2012-08-13_REVISION - M1982090 (2)

Home Browse Search

consists of an earthen dam which serves as a stormwater berm controlling upgradient runoff (Photo 2). The outfall along the eastern boundary of the pond was demolished as part of recent reclamation and will need to be re- constructed (Photo 2). Reuse of the sedimentation pond will require excavation of up to 6,200 cubic yards of fill and cap material. Excavated material from the pond will be stockpiled into a long berm up -slope from the pond excavation area (designated as "Stockpile 1" on Figure 2). The berm is expected to be 325 feet long, 65 feet wide, and average approximately 8 feet deep (Figure 2). The north slope of the berm will be graded to match the slope of the pond, and the south slope of the berm will be approximately 1:1.5 (V:H). The berm will serve as both a stockpile for topsoil/cap materials for future reclamation and a storm water barrier to control upgradient runoff. Any large trash and debris (e.g. scrap metal, timbers, etc.) contained in the fill material will be screened out and disposed of appropriately. The historic pond was an oval shape, approximately 188 feet long and 100 feet wide, with a total surface area of approximately 16,570 square feet (Figure 2). Historic records do not indicate the slope, average depth, or total volume of the pond. Those aspects of the pond are expected to be revealed as excavation is ongoing. Given the surface area (16,570 square feet), each foot of depth at a flow rate of 1,000 gallons per minute (gpm) provides for 125 minutes of detention time. For example, if the pond were to average 5 feet deep from its banks to the center, the total detention time for solids to fall out of suspension would be 10.4 hours. Personnel employed by previous operators have stated that the holding time of the historic pond at flow rates of 1,000 gpm was approximately 12 hours. Those personnel have also stated that the bottom of the pond was lined with 2 feet of limestone and that there was no synthetic or clay liner. It is important to note that the historic pond was deemed suitable for use during previous mining and milling operations, and was approved by both WQCD and DRMS' predecessor. CBCI is confident that re- constructing the pond to equal the historic footprint will be adequate to settle any potential suspended solids stirred up from construction activities at the 14L portal. The outfall of the pond will be constructed on the eastern boundary, similar to the outfall of the historic pond. A 40 foot long, 36 inch wide corrugated metal pipe (CMP) (6 inches wider than the inflow CMP) will be placed at the appropriate elevation to maximize detention time in the pond. The segment of the earthen dam surrounding and above the outfall culvert will be reinforced with geotechnical fabric and topped with large boulders and/or concrete to act as an overflow feature in the event that the culvert is blocked or flows exceed capacity. The outfall culvert will be oriented northeast and will convey flows approximately 40 feet away from the pond into Imogene Creek. Water rights for the discharge flowing from the 14L portal for mining and milling purposes have been maintained by the owners of the Camp Bird mine since 1941 (Attachment C). However, water storage rights have not been obtained by CBCI. As per August 10, 2012 phone correspondence between the Division of Water Resources (DWR) (Eric Weig, District 8 Water Commissioner) and CBCI (Mike Thompson), the utilization of the sedimentation pond as described herein is not considered a takings due to the relatively short detention time, lack of a pond liner, and close proximity to the nearest streams. Specifically, DWR clarified that usage of a pond located within 100 feet of the nearest receiving stream is not considered a takings and does not cause injury to other water rights. Equipment and supplies relied upon for the construction of the sedimentation pond is included in Attachment F. Technical Revision, Camp Bird Mine 112 Permit (Permit No. M- 1982 -090) Page 5