Item A: Public Hearing onMetro Plan Amendment (Delta Sand and Gravel)

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Oregon Department of Geology and Mineral Industries - Mine Dewatering and Ground W... Page 4 of 4 In certain cases altering the mine plan may suffice in mitigating off-site impacts. For example, if dewatering is causing unacceptable off-site declines during seasonal low water levels it may be possibh to mine in other portions of the site until water levels recover during the wet season. Extraction could then resume in those sensitive areas once ground water levels have recovered. This scenario assumes th mine plan affords this flexibility and the hydrogeology is compatible with such a plan. If modifYing the mine plan is not feasible then deepening or drilling new wells to provide water to the affected users ma: be required. This method of mitigation has been implemented at mine sites where DOGAMI and WRD determined that resultant water level declines from dewatering could be offset by accessing deeper portions of the affected aquifer. Corrective action consists of selecting a new well location and installin. the well to a sufficient depth that it has the capacity to produce ample water and tolerate simultaneous dewatering activities. At those sites where the hydrogeologic conditions preclude the option of drilling deeper wells due to pc ground water quality (i.e., high salinity) or limited aquifer thickness it may be necessary to provide watl to affected users by other means. This may include connection to a municipal water supply if available. Connection to a municipal water supply may also be preferable if the costs are less than drilling new wells. The final option for mitigation is ceasing dewatering activities, which is typically undesirable for the operator unless resource extraction through wet mining can be performed. In some cases total cessation dewatering can be avoided if site conditions are such that dewatering and mining can be performed duri the winter and spring without causing unacceptable off-site declines in the water table. Dewatering duri the winter and spring may also be restricted in the DOGAMI permit if the site is located within a floodplain due to concerns about potential pit capture during flood events. In addition to impacts to quantity operators need to follow practices to prevent degradation to ground water quality. This includes proper storage and handling of hazardous or regulated materials such as petroleum hydrocarbons or solvents which if introduced into an aquifer via spills can prove very costly (>$10,000.00) to remediate. Other sources for water quality degradation include backfilling of contaminated fill material into a pit or quarry. Permittees should be able to certifY that fill imported to a site is not contaminated with any of the substances regulated by DEQ such as metals or organic compounds. Finally, operators should know that DOGAMI's role is to provide them with assistance and advice on t1 regulatory and technical issues associated with mine dewatering. In doing so DOGAMI can help permittees protect their operations while ensuring compliance, preventing potential off-site impacts and prepare mitigation strategies when corrective action is required. Last modified 4/18/05 5:16:29 PM Environmental Law Alliance Worldwide (E-LI U.S. Office: 1877 Garden Avenue, Eugene, OR 97403 l Phone: 541.687.8 Fax: 541.687.0 elawus@elaw Copyright 2003 Environmental Law Alliance Worldwide IU.$.~r.~.gre~m~nt anq'H~GG~pt~pleLJ$~polic:;y file://X:\0290 Delta Sand & Gravel\04-0020 Pit Expansion\Hydrualic Barrier\Ore2:on Dena... 11/1 /200f1