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Ozone Microsparge System Pilot Test Status Report, Former Unocal Service Station#2859,Stockton,CA
<br /> June 6,2003
<br /> TPHg, benzene, ethanol, MtBE, tert-butyl alcohol, di-isopropyl ether, ethyl tert-butyl ether, tert-amyl
<br /> methyl ether, 1,2 -dicholorethane, or ethylene dibromide were not detected in wells MW-20 and MW-21
<br /> Groundwater Monitoring and Sampling
<br /> Quarterly groundwater sampling started in June 1988 Separate phase hydrocarbons have not been
<br /> observed in the wells Since monitoring of the wells began in the first quarter of 1993, groundwater
<br /> beneath the site has risen more than 20 feet The most recent monitoring and sampling event on February
<br /> 27 and 28,2003, depth to water in the wells ranged from 25 27 to 28 27 feet below top of casing During
<br /> this event, Groundwater flow in the shallow water-bearing zone was northeasterly at gradient ranging
<br /> from 0 01 to 0 03 Groundwater flow in the deep water-bearing zone during this event was southwesterly
<br /> at a gradient of 0 009 to 0 03
<br /> During the February 27 and 28, 2003 event, TPHg range hydrocarbons were reported in wells MW-11
<br /> (210 ppb), MW-15 (270 ppb), MW-2 (2,600 ppb), and MW-10 (47,000 ppb) Benzene was reported in
<br /> wells MW-15 (0 70 ppb), MW-11 (22 ppb), MW-2 (160 ppb), and MW-10 (2,100 ppb) MtBE was not
<br /> reporting in any of the site wells during the February 27 and 28, 2003 event
<br /> OZONE MICROSPARGE SYSTEM PILOT TEST
<br /> System Installation
<br /> As an interim remedial action measure, GR installed a C-SpargeTM system A C-SpargeTM system utilizes
<br /> ozone microsparging which is a process where by ozone is entrained in air and introduced into
<br /> groundwater The ozone is infected at low flow rates of 2-6 cubic feet per minute through specially
<br /> designed sparge points to create "microbubbles " As these microbubbles rise within the column of water,
<br /> volatile organic compounds (VOCs) are oxidized in the groundwater The current interim remedial
<br /> system is considered an ongoing pilot test to evaluate its effectiveness The system was operated
<br /> continuously except for brief down times due to mechanical failure
<br /> Eight ozone sparge points (SP-lA, SP-1B, SP-IC, SP-2A, SP-2B, SP-2C, SP-3A and SP-3B) were
<br /> installed at the Unocal site on March 4 through 8, 2002 (GR report#240072 06-2, Monitoring Well And
<br /> Sparge Point Installation Report, dated August 19, 2002) Based on the manufacturer's
<br /> recommendations, an approximate radius of influence of 20 feet for each point was used as design
<br /> criteria Three points were placed at a depth of approximately 30 feet bgs, three points were placed at a
<br /> depth of approximately 60 feet bgs, and two points were placed at a depth of approximately 90 feet bgs
<br /> The sparge point locations were chosen to introduce ozone into the areas of highest petroleum
<br /> concentrations, near the eastern property boundary of the Unocal site Sparge point locations are shown
<br /> on Figure 2 System operation started on August 14,2002
<br /> The C-SpargeTM system includes an ozone generator, air compressor, and a programmable
<br /> timer/controller Each sparge point has a dedicated line and is connected to the system by LDPE tubing
<br /> The LDPE tubing runs through Schedule 40 PVC conveyance piping for added protection
<br /> 240072 06 3
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