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R&B Trucking <br /> Project No.01-37.1.1 <br /> March 27,1990 <br /> Page 3 <br /> 3.0 Geology and Hydrology <br /> 3.1 Regional Geology <br /> The geographical area in Tracy consists of quarternary fluvial sediments and <br /> flood plain deposits from the San Joaquin Delta to the north. The sediments are <br /> mostly silts and clays with interbedded sands and gravels. The shallower <br /> sediments are darker in color and have an odor typical of a reducing <br /> environment. The sands range from fine to coarse and the silts have a varying <br /> degree of clay matrix. The clays vary in degree of plasticity ranging from <br /> slight to highly plastic. <br /> 3.2 Site Geology <br /> The following information was collected by using a 2 inch(O.D.) modified <br /> California split spoon sampling device. Each 2 foot sample was visually <br /> observed and was screened for hydrocarbons using a photo ionization detector <br /> (PID). <br /> The geology at this particular site is characterized by clay that contains <br /> interbedded layers of sand. This site was studied from the surface to a depth of <br /> 25 feet. The geology of the site is summarized as follows: <br /> 0 to 8 feet-clay <br /> 8 to 11 feet-sand <br /> 11 to 15 feet-clay <br /> 15 to 19 feet-sand <br /> 19 to 25 feet-clay with interbedded sand <br /> The upper clay is dark brown and is moderately plastic(when rolled the clay <br /> was able to be formed into a firm thread). The strength of the clay is said to be <br /> firm. This upper clay contains an amount of moist,fine grained sand. It was <br /> noted that the upper strata(0 to 9 feet)of monitoring well 2 consisted of a dark <br /> brown,fine to medium grained poorly sorted sand that had a silt matrix. This <br /> may have been fill not native soil. <br /> The underlying moist sand encountered at 8 to 11 feet is fine to medium grained <br /> and contains an abundant clay matrix. From 11 to 15 feet a clay layer was <br /> encountered. This clay is light brown and has moderate plasticity. The <br /> hardness of the clay ranges from soft to firm and the moisture ranges from dry to <br /> wet. The drier clay is more friable(crumbles easily). It was noted at this <br /> depth that the clay contained fragmented hardpan. <br /> From 15 to 19 feet is a sand layer. This sand is dark brown and ranges from fine <br /> to coarse grain. It is poorly sorted and contains a clay matrix that decreases <br /> with depth. The clay layer encountered from 19 to 25 feet is interbedded with <br />