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Equipment Report Equipment Operations and Limitations Corporate Location: 750 Patrick's Place Office # 888-858-9830 Brownsburg, IN 46112 Fax # 888-858-9829 htW://www.BHUG.com Similarly there are several factors that can impact the effectiveness of GPR surveys: • Subsurface Material / Soil Composition — Soil composition and subsurface material is the most important factor impacting the effectiveness of GPR. The more conductive the subsurface material, the less effective the GPR survey will be. GPR works best in sandy soils, and is least effective in heavy clay soils or where the subsurface material contains a large volume of highly conductive backfilled debris or material (i.e. metal scraps or slag sand). Midwestern soils generally have a high clay content and create significant challenges to completing an effective GPR survey. As a general rule, the smaller the particulate matter that the subsurface material is composed of, the greater the inhibiting effect on the GPR signal. • Composition of the Subsurface Target — The inherent electrostatic reflectivity of a target will impact the effective identification of the target. Lightweight subsurface material, such as PVC, are generally more transparent to radio waves and will reflect a substantially smaller percentage of the radiated signal. This will result in a smaller and more minor reflection signature, making effective interpretation more difficult. Some materials are completely transparent to radio waves and can only be identified if a reflective material (i.e. water) is contained within the target pipe. • Moisture Content of the Subsurface Material — Water, when combined with dissolved ions (salt) has an inhibiting effect on GPR signals, and signals can often not effectively penetrate saturated soil material, when the soil is slightly conductive. The addition of more water increases the conductivity of the soil and more significantly inhibits the effective signal penetration. • Depth — The GPR signals have a finite effective penetration depth. The deeper the target, the less likely it will be effectively identified. As the signal penetrates the subsurface material it loses strength as the depth increases. Effective signal penetration can be defined as the depth at which the reflected signal no longer has sufficient power to reach the receiver antenna of the GPR. In other words, the effective survey depth is the depth at which the penetrating signal reaches a maximum of 50% of its emitted strength, although it should be noted that at this range only a 100% reflective target (i.e. metal) would have the potential to be detectable. • Target Size — The smaller the diameter of the target structure, the lower the probability of successful identification of the target during a GPR survey. The smaller the target, the less of a signal that will be reflected, decreasing the probability of a positive identification of the subsurface target. As a general (but not absolute) rule of thumb, for every I foot of depth you must have 1 inch in diameter in order to be observable. For example, a 3" diameter pipe must be less than 3 feet below grade in order to be observable during a GPR survey. EM Inductive Surveys can also be impacted by environmental factors. s Surface and Subsurface Material / Soil Composition — Highly conductive soils can prevent the identification of other conductive structures with this methodology. The presence of surface metal, including vehicles, fences, and debris, can swamp other readings and prevent the identification of subsurface targets. In addition, the presence of rebar reinforcement within concrete can have a similar effect and prevent identification of other structures. • Target Size — Small metallic targets may not be detected, since the mass of the target object must be large enough to impact the shape of the transmission field. Small objects may not have sufficient mass to cause a field distortion significant enough to be detected. • Target Depth — Deeper targets may not sufficiently distort the transmitted signal to allow for detection by the receiver. However, large high -mass targets are more likely to be detectable at significantly deeper depths, than lower mass targets. Summary of Equipment and Survey Effectiveness — EM locating is generally very effective in locating most subsurface utility lines. Electric, Telephone, and Cable TV can almost always be located using standard EM locating techniques. Also, many water lines can also be located. However, due to the continuous contact with the soil, and the common use of cast and ductile iron in water line construction, water lines can often prove difficult to locate. Additionally, water lines constructed of plastic are becoming more common and cannot be located using standard locating methodologies. Sewer lines (storm and sanitary) are very rarely locatable with standard techniques, unless a conductive tool can be introduced into the line (i.e. locating a sanitary lateral by running a rod containing metal through the line from a clean-out access point). All Blood Hound technicians carry a Jameson rodder for this specific purpose. GPR surveys are an effective way of locating and identifying subsurface obstructions prior to drilling or excavating activity. However, these surveys cannot and will not identify all subsurface utilities or other obstructions, in all circumstances. Midwestern soils in particular, present significant challenges to an effective GPR survey, and should not be relied upon as the only means of protecting underground utilities. EM Induction surveys provide another level of investigation, which when combined with traditional EM locating and GPR provide the most complete non-destructive process available for the protection of subsurface utilities and other structures. When Vacuum Excavation is employed, the possibility of a damaged utility is further minimized. In general, private utility locating surveys conducted by Blood Hound technicians are highly accurate and effective. However, there are numerous factors that can result in a line being mis-marked or left unmarked by our technicians, that are beyond the control of Blood Hound or its technicians. This includes, but is not limited to, a lack of adequate prints or available site knowledge, a lack of access to utilities (i.e. cleanouts, interior communications rooms, vaults, etc), a lack of visual indications of the utility's presence, a disruption of a conductive pathway (i.e. repair in a metal water line made with plastic), and commonly bonded lines creating undesired signal conduction pathways. While Blood Hound provides its employees with extensive training on ways to mitigate these and other issues, there are unfortunately occasions where these factors cannot be effectively eliminated. Utility Locating — Ground Radar — Vacuum Excavation — Sewer Camera — GPS/GIS Mapping 41