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DNR COLORADO <br /> co Division of Water Resources <br /> Department of Natural Resources <br /> Dam Safety Branch RECEIVED <br /> May 18, 2016 <br /> MAY 18 2016 <br /> Mr. Don W. Deere, P.E. <br /> Deere Et Ault Consultants, Inc. DIVISION OF RECLAMATION <br /> 600 South Airport Road, Suite A-205 MINING AND SAFETY <br /> Longmont, CO 80503 <br /> don.deere@deereault.com <br /> VIA EMAIL <br /> When replying, please refer to: <br /> STONEWALL SPRINGS CENTRAL DAM, DAMID 140139 <br /> Water Division 2, Water District 14 <br /> Construction File No. C-1927 <br /> SUBJECT: SEO Design Review Comments <br /> Dear Mr. Deere, <br /> This letter is in response to your submittal of the design package for proposed construction of <br /> Stonewall Springs Central Dam pursuant to Rule 5, 2-CCR 402-1 and CRS 37-87-105 for State <br /> Engineer review and approval prior to construction. Our office received your design submittal <br /> on March 14, 2016, which consisted of the application, design report, construction plans, and <br /> technical specifications. We have completed our review and have the following comments. <br /> After you have satisfactorily addressed the comments please resubmit the design package for <br /> our final review. <br /> General Comments: <br /> 1. We have the following concerns at the southwest corner of the site, nr. Sta. 50+00 (see <br /> boring CR-7): <br /> a. Overburden clay appears to be absent at boring CR-7. The dam would lie on alluvial <br /> sand Et gravel with potential for short seepage path through embankment and over the <br /> slurry wall. <br /> b. Consider if upstream slope of dam were to erode over time due to no slope protection <br /> on lower portion of slope; this could potential further shorten seepage path. <br /> c. This location would be upstream of Santa Barbara mine highwall. Consider potential <br /> for backward erosion piping of alluvial sands in this scenario. <br /> In our April 14, 2016 meeting, Deere Et Ault proposed that the foundation can be over- <br /> excavated in this reach and replaced with clay backfill in order to provide some minimum <br /> depth of clay above the sand Et gravel alluvium, say 3-ft. See more related comments <br /> below. <br /> 2. We recommend moving the slurry wall to the center of the dam embankment in order to <br /> prevent the potential short seepage path through the upstream toe of the dam <br /> embankment. Otherwise document why the upstream toe is the preferred location. <br /> 3. Provide a copy of recorded 50-ft access easement to SEO for south side of the proposed <br /> dam. At our April 14, 2016 meeting, Mr. Morley (dam owner) said he will do so. <br /> 4. Please discuss mining and reclamation impacts to the proposed dam and reservoir by all <br /> adjacent permitted mines, i.e. not limited to the Santa Barbara mine. <br /> ;my Cp . <br /> 310 E. Abriendo Ave. Suite B, Pueblo, CO 81004 P 719.542.3368 www.water.state.co.us 4 <br />