2010-09-14_ENFORCEMENT - M1977300 (2)

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September 13, 2010 3 of 6 water quality samples from the nearby excavation, and the sampling results do not indicate that water from the pipe had flowed into the excavation. No flow from the pipe was observed by Cotter personnel during the gamma survey conducted around the excavation on May 19. Routine inspections by Cotter personnel, including those required under the stormwater management plan, did not indicate any flow from the pipe prior to July 20. Numerous personnel were onsite in June and July during the ramp-up in surface water sampling, installation of the 50-gpm treatment system, and construction of the 100-gpm treatment system. None of the onsite personnel observed any flow from the pipe prior to July 20. These conditions indicate that leakage from the pipe may have occurred for only a short time before it was discovered, after which the end of the pipe was raised to prevent flow. The flow rate from the pipe was measured using a bucket and stopwatch, shortly after the flow was discovered. The "bucket test" indicated a flow rate of 1.95 gpm, and the end of the pipe was raised which successfully stopped the flow. When Mr. John Hamrick of Cotter Corporation called DRMS to report the pipe, he could not remember the exact flow rate and stated that the flow was "less than 10 gallons per minute". This ballpark figure was intended to be conservative, and he was correct in that 1.95 gpm is less than 10 gpm. Water that discharged from the pipe is expected to report to MW9 and Sump 1, based on groundwater flow directions in the alluvium and fill. The travel time required for water to reach MW9, under normal hydraulic gradients, is 89 to 146 days. The available evidence indicates that the pipe would have discharged for a very short time. If the pipe began flowing on July 19, the earliest arrival of pipe water at MW9 would be October 15, 2010, under normal hydraulic gradients. If water from the pipe flowed toward Sump 4, which is cross-gradient rather than downgradient of the pipe, the earliest arrival of pipe water at Sump 4 would be August 24, 2010, under normal hydraulic gradients. Pumping at Sump 4 and MW9 had been planned since June and the piping system was installed in July. Pumps were set in Sump 4 and MW9 in August, and pumping began on August 16 and August 19, respectively. Both pumps induced drawdown in the shallow aquifer which increased the hydraulic gradient (and therefore decreased the travel times) toward the pumps. The discovery of flow from the pipe on July 20 did not affect, and in fact was consistent with, Cotter's plans to capture contaminated groundwater that originated in, or reported to, the alluvium and fill. The source of water in the pipe was not known on July 20 when the pipe was discovered and a sample was collected and submitted for laboratory analysis. The analytical results received several weeks later do not indicate with certainty that mine pool water is the source, due to large differences in uranium concentrations (78%), molybdenum concentrations (18%), and radium-226 concentrations (0.6%). Cotter contacted COLOG to schedule a camera and magnetometer (i.e., directional indicator) investigation of the pipe and COLOG performed the work on September 13. COLOG's initial investigation was unable to advance survey equipment beyond a a bend in the pipe, and they will retum'with modified equipment at a later date to continue the investigation. Based on the results of the investigation, the conduit will be sealed as described in the EPP (Section 15). Regardless of the source, any flow will be captured by the water treatment system in the alluvium and fill, consistent with Cotter's conceptual model for groundwater flow and aquifer mitigation.