ARCHIVED REPORTS XR0011751 - Laserfiche WebLink

Home Browse Search

page 61 Werk P1nn far [ninon and Management of Floating product-7500 W 11th St., Tracy, CA. g ]le f ned Plume De f 9,4.2.3 Vacuum Extraction of LNAPL allon e week following installation of the three extraction wells, a 5,000-g Approximately on capacity vacuum truck will then be brought to the site to evacuate floating product from each. "— L will be skimmed from the water table using a 2-in. di=eter,vacuum tru truck' The LNAPL hOse Of track tip cut at 45 degrees, connected f clear o the flexible be tubing, which will eserve as a viewing port to will be equipped with a length o ped experienced operator using this permit identification of the type of fluid being pump exp 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 well while, at the same time, reducing the intake of groundwater into the truck. By performing the skimming operation slowly, a skilled operator can steadily draw LNAPL from the formation around the well onto the water surface in the well and suction it into the vacuum truck, while, at the same time, transferring a minimum volume of groundwater. — While this can be a challenging procedure when working in a 6-in diameter well, as opposed to an open excavation as was described in Section 9.4.1.4, the method is much more viable in a 6-in. diameter casing than is the case when using a 2-in. diameter well, where it is ^ essentially impossible to observe the exact location of the tip of the vacuum lance so that it can be properly positioned to achieve the desired effect. As was discussed in Section 9.4.1.4, the process of skimming LNAPL from the surface of groundwater by vacuum suction does lower the water table by a significant amount, but that draw-down induces a steep flow gradient in the direction of the extraction well and, if ^rte skimming is performed slowly, a sizable zone of influence develops in all directions around the well. This accelerates the rate at which floating product in the surrounding formation flows toward the well so more LNAPL can be removed over a given time period than is the case with skimmer systems that restrict drawdown to little more than the depth between the surface of the floating product and the LNAPL-groundwater interface. It is not economical to mobilize a vacuum truck to the site to extract less than 500 gallons of ,r LNAPL or groundwater from the extraction wells. If, at the time of any round of well , purging, the volume of floating product that can be extracted is less than that amount, `+ contaminated groundwater will be pumped from the wells to make up the difference. As was noted in Section 9.4.1.4, vacuum extraction of groundwater and direct shipment off-site for treatment is a very efficient means of accelerating groundwater remediation. When a round of free product skimming is complete and the wells have been allowed to come to equilibrium for at least 30 minutes, the thickness of floating product present in each well at that time will again be measured by the procedure described in Section 9.4.2.2 above. The vacuum truck will then transport the pumped product to a permitted treatment facility where the fuel products will be separated from the water and recycled in beneficial use. Note.: h If SJC has extensive experience in using vacuum extraction to remove floating •--r product from the surface of groundwater. We make no claims of first use of this SJC