WORK PLANS - Laserfiche WebLink

Home Browse Search

05 August 2015 AGE Project No. 06-1463 Page 3 of 5 disposal from well destruction and other activities will be prepared and submitted to the Central Valley Regional Water Quality Control Board. MASS CALCLUATIONS AND TREND ANALYSIS As required by SJCHED directive letter (Appendix A), adsorbed and dissolved mass estimates were calculated using historical soil and groundwater analytical data (Tables 1 and 2). Adsorbed mass calculations were performed based on soil samples collected prior to implementation of corrective action at the subject site; post-remediation adsorbed calculations could not be performed, as confirmation soil samples have not been collected in previously known impacted areas at the site. Additionally, pre- and post-remediation dissolved mass estimates as well as groundwater trend analysis were also performed for the subject site. Mass calculations and trend analysis are described in detail below. PRE-REMEDIATION ADSORBED TPH-G MASS Based on soil samples collected to date, the site appears to be primarily impacted by total petroleum hydrocarbons as gasoline (TPH-g), benzene, toluene, ethylbenzene, xylenes (BTEX) and MTBE constituents. Constituents of concern appear to be located around the tank pit area and radiate generally to the north and east from the suspected release point (Figures 3 and 4). The adsorbed hydrocarbon impact is most concentrated surrounding the entire tank pit area. Based on soil analytical data collected to date, the adsorbed plume is most concentrated in both vadose and saturated soil located between 15 and 35 feet bsg (Table 1 and Figure 3). For modeling and mass calculation purposes the pre-remediation adsorbed hydrocarbon plume was differentiated by one constituent (TPH-g) and split into two different depth specific intervals (10 to 40 feet bsg and from 40 to 60 feet bsg). When the data is plotted in plane view, the estimated volume of the petroleum hydrocarbon- impacted soil (pre-remediation) yields approximately 5,945 pounds of TPH-g, which is equivalent to 951 gallons of gasoline. Mass/volume calculations are included in Appendix B. PRE-REMEDIATION MASS OF DISSOLVED PETROLEUM HYDROCARBONS Figure 5 depicts the estimated extent of the pre-remediation dissolved hydrocarbon plume in plane view. Utilizing this figure, the mass of dissolved TPH-g in groundwater was determined by splitting the groundwater plume into different isocontours based on concentrations reported during the groundwater monitoring event conducted prior to initiation of corrective action. Further, the mass was calculated using the screening depth of wells installed at the site (height equal to 20 feet). Advanced GcoF;nvironmental,Inc.