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REQUEST FOR QUALIFICATIONS NO. 20-07-01 CONTINUING PROFESSIONAL CONSULTING SERVICES (CCNA) TAB D: PROJECT APPROACH AND UNDERSTANDING coordinate their work and the detailed information they can provide to the project and transfer that into the GIS. Each project depending on the scope will most likely be a combination of the tools used by the underground location company, such as Electro-Magnetic (EM) and Ground Penetrating Radar (GPR) methods used to identify detectable utility systems. All discoveries, designates, and markings will be reviewed with the surveyors onsite. A completed copy of the utility location survey will be reviewed by both the surveyors, the project manager and the GIS coordinator as part of the QA/QC process for the final deliverable. The following description outlines the methods used to confirm/verify existing utilities: EM - A transmitted signal is applied by directly coupling to a desired target. As long as the target is metallic, a receiver is used to detect the transmitted signal. Passive power detection is another technique used to locate naturally occurring magnetic fields present on power cables generating a 50/60Hz signal. Additionally, passive VLF signal can be detected on other metallic utilities that are typically long in length and are well grounded electrically. Some utility systems contain portions of non-metallic material and therefore may be un-locatable using the EM method. GPR – This method is used to identify nonmetallic utilities and other structures that are unidentifiable using traditional EM techniques. The GPR method transmits electromagnetic waves, which are pulsed at discrete/time intervals. The transmitted pulse radiates through the earth whereby a portion of the energy is reflected from interfaces of contrasting electrical properties (e.g. pavement and soil interface, soil stratigraphic changes and buried metallic objects) while the remaining energy continues until reaching additional reflectors where the process is repeated. Reflected energy is received by the antennae and recorded for real time processing and interpretation. Factors such as soil moisture, clay content and variations in the dielectric constants of materials control the effectiveness of the GPR method. Wet conductive soils severely attenuate GPR signals and thus affect the depth of exploration. GPR energy cannot transmit through ferrous objects since metal acts as a pure reflector. In order to accurately conduct a radar survey, orthogonal scans must be made across the target area. Confined or obstructed areas that restrict the scanning pattern can impede the data collected and reduce the accuracy of the desired results. Pipeline Inspection Systems – A transmitting Sonde located behind the camera head allows for horizontal locations of sanitary/drainage system. Provided that the system is accessible and passable, the camera will allow us to view features within the system. Any anomalies within the system will be noted. Our camera systems are typically used in systems measuring 2” to 8” inches in diameter. Vacuum Excavation – To further confirm a utility’s exact location, Vacuum Excavation can be used to expose any discoveries made through the previously outlined methods. Vacuum Excavation is a non- destructive technique used to safely expose utilities/objects using a combination of compressed and vacuum air. Once the utility has been exposed, vertical elevation, diameter and material type can be recorded. Conditions such as groundwater, hard, rocky soils, sub-surface obstructions and targets at deep elevations can limit the effectiveness/results of vacuum excavation. Ta rgets beyond the limitations of the Vacuum system may be “probed” with an air lance. This technique is effective in determining elevation and/or presence of underground objects but may be ineffective for D | Page 16