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Home > Site Information
South Weber
City Rep: M. Scott Peterson 
Community Rep: Jan Ukena
City Council Updates
InfoFairs
Operable Units:
OU 1
OU 2
OU 4
Hill AFB Project Manager: Barbara 'B' Hall
South Weber City Restoration Advisory Board Rep.: Randy Hilton
South Weber Community Restoration Advisory Board Rep.: Jan Ukena
HAFB Environmental Public Affairs: Barbara Fisher
Past disposal practices at Hill Air Force Base resulted in shallow groundwater contamination, which over the past several
decades has moved into the community of South Weber. No contamination from Hill AFB has been found in the drinking water.
The only known exposure pathway is through vapor intrusion, where chemicals in the groundwater can evaporate and move into
homes above areas of contamination. The Air Force offers free air sampling to residents in affected areas, and has tested
35 homes in OU-1. When appropriate, a vapor removal system is installed, and two have been installed in this area. Several
cleanup remedies are in place to prevent the spread of contamination. Recent samples have shown that in 2010, the OU-1
contamination plume was nearly half the size it was five years earlier. In addition to the chemicals in the groundwater,
arsenic is in the surface soil on the hillside between Hill AFB and South Weber; however, thorough studies have shown that
there is not a health risk.
Site Background
Operable Unit 1 includes areas of contamination on the northeast portion of Hill AFB and in the community of South Weber.
It is one of three cleanup areas in South Weber. Environmental investigations by the Air Force in the 1980s revealed that
industrial wastes had been dumped at Hill AFB landfills in the area from the 1940s to the 1970s, and in certain areas jet
fuel and other flammable chemicals made it into the environment from fire fighting training activities.
Contamination Sources
During the investigations, Hill’s environmental restoration staff identified several sources of contamination in the area.
These sources, the types of waste material, and the time frames the sites were used are listed below.
- Chemical Disposal Pits 1 and 2 (1952–1974)
Industrial liquid waste, primarily fuels and waste solvents
- Landfill 3 (1947–1967)
Domestic solid waste, waste solvents
- Landfill 4 (1967–1980)
Domestic and industrial waste
- Fire Training Area 1 (1958–1973)
Jet fuel and waste solvents
- Fire Training Area 2 (1973–1995)
Jet fuel and waste solvents
- Waste Phenol/Oil Pit (1954–1965)
Waste oils and phenols
There are also arsenic-contaminated sediments around seeps and springs located on private property on the steep hillside just
east of the base boundary. The most likely source of this contamination is from arsenic that occurs naturally in the soil.
The waste disposed of in the nearby landfills changed the geochemical properties of the groundwater, causing the arsenic to
dissolve out of the soil and into the groundwater. The dissolved arsenic traveled with the groundwater to the seeps and
springs on the hillside. When the groundwater emerged from the springs and contacted air, the water chemistry changed
again, causing the arsenic to deposit and concentrate on the soil around the springs. There were four main springs where
the water seeped from the hillside. All four have been dry since Hill AFB installed a groundwater extraction system in 2001.
Health Risk Issues
The OU-1 contamination has not affected local drinking water supplies. The drinking water for South Weber comes from deep
aquifers and mountain reservoirs, not from the contaminated shallow groundwater aquifer. In addition, the deep drinking
water aquifer is separated from the shallow aquifer by numerous clay layers which prevent contamination from moving downward.
Chemical vapors, however, have been found in some South Weber homes above the area of contamination since chemicals in the
shallow groundwater can evaporate and enter homes from the ground. Hill has implemented a program for testing homes located
above areas of groundwater contamination for chemical vapors. Where vapors are detected above action levels set by the Utah
Department of Environmental Quality (UDEQ) and the Environmental Protection Agency (EPA), the Air Force has installed and
will continue to install vapor removal systems which have successfully mitigated the problem.
Cleanup Remedies
The Air Force has implemented several actions to prevent additional groundwater contamination from moving off the base into
local communities. These remedies are documented in the Record of Decision, a legally required cleanup agreement between
the Air Force, the EPA, and the UDEQ. The two main components of cleanup actions at OU-1 are landfill caps and groundwater
extraction trenches.
- Landfill caps installed in 1985 and upgraded in 2001— Layers of natural and manmade materials cover contaminated
soil to prevent precipitation from coming into contact with and spreading contamination. These caps cover every source at
OU-1 except Fire Training Area 2 and the Waste Phenol/Oil Pit.
- Source Containment System installed in 2001— Four gravel-filled trenches with a combined length of more than
4,800 feet direct groundwater flow to drains and collection sumps. The groundwater is treated and discharged to the sewer.
These trenches are designed to cut off the flow of contaminated groundwater and prevent it from moving into the community
of South Weber.
Hill AFB began removing the arsenic-contaminated soil near some springs on the hillside in Fall 2008 and found more arsenic
present at the site than anticipated. As work progressed, it became clear that the hillside could not support extensive
excavation and shortly thereafter the soil removal was stopped due to slope instability concerns. Throughout the next year,
Hill AFB worked with stakeholders to determine the best approach to ensure acceptable risk to human health, manage slope
instability and meet regulatory requirements. The Air Force conducted a quantitative human health risk assessment (HHRA), or
detailed analysis, in 2010 to re-evaluate the situation. The HHRA, which hadn’t been conducted at the time the official
cleanup agreement was signed, indicated that the arsenic-contaminated soil did not need to be removed because it did not pose
a threat to human health. After the report was finalized in 2011, the EPA and the UDEQ agreed.
As part of the Record of Decision, contaminated groundwater in the South Weber valley will be allowed to dissipate and degrade
naturally. This process is closely monitored by Hill to ensure it is occurring as predicted. In June 2010, the Air Force
announced that the area of groundwater under South Weber with contaminant levels above drinking water standards has decreased.
Recent groundwater concentrations indicate the plume is almost half the size it was in 2005, due to a combination of natural
processes and the remedies installed by Hill. This fast reduction in plume size in the early stages of cleanup was expected,
but as contaminant concentrations decrease, less change will occur over time. Hill AFB officials estimate that cleanup
standards in the plume will be reached in the 2070s.
What’s Ahead
With all of the cleanup remedies in place at OU-1, the Air Force will continue to maintain and manage the systems to ensure
they operate as designed. The extraction trenches are inspected regularly and monitored to be sure the contaminated groundwater
does not continue to flow into the surrounding community.
Since 2000, Hill AFB has tested 35 homes in the OU-1 area for chemical vapors. The Air Force will continue to offer indoor
air sampling to those residents who live above areas of groundwater contamination.
The Air Force will complete a Five-Year Review in 2013 as required by environmental clean-up laws. This review, done by
third-party verifies that treatment systems and ongoing studies are protecting human health and the environment and are
meeting cleanup goals. The public has the opportunity to participate in this review.
Hill environmental cleanup documents are available for viewing by the public at the Hill Information Repository located at
the Stewart Library on the Weber State University (WSU) campus in Ogden and at WSU’s Davis Campus Library in Layton. For
hours of operation at the libraries, call the Stewart Library at 801-626-6403 or the WSU Davis Library at 801-395-3742.
Current as of February 2012
^ Back to Top
Hill AFB Project Manager: Kyle Gorder
South Weber Restoration Advisory Board Rep.: Randy Hilton
South Weber Community Restoration Advisory Board Rep.: Jan Ukena
Hill AFB Environmental Public Affairs: Barbara Fisher
Past disposal practices at Hill Air Force Base resulted in shallow groundwater contamination, which over the past several decades has moved into the community of South Weber. No contamination from Hill AFB has been found in the drinking water. The only known exposure pathway is through vapor intrusion, where chemicals in the groundwater can evaporate into homes above areas of contamination. The Air Force offers free air sampling to residents in affected areas, and has tested more than 20 homes in OU-2. When appropriate, a vapor removal system is installed, and two systems have been installed in homes this area. Several cleanup remedies are in place to prevent the spread of contamination and they are functioning effectively.
Site Background
Operable Unit 2 (OU-2) includes areas of groundwater contamination on the northeast side of Hill AFB and is one of three
cleanup areas in the community of South Weber. The contamination was discovered in 1983 on-base at a former waste disposal
site, and three years later contaminated groundwater was found in South Weber.
The on-base portion of OU-2 sits upon relatively flat ground while the off-base portion of the site consists of a steep,
terraced hillside. The hill slopes down three hundred feet to an agricultural and residential valley.
Contamination Sources
-
Chemical Disposal Pit 3 (Chem Pit 3) used from 1967-1975
Chem Pit 3, which consisted of two unlined trenches, was used to dispose of waste solvents from degreasing operations on the
base. Although the exact amount is unknown, it is estimated that as much as 50,000 gallons of waste solvents—primarily
trichloroethene (TCE)—were dumped at this site. This oily material, which is heavier than water, moved down through the
soil and pooled on top of a very thick clay layer about 35 feet beneath the ground surface.
Health Risks
The OU-2 contamination has not affected local drinking water supplies. The drinking water for South Weber comes from a deep
aquifer and mountain reservoirs, not from the contaminated shallow groundwater aquifer. In addition, the deep drinking water
aquifer is separated from the shallow aquifer by numerous clay layers which prevent contamination from moving downward.
Because chemicals in the shallow groundwater can evaporate and enter homes from the ground, chemical vapors have been found
in some South Weber homes above the area of contamination. Hill has implemented a program for testing homes located above
areas of groundwater contamination for chemical vapors. Where vapors are detected above action levels agreed upon by the
Utah Department of Environmental Quality (UDEQ) and the U.S. Environmental Protection Agency (EPA), the Air Force has
installed and will continue to install vapor removal systems which have successfully mitigated the problem.
Cleanup Remedies
The Air Force has implemented several actions to prevent additional contamination from moving off the base into local
communities. In 1991, the Air Force began the process of removing the oily, undissolved solvents. In 1996, the Record of
Decision (ROD), the legally required cleanup agreement between the Air Force, the EPA and the UDEQ, was signed to address
the remaining problems at OU-2, including contaminated groundwater, soil, and surface water.
The main components of cleanup actions at OU-2 are a groundwater containment wall and a source recovery system.
-
Source recovery system installed on base in 1993
Wells extract groundwater from the source area and deliver it to a nearby treatment plant. The treated water is then discharged to the Central Weber Sewer Improvement District (CWSID). Additional extraction wells were installed in the area after an additional pool of undissolved contaminants was discovered outside the containment wall.
-
Containment wall installed on base in 1996
An impermeable wall 60 feet below the ground surface surrounds the Chem Pit 3 source area to limit the movement of
contamination. As part of this remedy, a groundwater extraction trench was installed west of the wall to collect excess
groundwater which is treated and sent to the CWSID.
-
Interceptor trench installed in South Weber in 1997
A gravel trench directs groundwater flow to a pipe which discharges it to the CWSID and prevents contamination
from moving further into South Weber.
-
Spring Collection system installed in South Weber in 1999
An underground pipe collects groundwater in a spring area and discharges it to the CWSID.
-
Soil vapor extraction system installed on base in 2009
A vacuum system removed chemical vapors from below the ground and dispersed them into the atmosphere at undetectable
levels. Within a year of operation, this system reached cleanup objectives of removing contamination from the soil
above the groundwater. The system was shut down in 2010.
By late 2009, cleanup progressed to the point where the three-step treatment process of the source recovery system
could be simplified to a one-step process which continues to achieve the treatment required to maintain compliance
with the CWSID discharge limits. The UDEQ and the EPA agreed with the simplification and because this change differed
from the original plan described in the Record of Decision, a document called an Explanation of Significant Differences
(ESD) was prepared to provide the public with a description of the change and the reasons for it.
Hill AFB officials estimate that cleanup standards for the groundwater will be reached in the 2050s.
What’s Ahead
The Air Force will continue maintaining and managing the systems at OU-2 to be sure they operate as designed. The cleanup
remedies are inspected periodically, and wells are monitored to track any changes in the levels of groundwater contamination.
Since 2000, Hill AFB has tested 22 homes in the OU-2 area for chemical vapors. The Air Force will continue to offer indoor
air sampling to those residents who live above areas of groundwater contamination.
The Air Force will complete a Five-Year Review in 2013 as required by environmental clean-up laws. This review, done by a
third-party, verifies that treatment systems and ongoing studies are protecting human health and the environment and are
meeting cleanup goals. The public has the opportunity to participate in this review.
Hill environmental cleanup documents are available for viewing by the public at the Hill Information Repository located at
the Stewart Library on the Weber State University (WSU) campus in Ogden and at WSU’s Davis Campus Library in Layton. For
hours of operation at the libraries, call the Stewart Library at (801) 626-6403 or the WSU Davis Library at 801-395-3742.
Current as of April 2012
^ Back to Top
Hill AFB Project Manager: Alan Jones
Riverdale City Restoration Advisory Board Rep.: To be assigned by Riverdale City
Riverdale Community Restoration Advisory Board Rep.: Brian Wesoloski
South Weber Restoration Advisory Board Rep.: Randy Hilton
South Weber Community Restoration Advisory Board Rep.: Jan Ukena
Hill AFB Environmental Public Affairs: Barbara Fisher
Past disposal practices at Hill Air Force Base have resulted in shallow groundwater contamination, which over the past
several decades has moved into the communities of Riverdale and South Weber. No contamination from Hill AFB has been found
in the drinking water. The only known exposure pathway is through vapor intrusion, where chemicals in the groundwater can
evaporate and move up into homes above areas of contamination. The Air Force offers free air sampling to residents in
affected areas. When appropriate, a vapor removal system is installed to fix the problem. Two cleanup remedies are in
place to prevent the spread of contamination and they are operating effectively.
Site Background
Operable Unit 4 (OU-4) includes contamination in the northern portion of Hill AFB and in the communities of South Weber and
Riverdale. It is one of three cleanup areas in South Weber, and one of two in Riverdale. Trichloroethene (TCE), a cleaning
and degreasing solvent and the primary contaminant at this site, extends through the shallow groundwater from Landfill 1 on
base toward South Weber Drive. The off-base portion of the site is a steep, terraced hillside sloping into a residential and
agricultural valley.
Contamination Sources
-
Landfill 1-used from 1940s-1967
Waste oils and solvents from a refueling vehicle
maintenance facility at the former Ogden Arsenal
were reportedly dumped and burned at Landfill 1.
Health Risks
The OU-4 contamination has not affected local drinking water supplies. The drinking water for South Weber and Riverdale
comes from a deep aquifer and mountain reservoirs, not from the contaminated shallow groundwater aquifer. In addition,
the deep drinking water aquifer is separated from the shallow aquifer by numerous clay layers which prevent contamination
from moving downward.
Chemical vapors, however, may be found in some homes above the area of contamination since chemicals in the shallow
groundwater can evaporate and enter homes from the ground. Hill has implemented a program for testing homes located
above areas of groundwater contamination for chemical vapors. Where vapors are detected above action levels agreed
upon by the Utah Department of Environmental Quality (UDEQ) and the U.S. Environmental Protection Agency (EPA), the
Air Force has installed and will continue to install vapor mitigation systems.
Cleanup Remedies
The cleanup remedies for the contamination at OU-4 were formalized in the OU-4 Record of Decision, the legally required
cleanup agreement which was signed in 1994 by the Air Force, the UDEQ, and the EPA. At the time when the ROD was signed,
risks to human health associated with the contaminants at OU-4 were below levels considered by the EPA to be significant.
However, remedial action was warranted based on possible future risks and Hill AFB took a proactive approach to cleanup.
The following remedies are designed to contain and treat the source area of the contamination on the base and prevent the
contamination from spreading.
-
Soil cap installed on base in 1996
Layers of natural and manmade materials cover contaminated
soil to prevent precipitation from coming into contact with and spreading the contamination.
-
Horizontal drain collection system installed in South Weber on Hill AFB property in 1994
Three sets of three drains collect contaminated groundwater and discharge it directly to the Central Weber Sewer
Improvement District.
What’s Ahead
The Air Force will continue maintaining and managing the systems at OU-4 to be sure they operate as designed. The cleanup
remedies are inspected periodically and groundwater monitoring wells are sampled regularly to measure progress towards site
cleanup.
Since 2000, the Air Force has tested three homes in the OU-4 area for chemical vapors. The Air Force will continue to offer
indoor air sampling to those residents who live above areas of groundwater contamination.
The Air Force will complete a Five-Year Review in 2013 as required by environmental clean-up laws. This review, done by a
third-party, verifies that treatment systems and ongoing studies are protecting human health and the environment and are
meeting cleanup goals. The public has the opportunity to participate in this review.
Hill environmental cleanup documents are available for viewing by the public at the Hill Information Repository located
at the Stewart Library on the Weber State University (WSU) campus in Ogden and at WSU’s Davis Campus Library in Layton.
For hours of operation at the libraries, call the Stewart Library at (801) 626-6403 or the WSU Davis Library at 801-395-3742.
Current as of April 2012
^ Back to Top
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