2009-03-06_PERMIT FILE - C1981012A (6)

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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Rationale - Page 24, Permit No. CO-0000906 lua eva ether b. Ground Water Protection -Pond 6 is not lined a there brequeen ed by the Cons olorado Dischar he Permit Sysote6 currently meets the allowable exfiltration rate of 0 Regulations. Therefore, a compliance schedule groundwater protection prog amhas neece?sary,i ?s?f ? h beloand e installation of liners or the development of goun Permit Citation Due Date Code Event Description 50008 Preliminary Plan Investigate and submit conclusive information on the seepage from Part I.A.3. 06130109 Completed Pond 6 to determine if the allowable exfltration rate of 10' em/sec is exceeded. If liner integrity is the basis for determination that the seepage meets the criteria, then the report must be prepared by a professional engineer registered in Colorado. 53999 Submit Work If the study indicates that Pond 6 exceeds the allowable seepage rate Part I.A.3. 12131109 Plans of 10 cm/sec, the facility either (1) submit a work plan for the installation of a liner for Pond 6; (2) submit a work plan for the installation of monitoring wells; or (3) submit a letter stating that the point of compliance will be at the point of influent to Pond 6 along with a permit modification request. If the study indicates that Pond 6 discharges at a seepage rate less than 10-6 cm/sec, the remainder of this compliance schedule will be deemed complete. Part LA .3. I2131110 54299 Complete Work If the study indicated that Pond 6 exceeds the allowable seepage Plans rate of 10-6 cm/sec and the permittee has opted to line Pond 6, the permittee must submit a report completed by a professional engineer • registered in the state of Colorado indicating that the liners have been replaced. The report must certify that the liner material meets the allowable seepage rate of 10-6 centimeters per second or less, and that the placement was accomplished according to the manufacturer's requirements (i.e., all welds were tested and the liners were checked for holes prior to backfilling). Further, the permittee must submit a request for permit modification to eliminate both Outfal1033 limitations and monitoring requirements and Monitoring Wells 050A-050D limitations and monitoring requirements. If the study indicated that Pond 6 exceeds the allowable seepage rate of 10-6 cm/sec and the permittee has opted to install monitoring wells, notice of well completion must be submitted. Additionally, if the permittee has installed more or less monitoring wells than those specified in the permit, the permittee must submit a request for permit modification to add or eliminate extra groundwater monitoring wells' compliance points. c. Sediment Control Plan - In accordance with 40 CFR Part 434.82, a site-specific Sediment Control Plan must be developed. The Sediment Control Plan must be designed to prevent an increase in the average annual sediment yield from pre-mined, undisturbed conditions. The Sediment Control Plan must be approved by the permitting authority and be incorporated into the permit as an effluent limitation. The Sediment Control Plan must identify best management practices (BMPs) and also must describe design specifications, construction specifications, maintenance schedules, criteria for inspection, as well as expected performance and longevity of the best management practices. Using watershed models, the operator must demonstrate that implementation of the Sediment Control Plan will result in average annual sediment yields that will not be greater than the sediment yield levels from pre-mined, undisturbed conditions. The operator must use the same watershed model that was, or will be, used to acquire the SMCRA permit. The operator must design, implement, and maintain BMPs in the manner specified in the Sediment Control Plan.