ARCHIVED REPORTS XR0009954 - Laserfiche WebLink

Home Browse Search

f Working to Restore Nature I 2_2 Regional Geology and Hydrogeology The site is underlain by the Modesto Formation, which is composed of alluvial sediments that range in size from silt to gravel (Marchand and Allwardt, 1977) The Modesto Formation dips gently to the west (Wagner, et al , 1981) The site is in the Eastern San Joaquin County Groundwater Basin (California Department of Water Resources, 1980) According to personnel of the San Joaquin Public Health Services, the direction of regional groundwater flow is to the southwest and the depth to . 105'groundwater ranges from 45 to 50 feet below surface grade (bsg) The groundwater basin has been developed for intensive irrigation, domestic, industrial, municipal, and stock use 23 Site Geology and H,Lgeoloey Sediments in underlY g the site from ground surface to approximately 66 feet bsg consist primarily of clayey silt with silty sand and fine- to coarse-grained sand lenses From 66 feet to approximately 78 feet bsg, the sediments consist predominantly of fine- to coarse-grained sand, with some layers of silt The interpreted subsurface conditions are shown on Plate 3 and Plate 4, Geologic Cross-Sections A-A' and B-B' The traces of the geologic cross- sections are included on Plate 2 During drilling, groundwater was encountered at approximately 61 to 68 5 feet bsg From October 1991 to November 1993, static water levels have fluctuated from approximately 60 5 to 66 feet bsg, variations in depth to water between the wells during each monitoring generally reflect topographic variations across the site The rise and fall of water in the wells during 1992 appears to be due to seasonal fluctuations Because groundwater has been measured as high as 60 5 feet bsg in the monitoring wells (well MW-1, March 31, 1992), the top of the capillary fringe may have been less than 60 feet bsg during 1992 3"3-t3 3