WORK PLANS - Laserfiche WebLink

Home Browse Search

BACKGROUND In April 1986, one 350-gallon gasoline UST and associated piping were removed from the approximate location shown on Figure 2. A soil sample was collected from the bottom of the excavation. Analytical testing indicated the collected sample contained detectable concentrations of petroleum hydrocarbon constituents. The excavation was subsequently backfilled. REGIONAL HYDROGEOLOGY The site is located in the Northern San Joaquin Valley, part of the Great Valley Province, California, a large north-westward trending asymmetric structural trough. The trough is filled with as much as six miles of sediment ranging from Jurassic to Holocene. The immediate subsurface geology are Pleistocene and Recent alluvial deposits. These alluvial deposits consist of heterogeneous sequences of sands and gravels originating from active stream channels, and silts and clays originating from overbank and marsh depositional environments. The regional groundwater flow direction is expected to be north-northeast. According to the San Joaquin County Flood Control and Water Conservation District (FC&WCD), groundwater lies at approximately 16 feet below grade at an elevation of approximately 10 feet above sea level. SCOPE OF WORK - PHASE ONE Planning and Permits Smith Technology has completed the soil boring permit application for the advancement of six soil borings. The permit application for this scope of work and associated fees (check no. 1223) are attached to this workplan. Smith Technology will also schedule field personnel and equipment, notify Underground Service Alert to locate underground utilities as required, and perform any other necessary field preparation and job start-up activities. Advancement of Soil Borings To determine the extent of soil and groundwater contamination at the site, six soil borings will be advanced to approximately 30 feet below ground surface (bgs). One of the borings will be placed inside the estimated excavation area of the former UST. Two of the borings will be placed in the estimated upgradient direction of groundwater flow from the former UST, west-southwest of the former UST. The remaining three borings will be placed in the estimated downgradient direction of groundwater flow from the former UST, north to east of the former UST. Proposed boring locations are shown on Figure 2. The six borings will be advanced to using truck mounted Geoprobe® narrow diameter, direct push technology. Drilling will be conducted by a State-licensed (C57) drilling company. A field geologist will be present to log all soil samples. Descriptions of soil types encountered and sample collection intervals will be recorded on boring logs. Soil samples will be collected at five- w:\909543\reports\wkp.doe 2 • sNrrH