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1 Ell�yt® VIA ENSR International 10411 Old Placerville Road ` Suite 210 October 1, 2004 Sacramento,CA 95827-2508 ' HE FAX (916)362 8100 ' Ms Margaret Lagono OCC 0 4 2004 www ensr com San Joaquin Public Health Services ENVIRC��lE4v1 HEALTH 304 East Weber Avenue, 3rd Floor pERSAITISERVjCES ' Stockton, CA 95201-0388 RE Quarterly Groundwater Monitoring and Ozone Microsparge System Status Report, Third Quarter 2004 Former Unocal Station No 2859 ' 1665 Pacific Avenue, Stockton, California Dear Ms Lagono ' ENSR Corporation (ENSR) has been authorized by Union Oil Company of California (Unocal) to j prepare this report summarizing quarterly groundwater monitoring and the status of the ozone ' microsparging status through the third quarter 2004, for the site located at 1665 Pacific Avenue, Stockton, California (Figure 1) The work was performed in accordance with the field methods and procedures included in Attachment A The locations of former and current site features are illustrated on Figure 2 Groundwater Level Measurements ' Depth to groundwater measurements were recorded in monitoring wells MW-1 through MW-21, and in piezometer well NP-1 on July 6, 2004 (Table 1) Groundwater measurements from wells screened across water-bearing zone A (MW-1 through MW-11, MW-13, MW-15, MW-17, and ' MW-21) were used to construct the groundwater elevation contour map included as Figure 3 On July 6, 2004, the groundwater flow direction for water-bearing zone A was generally east- northeast with an average hydraulic gradient of approximately 0 003 feet per foot (ft/ft) with a ' second component of flow towards the southeast with an average hydraulic gradient of approximately 0 016 ft/ft Groundwater measurements recorded on July 6, 2004, from wells screened across water-bearing zone B (MW-12, MW-14, MW-16, MW-18 through MW-20 and ' NP-1) were used to construct the groundwater elevation contour map included as Figure 4 On July 6, 2004, the groundwater flow direction for water bearing zone B was divergent towards the north-northeast with an average hydraulic gradient of approximately 0 009 fV t and northwest with an average hydraulic gradient of approximately 0 0145 ft /ft Copies of the groundwater sampling ' information sheets are included in Attachment B A summary of groundwater elevations measured to date is presented in Table 1 ' Groundwater Sarnplina and Analytical Results Groundwater samples were collected July 7 through 9, 2004, from wells MWA through MW-21 and NP-1 The groundwater samples were submitted to California Laboratory Services (CLS) in Rancho Cordova, California for analyses of benzene, toluene, ethylbenzene and total xylenes (BTEX) by EPA Method 8021, and total petroleum hydrocarbons as gasoline (TPHg) by EPA J IProtectsy0694012859-3571FrnahReportsl3rd Qtr 04-QMR RSR12859 3rd Qtr 04-QMR RSR doc 35 Years of Excellence to Environmental Services