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SURFACE WATER HYDROLOGY The mine plan area is drained by two ephemeral drainages, Maitland and Gordon Arroyos. Surface flows in the arroyos occur only when significant runoff saturates the permeable alluvium. This only occurs when spring snowmelt is wmbined with precipitation events or intense thunderstorms in the summer and ' fall. During the remainder of the year, the arroyos are dry. Minor drainages in the area such as Gordon and Maitland Arroyos are influent, while major drainages such as the Huerfano and Cucharas Rivers are effluent. Because oC the ephemeral nature of Maitland and Gordan Arroyos, no quantity or quality measurements o[ surface runoff have been made to date. However, five crest stage gauges were installed in January 1983. The locations of these gauges are tabulated below and shown on Figure 1. 1 Maitland Arroyo SW-1 T275,R67W, Sec 36, SWl/4,NW1/4 ' Tributary to Maitland SW2 T27S,R67W, Sec 36, NWU4,SW1l4 Arroyo ' Maitland Arroyo SW-3 T27S,R67W, Sec 25, SEl/4,SEU4 Gordon Arroyo SW-4 T27S,R67W, Sec 25, NWl/4,NW1/4 ' Gordon Arroyo SW-5 T27S,R67W, Sec 25, NWl/4,NW1/4 ' Because of the existing conditions and maintenance costs, only Station SW-5 located downstream on Gordon Arroyo was monitored during 1988 as per the revised conditions of stipulation No. 1. During the visits to the site, no surface flows were observed in the arroyo. However, during the September visit to the ' site, the gauge was missing. A flow of two to three feet was measured from the high water line on the adjacent bridge. The gauge was either lost becatue of this flow event or because of vandalism. The gauge was replaced during that same visit to the site. ' During the 1988 NPDES monitoring, no surface water discharge was recorded over the year from the surface facilities sedimentation pond. Reporting forms were sent to the Colorado Department of Health during quarterly reporting periods. CMLRD also received copies of these reports. Inspection of the ' sediment pond was conducted in March, June, SeptembeY and December. Inspection reports are contained in Appendix 3. No major structural, erosional or operational problems were noted during the year.