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Mr. Don W. Deere, P.E. <br /> Stonewall Springs Central Dam, DAMID 140139, C-1927 <br /> May 18, 2016 <br /> Page 2 of 3 <br /> 5. Is there an easement for the outlet Et spillway return channel where it leaves the property <br /> per Dam Safety Rule 5.9.6.1.1? At our April 14, 2016 meeting, Deere Ft Ault and Mr. <br /> Morley have proposed re-aligning the spillway return channel to cut across Mr. Morley's <br /> property to Chico Creek. The future plan would be to construct other gravel pit <br /> reservoirs and at that time the spillway return flows would need to be routed safely <br /> through such other reservoirs. <br /> 6. Proposed phased construction: <br /> a. If reservoir sand Et gravel mining, as shown on C-1927 plans, is not completed with 5- <br /> years of SE0 approval then resubmittal of phase II plans and specs will be required. <br /> b. In general SE0 approval will be required for any future mining of sands and gravels <br /> within the reservoir and within 200-ft of the dam. <br /> 7. Filter compatibility: Were lab tests done to check for dispersive clays, specifically with <br /> respect to filter compatibility between overburden clay and underlying sand? <br /> 8. Slope stability Et soil strengths: Alluvial sand strength (phi 33°) was based on index values <br /> (Peck, Hanson Et Thornburn, 1974) for average blow counts for the entire site (N=17). For <br /> downstream slope stability of the south dam during mining of the Santa Barbara pit <br /> (borings CR-7 to CR-13), we are requesting a revised slope stability analysis using N=9 or <br /> phi=30° per Peck et al (1974), which we believe is more representative of conditions at <br /> CR-7 and CR-8. (Phi of 30° for the alluvial sand is also consistent with slope stability <br /> analysis at a neighboring gravel pit recently accepted by Division of Reclamation, Mining, <br /> and Safety). Otherwise please provide better justification for strength values for the <br /> alluvial sand, e.g., based on lab testing. <br /> 9. Seepage Analysis: <br /> a. The seepage analysis assigned a kh=1.0e-6 cm/s to the Pierre shale, into which the <br /> slurry wall is to be keyed. The field permeability test at boring CR-10 determined <br /> K=1.74e-5 cm/s at about 15-ft deep into the Pierre Shale (RQD and recovery were <br /> fairly low in same area). Please discuss this with respect to the proposed 3-ft key <br /> depth into unweathered bedrock and the field engineer's ability to determine <br /> appropriate key depth during construction (ref: spec. section 02168, 1.03G, 3.06A). <br /> b. Please describe expected seepage conditions at the Stonewall Springs Central dam <br /> prior to mining of the adjacent Santa Barbara pit and after its reclamation (Santa <br /> Barbara mine permit reclamation plan shows post-mining use as a reservoir). <br /> 10. Provide provisions for monitoring seepage at toe of the Santa Barbara highwatl during its <br /> active mining. <br /> 11. Drawing sheet 18: Was batter considered for concrete conduit encasement? At our April <br /> 14th meeting Deere Et Ault indicated they are open to adding batter to the conduit <br /> encasement. <br /> 12. Please consider construction safety issues associated with construction work in and along <br /> Xcel high voltage lines. <br /> 13. Emergency Action Plan and dam breach inundation mapping will be required as part of <br /> Rule 10 completion documentation prior to SE0 acceptance of the project. <br /> Mining Permit (DRMS): <br /> 14. At our April 14th meeting DRMS indicated that the Stonewall Springs mining reclamation <br /> plan will need to be amended prior to construction in order to show post-mining land use <br /> as a reservoir (currently approved for reclamation as range land). <br /> of 1010 . <br /> 310 E.Abriendo Ave. Suite B, Pueblo, CO 81004 P 719.542.3368 www.water.state.co.us �� C" <br />