Hill Air Force Base updates Clinton on TCE groundwater plume, indoor‑air sampling and mitigation options

Hill Air Force Base officials briefed the Clinton City Council on Feb. 11 about groundwater contamination plumes affecting shallow subsurface zones beneath Clinton, current cleanup systems, and the base’s indoor‑air sampling and mitigation program.

Lindsey Burt, remedial project manager for the Air Force, told the council the main contaminant of concern in Operable Unit 5 is trichloroethylene (TCE). "The upper aquifer is what's contaminated," Burt said, and she emphasized that Clinton’s drinking water comes from a much deeper Delta aquifer roughly 600 feet down and is naturally protected by clay layers.

Burt outlined remedies the Air Force has used: an aeration curtain along Sunset Main Street that volatilizes TCE in groundwater, a groundwater extraction trench at the Clinton border that captures and treats groundwater for permitted discharge to the sanitary sewer, and targeted subsurface injections of reagents and liquid activated carbon at source areas.

Julie McNeil, manager of Hill AFB’s indoor‑air program, described the free indoor‑air sampling the Air Force offers to households in the affected area. "We hang [a beacon sampler] from a tripod in the lowest livable space in the home for 26 days," McNeil said. If sampling shows concentrations above an action level set by the Environmental Protection Agency and the Utah Department of Environmental Quality and the source is confirmed as groundwater‑related vapor intrusion, the Air Force offers a vapor‑intrusion mitigation system — similar to a radon fan system — at no cost to the homeowner.

Program scale and results: McNeil said the Air Force identifies an area that expands the plume by a conservative 100 feet to ensure coverage; in Clinton there are 210 homes within the affected outline. Of those, 38 homes have been confirmed non‑detect in prior sampling, seven homes currently have mitigation systems installed, and 65 homes need either initial sampling or additional sampling. McNeil said the household heating season for sampling outreach runs from October through March and that March 7 is the last day the team can place samplers for the current heating season.

Public process and timeline: Burt said the aeration curtain has reached its design life and the Air Force plans to replace it with subsurface injections of liquid activated carbon within the next one to two years. She characterized progress over the last decade as substantial and said plume source‑area concentrations and lateral extent have decreased in monitored maps shown to the council.

When asked how long operation of the trench and treatment would continue, Burt said the program will run until the plume is remediated and added a time estimate in the meeting: "That's the time frame. Cool 24 years," reflecting the long‑term nature of the remedy.

Community engagement: the Air Force said it continues door‑to‑door outreach, mailing, newsletters and a QR signup for residents to schedule sampling, and it is soliciting a Clinton community representative to the Restoration Advisory Board. Spencer Arvey is the council’s current RAB representative; the Air Force said the RAB will meet April 24 and will vote on new community members.

Council reaction: council members thanked the Air Force presenters for regular updates and asked the base to continue outreach to homeowners and to provide proposed remedy plans for public comment as the aeration curtain is replaced.

Authorities and technical standards: presenters referenced the EPA drinking‑water standard and action levels used by EPA and the Utah Department of Environmental Quality for vapor intrusion screening and remediation planning.