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Mike Boulay -29- April 11, 2011 <br />Resources has raised this same concern (see Item 7 of this letter). If the <br />construction of any sediment ponds exposes groundwater, the pond must be <br />backfilled immediately until a well permit is obtained from the State Engineer. If a <br />well permit is obtained for these ponds another potential concern is that when <br />these ponds are full they would likely discharge through the bottom of the pond <br />directly to groundwater. Unlined pits discharging to groundwater may require <br />authorization from the Colorado Department of Public Health and Environment, <br />Water Quality Control Division and a CDPS discharge permit may be necessary. <br />One option would be to line the ponds but this is not discussed and there are no <br />plans presented for pond liners. Given the fact that pond bottom elevations are <br />very close to the groundwater table, the Division is requesting that the plan <br />designs and discussion for each of the ponds be reviewed and revised <br />accordingly. Please elaborate on whether or not groundwater is likely to be <br />encountered at each pond location and provide appropriate mitigation plans. <br />Otherwise show that the appropriate permits have been obtained for exposing <br />groundwater from the Division of Water Resources. If CAM intends to discharge <br />through the pond bottoms, please contact the Water Quality Control Division to <br />determine if a CDPS Permit is required. <br />CAM : The projected groundwater elevation as shown on Figure 2 in the AVF <br />Report (Exhibit 14) at the location of ponds 1 and 2 is approximately 4455'. The <br />elevation bottom of pond 1 is 4463' and pond 2 is 4460' and therefore <br />groundwater is not likely to be exposed. In addition, the concern about the <br />sediment pond discharging to the groundwater is unlikely. Please see discussion <br />presented on page 2.05-51. <br />53. Sediment Ponds #1, #2, #3, and #5 appear to be incised, based on the details <br />shown on Maps 13 and 14. No embankments are proposed to be constructed for <br />these four ponds, and dewatering will occur as needed by pumping to Reed <br />Wash. <br />Sediment Pond #4, however, is located immediately adjacent to Reed Wash and <br />has been designed with an emergency spillway. Details of Pond #4 are provided <br />on Map 14. The spillway elevation appears to coincide approximately with the <br />existing ground surface. It appears that an embankment is proposed along the <br />outermost edge of the pond (Section I-I'), in order to provide sufficient freeboard <br />above the spillway. It is unclear, from this drawing, what is the intended vertical <br />limit (depth below ground surface) of embankment construction. The fine- <br />grained in-situ soils may be unsuitable material to effectively form the lower <br />reaches of the impounding structure. <br />The Division has determined that a detailed design plan for this structure <br />(Sediment Pond #4) is required, as described in Rule 2.05.3(4)(a)(ii)(A) and (B), <br />to ensure compliance with the safety factor requirements of Rule 4.05.6 and Rule <br />4.05.9.