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GEOMATRIX through LP-7; Table 1 and Figure 1). Groundwater monitoring results detected elevated concentrations of dissolved solids in these monitoring wells. The shallow groundwater monitoring data indicate a historical release (or releases) from the area of the ponds (Geomatrix, 2003). Occidental monitors shallow, intermediate, and deep groundwater intervals on a quarterly basis. Occidental's monitoring activities do not include Simplot's monitoring wells. Occidental's monitoring is limited to field measurements and laboratory analyses of Occidental's COCs. Occidental also monitors the groundwater remediation systems that include groundwater extraction wells, a water treatment system, and groundwater injection wells that discharge treated water below the Corcoran Clay. Occidental has modeled the remediation system's ability to capture the plumes of organic COCl. As part of a Application for"Designation of A Groundwater Containment Zone" (The Source Group [TSG], 2001), Occidental proposed to continue the current operation of the remediation system(500 to 600 gallons per minute combined) for the 6 months from May through October of each year. TSG has evaluated the potential for hydraulic control of CDCs in groundwater and found that the proposed seasonal pumping would provide"plume containment over the next 30 years." 3.0 SITE HYDROLOGY The physical site setting and site hydrology are.summarized in the following sections based on the Water Quality Protection Standards (WQPS) (Geomatrix,2003). 3.1 SITE LITHOLOGY Several previous investigators have studied the geology of the site. The results of these investigations are summarized in cross-section diagrams provided in the February 2001 Detection Monitoring Program Work Plan for the site by Geomatrix Consultants, Inc. (Geomatrix) (Geomatrix, 2001a). These diagrams indicate the area under the ponds is underlain by about 10 to 15 feet of sandy soil. Beneath the uppermost sandy soil layer are layers of finer soil types including clays and silts. The uppermost aquifer is contained in the sandy soil layer. Boring logs from the installation of monitoring wells LP-4 through LP-7 are in general agreement with the cross-section diagrams previously described and confirm that the uppermost aquifer is contained in the surficial sandy layer(Geomatrix, 2001b). 3.2 GROUNDWATER OCCURRENCE Groundwater beneath the site occurs in the uppermost aquifer at elevations of about 5 to 9 feet above mean sea level (Geomatrix, 2001 a). The apparent lateral direction of groundwater flow 1:\6000s\6741.000\Archive\6741.13.doc 3