Excavation of Source Material Near Adjacent Building



Excavation of Source Material Near Adjacent Building

Presenter:  Jennifer  Williams (AECOM)
Authors:  Jennifer Williams, Roger Beck and Mark McCabe (AECOM), Sidney Wuellner-Rice (NiSource)


The former MGP facility is located in Logansport, Indiana and encompasses approximately 0.63 acres in a commercial and residential area.  NIPSCO historically retained ownership of less than 0.2 acres on the eastern portion of the former MGP, which is currently a fenced, gravel covered lot containing a regulator station. In 2010, NIPSCO acquired the western 0.43-acre portion of the property, which included two commercial businesses, a pool supply store and auto body repair shop.  NIPSCO fenced the parcels and demolished the former buildings in November 2011.      To eliminate the potential for direct contact with MGP residuals in surface soils and to prevent the mobilization of constituents of interest exceeding Indiana Department of Environmental Management (IDEM) Remediation Closure Guide (RCG) screening levels to potential receptors through offsite migration of dissolved phase constituents, a targeted removal of MGP source material is proposed in conjunction with the use of institutional controls.  Due to the source area’s proximity to an adjacent building, the remediation will involve a setback and slope from the building during subsurface soil removal.       NiSource successfully negotiated with IDEM that the setback approach would address approximately 75% of the source material.  To address the remaining material, the adjacent building would require underpinning and present an unnecessary risk to the structure.  Shallow soil in the area will be excavated and stored on-site for future use as backfill.  The remaining excavation will be off-set from the adjacent buildings five feet and sloped at a ratio of 1.5:1 down to bedrock to protect those structures.  This will allow for the removal of approximately 1,300 cubic yards of impacted soil and saturated media, with approximately 300 cubic yards of impacted media remaining in the offset/sloped area.    Once the excavation is advanced below the water table, sumps will be installed to pump the water to an on-site treatment system, and pretreated by filtration through activated carbon for subsequent management at the publically owned treatment works under permit.  Additionally, residual source material is likely present within the bedrock.  As part of the site restoration, a network of piping will be installed on top of the exposed bedrock to facilitate the addition of chemical oxidation reagents should the soil remediation not be adequate to control the dissolved phase plume within the property boundary and additional treatment is required.

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