SITE INFORMATION AND CORRESPONDENCE

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NORCAL Field Survey The field survey was performed using a Geophysical Survey Systems, Inc. SIR-3 ground penetrating radar 'system with 120 Megahertz and 500 Megahertz antennas. GPR data were obtained from traverses over the suspected tank an pipeline locations in order to identify the tank boundaries and define the J linits of the fill excavation. The length of several of the traverses was limited due to nearby debris and obstructions. The traverse locations are shown on the enclosed site map. Each traverse was surveyed with the 500 Xegahertz antenna. Several of the traverses were also surveyed with the 12 Megahertz antenna for comparison of the results in regards to depth of penetration and resolution. Upon completion of the field work, we reviewed the GPR profiles and propose test boring locations based on recomm—andationsby Kennedy/Jenks/Chilton sit representative, Mr. Dan Graff. We then obtained additional GPR data over f the recommended boring locations from traverses oriented perpendicular to the previous ones. The perpendicular' traverses were to insure that pipelines and other possible drilling obstructions did not exist at the precise drilling locaticn. Results Typically, buried tams are manifested on. the GPR records as a str-cmg reflecting horizon. However, depending upon thesiteconditions, the deptl the tank may be only faintly defined. In these situations of burial etc. Y y _ Y indirectevidence of the tank may exist on the GPR records in the f orn of a characteristic radar signature from the material overlying the tank. This siSmature corresponds to the disturbed nature of the fill. Also, in many cases the .electrical properties of the fill contrasts with those of the surrounding native mate-rial producing a noticeable change on the radar profile. The GPR records obtained at this site do not exhibit definitive indications of buried tanks or disturbed strata that could represent fill material covering the tanks as subsurface definition is limited. The records do, however-, resolve several pipelines related to the tanks and nearby p=ps. The GPR depth of penetration with the 500 Megahertz antenna at this area ap_ears to be limited to a few feet. The 220 Megahertz antenna did not provide significantly greater penetration. The GPR records obtained with this antenna do not indicate strong reflecting horizons indicative of buriF tanks. However, these records are affected by interference patterns due tc cultural features such as buildings and fences in close proximity to the G: t tr a.'erses. It ac�ears that certain site conditions exist Leat do not allcw the clear de -eC,:±cn of underrpround tams by conLentlonal . ad-ar J-attccs• =`'ese conditions are tynicallY: 1 ) a brackish water _able that is e!„ l lower -'-an