2020-12-02_PERMIT FILE - M2020061

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10/8/2020 Federal Register::National Oil and Hazardous Substance Pollution Contingency Plan:Partial Deletion of the California Gulch Superfund... The State,the EPA and certain Potentially Responsible Parties(PRPs)have conducted various studies and investigations to evaluate the nature and extent of contamination generally at the Site,and specifically within OU3.Remedial Investigations(RIs)began in 1986 within the Site,including mine waste rock piles,tailing disposal areas,surface water and aquatics,groundwater,smelter sites,residential/populated area soils,slag piles,and terrestrial studies. Concurrent with the various investigations and studies,risk assessments were conducted at the California Gulch Superfund Site.Some included the Preliminary Baseline Risk Assessment(Preliminary BRA),and the Final Baseline Human Health Risk Assessments(Final BRA):Part A,Part B,and Part C.For human health risk issues at OU3,the Preliminary BRA and the Final BRA Part C,Evaluation of Worker Scenario and Evaluation of Recreational Scenarios,were most pertinent.The Preliminary BRA indicated that lead and arsenic are responsible for the majority of human health risks at the Site.Therefore,arsenic and lead were used as indicator contaminants for risk in the Final BRA. EPA and D&RGW entered into an Administrative Order on Consent(1991 D&RGW AOC)on December 3, 1991.The 1991 D&RGW AOC required D&RGW to perform remedial investigations of major lead slag piles and one zinc slag pile within the Site.In 1992,D&RGW completed a remedial investigation(1992 OU3 Slag RI)of the major lead slag piles and the zinc slag pile within the Site.Slag was found to have elevated levels of zinc,lead,arsenic and cadmium along with a low acid-generating potential,and a neutral to basic pH.Fine slag,which is less than 3/8 of an inch,was found to have elevated lead levels.The fine fraction of slag was the only part of the slag that may present an unacceptable risk because fine slag poses an inhalation hazard. EPA and D&RGW entered into a Consent Decree on September 15,1993(1993 D&RGW CD)for the completion of investigation,feasibility studies,and remediation activities to be performed for OU3.The 1993 D&RGW CD stated EPA's concerns regarding the fine fraction of the stockpiled slag at the AV Smelter site and the potential for particulate release during ballast operations as a potential human health exposure pathway.The 1993 D&RGW CD required D&RGW to perform a feasibility study for stockpiled fine slag and to submit an operations plan before initiating any ballast operations. In 1993,the EPA conducted a Screening Feasibility Study(1993 SFS)to initiate the overall CERCI A FS process at the California Gulch Site.The purpose of the SFS was to develop general response actions and identify an appropriate range of alternatives applicable to the various contaminant sources to be considered during feasibility studies for the California Gulch Site.The 1993 SFS for Remedial Alternatives examined several remediation alternatives for slag located❑at the Site based on specific criteria,such as relative cost, F� Start Printed implementability,and effectiveness.The three remedial alternatives for slag retained for further evaluation Page 6774 were:No action,institutional controls,and resource utilization.The La Plata and Harrison Street Slag piles did not contain fine slag.Therefore,no further action was necessary.Because the AV Smelter pile contained fine slag,more investigation was required. In July of 1995,D&RGW submitted a ballast operations plan to EPA.Following EPA's approval of the plan, ballast operations commenced in August 1995 but ceased soon thereafter for lack of a profitable market for the slag.Ballast operations involve the sorting of larger slag so that the size fraction of greater than 3/8 inch and less than 21/2 inches is produced for road ballast.The undersized fraction(i.e.,less than 3/8 inch),or sorted fine slag,that is produced by the sorting process is stockpiled along with the previously sorted fine slag at the Arkansas Valley pile. https://www.federairegister.gov/documents/2016/02/09/2016-02601/national-oil-and-hazardous-substance-pollution-conti ngency-plan-partial-deletio... 12/16