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Well Destruction Work Plan Advanced Environmental Concepts, Inc. V CONSTITUENT TPH-G MTBE BENZENE TOLUENE ETHYLBENZENE XYLENES ' �pf L.,...;r g L.'P r,?erg:•.•?u::F:ny SAMPLE I.D. ..# ?..:, .x..,..."£a..ur;. a:.as�:•.}. � .a.} w.��. a3' u: �:...".+`'.`:.r}'..ki?t�,�}C�r'4"•:,•.+: ¢• �d '{�{fb'.•L9{ Ja•' �e/i l A L. a •.}y:`: J-1,2,3,4 ND ND ND ND ND ND v.. DETECTION 1.0 .005 .005 .005 .005 .005 LIMIT I --J The floor of the excavation was covered with a 1-foot thick layer of drain rock and then backfilled with the clean material which had previously been removed from the "borrow pit"during construction of the treatment cell. In order to evaluate the groundwater condition beneath the property following completion of the remedial �. excavation and to calculate the hydraulic gradient beneath the site, a total of 3 groundwater monitoring wells were installed,developed,and sampled in accordance with AEC's August 1998 "Confirmation Water Sampling Work Plan". San Joaquin County approved the workplan prior to implementation and provided oversight of the procedures. The following sections describe methods and procedures performed and results of laboratory analyses of samples collected during the post-remedial excavation groundwater assessment(Figure 2). Soil and water samples were analyzed by Baseline On-Site Analysis, a California certified analytical laboratory located in Huntington Beach, for TPH-gasoline, MTBE, and BTXE according to EPA methods 8015 modified and 8020, respectively. On November 5, 1998,AEC performed a second round of sampling. Mr. Mike Infurna, SJCEHD was present to witness this sampling event. Once again, the three wells were purged of a minimum of four casing well volumes. Measurements of pH,temperature, and conductivity were recorded and depth to groundwater was measured. Based on the above stated work and subsequent laboratory results the following findings were made: • Based on the results of laboratory analyses of sail samples collected during the assessment phase, the vertical extent of gasoline contamination within soil was delineated between 4 and 14 feet BGL. Groundwater sample analyses indicated the presence of concentrations as high as 28,900 parts per billion gasoline and 1,030 parts per billion benzene prior to the remedial excavation and backfilling procedures. Groundwater sample analyses performed after the completion of the remedial action ,r indicated no detectable concentrations of gasoline range petroleum hydrocarbons and trace to non detectable volatile organic compounds. • Petroleum hydrocarbon-impacted soil was excavated to a total depth of 13 to 20 feet SGL throughout the former UST emplacement area. Clean borrow fill material mined from an adjacent parcel was used to backfill the excavation,which was first lined with a minimum of one foot drain rock. • Ground water beneath the site was encountered between 12 and 15 feet BGL within the three assessment borings completed as monitoring wells. No gasoline-range petroleum hydrocarbons, and trace to non detectable volatile organic compounds were detected within samples collected and analyzed from these wells during September 1998, and November 1998. After reviewing the results,San Joaquin County Environmental Health Department (SJCEHD) agreed that the remediation actions were sufficient and that no further work was required. Site closure would be granted once Project: AEC 98V-1950 5 •ENVIRONMENTAL CONCEPTS WITH DESIGN IN MIND - 4400 ASHE ROAD.#206 • BAKERSFIELD.CA 93313 805/831-1546 FAX 805/831.1771 V