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Fourth Quarter,2002 Quarterly Groundwater Monitoring Report <br /> L= Eckert Cold Storage,Manteca,California <br /> January 10,2003 <br /> Page 2 <br /> �.., Summary of December 9,2002 Quarterly Groundwater Monitoring Event <br /> ✓ Field Activii _ <br /> Number of monitor wells 8 Number of monitor wells sampled 7 <br /> Number of domestic wells 1 Number of domestic wells sampled 1 <br /> Date(s)monitored and sampled 1219/02 <br /> Site Hydrology <br /> Average depth to groundwater below 18.73 ft bgs Average increase(+)/decrease(—)in -1.96 feet <br /> monitor well measuring points depths to groundwater since lasts lin (shallower) <br /> A roximate Voundwater flow direction Northwest <br /> Groundwater Contamination <br /> Wells containing free product None Wells with petroleum hydrocarbon 3 <br /> odors noted <br /> Number of wells with concentrations 3 Number of wells with concentrations at 5 <br /> below MCLS for any reported or above MCLS for any reported <br /> contaminant contaminant <br /> Nature of contamination: BTEX, Range in concentrations: <br /> La TPH-G, Benzene(pg/L) <0.5—1,900 <br /> Oxygenates Toluene(,ug/L) <0.5—8.2 <br /> /Additives Ethyl Benzene(pg/L) <0.5—160 <br /> Total Xylenes(µg/L.) <1.0--400 <br /> +� TPH-G(mg/L) <0.05—7.7 <br /> MTBE(µg/L) <0.5—13 <br /> 1,2-DCA(pg/L) <0.5—18 <br /> Tert butanol <0.5 -190 <br /> FIELD OBSERVATIONS <br /> .,,we No separate phase petroleum was noted in the wells, but a strong petroleum odor was noted in <br /> groundwater recovered from MW-1 and MW-8; a slight petroleum odor was noted in MW-3; and a <br /> moderate "earthy" odor was noted in MW-7. A broken sheen was observed in the groundwater purged <br /> from MW-1. Field observation sheets are included in Attachment B. <br /> GROUNDWATER ELEVATIONS <br /> The average groundwater elevation was approximately 1.96 feet higher on December 9, 2002 than the <br /> i" previous sampling event conducted on September 30, 2002. The groundwater elevation contours (Figure <br /> 3, Attachment A) estimated from the depth to water measurements indicate the groundwater gradient was <br /> generally towards the northwest on December 9, 2002. <br /> Historical groundwater data collected by WHF, Inc. (previous consultant) indicates a highly variable <br /> gradient at the site. Review by Condor of historical groundwater gradient information provided by WHF <br /> indicates there are potential inconsistencies in the data and possibly components of the interpretation of <br /> those data, especially related to MW-5 measurements. However, Condor agrees that the general historical <br /> groundwater gradient is predominantly towards the northwest at the site. The highly variable gradient at <br /> 60 the site may be related to domestic/supply well pumping both on site and off site. At times in the past, the <br /> water table slope has been very flat (very gentle groundwater gradient). When this occurs, any slight <br /> variability in groundwater measurements and the tolerance for error for the water level measurement <br /> devices can result in apparent groundwater elevation contours that are not particularly coherent. <br /> Therefore, when the water table at the site is relatively flat, it may be more representative to depict the <br /> groundwater gradient with a three-point construction using groundwater elevation data from three site <br /> monitor wells that circumscribe the site, allowing triangulation of the contaminant plume, including the <br /> contaminant source area. Consistent with this, Figure 4, Attachment A, shows the groundwater gradient <br /> direction and magnitude using monitor wells MW4, MW-6, and MW-7. On December 9, 2002 the <br /> La CON) OR <br />