ARCHIVED REPORTS_2019 SOIL MGMT PLAN (JULY-REVISED)

Home Browse Search

22 February 2019 AGE-Project No. 14-3154 Page 6 of 12 6.2. HYDROGEOLOGIC SETTING The site and surrounding area lie within the San Joaquin Valley Groundwater Basin, Eastern San Joaquin Subbasin (5-22.01). This subbasin is bound on the south, southwest, and west by the Modesto, Delta-Mendota, and Tracy Subbasins, respectively, and on the northwest and north by the Solano, South American, and Cosumnes Subbasins. The Eastern San Joaquin Subbasin is drained by the San Joaquin River and several of its major tributaries namely, the Stanislaus, and Calaveras, and Mokelumne Rivers. The San Joaquin River flows northward into the Sacramento and San Joaquin Delta and is discharged into the San Francisco Bay. Annual precipitation within the subbasin ranges from about 11 inches in the southwest to about 25 inches in the northeast. Generally, the subsurface of the subject property consists of silts and silty sands from the surface to 10 feet bsg, then grades into fine to medium sands at approximately 10 feet bsg and extending to 20 feet bsg; groundwater at the subject property is encountered in the fine to medium sands. Based on groundwater data collected between May 2015 and November 2018 from monitoring wells located on Parcel A (W-1R through W-8), groundwater has been encountered between approximately 12 and 16 feet bsg; and the groundwater flow direction has varied toward the northeast to the south at low (0.0004 ft/ft) to moderate (0.02 ft/ft) hydraulic gradients. During 2017 and 2018, groundwater flow direction has been consistently towards the south and southwest. Locally, groundwater flow direction in the southeasterly portion of the subject property may be affected by the current groundwater extraction remediation being performed at the adjacent JR Simplot property. The property is located at an elevation of approximately 15 feet above mean sea level (MSL), in an area of low topographic relief and regional groundwater flow and slope of the area is toward the general southwest, which is consistent with the overall groundwater flow direction inferred at the site and in the area. There are no surface water features on the property. The nearest surface water feature in the vicinity is the San Joaquin River located approximately 1.5 miles to the west. 6.3. SOLID WASTE AND IMPACTS Following excavation and removal activities within the WU1 area on Parcel A, verification samples will be collected to confirm solid waste was removed to below acceptable screening levels and the soil is not impacted above acceptable screening levels. 6.4. SOIL-GAS IMPACTS Soil-gas samples have not been collected from disposal area WU1 at Parcel A. However, soil-gas samples were collected beneath WU1 at Parcel B. An evaluation of soil-gas