Groundwater Sampling & Conceptual Site Model – USEPA Region 3

This Potential Responsible Party (PRP) Group consists of 10 industrial and manufacturing companies identified by USEPA as having responsibilities for the landfill site—a former 60-acre sand-and-gravel quarry that was operated as a landfill from 1960-68 and received 1.9 million cubic yards of municipal and industrial wastes. (USEPA, 1998).

The landfill site is bounded to the west and north by railroad tracks and to the south and east by a creek, which eventually discharges to the Delaware River. The landfill has been studied extensively over the past 30 years. A pump and treat groundwater remediation system operated from 1992 until approximately 2008. Based on post-remedial groundwater monitoring results, in 2017 USEPA requested the PRP Group further investigate downgradient areas of the landfill site and develop an updated Conceptual Site Model (CSM). EHS Support was retained by the PRP Group to complete a scope of work that included four quarterly groundwater sampling events, vertical groundwater flow analysis in long screen monitoring wells, and the development of an updated CSM.

Based on a detailed review of groundwater sampling results and development of a preliminary CSM, the following data gaps were recognized:

  • Configuration of the groundwater flow system downgradient of the landfill
  • How, and to what extent metals are being removed by precipitation between the landfill and a residential drinking water wellfield?

To address these data gaps, EHS Support developed a Sampling and Analysis Plan (SAP) for USEPA review. The SAP included the following key tasks aimed at collecting additional groundwater geochemistry information to address the identified data gaps:

  • Oxygen/hydrogen stable isotope analysis in sitewide groundwater, the creek, and the Delaware River
  • Organic acid analysis in sitewide groundwater
  • Methane and carbon dioxide gas analysis in sitewide groundwater

It is expected that the SAP will be approved by the USEPA in early 2021 and sampling groundwater for the additional groundwater geochemistry information will be performed soon thereafter, in order to prepare a final CSM.


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