Retrospective Study of Closed Leaking Underground Storage Tank UST Sites in Wisconsin

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Retrospective Study of Closed Leaking Underground
Storage Tank (UST) Sites in Wisconsin

• A.M. Pelayo, T.A. Evanson, J.M. Bahr and M.E.
  Gordon
• Wisconsin Department of Natural Resources
• Bureau for Remediation Redevelopment
• aristeo.pelayo_at_wisconsin.gov
• GSA, Oct. 7, 2008

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What is Closure?

• State regulator agrees with request from
  responsible party that NO FURTHER ACTION is
  necessary.
• Closure involves proper abandonment (i.e.,
  filling and sealing) of all monitoring wells.

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Brief Administrative History Affecting WI UST
Closures

• Nov. 1996 Allowed flexible closure for sites
  that may still exceed state cleanup standards
• May 2001 Implemented web-based GIS Registry of
  Closed Remediation Sites (http//dnrmaps.wi.gov/i
  mf/imf.jsp?sitebrrts2)
• 1999-2000 Huge influx of closures
• (1,378 ? now in GIS Registry)

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Retrospective Study

• 1. Database
• Devised a stratified random sampling to select
  sites for review
• Compiled site-specific information (133 site
  reviews)
• Evaluated collective data for metric(s) to
  determine effectiveness of NA as a remedy
• 2. Post-closure fieldwork at 10 sites
• Did forecast prove to be true?

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Stratified-Randomly Selected Sites
ClosuresReviewed
133 Sites from 45 counties
Milwaukee, Brown and Dane had 34 of sites
reviewed.
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DB Queries
38 sites (or 29) implemented NO remediation.
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Depth to Groundwater
10
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Highest Concentrations in GW Samples from the
Database Sites
37 Sites (or 28) have NO Naphthalene data!
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HISTORICAL Maximum Benzene in Groundwater
10
CLOSURE Maximum Benzene in Groundwater
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• Median Time Interval
• 3.5 yr for sites with active remediation
• 1.1 yr for MNA-sites

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Synopsis Database Study

• Collectively, a factor of 10 reduction in maximum
  benzene concentration
• Short monitoring period, even shorter for sites
  that were not remediated

Will we see similar decrease 5 years post closure?
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Post-Closure Field Study
Former Retail Station
Non-Commercial Site
10 Field Sites in the WI Closure Protocol Study
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Post-Closure Investigation

• Installed monitoring wells
• Near locations where previous site investigation
  (SI) detected benzene
• Further downgradient than SI
• Used GeoProbe, except at 2 of the 10 sites. PC
  water-table wells had screens as long as SI
  wells.

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Total BTEX Plumes
Keller, 2005 Greve, 2007
Closure
Post-Closure
Closure (Blue) Outline
Post Closure Outline
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Groundwater flow variabilityTotal BTEX Plume
Greve, 2007
2005
Former Grandmas Restaurant sites plume axis
shifted roughly 40.
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Benzene Maximums
Red Post-Closure gt Closure
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Out of the 10 Field Sites ...

• We found 5 sites with benzene levels higher than
  their respective closure maximums.
• BUT ... We did not find benzene in as many wells
  as previously found for all 10 sites.

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SI
SI benzene detection (1991 to 1999)
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Post-Closure
P-C benzene detection (2005 - 2006)
BTEX Plume
Benzene Detections
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Q Did we miss the B plume in our Post-Closure
investigation?

• A Perhaps. But if we missed B, why are we
  finding TEX at locations farther than previously
  found?
• Lets look further at the Naphthalene data.

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Naphthalene Detections (at Water-Table
Monitoring Wells)
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Naphthalene Improvement?
Red Post-Closure gt Historical Max
Yellow Improvement, but not by a factor of 10!
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Post-Closure VOC Plume

• Characteristic has changed over time
• P-C benzene levels at the source wells about as
  high as closure max, but benzene plume more
  spatially constrained, tending to remain near the
  source.
• P-C naphthalene levels at the source wells as
  high as historical max, and plume extended
  farther from the source.

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Post-Closure
Post-Closure BENZENE detection
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Post-Closure
Post-Closure NAPHTHALENE detections
BTEX Plume
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Conclusion/Recommendation After the Study

• Contaminant concentrations in source zones are
  relatively unchanged 5 6 years post-closure.
• Unable to make realistic projections of when
  standards will be met in groundwater.
  (Monitoring lt 5 yrs Time to reach standards
  10s of Decades or Longer)
• Effective land use controls are needed far into
  the future to account for the long period of time
  contaminants are likely to remain in soil and
  groundwater.