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' 16 December 2004 • AGE-NC Project No. 95-0137. Page 2 of 5 2.2. COLLECTION AND ANALYSIS OF GROUND WATER SAMPLES Water samples were collected from the purged wells using new disposable plastic bailers after ; allowing the wells to achieve a minimum 80%recoveryof the pre-purge water volume. Each sample was transferred into three 40-milliliter(ml)EPA-approved volatile organic analysis(VOA)vials and into one 1-liter amber bottle. Samples were properly labeled, stored in a chilled container and ' transported under chain of custody to Cal Tech Environmental Laboratories (CTEL) a California Department of Health Services (DHS)-certified laboratory. Each sample was analyzed for: • Total petroleum hydrocarbons quantified as gasoline-and diesel (TPH-g and TPH-d) in accordance with EPA Method 8015 Modified; and i • BTEX compounds and the oxygenating fuel additives: methyl tertiary butyl ether(MTBE), tertiary butyl alcohol(TBA),di-isopropyl ether(DIPE),ethyl tertiary butyl ether(ETBE)and tertiary amyl methyl ether (TAME), 1,2-dibromoethane (EDB) and 1,2-dichloroethane (1,2-DCA) in accordance with EPA Method 8260B. ' . 2.3. SOIL-VAPOR EXTRACTION REBOUND-RESPONSE TEST A full scale SVE and in-situ air sparging system had been in operation at the site since December 2000. During an approximately four-year remedial period, the petroleum-hydrocarbon concentrations in soil and ground water had declined to the point where utilizing the unit was no ' longer cost effective in terms of the remedial goals.Remedial operations ceased in January 2004 due to malfunction of the equipment; since a soil-vapor sample collected in Fourth Quarter 2003 did not have detectable hydrocarbon concentrations, the SVE equipment was not restarted. ' At the direction of the EHD, the SVE system was restarted on 05 October 2004 to perform a soil- vapor extraction rebound-response test. The system was monitored weekly for the first two weeks; then monthly during operation and after re-start events.During each monitoring event,the SVE flow ' rate, vacuum (potential) and concentrations of hydrocarbons in the extracted soil-vapor were measured and a soil-vapor sample was collected by AGE personnel. A magnehelic vacuum gauge ' was used to measure'the vacuum potential at the two inch influent line between the blower and extraction wells; the flow rate of extracted soil-vapor (influent) was measured using an direct measure flow meter. The organic vapor concentrations in the extracted soil-vapor stream was ' measured after the SVE blower using an organic vapor meter (OVM) equipped with a photo- ionization detector: PID (Thermo Environmental 580, 10.0eV, calibrated to isobutylene 100 ppb). Field measurements recorded are summarized in Table 4. 1 , ' Advanced Geo E nvi ron mental,Inc.