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Summary of Additional Source Assessment Modifications of Work RLan 2000-2001 The PHS-EHD representative and field geologist discussed the sampling as the borehole drilling, sampling and borehole sealing progressed on April 25, 2000 Field observations during drilling indicated that contaminants were not widespread at the originally selected MW-9 and MW-3 locations, hence a modification to the fieldwork and sampling was approved by PHS-EHD in the field The modifications included the following; advancing five boreholes near the originally selected locations, returning to the site at a later date to mark utilities for borehole drilling and to search for additional possible contaminant sources both at the original tank pit and elsewhere, and a discussion with PHS-EHD regarding a review of previous work and the revision of the work plan prior to returning to the field to continue assessment Wright met with the PHS-EHD representative in late April 2000 and discussed the amended approach to additional plume definition in April 2001 • Conducting a surface geophysical survey with ground penetration radar to search for anomalous indications of possible contaminant sources (discussed above) • Performing utility location with the City of Tracy and Westside irrigation line owner to locate lines so that borings can be advanced to collect more lateral and vertical assessment data near MW-9 ® Inspecting the welding building for indications of potential contaminant sources (such as oil/water separators and sand traps) None were observed Advancing exploratory bonngs through the former tank pit and east and south of MW- 9 for additional vertical and lateral subsurface assessment in those areas (see Figure 2) Additional field modifications were added during the April 19, 2001 work This consisted of moving borehole locations to attempt to delineate the edges of the contaminant plume based upon drilling field observations The final borehole locations are presented on Figure 1 and presented on our June 6, 2001 report(see References) Geo h sical Survqy Norcal Geophysical performed a surface geophysical on January 16, 2001 in the area of the former tank pit and in areas suspected of possible tank presence This work was suggested by PHS-EHD to rifle out possible sources of petroleum hydrocarbons given the contaminant trends observed at well MW-9 The survey consisted of magnetometer and ground penetrating radar equipment sweeping the area (see attached report Norcal report) The magnetometer survey searches for burred metallic objects and ground- penetrating radar (GPR) uses microwaves to penetrate the subsurface to depths of about 5 to 10 feet The responses of buried objects to this equipment indicate possible targets for additional subsurface study and provides data to evaluate buried objects Page 4