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y ;A LNORCAL L Eie 1d Survev 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 and pipeline locations in order to identify the tank boundaries and define the limits 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 Megahertz antenna. Several of the traverses were also surveyed with the 120 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 proposed _test boring locations based on recommendations by Kennedy/Jenks/Chilton site representative, Mr. Dan Graff. We then obtained additional GPR data over 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 location. Results Typically, buried tanks are manifested on the GPR records as a strong reflecting horizon. However, depending upon the -site conditions, the depth L of burial etc. , the tank may be only faintly defined. In these situations indirect evidence of the tank may exist on the GPR reoords in the form of a characteristic radar signature from the material overlying the tank. This L signature corresponds to the disturbed nature of the fill. Also, in many cases the electrical properties of the fill contrasts with those of th® surrounding native material producing a noticeable change on the radar L profile. The GPR records obtained at this site do not exhibit definitive indications of buried tanks or disturbed strata that could represent fill material L covering the tanks as subsurface definition is limited. The records do, however, resolve several pipelines related to the tanks and nearby pumps. The GFR depth of penetration with the 500 Megahertz antenna at this area appears to be limited to a few feet. The 120 Megahertz antenna did not provide significantly greater penetration. The GPR records obtained with this antenna do not indicate strong reflecting horizons indicative of buried tanks. However, these records are affected by interference patterns due to L cultural features such as buildings and fences in close proximity to the GPR traverses. It appears that certain site conditions exist that do not allow the clear detection of underground tanks by conventional radar methods. These conditions are typically: 1) a brackish water table that is .shallower than k S