WORK PLANS_PART 1 FILE 1 - Laserfiche WebLink

Home Browse Search

OCC Lathrop Site Soil and Groundwater Samplin, ork Plan April 28, 2000 2.4 SITE STRATIGRAPHY Geologic logs collected during installation of groundwater monitoring wells and pumping wells at the site indicate that the site is underlain by laterally discontinuous lenses of inter-bedded alluvial sands, silts, and clays, with occasional gravel zones. These strata are highly variable in both thickness and horizontal extent, with thickness varying from less than a foot to more than forty feet. Previous studies have subdivided the strata underlying the site into four general layers. Layers 1 through 3 were based on observations contained in geologic logs, depth to the screened intervals of monitoring wells installed at the site, and correlation between groundwater elevations observed in the monitoring wells. The fourth layer is represented by the Corcoran Clay. Layer 1 extends from ground surface to approximately 65 feet below ground surface (bgs). Layer 2 extends from the bottom of Layer 1 to approximately 115 feet bgs. Layer 3 extends from the bottom of Layer 2 to the top of the Corcoran Clay. The Corcoran Clay is estimated to occur at approximately 200 feet bgs. A summary of the depths to the top of each layer is provided in Table 1. 3.0 SCOPE OF WORK 3.1 SOIL SAMPLING Pursuant to correspondence and conversations with Miller Springs and the Regional Board, TSG has proposed collection of additional soil and groundwater data from one additional location at the Site. Soil samples will be collected by advancing a borehole through the estimated center of the pesticide plume mass as indicated by the results of the most recent groundwater sampling data (Figure 1). The soil boring will be completed from ground surface to the top of the Corcoran Clay (estimated at approximately 200 feet bgs) using an air-rotary drilling rig and 8-inch-diameter driven casing. Soil samples will be collected at 10-foot intervals using 2-inch diameter split-spoon samplers fitted with acrylic sampling sleeves, beginning at approximately 20 feet bgs and extending to the top of the Corcoran Clay. Geologic logs describing conditions encountered during installation of the borehole will be prepared by the field geologist using Unified Soil Classification System (USCS) terminology. Selected soil samples will be submitted for laboratory analyses for pesticides (EDB, DBCP, and Sulfolane), California Title 22 Metals, total organic carbon, cation exchange capacity, soil pH, and porosity. Soil samples will be collected in laboratory-supplied containers and stored on ice pending transportation to the analytical laboratory. All downhole drilling equipment, soil sampling and coring equipment will be decontaminated by steam cleaning prior to initiating work. A summary of the proposed analyses and analytical methodologies for soil sampling is provided in Table 2. 3.2 WATERLOO MULTILEVEL GROUNDWATER MONITORING SYSTEMSTm Following collection of the soil samples, a Waterloo Multilevel Groundwater Monitoring SystemTM (Waterloo System) will be installed in the borehole to allow collection of groundwater samples. The Waterloo System will consist of a series of 7 groundwater-sampling ports set inside a 2-inch diameter PVC monitoring well casing with screened intervals set at the locations of the groundwater sampling ports. Sand filter packs will be placed in the annulus of the borehole from approximately 1 foot above to 1 foot below each sampling port. Well seals consisting of approximately 1 foot of hydrated bentonite chips or pellets will be placed above the upper sand pack at each sampling interval. After placement of the bentonite seal at the uppermost sampling interval, the borehole will be finished to the surface with cement grout containing approximately 5 2 The Source Group,Inc.