PILOT MICROGRAVITY INVESTIGATION TO DELINEATE HIGH DENSITY TEL DNAPL

Past manufacturing processes at a southern New Jersey chemical manufacturing facility resulted in the release of multi-component Dense Non-Aqueous Phase Liquids (DNAPLs) to the shallow aquifers beneath the facility. These liquids included tetra alkyl lead compounds, e.g. tetra ethyl lead or TEL, historically used as anti-knock fuel additives in leaded gasoline. These compounds are toxic to unprotected workers and will persist as long-term sources of dissolved contaminants to groundwater plumes within the aquifer. Regulatory agencies require that, whenever possible, the site treat or recover DNAPL sources to reduce groundwater contamination. Challenges identifying and delineating TEL DNAPL source zones are substantial in terms of cost, technical ability to find elusive residual and pooled mass, and worker safety. Therefore, the site remediation team is evaluating non-intrusive means to safely delineate source areas quickly without the time and expense of drilling programs.

The aquifer impacted by TEL DNAPL is a 25-foot thick layer of alluvial quartz sand and gravel with lesser amounts of silt and traces of clay. Underlying the aquifer is a 10-foot thick layer of clayey silt which acts as an aquitard. It is known that pools of this high-density TEL DNAPL (specific gravity of 1.4 to 1.6) have penetrated the groundwater surface, migrated downward, and are now resting in undulations in the surface of the aquitard.

A microgravity geophysical investigation involves the precise measurement of the earth's gravitational field along a linear or grid pattern. Gravity variations occur at interfaces marked by a density contrast, including geologic layers, faults, fractures and subsidence zones. It is hypothesized that density differences created by the TEL DNAPL will be discernible through observed deviations in microgravity measurements. A pilot study utilizing microgravity was completed in December 2018. The pilot study consisted of the collection of data from two microgravity grids suggest anomalous microgravity readings that could be, but has not yet been confirmed, as indicative of density differences created by TEL DNAPL. Additional studies are proposed to further investigate these observations.