Remediation of TPH and MtBE Using Ozone Sparging, Under California'sPay-for-Performance Program

摘要

LACO ASSOCIATES chose an active service station in Crescent City, California, as our first project fundedrnunder the State of California's new Pay-for-Performance (PFP) program for the remediation of sorbed-phasernhydrocarbon contamination. LACO selected this project for the PFP program based on our experience with thernsite and 10 years of boring and monitoring well data. Additionally, the responsible party was interested inrnutilizing the State's program. The site has been a service station since the 1950s, and an environmentalrninvestigation has been under way since the USTs were upgraded in 1991. The investigation is under thernregulatory oversight of the California Regional Water Quality Control Board, North Coast Region. The resultsrnof soil and groundwater samples collected in borings and monitoring wells early in the investigation indicated arnsorbed-phase TPHg (approximately 700 kg) and dissolved-phase fuel oxygenate plume (approximately 5 kg andrn250 feet in length). Additionally, some residual NAPL was present on site. Later work determined that the fuelrnoxygenate plume probably flows towards, and possibly under, an unused domestic well. Our review of the datarnsuggested the presence of two distinct sources of sorbed-phase contamination; one is an older source ofrndegraded gasoline, depleted in benzene and MtBE, enriched in ethylbenzene and xylenes, and apparently relatedrnto the former tank cavities. The second source appears to be related to the pump islands. The TPHg is much lessrndegraded, and is relatively enriched in the volatile gasoline constituents. Sorbed-phase contamination has beenrndetected in borings immediately adjacent to a state highway, leading to the assumption that the plume extendsrnbeneath the highway. In fact, during the first three quarters of 2002, free product up to 0.32 feet thick has beenrnmeasured in a monitoring well within the highway right-of-way.rnA remedial action plan for the secondary sources was prepared for the site in June and approved in Augustrn2002, before the conversion of the project to PFP. After evaluating three potential remedial technologies, ourrnopinion was that ozone sparging was the most feasible for the desired 3 to 5 year timeframe. Additionalrnremediation for the groundwater plume will be planned later, if it is still necessary after the completion of thernPFP.rnThere were some logistical problems to overcome in the planning of this project. First, it is a relatively smallrnsite, at less than 14,000 square feet. Additionally, as the goal of the PFP program is soil remediation, we neededrna plan to remediate the secondary source from under the highway. A sparge well network was installed,rnconsisting of 16 microporous sparge points in 9 sparge wells. This is a proprietary technology, installed underrnlicense from K-V Associates. In order to remediate the sorbed-phase contamination under the highwayrneffectively, we installed three sparge wells at a 30° angle from vertical and equipped each with two individualrnsparge points, one at 20 vertical feet below ground surface (bgs) and one at 15 vertical feet bgs. The threernangled wells were installed with a hollow-stem rotary auger rig. The remaining six wells are a combination ofrndual-point and single-point wells and were installed vertically using a direct-push rig. Each sparge point isrnconnected to a port on one of the two master panels, each of which has an ozone generator. The connectionsrnwere arranged to allow control of the sparge points in the core of the plume independent of those in distal wells.rnThe system was installed in October and November 2002. Oxygen concentrators were added later to increasernthe saturation of ozone injected. The Preliminary Remedial Action Goals (PARGs), I.e., the remedial goals byrnwhich progress of the PFP will be gauged, were negotiated and baseline concentrations were determined byrncollecting duplicate samples with the regulatory agency. The split samples were analyzed by differentrnlaboratories and required an accuracy of within 100%. Performance monitoring was scheduled bimonthly forrnthe first quarter, monthly until the end of the third year, and quarterly for any additional time needed to meetrnPARGs.rnIn the first six weeks, before the oxygen concentrators were installed, TPHg concentrations in the core of thernolder secondary source decreased by 91% and TPHd concentrations decreased by 99.8%. After installation ofrnone oxygen concentrator, TPHg reduction was 95% and 99.98% for TPHd. Concentrations of BTEX