NPL Partial Site Deletion NarrativeCalifornia Gulch
OU8 also known as Lower California Gulch is defined by the 500-year floodplain of the California Gulch from immediately below the boundary of the Yak Tunnel Water Treatment Plant (OU1) to the point of confluence of California Gulch with the Arkansas River, and includes the Colorado Zinc-Lead (CZL) Tailing Impoundment outside the 500-year floodplain. OU8 is approximately 97 acres in size and 4.3 miles long.
The CZL tailing impoundment was an operating flotation mill that processed zinc-lead ores sporadically between 1925 and 1940 and is the only tailing impoundment in OU8. The CZL site covered approximately 1.6 acres at an average depth of 7 feet and contained an estimated 17,000 cubic yards of tailing. The Gaw waste rock pile represents the only deposit of waste rock identified within OU8. Waste rock from underground mining was frequently dumped near mineshafts within the site and has added to the contamination. Site-wide studies identified about 6.3 acres of non-residential area soils with elevated levels of contamination.
Historically, tailing impoundments have resulted in fluvial deposits of tailing being transported by surface flows and deposited at specific areas within OU8. During high flow events, stream sediments originating from source areas upstream of OU8 were transported by California Gulch and associated tributaries into OU8. The stream sediment in Lower California Gulch was contaminated with mine wastes and associated metals from upstream sources. The soluble metals contained in runoff have contributed to the contamination of surface water and sediments.
No Further Action was the selected alternative for the CZL Tailing Impoundment since all tailing were removed from this area in a 1995 Removal Action. No action was the selected alternative for the Gaw waste rock pile since site-wide studies showed that the waste rock pile was not a source of contamination to surface water or ground water. Remedial action activities for OU8 began in August 2001 by the responsible party, Resurrection Mining Company. Containment was the selected alternative for non-residential soils and fluvial tailing within OU8. Approximately 4.5 acres of poorly-vegetated upland soils were regraded and revegatated. For fluvial tailing, response actions included regrading, revegetation, riprap or erosion-control, and institutional controls. Remediating the contaminated stream sediment included removal of sediment, channel improvements, and institutional controls. Construction was completed in September of 2002. The five-year review in 2007 noted that all remedial actions in OU8 have been completed.
The EPA, with concurrence of the State of Colorado through the Colorado Department of Public Health and Environment has determined that all appropriate response actions under CERCLA, other than operation, maintenance, monitoring and five-year reviews, have been completed. Therefore, EPA is deleting all of OU8 including the impounded tailing, non-residential area soils, waste rock, fluvial tailing and stream sediment from the NPL.