2019 Umiat Landfill Decision Document
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United States Army Formerly Used Corps of Engineers Defense Sites Program DECISION DOCUMENT ______________________________________ Hazardous, Toxic, and Radioactive Waste Project # F10AK0243-08 Umiat Air Force Station Formerly Used Defense Site Umiat, Alaska September 2019 Prepared By: U.S. Army Corps of Engineers - Alaska District Environmental Engineering Branch P.O. Box 6898 JBER, Alaska 99506-0898 [This page intentionally blank] EXECUTIVE SUMMARY This Decision Document (DD) presents the selected remedy for the Umiat Air Force Station (AFS) Formerly Used Defense Site (FUDS) Hazardous Toxic and Radioactive Waste (HTRW) project titled Umiat Landfill, Project Number F10AK0243-08. The selected remedy decision is based upon the Administrative Record for this site. The former Umiat AFS is located along the Colville River in the arctic foothills north of the Brooks Range, Alaska, approximately 105 miles southwest of Deadhorse, 170 miles southeast of Utqiaġvik (Barrow), and 65 miles southwest of Nuiqsut. The landfill is located partially on land owned by the Bureau of Land Management and partially on land owned by the State of Alaska, Department of Transportation and Public Facilities. The Umiat Air Force Station property consists of eleven separate projects, five of which are currently open. The Umiat Landfill project addresses impacts associated with the approximately 8-acre Umiat AFS landfill located about one-half mile east of the Umiat AFS cantonment facilities, within a seasonal slough of the Colville River. The Umiat Landfill project represents 95% of the remaining liability at the Umiat AFS property. Additional open projects at the Umiat AFS property include Umiat Test Well 7, Umiat Test Wells 2, 4, 5, 6, 8, 10, 11; Umiat Main Pad and Airfield; and Umiat Test Well #9 Drainage. The overall cleanup strategy for the Umiat AFS property includes pursuing implementation of land use controls and/or no further action at the Umiat Test Wells 2, 4, 5, 6, 8, 10, 11, and Umiat Test Well #9 Drainage. Umiat Test Well 7 and Umiat Main Pad and Airfield will be addressed in the future after completing other open projects. The Umiat Landfill is located in an intermittently flooded side drainage channel of the Colville River, a short distance east of the main Umiat facilities and runway. Records indicate the landfill was created during a 1973 site-wide demolition and cleanup effort by the Navy in which 409 tons of junk equipment and scrap metal and approximately 86,600 crushed drums were reportedly buried in stable areas of the flood plain. Most of the drums were buried at the east landfill, including over 7,000 drums hauled from the surrounding exploratory-well sites. The eight acre landfill includes six distinct debris cells. Based on geophysical surveys, the estimated depth of the buried debris ranges from 4 to 17 feet below ground surface, with an average depth of 14.5 feet. The estimated volume of debris is approximately 100,000 cubic yards. The landfill contains junk equipment, crane parts, scrap metal, and crushed steel drums. Buried debris is known to include contaminant sources such as lead-acid batteries and transformers. The landfill is suspected to contain drums and other containers with unknown contents that may have leaked and contaminated the underlying soils. The Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) contaminants of concern (COCs) identified in soil include the pesticides 4,4’ dichlorodiphenyltrichloroethane (DDT) and 4,4’ dichlorodiphenyldichloroethane (DDD), as well as lead, and polychlorinated biphenyls (PCBs). CERCLA COCs present in groundwater include 1,1,2,2 tetrachloroethane, DDT and DDD. Petroleum hydrocarbon contamination also exists in soil and groundwater at the site above State of Alaska cleanup levels. Petroleum hydrocarbon contamination that is associated with the Umiat Landfill and commingled with CERCLA hazardous substances will be addressed under this DD. Decision Document 2019 Umiat AFS, Landfill, F10AK024308 Page iii Umiat, Alaska The selected remedy is Alternative 7, which involves removal of the landfill from the Colville River channel, removal of PCB-contaminated sediments located near the landfill, onsite treatment (locally in Umiat) or offsite transportation and disposal of hazardous substances and contaminated soil/sediment, and disposal of inert debris and treated soils in an inert waste monofill located on the FUDS Property. The estimated cost of the remedy is approximately $160 million, including a remedial design phase of $4 million over two to three years. After the selected remedy is successfully implemented, unlimited use/unrestricted exposure will be achieved under CERCLA. Because the remedy is anticipated to take more than five years to implement, one CERCLA policy five-year review will be conducted within five years of the start of the remedial action construction phase to ensure the remedy is, or will be, protective of human health and the environment. The monofill will be visually inspected annually post-construction for five years for signs of erosion, inadequate vegetative cover, settlement or sidewall slumps, pooling of water, or other indications that maintenance is needed. One periodic review will be conducted to evaluate the closure of the monofill. Other potential remedial alternatives considered include: No Action, Land Use Controls (LUCs); LUCs and Contaminated Hot Spot Sediment Removal; Containment, Capping, and LUCs; Excavation and On-Site Disposal; Excavation and Off-Site Disposal; Excavation, On-Site Disposal, and Off-Site Disposal; and Step-Wise Implementation of Interim Actions. The remedy is protective of human health and the environment, and complies with Applicable or Relevant and Appropriate Requirements. Cumulative risk calculations indicate a human cancer risk of 8 x 10-3 and a non-cancer hazard index of 4. After implementation of the remedy, risks will be within the National Oil and Hazardous Substances Pollution Contingency Plan acceptable risk range of 1 x 10-4 to 1 x 10-6 and 1. Decision Document 2019 Umiat AFS, Landfill, F10AK024308 Page iv Umiat, Alaska TABLE OF CONTENTS 1.0 DECLAR ATIO N .......................................................................................................... 1 1.1 Site Name and Location ......................................................................................... 1 1.2 Statement of Basis and Purpose............................................................................ 1 1.3 Assessment of Site ................................................................................................. 1 1.4 Description of Selected Remedy ............................................................................ 1 1.5 Statutory Determinations ........................................................................................ 3 1.6 Decision Document Data Certification Checklist ................................................... 4 2.0 DECISION SUMMARY............................................................................................... 6 2.1 Site Name, Location, and Brief Description........................................................... 6 2.2 Site History .............................................................................................................. 7 2.2.1 Umiat Land Ownership History........................................................................ 7 2.2.2 Landfill History .................................................................................................. 8 2.3 Summary of Site and Remedial Investigations...................................................... 8 2.3.1 1986 Hazardous Waste Sampling and Analysis ............................................ 9 2.3.2 1994 Phase I RI ............................................................................................... 9 2.3.3 1996 Phase II RI .............................................................................................. 9 2.3.4 1996 Environmental Site Assessment .......................................................... 11 2.3.5 1997 Phase III RI ........................................................................................... 11 2.3.6 1998 Field Investigation ................................................................................. 13 2.3.7 1999 Field Investigation ................................................................................. 14 2.3.8 2013 RI Summary Report .............................................................................. 14 2.3.9 2017 Groundwater Sampling......................................................................... 14 2.4 Geophysical Surveys ............................................................................................ 14 2.4.1 1994 Geophysical Survey.............................................................................. 15 2.4.2 2005 Geophysical Report .............................................................................. 15 2.4.3 2011 Geophysical Survey.............................................................................. 15 2.5 Hydrologic Analysis of Umiat Landfill................................................................... 16 2.5.1 2011 Hydrologic Analysis .............................................................................. 16 2.5.2 2017 Hydrologic Analysis .............................................................................. 16 2.6 Landfill Inspections and Interim Removal Actions..............................................