ARCHIVED REPORTS_XR0007998 - Laserfiche WebLink

Home Browse Search

Updated Site Conceptual Model and First Quarter 2002 Monitoring and Remediation Report Cleanup and Abatement Order No 5-00-707 EAI Project No 1232 5.5 Analytical Testing Results 5 5 1 Units A and B Wells For Units A and B, similar or lower hydrocarbon concentrations were generally observed during this sampling event when compared to the prior quarters data Figure 17 summarizes the TPH-G, BTEX, and MTBE concentrations in ground water for the March 2002 ground ' water sampling event No MTBE, TBA, DIPE, ETRE, TAME, or EDB above laboratory reporting limits were detected in any of the ground water samples 5 5 2 Units C and_D Wells (MW-8D, MW-23S/D, and MW-24S/D) Similar or lower hydrocarbon concentrations were generally observed during this sampling event when compared to the prior quarters data The exceptions were wells MW-23S and MW- 23D, where significantly higher concentrations of hydrocarbons were observed (see Table 1) Well MW-23S was selected for deep air sparging on the Unocal site Sparging on well MW- 23S was performed on February 20, 2002, approximately 10 days prior to a ground water monitoring event All other air sparging wells on Unocal and Montgomery sites were cut off the air sparging header to allow the compressor to develop the pressure sufficient to overcome the column of water above well MW-23S perforation (approximately 60 feet) Sparging was performed for one hour at a compressor pressure discharge of 45 psig No increase in VOC held reading and analytical testing at the inlet of the oxidizer was observed Analytical results of ground water in wells MW-23S and MW-23D showed a sharp increase in the concentration of dissolved hydrocarbons, e g , <50 gg/L of TPH-G in December 2001 to 25,000 gg/L of TPH-G in March, 2002 for well MW23-S (see Table 6) Apparently, deep sparging resulted in mixing ground water in the vicinity of the sparging wells It is difficult to assess the affected area, however, using a rule of thumb that radius of influence is equal to the distance from the ground water surface to the sparging point, it is assumed that an area within a 60-foot radius was affected No further dee sparging will be conducted until after review and evaluation of ground water quality data from the next monitoring event in dune 2002 Based on these data, a recommendation regarding deep sparging will be made 5 5 3 Well MW-9 and Other Perimeter Wells In September 2001 and December 2001, down gradient well MW-9 contained TPH-G at concentrations of 1,070 gg/L and 58 gg/L, respectively In March 2002, the TPH-G concentration in this well was below the detection limit of<50 gg/L This indicates that the remediation system is able to contain the plume Further, the limits of the plume appear to be ' defined by perimeter wells MW-17, MW-15, MW-14, MW-13, MW-18, MW-27, MW-9, MW- 7 and MW-5 These sentinel wells will continue to be monitored to assure the plume is stable . and not migrating BHM 1232RQ231 -10- ENVIRONMENTAL AUDIT, INC