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Nationwide Insurance, - Center for Radiation Oncology, 7315 Green Slope Drive, Zephyrhills, FL Lab No. 190442 Page 6 maximum deviation from a 10ft. straight edge to be 1/2" to account for surface irregularities in finishing the slab. Additionally, ACI Standard Specifications for Tolerances for Concrete Construction and Material (ACI 117-90) Section 4.3.1.1 shows an allowable tolerance for top of slabs to be plus or minus 3/4" (1.5 inches total). The exception to this is exterior slabs, which are typically finished to slope away from the structure to allow for drainage and may exceed ACI tolerances. Corrections to the survey data have been made to compensate for differences in floor covering thickness effectively bringing the survey data down to the level of the floor slab. Based on the results of the floor elevation survey, it appears that some post- construction settlement has occurred to the main floor along the western side of the building. Please refer to the floor survey drawing (Figure 3.) for a colorized contour drawing of the measured elevation differential discussed. Ground Penetrating Radar (GPR) Principles & Methods The ground penetrating radar equipment used was a RAMAC X3M manufactured by MALA GeoScience in Mala, Sweden. The setup used consisted of the RAMAC monitor control unit coupled to the X3M which was attached to a 250 MHz antenna mounted on a self-contained cart. The cart has a calibrated measuring wheel electronically coupled to the control unit which allows precise linear measurements to be obtained along the transect line during the field work. These measurements and distances can be translated into accurate locating of subsurface features when they are identified. Ground Penetrating Radar (GPR) is also known as subsurface interface radar or impulse radar and can provide a nearly continuous profile of the subsurface conditions. High electromagnetic frequencies (typically between 40 MHz - 2.5 GHz) are transmitted from an antenna that is usually located on or near the ground surface. The electromagnetic pulse is transmitted into the ground and reflections return where there is an interface between subsurface materials of differing dielectric properties. The antenna has electronics that function as a transmitter and a receiver. The reflections returned from the subsurface are relayed from the receiver to the digital control unit and are recorded on an internal hard disk. Depths to the reflected interfaces can be calculated using depths from boring data or can be estimated by using known propagation rates for similar materials. GPR does not specifically identify the subsurface materials, but it does identify when a change in the subsurface strata has taken place. This can be very useful in documenting the continuity of subsurface layers such as a confining layer for ponds and landfills, identifying potential areas of karst erosion and locating underground pipes or other utilities. Ground Penetrating Radar Study The site was surveyed using a measuring wheel and/or a 200-foot tape measure, and an approximate scale drawing was prepared. A total of thirty-six transect lines were laid out over accessible parts of the yard and were labeled T 1 through T36. Optimum results were achieved using the 250 MHz antenna at a time range of 120 nanoseconds (ns). The GPR study was done across accessible areas of the property with 2,900 linear feet of transect lines being completed. Central Florida Testing Laboratories, Ine. 12625 - 40th Street North, Clearwater, FL 33762