HILL AIR FORCE BASE -- Hill Air Force Base is proposing to remove 465 homes from an indoor air sampling program that tests for chemical vapor oozing from contaminated groundwater.
The homes, which are situated in both Weber and Davis counties, are part of a nearly two-decade initiative at the base to protect residents from the chemical vapors that are a byproduct of years of improper waste disposal.
Decades ago, before environmental laws regulated how certain chemicals were disposed, Hill workers dumped a variety of toxic aircraft-cleaning material into disposal pits. As years went by, the chemicals bled into the ground and eventually contaminated the shallow groundwater, which moved the chemicals off the base and into the communities surrounding it.
The Air Force began testing homes around the base in the early 2000s, after it was discovered that the vapors from the contaminated groundwater could seep into homes.
In an email to the Standard-Examiner, Mark Roginske, Hill's Indoor Air Program manager, said the base has collected more than 9,000 indoor air samples from nearly 2,000 homes since testing began. Many of the homes have been sampled multiple times. From those tests, Hill has determined that vapor intrusion is most likely to occur in specific areas in six cities: Clinton, Layton, Riverdale, Roy, South Weber and Sunset.
Roginske said there are approximately 1,200 homes in those areas.
"We hope to be able to sample in all of the homes in these areas," he said.
Maps showing areas eligible for air sampling testing can be found at www.hill.af.mil/iap. Roginske said vapors from the groundwater contamination do not enter every home; workers have found, for example, vapor in one home but not in the home next door.
While the base works to test those 1,200 homes, 465 residences in the same areas will likely be removed from the program. Roginske said those homes have been sampled and determined to have no vapor intrusion at a level that would require mitigation.
"These homes are now being proposed for 'graduation' from the indoor air sampling program this year," Roginske said in the email. "If approved, (they) will receive no additional sampling unless groundwater or other conditions change."
Mitigation "action levels" for known chemical contaminants were developed using research on vapor intrusion and in conjunction with the Utah Department of Environmental Quality and the U.S. Environmental Protection Agency, Roginske said.
"The action levels are very conservative, in the part-per-billion range, and have extra layers of safety built in to ensure protection of sensitive populations, such as children and the elderly," he said.
If tests determine mitigation is required, Roginske said, the Air Force will install a system that sucks vapor from the home. The system consists of a pipe installed through a home's basement floor, along with a small fan, installed in the attic or on the outside of the home. The fan is attached to the pipe and sucks the vapor from beneath the basement and pushes it through the pipe before it can enter the home.
Roginske said more than 120 systems have been installed to date. All costs associated with the systems and sampling are paid by the Air Force.
Hill Environmental Affairs spokeswoman Barbara Fisher said the base's testing system changed last year.
The base once used volleyball-sized silver canisters that were under a vacuum and collected a 24-hour indoor air sample. Now, testers use smaller sampling devices that collect samples over a 26-day period, recording the average concentration of chemicals in the air over the entire sampling period.
Roginske said contaminant concentrations can vary from day to day, affected by changes in weather, outside temperature, furnace use, opening of windows and doors and several other factors.
The Air Force offers indoor air testing annually during the heating season, November through March, when home heating systems are operating.
If you think your home needs to be sampled, visit www.hill.af.mil/iap or call 385-474-8577.