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AXOM
<br /> Mr. James L. L. Barton
<br /> Regional Water Quality Control Board -Central Valley
<br /> October 27, 2010
<br /> Page 2
<br /> MW-18, MW-18D, MW-19S, MW-19D, MW-21S, MW-21D, MW-22S, MW-22D, MW-25S,
<br /> MW-25D,AS-26, MW-27, MW-28, MW-29, and MW-30
<br /> Hydrostratigraphic unit C- MW-23S, MW-24S, and MW-32
<br /> Hydrostratigraphic unit D- MW-8D, MW-23D, MW-240, and MW-31
<br /> Groundwater elevation maps for hydrostratigraphic units A/B, C, and D are included as Figures 3, 4,
<br /> and 5, respectively. Groundwater flow in hydrostratigraphic unit A/B (Figure 3) is generally to the
<br /> east with an average gradient of 0.020 feet per foot (ft/ft), while flow in hydrostratigraphic unit C
<br /> (Figure 4)is to the northeast at an average gradient of 0.064 ft/ft. Groundwater flow in
<br /> hydrostratigraphic unit D (Figure 5) is to the southeast at an average gradient of 0.004 Wit.
<br /> Tabulated results of depth to water (DTW)measurements are included in Table 2, and well
<br /> construction details are included as Table 1. The groundwater elevations for third quarter 2010 are
<br /> consistent with those observed historically.
<br /> Groundwater Sampling and Analytical Results
<br /> Groundwater samples were collected on August 27, 2010, by G-R from the following monitoring wells:
<br /> Hydrostratigraphic unit A/B-MW-1, MW-2, MW-3, MW-4, MW-5, MW-6, MW-7, MW-9R,
<br /> MW-10, MW-10A, MW-11, MW-12, MW-13, MW-14, MW-14A, MWA5R, MWA6, MW-17,
<br /> MW-18, MW-18D, MW-19S, MW-19D, MW-21S, MW-21D, MW-22S, MW-22D, MW-25S,
<br /> MW-25D, AS-26, MW-27, MW-28, MW-29, and MW-30
<br /> Hydrostratigraphic unit C-MW-23S, MW-24S, and MW-32
<br /> Hydrostratigraphic unit D- MW-8D, MW-23D, MW-24D, and MW-31
<br /> As identified in the G-R field sheets (Attachment A), the monitoring wells were purged as noted on
<br /> each Well Monitoring/Sampling Field Data Sheet. Laboratory analytical results with chain-of-custody
<br /> (COC) documentation are included as Attachment B. Current and historical analytical results are
<br /> summarized in Tables 2 through 7. For total petroleum hydrocarbons as gasoline (TPHg) and
<br /> benzene,toluene, ethylbenzene, and total xylenes (BTEX)the data are presented in Table 2; volatile
<br /> organic compounds (VOCs) in Table 3; and additional VOCs detected in groundwater in Table 4.
<br /> Historical groundwater monitoring and analytical data are included in Tables 5 through 7.A data
<br /> validation checklist is included as Attachment C. The data validation found no discrepancies
<br /> resulting in questionable data.
<br /> The primary constituents of concern in groundwater beneath the Site are TPHg and benzene. Maps
<br /> showing the dissolved concentrations of TPHg in groundwater from hydrostratigraphic units A/B, C,
<br /> and D are presented as Figures 6, 8, and 10, respectively. Maps showing the dissolved
<br /> concentrations of benzene in groundwater from hydrostratigraphic units A/B, C, and D are presented
<br /> as Figures 7, 9, and 11, respectively. All monitoring wells were non-detect for 1,2-DCA during the
<br /> third quarter 2010. Charts depicting dissolved concentrations of TPHg and benzene versus time for
<br /> groundwater monitoring wells MW-2, MW-3, MW-4, MW-6, MW-8D, MW-11, and MW-25D are
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