High Resolution Site Characterization for VOCs:

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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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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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PSG Survey Findings: Chlorinated compounds were present at significant measurements on eastern side of site Results for Trichloroethene (TCE)

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Findings: Results for Tetrachloroethene (PCE)

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PSG Survey Findings: Results for 1,1,2,2-Tetrachloroethane (R-130)

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PSG Survey Findings: Results for Total VOCs

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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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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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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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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

[email protected]

www.beacon-usa.com

Obrigado!

Documents

High Resolution Site Characterization for VOCs: