Reservoir were about 15 and 13 percent lower, respectively, than the previous annual mean specific conductances of 538 and 284 µS/cm, respectively for water year 2005. The annual mean specific conductance for Fresh Pond Reservoir decreased from 553 µS/cm in the 2005 water year to 514 µS/cm in the 2006 water year.
Water samples were collected in nearly all of the subbasins in the Cambridge drinking-water source area and from Fresh Pond during water year 2006. Discrete water samples were collected during base-flow conditions with an antecedent dry period of at least 4 days. Composite samples, consisting of as many as 100 subsamples, were collected by automatic samplers during storms. Concentrations of most dissolved constituents were generally lower in samples of stormwater than in samples collected during base flow; however, the average concentration of total phosphorus in samples of stormwater were from 160 to 1,109 percent greater than the average concentration in water samples collected during base-flow conditions. Concentrations of total nitrogen in water samples collected during base-flow conditions and composite samples of stormwater at USGS stations 01104415, 01104460, and 01104475 were similar, but mean concentrations of total nitrogen in samples of stormwater differed by about 0.5 mg/L (milligrams per liter) from those in water samples collected during base-flow conditions at U.S. Geological Survey stations 01104433 and 01104455. In six water samples, measurements of pH were lower than the U.S. Environmental Protection Agency (USEPA) national recommended freshwater quality criteria and the USEPA secondary drinking water-standard of 6.5 pH units. Concentrations of dissolved chloride in all water samples collected during base-flow conditions from USGS stations 01104405, 01104415, 01104420, 01104433, and 01104455 exceeded the USEPA recommended freshwater quality criterion of 230 mg/L. With the exception of one sample collected during base-flow conditions at USGS station 01104455, chloride concentrations in all of the respective samples also exceeded the USEPA secondary drinking-water standard of 250 mg/L. Concentrations of dissolved chloride in several composites of water collected during storms at USGS stations 01104415 and 01104433 also exceeded the USEPA recommended freshwater quality criterion and secondary drinking-water standard. Concentrations of dissolved sulfate in all water samples were below the USEPA secondary drinking-water standard of 250 mg/L.
Twenty pesticides and caffeine were detected in water samples collected from the primary streams and tributaries to the Cambridge Reservoir and Stony Brook Reservoir, and in raw water collected from the Cambridge water-treatment facility intake from the Fresh Pond Reservoir in water year 2006. Caffeine was detected in 77 percent of all water samples. Imidacloprid, siduron, and carbaryl were the most frequently detected pesticides. The compounds 2,4-D, MCPA, and triclopyr were detected only in samples of stormwater. Caffeine, metalaxyl, and siduron were detected more frequently in water samples collected during storms than in water samples collected during base-flow conditions. Caffeine, 2-hydroxy-4-isopropylamino-6-ethylamino-s-triazine, carbaryl, imidacloprid, norflurazon, and siduron also were detected in raw water from the Fresh Pond Reservoir.
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Smith, K.P., 2008, Hydrologic, water-quality, and meteorological data for the Cambridge, Massachusetts, drinking-water source area, water year 2006: U.S. Geological Survey, Open-File Report 2008–1175, 164 p.
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