Third Time’s a Charm (Third and Final Remediation of a Former MGP)

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Poster:

Third Time’s a Charm (Third and Final Remediation of a Former MGP)

Presenter:  Shawn Fiore (Haley & Aldrich, Inc.)
Authors:  Shawn Fiore (Haley & Aldrich, Inc.), Marc Okin (NiSource, Inc.)

Abstract:

The performance of three separate soil remediations at a 1-acre former MGP emphasizes the importance of a thorough subsurface characterization prior to remediation, even for an apparently “simple” MGP site.   This MGP operated between 1874 and 1927; former structures included four holders (including a Horton sphere), a retort building, a purifying facility, and a tar well, all removed prior to 1945.      A site characterization study, completed prior to 1995, indicated that MGP residuals were present in shallow fill and the underlying sand unit.  A clay confining unit underlying the sand prevented contaminant migration to an underlying outwash sand and gravel unit, used locally as a source of drinking water.   The extent of contamination appeared to be adequately delineated for the selected “dig-and-haul” soil remedy.    In 1998, a soil remediation encompassed almost the entire site, except for an area adjacent to buried utilities, including high pressure gas lines and excavation side-slopes.  Soil was removed down to the clay unit, but no shoring was used and some coal tar remained beneath the site utilities and fence line. The State regulator granted No Further Action status and a Covenant not to Sue for site soils in 2001.    A TarGOST® characterization program delineated the extent of MGP residuals remaining at the site and beyond.   Results indicated that MGP residuals had re-contaminated much of the footprint remediated in 1998.  The detection, via the TarGOST® program, of site contaminants in groundwater prompted a second soil removal action in 2010, during which it was discovered that the extent of remaining MGP residuals was greater than expected.     A final remediation performed in 2015 included relocation of buried utilities in the work area, remediation of remaining MGP residuals, and re-construction of the adjacent street.  Ongoing groundwater monitoring has shown generally positive results and final closure is expected in 2018.

 

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