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Ozone Microsparge System A0. nnual Status Report—Former 76 Station No 6981,Stockton,California <br /> Seiptember 2,2003 <br /> i <br /> Groundwater samples from MW-16 and VW-7 were analyzed for TPHg, benzene, toluene, <br /> ethylbenzene, and total xylenes (BTEX) and MtBE by- EPA Method 8260B Groundwater <br /> analytical results for the two wells are presented in Table 1 The complete laboratory analytical <br /> reports and chain of custody records for the monthly groundwater sampling covered by this report ti " <br /> are attached in Appendix B <br /> , <br /> OBSERVATIONS <br /> TPHg Concentrations <br /> ' <br /> Curretif TPHg Concentrations, <br /> Figures 3 and 4 illustrate the TPHg concentrations from quarterly and monthly sampling events of <br /> December 2000 through July 2003 . During the current reporting period (12130102 through <br /> 7122103), TPHg has increased from non detect (<50) on December 30, 2002 to 170 parts per billion <br /> (ppb)on July 22; 2003 in MW-16 The TPHg concentration in MW-16 during this reporting period <br /> fluctuated between'non detect and 240 ppb During the same reporting period, the TPHg <br /> concentration in VW-7 decreased from 24,000 ppb on December 30, 2002 to 3,500 ppb on July 22, <br /> 2003 This is an 85%decrease during the time period <br /> Historical TPHg ConcentrationG <br /> The TPH level reported in MW-16 on December 12, 2001, prior to the system startup, was 5,600 <br /> 3 <br /> ppbl The most recent sampling results, on July 22, 2003, reported the TPHg concentration in <br /> MW-16 as 170 ppb This reported concentration demonstrates a 97% decrease since the system <br /> was placed into operation The TPHg concentration reduction in VW-7 from 29,000 ppb on <br /> December 12, 2001, to 3,500 ppb on July 22, 2003 represents a 88% decrease over the same time <br /> period ,Historically, TPHg concentrations from the initial groundwater sampling events (8/21/99) <br /> to the most recent sampling event (7122103) have decreased by 91% in well MW-16 and VW-7 <br /> - Additionally, the maximum TPHg concentrations have decreased from 15,000 ppb to <50 ppb in <br /> well MW-7, from 5,600 ppb to 170 ppb in well MW-16, and from 37,900 ppb to 3,500 ppb in well <br /> VW-7 <br /> r , <br /> n <br /> 140124 08 <br /> 3 <br />