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ATC Associates Inc. :VYJ 1 117 Lone Palm Avenue,Suite 201 Modesto,Californiaa 95351 209-579-2221 AS 6 0 C 1 ATE 6 I N C. Fax:209-579-2225 Advancement of Soil Borings To evaluate the vertical and lateral extent of impacted groundwater at the site, six soil borings employing direct push technology and cone penetrometer testing (CPT) methods will be advanced to approximately 130 feet bgs. One CPT soil boring will be advanced in the vicinity of existing well MW6 to evaluate the deeper subsurface conditions in this location. Five additional CPT borings will be advanced west, northwest, and east of the site to evaluate the lateral extent of impacted groundwater and provide data for future wells at these locations, if necessary. Drilling will be conducted by a State-licensed C57 drilling company. A field geologist will be present to supervise drilling activities, evaluate sample depths, and collect groundwater samples. Proposed boring locations are shown on Figure 2. At each of the proposed locations, a cone mounted with sensors at the tip will be advanced into the soil using direct push rods. The sensors will test the response of the soil to the force of the penetrating cone and this will allow the subsurface stratigraphy to be characterized. The borings will be advanced until a significant clay layer is encountered that appears to separate the shallow aquifer from the deeper water bearing zones. To be considered significant, the clay layer will need to be approximately five feet in thickness or greater. For estimating purposes, ATC is assuming the CPT borings will be advanced to approximately 130 feet bgs, if subsurface conditions allow it. Once a significant clay layer has been discovered and the boring is advanced into an identified deeper water bearing zone,the CPT boring will be terminated. After the subsurface materials have been characterized and evaluated,a field geologist will select sample depths for collecting discrete groundwater samples. For each discrete sample, a direct push HydropuncO boring will be advanced adjacent to the initial CPT boring and a groundwater sample will be collected fiom the selected shallow and deeper water bearing zones. Following the collection of groundwater samples, the borings will be grouted to the surface with a neat cement slurry mixture using a tremmie pipe. ATC estimates a minimum of two groundwater samples will be collected from each boring after evaluating the CPT logs for potential water bearing zones seperated by suspected overlying aquatards and/or significant clay layers. Groundwater samples will be collected using Hydropunche type groundwater sampling system. The system includes an expendable drive point attached to poly vinyl chloride(PVC) or stainless steel filter screen threaded onto the leading end of the direct push rods. While the sampler is advanced, O-ring seals and the expendable drive point will provide a watertight system to ensure sample integrity. When the Hydropunce type groundwater sampling system has been advanced to the desired depth, the expendable drive point is held in place by the surrounding soil while the direct push rods are retracted. Once retracted,up to 60-inches of PVC or stainless steel filter screen with slot sizes of 0,010 inches will be exposed allowing for groundwater infiltration. A stainless steel bailer will be lowered inside the hollow push rods until it is immersed in groundwater. I wA25291GCP0rIS wkpCPT.dM 4 i