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May 2011 Project No. 1001-0343 a•.aoiaK a.wa activities. During the course of the pre-assessment site visit, Padre will demarcate the surface location of each proposed drill hole location with a painted white symbol. Immediately following the site visit, USA will be notified. As part of the notification, USA will be informed of the type of work planned, including the number of drill hole locations, and will be requested to identify all underground utilities in the vicinity of the Project Site that may be in conflict with the proposed drilling locations. 3.4 DRILL HOLE ADVANCEMENT Prior to the advancement of drill holes through the base of the 8,000-gallon UST, the following UST closure activities will be performed by others: • Remove remaining fuel from the UST; • Remove equipment(sump, fill port, etc.)to allow access for drilling rod; • Remove interstitial fluid and triple rinse interstitial space; • Triple rinse UST; • Inert UST(dry ice)and measure vapor levels; • Insert 4-inch PVC casing into each manway to the base of the UST; and • Introduce initial amount of 2-sack concrete slurry into the UST to secure the PVC casing in-place to create a drill hole conduit. Padre proposes to advance two vertical drill holes (DH-1 and DH-2)through the base of the UST to a depth of approximately 15 feet (2 feet into native soil material) to facilitate the collection of soil samples. Based on groundwater levels measured at a nearby( -650 feet west) LUST site (-650 feet west), Padre anticipates that groundwater will be encountered. The proposed drill hole locations are shown on Plate 3-Drill Hole Locations. The proposed drill holes will be completed by advancing 2-inch diameter direct push drill rod using Geoprobe drilling technology. The drill rod will be advanced through 4-inch PVC conduit placed inside the UST and subsequently through the base of the fiberglass UST. Undisturbed soil samples will be collected at each drill hole location in 5-foot continuous core liners. A conceptual plan of the drill hole advancement through the UST is shown on Plate 4 - Drill Hole Conceptual Plan. In addition to soil samples collected for chemical analyses, soil from each sampled interval will be retained for field screening and lithologic logging purposes. Field screening will be completed using a hand-held photoionization detector (PID). Soil classification will be completed by a Padre geologist in accordance with the Unified Soil Classification System (USCS). The soil samples selected for chemical analyses will be sealed, labeled, and preserved on ice in the field. Grab groundwater samples will be collected using either teflon tubing fitted with a check- valve, or using a new, disposable bailer lowered through %-inch PVC piping fitted a five-foot screened section. The temporary wells will be purged of approximately 0.5 to 1 gallon of water prior to collecting a sample. The groundwater samples will be transferred to appropriate sample 10.0343.TWP HSP assessment revised -4-