Uncontrolled Surface Flow Areas
Under the proposed remedy, most of the stormwater impacted by historic mining would be captured and would
be managed in existing stormwater best management practices (BMPs) controls and by additional stormwater BMPs proposed at other locations throughout Butte, including Diggings East, Northside Tailings, Buffalo Gulch, and Grove Gulch. Under the proposed remedy, areas remaining outside the influence of these BMP projects would be evaluated to assess the potential impact of historic mining sources in those areas on surface water quality in Silver Bow and Blacktail Creeks, and additional BMPs would be constructed in these remaining areas to improve water quality in the creeks.
The proposed remedial activities would be performed by Atlantic Richfield Company and would include:
- Site Evaluations - Atlantic Richfield Company would evaluate the remaining areas where stormwater is not captured in existing or proposed BMPs and may drain to Blacktail and Silver Bow Creeks to determine whether these areas have been impacted by historic mining activities and if they contribute to the degradation of surface water quality.
- Remedial Action - If an area is determined to be contributing contaminants of concern and impacting Blacktail Creek or Silver Bow Creek water quality, an appropriately sized BMP would be proposed. A work plan would be developed detailing where and how the BMPs would be constructed to reduce or prevent contaminated stormwater and sediments from reaching Blacktail and Silver Bow Creeks. Following construction, each BMP would be integrated into the stormwater operation and maintenance program for BPSOU.
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- There are 12 remaining sub-drainages, covering an approximate area of 875 acres, that would be evaluated.
- The BMPs installed in these sub-drainages would be sized up to the 6-month, 24-hour Type I Soil Conservation System (SCS) design storm. The actual type and size of each BMP would be determined during the design period.