A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Technology
News & Trends
EPA 542-N-14-006 | Issue No. 70
Summer 2015
ThisissueofTecAino/ogy News and Trendshighlightsinvestigation
andmitigatiorc>fvaporintrusionatomearcontaminatedsites,witha
focusonsummarizinghovwaporintrusionwasaddressedatthree
siteswhereresponseactionsareunderway.Vaporintrusionisthe
generaltermgiventomigrationofhazardousvaporsfromany
subsurfacevaporsource,suchascontaminatedsoibrgroundwater,
throughthesoilandintoanoverlyingbuildingorstructureAwide
varietyofchemicabontaminantscangiveoffvapors.whichcan
migratetowardsandenterbuildingsorotherenclosedspaces.These
vaporscanenterbuildingsthroughcracksinbasementsand
foundations,aswellasthroughconduitsandotheropeningsinthe
building envelope. Vapor intrusion is a potential human exposure
pathway-a way that people may come into contact with hazardous
vaporswhileperformingtheirday-to-dayindooractivitiesDepending
uponbuilding-andsite-specificcircumstancesjndoorconcentrations
ofchemicalvaporsarisingfromthevaporintrusionpathwaymay
threatenhumanhealthorBafety.Whenhumanhealthorsafetyis
threatenedbyvaporintrusion,responseactioniswarranted.
EPA collaborates with potentially affected stakeholders and with state
agencies when evaluating potential vapor intrusion associated with
contaminated sites under federal jurisdiction. Some states also
maintain their own vapor intrusion programs that may include tailored
guidelines, such as the new North Carolina Division of Waste
Management Vapor Intrusion Guidance or the Massachusetts
Department of Environmental Protection Vapor Intrusion Guidance.
Featured Articles
Vapor Intrusion
Associated with Multiple
Contaminant Sources
Evaluation of Vapor
Intrusion in Complex
Geologic Setting
Petroleum Vapor Intrusion
Assessment: Multiple
Lines of Evidence Lead to
Mitigation at Utah
Gasoline Fueling Station
Resources
New EPA Guidance:
OSWER Technical Guide
for Assessing and
Mitigating the Vapor
Intrusion Pathway from
Subsurface Vapor Sources
to Indoor Air
New EPA Guidance:
Technical Guide for
Addressing Petroleum
Vapor Intrusion at Leaking
Underground Storage
Tank Sites
New Tool: Vapor Intrusion
Screening Level (VISL)
Calculator
EPA Website: Vapor
Intrusion
NIEHSSuperfund
Research Program Briefs:
Process Models and
Unattended Vapor
Intrusion Monitoring
ESTCP Demonstration
Projects: Use of
Compound-Specific Stable
Isotope Analysis to
Distinguish Between
Vapor Intrusion and Indoor
Sources of VOCs; Use of
On-Site GC/MS Analysis to
Distinguish between Vapor
Intrusion and Indoor
Sources of VOCs
Key Elements of the Conceptual Model of Soil Vapor Intrusion
Source: OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway
from Subsurface Vapor Sources to Indoor Air
June 2015 1
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Vapor Intrusion Associated with Multiple Contaminant Sources
Contributed by Rachel Loftin. U.S. EPA Region 9
The Motorola 52nd Street Superfund site in Phoenix, Arizona, encompasses a large contaminated groundwater
plume extending approximately seven miles from the former Motorola 52nd Street electronics manufacturing
facility where the original release of chemicals occurred. The site also includes several downgradient sources of
contamination, including the Honeywell jet engine manufacturing facility. Remediation systems have operated
throughout the site since the early 1990s to contain and treat the groundwater and address soil and soil vapor
contamination. Over the past four years, site work also has involved evaluating and mitigating vapor intrusion in
neighborhoods overlying the plume in the eastern portion of the site.
Trichloroethene (TCE) and tetrachloroethene (PCE) associated with past industrial spills are the primary
contaminants of concern. The site is defined by three operable units (Oils) (Figure 1). In OU1, the eastern portion
of the plume, the first water-bearing zone is the Basin Fill/alluvium. Here, the depth to groundwater ranges from
approximately 20 to 40 feet below ground surface (bgs) and the Basin Fill/alluvium consists of interbedded alluvial
silt and gravel that overlie fractured bedrock encountered at approximately 20 to 60 feet bgs. At the Motorola
Plant property located in OU1, dense non-aqueous phase liquid (DNAPL) is present in the fractured bedrock.
Hydraulic conductivity of the bedrock, which varies from 0.001 to 2 feet per day, is strongly influenced by the
presence and frequency of fractures. In OU2, the central portion of the plume, the first water-bearing zone is the
Salt River Gravel. Here, the bedrock is encountered at greater depths and the depth to groundwater is between
approximately 50 and 75 bgs. In the western portion of the plume, OU3, groundwater is first encountered in the
Salt River Gravel at yet greater depths, approximately 75 to 100 feet bgs. Groundwater remediation as well as
vapor intrusion evaluation is complicated by northwest to southeast trending bedrock ridges protruding from the
alluvium at the northeast portion of OU1 and the southern boundary of OU2.
NAME
MOTOROLA 5ZNO STREET
&
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Two groundwater extraction and treatment plants are addressing the volatile organic compound (VOC) plume.
The "Motorola 52nd Street Treatment Plant" has treated OU1 groundwater since 1992. As of 2014, this remedy
had treated more than 3.6 billion gallons of groundwater and removed more than 24,269 pounds of TCE.
Additional treatment has included soil vapor extraction and air sparging systems at OU1 source areas.
The second groundwater treatment plant addresses OU2 groundwater extracted from three wells at the OU2
western boundary downgradient of the Honeywell 34th Street facility, approximately three miles downgradient of
the former Motorola facility. As of 2014, the OU2 remedy had treated more than 13.3 billion gallons of
groundwater, removed more than 14,000 pounds of VOCs, and contained the OU2 groundwater plume sufficiently
to prevent plume migration into OU3. Although not a component of the Superfund remedy, a third treatment
system located on the Honeywell 34th Street facility comprises a biologically-enhanced soil vapor extraction
system (BSVE) for petroleum hydrocarbons emanating from underground storage tanks leaking jet fuel. From
startup in 2009 to 2014, the BSVE system removed more than 10.6 million pounds of petroleum hydrocarbons
and 350 pounds of VOCs.
Since 2011, Freescale (on behalf of Motorola) has conducted an OU1 vapor intrusion evaluation using multiple
lines of evidence. First, existing groundwater and soil vapor data and almost two decades of groundwater
monitoring data were used to identify areas of elevated TCE and PCE concentrations. Those areas were targeted
for additional soil vapor monitoring wells using a "step-out" approach. Afield analytical lab was used to expedite
field decisions regarding where to place step-out soil vapor wells and when to proceed directly to residential
indoor air and sub-slab sampling. Pre-determined subsurface soil vapor, sub-slab and indoor air investigation
action levels were established exclusively for the Motorola 52nd Street Superfund site using EPA's regional
screening levels and modified soil gas human health screening levels (SGHHSLs) with attenuation factors to
reflect specific conditions in Arizona. When the soil vapor data exceeded the SGHHSLs for TCE or PCE and met
the soil vapor action level, sub-slab and indoor air were immediately sampled at nearby residences.
The step-out approach for soil gas sampling used baseline data
collected from 26 original soil gas sampling points where a SGHHSL
was exceeded. Factors affecting selection of step-out sampling from
the 26 locations included spacing of nearby sampling locations,
magnitude of SGHHSL exceedance and nature of adjoining
property. Soil gas sampling at the 26 original sampling points led to
21 "step 1" locations. Of these, eight exceeded a SGHHSL and led
to identification of 19 "step 2" locations. This stepwise process
continued until "step 4," when sampling indicated no SGHHSL
exceedance. Along the study area perimeter, a mobile laboratory
also was used to facilitate field decisions regarding step-out
sampling where TCE or PCE soil gas concentrations exceeded a
SGHHSL. As a result of this process, 53 additional semi-permanent
sampling locations were identified and a total of 79 soil gas implants
were installed. Each soil gas implant has two microfilter sampling
tips emplaced at 5- and 15-foot depths inside a 2- to 4-inch diameter
... Dry Granular Bentonile
borehole (Figure 2).
isi..id.«, II J Silica Sand Filter Pack
Microfilter Sampling Tip
Street
Flush Mounted Traffic Rated Vault
(approx 6-inch diameter)
Bentonite Slurry
0.125 inch diameter tubing
Dry Granular Bentonite
Silica Sand Filter Pack
Microf Her Sampling Tip
Bentonite Slurry
Figure 2. Design of implants for soil gas
sampling at the Motorola site.
-------
Two consecutive rounds of soil gas sampling were conducted at the 79 implant locations. The samples were
collected in air-tight glass syringes and submitted to the mobile laboratory or in SUMMA® canisters that were
shipped to fixed laboratories. The analytical results were compared to the SGHHSLs to identify several areas
where an investigation of indoor air and sub-slab soil gas was warranted (Figure 3).
K
SV76
O
SV77
0
I
ranadaftd
ret Detected Below Residential SGHHSL
Figure 3. Areas identified for indoor air investigations associated with the Motorola 52nd Sfreef site.
As a second line of evidence for the need to sample sub-slab soil gas or indoor air, concentrations of chemicals of
concern in groundwater were compared to the soil gas results to identify any correlation and to evaluate whether
the data distribution was consistent with the conceptual site model. A comparison of the TCE soil gas
concentrations to the TCE concentration contours in groundwater showed a rough correspondence in most areas
-------
(Figure 4). Elevated soil gas concentrations in one area of OU1 generally coincided with the location of the
subsurface bedrock ridge believed to locally alter groundwater flow directions and unexpectedly create a
preferential flow and transport pathway directed to the northwest. In contrast, comparison of PCE soil gas
concentrations to the groundwater concentration contours showed a lower correlation.
Figure 4. Overlay of OU1 TCE soil gas results (pg/m) and groundwater concentration contours (pg/L).
Todate, a minimum of two rounds of indoor air sampling has been completed at 116 locations including four
schools and seven commercial buildings, during both cool and warm seasons. Where detected, indoor air TCE
concentrations have ranged from 0.13 ug/rn3 to 24.0 ug/rn.3 A minimum of two rounds (warm and cool season) of
sub-slab s ampling occurred a t r esidential buildings but no t a t c ommercial bui Idings because u nderground
infrastructure made sub-slab sampling impractical. Where detected, residential sub-slab TCE concentrations have
ranged from 2.0 ug/m3 to 43,000 ug/rn.3
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In 2014, the U.S. Environmental Protection Agency (EPA)
deployed a trace atmospheric gas analyzer (TAGA) mobile
laboratory (Figure 5) to confirm soil gas, outdoor air and
indoor air concentrations at OU1 and to determine where
the highest existing groundwater and soil gas VOC
concentrations in OU1 and OU2 may lead to vapor
intrusion. Use of the mobile equipment to collect soil gas
samples from temporary soil vapor monitoring wells
enabled field staff to quickly access data for field decisions
concerning where step-out soil gas samples or indoor air
samples should be collected. It also facilitated mitigation
decisions by allowing room-by-room indoor air data
collection in several homes. In OU2, the TAGA equipment
was used to conduct indoor air sampling in a residential
area where the temporary soil vapor probe data indicated
a potential for vapor intrusion. In OU3, TAGA data helped
determine that vapor intrusion is not occurring but identified
a small soil vapor plume surrounding an existing soil vapor
well in a commercial area. During
the TAGA event, an additional 51
soil vapor probes were installed to
15 feet bgs and sampled, eight
homes received indoor air room-by-
room sampling, and the outdoor
perimeter of one home was
sampled.
To date, EPA has installed 16 sub-
slab depressurization mitigation
systems at OU1 residences where
indoor air TCE concentrations
exceeded the 1.0 ug/m3 indoor air
action level specifically
established for the Motorola 52n
Street Superfund site. Most
Figure 5. EPA TAGA mobile laboratory operating
at the Motorola site.
•if
Dowell
Northside
(Almeria St
pi
-.nd
Figure 6. Neighborhoods near the Motorola 52"° Street Plant (also known
as the "M52 facility property") that were evaluated for vapor intrusion.
mitigation systems are located in the Almeria neighborhood
north of the OU1 bedrock ridge and north of McDowell Road
(Figure 6).
At the Motorola 52nd Street Superfund site, the sub-slab
depressurization mitigation system, which also mitigates radon
gas, consists of suction points and a pipe extending from
beneath the sub-slab vertically to vent soil gas 1-2 feet above
the roof line. A fan attached to the pipe draws the soil vapors
through the pipe to discharge to the outdoors (Figure 7). The
sub-slab depressurization system includes a manometer and
alarm so that homeowners may check and report on its
operation. At each home, Freescale conducts operation and
maintenance checks of the mitigation system and collects
indoor air samples 45-60 days after installation, then semi-
annually for two years and annually for the following two years.
More frequent checks occur if indoor air results or a homeowner
reports an issue with the system.
Figure 7. General schematic of a typical
sub-slab mitigation system at the
Motorola site.
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Seepage of the DNAPL into the system of fractured
bedrock under the Motorola facility property at OU1 has
made prediction of potential vapor intrusion challenging.
For example, residences surrounding the Motorola facility
original source areas and one pilot-scale DNAPL
extraction well unexpectedly exhibit no vapor intrusion
(Figure 8). In contrast, the highest incidences of vapor
intrusion are evident where DNAPL is the source of the
higher TCE groundwater concentrations leading to higher
soil vapor levels, as in the Almeria neighborhood located
northwest of the Motorola Plant property and the OU1
bedbrock ridge (Figure 6). A bedrock pilot study to
evaluate effectiveness of using groundwater wells to
extract the DNAPL is nearly complete. TCE concentration
mapping during the first year of the study (Figure 9) showed
that pilot-scale groundwater extraction was effectively
extracting DNAPL and moderately reducing the
groundwater plume in OU1.
Figure 8. The Motorola 52na Street Plant, a DNAPL
extraction well (at street end) and adjacent homes
where TCE vapor intrusion was not detected.
Since 2001 the groundwater table has declined by an average of 16 feet, consequently decreasing the rate of
groundwater extraction for treatment at certain remedial extraction wells. The lower groundwater table also may
cause localized increases in VOC concentrations in soil vapors. Additionally, groundwater mounding along the
bedrock ridge may be leading to soil gas accumulation in neighborhoods located in the vicinity of the bedrock
ridge in OU1.
EPA will continue to monitor OU1 homes and apartment units equipped with indoor air mitigation systems through
2016. The OU1 vapor intrusion investigation will begin on the former 90-acre Motorola facility property in the fall of
2015. An OU2-wide vapor intrusion investigation will be conducted in 2015-2016. Completion of final remediation
plans for long-term extraction and treatment of groundwater and vapor intrusion, as needed, in both OU1 and
OU2 is expected in 2016. The OU1 final remedial investigation will also address DNAPL in bedrock.
South
North
BEDROCK PILOT STUDY
TCE CONCENTRATION (ug/L) AFTER ONE YEAR
OF OPERATIONS
N-S CROSS SECTION ALONG SO™ ST.
AUGUST-SEPTEMBER 2010
Figure 9. Early findings during the five-year bedrock study of the Motorola site.
-------
Evaluation of Vapor Intrusion in Complex Geologic Setting
Contributed by Mitch Cron and Roy Schrock, U. S. EPA Region 3, and Kevin Kilmartin, Tetra Tech, Inc.
Remediation of the Crosslev Farm Superfund site in Berks County, Pennsylvania is focusing on containment and
treatment of a groundwater contaminant plume that has migrated offsite, wellhead treatment of impacted
residential wells, and vapor intrusion mitigation at residences overlying the plume. The cleanup is challenged by a
groundwater flow system that is not yet fully defined and the presence of dense non aqueous-phase liquid
(DNAPL) in deep fractured and highly faulted bedrock which juxtaposes various lithologies. An adaptive
management approach involving multiple lines of evidence provides a better understanding of the quality of
shallow groundwater at and just below the water table and offers flexibility in decisions regarding the need for
residential vapor intrusion mitigation systems.
Groundwater surrounding the site is contaminated due to past disposal of drums containing trichloroethene (TCE)
likely used as a degreaser for nearby industrial activities. The drums were improperly disposed of at Crossley
Farm in a 24-acre area known as Blackhead Hill. Leakage from these drums contaminated groundwater
extending approximately 2.5 miles downgradient along Dale Valley (Figure 1). During site investigations, TCE
DNAPL and dissolved-phase concentrations as high as 1.3 grams per liter (g/L) were detected in groundwater. A
total of 39 different volatile organic compounds (VOCs) have been detected in the source area groundwater.
L£ E. .
C I C H-l L -IT •
* --r* RESCEMCE ^TTH vl WITKJnCN S'^TEM
D'.-:. SfKHS LJCfiTlOl
Figure 1. Mapping of estimated TCE concentrations at water table
and locations of associated vapor intrusion at residences.
-------
The region atop Blackhead Hill (including the contaminant source areas) is in a groundwater recharge zone. The
site's highlands are underlain by crystalline bedrock, and the adjacent valley is primarily underlain by dolomite.
The overburden includes weathered bedrock, saprolite, colluvium and alluvium. Groundwater in the area is
generally encountered less than 100 feet below ground surface and occurs within two flow zones comprising
geologic units of different lithology but with similar hydrogeological properties. The upper flow zone comprises the
soil and saprolite, while the lower consists of the less-fractured, bedrock beneath the saprolite. Interconnected
networks of fractures within the bedrock serve as the primary groundwater migration pathways within the lower
zone. The vertical extent of the plume is not fully defined due to present inability to identify the base of the
groundwater flow system within the fractured bedrock. Beneath the valley, the water-bearing fractures exist as
deep as 300 feet.
Hundreds of springs exist along the steep hillsides flanking the valley or close to a creek flowing through the
valley. The quality of shallow groundwater discharging onto ground surfaces has been investigated by sampling
13 springs, and TCE has been detected in several springs. Contaminated springs were also discovered
discharging directly into several residents' basements. Consequently, the springs are considered one of the
potential exposure pathways associated with vapor intrusion. Springs with TCE concentrations of 2-3 micrograms
per liter or higher, for example, could produce localized air concentrations equal to levels found in nearby
residences. Remedial investigations confirmed that vapors emanating from shallow contaminated groundwater
were moving into localized air at some spring locations. As a result, potential risks from the groundwater plume on
outside ambient air were evaluated during the subsequent feasibility study. Based on multiple rounds of air
sampling, EPA concluded that ambient air at the site does not represent a threat to human health.
Remedial activities at this National Priorities List site began in 1998, when the U.S. Environmental Protection
Agency (EPA) uncovered, removed and disposed of approximately 1,200 drums at a RCRA Subtitle D-permitted
hazardous waste facility. Approximately 15,000 tons of contaminated soil also were removed. From 2000 to 2010,
EPA installed 55 carbon-treatment systems in nearby homes where TCE was detected in private wells at
concentrations reaching 2.9 milligrams per liter. In 2012, an onsite groundwater treatment facility began operating
to contain the plume. The groundwater is extracted at four extraction wells and treated via vacuum extraction, air
stripping and vapor-phase carbon treatment.
In 2006, EPA began sampling the indoor air and sub-slab soil vapor of 24 residences with private wells containing
high TCE concentrations and overlying the groundwater plume. In place of risk analysis, venting systems were
conservatively installed at the two homes where TCE was detected in indoor air at detectable concentrations.
Follow-on vapor intrusion evaluations at other residences have utilized a three-pronged approach involving
analysis of groundwater samples taken from wells and springs, soil vapor samples from the sub-slab of
residences and indoor air samples from within residences. The groundwater samples are used to define the local
groundwater conditions near the water table in order to evaluate if vapor intrusion is a potential concern. The sub-
slab samples were used to determine if VOC vapors from the plume have migrated toward the houses. Results
were used to evaluate the extent (if any) to which the sub-slab vapors are migrating into the residence. The
results were used to determine whether vapor intrusion could reasonably be expected to threaten human health,
defined as an excess cancer risk of greater than 1E-5 (one additional chance in 100,000) or a hazard index of
greater than 1 (based on target organ effects). Human health risks were calculated using the actual indoor air
concentrations, and/or the sub-slab concentrations, assuming an attenuation factor across the slab of 0.1. In
general, 26 of the 39 VOCs (including TCE) that exist in source area groundwater were also detected in sub-slab
vapor throughout the extent of the plume. Based on the multiple lines of evidence, vapor intrusion mitigation
systems were required at 20 of the 39 residences where sampling was conducted. The multiple lines of evidence
consist of: 1) the presence of VOCs in contaminated groundwater underlying the residence (the potential for
vapors to exist); 2) the presence of VOCs in the sub-slab vapor samples (proof that the VOCs are partitioning into
the vapor phase and migrating to the surface); and 3) direct measurements (indoor air samples) or indirect
measurements (sub-slab samples with attenuation factor) to show that vapors exist (or have the potential to exist)
at concentrations that are not protective of human health.
EPA has installed systems at 19 of the affected homes; one homeowner chose not to participate in the mitigation
program. Since homes in this neighborhood range in age from relatively new (less than 10 years) to well over 200
years, their construction techniques varied widely and prevented application of a standard design for the
mitigation systems. Also, many of the older homes include multiple additions of varying ages and construction
types, which often triggered the need for multiple mitigation systems within an individual residence.
-------
The mitigation systems commonly involve sub-slab depressurization (radon-type equipment [Figures 2 and 3]),
sub-membrane depressurization (including a vapor barrier [Figure 4]), sump hole suction, block wall
depressurization, or air cleaning using activated carbon filters. As needed, other installation activities include
sealing cinder block or fieldstone basement walls, pouring slabs in homes originally constructed with dirt- or
gravel-floored basements (Figure 5), patching existing slabs, and demolishing and replacing some slabs beyond
repair. French drains were installed within several slabs to prevent the discharge of contaminated spring water
into the basement.
Figure 2. Typical residential exterior exhaust
stack for a sub-slab depressurization system
near the Crossley Farm site.
Figure 3. Interior plumbing of the typical sub-slab
depressurization systems, including a U-tube
manometer providing real-time measurements.
Figure 4. Installation of high-density polyethylene
sheets serving as vapor barriers in several homes
near the Crossley Farm site.
Figure 5. Slab construction using a synthetic base
layer into which concrete was poured for homes
with basements having dirt floors.
The O&M excludes energy costs, which are borne by the homeowner. The Pennsylvania Department of
Environmental Protection (PA DEP) will operate the mitigation systems until the cumulative risk presented by all
remaining site-related compounds in sub-slab soil vapor during four consecutive calendar quarters is below a 1E-
6 cancer risk level and the non-cancer hazard index is less than or equal to 1. Future re-evaluation of sub-slab
soil vapor will begin when maximum contaminant level (MCLs) for TCE and associated VOCs are met in onsite
and selected offsite monitoring wells; the current MCL for TCE is 5 ug/L
The PA DEP and EPA will continue jointly sampling more than 100 local wells and selected springs at least once
every two years to determine if more treatment units for well water or indoor air are needed. To avoid future risk,
EPA and PA DEP are working with local authorities to implement institution controls such as construction permits
that require consideration of potential drinking water and soil vapor contamination, and mitigation measures.
10
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Petroleum Vapor Intrusion Assessment: Multiple Lines of Evidence Lead to Mitigation at Utah Gasoline
Fueling Station
Contributed by Robin Davis. Utah Department of Environmental Quality
The Utah Department of Environmental Quality (UDEQ) recently completed an investigation for potential
petroleum vapor intrusion (PVI) at the Hoagies Petro Mart V fueling station located in Farr West, Utah, where
leaking underground storage tanks (USTs) released gasoline into soil and groundwater. From March 2013 to July
2015, UDEQ used PVI screening criteria similar to that established in EPA's Technical Guide For Addressing
Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites ("PVI Guide") to gain a thorough
understanding of the February 2013 release and evaluate the PVI pathway. The potential for PVI was determined
highly likely due to presence of free product less than 15 feet below ground surface (bgs) under the site
convenience store, and extremely high sub-slab vapor concentrations of total petroleum hydrocarbon (TPH),
benzene, and gasoline. PVI was confirmed through collection of indoor air samples from the convenience store in
April 2015, which indicated the presence of TPH, gasoline, and benzene vapors at concentrations that exceeded
risk-based screening levels. Based on these findings, UDEQ has determined that vapor intrusion mitigation is the
next appropriate step.
The 1.2-acre Hoagies Petro Mart V site
consists of a typical 2,400-square foot
convenience store built slab-on-grade
on engineered fill, a fuel dispenser
island with adjacent USTs, a car wash,
and areas for driving and parking. The
site is bordered by farmland to the
north and west, and a major road along
with houses to the south and east. A
leaking UST was discovered in
February 2013 as a result of loss in
product inventory (approximately 1,500
gallons of gasoline). The source of the
loss was traced to a faulty submersible
pump that fits in the UST below ground
and pumps product to the fuel
dispenser when activated to fill a car's
gas tank.
Site investigations began in April 2013.
Ten direct-push wells were installed
around the property to define the
magnitude and extent of groundwater
and soil contamination (Figure 1). The
wells were installed to a depth of 10
feet below the water table, which
ranged from approximately 8 to 14 bgs.
Five of the wells were constructed of
15 feet of 2-inch-diameter slotted PVC
screen, while the remaining wells used
15 feet of 4-inch-diameter screen. Soil
O - 2-Monitoring Well Location
» = 4"Monltoring Well Location
Figure 1. Monitoring well and utility line locations at the Hoagies Petro Mart
Vsite.
samples were collected from the borings at 5,10,15, and 20 feet bgs at each well location. Groundwater samples
were collected from each well for two to four quarters between May 2013 and June 2014. Each water and soil
sample was analyzed for total petroleum hydrocarbon-gasoline range organics (TPH-GRO); total petroleum
hydrocarbon-diesel range organics (TPH-DRO); MTBE; benzene, toluene, ethylbenzene, and xylenes (BTEX),
and naphthalene.
Results from the initial sampling of soil and groundwater indicated that five of the monitoring wells (MWs) located
closest to the fuel dispenser island and convenience store - MW-2, MW-3, MW-4, MW-5 and MW-8 - contained
11
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BTEX and TPH-GRO levels exceeded Initial Screening
Levels (ISLs) and Utah's Tier 1 Screening Criteria1 (Table
1). Contaminant concentrations exceeding both screening
criteria for soil were found at depths ranging from 9 to 30
bgs. A total of 29 soil samples were collected, with benzene
exceeding Tier 1 criteria in nine samples, toluene in seven
samples, ethylbenzene in three samples, and TPH-DRO in
three samples.
Seven additional 2-inch monitoring wells were installed in
September 2013 west of the existing wells to further
delineate the extent of the contamination and better define
site hydrogeology. Four of the wells were installed on the
adjacent property. Additional groundwater samples were
collected from all wells from September to October 2013.
The majority of the wells west of the tank holding location
and fuel dispenser island contained BTEX and TPH-GRO,
including offsite wells, while one well contained an inch of
free product at the water surface. The results indicated
westward migration of contaminants with groundwater flow
and the presence of contamination underneath the
convenience store. Soil samples collected concurrently at
all well locations indicated that at a depth of 9 feet, benzene
and TPH-GRO were present in soil at concentrations up to
32.4 mg/kg and 5,280 mg/kg, respectively. Benzene and
TPH-GRO in groundwater ranged up to 39.1 mg/L and 118
mg/L, respectively. This information prompted the collection
of sub-slab vapor samples in June 2014, as well as further
concurrent groundwater sampling to better define the extent
of the release, determine the potential for vapor intrusion
and identify the remediation methods appropriate for the
site.
Benzene
Soil (mg/kg)
Groundwater (mg/L)
Toluene
Soil (mg/kg)
Groundwater (mg/L)
Ethylbenzene
Soil (mg/kg)
Groundwater (mg/L)
Xylenes
Soil (mg/kg)
Groundwater (mg/L)
Naphthalene
Soil (mg/kg)
Groundwater (mg/L)
MTBE
Soil (mg/kg)
Groundwater (mg/L)
TPH-GRO
Soil (mg/kg)
Groundwater (mg/L)
TPH-DRO
Soil (mg/kg)
Groundwater (mg/L)
Initial Screening
Levels
0.2
0.005
9
5
142
51
0.3
150
500
Tier 1 Screening
Criteria
0.9
0.3
25
23
142
51
0.3
1500
5000
10
Table 1. Utah's Initial Screening Levels and Tier 1
Screening Levels for benzene, toluene, ethylbenzene,
xylenes, MTBE naphthalene, and total petroleum
hydrocarbon-gasoline range and diesel-range organics
in soil and groundwater.
In June 2014, two sub-slab vapor monitoring points (VMPs) were installed inside the convenience store for
collection of soil vapor samples beneath the building foundation and directly above the contamination. Data
collected from the VMPs indicated high sub-slab soil vapor concentrations of TPH C5-C8 aliphatics (8.9 and 57
million micrograms per cubic meter [ug/m3]), benzene
(17,000 and 850,000 ug/m3) and TPH as gasoline in the C5-
C12 aliphatic range (3.5 and 20 million ug/m3). One of the
VMPs exhibited a sub-slab soil vapor methane
concentration of 72,000 parts per million by volume (ppmv).
Contaminant concentrations detected in sub-slab soil vapor
underneath the convenience store exceeded Utah's
standards for commercial land use (10,233 ug/m3 for TPH
C5-C8 aliphatics and TPH as gasoline C5-12 aliphatics, and
16.4 ug/m3 benzene, Table 2), indicating a high potential for
vapor intrusion risk.
Compound
Benzene
Hexane (C5-C6
aliphatics)
Heptane (C7-C8
aliphatics)
Commercial
Sub-Slab
(ug/m3)
16.4
10,233
10,233
Commercial
Indoor Air
(ug/m3)
0.493
307
307
Table 2. Utah's screening levels for compounds in sub-
slab soil vapor and indoor air on commercial land.
Groundwater samples collected in June 2014 provided an additional line of evidence for high risk of vapor
intrusion into the convenience store. Free product was more prevalent than during October 2013, and found in six
wells, ranging from 2 to 15 inches in thickness. Though free product was removed from the wells (approximately
97 gallons of groundwater plus free product were recovered) and was not found in July and October 2014,
additional product was found in five of the wells in April 2015 ranging from 1 to 19 inches thick (Table 3; Figures
2,3, 4, and 5). Wells were pumped three times to remove the product. Because the initial vertical separation
11SLs were derived by selecting appropriate federal/state maximum contaminant levels. Utah's Tier 1 Screening Criteria are risk-based
and non-risk based screening levels defined in the Guidelines for Utah's Corrective Action Process for Leaking Underground Storage Tank
Sites.
12
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between the free product and the base of the convenience store was less than 15 feet, as recommended in EPA's
PVI Guide, it was considered further evidence for the need to install a mitigation system.
Additional sub-slab soil vapor samples, as well as indoor
and outdoor air samples, were collected in April 2015 to
confirm the presence of PVI and gather the necessary data
for selecting an appropriate mitigation system. Indoor air
concentrations of benzene, TPH, and gasoline exceeded
Utah's risk-based screening levels for commercial buildings
(Table 4). One outdoor air sample was collected for eight
hours in low wind conditions (northerly wind of 5 miles per
hour). Outdoor air contaminant concentrations were lower
than those in the indoor air, which ruled out ambient air as
the source of indoor air contamination and confirmed PVI
from the subsurface source. Two additional pieces of
information identified during sub-slab soil vapor sampling in
April 2015 provided critical lines of evidence, as specified in
the EPA PVI Guide, which confirmed the presence of PVI
and helped determine appropriate action. Depleted oxygen
and enriched carbon dioxide were evidence of that
contamination was biodegrading aerobically but still present.
The presence of methane indicated that gasoline is likely
unweathered (source weathering is also a screening
criterion specified in the EPA PVI Guide).
Monitoring
Well
MW-3
MW-4
MW-5
MW-8
MW-11
MW-12
October 201 3
Benzene
Concentration
(mg/L)
39.4
36.1
2.13
Free product
(1 inch)
2.00
6.12
June 2014
Benzene
Concentration
(mg/L)
Free product
(2 inches)
Free product
(3 inches)
Free product
(3 inches)
Free product
(2 inches)
Free product
(15 inches)
Free product
(8 inches)
April 2015
Benzene
Concentration
(mg/L)
Free product
(1 inch)
17.9
Free product
(5 inches)
Free product
(1 1 inches)
Free product
(17 inches)
Free product
(19 inches)
Table 3. The thickness of free product increased
between monitoring events in October 2013, June
2014, and April 2015. Wells 3, 4 and 8 are close to the
convenience store.
As an immediate mitigation measure, an indoor air carbon filter treatment system is currently being installed
to remove vapors inside the building. In addition, based on indoor air and sub-slab soil vapor samples, as well as
the determination that the building slab material is permeable fill (sand as base material for the 4-inch thick
cement slab with an 11-12 inch base layer), a pilot test is underway to determine if sub-slab vapors can be
removed from points external to the building. This test involves applying a vacuum to existing groundwater
monitoring wells around the building and measuring the effectiveness of removing the sub-slab vapors and
preventing further PVI. Cleanup technologies being considered to remediate the contaminant source include soil
vapor extraction and multi-phase extraction.
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Hoagles Retro Mart V
UDEQ Facility #1200424, NAF
2700 NORTH STREET
O
QRQUtCntVATER FLCW DWECTOM
SOIL CowAMHUTOW * UOEO SCCEEHNC LEVELS
HAYJOli
SCMf: !••«
• - 4" Mctmcfwe wcu L
T •VMPtXKATICm
LKAPL TIICXIC3I. FLTT H
HOAOFS PFTBO MMT V
!7 UDEQ SCREEN
O =2" MONITORING WELL LocaiwN
9 = 4" MOHiTORm-G WELL LOCATION
V =V»PLOC«T10KS
TPH-GRO. mg/L
LKAPL THICKNESS, FEET n
HOAGIE5 PETRC MART V
2705 NORTH 2000 WEST
FARR WEST, JTAH
Figure 4. TPH-GRO concentrations and free product
(LNAPL) thickness in June 2014. Free product was
found in six wells.
Hoagies Petro Mart V
UDEQ Facility #1200424, NAF
TPH-GRO i-iisj LI & LNAPL Thickness
-------
Indoor Air
(8 hours)
Indoor Air
(24 hours)
Outdoor Air
(8 hours)
Sub-slab
beneath
main store
Sub-slab
beneath
back room
Commercial
Indoor Air
Screening
Level
Commercial
Sub-Slab
Screening
Level
TPH C5-
C8
Aliphatics
|jg/m3
2,150
6,600
<100
20,000,000
610,000
307
10,233
TPH as
Gasoline
(TPHC5-C12
Aliphatics)
|jg/m3
2,200
6,400
<100
8,700,000
420,000
307
10,233
Benzene
|jg/m3
55
210
0.42
330,000
690
0.5
16.4
Toluene
|jg/m3
13
14
2
<20,000
<4,000
7,154
243,667
Ethyl-
benzene
|jg/m3
2
4
<0.44
<10,000
<2,000
1,482
49,333
Xylene
|jg/m3
12
25
0.98
<10,00
0
<2,000
148
4,933
Naph-
thalene
|jg/m3
<0.53
<2.7
<0.53
<2,000
<400
4
146
MTBE
|jg/m3
<0.73
<3.6
<0.73
<10,00
0
<2,000
4,395
146,00
0
Methane
%
7.2
0.012
02
%
8.3
11
C02
%
8.4
4.6
Table 4. Indoor and outdoor air, and sub-slab soil vapor samples collected in April 2015, indicate TPH, gasoline, and
benzene levels exceed risk-based screening levels for commercial indoor air (contaminants exceeding screening levels
are highlighted).
New EPA Guidance: OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion
Pathway from Subsurface Vapor Sources to Indoor Air
EPA's June 2015 final vapor intrusion guide (OSWER publication 9200.2-154) presents current technical
recommendations of the EPA for assessing and responding to vapor intrusion. The guide clarifies topics such as
weighing multiple lines of evidence; statutory authorities for preemptive mitigation or other early actions; options
for mitigation systems (including their operation, maintenance and monitoring); termination of response actions;
and the role of institutional controls in final cleanup plans when subsurface vapor sources are present. The guide
is intended for use at any site (and any building or structure on a site) being evaluated by EPA pursuant to the
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) or the corrective action
provisions of the Resource Conservation and Recovery Act (RCRA), EPA's brownfield grantees, or state
agencies acting pursuant to CERCLA or an authorized RCRA corrective action program where vapor intrusion
may be of potential concern. The guide pertains to all of the various vapor-forming chemicals that may occur as
subsurface contaminants at these sites, which include many non-chlorinated compounds (petroleum
hydrocarbons, for example) and compounds that are not used as solvents. One of the main purposes of this guide
is to promote national consistency in assessing the vapor intrusion pathway at these sites.
New EPA Guidance: Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking
Underground Storage Tank Sites
EPA's June 2015 petroleum vapor intrusion guide (EPA510-R-15-001) focuses on releases of petroleum-based
fuels, including petroleum hydrocarbon (PHC) and non-PHC fuel additives, from underground storage tanks
(USTs) regulated under Subtitle I of the Solid Waste Disposal Act of 1984, which are typically located at gas
stations. The guide may also be helpful when addressing petroleum contamination at comparable non-UST sites.
Supporting technical information in the guide addresses topics such as light non-aqueous phase liquid, seasonal
and weather effects and vapor intrusion attenuation factors.
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New Tool: Vapor Intrusion Screening Level (VISL) Calculator
The Vapor Intrusion Screening Level (VISL) Calculator is a technical resource developed by EPA that: (1)
identifies chemicals considered to be typically vapor-forming and known to pose a potential cancer risk or
noncancer hazard through the inhalation pathway; (2) provides generally recommended screening-level
concentrations for groundwater, near-source soil gas (exterior to buildings), sub-slab soil gas, and indoor air
based on default exposure scenarios and default risk management benchmarks; and (3) facilitates calculation of
site-specific screening levels and candidate cleanup levels based on user-defined target risk levels, exposure
scenarios, and semi-site-specific or site-specific attenuation factors. The VISL Calculator is an MS Excel
workbook that was first published online in 2012. It has been updated periodically as new toxicity information
became available and was recently updated to coincide with release of the OSWER Technical Guide. To download
the spreadsheet calculator, visit EPA's online compendium of technical information.
EPA Website: Vapor Intrusion
EPA's Vapor Intrusion website is a resource for key information on vapor intrusion for both the general public and
environmental professionals. The website contains basic information about vapor intrusion, technical and policy
documents, tools and other resources to support vapor intrusion investigations. It also provides access to
technical reports focused on topics such as conceptual model scenarios for the vapor intrusion pathway and
mitigation approaches for vapor intrusion.
NIEHS Superfund Research Program Briefs: Process Models and Unattended Vapor Intrusion
Monitoring
The National Institute of Environmental Health Sciences (NIEHS) Superfund Research Program funds university-
based multidisciplinary research on human health and environmental issues related to hazardous substances.
The central goal of the program is to understand and break the link between chemical exposure and disease.
Measuring Vapor Intrusion to Estimate Underground Contamination (Research Brief 238) describes process
models developed by Brown University researchers to predict the concentrations of vapors that enter indoor
environments. Developments toward Low-Cost, Unattended Vapor Intrusion Monitoring (Research Brief 236)
describes an inexpensive vapor intrusion monitoring system developed by NIEHS Superfund Research Program-
funded scientists from the chemical sensor company Seacoast Science.
ESTCP Demonstration Projects: Use of Compound-Specific Stable Isotope Analysis to Distinguish
Between Vapor Intrusion and Indoor Sources of VOCs; Use of On-Site GC/MS Analysis to
Distinguish between Vapor Intrusion and Indoor Sources of VOCs
Two projects on distinguishing vapor intrusion from indoor sources of volatile organic compounds (VOCs) merited
the Environmental Security Technology Certification Program (ESTCP) 2014 Project-of-The-Year Award for
Environmental Restoration. Use of Compound-Specific Stable Isotope Analysis to Distinguish Between Vapor
Intrusion and Indoor Sources of VOCs (ER-201025) demonstrated use of a step-by-step protocol that can provide
an independent line of evidence to determine whether or not buildings are impacted by VOCs. Use of On-Site
GC/MS Analysis to Distinguish between Vapor Intrusion and Indoor Sources of VOCs (ER-201119) validated a
step-wise investigation procedure using portable, commercially available gas chromatograph/mass spectrometer
analysis and real-time decision making to distinguish between vapor intrusion and indoor sources of VOCs.
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