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High Resolution Site Characterization for VOCs: A Cost-Effective Approach to Identify Source Areas
and Delineate Contaminant Plumes
Presented by: Harry O’Neill
President Beacon Environmental Services, Inc.
22 October 2012
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Case Studies
Case Study #1 Undeveloped, Wooded Lot
Case Study #2 Heavily Developed Urban Area
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Case Study #1: Source Area Identification
Objectives: Identify sources of contamination in gw
Challenges: Legacy contamination remains from undocumented activities Heavily wooded area Area receives significant rainfall
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Case Study #1: Source Area Identification
Sampling Plan: Basic grid with 10 meter spacing, as well as 20 and 40 m spacing in areas of less concern
Focused in area where operations were previously conducted at the site 64 Passive Soil Gas Sample Locations
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Case Study #1: Source Area Identification
PSG Survey Findings: Chlorinated compounds were present at significant measurements on eastern side of site Results for Trichloroethene (TCE)
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Case Study #1: Source Area Identification
Findings: Results for Tetrachloroethene (PCE)
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Case Study #1: Source Area Identification
PSG Survey Findings: Results for 1,1,2,2-Tetrachloroethane (R-130)
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Case Study #1: Source Area Identification
PSG Survey Findings: Results for Total VOCs
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Case Study #1: Source Area Identification
Soil Sampling: Soil samples were collected at locations reporting highest measurements in the PSG survey, as well as at contaminant boundary areas and areas reporting non-detects. Contamination was expected to be found closer to where site activities occurred.
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Case Study #1: Source Area Identification
Soil Sampling Results: Samples collected at 1 to 1.5 m depth at multiple intervals of soil column using Terra Core sampler Strategy was to sample at “hot spots” and confirm the non-detects from the passive soil gas survey
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Case Study #1: Source Area Identification
PSG and Soil Results: Soil samples confirmed the results of the PSG survey and identified a significant source area. An additional source area is expected to be present where the second highest soil sample was collected. The next phase includes collecting additional samples to identify the exact location of this more discrete release.
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Case Study #1: Source Area Identification
PSG and Soil Results: Soil sampling alone likely would not have identified source areas, as evident at location reporting low soil concentrations. The PSG survey just as importantly indicated where no additional sampling is required as was confirmed with the soil sampling. Two GW wells are being installed at “hot spots.”
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Passive Soil Gas Sample Collection Kit
Passive Soil Gas Technologies are typically provided through sample collection kits and
only require hand tools for sample collection.
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ASTM Standards D5314 and D7758 Compliant
The sorbents need to be hydrophobic and the housing of the PSG Samplers should not contain sorptive materials (e.g., PDMS or other membranes) that may compete with the
sorbents and bias results
Two types of adsorbents to target a broad
range of compounds
Two pairs for duplicate or confirmatory
analysis
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Installation Depth Options
Samplers can be installed in holes as
shallow as 10 cm
Typically installed in holes advanced to
30 cm to 1 m depth
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Benefits – Spatial Variability
Overcomes the challenges of SPATIAL VARIABILITY of
subsurface contamination by allowing you to collect
a high resolution data set
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Benefits – Temporal Variability
Overcome the challenges of the TEMPORAL VARIABILITY
of soil gas concentrations by collecting time-
integrated measurements over several days or weeks
Soil gas concentrations
can change daily and
even hourly at the
same location,
especially if no
impervious surfacing
(i.e., cap) present. Chart courtesy of
Ion Science
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Benefits – Sustainable Technology
IN THE FIELD No waste from soil cuttings are generated when sampling.
Only hand tools required to collect samples -- no DPT or drill rigs.
In-situ sample collection onto adsorbents that are reused, no waste.
IN THE LAB
Samples analyzed using thermal desorption-gas chromatography/ mass spectrometry (TD-GC/MS) instrumentation.
No solvents are used for sample extraction.
Green CharacterizationTM
A green site investigation relies on information gained from a thorough preliminary assessment that identifies target areas and
site conditions through minimally intrusive techniques. -- USEPA OSWER Dec. 2009
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Benefits of HRSC
High Density, Low Cost Low Density, High Cost
High Resolution Site Characterization (HRSC)
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Routine Targets
Halogenated compounds
• PCE
• TCE
• DCEs
• Vinyl chloride
• TCA
• Carbon tetrachloride
• Chloroform
• Freons
• Chlorobenzene
• Dichlorobenzenes
• Trichlorobenzenes
Complex mixtures
• Stoddard solvent
• Paint thinners
Petroleum Blends
• Gasoline
• Fuel oil
• Diesel
• Jet Fuel
BTEX, MTBE and PAHs
• Naphthalene
• 2-Methylnaphthalene
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Additional Targets
Heavier PAHs
• Acenaphthalene, Fluorene, Pyrene
Ketones
Alcohols
Explosives
Pesticides
Chemical Warfare Agent (CWA) and Breakdown Products
• Mustard, GB, VX, 1,4-Thioxane, 1,4-Dithiane, Thiodiglycol
Mercury (Hg)
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Applications
• Identify source areas and release locations of VOCs/SVOCs
• Focus soil and groundwater sampling locations
• Focus remediation plans
• Identify vapor intrusion pathways
• Track groundwater plumes
• Monitor remediation progress
• TRIAD Approach – Expedited Site Characterization
PSG surveys are routinely performed to:
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Case Study #2: Identify Source Area and Track Plume
Objective: Identify Source of PCE in Monitoring Well
PCE concentration in groundwater is 6.8 ug/L
Challenges: Urban Environment Multiple potential source areas present Gaining access to properties difficult PCE concentration at low ppb level in gw at 5 m depth
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OVERALL GRID PATTERN
74 PSG Samplers
Sampled near PRPs and in
public right of ways.
Groundwater was
approximately 5 meters bgs
10 m spacing near two
dry cleaners
Typically 30 m spacing along
public right of ways
Case Study #2 – PSG Sampling Plan
Inferred GW flow
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Case Study #2 – PSG Sampling Plan
GRID NEAR
DRY CLEANERS
Locations of
former and active
dry cleaners
Location of MW-1
which reported
6.8 ppb of PCE
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Definitively identified
PCE releases from
former and active dry
cleaners.
Non-Detects Excluded
out other PRPs
Tracked plume to
downgradient well
contaminated with
PCE by sampling in
public right of ways.
Case Study #2 – Results
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Case Study #2 – GW Results
PSG Data and GW data correlated very well
GW data isoconcentration maps confirming PSG findings
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Case Study #2 – Findings
Findings:
• PSG data for PCE ranged from non detects (<10 ng) to 29,117 ng
• Sources of PCE releases were identified
• PCE measurement of 29,117 ng equated to 17,000 ug/L in gw
• PSG data identified migration pathways from source areas to impacted
monitoring well – plumes commingled
• Investigation only required sampling in public-right-of-ways
• PCE measurement of 125 ng equated to 6.8 ug/L in gw – SENSITIVE METHOD
• A minimal number of grab groundwater samples were required to confirm
results, which significantly minimized costs.
Reference: Clarke, et al, Preliminary Investigation of a Perchloroethylene (PCE) Groundwater Plume using a Passive Soil Gas Survey, REMEDIATION, Wiley Periodicals, Vol. 18, No. 4.
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Conclusions
• Passive soil gas methods allow for the rapid collection of data to produce
high resolution data sets targeting a broad range of VOCs and SVOCs
• High resolution site characterization allows you to better delineate
contamination and refine the conceptual site model (CSM)
• PSG samples can be collected in areas where difficult to access with
equipment, as well as sampling in public right of ways when site access is
not possible. In addition, creates minimal disturbance to site operations.
• Time-integrated measurements simultaneously collected over several days
or weeks offer a sensitive method for tracking groundwater contamination
even at low concentrations
• Sampling can be performed by your own staff using basic hand tools
• Able to reduce the number of required soil and groundwater samples, which
reduces the overall project costs.
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Questions?
Please contact us if you have any questions:
Beacon Environmental Services, Inc.
Harry O’Neill
Bel Air, MD USA
1-410-838-8780
www.beacon-usa.com
Obrigado!
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