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II 11 11 11 1 1 1 1 [I �+ GILES ENGINEERING (:")SSOCIATES, INC. In -Shape Health Club Tracy, California Project No. 2E-1108004 Page 2 3. 3.1 3.2. MAGNETOMETER SURVEY The purpose of a magnetometer survey is to identify magnetic anomalies that are not associated with surface features or structures. The identification of magnetic anomalies may provide insight regarding the potential presence of large buried ferrous objects, such as USTs. Limitations The performance of a magnetometer survey does not guarantee complete assurance of the presence (or absence) of USTs. Based on the science of magnetometry and on Giles field experience, magnetometer surveys have up to an 85% probability of identifying UST(s), but may be limited by local site features. The strength and detectability of a magnetic field produced by a ferrous metal object (i.e., iron or steel) is dependant upon the object's size, depth, and degree of oxidation (corrosion). Non-ferrous metals, fiberglass, polyethylene (plastic), and significantly oxidized USTs may not produce a detectible magnetic field. Magnetic fields typically associated with USTs may be masked or altered beyond identification by other natural and man-made features which also produce magnetic fields. Natural features known to cause magnetic fields include: iron -rich soil and rock, local variances in soil types (native vs. fill) and geomagnetic storms. No definitive conclusions can be made feet of man-made features. Man-made buildings, rebar, reinforced footings, automobiles, scrap -iron, chain-link underground/aboveground utilities. Methods and Procedures or ascertained from areas surveyed within twenty features known to emit magnetic fields include: sign posts, billboards, outdoor lighting poles, fencing, ferrous buried/surface debris, and The magnetometer survey was conducted using a Geometries, Inc. G-858 cesium vapor magnetometer. The Geometric G-858 magnetometer functions as a total field magnetic sensor, where both vertical and horizontal magnetic field components are measured and stored. The survey layout consisted of end-points for each parallel line marked with paint, traffic cones or flags. Total magnetic field readings were collected in a "continuous" (1 measurement per 0.1 second) cycle; while walking the parallel lines over the survey areas. The survey area was established using 5 -foot parallel line spacing. The survey area was completed in the parking lot of the Site, and measured 100 feet west to east, by 295 feet south to north.