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Ozone Microsparge System Pilot Test Status Report,Former Unocal Service Station#2859,Stockton,CA
<br /> June 6,2003
<br /> • The baseline TPHg concentration in well NP-1 was less than the reporting limit TPHg
<br /> concentrations in well NP-I were less than the reporting limit during the remainder of the test period
<br /> except on four occasions, as shown on Graph 4
<br /> Benzene Concentrations
<br /> • Benzene concentrations in MW-2 decreased from 2,500 ppb at test baseline to 55 ppb, as shown on
<br /> Graph 1
<br /> • On August 9, 2002, the benzene concentration in well MW-10 was 3,600 ppb (baseline) Within one
<br /> month of operation, benzene concentration increased to 8,800 ppb (9120102 sampling event)
<br /> Following the initial increase,benzene concentration decreased to 210 pbb,as shown on Graph 2
<br /> • As shown on Graph 3, benzene concentrations in well MW-11 decreased from 560 (baseline)to 0 90
<br /> ppb (2121103 sampling event) Following the decrease, benzene concentrations increased to 1,600
<br /> ppb on March 21, 2003
<br /> • Baseline benzene concentration in well NP-1 was below the reporting limit Benzene concentrations
<br /> in well NP-I were less than the reporting limit during the remainder of the test period except on four
<br /> occasions, as shown on Graph 4
<br /> Groundwater chemical analytical data through March 21, 2003 are included in this report (Table 1)
<br /> Groundwater chemical analytical data presented in this report collected prior to August 9, 2002 is
<br /> included in Appendix B Laboratory analytical reports and chains-of-custody documentation for the
<br /> monthly sampling are included as Appendix C
<br /> DISCUSSION
<br /> • During the most recent groundwater sampling event (February 27 and 28, 2003 event), petroleum
<br /> hydrocarbon concentrations were below laboratory reporting limits in the off-site wells MW-4, MW-
<br /> 5, MW-7, MW-8, MW-9, MW-17, MW-18, MW-19, MW-20, and MW-21 With the exception of
<br /> wells MW-2, MW-10, MW-11 and MW-15, petroleum hydrocarbon concentrations were below
<br /> laboratory reporting limits in the on site wells MW-1, MW-3, MW-6,MW-12, MW-13, MW-14, and
<br /> MW-16 during the most recent groundwater sampling event Groundwater analytical results are
<br /> graphically depicted on Figure 3
<br /> • During the most recent groundwater monitoring event,groundwater flow in the shallow water-bearing
<br /> zone was northeasterly at gradient ranging from 0 01 to 0 03 (Figure 4) Groundwater flow in the
<br /> deep water-bearing zone was southwesterly at a gradient of 0 009 to 0 03 (Figure 5)
<br /> • Sample results from wells MW-2, MW-10 and MW-11 indicate that the ozone microsparge system
<br /> appears to be effective as evidenced by the decreasing petroleum hydrocarbon concentrations All
<br /> three wells are within the estimated radius of influence of one or more sparge points The screened
<br /> intervals of wells MW-2, MW-10, and MW-11 are at approximately the same depth as the nearby
<br /> sparge points(depth= 30, 60, 90)
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