2015-10-08_REVISION - C1981041 (12)

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approximately one (1) cubic yard of concrete. The end of the South Portal dewatering pipe was buried in the portal backfill. Grading of the portal area after sealing the portals began with installation of a french drain shown on Exhibit 6C of the PAP. The french drain system has three branches. Two of the branches intercept minor seepage from the portal seals. The third branch is designed to intercept water from the hillside southwest of the conveyor entry. This third leg extends above the level of the portal entries to intercept seepage along the existing hillside. This seepage is believed to originate from a pond located above and to the southwest of the portal. The french drain system explained above has handled minor seepage from the mine portal seals since it was installed during 2008. The minor seepage typically evaporates and soaks into the ground before it reaches the end of the north collection ditch shown on Figure 6C of the PAP. Prior to sealing the portals, the seepage from the hillside was conveyed on the ground to a drain. This drain was used to convey storm water, along with seepage, from the portal area to Pond 8. Pond 8 was reclaimed and seeded in October 2011. There was a heavy snowpack during the winter of 2010 to 2011. In the spring of 2011, a landowner above the mine (Mr. Fontanari) was able to fill a water storage pond (Carey Pond) that had not been filled since the portals had been sealed. The dip of the mine workings is about 2 to 5 degrees north 30 degrees east. The pond is located roughly south 20 degrees west of the mine portal. During late spring 2011, water from the pond percolated through the rock strata and significantly increased the flow in the french drain system. Flows varied from 2 to 15 gpm during late spring and summer of 2011. Late in 2011, the flow rate through the french drain system returned to the normal minor flow. The increase in flow rate also occurred during late spring and summer of 2012 and flow was collected in sediment Pond 9. The pond located southwest of the mine portals was initially believed to be solely responsible for the increase in flow rate in the french drain system. In years when the pond was dry, there was no flow increase in the french drain system. Technical Revision No. 63 was submitted in November 2012 and was approved by the Division in February 2013. The purpose of TR -63 was to incorporate a discussion of the flow variations in the french drain system at the south portal and to provide a new design for the drainage ditch H -H that crosses the former location of Pond 9. The flow variation in the french drain is believed to be caused by groundwater seepage that originates from the Carey pond located southwest of the portal. According to SCC personnel, during years the pond contains water, flow from the french drain increases. Pond 9 was reclaimed and Ditch H -H redesigned at the location of former Pond 9 in April 2013. To address Mr. Fontanari's concern about irrigating the land above the south portals and filling the Carey pond for that purpose, the existing drainage design would convey the water seepage (if any, after evaporation and soaking into the ground) from the hillside through the french drain system down to ditch H -H and eventually discharge to the Colorado River via a culvert beneath Interstate 70. The underground mine workings at the site of the Carey Pond and adjacent Fontanari property are approximately 110 feet below ground surface. It is reasonable to assume that some percolation into the permeable soil may occur, but prior to Spring of 2011 there had been no strong evidence of increased mine discharge as a result of any water diversion practices. As described in detail below in the Findings document, an estimated 166 acre-feet of water was applied by Mr. Fontanari in a concentrated manner to the ground surface directly above the mine workings and portal entries. Now there appears to be a direct correlation between water applied at the surface and discharge from the South Portal. It is less clear if there is a direct impact on Outfall 016. The outflow from Outfall 016 has remained very stable in the past. With the water application in late May -June of 2014 on Mr. Fontanari's property above the South Portal, there has been a gradual Page 24