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_28_ excavating several backhoe pits. Ground water was encountered only in the alluvium in direct contact with the river. The thickness and lateral extent of the saturated alluvial material is limited. The water table depth in the alluvial wells ranged from about 4 to 5 feet below the ground surface, and was largely controlled by the water level in the river. Drill holes and backhoe pits encountered no ground water in the strath terraces and no prominent springs were observed near the contact between the strath alluvium and bedrock. This indicates that the strath terraces do not contain a water table aquifer and that these deposits are not hydrologically connected to the alluvial terraces adjacent to the Middle Fork and mainstem of the Purgatoire River. Auger hole tests were performed to determine the hydraulic conductivity, (permeability) of the alluvial flood plain materials. The permeability determined from the auger hole tests ranged from 0.014 ft/d to 2 ft/d. Attempts to conduct an auger hole test at one hole failed because the permeability was too high. A pump test was performed on that hole, and from the observed drawdown, the permeability was estimated to be about 1,880 ft/d. The alluvial flood plain ground water is acalcium-bicarbonate type water with a chemistry similar to that of the Purgatoire River (see permit application Exhibit 6, figures 12 and 14), but with slightly higher concentrations of the major ions. The only significant difference with respect to the major ions is an elevated sodium concentration in the alluvium relative to that in the stream. Although seepage from the Allen Mine refuse pile has high sodium concentrations, mining activities are not the sole cause of the elevated sodium levels. Sodium is high in all four wells. The sodium is probably being contributed, in part, by the dissolution of one or more sodium salts contained in the soils or alluvium. Concentrations of major ions and the conductivity of alluvial wells at the downstream Maxwell Mine site are less than the concentrations and conductivities of wells at the Allen Mine site (Exhibit 6, Table 3). This is probably the result of inflows of better quality water from the North Fork of the Purgatoire that joins the Middle fork of the Purgatoire between the two mine sites. D. Surface Water The Purgatoire River, a tributary of the Arkansas River, is the major surface drainage feature of the area. The headwaters of the Purgatoire are located on the eastern slope of the Sangre de Cristo Range west of the study area. The three major branches of the river, the North fork, Middle Fork, and South Fork, all converge within the study area. The Allen Mine is located on the Middle Fork, about 1.5 miles upstream of the confluence of the North and Middle forks of the river. The Maxwell Mine is located downstream of the confluence of the North and Middle forks of the Purgatoire River, and approximately two miles upstream of the confluence of the South Fork and the main stem of the Purgatoire River at Weston.