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. summary recorded at a location northeast of Avondale and west of the Pueblo Ordinance Depot on the northern side of the Arkansas River (WRCC 2002). The meteorological data was collected at this location for a period of record from July 1, 1954, to December 31, 2001. Existing Water Quality The existing water quality in the Saint Charles River and Arkansas River is summarized below. This information is provided to support the conclusion that it is unlikely that the water quality of the adjacent arroyos, the Saint Charles River and ultimately the Arkansas River would be impacted by the mining operations proposed. The Upper Arkansas watershed is generally considered to be good water quality with low vulnerability to degradation upstream from the City of Pueblo and is meeting 80 to 100 percent of the uses designated (EPA 2002b). The proposed mine permit boundary and associated arroyos drain to the portion of the Saint Chazles River identified as segment 6 of the Middle Arkansas River Basin within Region 7 regulated by the Classifications and Numeric Standards for the Arkansas River Basin, Regulation No. 32 (CDPHE 2002b). The segment includes the reach from the CF&I diversion canal near Burnt Mill to the confluence with the Arkansas River. Designated uses for the segment include aquatic life (warm 2), recreation (2), water supply, and agriculture and all of these uses are being fully supported (CDPHE 2002a). The mainstem of the Arkansas River from above the confluence with Fountain Creek to the Kansas state line (water body identification number COARLAOI) is included on the Colorado 303(d) list of impaired waterbodies. Identified parameters of concern for this reach include iron, . manganese, sulfate and selenium with causes being agriculture and natural factors (CDPHE 2002b). This segment of the Arkansas River is designated as use protected and only partially supporting the designated uses that include aquatic life (warm 2), recreation (2), water supply, and agriculture (CDPHE 1998). Within Pueblo County, the Arkansas River system is subjected to point and nonpoint source pollution and/or discharges from agricultural, municipal, and industrial sources (Cain et al. 1980). The wastewater treatment plant in Pueblo contributes a major municipal discharge, and the outfall is located approximately five miles upstream from Arkansas River and Saint Charles River confluence. The Arkansas River serves as the primary agricultural irrigation supply in the lower basin for approximately 300,000 acres of irrigated land (Lewis and Brendle 1998). Water is diverted from the Arkansas River for irrigation by a system of major and minor canals, supplemented by wells in the adjacent alluvial aquifer. In most years, the demand for irrigation waters exceeds the available supply in the basin. Cain (1984) found that specific conductance in the Arkansas River significantly increases from the Pueblo Reservoir to the Colorado-Kansas state line. Similarly, specific conductance of irrigation return flows tend to increase downstream as does the specific conductance of groundwater utilized for imgation (Cain 1984). Specific conductance increases from a median of 500 microsiemens per centimeter (µS/cm) near Pueblo to about 3,900 µS/cm at Lamar (refer to Figure H-1) (Lewis and Brendle 1998). These specific conductance values correspond to a range of total dissolved solids (TDS) concentrations of approximately 340 milligrams per liter (mg/L) to 3,600 mg/L. Specific conductance and TDS levels increase in the Arkansas River in the downstream (or • easterly) direction due to increased use of surface and ground water resources. The proportions of major ions also shift in the downstream direction from calcium-magnesium and bicarbonate