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In addition to the inorganic constituents, all of the groundwater samples collected <br />were analyzed for selected pesticides. A listing of pesticides was compiled for analysis <br />based on those substances that have recently been, or are currently being utilized in the <br />Arkansas River Valley according to agricultural officials there. Budget restrictions would <br />not allow testing for all pesticides used in the study area. To reduce the analysis cost, each <br />pesticide was weighted according to its chemical properties of persistence and mobility in <br />the environment, amount of active ingredient used per acre, and the amount of acreage <br />within the study area that the pesticide was used on. Pesticides were then selected according <br />to their final score and the ability of the laboratory to detect their presence. <br />GROUND WATER MONITORING RESULTS <br />The results from this sampling program have been entered into the CDPHE <br />Groundwater Quality Data System, a database specifically designed and maintained by the <br />WQCD to store ground water quality data. Reports may be generated from the database on <br />ground water quality in any area of the state from all data sources available. A complete <br />printout of all water quality data from this survey is provided in Appendix A. <br />Analysis of the laboratory results indicates that ground water in portions of the study <br />area has been impacted by nitrates and certain peicides. The major inorganic contaminant <br />of concern is nitrate. Nineteen (19) of the one hundred thirty nine (139) wells sampled (14%) <br />showed nitrate levels in excess of the EPA standard for drinking water (10 mg/L) (Figure 2). <br />One hundred twelve (112) wells (80 %) tested positive for nitrate but were below the EPA <br />standard. Eight (8) wells (6 %) tested below the detection level of 0.5 mg/L. <br />Nitrate below <br />detection level <br />of 0.5 mg/L 1 39.1 mg /L <br />6 °/� U <br />14% 18 10-19.9 <br />_.., mg /L <br />Nitrate present at <br />0.5 - 9.9 mg/L Nitrate exceeds <br />Dri nking Water Standard <br />of 10 mg /L <br />Colorado Dept. Health 1994 <br />FiGun 2 - Nitrate levels in Arkansas Valley wells Chart showing distribution of <br />nitrate levels in the Arkansas River Valley alluvial aquifer, 1994. <br />7 <br />EJ <br />1 7' <br />M <br />r <br />1 <br />