REUBER, Eric J., ejreuber@usgs.gov, U.S. Geological Survey, Columbia, SC 29210

During spring and summer 1996, water-quality samples were collected from 30 shallow monitoring wells installed in the Lower Coastal Plain of South Carolina, which is an area characterized by agricultural land use.  This study was completed as part of the National Water-Quality Assessment Program in the Santee River Basin and Coastal Drainages Study Unit.  The wells were completed in sand to clayey sand sediments with screened intervals ranging from 10 to 30 feet below land surface.  Water levels measured in the wells ranged from about 5 to 22 feet below land surface.
    Results of the water-quality analyses indicated that water samples collected from the wells were typical of shallow ground water in the area; pH was low, dissolved oxygen concentrations were high, and concentrations of dissolved ions were low.  Dissolved-oxygen concentrations in water samples ranged from 0.2 to 9.7 milligrams per liter, and specific conductance values ranged from 100 to 300 microsiemens per centimeter at 25 degrees Celsius.  Analyses also indicated that the shallow ground water was characterized as a calcium bicarbonate type water.
    Nearly all of the samples had nitrate concentrations above background levels, and 12 of the 30 samples had concentrations that exceeded the U.S. Environmental Protection Agency’s maximum contaminant level of 10 milligrams per liter.  Nitrate concentrations ranged from 0.34 to 23 milligrams per liter with a median concentration of 5.54 milligrams per liter.  Dissolved phosphorus concentrations generally were low with all but one sample having a concentration less than 0.1 milligram per liter.
    Water samples were analyzed for 17 separate pesticides; concentrations of detected pesticides generally were low.  Although maximum contaminant levels have not been established for 13 of the 17 pesticides detected, no concentrations exceeded applicable U.S. Environmental Protection Agency maximum contaminant level.  Atrazine, deethylatrazine (a metabolite of atrazine), metolachlor, alachlor, simazine, and tebuthiuron were the only pesticides detected in more than one well.   Atrazine was detected in water samples from 14 wells, and deethylatrazine was detected in samples from 18 wells.  The two highest concentrations were detected for bentazon and tebuthurion at 11.5 and 1.90 micrograms per liter, respectively.  All other pesticide detections were less than 0.01 micrograms per liter.
    Of the 17 pesticides analyzed, 14 were agricultural herbicides and 3 were the insecticides carbofuran, diazinon, and dieldrin.  Terbuthiuron, a nonagricultural herbicide used primarily on right-of-ways and industrial sites, was detected in two wells.