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Y E rJ AECOM
<br /> AECOM Environment 2��9
<br /> 10461 Old Placerville Road, Suite 170 e°,
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<br /> Sacramento,California, 95827-2508
<br /> T916.362.7100 F916.362.8100 www.aecom.com ENV,t;JNKf,EN I HEALI H
<br /> PE` 'M',J/SERVICES
<br /> ' April 8, 2009
<br /> Mr. James L. Barton
<br /> ' Central Valley Water Board
<br /> 11020 Sun Center Drive, Suite 200
<br /> Rancho Cordova, California 95670-6114
<br /> ' Subject: Quarterly Groundwater Monitoring and Remediation Status Report and Updated Site
<br /> Conceptual Model for the First Quarter of 2009
<br /> Cleanup and Abatement Order No. 5-00-707
<br /> ' 5400 and 5606 Pacific Avenue, Stockton, California
<br /> Chevron #306620 (former Unocal#5098)
<br /> AECOM Project#01231-154-OM19/M109
<br /> 1 Dear Mr. Barton:
<br /> ' AECOM Environment (AECOM), on behalf of Chevron Environmental Management Company(CEMC), is
<br /> submitting the Quarterly Groundwater Monitoring and Remediation Status Report and Updated Site
<br /> Conceptual Model for the First Quarter of 2009. This report documents first quarter monitoring activities
<br /> ' for the former Montgomery Ward, LLC (Wards) auto service center located at 5400 Pacific Avenue and
<br /> former Unocal Service Station#5098 located at 5606 Pacific Avenue, Stockton, California (Figure 1),
<br /> which are referenced collectively as the Site. Groundwater monitoring and sampling has been conducted
<br /> ' pursuant to requirements of Cleanup and Abatement Order(CAO) No. 5-00-707 issued to Wards, Unocal,
<br /> Surry California Limited Partnership, and Stone Brothers and Associated General Partnership (Stone
<br /> Bros.) on September 8, 2000 by the Central Valley Water Board (CVWB). The locations of former and
<br /> ' current site features and monitoring wells are presented on Figure 2.
<br /> Gettler-Ryan Inc. (G-R) was contracted by CEMC to perform the quarterly groundwater monitoring,
<br /> ' sampling, and report preparation for the Site. The first quarter 2009 monitoring event was performed on
<br /> January 7, 2009 with an additional event on January 17, 2009 to collect samples from MW-18D that were
<br /> inadvertently missed during the event on January 7, 2009. The G-R report is included as Attachment A.
<br /> ' Groundwater Level Measurements
<br /> Groundwater depth was measured and recorded for the following groundwater monitoring wells on
<br /> January 7, 2009: Hydrostratigraphic unit A/B-MW-1, MW-2, MW-3, MW-4, MW-5, MW-6, MW-7,
<br /> MW-9R, MW-10, MW-10A, MW-11, MW-12, MW-13, MW-14, MW-14A, MW-15R, MW-16, MW-17,
<br /> MW-18, MW-18D, MW-19S, MW-19D, MW-21S, MW-21D, MW-22S, MW-22D, MW-25S, MW-25D, AS-26,
<br /> ' MW-27, MW-28, MW-29, MW-30; Hydrostratigraphic unit C-MW-23S, MW-24S, MW-32; and
<br /> Hydrostratigraphic unit D- MW-8D, MW-23D, MW-24D, and MW-31. Included in Attachment A are the
<br /> groundwater elevation maps for hydrostratigraphic units A/B, C, and D, which are labeled in the G-R report
<br /> ' as Figures 1, 2, and 3, respectively. Groundwater flow in hydrostratigraphic unit A/B (Figure 1 of
<br /> Attachment A) is generally to the east at a variable gradient of 0.002 to 0.01 feet per foot(ft/ft), while flow
<br /> in hydrostratigraphic unit C (Figure 2 of Attachment A) is to the north-northeast at an average gradient of
<br /> 0.002 ft/ft. Groundwater flow in hydrostratigraphic unit D (Figure 3 of Attachment A) is to the north-
<br /> northeast at a gradient of 0.004 to 0.005 ft/ft. Tabulated results of depth to water(DTW) measurements
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