2012-10-25_HYDROLOGY - M1977348 - Laserfiche WebLink

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October 2012 Attorney Work Product, Confidential and Privileged 6 ■ How does the current extent of impacted groundwater and site geology compare to the construction of surrounding wells (i.e., what is the likelihood that other nearby wells may be impacted and are they in the same aquifer)? • Is there a well that is currently representative of background conditions in the same formations that is now showing evidence of impact? 103- 81640A If these tasks suggest that groundwater in the vicinity of the Site has been impacted by CKD disposal, then the DRMS issue regarding what steps should be taken to minimize the current and future impact(s) to site groundwater will be evaluated. Details of the SOW tasks are presented below. 2.1 Field Investigation Health and Safety It is anticipated that the hazard level of work will be relatively low and can be performed in Level D protective clothing (e.g., hardhat, safety glasses, hearing protection, steel -toed boots, and gloves). All field personnel and drilling subcontractor will, at a minimum, have OSHA 10 hour training for Construction training in compliance with 29 CFR 1926.21, and the drilling contractor will be Browz Certified. 2.2 Drilling and Well Installation The well installation requested in the DRMS's June 25 letter is planned to consist of three additional groundwater monitoring wells at the Site, to be identified as MW -5 through MW -7. The proposed locations are shown on Figure 4. MW -6 and MW -7 locations were selected because they are geologically down -dip and hydrogeologically downgradient from the CKD disposal area and the existing monitoring wells. The locations are also near current access roads on the Site and will allow access using a truck mounted drill rig. Upgradient locations were similarly evaluated for well installation; however, suitable sites could not be identified that would also intercept the same geologic units as those intercepted by the existing monitoring wells. In lieu of an upgradient well, a background well (MW -5) located north of the CKD area (with no possible impact from CKD), but in the same geologic units was existing wells MW -2, MW -3, and MW -4 is proposed. Based on information from monitoring wells MW -1 through MW -4 installed at the Site and our understanding of the Site geology, it is anticipated that the new wells will be completed at depths of between approximately 100 and 200 feet. However, the proposed approach will be to install the wells at the first encountered groundwater or a maximum of 20 feet into the Codell sandstone, whichever occurs first. 2.2.1 Utilities Prior to drilling activities, a utility locate will be requested and a notice of intent (NOI) to drill monitoring holes will be filed with the Colorado Division of Water Resources. 2.2.2 Method of Drilling It has been assumed that all drilling can be accomplished with casing advancer drilling methods. Fill samples would be collected with either split spoons or a CME style dry core sampler, and HQ coring will \10 \81640\ 0400\ characterizationpin_ fnl- 23octl2\ characterizationpin_fnl- 23octl2 docx Golder Associates