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jCOLORADO <br /> ics W � Division of Water Resources <br /> Departrnent of Natural Resources <br /> July 24, 2019 <br /> Mr. Ben Langenfeld, P.E. <br /> Greg Lewicki and Associates <br /> Transmission via email: beni@lewicki.biz <br /> RE: RALSTON QUARRY GROUNDWATER SEEPAGE EVALUATION <br /> DRMS M-1974-086-AM4 <br /> SECTIONS 4, 5, AND 8-TWP. 3 SOUTH, RNG. 70 WEST, WATER DIVISION 1, WATER <br /> DISTRICT 7 <br /> Dear Mr. Langenfeld: <br /> This letter is in response to the information provided on June 26, 2016 on the groundwater <br /> seepage evaluation for the Ralston Quarry Mine, Division of Reclamation Mining and Safety <br /> ("DRMS") Permit No. M-1974-086, as required by the technical revision approval (AM4) for the <br /> permitted area of the quarry mine. The Applicant was required to demonstrate to the State <br /> Engineer that the volume of ground water seeping into the quarry mine is within the State <br /> Engineer's allowable leakage rates as referenced in the August 1999 State Engineer Guidelines <br /> for Lining Criteria for Gravel Pits ("1999 SEO Guidelines") in order to avoid obtaining a <br /> substitute water supply plan ("SWSP") or a well permit for the site. <br /> According to the information provided, Ralston Quarry is located in very low permeability <br /> basalt material surrounded by Pierre Shale. A hydrologic analysis of the basalt formation was <br /> performed by Brierley and Associates ("Brierley") to determine if the basalt formation at the <br /> quarry mine is hydraulically isolated from the regional ground water table. As part of this <br /> analysis in 2013, Brierley installed several monitoring holes at the site (designated as BA-3 <br /> through BA-8 and BA-7A, BA-8A and BA-8B) and water levels readings were recorded in June <br /> 2013, July 2013, August 2013 and again in May 2019. Depth of ground water level measured at <br /> these monitoring holes ranged from 6.6 feet in BA-813 (July 2013) to 12.6 feet in BA-8A (August <br /> 2019). However, monitoring hole BA-5 was dry when measured in 2013 and 2019. The <br /> monitoring hole BA-5 is located closest to the lowest point on the quarry mine and this hole <br /> was completed to a depth of 100 feet. Brierley concluded that the source of water in the <br /> other monitoring holes was most likely surface water that flowed into the boreholes via <br /> fractures in the basalt. In addition packer tests were performed to determine the <br /> permeability of the basalt formation. The packer tests determined a very low hydraulic <br /> conductivity for the basalt formation at the site ranging from 9.3 x 10-7 cm/sec to 2.4 x 10-5 <br /> cm/sec. Based on the above, Brierley further concluded that due to the low permeability of <br /> both the basalt and the shale that surrounds the mine site, the quarry mine is considered a <br /> closed hydrologic system and the water table in the quarry is isolated from the regional <br /> ground water. <br /> In order to demonstrate that the groundwater seepage at the quarry mine is below the State <br /> Engineer's allowable leakage rates as referenced in the 1999 SEO Guidelines, Brierley <br /> conducted a new seep water analysis for the site using a SEEP/W model based on the packer <br /> test data results from the original 2013 investigation. A worse-case permeability value of 2.5 <br /> 1313 Sherman Street, Room 821, Denver, CO 80203 P 303.866.3581 www.cotorado.gov/water I ^{ S o' <br /> Jared S. Polis, Governor { Dan Gibbs, Executive Director I Kevin G. Rein, State Engineer/Director <br /> ��876 <br />