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Analyses performed by Exelchem identified elevated concentrations of hydrocarbons in the samples
<br /> collected from MW-1 (6,700 ppb gasoline, 162 ppb benzene, 262 ppb toluene, 618 ppb ethylbenzene, and
<br /> 699 ppb xylenes), MW-3 (177 ppb gasoline, 34.3 ppb benzene, 8.7 ppb ethylbenzene, and 2.7 ppb xylenes),
<br /> MW-4 (1,810 ppb gasoline, 352 ppb benzene, 3.0 ppb toluene, 214 ppb ethylbenzene, and 11.1 ppb
<br /> xylenes), and MW-5 (1,490 ppb gasoline, 191 ppb benzene, 4.1 ppb toluene, 95.3 ppb ethylbenzene, and
<br /> 57.2 ppb xylenes). Lower concentrations of hydrocarbons were found in the samples collected from MW-2
<br /> (57 ppb gasoline), MW-6 (94 ppb gasoline, 6.0 ppb benzene, 2.1 ppb ethylbenzene, and 1.5 ppb xylenes)
<br /> and MW-9 (69 ppb gasoline and 1.7 ppb benzene). Hydrocarbons were not detected in the samples
<br /> collected from MW-7, MW-8, and MW-10. Low concentrations of MTBE were detected in the groundwater
<br /> samples collected from MW-2 (0.7 ppb), MW-3 (1.1 ppb), MW-4 (18.5 ppb), MW-5 (7.3 ppb), and MW-6 (1.1
<br /> ppb); however, it was not detected in any of the other samples. TBE, DIPE, ETBE, and TAME were not
<br /> detected in any of the samples.
<br /> The highest concentrations of hydrocarbons appear to remain onsite in the vicinity of the pump islands (MW-
<br /> 1) and sidegradient of the former tank bed (MW-4, MW-5). When compared to the April 1999 sampling
<br /> event, hydrocarbon concentrations increased in MW-1 while they decreased in MW-2, MW-3, and MW-5.
<br /> Hydrocarbon concentrations remained relatively unchanged in each of the wells. Changes in hydrocarbon
<br /> concentrations are most likely a result of groundwater elevation fluctuations. Additional monitoring data will
<br /> be collected to further evaluate the dissolved hydrocarbon plume.
<br /> Purge water generated during sampling activities was disposed of by Integrated Wastestream Management.
<br /> Remediation Activities—Third Quarter 1999
<br /> In August and September 1999, SECOR installed a vapor extraction/air sparging system at the subject site to
<br /> remediate hydrocarbon-impacted soils and groundwater. The system is expected to began operation in
<br /> December.
<br /> The vapor extraction system consists of ten wells (W-1 through W=8. MW-1 and MW-3) manifolded within the
<br /> remediation compound. Vapors will be extracted with a blower and destroyed with a catalytic oxidizer with a
<br /> destruction efficiency of at least 95%. The air sparging system consists of 4 wells (AS-1 through AS-1). An
<br /> air compressor will be used to introduce air into the sparging wells, and vapors would be recovered and
<br /> destroyed with the SVE system.
<br /> The following subcontractors performed services associated with the installation of the remediation system:
<br /> 1. California Utility Surveys. Performed utility locating services prior to well installation and system
<br /> operation
<br /> 2. V & W Drilling. Installed 4 air sparging wells to a depth of 90 feet bgs to 100 feet bgs for use in
<br /> remediation system.
<br /> 3. H2Oil Recovery Equipment. Supplied compressor for air sparging system
<br /> 4. Cornerstone Environmental. Installed system piping, constructed treatment pad, secured contractors
<br /> for electrical, gas, and telephone hookups for remediation system
<br /> Subcontractors to Cornerstone Environmental Included:
<br /> 1. Pacific Trench Safety Co. Provided trench plates for site safety.
<br /> 2. Harrington Industrial Plastics, Inc. Provided 1-inch diameter air sparging piping, couplings, and
<br /> fittings; 2-inch diameter vapor extraction piping couplings and fittings; and piping, valves, and connectors
<br /> for remediation system compound.
<br /> 3. West Genera. Provided sound panels for remediation system noise reduction.
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