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Morita Brothers 10 May 6, 1992 <br /> a,-which integrates the geology, the location of the former tanks and dispensers, and <br /> ' the distribution of gasoline hydrocarbons in the subsurface to yield an <br /> interpretation of limit of gasoline hydrocarbons in excess of RWQCB recommended <br /> guidelines (Figure 3) <br /> 3 3 Hydrogeologv <br /> The San Joaquin Valley is filled with up to six vertical miles of sediment Fresh <br /> groundwater is produced from wells tapping confined and unconfined aquifers <br /> found above and below the Corcoran Clay of the Tulare Formation The Corcoran Clay <br /> acts as the main confining layer in the San Joaquin Valley Groundwater with <br /> ' higher salinities can be found both above and below the Corcoran Clay Salinities in <br /> the groundwater below the subject sight are within potable drinking water <br /> ' guidelines Groundwater flow is from the valley flanks to the axis and then north <br /> towards the Sacramento Delta Locally, the depth to groundwater is approximately 80 <br /> feet and general groundwater flow direction is north-northeast This direction is <br /> away from the San Joaquin River Delta which is acting as a source of recharge due to <br /> ' the drawing down of the aquifer by municipal water supply wells in the city of <br /> Stockton <br />' 3 4 Soil Vapor_„Monitoring <br /> Soil samples collected during: drilling were monitored with a photo-ionization <br />' detector (PID) to evaluate organic vapor concentrations The PTD was calibrated with <br /> an isobutylene standard of 100 parts per million (ppm) and contained an It 8 <br /> electron volt (eV) lamp, capable of detecting benzene (9 25 eV) Table 3- Soil Organic <br /> Vapor Concentrations, graphically presents the PID readings Appendix A - Boring <br /> Logs, presents the PID readings as they were recorded in the field <br /> EB-81p1_2 9204-EO44 RPT <br />