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DETERMINATION OF NATURE AND EXTENT OF GROUND WATER CONTAMINATION IN BOISE CITY AND BOISE URBAN PLANNING AREAS, ADA COUNTY, IDAHO
Description:
From Jun 93 through Sep 94, a total of 818 ground water samples were collected from 515 wells throughout the Boise area (17050114) to analyze the ground water quality in the shallow (<150 feet below land surface - 317 wells), intermediate (150-250 feet below land surface - 63 wells), and regional (>250 feet below land surface - 96 wells) water-yielding zones of the regional ground water system (plus 39 wells of unknown well depths). Samples were analyzed on-site for specific conductance, water temperature, pH, and dissolved oxygen (when possible). Samples were collected for analyses of total and fecal bacteria, HACH nitrite/nitrate, volatile organic compounds (VOCs), and selected samples for metals, ions, nutrients, radon, and pesticides. Countable total coliform colonies were found on the plates from 82 wells. Countable fecal coliform colonies were found in 8 wells. The behavior of bacteria over the one year span were studied in 10 wells, the samples were taken monthly on average and more frequently prior to and following the irrigation season. Bacteria diminished in the winter and increased in the summer. The range for nitrite/nitrate was <0.01 to 17 mg/l, with an average of 2.28 mg/l. VOCs were found at detectable levels in 60 samples with one or more organic compounds. Maximum Contaminant Levels (MCLs) were exceeded in 9 of the 60 samples, tetrachloroethylene was found in 4 of the samples (all wells were <150 feet deep) and trichloroethylene in one of the samples (unknown well depth). Water levels to the first zone below land surface were measured periodically in 12 wells, along with 9 USGS observation wells with recorders. The shallow water-yielding zone of the Boise area consistently had the most impacted water quality. Water Quality Status Report No. 114. Prepared by: Linda Boyle, DEQ-SWIRO, January 1995. Idaho Dept of Health and Welfare, Division of Environmental Quality. 25 pp plus appendices.