Excel provided technical consulting for redirection of a Remedial Investigation of mercury, lead, cadmium, and arsenic contamination in soil and groundwater at a former pharmaceutical manufacturing facility in central New Jersey. The work scope included an in-depth review of existing analytical, geochemical and hydrogeological data and design and implementation of a focused field investigation to address data gaps as necessary to technically support a natural attenuation proposal for groundwater coupled with the site-wide soil remediation being proposed by the client. Specifically, Excel completed the following:
- In-depth evaluation of mercury, lead, cadmium and arsenic concentrations in groundwater to document current and historic concentration trends in groundwater, including statistical analyses.
- Performed a detailed evaluation of the lateral and vertical distribution of metal concentrations in soil and evaluated the findings in comparison to the groundwater concentration trends and information regarding potential source areas.
- Verified soil stratigraphy across the site and prepared geologic cross-sections to graphically illustrate naturally occurring contaminant attenuation features.
- Assessed the site-specific relationship between metal concentrations in soil and groundwater through a detailed evaluation of the site-specific geochemical conditions in relation to the anticipated behavior of the various metals in the subsurface.
- Documented a statistically significant, pre-soil remediation, decreasing trend in mercury, lead, and cadmium concentrations which supported the natural attenuation argument.
- Designed and implemented a focused field investigation which included:
- Performance of soil borings with collection of soil samples for metals analysis from both the saturated and unsaturated zones as necessary to verify source areas,
- Conducted specialized soil leaching tests to evaluate the potential for impact to groundwater related to the leaching of metals from unsaturated soils,
- Collection of groundwater samples for metals speciation analyses to verify the form of the various metals in groundwater,
- Performance of in-line testing of groundwater for accurate quantification of groundwater geochemical and redox conditions,
- Conducted in-field measurements of reactive metals parameters for verification of laboratory analytical results.
- Based on an in-depth evaluation of the data generated from the focused field investigation, we determined that elevated arsenic concentrations in groundwater were attributable to the reducing geochemical conditions associated with biodegradation of organic contaminants, including benzene; and that restoring the subsurface to neutral and oxidizing conditions would effectively immobilize dissolved arsenic.
- The data also was used to verify the preliminary conclusion that mercury, lead, and cadmium concentrations in the soil and groundwater system had stabilized under pre-soil remediation conditions and that soil remediation to the NJDEP-approved cleanup levels will further reduce the potential for any impact to groundwater.
- The data were factored into the findings of the initial investigation to design a refined technical strategy for the remediation of metals in soil and groundwater, including specific recommendations for depth and extent of soil remediation.
Project Outcome: Project data support the conclusion that the proposed soil remediation will be protective of post-soil remediation groundwater quality for mercury, lead, cadmium, and arsenic. Post soil remediation groundwater quality monitoring will be used to verify the restoration of residual metal concentrations in groundwater to the applicable groundwater cleanup criteria via natural attenuation mechanisms. The data generated during the focused investigation have also been used to fine-tune the scope of bench scale and pilot scale testing of a soil washing system which will be used to treat contaminated soil excavated from the site prior to onsite reuse as backfill.