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60// to 141 :--l.he " 1994 monitoring program focused on groundwater quality monitoring in one of Colorado's major agricultural regions, the Arkansas River Valley, The monitoring program included sample collection, laboratory analysis, and data analysis and storage, Upon completion of the full analysis, which will include integration with previous and current studies by other agencies, this sampling program will provide the basis for determining a groundwater quality baseline for this region, The Ag Chemicals Program of the Water Quality Control Division sampled one hundred thirty nine (139) domestic, stock, and irrigation wells throughout the shallow alluvial aquifer that lies along the Arkansas River. The Arkansas valley sampling program was the first effort to screen the entire shallow aquifer to establish the possible impacts and magnitude of agricultural chemical contamination, The Arkansas valley is characterized by intense irrigation agriculture encompassing both surface water diversions and large capacity irrigation wells for irrigation water supplies, The wells supply surface and center-pivot Nitrate below detection level of 0,5 mg/L ~ 80% Nitrate present at 0,5 - 9,9 mg/L Colorado Dept. Health 1994 IrrIgation systems from the shallow unconfined aquifer, This shallow aquifer is also a significant source for domestic and municipal water supplies throughout the valley, All wells were sampled once between July and December, I 994, Wells were selected for sampling based on the following factors: located within the unconfined valley fill aquifer, cooperation of the well owner, no known construction deficiencies, history of contamination or other local factors that would render the sample unrepresentative of regional ground water quality, All field sampling was performed by Brad Austin and John Colbert of CDPHE. Field sampling procedures followed the protocol developed by the Ground Water Quality Monitoring Working Group of the Colorado Nonpoint Source Task Force, Well samples were analyzed for basic water quality components (calcium, sodium, sulfate, etc.) dissolved metals, and selected pesticides, The basic and metals analysis was performed by the Soils Laboratory at Colorado State University with all samples split with the Colorado Department of 14% 18 10 -19,9 mg/L 1 39,1 mg/L ~ Nitrate exceeds Drinking Water Standard of 10 mg/L Nitrate levels in domestic wells in the Arkansas Valley, July - December 1994, Values are given in milligrams per liter or parts per million, Page 2