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z- Geology and Hydrology of the Site A thorough geological Investigation was conducted on this property. it was accomplished by drilling a series of borings, all of them going to a depth of 16 to sixtean borings started, fifteen were completed. 17 feet. Out of Honing 5 was not completed because ground water was encountered at a depth of five feet. At that point the boring was abandoned and plugged with clay. The geology and hydrology of this property is controlled by an interplay of a several factors, including fill material used to level the property, leaking Irrigation pipelines, shallow ground water, and a bimodal distribution of sediment type, These factors will be discussed in detail below. The sediments studied during this project is characterized by two main types. Sand r,3 predominates in the upper 7 to 9 feet of soil, while clay predominates in the lower portion (down to 17 feet). The upper horizon tends to be well sorted, fine to medium grained, quartz rich sand, with interbeds of clay or clay rich sand (see the boring logs given in Appendix A). Usually the top 3 to 4 feet are are composed of fill material that was brought in years ago to level the property. This material is composed predominantly of sand, but also has clay, silt, and gravel and debris of various kinds idI (i.e., wood, metal, and concrete). An underground tank was also discovered. During soil s = borings this debris hindered the drilling progress, resulting in a longer drilling time. The lower portion of strata is a soft, moist to wet clay with a high sand content. Clayey sediments 1 to 2 feet above the ground water tend to be very moist due to capillary action. It is this clay rich horizon that has become discolored from the contamination. Apparently gasoline spread laterally on top of the ground water or capillary zone and has J been wicked through the sediments. Over time, microbial degradation of the gasoline has created a reducing environment in the sediments, resulting in the bluish gray color. Three cross sections are given to show the stratigraphic relationship of±he sediments (Figures 3, 4 & 5). The saturated zone is characterized by a very soft clayey sand or clayey silt. Often this sediment did not remain in the the sampling chamber, but would be pushed right out the top by stiffer sediments comingin from bottom. of this noa it was difficult to collect a representtivesol samplefrom e waterbearigstr t Typically the borings terminated at 15 feet. At the bottom of the boring we took a split spoon sample from was taken 15 to 17 feet. This sample was used for geologic purposes only, and not for tab analysis. The aquitard (or clay barrier) which supports this shallow ground water, has a lower sand content then the clay layer above the ground water, typically is stiff and well compacted, and has a low moisture content. The thickness of th€s unit was not investigated and was only penetrated by about 12 to 18 inches. —� Ground water was first encountered between 12.5 to 13 feet below the surface, This water layer should be classed as a perched aquifer because it is probably not part of the lower aquifer system. We expected this shallow water to be in low supply because it was late in the summer of a dry year. However, this perched water was In abundant supply. Leakage from the irrigation pipeline that runs diagonal across the back of the property is probably the source for recharging this perched water. Evidence that this pipeline r, leaks Is two fold: 1) the swampy nature of the_ground-surface just-to-the-north-side of --- - -- - ---the-properly-(Plate;1), an2) while drfll€ng boring #5, ground water was encountered --at 5 feet, the water level continued to rise in the bore hole until it was plugged with clay, 6