ARCHIVED REPORTS XR0000133 - Laserfiche WebLink

Home Browse Search

I Regarding groundwater gradient and flow direction, Figure 3 presents a graphical interpretation of the data obtained by measurement of water levels in all monitoring wells and conversion of the depth-to-water measurements to Mean Sea Level (MSL) elevations The groundwater gradient is approximately 0 0067 feet per foot and the flow direction is generally toward the ' south and east. The flow direction is consistent with that most commonly observed at the site during previous sampling events ' With the flow direction generally south and east, monitor well MW-5 continues to provide groundwater quality data downgradient from the former tank site While low concentrations of benzene were seen in this well during the first three quarters of monitoring (October 1992 through March 1993), benzene has not been detected during the last two quarters which continues to indicate there is no discernable migration from the site ' Because the depth to groundwater varied significantly at the site over the history of the project and the relationship of groundwater depth to hydrocarbon residues in the soils is an issue of interest to potential future remedial activities, Figure 4 presents a chronology of MSL water ' levels at monitor well MW-2 Well MW-2 has been selected to represent water levels at the site due to its central location As shown by Figure 4, the groundwater level at the site steadily rose approximately 12 feet between October 1992 and June 1993. As the groundwater levels have been reasonably stable over the past three quarters at levels significantly higher than the lowest level recorded in late 1992, it is important to note that groundwater chemical concentrations have not increased along with the using groundwater levels This continuing lack of correlation adds confidence to the belief that either no hydrocarbons are bound up in the soils of the previously saturated zone or, ' if they do exist, they are not being mobilized 3.0 REMEDIAL PROGRAM STATUS As noted in the "Future Planned Activities" section of the 1st Quarter 1993 Report, continued ' future quarterly monitoring was anticipated to provide seasonal data on groundwater quality, depth and direction for the purposes of evaluating remedial needs The relationship between groundwater quality and depth is particularly important now that groundwater at the site has ' risen without producing higher chemical concentrations It is therefore increasingly unlikely that hydrocarbons are present or mobile in the previously saturated zone This data suggests that remediation of the previous saturated zone is unnecessary and that the primary environmental issue at the site is solely groundwater quality in a limited area near the center of the site San Joaquin County EHD has asked that feasibility work be conducted toward development of ' a remedial plan for the site by April 25, 1994 be conducted Planning is now under way to determine which issues, if any, need to be addressed 6 oviv9a ' STK RPTSIAREWQTR WP