SU0004149 - Laserfiche WebLink

Home Browse Search

excavations which include the existing permitted Quarry Excavation permit for Teichert Aggregates (QX-91-5), and the existing and proposed expansion for a Quarry Excavation permit for Brown Sand (QX-94-1). The project site is also within the "Buffer Area" of the San Joaquin Kit Fox Habitat Conservation Plan (HCP). Geological Setting x t FThe project site and the surrounding area is underlain by an Alluvial Fan Deposit from the Holocene Age formed by Hospital Creek. The deposit is more than 150 feet in depth consisting of silty gravel interlaced with silty clay areas up to twenty feet in depth. Overburden consists of silty clay to an average depth of four feet. The Hospital Creek drainage is located in the Diablo Range southwest of Tracy, California. s� Flow in this drainage is confined to the winter and spring months and is historically dry during the summer and fall. The drainage has a steep hydraulic gradient and extends from the easterly slopes of Mt. Oso. The Alluvial Fan Deposit consists of sedimentary, metavolcanic, and ultramafic rocks with sand and clay matrix. The portions of the fan on this project have been sampled to a depth of 125 feet and were consistent with other borings in the area. Maximum size of the gravel was less than 18 inches. According to the proponent, the fine matrix of the deposit provides a dense and stable foundation for excavation slopes. The proposed project would extract the gravel from the fan deposit to a depth of approximately 125 feet. Bottom of the excavation would be 10 feet above the existing water table. Soil from striping and clay pockets found during excavation would be stockpiled for future use in the reclamation of the project. At the conclusion of the excavation, five feet of top soil and fines from the proposed settlement basins would be placed on the pit floor to bring it up to a finished elevation of 120 feet. There is no evidence of soluble heavy metals or other materials of a chemical nature that would contaminate surface runoff or groundwater. All wash water would be contained on the project site for recycling use. Hydrology The groundwater table depicted on the drill log of a well drilled on the west side of the property in 1991 showed the water table at a depth of approximately 135 feet. Quarry excavation would extend to 125 feet, which is ten feet above groundwater. No excavation would be done below the water table. The natural slope of the project site is to the northeast in the direction of the proposed aggregate processing plant location. Surface water drainage would be confined to the project site with no runoff to adjacent property. All wash water used in aggregate production would be recycled and confined to settlement ponds on the project site. Surface or process water would not be discharged from the project site. Fresh water to Draft Environmental Impact Report 3-4 ER-96-3