United States Environmental Protection Agency 1200 Pennsylvania Avenue, N.W. March Washington, D.C. 20460 2011 Office of Solid Waste and Emergency Response Support Document for the Revised National Priorities List Final Rule – ACM Smelter & Refinery Support Document for the Revised National Priorities List Final Rule ACM Smelter and Refinery March 2011 Site Assessment and Remedy Decisions Branch Office of Superfund Remediation and Technology Innovation Office of Solid Waste and Emergency Response U.S. Environmental Protection Agency Washington, DC 20460 Table of Contents Executive Summary ....................................................................................................................................v Introduction................................................................................................................................................vi Background of the NPL.........................................................................................................................vi Development of the NPL.......................................................................................................................vii Hazard Ranking System.......................................................................................................................vii Other Mechanisms for Listing ............................................................................................................viii Organization of this Document.............................................................................................................ix Glossary ..................................................................................................................................................ix 1. List of Commenters and Correspondence ........................................................................................1 2. Site Description ...................................................................................................................................3 3. Summary of Comments......................................................................................................................4 3.1 Need for Listing...........................................................................................................................5 3.2 Purpose of NPL ...........................................................................................................................6 3.3 Impacts of Listing .......................................................................................................................7 3.4 Previous NPL Decision (Rationale for Listing) ........................................................................7 3.5 Liability........................................................................................................................................8 3.6 Risk Associated with Site............................................................................................................9 3.7 Permitted Releases and Regulatory Limits.............................................................................12 3.8 Adequacy of Site Description...................................................................................................12 3.9 Extent of Site .............................................................................................................................13 3.10 Comments on HRS....................................................................................................................14 3.11 Scoring Other Pathways...........................................................................................................15 3.12 Consideration of Response Actions / Current Conditions.....................................................16 Sources Identified at Proposal .............................................................................................................17 i ACM Smelter & Refinery NPL Listing Support Document March 2011 3.13 Additional Sources ....................................................................................................................17 Source 4 – Slag Waste ........................................................................................................................18 3.14 Source 1......................................................................................................................................19 3.14.1 Hazardous Substances Associated with Source 1 ...............................................................19 3.14.2 Source 1 Delineation/Inference of Contamination..............................................................21 3.14.3 Sampling Procedures...........................................................................................................23 3.14.4 Other Sampling/Current Conditions ...................................................................................24 3.14.5 Source 1 Hazardous Waste Quantity...................................................................................26 3.14.6 Source 1 Containment.........................................................................................................28 3.15 Source 2......................................................................................................................................29 3.15.1 Source 2 Eligibility and Consideration of Response Activities ..........................................29 3.15.2 Association of Hazardous Substances with Source 2 .........................................................32 3.15.3 Source 2 Hazardous Waste Quantity...................................................................................33 3.15.4 Source 2 Containment.........................................................................................................35 3.16 Other Possible On-site Sources................................................................................................37 Surface Water Scoring at Proposal .....................................................................................................38 3.17 Evaluation of the Surface Water Pathway..............................................................................38 3.18 Description of Pathway.............................................................................................................41 Likelihood of Release............................................................................................................................44 3.19 Likelihood of Release - Observed Release by Direct Observation........................................44 3.19.1 Documentation of Observed Release by Direct Observation..............................................45 3.19.2 Quantity of Slag Dumped into the Missouri River .............................................................46 3.20 Surface Water Likelihood of Release - Observed Release by Chemical Analysis...............48 3.20.1 Surface Water Observed Release - Significant Increase.....................................................51 3.20.1.1 Contamination Levels below Regulatory Limits ..............................................................52 3.20.1.2 Releases in Other Aquatic Media......................................................................................53 3.20.1.3 Bias of Conclusions/Current Conditions...........................................................................54 3.20.1.4 Downstream Contaminant Levels.....................................................................................56 3.20.2 Surface Water Observed Release - Attribution...................................................................58 3.20.2.1 Attribution of Releases to On-Site Sources ......................................................................61 3.20.2.2 Other Possible Off-Site Sources........................................................................................63 3.20.2.3 Permitted Storm Water Discharges...................................................................................65 3.20.3 Surface Water Observed Release - Adequacy of Background............................................65 3.21 Potential to Release ...................................................................................................................66 Surface Water – Drinking Water Threat............................................................................................67 3.22 Surface Water - Drinking Water Threat ................................................................................67 Surface Water – Human Food Chain Threat.....................................................................................68 ii ACM Smelter & Refinery NPL Listing Support Document March 2011 3.23 Surface Water - Human Food Chain Threat Waste Characteristics ...................................69 3.23.1 Toxicity/Persistence/Bioaccumulation................................................................................69 3.23.2 Human Food Chain Threat Waste Quantity........................................................................71 3.23.3 Human Food Chain Threat Waste Characteristics ..............................................................72 3.24 Surface Water - Human Food Chain Threat Targets............................................................73 3.24.1 Targets Subject to Actual Contamination ...........................................................................76 3.24.2 Consideration of Existing Fish Tissue Data........................................................................77