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Ms Elizabeth Thayer <br /> February 22, 1993 <br /> Page 3 <br /> a) Keep the water table from rising as a result of vapor extraction so that vapors can <br /> be withdrawn from the hydrocarbon-affected soil 1 to 2 feet above the current water <br /> table, and <br /> b) Recover and treat hydrocarbon-affected groundwater from these wells, and <br /> c) Expedite remediation by extracting as little clean or upgradient water as is feasible <br /> Actual pumping rates will vary depending on water elevations in each well and the <br /> performance of TEX-1 <br /> All extraction wells will be plumbed to the treatment area by PVC piping placed below <br /> ground. The extracted groundwater will be treated by three 1,000 pound granular <br /> activated carbon (GAC) units connected in series, located in the treatment area as shown <br /> on Figure 1 <br /> Treated groundwater is to be discharged into the City storm drain system Piping from <br /> the treatment area to this storm drain located on Tracy Boulevard will be installed <br /> . underground, as shown on Figure 1 <br /> Breakthrough for each 1000 pound GAC unit is expected to be on the order of 30 days, <br /> assuming an annual average flow of 20 gpm, annual average total petroleum hydrocarbons <br /> (TPH) concentration of 20 parts per million, and 7% efficiency for the removal of TPH <br /> by the GAC units. (See sample calculation enclosed as Exhibit A ) The first two GAC <br /> wets will be replaced once breakthrough has occurred from both these units At that time, <br /> the third GAC unit will be switched to the first in the series, and the two new GAC units <br /> will become the second and third in the series. <br /> 3 Figure 1 shows the locations of the extraction wells. The flow path of the proposed <br /> discharge is shown on Figure 2 The storm dram runs north beneath Tracy Boulevard to <br /> Larch Road, then east on Larch Road to a storm dram ditch, then north into Sugar Cut, <br /> winch ties into Old River <br /> 4 The City provides water to the area within 0.5 mile of the site, and there are no City wells <br /> within that radius However, there are reportedly some private domestic wells along <br /> Clover Road and Larch Road west of the site that may still be in use The location of <br /> known wells is included as Exhibit B There are no surface waters within 0 5 miles of <br /> the site There was formerly a seasonal swampy area southeast of the site, which is <br /> shown on the map on Figure 2, however, this area has been filled m, and the swamp no <br /> longer exists <br /> Brown and Caldwell <br /> � <br /> onsuf La r-,IS <br />