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3.0 PROBLEM ASSESSMENT The investigation has taken place in three distinct phases. Each phase began with new drilling, which was followed by a period of monitoring before the next phase of assessment was undertaken. The assessment is summarized below. 3.1 Phase 1--Groundwater Flow Direction The main objective of the first phase of the investig4tion was to identify the groundwater flow direction and measure the hydraulic gradient. Two monitoring wells were installed, making it possible to use the three-point method to map the hydraulic gradient and determine the flow direction. 3.1.1 Assessment Procedures and Results Monitoring wells KF-1 and KF-2 were installed in December 1994. Soils Exploration Service used a truck-mounted hollow-stem auger rig to drill both borings to a depth of 30 feet and construct wells using 4-inch diameter PVC casing. Groundwater was encountered at a depth of 18 feet, and screened well casing was installed from 30 feet to 15 feet. Soil samples were collected at 5-foot intervals, and three samples _(10, 15, and 20 feet) from each boring were retained for laboratory analysis. Boring logs were prepared for each well, and are included in Appendix A. After the well casings were surveyed, the depth to groundwater was measured and water samples were collected for analysis, and a hydraulic gradient map was constructed. The results were resented in the Fourth Quarter 1994 Report, which was submitted to PHS/EHD p Q in January 1995. The groundwater elevation data(Table 1) indicated that the general flow direction was due east, at a gradient of approximately 0.01 ft/ft. , Very little petroleum contamination ,was detected in any of the soil samples. The laboratory reported that TPH-g concentrations were below detection limits in all six samples and benzene was detected in only one sample, ata concentration of 0.01 mg/kg [parts per million (ppm)]. Toluene, ethylbenzene, and xylene were also either absent or detected at minimal concentrations (Table 2). All of these analytes were detected in the three water samples, with the highest concentrations in the original well (KF-3) that had been drilled in 1990 (Table 3). Groundwater concentrations were at least 100 times greater than soil concentrations, implying that groundwater contamination was the more serious concern. The wells were monitored Arid sampled again in March and October of 1995, and seasonal changes in contaminant concentrations were, reported (Table 3). During that time, the groundwater flow direction varied from east to southeast. In much of 1996 and 1997, financial difficulties intervened and monitoring and other activities were discontinued until the fourth quarter of 1997. The samples collected in late 1997 were analyzed for gasoline oxygenates as well as TPH-g and BTEX. Methyl- tertiary-butyl ether (MTBE) and tertiary-butyl alcohol (TBA) were detected in two of the three wells. Groundwater flow was northeastward at that time. 2