2018-10-16_PERMIT FILE - M2018039 (2)

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Mr. Jared Ebert RE: Lamb Lakes Site M-2018-039 October 15, 2018 suitable as a growth medium, the materials may be used to supplement previously stockpiled topsoil and used during site reclamation. Rule 6.4.5 —Exhibit E—Reclamation Plan 4. The reclamation sequence is anticipated to be from Lamb A, south through Lamb B and Lamb C. Pit dewatering and slurry wall construction will effectively occur concurrently. For each pit, the lake shall only be dewatered once slurry wall construction has been contracted and scheduled. The lake dewatering shall occur so that additional excavation, backfill, and side slope maintenance can be performed during or prior to slurry wall construction. From previous experience at the Treiber Lakes site (M-2011-049), it is anticipated that the reclamation process of dewatering, excavation, backfill, and slurry wall construction will take 2-3 months for each lake. Rule 6.4.7 —Exhibit G—Water Information 5. Site-specific groundwater information for the property is limited. Available site-specific and other alluvial information and evaluations are included in the attached Hydrogeologic Evaluation (see Attachment B). The evaluation provides an assessment of historic baseline groundwater conditions, potential impacts from lake dewatering and slurry wall construction, and recommendations for a groundwater monitoring plan. During lake dewatering, and prior to slurry wall construction, operations may affect groundwater systems hydraulically connected to the Cache la Poudre River. Replacement of river depletions to mitigate these impacts will be covered under the Substitute Water Supply Plan (SWSP) obtained from the Colorado State Engineer's Office (SEO). Additionally, a well permit for exposed groundwater in the proposed permit area has been, or will be, obtained from the SEO. The dewatering also has the potential to impact alluvial groundwater wells near the site. A well permit application search of the SEO database was used to locate wells near the proposed permit area. The Water Resource Map (Exhibit C-6) illustrates existing recorded well permit applications within 600 feet of the proposed permit boundary. Although there may be other wells in the area, they are not recorded with the SEO. As stated in the application, it appears that many of the wells identified within 600-feet of the proposed permit boundary were historically associated with the lands that have been mined and no longer exist. The Hydrogeologic Evaluation (Attachment B) suggests that significant dewatering impacts are not likely to extend much more than 650 feet from the edge of the dewatered lakes. With this impact assessment, there are few alluvial wells within the potential dewatering drawdown area to be affected. Additionally, the lakes are to be dewatered individually and only immediately prior to slurry wall construction, minimizing the extent and duration of any potential dewatering impacts. Page 2 of 7