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highest manganese detections recorded for surface water monitoring were in water collected from station location RS-3 situated on the southern permit boundary in an intermittent tributary flowing to the Rito Seco (CDMG, 1994). Manganese detections were consistently higher at the RS-3 location and, though the flow rate of the tributary is very low, it may contribute to the elevated levels of manganese at downstream locations RS-2 and RS-5 (Table 3; Attachment 1). Iron concentrations (total) in samples collected at the RS-1 location prior to the commencement of current operations ranged from 0.01 mg/L to 0.41 mg/L Iron concentrations in samples collected from the RS-5 location, downstream of site operations, on August 20 and November 2, 1988 were 1.2 and 0.56 mg/I., respectively. These concentration were equal to or greater than three times the corresponding iron concentration detected in samples collected from the RS-1 on those dates (Attachment 1). Geology and Hydrogeoloav The area of the site is on the edge of the San Luis Basin eastward tiwng graben (CDMG, 1990). Stratigraphy in the site vicinity is comprised of four basic units described from the surface: quanternaryalluvium/alluvial fan material; tertiary Sante Fe Conglomerate {USGS, 1979); precambrian pink granitic gneiss; and biotite/biotite-amphibole gneiss (BMG, 1988; BMG, 1994). Local ground water underlying the site occurs in the Sante Fe Conglomerate and the Precambrian biotite and biotite-amphibole gneiss ore zone (BMG, 1988). Refer to the SAP (MK, 1995) for a more detailed discussion of the geologic setting. Site Hy~roloav The RRo Seco River flows adjacent to site operations. RRo Seco River flow is diverted via a ditch into the Salazar Reservoir approximately 2 miles downstream. Two miles downstream of the Salazar Reservoir, the Rito Seco River drains into Culebra Creek. The remainder of the 15-mile target distance limit occurs within Culebra Creek (USGS, 1983). Flow gaging recorded in 1988 at Station RS-1, located on the Rito Secc River at the western edge of site operations, documented a monthly flow rate ranging from 4.6 to 8.8 cubic feet per second (cfs)(BMG, 1988). RRo Seco River water pH measurements recorded during SI field activities ranged from 7.37 (upstream of site operations) to 8.69 (adjacent to Salazar Res.) standard units. Physical parameters of RRo Seco water measured at sample locations during SI field activities are summarized below: anolxeoc~~airoomnc - 3 - !~ 4 m/~4'~J