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'Ny <br /> � ////APEX <br /> 7844 Madison Avenue,Suite 106 - Fair Oaks,U 95628 <br /> E N V I R 0 T E C H , I N C , 1 800 242 5249 • Ph 916 535 0200 • Fax 916 535 0207 <br />' Aprii 2, 1999 <br /> Mr Jeffrey Wong <br /> San Joaquin County Public Health Services, Environmental Health Division <br /> 304 East Weber Avenue, Third Floor <br />' Stockton, California 95202 <br /> Subject Mass Balance for Remaining TPHg <br /> Colberg Boat Works <br /> 401 North Stockton Street, Stockton, California <br /> Apex Project No COL01 001 <br /> ' Dear Mr Wong <br /> Apex Envirotech, Inc (Apex), on behalf of Ms Lynn Swanson and Colberg Boat Works, is <br /> pleased to provide this report estimating the remaining mass of total petroleum hydrocarbons, as <br /> gasoline, in the soil and groundwater at Colberg Boat Works, located at 401 North Stockton <br /> Street, Stockton, California (Figure 1) <br /> This report is based, in part, on information obtained by Apex from Ms Swanson and Colberg <br /> ' Boat Works and is subject to modification as newly acquired information may warrant <br /> BACKGROUND <br /> Colberg Boat Works has been monitored quarterly for hydrocarbon constituents in the <br /> groundwater since July of 1997 On September 28, 1998, Apex prepared a Workplan For Pilot <br /> Test and Feasibility Analysis which proposed using magnesium peroxide socks placed in <br /> monitoring well MW-3 Magnesium peroxide introduces dissolved oxygen into the groundwater <br /> to stimulate removal of hydrocarbons On January 20, 1999, Apex submitted an Addendum to <br /> Workplan For Pilot Testing and Feasibility Analysis which modified the previous workplan and <br /> called for injection of magnesium peroxide utilizing direct push technology This method would <br /> allow greater amounts of magnesium peroxide to be used and it would cover a wider area <br /> Mr Wong has requested that a mass balance be completed for the remaining TPHg constituents <br /> before Apex proceeds with the ORC injection The letter requesting this mass balance <br /> estimation is included as Appendix A <br /> MASS BALANCE OF RESIDUAL TPHg <br /> In order to calculate the total amount of TPHg remaining at the subject property, it is necessary <br /> • to calculate remaining TPHg in both the soil and the water Soil sampling performed during the <br /> installation of the six monitoring wells was used to determine the mass of TPHg in soil T <br /> only hydrocarbon impacts to soil were detected at 15 feet below grade (bg) in soil born -3 <br />