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2016 Recommended Modifications to the West Elk Mine Hydrologic Monitoring Network 35 <br />3.1 Gribble Gulch Surface Water Monitoring Sites <br />Lower Gribble Gulch is the only surface water monitoring site in the Gribble Gulch area (Table <br />2). <br />3.1.1 Lower Gribble Gulch <br />Gribble Gulch is an ephemeral stream that flows only in response to storm events and spring <br />runoff. The Lower Gribble Gulch monitoring site is about 1,800 feet north of B -Seam Panel 8 <br />and about 1,500 feet west of B -Seam Panel 7. Mining activity in this area was completed in <br />August 1997. <br />Lower Gribble Gulch has been monitored since 1977, though the only data available for analysis <br />are routine flow data collected since 2000 and water quality data collected since 2000. On the <br />majority of the monitoring dates, Lower Gribble Gulch was found to be dry. Large flows were <br />measured in May and June 2008, with a maximum flow of 1.88 cubic feet per second (cfs) on <br />May 7, 2008 (Figure 28). The unusual high flow was in response to a particularly heavy snow <br />melt cycle. Flow above 0.25 cfs was also found in May 2011. Lower Gribble Gulch has always <br />been dry by August, which indicates that it is ephemeral and has no base flow. A time -series <br />flow graph for Lower Gribble Gulch is shown on Figure 28. <br />Figure 28. Flow in Lower Gribble Gulch <br />Time -series water quality data from Lower Gribble Gulch do not indicate any adverse trends in <br />water quality. The laboratory ECs for this stream for the period of record are steady, ranging <br />from 694 to 860 µmhos/cm and averaging 785 µmhos/cm. In comparison, the single baseline <br />laboratory EC value was 1,250 µmhos/cm. TDS values for this stream for the period of record <br />are also stable, ranging from 470 to 550 mg/L, and averaging 498 mg/L, compared to baseline <br />values ranging from 24 to 60 mg/L. There are no baseline values for field pH for this site <br />(WWE, 2001) for comparison; however, one baseline certified laboratory pH value is available <br />for comparison. The field pH values for this stream over the period of record are relatively <br />August 2016 HydroGeo, Inc. <br />