_GENERAL DOCUMENTS - C1981017 (304)

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COLORADO DEPARTMENT OF PUBLIC HEALTH&ENVIRONMENT Water Quality Control Division WQCD-P-B2 Cherry Creek Drive South Denver, Colorado 80246-1530 RATIONALE STORMWATER DISCHARGES ASSOCIATED WITH METAL MINING OPERATIONS AND MINE-WASTE REMEDIATION GENERAL PERMIT IN COLORADO SECOND RENEWAL COLORADO DISCHARGE PERMIT NUMBER COR-040000 L INTRODUCTION The permit is for the regulation of stormwater runoff associated with metal mining operations and mine-waste remediation projects. The term "metal" is used to distinguish this permit from the general permit for coal mining with surface discharge only, and the general stormwater permit for sand and gravel mining and processing (and other nonmetallic minerals). Other terms are defined in the permit. This Rationale will briefly explain the background of the stormwater program, activities which are covered under this permit, how to apply for coverage under this permit, and the requirements of this permit. II.CHANGES IN RENEWAL PERMIT Minor updates have been made throughout the permit. They do not affect the substance of the requirements. The Rationale discussion on the Exemptions for Small Municipalities (Section IV.G) has been changed to include the March 10, 2003 deadline for permit coverage for municipally-owned industries. This did not involve any changes to the permit. In addition, the Rationale discussion on the Exemption for Pre-operational Mines (Section IV.D) has been changed to address the need for construction permits for sites disturbing between 1 and S acres starting July 1, 2002, in addition to the discussion in the previous version of the Rationale for sites disturbing over 5 acres. This did not involve any changes to the permit. III. BACKGROUND The federal Clean Water Act requires that industrial stormwater discharges be regulated under the National Pollutant Discharge Elimination System ("NPDES")program. (Note:the Colorado Program is referred to as the Colorado Discharge Permit System, or CDPS, instead of NPDES.). The Water Quality Control Division ("the Division") has stormwater regulations (S CCR 1002-61) in place. These regulations specifically include mining operations where stormwater has come into contact with any overburden, raw material, intermediate products, byproducts,finished products or waste products, as industrial facilities which must obtain stormwater discharge permits. Other federal regulations, specifically 40 CFR subchapter N(mining operations are covered in sections 434, 436 and 440), were developed to control the quality of discharges from mills and mine drainage. Mine drainage is water drained, pumped, or siphoned from active mining areas. This water is generally classified as "process water"and is covered under the pre-existing Colorado Discharge Permit System (CDPS).