A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Technology
News & Trends
EPA 542-N-13-002 | Issue No. 64, May 2013
This issue of Technology News & Trends highlights vapor intrusion (VI), which generally refers to
migration of hazardous vapors from any subsurface contaminant source such as contaminated soil or
groundwater through the vadose zone and into indoor air. Vapor intrusion can occur in a broad range of
land use settings, including residential, commercial, and industrial properties, and can affect buildings
with virtually any type of foundation such as basement, crawl space, or slab on grade. Assessing human
health risks posed by VI and determining the optimal method for mitigation, where needed, is typically
complicated by variance in natural attenuation of migrating vapors and the mixing of those vapors with
other sources of indoor air contaminants. Assessment also can be difficult due to heterogeneous
subsurface conditions and preferential pathways for vapor migration and soil gas entry.
The VI pathway has become a standard consideration during investigations at hazardous waste sites,
especially those subject to the Superfund, underground storage tank (UST), and Resource Conservation
and Recovery Act programs operated by federal or state agencies. The U.S. Environmental Protection
Agency (EPA) currently is finalizing its guidance on subsurface VI. In addition, 24 states issued draft or
final VI guidance as of April 2013, and other state guidance continues to evolve. Earlier this year, for
example, the New Jersey Department of Environmental Protection updated its Vapor Intrusion Technical
Guidance for use in evaluating VI pathways at contaminated sites within New Jersey. Later this year,
Vl-related guidance or rulemakings are anticipated in Illinois and Pennsylvania. In some states, VI
guidelines have been incorporated into broader guidance or into programs covering voluntary cleanup or
underground storage tanks.
• - Stand-Alone Vapor Intrusion Guidance (19 slates)
• - Dralt Vapor Intrusion Guidance (5 states)
• - Vapor Intrusion Guidelines within Broader Guidance {8 stales)
4 - Vapor Intrusion Guidelines within Voluntary Cleanup Program (6 stales)
- Vapor Intrusion Guidelines within UST Cleanup Program (8 stales)
Q - No Slate Guidance or Guidelines (4 states)
Courtesy of GrKticrpt, ay prepared far Ifte
Assessment and Mitigation: Defining and Addressing Vapor Pathways
in a Mixed Use Area
Contributed by Vickie Meredith (WYDEQ), Jeff Kurtz (EnviroGroup, Ltd.), and Coleman Hovt
Technology News & Trends
May 2013 Issue
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(EnviroGroup, Ltd.)
In 2010 and 2011, the Wyoming Department of Environmental Quality (WYDEQ) installed mitigation
systems in 24 residences and one commercial building to prevent intrusion of trichloroethene (TCE) and
tetrachloroethene (PCE) vapors from an orphan site in downtown Cheyenne. The source had been
previously identified as a 20-acre groundwater PCE plume. A three-phase investigation conducted
between 2009 and 2011 included the collection of groundwater, soil gas, indoor air, and sub-slab vapor
samples to evaluate the potential for vapor intrusion (VI) in area buildings. Residential buildings in areas
of high soil vapor PCE concentrations (above 810 micrograms per cubic meter [ug/m3]) were offered
pre-emptive mitigation systems, while buildings in the surrounding areas were investigated further before
potentially being selected for mitigation.
PCE and TCE were discovered in area groundwater in 2002 following a Phase II environmental site
assessment conducted as part of a proposed expansion for a local grocery store. A more thorough site
investigation was conducted in 2003 and 2004 to evaluate the nature and extent of this groundwater
contamination and the potential for VI. The investigation identified a 20-acre groundwater PCE plume
located 10-20 feet below ground surface (bgs) and low levels of TCE. PCE levels ranged as high as 450
micrograms per liter (ug/L) in groundwater samples and as high as 54,259 ug/min soil gas samples.
Based on these investigations, potential contaminant sources were determined to include two former
auto repair shops, a former printing shop, as well as existing and former dry cleaners.
A follow-up study was conducted in 2009 to further evaluate the nature and extent of volatile organic
compounds (VOCs) in soil vapor and groundwater, the potential for VI, and whether VI controls were
warranted for site buildings. Eighty-three shallow soil vapor probes (to a depth of 5 feet bgs) and 31
sub-slab vapor probes were installed and sampled throughout the area (Figure 1). Groundwater samples
were collected from 18 permanent wells (mainly screened from 7 to 17 feet bgs across the water table),
three temporary groundwater monitoring points (installed to depths of 10 to 17 feet bgs), two existing
monitoring wells, two private wells, and four sumps in the study area. PCE and TCE concentrations in soil
vapor samples were analyzed in a mobile laboratory, which provided real-time information on the nature
and extent of VOCs and allowed rapid evaluation or suspected source areas, transport pathways, and
potentially impacted buildings. To demonstrate cpmparability of mobile laboratory sample results,
samples also were collected from 16 of the 83 soil vapor probes for fixed-based VOC laboratory analysis.
Soil vapor data were used to evaluate plume extent and better define and characterize source areas.
Twenty outdoor air samples were collected concurrently in the vicinity of indoor air and sub-slab vapor
samples to provide information on ambient levels of PCE and TCE.
Technology News & Trends 2 of 9 EPA 542-N-13-002 | Issue No. 64
May 2013 Issue clu-in.org/newsletters
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Figure 1. Inferred PCE concentrations and soil vapor sampling locations.
Eighteen soil vapor samples collected during the 2009 sampling event indicated the presence of PCE
above the WYDEQ soil vapor screening level of 810 ug/m3, which was sejected by WYDEQ based on a
IxlO-5 target indoor air concentration cancer risk level of 8.1 ug/m3. Buildings in the area above this
screening level were considered to have the highest potential for VI risk. All 32 owners of residential
buildings in the high PCE zone were offered pre-emptive mitigation and indoor air testing, of which eight
accepted and 18 chose indoor air testing prior to installation of mitigation systems. A total of 14
pre-emptive mitigation systems were installed. The owners of the 31 commercial buildings in this zone
were offered indoor air and sub-slab vapor testing to determine the need for further action. An additional
19 homes peripheral to the high PCE zone were offered indoor air testing. Only two of these peripheral
homes were found to have indoor air PCE concentrations above the screening level.
From July to August 2010, a second phase of the investigation was implemented to further define the
extent or PCE in soil vapor along the western edge of the high PCE zone. Eleven soil vapor samples
indicated PCE concentrations above 810 ug/rr?, leading to the expansion of indoor air and sub-slab
testing areas in early 2011 to include an additional 34 residential buildings. The investigative zone was
further expanded in July 2011 to the southern and western edges of the previously examined areas, but
no additional areas of high soil vapor PCE were identified.
Technology News & Trends
May 2013 Issue
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Over the course of the three investigative phases, indoor air samples were collected from a total of 52
homes, three apartment buildings, and 30 commercial buildings. PCE was detected (detection limit 0.22
ug/n?) in nearly all indoor air samples, with measured concentrations ranging as high as 62 ug/m3. PCE
exceeded screening levels (residential=8.1 ug/m3; commercial=27.2 ug/m3) in 13 residential and 2
commercial buildings. TCE was detected (detection limit 0.17 ug/m3) at concentrations ranging up to 5.6
ug/m3. Six of the residential and none of the commercial buildings sampled exceeded TCE screening
levels (residential=0.9 ug/m3; commercial=4.2 ug/m3). The possibility of indoor VOC sources was
eliminated by completing a chemical inventory and questionnaire for each building prior to sampling.
Residents also were asked to avoid bringing dry-cleaned clothes into their homes for 1-2 weeks prior to
testing. In buildings where indoor VOC sources were suspected, WYDEQ collected additional samples or
examined soil gas and groundwater ratios of TCE and PCE.
Mitigation systems were installed in 24 residences (including 14 pre-emptive mitigation systems) and one
commercial building over the three-year investigative period. These buifdings included single-level
residential, multiple-level residential, and commercial structures with poured concrete, block, and brick
foundations. Basements and/or crawlspaces were present in each building. The type of mitigation system
selected was based on the number of buildings over the plume, their size and basic structure, and the
presence of unsaturated and semi-permeable soils below the slab.
Figure 2. SMD and SSD vent lines, penetrating
the concrete foundation wall.
A combination of mitigation technologies was selected based on site-specific conditions. Nine residences
received sub-slab depressurization (SSD) systems, which use a fan to remove air from underneath the
slab and exhaust it above the building, creating a negative pressure. A minimum negative pressure below
the entire slab of -0.003 inches water column compared to indoor air pressure was considered sufficient.
Eight residences and the commercial facility received a combination of SSD and sub-membrane
depressurization (SMD) systems; SMD systems (used in accessible crawlspaces) involved installation of a
membrane over a perforated pipe on the dirt floor and use of a fan to remove air from below the
membrane and exnaust it above the building (Figure 2). Simple crawlspace ventilation, which increases
the air exchange rate for a crawlspace, was utilized in two residences where only a crawlspace was
present but inaccessible. A combination of two or all three systems was employed in the remaining five
residences. Several low-vacuum/high-flow fans were used primarily on crawlspace foundations or slabs
with coarse sub-slab fill, and a single higher vacuum/lower flow fan was used on basement or slab on
grades with sand or lower permeability fill.
Performance testing was conducted in 17 of the 25 buildings with the heating, ventilation, and air
conditioning (HVAC) units operating under normal conditions. The buildings requiring performance tests
were those with either partial or complete crawl space ventilation mitigation systems or other types of
systems with poor mitigation system diagnostics. Based on test results, two of the buildings required
system enhancements. After system upgrades, both of these buildings, operating under normal HVAC
conditions, had indoor air results well below screening levels. Contaminant concentrations were below
screening levels in the remaining buildings undergoing performance testing.
Technology News & Trends 4 of 9 EPA 542-N-13-002 | Issue No. 64
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Location
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performance data and in consideration of relative operational costs. Sub-membrane depressurization was
considered in several homes with dirt-floor basements but dismissed due to concerns about long-term
integrity of the membrane fabric. Instead, new concrete was poured where necessary.
The SSD systems were of a typical design that includes four-inch-diameter PVC piping installed through
the basement floor and into the sub-slab extraction pit. The piping routes outside the home and attaches
to a single, continuously operating low-pressure mitigation fan (typically 90 watts). Piping extends from
the fan to above the roofline, where vapors discharge to the atmosphere.
Figure 1. Configuration of exterior
components in each installed VI
mitigation system.
Other system components include a manometer for continuous pressure measurements, an exhaust pipe
cap to prevent debris and rain from entering the exhaust system, a low-decibel alarm to warn of
unintended system shutdown, and a minimum of two permanent monitoring points in the floor for
pressure field extension tests (PFETs). A %-inch inner diameter condensation bypass tube also was
instajled adjacent to the fan to prevent excess moisture from entering the impeller (Figure 1). In some
buildings, air-tight sump pumps were also installed. Some buildings required more than one extraction
pit to achieve a negative pressure field. In these cases, piping from each extraction pit was fitted with a
ball valve to manually regulate pressure flows between extraction pits.
As part of the planning process, EPA met with each property owner and tenant to gain consent for
property access. EPA inspected each basement to evaluate factors such as household contents, physical
access, available working space, foundation type and integrity, electrical controls, and any unique issues
such as structural challenges, dirt floors, asbestos, and inadequate electrical service. Electrical permits
were required at all properties, and cpnstruction permits were required for buildings where concrete slabs
were installed. EPA then met again with each property owner and tenant to discuss the proposed system
layout.
To ensure adequate flow and fan/pipe sizing in each building, PFETs were performed by drilling three
1-inch holes in the slab: one in the location of the planned extraction pit and one at each of two
permanent monitoring points. Using a shop vacuum, suction was applied to the extraction pit hole.
Resulting negative pressures were measured at the two monitoring holes using a digital
micromanometer. Where concrete slabs were installed to replace dirt floors, PFETs were performed after
the poured concrete fully cured. PFET results confirmed that a 90-watt fan would provide sufficient
vacuum for all 43 homes; however, several buildings required a second or third extraction pit to
generate a sufficient negative pressure field and the large Town Hall required a 140-watt fan. Based on
the collective inspections and PFET results, one set of design specifications was developed and applied to
a unique system configuration for each property.
Prior to installing each SSD system, below-grade foundation walls and slabs were sealed and basement
contents were removed and temporarily stored in room-sized storage and shipping containers. Portipns
of drywall also were removed from some finished basements. The extraction pit was created by cutting a
12-inch concrete square from the slab and then removing sub-material to a depth of about 12 inches to
Technology News & Trends 6 of 9 EPA 542-N-13-002 | Issue No. 64
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maximize air flow. During interior pipe installation, care was taken to ensure the pipes maintained a
slight slope to the extraction pit, in order to drain excess water from sub-slab moisture and exhaust stack
condensation. Electrical work included installing two dedicated circuits for the fan and alarm.
Municipal permit inspections were performed by the local jurisdiction's building department. After a
system had operated for about two weeks, its baseline vacuum pressure was measured by the
manometer as 1 to 2 inches of water column and recorded. A final PFET was performed at that time using
the permanent monitoring points to confirm an adequate negative pressure field was present under the
slabs. A minimum vacuum pressure of 0.004 inches of water column (1 Pascal) was considered adequate
and achieved in all systems. Since a negative pressure was being applied, a backdraft test was
conducted in each building to ensure noxious gases from the HVAC system would continue venting
outside the building.
Figure 2. Instruction sheet with
basic information about the system,
explanation on how to respond to
an alarm alert, and contact
information.
A laminated instruction sheet attached near the system's alarm helps the property owner or tenant
operate the system (Figure 2), and a dedicated hotline is available for owners with additional questions
or experiencing an alarm alert. Maintenance and monitoring (M&M) of VI mitigation systems associated
with this Superfund site is provided by the Massachusetts Department of Environmental Protection
(MassDEP). The 10-year M&M plan developed jointly by EPA and MassDEP requires PFETs on about 25%
of the systems each year, with the objective of verifying an adequate negative pressure field beneath the
slabs. Visual basement inspections are performed each year on the remaining systems to verify
conditions of the fan and piping and to confirm that the manometer pressure has remained constant.
EPA's Region 1 office spent $1.2 million to design and install the SDD systems. The average system cost
of nearly $30,000 is higher than suggested in available guidance due in part to the general age and
construction of the mitigated buildings. A majority of the buildings had fieldstone walls and dirt-floor
basements. In the few buildings with poured concrete basements, the average cost was below $10,000.
The cost of electricity needed to operate each system, estimated at $10-$20 per month, is the property
owner's responsibility. MassDEP committed $600,000 to fund M&M of the systems over 10 years.
CLU-IN: Vapor Intrusion
Technology News & Trends
May 2013 Issue
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This issue area of the CLU-IN website provides an overview and compendium of guidance materials, site
investigation tools, mitigation methods, and other information resources to help address volatile
chemicals migrating from contaminated groundwater or soil.
EPA Office of Solid Waste and Emergency Response (OSWER): Vapor
Intrusion
This website provides key information on VI for members of the public who may be interested in this
topic, including community leaders and environmental professionals. This resource provides basic
information about VI. technical and policy documents that may be used to support environmental
investigations, and highlights of current and upcoming Agency activities related to VI.
National Priorities List (NPL): Vapor Intrusion and the Superfund
Program
This EPA website provides key information on VI in context of the Superfund program. It provides
electronic links to general information about VI and features details regarding potential addition of a
subsurface intrusion (including VI) component to the Hazard Ranking System used to place uncontrolled
waste sites on the NPL.
Underground Storage Tanks: Petroleum Vapor Intrusion (PVI)
Compendium
The PVI Compendium maintained by EPA's Office of Underground Storage Tanks (OUST) provides
electronic links to information on fate and transport, site characterization, soil gas sampling, remediation,
and EPA or state guidance concerning migration of vapors from petroleum hydrocarbons such as gasoline,
diesel, or jet fuel. Materials available for downloading include the "PVI Database," which contains relevant
data from 74 sites.
Recent Publications:
» Fluctuation of Indoor Radon and VOC Concentrations Due to Seasonal Variations: This September
2012 report (EPA/600/R-12/673) presents a full year of weekly measurements of sub-slab soil gas, external
soil gas, and indoor air on a single house that is impacted by VI of radon and volatile organic compounds
(VOCs). In addition, the research evaluated the long-term performance of sorbent-based sampling devices for
time-integrated measurement of indoor air levels of VOCs
• Evaluation Of Empirical Data To Support Soil Vapor Intrusion Screening Criteria For Petroleum
Hydrocarbon Compounds : This January 2013 report (EPA 510-R-13-001) evaluates empirical data and
selected modeling studies of petroleum hydrocarbon vapor behavior in subsurface soil at petroleum-UST
release sites and describes how these vapors can affect subsurface-to-indoor air VI. The report presents an
inclusion distance approach for screening petroleum release sites for VI. EPA's OUST developed the approach to
improve the efficiency of investigating sites involving petroleum release and to focus resources on sites of most
concern for petroleum VI.
Draft Final Guidance: Subsurface Vapor Intrusion Guidance
On April 16, EPA released for public input two draft final VI guidance documents: one general guidance
applying to alj compounds and one focused guidance applying to petroleum hydrocarbons released from
USTs. When final, this guidance will help ensure that VI exposure assessment and mitigation actions to
protect human health are undertaken in a technically, scientifically, and nationally consistent manner.
Public comments must be submitted by June 24, 2013. Interested stakeholders can also register online
for email updates about development and anticipated release of the final guidance from EPA's OSWER.
nis newsletter as a means or disseminating userui information regarping innovative ana alternative treatment
technologies and techniques. The Agency does not endorse specific technology vendors.
Technology News & Trends 8 of 9 EPA 542-N-13-002 | Issue No. 64
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