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September 26, 1988 Harding Lawson Associates 17060, 006. 03 Mr. Hal Yiller The Southland Corporation Page 2 beneath the store could act as a conduit for gasoline and allow vapors to enter the building via sewers or other channels. With the approval of The Southland Corporation, we performed a vapor survey using three screening tools: the TIP-1, the Organic Vapor Analyzer (OVA) , and the Gastech. Each of these tools is calibrated to a different organic vapor and each instrument was used to measure the presence of volatile organic vapors at 12 locations at the site, of which five were inside the store and near conduits. Measurements were taken in the breathing zone and along the floor, as indicated in Table 1. See Plate 2 , attached for these locations. As measured by the OVA and the Gastech, concentrations were nondetec,::able in all_Ipcations in and around the store except a: one point near the pump island (the reading was taken while gasoline was being dispensed to an automobile) . The TIP Leasured very low concentrations, i.e. , below . 5 parts per million (ppm) , within the parking lot, and 4 . 5 and 14 ppm at the pump island while product was being dispensed. Within the convenience store, the TIP recorded very small concentrations of vapor ( . 1 and . 2 ppm) , near the cash register. In the storeroom at the back of the convenience center, the TIP measured concentrations of 0. 5 and 7 . 0 ppm. Because the storeroom was being cleaned at the time of our survey, we believe that these vapors were associated with the cleaning products. In addition, the store's front door was left open for one hour before our survey. We conclude that no significant vapors are migrating into the store from below the concrete slab. Another concern of Mr. Boggs, as stated in his draft letter, was the concentration ( . 1 ppm) of total petroleum hydrocar- bons (TPE) as gasoline measured in monitoring well MW-14 . This well had nondetectable concentrations of benzene, ethylbenzene, toluene, and xylenes (BTEX) . To investigate the presence of TPR, Mr. Boggs would require additional shallow ground-water monitoring wells between MW-2 and MW- 12 . MW-14 is the only well north of the convenience store with any detectable fuel constituents. To confirm that the TPH finding was an anomaly, and not related to the fuel con- stituents in ground water south of the convenience store, HLA purged and resampled MW-14 on September 15, 1988 . The latest results indicate no detectable concentrations of BTEX