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• dominated waters to sodium-chloride and sulfate dominated waters. Other parameters that tend to increase as the Arkansas River flows east of Pueblo are stream temperature, nitrite (NOz), nitrate (NOS), and suspended solids (Cain 1984). These parameters aze associated with the municipal and industrial wastewater discharges, (which have the greatest impact water quality immediately east of Pueblo), and agricultural activities within the basin (Cain 1984). Lewis and Brendle (1998) sampled three locations between Pueblo Reservoir and the John Martin Reservoir near Las Animas and found [hat streamflow and specific conductance were primarily affected by Pueblo Reservoir operations. The mixing of seasonally high and low conductance waters was found to narrow the annual range of specific conductance values by increasing and decreasing the dilution potential of the river (Lewis and Brendle 1998). The Pueblo Reservoir regulates streamflow in the Upper Arkansas. Historical data indicate that degradation of surface water quality has likely occurred in the area related to irrigation return flows, municipal and industrial discharges, and surface water impoundments. Water quality data have been collected by the USGS from three stream gaging stations located in the vicinity of the mine identified on Figure H-1. These stations are located downstream from the mine on the Saint Charles River and upstream and downstream of the confluence of the Saint Charles River with the Arkansas River. Data from these stations were reviewed to assess existing water quality in the watershed. Gaging stations are located on the Saint Charles River at Vineland (07108900), and on the Arkansas River at Moffat Street in Pueblo (07099970) and at Avondale (07109500). Table 1 indicates the average annual and peak flow discharge at the identified gaging stations. Table 2 • presents mean values (where available) collected at the gaging stations for parameters of concern relevant to the proposed mining operations. These values are indicative of the water quality upstream of the mine site on the Arkansas River and downstream of the mining operations on both the Arkansas River and the St. Charles River where any impacts would be realized. The [wo gaging stations on the Arkansas River are included in segment la of the Lower Arkansas River Basin within Region 7 and have the same designated uses but have varying water quality standards as compazed with segment 6 of the Saint Chazles River (CDPHE 2002). •