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• JI • SURFACE WATER QUANTITY Seneca Coals Ltd. used the University of Arizona "HYMO" program, a hydrological modeJ~ing program to evaluate peak runoff volume, peak discharge, peak velocity and the associated sediment yield for different precipitation events on existing and post-mining contours. Peak runoff volume, peak discharge, peak velocity and the associated sediment yield were evaluated for the 10, 25 and 100-year, 29-hour precipitation events on 27 different watersheds in the Seneca permit area. The results show that mining operations should not adversely affect the peak velocities in the various reaches. The model predicts that peak velocities and peak runoff volumes will be slightly reduced overall. As discussed in the groundwater section, the flow in Grassy Creek, Little Grassy Creek, and in the unnamed tributary to Fish Creek, will be increased due to additional groundwater discharging into the system. QUALITY It is inevitable that the mining operations at the Seneca II mine site will affect the quality of surface water in the area. The disturbance of strata during the mining process exposes more surface area of the rocks for the solution of minerals and increases the amount of solute available for transport. Also, surface mining greatly enhances the probability of erosion and subsequent sediment yield. A11 drainage from the disturbed area is collected in sedimentation ponds on site and is treated before discharge into adjacent surface waters. Since the discharge from the mine site is required to meet the effluent limitations of the CAfLRD and the NPDES permit, the impact to the surrounding surface waters is minimized. The "HYMO" program predicts an increase in sediment yield from all watersheds as a result of mining. Water quality data for the NPDES 002 and 003 (Tables 7-3I and 7-32) indicate that Seneca Coals Ltd. has been successful in meeting the effluent limitations for suspended solids. As reclamation continues and vegetation is re- established, the sediment load will decrease. The concentration of total dissolved solids in surface water at the Seneca II mine site is high, due to surface runoff and groundwater discharge from spoils. Although spoil leachate has a TAS concentration of approximately 3771 mg/1 at the lysimeter site, the NPDES 002 and 003 discharge points average 2575 mg/1 and 1089 mg/1 respectively. This data shows that the Seneca II mine is increasing the TDS con- centration of Grassy and Little Grassy Creeks. The mine is also expected to increase the TDS concentrations in the unnamed tributary to Fish Creek. These TAS concen- trations in the Seneca mine discharge are within the limits established by the NPDES permit. Additionally, it is anticipated that tine total dissolved solid load created by mining will slowly diminish after final reclamation of the mine, as the spoil weathering process reaches equilibzium. Arsenic, boron, iron, manganese, lead, and nitrate concentrations in the Seneca mine discharge have all, at some time, exceeded the National Water Quality Criterion established by the EPA in 1976. The problems causing excess arsenic, boron, lead and nitrate have been corrected and the Seneca mine effluent is currently meeting the standards for these parameters. Seneca Coals Ltd. will continue to monitor for these parameters and, if the problem reoccurs, steps will be taken to rectify the problem. Iron and manganese levels are still slightly above National Water Quality Criterion, however, the discharge is meeting NPDES effluent limitations and no additional treatment is required.