Large-Scale Pilot Test for Remediation of Submerged Petroleum Hydrocarbons on a 1-1/2 Acre Pilot Plot at a Refinery Redevelopment Site

摘要

A large-scale (1(1/2) acre) pilot test was conducted prior to the preparation of a feasibility study for the remediation of shallow soil and groundwater at a former refinery in Southern California. An approximately 80-acres parcel is under consideration for redevelopment. Petroleum hydrocarbon (HC) impacts to soil and groundwater, including non-aqueous phase liquids (NAPL), have been observed. Due to rising water levels, most of the HC is trapped at depths down to 40 feet beneath the existing water table. An estimated 70% of the contaminant mass (including residual NAPL) is submerged. An additional constraint on potential remedial options is the predominantly fine-grained soils (silt-clay mixtures and very fine-grained sand). The following pilot studies were conducted to evaluate the efficacy of dewatering, soil vapor extraction (SVE), and air sparging (AS):rn1. The potential to dewater and expose additional contaminant mass for remediation was examined by continuous groundwater withdrawal over 1(1/2)V2 acres. Nineteen extraction wells on approximately 80-foot centers were pumped continuously for 7 months. Water table depression was monitored using multi-level piezometer nests and neutron logging.rn2. SVE was tested using various options: SVE from shallow vadose zone via a single well, multiple wells, and a horizontal well; and SVE from the dewatered zone via single and multiple wells. A network of 40+ multi-depth monitoring points was used to establish radius of influence (ROI) of each option and efficacy of contaminant removal.rn3. Pulsed AS into two very fine-grained sand layers was tested to evaluate the ability to deliver and recover injected air. Tracer gases, helium (He) and sulfur hexafluoride (SF_6) were used for the two sparged depths. Electrical resistivity tomography (ERT) was used to map changes in percent saturation within sediment in the sparged area.