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09 August 2000 . . AGE-NC Project No.'95-0106 , Page 4 of 10 Contaminant Level (MCL)for drinking water. In general, the hydrocarbon concentrations in samples '. collected from monitoring well MW-4 fluctuate somewhat but.appear to be gradually declining over , time, Hydrocarbon concentrations in samples.from MW-I also fluctuate, appeared to decline up,to early 1999; at which time the concentrations rebounded; since that time, concentrations appear to have stabilized`or-declined slightly. The occurrence of TPH-g and BTEX in ground water encountered in an off-site; down-gradient well , (MW4) Indicates that dissolved hydrocarbons had migrated north of the site: The lateral extent of the impacted ground water around MW4 has not been delineated in all directions. The plume is ' generally constrained on the West-by monitoring well MW-5, on the northeast and east by MW-6 and. MW-3, respectively, and on the eastand south by MW-7_and.MW-2, respectively..However,-the plume is not'coristrained north and westf MW-4., AGE interprets the-data,to show that plume migration had reached its present extent at the time the monitoring wells were installed, and additional migration has not been detected since the.monitoring system was installed. The concentrations in MW-4 are probably declining as a result of natural Y ' attenuation processes affecting the"stabilized"plume. Hydrocarbon concentrations in samples from MW-I' may fluctuate more due to the well's close proximity to impacted soil left in place near the,farmer UST site. 2.5. STRATIGRAPHY Tan, silty clay soils-'were encountered from the surface to depths of approximately six feet bsg, in,,, each boring. Gray,'silty clay was encountered between six and"ten feet bsg during the installation of. the ground water monitoring well's and borings. ' Coarse sand.was locallyencountered below .the clay,-between 10-and 23 feet bsg" iri the borings Y' , established to that depth. Gravel occurred below the sand,from 23 feet bsg to-25 feet bsg, in boring' ' MW-6. Based"upon soil samples submitted for geotechnical analysis,'the upper clay layer appears to have . ' a lower permeability'than the saturated, sand and gravel locally.encountered below approximately . 10 feet bsg. Ground water is present in the sand, however it,appears that the clay immediately. overlaying 'the, sand may retard the vertical migration.'of ground water and hydrocarbons. A" I' stratigraphic cross section of the soils at the site;including the area of unsaturated impacted-soil, is depicted in Figure 3 - Stratigraphic Cross Section. . Advanced GeoEnvironmental,Inc.