ARCHIVED REPORTS_XR0011634 - Laserfiche WebLink

Home Browse Search

---------- ----------- Ozone ---------Ozone Microsparge System First Semi-Annual Status Report—76 Branded(Former BP)Facility No. 11195,Lathrop,California September 2 2003 OBSERVATIONS TPHg Concentrations Figures 4 and 5 illustrate the TPHg concentrations from quarterly and monthly sampling events of November 2002 through June 2003. The TPHg concentration reported in MW-3 and MW-10 on November 18,2002, prior to.the startup of the system were <500 parts per billion(ppb). The TPHg concentration has remained non detectable in MW-10. Since November 18, 2002, the laboratory has reported TPHg concentrations in MW-3 on three different occasions at concentrations of 320, 6,700, and 140 ppb. The laboratory reported that the discrete peak in each of these concentrations was at MtBE, and based on MtBE concentrations in MW-3, it is likely that a portion of the reported TPHg concentrations are a result of MtBE interference. Benzene Concentrations The benzene concentration reported in MW-3 and MWE-10 on November 18, 2002 was <5.0 ppb. Benzene has remained at non-detectable concentrations for the entire period covered by this.report. MtBE Concentrations Figures 4 and 5 illustrate the MtBE concentrations from monthly and quarterly sampling events of November 2002 through June 2003. The MtBE concentrations in MW-3 and MW-10 on November 18, 2002 were reported at 1,300 and 860 ppb,respectively. The last sampling results, on June 20, 2003, reported the MtBE concentration in MW-3 as 180 ppb. This is a decrease of 86% during the time period. In well MW-10, MtBE has declined from 860 ppb to 1.5 ppb, a reduction of over 99%. DISCUSSION OF RESULTS Initially, there were increases in hydrocarbon concentrations (MtBE and TPHg) in the groundwater in the immediate vicinity of the USTs. This is believed to be due to desorption of hydrocarbons from soil caused by the mechanical scrubbing action of the microbubbles. In terms of overall treatment, this desorption is necessary to achieve effective, long-term results. The ozone treatment appears to be effective at decreasing hydrocarbon concentrations in groundwater. Over the evaluation period, MtBE concentrations decreased by approximately 86% in well MW-3, and by over 99% in well MW-10. Although TPHg concentrations were detected in MW-3,the current TPHg concentrations are at low levels. The other monitoring wells at the site have demonstrated similar results after the first six months of treatment. Well MW-12 remains not detected for all analytes. Analytical results from wells MW-1, 140193.16 3