Open-File Report 2011–1077
Records of water quantity, water quality, and meteorological parameters were continuously collected from three reservoirs, two primary streams, and five subbasin tributaries in the Cambridge, Massachusetts, drinking-water source area during water years 2007–08 (October 2006 through September 2008). Water samples were collected during base-flow conditions and storms in 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. Composite samples of stormwater also were analyzed for concentrations of total petroleum hydrocarbons and suspended sediment in one subbasin in the Stony Brook Reservoir drainage basin. 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 ranged from about 30 to 95 percent of capacity during water years 2007–08. Monthly reservoir contents for the Stony Brook Reservoir ranged from about 47 to 91 percent of capacity during water years 2007–08, while the monthly reservoir storage values for Fresh Pond Reservoir were maintained at greater than 92 percent of capacity. If the average water demand by the city of Cambridge is assumed to be 15 million gallons per day, the volume of water released from the Stony Brook Reservoir to the Charles River during water years 2007–08 represents an annual surplus of about 107 and 94 percent, respectively. The annual precipitation total of about 47 in (inches) recorded at the Cambridge reservoir during water year 2007 was about 5 to 21 percent lower than recorded totals for the previous four water years, whereas the annual precipitation total of about 62 in. during water year 2008 was about 5 to 32 percent higher than recorded totals for water years 2002–07.
In general, most monthly mean specific-conductance values for water year 2007 for U.S. Geological Survey (USGS) stations on the two primary streams and four subbasin tributaries in the Cambridge, Massachusetts, drinking-water source area were below the previous median monthly values and often were below the previous minimum monthly values for available data since water year 1997. The annual mean specific-conductance value for Fresh Pond Reservoir during water year 2007 was 483 μS/cm (microsiemens per centimeter), which was lower than the prior three water years. The monthly mean specific-conductance values for streamflow for Hobbs Brook below the Cambridge Reservoir for December through July 2008 were greater than the 75th percentile for historical data since water year 1997. These relatively high values were caused by the inflow of high specific conductance water from the tributaries when the reservoir water level was low at the onset of winter. Increased rainfall in the watershed beginning in February 2008 caused monthly mean specific-conductance values for Hobbs Brook to decrease to about 700 μS/cm by the end of the water year. Monthly mean specific-conductance values for many of the other USGS stations were higher than historical values for several months during the winter of water year 2008. The large amount of rainfall in the watershed also caused the monthly mean specific conductance at these stations to decline to near-median values or to values within the interquartile range for available historical data. The annual mean specific conductance for Fresh Pond Reservoir during water year 2008 was 497 μS/cm, slightly greater than the corresponding value for the prior year.
Water samples were collected in nearly all of the subbasins in the Cambridge drinking-water source area and from Fresh Pond during the study period. Discrete water samples were collected during base-flow conditions with an antecedent dry period of at least 3 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 conditions; however, the difference between the average concentration of total phosphorus in samples of stormwater and for samples collected during base-flow conditions in the tributaries ranged from 0.10 to 0.23 mg/L (milligrams per liter). Concentrations of dissolved calcium, sodium, chloride, and sulfate in water samples collected in the drinking-water source area (excluding Fresh Pond Reservoir) ranged from 2.99 to 75.8 mg/L, 7.47 to 534 mg/L, 11.4 to 1,050 mg/L, and 2.85 to 47.2 mg/L, respectively. The concentration of total phosphorus and total nitrogen in water samples for all subbasins ranged from 0.006 to 0.53 mg/L, and 0.42 to 3.14 mg/L, respectively.
In 3 of 81 water samples, measurements of pH were less than the U.S. Environmental Protection Agency (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 01104410, 01104415, 01104420, 01104433, and 01104455 were near or exceeded the USEPA secondary drinking-water standard of 250 mg/L. All samples collected during base-flow conditions at USGS stations 01104415 and 01104433, and five of six samples collected at USGS station 01104455 exceeded the secondary drinking-water standard for chloride. The concentration of chloride in composite samples of stormwater also exceeded the standard at USGS stations 01104415, 01104433, and 01104455 for a few winter storms. Concentrations of dissolved sulfate in all water samples were below the USEPA secondary drinking-water standard of 250 mg/L. Concentrations of dissolved sodium for all samples collected in the drinking-water source area exceeded the Massachusetts drinking water guideline (20 mg/L) with the exception of three composites samples of stormwater collected at USGS stations 01104455 and 01104475.
Eighteen pesticides and caffeine were detected in water samples collected in 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 during water years 2007–08. Caffeine was detected in 54 percent of 80 water samples at concentrations ranging from 0.004 to 0.557 micrograms per liter. Caffeine was detected in water samples collected at all USGS sampling stations except for 01104390, 01104410, 01104453. Imidacloprid, siduron, and norflurazon were the most frequently detected pesticides, with measureable concentrations in 29 to 32 percent of all water samples collected in the drinking-water source area. Caffeine, 2,4-D, and benomyl were more frequently detected in water samples collected during storms than in water samples collected during base-flow conditions. Imidacloprid, siduron, and 2,4-D were frequently detected in water samples from the tributaries to the Cambridge and Stony Brook Reservoirs. Trace amounts of caffeine, carbaryl, dinoseb, norflurazon, and siduron were also detected in water from the Fresh Pond Reservoir.
First posted June 8, 2011
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Smith, K.P., 2011, Surface-water, water-quality, and meteorological data for the Cambridge, Massachusetts, drinking-water source area, water years 2007–08: U.S. Geological Survey Open-File Report 2011–1077, 109 p., at https://pubs.usgs.gov/of/2011/1077.
Purpose and Scope
Description of Monitoring Network
Continuous Data Collection
Sample Collection and Analysis
Data for the Cambridge Drinking-Water Source Area
Specific Conductance Data