Robin-PVI Workshop 25th Tanks Conf Phx, 9-13-15

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Text of Robin-PVI Workshop 25th Tanks Conf Phx, 9-13-15

  • by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks rvdavis@utah.gov 801-536-4177

    Developing and Applying Screening Criteria for the

    Petroleum Vapor Intrusion Pathway

    Petroleum Vapor Intrusion Workshop Sunday September 13, 2015

    1:00 pm 5:00 pm

    25th National Tanks Conference Phoenix, Arizona

  • Understand why petroleum vapor intrusion (PVI) is very rare despite so many petroleum LUST sites

    Show mechanisms, characteristics, degree of vapor bioattenuation

    Show distances of vapor attenuation relative to source strength

    Understand causes of PVI

    Apply as Screening Criteria, screen out low-risk sites, avoid unnecessary investigation, soil gas/air sampling

  • Field Data from 3 Countries, Published Field Studies

    Paired, concurrent measurements of source strength and associated soil gas measurements

    Source strength: LNAPL in soil and GW, dissolved-phase

    1000s of sample points and measurements at 100s of sites

    Extensive peer review and quality control checks

    Distances of vapor attenuation quantified

    EPA Database Report of Empirical Studies, Jan. 2013

    Some US States

    Australia 2012

    ITRC October 2014

    EPA final PVI June 2015

    Guidance Documents Issued:

  • 124/>1000

    Perth Sydney

    Tasmania

    Australia

    Davis, R.V., 2009-2011 McHugh et al, 2010 Peargin and Kolhatkar, 2011 Wright, J., 2011, 2012, Australian data Lahvis et al, 2013 EPA Jan 2013, 510-R-13-001

    REFERENCES

    4/13

    70/816

    Canada

    United States

    MAP KEY

    # geographic locations evaluated

    # paired concurrent measurements

    of subsurface benzene soil vapor

    & source strength

    70

    EPA OUST Jan. 2013

    Australian sites evaluated separately

    816

    Petroleum Vapor Database of Field Studies

  • January 2013

    Petroleum Database Report

    Compilation of field data: LNAPL in soil & GW, & dissolved sources, and concurrent associated vapor data

    http://www.epa.gov/oust/cat/pvi/PVI_Database_Report.pdf

  • http://www.epa.gov/oust/cat/pvi/pvi-guide-final-6-10-15.pdf

    June 2015

    Final PVI Guide

    Thickness of clean, non-source soil required to attenuate vapors associated with LNAPL in soil & GW, & dissolved

    sources

  • EPA OUST PVI Guide, Figure 1 Decision Flow Chart for Evaluating PVI

  • CAPILLARY ZONE

    a) LNAPL SOURCE

    UNSATURATED ZONE

    SATURATED ZONE

    sharp reaction

    front

    O2

    VOCs

    b) DISSOLVED-PHASE SOURCE

    CAPILLARY ZONE

    UNSATURATED ZONE

    SATURATED ZONE

    high massflux

    limited mass flux

    sharp reaction

    front

    constituent distributions

    O2

    VOCs

    constituent distributions

    Conceptual Characteristics of Petroleum Vapor Transport and Biodegradation

    After Lahvis et al 2013 GWMR

    O2/Hydrocarbon

    Vapor Profile

    O2/Hydrocarbon

    Vapor Profile

    KEY POINTS

    LNAPL sources have high

    mass flux, vapors attenuate

    in longer distances than

    dissolved sources

    Aerobic biodegradation of

    vapors is rapid, occurs over

    short distances

    Oxygen demand is a

    function of source strength

    0

    1

    0

    1

  • UST system

    Dissolved contamination

    Clean, Non-Source Soil

    High vapor concentrations, high mass flux

    from LNAPL & soil sources

    Low vapor concentrations, low

    mass flux from dissolved sources

    Define extent & degree of contamination

    Apply Screening Criteria Building

    Collect Basic Data, Characterize Site, Construct Conceptual Site Model

    LNAPL in soil

    LNAPL in soil & GW

    Soil Boring/MW Soil Boring/MW

    Utility line

  • >100 years of research proves rapid vapor biodegradation by 1000s of indigenous microbes

    Studies show vapors biodegrade and attenuate within a few feet of sources

    No cases of PVI from low-strength sources

    Causes of PVI are well-known

  • Causes of Petroleum Vapor Intrusion

    Preferential pathway: sumps, elevator shafts

    High-strength source in direct contact with building (LNAPL, high dissolved, adsorbed)

    Groundwater-Bearing Unit

    BUILDING

    Unsaturated Soil

    Affected GW

    LNAPL

    LNAPL

    4 1

    3

    LNAPL

    High-strength source in close proximity to building, within GW fluctuation zone

    2

    Drawing after Todd Ririe, 2009

    High-Strength Sources Direct contact or close proximity to buildings

    Preferential pathways: engineered & natural

    Preferential pathway: bad connections of utility lines; natural fractured and karstic rocks

  • (ITRC PVI Tech Reg, 2014)

    Preferential Pathway: Engineered

    Petroleum Source

  • (ITRC PVI Tech Reg, 2014)

    Preferential Pathway: Natural

  • 1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

    0

    5

    10

    15

    0 5 10 15 20

    Benzene (ug/m3)

    O2 & CO2 (% V/V)

    Coachella, CA COA-2 (Ririe, et al 2002)

    1.E+001.E+021.E+041.E+061.E+08

    -5

    0

    5

    10

    15

    20

    0 5 10 15 20 25

    Benzene (ug/m3)

    Salina Cash Saver VMW-1 (UDEQ 7/27/07)

    OA

    IA

    LNAPL

    LNAPL

    1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

    0

    5

    10

    15

    0 5 10 15 20 25

    Benzene (ug/m3)

    Dep

    th,

    fee

    t b

    elo

    w g

    rad

    e

    O2 & CO2 (% V/V)

    Beaufort, SC NJ-VW2 (Lahvis, et al., 1999)

    Oxygen

    Carbon Dioxide

    Benzene

    Benzene in GW

    16,000 ug/L

    Signature Characteristics of Aerobic Biodegradation of Subsurface Petroleum Vapors

    Vapors aerobically biodegraded by oxygen-consuming microbes, waste product carbon dioxide

    Vapors attenuate in short distances

  • Vapor Bioattenuation Limited by Contaminated Soil

    1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

    0

    5

    10

    15

    0 5 10 15 20

    Benzene (ug/m3)

    De

    pth

    , fe

    et

    be

    low

    gra

    de

    O2 & CO2 (% V/V)

    Conneaut, OH VMP-1 (Roggemans, 1998; Roggemans et al., 2001)

    Oxygen

    Carbon Dioxide

    Benzene

    LNAPL in Soil (sand, silty sand)

  • 8/26/06 6/27/07

    Importance of Shallow Vapor Completion Points

    Shallower point confirms attenuation above contaminated soil zone

    Shallow completion too deep

    Example of apparent non-attenuation until shallow vapor point installed in non-contaminated soil

    Good vapor point completion ensures atmospheric influences are none/minimal

    VW-11 Hals, Green River, Utah

    No attenuation within contaminated soil zone

  • Probe A3 (TCE - Normalized)

    0

    0.2

    0.4

    0.6

    0.8

    1

    1.2

    1.4

    1.6

    1.8

    2

    13

    :50

    :09

    10

    :50

    :26

    7:5

    0:4

    4

    4:5

    1:0

    4

    1:5

    1:4

    3

    22

    :53

    :46

    5:4

    3:2

    9

    2:4

    3:4

    7

    23

    :44

    :04

    20

    :44

    :22

    17

    :44

    :39

    14

    :44

    :57

    11

    :45

    :15

    8:4

    5:3

    2

    16

    :02

    :01

    13

    :02

    :18

    10

    :02

    :36

    7:0

    2:5

    5

    4:0

    3:1

    2

    1:4

    3:5

    6

    22

    :44

    :15

    7:0

    6:4

    1

    4:0

    6:5

    9

    1:0

    7:1

    9

    22

    :07

    :58

    19

    :11

    :25

    Time (3/16/07 to 4/10/07)

    No

    rma

    lize

    d C

    on

    ce

    ntr

    ati

    on

    Probe A3-3' (Port 9)

    Probe A3-8' (Port 10)

    Probe A3-17' (Port 5)

    Soil Gas Temporal Study, EPA-ORD

    3 bgs

    8 bgs

    15 bgs

    >500 points per probe collected once per hour over 4 week period

    Soil gas concentrations varied by

  • 1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

    0

    5

    10

    15

    0 5 10 15 20 25

    Benzene (ug/m3)

    O2 & CO2 (% V/V)

    Santa Clara, UT VW-4 1/19/2009

    4 feet Benzene in GW 3180/ ug/L

    1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

    0

    2

    4

    6

    8

    10

    0 5 10 15 20 25

    Benzene (ug/m3)

    De

    pth

    , fe

    et

    bg

    s

    O2 & CO2 (% v/v)

    Jacksons, UT VMW-4 9/29/08

    Oxygen, %

    Carbon Dioxide, %

    Benzene, ug/m3

    Benzene in GW

    12,000 ug/L

    4.94 feet

    Method for Determining Thickness of Clean Soil Required to

    Attenuate Vapors Associated with Dissolved Sources

    Thickness of clean soil needed to attenuate vapors

    = Distance between top of dissolved source and deepest clean vapor point

  • 0

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    1 100 10,000 1,000,000

    Th

    ick

    ne

    ss

    Cle

    an

    So

    il R

    eq

    uir

    ed

    to

    Att

    en

    ua

    te T

    PH

    Va

    po

    rs

    , fe

    et

    TPH, dissolved, ug/L

    Near-Slab Multi-Depth, Sub-Slab

    TPH: Soil Vapor & Dissolved Paired Measurements

    All Soil Types

    0

    1

    2

    3

    4

    5

    6

    7

    8