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10/8/2020 Federal Register::National Oil and Hazardous Substance Pollution Contingency Plan:Partial Deletion of the California Gulch Superfund
<br /> EPA agreed,pursuant to a May 2,1994 Consent Decree(1994 CD),to divide the Site into 12 operable units
<br /> (OUs).The OUs are as follows:OU1,Yak Tunnel/Water Treatment Plant;OU2,Malta Gulch Tailing
<br /> Impoundments and Lower Malta Gulch Fluvial Tailing;OU3,D&RGW Slag Piles/Railroad
<br /> Easement/Railroad Yard;OU4,Upper California Gulch;OU5,ASARCO Smelter Sites/Slag/Mill Sites;OU6,
<br /> Starr Ditch/Stray Horse Gulch/Lower Evans Gulch/Penrose Mine Waste Pile;OU7,Apache Tailing
<br /> Impoundments;OU8,Lower California Gulch;OU9,Residential Populated Areas;OUio,Oregon Gulch;
<br /> OU1i,Arkansas River Valley Floodplain;and OU12,Site-wide Surface and Groundwater.With the exception
<br /> Of OU12,the OUs pertain to distinct geographical areas corresponding to areas of responsibility for the
<br /> identified responsible parties and/or to distinct sources of contamination.To date,OU2,OU4,OU5,OU7,
<br /> OU8,OU9,and OUio have been partially deleted from the NPL.
<br /> The background and history,the Remedial Investigations and Feasibility Studies(RI/FS),Removal and
<br /> Response Actions,Selected Remedies,Cleanup❑Standards,and Operation and Maintenance activities for ❑Start Printed
<br /> OU1 and OU3 are discussed below. Page 6771
<br /> 0U1 Background and History
<br /> Operable Unit 1(OU1)consists of the Yak Tunnel and Water Treatment Plant.The Yak Tunnel and Yak
<br /> Tunnel Water Treatment Plant are located to the southeast of the City of Leadville.A map of OUi can be
<br /> found in the docket at www.regulations.gov(http://www.regulations.gov)under Docket ID no.EPA-HQ-
<br /> SFUND-1983-0002.The Yak Tunnel was constructed to dewater mines and to facilitate mineral exploration
<br /> and development.The tunnel was driven in 1895,as an extension of the Silver Cord Tunnel,to drain the Iron
<br /> Hill mines.The Yak Tunnel was extended several times,with the last extension occurring in 1923.The Yak
<br /> Tunnel extends underground approximately 31/2 to 4 miles into Iron Hill and Breece Hill.The tunnel has
<br /> several major laterals and drifts that extend from the tunnel into various mine workings,such as the
<br /> Horseshoe,the Rubie,the North Mike,the South Mike,the Ibex No.4,the Little Winnie,the Resurrection
<br /> No.1,the Fortune,the Resurrection No.2,and the Dolly B.The EPA estimated that 6o,000 feet of tunnels
<br /> and major laterals and 55 to 74 million cubic feet of void space are associated with the tunnel mining
<br /> activities.At the time of the ROD in March 1988,studies indicated that a combined total of 210 tons per year
<br /> of cadmium,lead,copper,manganese,iron,and zinc were discharged from the Yak Tunnel into California
<br /> Gulch,which drains into the Arkansas River.Surface water contamination is the major impact of the Yak
<br /> Tunnel discharge.Shallow alluvial ground water and stream sediment may have been impacted by historic
<br /> releases from the Yak Tunnel.
<br /> OU1 Remedial Investigations and Feasibility Study (RI/FS)
<br /> The State,the EPA and certain Potentially Responsible Parties(PRPs)conducted various studies and
<br /> investigations to evaluate the nature and extent of contamination generally at the Site.Remedial
<br /> Investigations(RIs)began in 1986 within the Site,including mine waste rock piles,tailing disposal areas,
<br /> surface water and aquatics,groundwater,smelter sites,residential/populated area soils,slag piles,and
<br /> terrestrial studies.The Yak Tunnel/California Gulch Remedial Investigation(1986 RI)evaluated the human
<br /> health and environmental impacts due to historic mining activities.
<br /> In May 1987,the Phase I Remedial Investigation(1987 Phase I RI)confirmed that the Yak Tunnel is a
<br /> significant source of metals contamination.Results of this study indicated that 75 to 8o percent of the
<br /> cadmium,manganese,and zinc detected at the confluence of California Gulch with the Arkansas River
<br /> originates from the Yak Tunnel.Historical information along with data collected during the 1987 Phase I RI
<br /> https://www.federairegister.gov/documents/2016/02/09/2016-02601/national-oil-and-hazardous-substance-pollution-contingency-plan-partial-deletion-... 7/16
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