Remedial Investigation and Landfarming, Gulkana, Alaska

Brice performed a remedial investigation (RI) and remedial action (RA) at the Federal Aviation Administration (FAA) Gulkana Station at the Gulkana Airport in Alaska. The primary contaminant sources and suspected release mechanisms are leaks and spills of petroleum hydrocarbons from fuel storage and distribution systems (i.e. tanks and piping) and from drums. Brice implemented land farming to achieve the project objectives. At project completion, Brice prepared a final report that documents the field work, summarizes sample results, presents risk calculations showing that the soil direct contact, outdoor air inhalation, and vapor intrusion exposure routes at Buildings 303, 600, 601, and 605 meet residential risk criteria, and calculates risk for Building 300.

Planning Documents. Brice prepared a 350 Determination request, an ADOT&PF work permit, Stormwater Pollution Prevention Plan (SWPPP) and a work plan for FAA and ADEC review and approval. Brice also performed the remedial design for the land farming of fuel-contaminated soils, dividing the site into three areas (44,500 square feet, 11,500 square feet, and 13,000 square feet).

Remedial Investigation. Brice performed a remedial investigation at Building 300 by advancing Ultra-Violet Optical Screening Tool (UVOST) and laser-induced fluorescence (LIF) probes to complete in-situ soil screening. Based on the UVOST screening results, we advanced soil borings and collected soil samples to characterize the petroleum contamination. We incorporated analytical results into the HRC to assess risk to human health. Surveyed the horizontal and vertical extents of all sample locations.

Remedial Action. At Buildings 303 and 600, Brice excavated 2,000 tons of fuel-contaminated soils shown to cause unacceptable risk via soil direct contact, outdoor air inhalation, and vapor intrusion exposure routes. We guided the excavations using PID field screening procedures. Brice transported 360 tons of soil with contaminant concentrations greater than the ADEC’s 18 AAC 75 Table B2 Maximum Allowable Concentrations to a thermal treatment facility in North Pole, Alaska.

Land Farming. Prior to construction of the unlined land farm, Brice developed a SWPPP in accordance with the 2016 Construction General Permit (CGP) for Storm Water Discharges from Large and Small Construction Activities. A Notice of Intent (NOI) to operate under the CGP was filed with the Alaska Pollutant Discharge Elimination System (APDES) program. The land farm was prepped and best management practices (BMPs) such as silt fencing were placed around the perimeter to limit or control sediment runoff. Signs were posted at the gate entrance to notify workers and site visitors of the land farm and potential site hazards, and inspections were performed in accordance with the SWPPP. We land farmed 1,640 tons of the excavated soil with contaminant concentrations that exceeded risk criteria but were less than the ADEC’s Maximum Allowable Concentrations.

Sampling. We performed incremental sampling methodology (ISM) to collect confirmation samples from the excavation limits and land farmed soil to document that site conditions were protective of human health; as well as soil gas sampling following excavation at Building 303 to document that the remaining soil and groundwater concentration did not cause a vapor intrusion risk.

In 2018, EPA updated slope factors for several PAH compounds and ADEC amended the soil and groundwater cleanup levels listed in 18 AAC 75, Tables B1, B2, and C. Based on EPA slope factors and ADEC cleanup levels prior to the 2018 revisions, Buildings 601 and 605 had soil concentrations that posed unacceptable risk to human health. Using the updated HRC with current EPA slope factors and ADEC cleanup levels, we evaluated risk to human health using the existing site conditions and sample data to document that the soils remaining in place meet the ADEC risk criteria.

Performance Highlights

• Saved the client ~$3 million using the Hydrocarbon Risk Calculator (HRC) to achieve Cleanup Complete determinations which reduced the amount of soil requiring offsite treatment and disposal by approximately 80%
• Received an overall rating of ‘Exceptional’ in a PPQ dated 4/29/2019