Gowanus Canal Superfund Site. III: Leaching of In Situ Stabilization/Solidification Mix Designs

Abstract

An in situ stabilization/solidification (in situ S/S or ISS) field pilot was conducted in the Gowanus Canal on the manufactured gas plant (MGP) impacted sediments using 9 mix designs including 5%–10% by dry weight (wt%) type I/II Portland cement (PC), type V PC, and NewCem (NC) slag cement in various combinations. Naphthalene was the primary contaminant with total contents between 187 and 54,500 mg/kg and a median value of 1,320 mg/kg. A mobile nonaqueous phase liquid (NAPL) was observed in many of the untreated sediment samples. USEPA 1316 testing modified (M) for organics showed that 7 out of 9 untreated samples had naphthalene effective solubilities on the order of 11.5–14 mg/L and its leaching was solubility controlled. Leaching of S/S-treated samples using USEPA 1315M was completed using polydimethylsiloxane (PDMS) liner inserts and in both deionized (DI) and saltwater (SW) baths to compare the impact of simulated brackish conditions (approximately 22.4 g/L salt) on the leaching of volatile organic compounds (VOCs). The main differences were that the pH of the DI water bath was approximately 3–3.5 units higher than the SW bath but the conductivity of the latter was typically 30–50 times greater. Visible crusts were observed on all SW bath samples, the most significant crusts being associated with the lowest VOC leaching rates. Dissolved organic carbon (DOC) leaching was relatively unaffected by bath type. The naphthalene percent leaching reductions (% LRs) for the top five mixes (> 97% LRs) versus the untreated sediment were 5%–14% higher under SW conditions, presumably due to the surface crusts. The interval mass releases from the top 3 mixes under SW conditions were approximately100 times lower than the corresponding DI water bath values. Because 3 out of the top 5 mixes were the 60/40 (w/w) type V PC/NC blend, a minimum dose of 7.5 wt% of this blend was recommended for remedial construction.