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' Phase 11 Environmental Site Assessment Mountain House Neighborhood G July 9,2002 Page 2 C Commissioner's office regarding potential pesticide use at the site from 1996 through July 2001, indicates pesticides and herbicides were applied at the site during those years. 3.0 ENVIRONMENTAL SETTING The site is located in the Great Valley Geomorphic Province in the northern portion of the San Joaquin Valley. The San Joaquin Valley is a northwest-trending, fault-bounded syncline tilled with up to six vertical miles of lithified non-marine and marine sediments and nonlithifted non-marine sediments. Regionally, the Iithology of the upper 3,000 feet of sediments are derived from theCoast Range Mountains to the west and the Sierra Nevada Mountains to the east. The Coast Range Mountains are approximately five miles west of the site and the Sierra Nevada Mountains are approximately 40 miles northeast of the site. Vegetative cover consisting primarily of alfalfa was present at the site during soil sample collection activities conducted as part of the Phase II. Stressed vegetation or stained areas were not observed during sampling activities conducted at the site. The site and surrounding properties were observed to be generally level during the sampling activities. The land surface in the vicinity of the site is nearly level with a very slight slope to the northeast. The elevation of the site ranges from approximately 65 to 75 feet above the National Geodetic Vertical Datum of 1929. The site is bounded by agricultural land. Surrounding properties within a mile of the site have historically been used for agricultural purposes. Access to the site is provided by the dirt roads mentioned in Section 2.0. Soils encountered in the general vicinity of the site are identified as belonging to the Capay-Stomar Zacharias general soil map unit. Soils encountered in the immediate vicinity of the site are identified primarily as Stomar clay loam, 0 to 2 percent slopes. This soil type is characterized by slow permeability, is well drained, and is typically located on alluvial fans that have nearly level relief and is formed from alluvium derived from sedimentary rock sources. The surficial soils observed at the site appeared to be generally similar throughout the site. Because pesticide and herbicide applications are typically restricted to crops and the soil surface, the potential for these materials to impact groundwater at the site is considered to be minimal. Residual concentrations of pesticides and herbicides are likely to be confined to the upper 6 to 12 inches of soil as a result of surficial application. The scope of work performed by Condor as part of this Phase Il did not include groundwater investigation activities to accurately determine the potentiometric surface below the site. No piezometers or groundwater monitoring wells were installed. Pumping of site groundwater for drinking water or any other purpose is not anticipated in the future. Additionally, there are no natural surface water bodies at the site. 4.0 SOIL SAMPLING PROCEDURES Condor personnel collected soil samples from the site on September 28, 2001. The soil sampling procedures were conducted in general accordance with the soil sampling plan described in the work plan and with soil sampling plans developed by Condor and utilized to conduct Preliminary Endangerment Assessments at similar properties in the San Joaquin Valley. The field sampling plan was developed using information contained in the DTSC Preliminary Endangerment Assessment Guidance Manual, dated January 1994 (Second Printing, June 1999) and the Interim Guidance for Sampling Agricultural Soils, prepared by Mr. Brad Parsons of the DTSC,dated June 2000. iJ CONDOR