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Figure 2. Comparison of leachate pH and specific conductance data (5 minute and 18 hour) for 13 mine-wastes included in this study. Leachate Geochemical Comparisons and Trends for All Sites Following is a brief summary comparing selected leachate geochemistry for all 13 sites. pH and Specific Conductance Figure 2 shows the data and trend lines for all 13 mine-waste leachate samples for pH and specific conductance over time. In this plot, pH data from the 5-minute USGS field leach test are compared to pH data from the 18-hour leach test. Leachate pH values went down over time in leachate produced from the Togo, Arabella, Lower Radical, and Jack Pine mine-waste composites. The lowest pH (3.0) was found in leachate from the Togo mine-waste (located in the upper Snake River watershed). However, the greatest drop in pH over time occurred in the leachate from the Lower Radical mine-waste (upper Deer Creek watershed), which dropped from pH 4.8 in the 5-minute leachate to pH 4.6 after 18 hours (4.2 pH units). Other mine-waste leachates that dropped in pH over time were: Togo (-0.1), Arabella (-0.1), and the Jack Pine (-0.1). The largest increase in pH occurred in leachate from the Santiago mine-waste composite (Leavenworth Creek watershed), which showed a spike in pH from 3.6 after 5 minutes to 5.2 after 18 hours (+1.6 pH units). pH also increased over time in leachate from the Wild Irishman (+1.1), Lower Chatauqua (+0.4), Superior and Cashier (+0.3), Waldorf (+0.2), and the Burke and General Teller (+0.1). The pH in leachate from the Grizzly mine-waste stayed the same over time. pH trends produced from the 5-minute leach test correlated to pH trends produced from the 18- hour leach test. Figure 2 also shows specific conductance data and trends for all 13 mine-waste composites. 18- hour leachate values for specific conductance ranged from 8.78 pS/cm in the General Teller leachate (located in Upper Deer Creek watershed) to 1,730 µS/cm for leachate from the Santiago mine-waste (located in the Leavenworth Creek/Clear Creek watershed). Other leachates with high specific conductance were the Waldorf (located in the Leavenworth Creek/Clear Creek watershed) (1,092 µS/cm), and the Togo (718 µS/cm) (located in the Upper Snake River watershed). Generally, the leachate specific conductance trend line for the 13 leachates corresponded very well to the trend for pH. That is, leachate samples with higher pH had lower specific conductivities and leachates with lower pH values had higher conductivities. Also, the relatively simple 5-minute test does a good job portraying the general trend for specific conductance for these 13 sites. Figure 3. Comparison of leachate sulfate data (5 minute and 18 hour) for 13 mine-wastes included in this study. Sulfate Figure 3 shows the 5-minute and 18-hour leachate sulfate concentration, and the sulfate trend for all 13 sites. Sulfate concentration was generally low (<200 mg/L) at I 1 of the 13 sites. However, the Waldorf and Santiago mine-wastes, located in the Leavenworth Creek/Clear Creek watershed, had much higher sulfate concentration, with 443 mg/L in the 5-minute Waldorf leachate and 736 mg/L sulfate in the 5-minute Santiago leachate. Like many of the other geochemical data, sulfate data produced using the simple 5-minute USGS field leach test gives an accurate indication for the sulfate trend produced after 18 hours. This comparison indicates that leachate sulfate trends are fairly predictable and that none of the samples fell out of line or Hageman_SIR_2508.doc 7 7/21/2004 2:50 PM