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TETRA TECH MEMO <br /> To: Mike Refer and Connie Davis, Aggregate Industries <br /> Cc: Tim Flanagan, Steve Cox; Fowler, Schimberg& Flanagan <br /> From: Tom Hesemann, R.G., C.E,G. and Gary Linden, R.G.; Tetra Tech <br /> Date: September 23, 2016 <br /> Subject: Response to Equity Funding Technical Revision Comments dated September 21, 2016 <br /> This memo addresses Technical Revision Comments submitted by Equity Funding on September 21, 2016. <br /> The Equity Funding comments were in response to the Second Adequacy Review and Technical Revision to <br /> Permit No. M-20014-031 (the Hazeltine Mine)submitted to the Colorado Division of Mining and Reclamation <br /> Safety(DRMS)on September 21,2016. <br /> Item I. Aggregate Industries Must First Apply for an Amendment to 404 Permit <br /> The Orr Drain(Drain)will be operated to mirror the pre-mining ground water regime. That is to maintain the <br /> jurisdictional wetlands and keep water table within one to two feet of the ground surface in the area of the Orr <br /> property. <br /> Item 11. Groundwater should be the Focus of the Amendment Application <br /> Surface water from the Bull Seep and Fulton Ditch turnouts serves as a source of groundwater infiltration at the <br /> site. Therefore, surface water must be addressed. As to groundwater,the Drain will be excavated to a depth <br /> approximately four feet below the ground surface. Thus the Drain will capture both infiltrating surface flows as <br /> well as groundwater. Groundwater levels will be monitored in monitoring wells MW-2, MW-11 a,and MW-11 b in <br /> order to monitor the mitigation effects of the Drain. <br /> Item 111. Technical Errors in the Design <br /> A. Aggregate Industries' (AI)construction of the slurry wall and relocation of the Bull Seep have <br /> contributed to the raised elevation of the groundwater, both by blocking the natural groundwater flow <br /> and by the increased infiltration of flows from the Bull Seep and the Fulton Ditch turnouts. As <br /> mentioned above,the Drain is designed to collect infiltrating surface water,surface water from <br /> groundwater seepage, and groundwater. The mitigation effects will be monitored in wells HZMW-2, <br /> HZMW-11 a, and HZMW-11 b. These wells were monitored both prior and after construction of the <br /> slurry wall and the relocation of the Bull Seep. <br /> B. As mentioned above,the Drain addresses infiltrating surface water,surface water from groundwater <br /> seepage, and groundwater. Mitigation effects will be monitored in existing wells HZMW-2, HZMW-11 a, <br /> and HZMW-11 b. Lowering the top of the slurry wall would be a violation of the site reclamation plan as <br /> approved by the DRMS and the State Division of Water Resources(DWR). The DWR has reviewed <br /> the plan and has no concerns with the depth of groundwater at the site. Furthermore the site is <br /> operated under an approved Temporary Substitute Supply plan. The City of Thornton will likewise <br /> operate the facility under a permanent Plan for Augmentation. <br /> C. Al has an obligation under its USACE permit to maintain wetland vegetation along the Bull Seep. The <br /> proposed Drain will do that. However,Al has no obligation or authority to manage storm flows in the <br /> Bull Seep or discharges from the Fulton Canal. <br /> Tetra Tech <br /> 1900 S.Sunset Street,Suite I-E, Longmont, CO 80501 <br /> Tel 303-772-5282 Fax 303-772-7039 www.tetratech.com <br />