2012-09-28_REVISION - M1977307 (27)

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1.0 Introduction The Colorado Department of Reclamation, Mining and Safety (DRMS) revised regulations for a Designated Mining Operation (DMO) requires an Engineered Stormwater Management Plan ( ESWMP), commonly referred to as a Drainage Design Plan, to ensure that waste rock and ore stockpiles are protected from design storm events that could potentially erode and transport materials offsite from mining operations. In addition, this plan provides site information and plans to control stormwater runoff from the site, including best management practices (BMPs) to minimize soil disturbances, control erosion and sedimentation during operation and post - reclamation, prevent run -on from offsite areas from flowing across the site, and reduce the potential for pollutants being transported by stormwater runoff. 2.0 Approach The goal of the ESWMP is to protect the waste rock stockpile and ore stockpile areas during mining operations and long -term protection of the waste rock area after remediation has been completed. The approach used in this plan is to prevent offsite run -on from entering the active surface mining area by diverting offsite surface flows above the stockpile areas via berms or diversion ditches, and preventing onsite runoff from leaving the site, or containing it long enough to allow sediment to settle in the retention pond. This plan defines the drainage areas above the mining site, delineates the onsite drainage area, determines the amount of runoff from 10 -year, 24 -hour and 100 -year, 24 -hour precipitation events, routes offsite runoff around the site, and contains or controls onsite precipitation and subsequent runoff. Similar to the SWMP regulated by the Colorado Department of Public Health and Environment ( CDHPE), this plan also focuses on potential sources of pollution, particularly petroleum compounds and other potentially hazardous materials. Prevention of unintended discharge using secondary containment structures to minimize the potential for spills or leaks from containment structures, reporting requirements to the CDPHE, and BMPs related to storage and containment are important components of a conventional SWMP regulated by CDPHE and incorporated into this plan. 3.0 Location The CM -25 mine is located in southwestern Colorado approximately 1.2 miles south - southwest of the former town of Uravan, Colorado. The mine is accessed via County Road EE22 from Uravan to the Club Mesa area. It sits on a small mesa located just above and west of the Uravan tailings disposal site. Attachments to this document include a portion of a USGS topography map indicating the general location of the mine. The portal is located in a small drainage on a hill side that slopes in a general easterly direction. Most surface runoff from the area will eventually flow into Hieroglyphic Canyon, an ephemeral drainage to the south that flows east, eventually discharging to the San Miguel River at Uravan. ESWMP -1