|
• Ozone Microsparge System Annual Status Report—Former Tosco(76)Statton No 6981, Stockton,California
<br /> March;2003 `
<br /> MtBE
<br /> Figures 3, 4, and 5 illustrate the MtBE concentrations from quarterly sampling and monitoring
<br /> events of December 2001 through December 2002 The MtBE concentration reported in MW-16
<br /> on December 12, 2001 was 250 ppb The last sampling results, on December 30, 2002, reported
<br /> the MtBE concentration in MW-16 as <2 0 ppb This is a decrease of 99% during the year The
<br /> MtBE concentration in VW-7 was reported as 33 ppb on December 12, 2001, and <100 ppb on-
<br /> December 30, 2002 MtBE has not been detected since July 2002 (detectton limits have varied
<br /> from 5 ppb to 100 ppb) in VW-7 suggesting that it is no longer present in VW-7, which represents a
<br /> greater than 84% decrease in MtBE The MtBE concentration in MW-7 was reported as 190 ppb
<br /> on December 12, 2001, and <2 0 ppb on December 30, 2002 This is a decrease of 99%
<br /> Historically, MtBE concentrations from the initial groundwater sampling events (7124196 in MW-7
<br /> and 8121199 in MW-16 and VW-7) to the most recent sampling event (12130102) have decreased by
<br /> over 99% in wells MW-7 and MW-16, and by over 80% in well VW-7 Additionally, maximum
<br /> MtBE concentrations have decreased from 320 ppb to <2 0 ppb in well MW-7, from 250 ppb to
<br /> <2 0 ppb in well MW-16, and from 510 ppb to <100 ppb in well VW-7
<br /> Monitoring Well MW-16
<br /> In MW-16, located downgradient of the former USTs, TPHg, benzene, and MtBE showed a large
<br /> decrease in concentrations Groundwater sample results from the quarterly monitoring program
<br /> reported TPHg, benzene and MtBE concentrations of 5,600 ppb, 160 ppb and 250 ppb,
<br /> respectively, on December 12, 2001, before the system startup December 30, 2002, sampling data
<br /> indicated TPHg, benzene and MtBE at <50 ppb, 0 53 ppb and <2 0 ppb, respectively These
<br /> concentrations represent a reduction of 99% for TPHg, benzene, and MtBE
<br /> DISCUSSION OF RESULTS
<br /> The ozone treatment appears to be effective at decreasing TPHg, benzene and MtBE concentrations
<br /> in groundwater Over the evaluation period, concentrations decreased by over 99% and 17%
<br /> (TPHg) in MW-16 and VW-7, respectively For the same time period, benzene concentrations in
<br /> groundwater have been reduced by 99% and 76%, respectively MtBE has decreased 99% in
<br /> MW-16, 99% in MW-7, and has not been detected in VW-7 since July 2002
<br /> Groundwater concentrations for TPHg and benzene for MW-7 have been below detection limits in
<br /> most cases since 1997 The sampling event on September 30, 2002 detected the highest
<br /> concentrations of TPHg and benzene since 1994 During the December 30, 2002 sampling event,
<br /> the concentrations have returned to below detection limits The September 30, 2002 sampling
<br /> event concentrations appear to be anomalous, and future sampling events will verify if the
<br /> September 30, 2002 sampling event concentrations were an anomaly
<br /> 140124 08
<br /> 4
<br />
|