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Date: March 22, 2000 <br /> Quarter: 4099 ` <br /> ARCO QIiARTERLV GROUNDWATER MONITORING: REPORT <br /> 1-1ciht4 No.: 4493 Address 205 North Center Street, S'tockton, C'A <br /> ARC'() Lnvirowrwntal PnginGcr- Chuck Carmel <br /> COIINLJllln;l, U0. Contact Person I&VOR Intemationul Incorporated RustN Bcnkosky <br /> Consultant Projrct No.: 077.41819.007 <br /> Primary Agcncy'RUgUlaiory 11) No,: San Joaquin County knvironmental l Icalth Department <br /> Assembly Bill 681 Stains: Properly Owned by City ol-Stock-ton - — <br /> WORK PERFORMED THIS QUARTER ([Fourth Quarter - 7999): <br /> I. Conducted quarterly groundwater monitoring and sampling. <br /> 2. Prepared and submitted quarterly groundwater monitoring report. <br /> 3. Submitted work plan to the San Joaquin County Environmental Health Department for the investigation of the <br /> vertical and lateral extent of the 1VItBE plume. <br /> WORK PROPOSED FOR NEXT QUARTER (First Quarter-2000): <br /> 1. Conduct quarterly groundwater monitoring and sampling. <br /> 2. Prepare and submit quarterly groundwater monitoring report. <br /> 3. Perrorm vertical and lateral investigation ai'thc ;vlt3F plume. <br /> Q I;JART E ISL:' RES LILTS S UM MARY <br /> Current Phase of Project: _Mon itoring/Assessment <br /> Frequency of Groundwater Sampling: MW-1 through MW-4 are sampled quarterly. <br /> Frequency of Groundwater Monitoring: Quarterly <br /> Is Free Product(FP) Present On-Site:, No <br /> Current Remediation Techniques: Natural Attenuation <br /> Approximate Depth to Groundwater: 14.39 to 15.53 <br /> Groundwater Gradient: East @ 0.005 <br /> DISCUSSION: <br /> TPlIg was reported in one of the four wells sampled this quarter at a concentration of 7,830 ppb(MW-4). Benzene <br /> was reported in two wells sampled this quarter at a maximum concentration of 260 ppb(MW-4). MtBE was <br /> reported in two wells sampled this quarter at concentrations of 677 ppb (MW-3)and 1,310 (MW-4). TCE was <br /> detected in two wells sampled at concentrations of 37.6 ppb(MW-1) and 53.4 ppb(MW-2) (upgradient wells). <br /> PCE was not detected in any of the four wells this quarter. Concentrations were generally consistent with historical <br /> data. Groundwater elevations across the site decreased by an average of 2.83 feet this quarter and flow was easterly <br /> with a hydraulic gradient of 0.005 ft/ft. ARCO station demolition activities were completed in April 1999 and this <br /> i <br /> site is currently vacant. <br /> i <br /> i <br />