2015-07-30_ENFORCEMENT - C1981014 (4)

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opinion that it is technically infeasible and economically unreasonable for the operator to re -drill a new monitoring well in an effort to abate NOV CV -2013-002. Rationale for Vacating NOV CV -2013-002 MWNW, or an effective replacement (MWNW-2), could have provided data that would assist EFCI and the Division in assessing the impacts of the Southfield mine on groundwater quantity and quality. Without it, the assessment must be based on data from the three remaining active monitoring points, historical records from abandoned monitoring points, historical observations of mine inflows, and historical water quality sampling of mine inflows. Although the additional data obtained from MWNW-2 would improve the quality of the assessment, its value is greatly outweighed by the health/safety risk and cost of attempting to collect it: Value It was established, when the permit for the Southfield mine was first issued, that groundwater impacts would be limited to a relatively narrow stratigraphic sequence of coal seams inter- bedded with sandstones, mudstones, and shales, within which there was the potential for discontinuous perched saturated zones. It was also established at that time that there was no potential for permitted mining operations to impact any regional aquifer. The Colorado Division of Water Resources recognizes that groundwater obtained from coal zones is known to be of degraded quality and advises against completing wells for domestic or agricultural purposes in these zones. Furthermore, baseline data is indicative of relatively poor quality water. Because of these factors, it is the Division's opinion that the value of the additional data from MWNW-2 would be limited. Cost With the TR -46 revision application, EFCI provided a bid from a drilling contractor and a brief summary of the failed attempts they had made to secure an additional bid. The only contractor who bid on the job proposed the use of Nitrogen gas to mitigate the risk of sparks and estimated the job cost at approximately $70,000. The Division has concerns about the efficacy of Nitrogen gas for spark suppression in this context, but the cost estimate is a helpful guide. For due diligence the Division made attempts to contact alternative drillers. Of these, Layne Drilling proposed a mud rotary technique and estimated a cost of $100,000-150,000 based on assumptions that no steering would be needed, and no voids would be encountered above the target zone. Since both of those assumptions may prove to be invalid actual costs could well be in excess of the estimate. Risk During the process of preparing and reviewing TR -46, EFCI and the Division reached agreement that it must be assumed that methane gas is present in the abandoned workings and that it is quite possible that this gas would be within the explosive range. Based on this reasonable assumption, there is an objective risk of igniting trapped methane by drilling into the workings, and this ignition could cause an underground fire. Although the risk has not been quantified, the presence of active underground fires in the area leads to the conclusion that it is significant. Specialized drilling techniques can mitigate the risk, but not entirely negate it, by creating an inert environment around the drill bit. In the case of MWNW-2, the effectiveness of those techniques would be compromised by the presence of a void which would mean that fluids could not be circulated.