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0285) <br />Based on the land use and hydrogeologic factors, the potential exists for migration of <br />agricultural chemicals into the ground water in this area. <br />During the preliminary planning for sampling, CDPBE contacted interested parties to <br />inform them of the sampling program and SB 90 -126, and how we envisioned its <br />implementation. CDPBE has coordinated closely with federal agencies, county extension <br />agents, conservancy districts, and local health officials in the project area. <br />GROUND WATER MONITORING PROGRAM <br />The monitoring program presented in this report focused on groundwater quality <br />monitoring in one of Colorado's major agricultural regions, the Arkansas River Valley. A map <br />of the study area and sample locations is provided in Figure 1. The monitoring program <br />included sample collection, laboratory analysis, and data analysis and storage. Upon <br />completion of the full analysis, which will include integration with previous and current <br />studies by other agencies, this sampling program will provide the basis for determining a <br />groundwater quality baseline for this region. <br />The Ag Chemicals Program of the Water Quality Control Division sampled one <br />hundred thirty nine (139) domestic, stock, and irrigation wells throughout the valley (Figure <br />1). This sampling program was the first effort to monitor the entire Arkansas River Valley <br />alluvial aquifer to establish the possible impacts and magnitude of agricultural chemical <br />contamination. This region is characterized by intense irrigation agriculture encompassing <br />both surface water diversions and wells for irrigation water supplies. The wells supply surface <br />and center -pivot irrigation systems from the shallow unconfined aquifer. In August 1995, a <br />confirmation sampling program was conducted to confirm pesticide detections and elevated <br />nitrate levels measured in 1994. <br />Wells were selected for sampling based on a favorable location within the shallow <br />alluvial aquifer, general well and site conditions, and cooperation of the well owner. The <br />wells were sampled once between July and December, 1994 by Brad Austin and John Colbert <br />of CDPBE. Field sampling procedures followed the protocol developed by the ground water <br />Quality Monitoring working group of the Colorado nonpoint task force. <br />Well samples were analyzed for basic water quality constituents, dissolved metals, and <br />selected pesticides. A list of analytes is presented in Table 1. The basic inorganic analysis <br />was performed by the Soils Laboratory at CSU with all samples split with the CDPBE <br />Laboratory for nitrate. Comparison of these split parameters shows consistent results <br />between the two laboratories. <br />2 <br />