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Date: June 14,2004 <br /> Quarter: 2nd Quarter,2004 <br /> ARCO QUARTERLY GROUNDWATER MONITORING REPORT <br /> Facility No.: 5450 <br /> Address: 1617 West Fremont Street, Stockton, CA <br /> ARCO Environmental Engineer: Paul Supple_ <br /> Consulting Co./Contact Person: URSNernon Elarth <br /> Consultant Project No.: 38466523.01-058 <br /> Primary Agency/Regulatory ID No.: San Joaquin County Environmental Health Department <br /> Assembly Bill 681 Status: Property owned by Atlantic Richfield Company <br /> WORK PERFORMED THIS QUARTER (Second 2004): <br /> 1. Performed quarterly groundwater monitoring and sampling. <br /> 2. Prepared and submitted quarterly groundwater monitoring report. <br /> WORK PROPOSED FOR NEXT QUARTER (Third 2004): <br /> 1. Perform quarterly groundwater monitoring and sampling. <br /> 2. Prepare and submit quarterly groundwater monitoring report. <br /> QUARTERLY RESULTS SUMMARY (Second 2004): <br /> Current Phase of Project: Monitoring <br /> Frequency of Groundwater Sampling: MW-2 through MW-4 sampled quarterly <br /> Frequency of Groundwater Monitoring: Quarterly <br /> Is Free Product (FP) Present Onsite: No <br /> Current Remediation Techniques: Natural attenuation <br /> Approximate Depth to Groundwater: 10.73—12.80 feet below ground surface (ft bgs) 1 <br /> Groundwater Flow and Gradient: North-Northwest @ 0.03 feet/foot (ft/ft) <br /> ANALYTICAL DATA REVIEW: <br /> Please note that as of April 1,2004, the laboratory has changed the carbon range for gasoline range organics (GRO) <br /> from C6 — C10 to C4 — C12 (to include the oxygenates). The resulting data may be impacted by the potential <br /> inclusion of additional total petroleum hydrocarbons as gasoline (TPHg) and non-TPHg analytes within the revised <br /> carbon range,which may result in a higher reported concentration. Where the resulting GRO concentration is based <br /> on a single analyte(i.e.,a non-TPHg analyte or a single TPHg analyte),the analyte will be identified if possible. <br /> Based on the review of the analytical and hardcopy data (chain-of-custody records, blanks, dilutions, holding times, <br /> LCS/LCSD results, MS/MSD results, and surrogate recoveries), the data are acceptable as reported by the <br /> laboratory. <br /> DISCUSSION: <br /> Gasoline range organics (GRO), benzene, toluene, ethylbenzene, and total xylenes (BTEX) were reported as below <br /> laboratory detection limits in all groundwater samples collected from site wells this quarter. Methyl tert-butyl ether <br /> (MtBE) was detected in MW-2 at 4.2 micrograms per liter(l.tglL),the lowest concentration reported historically,and <br /> in MW-4 at 0.54 pg/L. No other analytes were detected above method detection limits. <br /> KAWpr mVS BP ARC0054501Qumterlyl2 QTR 8415450 GWMR 2Q84.&c Page 1 <br />