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 GSA, Oct. 7, 2008

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.

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” ( ) : Huge influx of closures (1,378  now in GIS Registry)

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?

Closures Reviewed 133 Sites from 45 counties Milwaukee, Brown and Dane had 34% of sites reviewed. Stratified-Randomly Selected Sites

DB Queries Monitoring Wells Total number of wells with GW data Median: 7 wells Remediation Soil Excavation?85 Yes Pump and Treat?33 Yes 38 sites (or 29%) implemented NO remediation.

Depth to Groundwater ≤10’

Highest Concentrations in GW Samples from the Database Sites 37 Sites (or 28%) have NO Naphthalene data!

HISTORICAL Maximum Benzene in Groundwater

CLOSURE Maximum Benzene in Groundwater

Median Time Interval: 3.5 yr for sites with active remediation 1.1 yr for MNA-sites

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?

10 Field Sites in the WI Closure Protocol Study Former Retail Station Non-Commercial Site Post-Closure Field Study

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.

Total BTEX Plumes Closure (Blue) Outline Post Closure Outline [Keller, 2005] [Greve, 2007] Closure Post-Closure

Groundwater flow variability Total BTEX Plume [Greve, 2007 ] Former Grandma’s Restaurant site’s plume axis shifted roughly 40°.

Benzene Maximums Red Post-Closure > Closure

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.

SI SI benzene detection (1991 to 1999)

Post-Closure P-C benzene detection ( ) Benzene Detections BTEX Plume

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? Let’s look further at the Naphthalene data.

Naphthalene Detections (at Water-Table Monitoring Wells)

Naphthalene Improvement? Red Post-Closure > Historical Max Yellow Improvement, but not by a factor of 10!

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.

Post-Closure Post-Closure BENZENE detection

Post-Closure Post-Closure NAPHTHALENE detections BTEX Plume

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 ~ < 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.