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rI During the week of May 9, 1997, URS Greiner, Inc. completed the PSI. The scope of the PSI included the drilling of 4 soil borings on the Nelson Ready-Mix site. Soil and groundwater-grab samples were collected for analysis from each of the 4 on-site soil borings. Soil and groundwater- grab samples collected from soil boring (SB-1), drilled on the west side of the former UST excavation, and from SB-2, drilled on the east side of the former UST excavation contained elevated concentrations of TPH-as-diesel. Concentrations of TPH-as-diesel in soil were reported as high as 6,000 mg/kg at a depth of 15 feet bgs. Concentrations of TPH-as-diesel in groundwater were reported as high as 590,000 micrograms per liter(µg/1). Benzene was also detected in groundwater at a concentration of up to 3.6 µg/l. Methyl tertiary butyl ether(MTBE) was not detected in any of the soil or groundwater-grab samples analyzed. The soil sample analytical results are summarized in Table 1 and the groundwater-grab sample analytical results are summarized in Table 2. On May 28 and 29, 1998, Wright Environmental Services, Inc. drilled 3 soil borings for soil and groundwater-grab sampling and 3 additional soil borings for soil sampling and the installation, development, surveying and sampling of 3 monitoring wells. During drilling, groundwater was first encountered between 13 and 19 feet bgs. Prior to groundwater purging and sampling, the static depth-to-groundwater ranged from 12.37 feet bgs in MW-2 to 13.25 feet bgs in MW-3. Following a wellhead elevation survey, the groundwater gradient was calculated at 0.00025 foot/foot in a northerly direction. The well construction details and groundwater monitoring data are included in Table 3. The highest concentration of petroleum hydrocarbons detected in groundwater during this investigation (13,000 µg/i of TPH-as-diesel, 2,800 µg/1 of TPH-as-gasoline and 2.2 µg11 of benzene) was in the groundwater-grab sample collected from SB-7, near the former UST. The groundwater sample collected from MW-1, located approximately 40 feet east of the former UST contained 2,000 µg/I of TPH-as-diesel and 420 µg11 of TPH-as-gasoline. MTBE was detected at 1.1 µg/l in MW-1 and at 0.65 µg/1 in MW-3. No other alcohol- or ether-based oxygenate compound was detected in any of the groundwater samples analyzed. The lateral extent of impacted groundwater was defined to the east of the former UST by MW-2 and to the south of the former UST by MW-3. The lateral extent was not defined to the east of MW-1 and to the north, under the State Highway 99 right-of-way. The results of the groundwater-grab sample analyses are summarized in Table 2 and the results of the groundwater monitoring well samples are included in Table 4. 3