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Work Plan for Refined Plume Definition and Management of Floating Product-7500 W 11th St., Tracy,CA. Page 51 ,.., (quantified as Gasoline) Benzene EPA Method 8020 Toluene EPA Method 8020 �.. Ethyl benzene EPA Method 8020 Total Xylene Isomers EPA Method 8020 IRW 9,4.1.4 High-volume Extraction of Floating Product Following a minimum 24-hour delay after the cut-off trench has been excavated, a 5,000- gallon capacity vacuum truck will be used to evacuate floating product from the trench. The • floating product removal operation will be achieved using a 2-in, diameter, steel lance connected to the flexible intake hose of the vacuum truck. An experienced operator using this equipment can control the mixture of air and product drawn into the lance in such a way as to �— maximize the removal of floating product from the trench while, at the same time, reducing the intake of groundwater to a minimum. Plate 1 shows the equipment in use at the 7500 West Eleventh Street site when some 2,000 gallons of free product and emulsified LNAPL were removed from the water table in December 1998 (Dietz Irrigation 1999a). Plate 2 shows a similar operation that was used to remove large volumes of LNAPL from the water table beneath a remediation site in Emeryville, California. tW�� Because the cut-off trench is open and has large dimensions, the operator has a clear view of the suction end of the vacuum lance. She or he will be able to skim LNAPL from the water table in the open trench at a slow but steady pace so that the minimum practical amount of groundwater is extracted at the same time. When performed at the proposed scale, the process inevitably lowers the water table by a significant amount. This effect, however, is beneficial because, by causing draw-down, the process induces a steep flow gradient in the direction of the cut-off trench and, if skimming is performed slowly, a sizable zone of influence develops in all directions around the trench. Those hydraulic effects, in turn, cause floating product on the surrounding groundwater to flow toward the trench where it can be evacuated by means of the vacuum lance. An experienced and observant operator is able to adjust the rates of extraction of floating product and the degree of draw-down of the water table in the trench so as to achieve an optimal balance between the total of floating and emulsified free product that is extracted and the volume of groundwater that is transferred into the vacuum truck and requires off-site treatment and disposal. When the floating product extraction operation is complete, the vacuum truck will transport the pumped product to a permitted treatment facility where the fuel products will be `~ separated from the water and recycled in beneficial use. Initially, floating product will be suctioned out of the cut-off trench while the excavation remains open. It is expected that up to three repetitions of the floating product removal v SJC b-