Gowanus Canal Superfund Site. V: Evaluation of ISS Cylinder Sample Crusts Formed During EPA 1315M Testing

Abstract

The main purpose of treatability testing is to tailor a proposed remedial approach and related testing to site-specific conditions to ensure the maximum possible applicability of the bench-scale results at the full scale, and thus the success of the approach. One such adaption involves the use of modified (“M”) EPA 1315 tests to assess the leaching of volatile organic compounds (VOCs) under simulated brackish-water conditions to provide insights into the mass transfer rates that result from the in situ stabilization/solidification (ISS) of sediments at coastal sites heavily impacted by nonaqueous-phase liquids (NAPLs). As shown in this study, the use of saltwater (SW) baths during EPA 1315M testing can result in the formation of surface crusts on ISS samples and mass-transfer reductions in naphthalene, this effect being very pronounced in Gowanus Canal sediments. At the same time, the pH of the SW bath can drop from greater than 11 for a corresponding deionized water (DIW) bath to approximately 8, thus enabling biological activity. The newly formed ISS sample crusts (primarily aragonite and brucite) were similar in many respects to crusts that form on concrete under marine exposure conditions, based on mineralogical and x-ray-based analyses. However, surprisingly, while some SW baths were shown to be biologically active based on gene-probing analyses, petroleum hydrocarbon degraders, when present, did not necessarily reduce the observed leaching rates. The authors concluded that, while the surface crusts do appear to be associated with mass-transfer reductions, to varying degrees, remedial design should conservatively proceed on the basis of EPA 1315M tests utilizing DIW baths only, and any crusts potentially occurring under field conditions constitute an inherent benefit.