Acid Tar Lagoon Remediation I: Baseline Geo‐Environmental Characterization and Preliminary Stabilization/Solidification Mix Designs

ABSTRACT This paper reports on a US project‐based treatability study that describes the baseline geo‐environmental characterization and pH buffering of soil surrogates containing 20 (S2X) or 40 (S4X) percent acid tar by volume (where X denotes testing phase) and various stabilization/solidification (S/S) mix designs using powdered ladle slag (PLS), a 60/40 (w/w) blend of Type IL Portland Cement (PC) and Grade 120 NewCem (NC) slag cement, and bentonite (B) for some mixes. The soil surrogates reflected the expected in situ S/S (ISS) profile comprising an ISS rig working platform, residual tar, bottom lagoon liner materials, and shallow subsurface soils after the bulk tars are excavated for incineration. The total benzene content of the S41, S42, and S22 soil surrogates averaged 16,300, 24,000, and 10,568 mg/kg, respectively, with corresponding sulfur contents of 28,350, 93,500, and 43,500 mg/kg and pH values typically less than 0.5. EPA 1313 testing on the S41/S42 soil surrogates tracked the leaching of EPA target analyte list (TAL) metals over a range of pH and also indicated that it took about three equivalents of base addition to maintain pH conditions above 8 to ensure the long‐term stability of the ISS mixes. EPA 1316 M leaching of volatile organic compounds indicated that the S41, S42, and S22 media were characterized by benzene effective concentrations of 497, 406, and 318 mg/L, respectively. The S41 and S42 surrogates were extremely challenging to solidify, requiring 5 wt% PLS + 35 wt% PC/NC to exceed the relatively modest unconfined compressive strength (UCS) target of 276 kPa (40 lb/in 2 ). Regardless of UCS, most ISS mixes met the permeability criterion of less than 1 × 10 −6 cm/s. The minimum ISS reagent dose satisfying the UCS, K, and residual pH buffer capacity (3 meq/g) targets for 28‐day cured mix designs for the S22 soil surrogate was 5 wt% PLS + 30 wt% PC/NC + 0.5 wt% B. This was the minimum reagent dose proposed for long‐term leaching and field pilot testing.