Utility-Locating Technology Development Using Multisensor Platforms (2014)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

110 A p p e n d i x C C.1 purpose The purpose of this Standard Operating Procedure (SOP) is to provide general procedures for geophysical data collection during subsurface utility field investigations using the SHRP 2 R01B time domain electromagnetic induction (TDEMI) digi- tal geophysical mapping (DGM) prototype system, also known as the transient electromagnetic method (TEM) system. This SOP is to be used in conjunction with the SOP for TDEMI DGM data processing (see Appendix D). C.2 Scope This SOP applies to the collection of TDEMI geophysical and associated spatial location coordinate data. A real-time kinematic (RTK) global navigation satellite system (GNSS) will be coupled with the geophysical instrument(s) to record the x and y coordinates for the collected geophysical data points. The SHRP 2 R01B TEM 5 × 1 sensor array will be the detection platform to be tested and calibrated in an area that represents specific site conditions. The objective of the geo- physical survey is to detect subsurface metallic objects that are utilities and/or other client-defined targets of interest to ASCE 38-02 standard’s Quality Level B (QL-B) infor- mation. The purpose of the DGM surveys is to provide information which may be used to support the determina- tion of exactly where the utilities and targets of interest are located. C.3 Maintenance The Project/Site Geoscientist, in collaboration with the qual- ity control (QC) Geoscientist, is responsible for the mainte- nance of this SOP. Approval authority rests with the Project Manager (PM). Approval authority is the power conferred on the PM to commit the geophysical service provider to the procedures, objectives, and data quality standards as set forth in this SOP. C.4 equipment The following is a list of equipment that will be necessary to complete a DGM survey with the geophysical instrumenta- tion for the project: • SHRP 2 R01B TEM geophysical sensor(s) and acquisition computer; • Appropriate signal and power cables for all instruments; • RTK GNSS rover/receiver, GPS base station (if applicable), data logger, antennas; • Sufficient batteries for daily operation of all instrumenta- tion; and • Instrumentation platform (cart, wheels, GPS mast, tow vehicle). The following additional equipment and forms will be assembled by the Site Geoscientist(s): • Task-specific field data logbook, QC tests form, survey report form; • Pin flags, spray paint, traffic cones, tape measures, 10 ft of metal linked chain, miscellaneous items necessary for data collection; • Digital camera, USB thumb drive; and • Personal protective equipment (as required by current health and safety plan). C.5 personnel Requirements and Responsibilities All personnel assigned to the geophysical investigation team must demonstrate the ability to perform assigned tasks asso- ciated with the geophysical investigation with the equipment Standard Operating Procedure for TDEMI Digital Geophysical Mapping Data Collection

111 at the designated project location. For TDEMI DGM activi- ties this equipment includes • RTK GNSS; and • SHRP 2 R01B TEM 5-by-1 sensor array on metal-free platform a. Five coils; b. Five preamps; c. Approximately 20 ft of cabling for five transmit/receive coils; d. National Instruments (NI) electronics box with embed- ded computer and analog-to-digital (A/D) card; e. G&G Sciences electronics box attached to NI box; f. Power cables for NI box and G&G box; g. Package of NI software and CDs; h. AC power or 18-30 V DC for the NI box, and +12 and -12 volts for G&G box; i. External monitor, mouse, and keyboard (once the networking is configured, a laptop computer and a network cable to “Remote Desktop” onto embedded computer can be used); and j. USB flash drive. Before the initiation of geophysical survey data collection, a project briefing will be held for all personnel responsible for geophysical surveying, the downloading of data, and quality control of data. Survey methodology, data requirements, field note protocol, data naming conventions, and raw data organi- zation will be explained in detail. The briefing will include an overall discussion of the survey approach and how the data collection and field documentation tasks integrate into the overall QC and project management program. The briefing will also include review of the internal QC procedures listed in this SOP. The Field Lead will be responsible for providing this briefing and any follow-up training deemed necessary. C.6 preparatory Activities C.6.1 Survey Layout and Methods Before conducting the subsurface geophysical investigation, the field investigation team must have accurate knowledge of the precise location(s) of the survey area boundary. Although it is the client’s ultimate responsibility to provide the exact survey area boundaries for any given project, the geophysical service provider (PM and/or Project/Site Geoscientist) shall attempt to gather sufficient geo-referenced site information through reasonably ascertainable means before mobiliza- tion to the project site. The survey area boundary information shall include geo-referenced points, lines, and/or polygons that are all referenced to a specific and consistent coordinate sys- tem. If possible, an electronic geo-referenced base map should be created and loaded into the data acquisition and process- ing software for assurance purposes. This base map should include the project coordinate system and correct distance units. On arrival at the project site and before performing DGM data collection activities, the geophysical service pro- vider and/or a land surveyor shall check the points shown on the base map with RTK GNSS equipment to ensure location accuracy. The field investigation team shall then determine the most appropriate means for the survey area boundary to be identified and recognized by the DGM operator during data acquisition. Either the DGM operator will have a heads- up computer display showing his/her location in relation to the survey boundary, or the survey boundaries shall be delin- eated by markings (flags, paint, traffic cones, etc.) or perma- nent reference points in the field (buildings, street boundaries, fence lines, etc.). Once the project areas that will undergo DGM have been identified and sufficiently delineated, the geophysical inves- tigation team must determine an optimal data acquisition design. Data shall be collected by traversing along equally spaced parallel paths, unless site conditions and/or the proj- ect plan call for an alternate data collection scheme. If possi- ble, data should be collected perpendicular to the orientation of suspected utility orientations. If data collection perpen- dicular to utility-orientation cannot be achieved or is not practical, data may be collected in a direction parallel to sus- pected utility location with a portion of data (≥5%) collected as tie lines or repeat data, where data is collected perpendicu- lar to the main data acquisition orientation. Any changes to the field plan must be made by the PM (if present) or Field Lead (if PM is not present). C.6.2 Data Collection Parameters Final data collection parameters will be determined on the basis of project requirements, site conditions, and the adap- tive detection/positioning capabilities of the geophysical instru- mentation system. If possible, an evaluation of a site-specific sample of DGM data will be evaluated by the field team before the commencement of data acquisition to better define optimal parameters. These parameters include • Lane spacing—determined by detection footprint of the geophysical system and project requirements. • Sensor height—usually fixed on the basis of the instru- ment platform; sensors closer to the ground surface offer greatest sensitivity. • Data collection speed (≤3 mph)—because data are usually recorded on set time intervals, slower acquisition speeds offer higher down-line data density. • Comprehensive coverage—complete inclusive coverage offers greatest detection capability.

112 • Noise threshold—detection capabilities of electromagnetic induction (EMI) instruments can be adversely affected by natural and/or cultural features (high ambient moisture, surface or near-surface metal, lightning, power lines, etc.). C.7 Geophysical data Collection procedures C.7.1 Daily Data Collection The following set of general procedures will be followed for each field day: 1. Hold tailgate safety and daily project objectives meeting; tailgate safety forms will be filled out and signed by all field investigation team members. 2. Set up equipment. 3. Perform morning QC tests and checklist as described in Section C.8 of this SOP. 4. Send field team to production area. Remove any metallic debris from the production area if possible. 5. Activate the geophysical and RTK GNSS instrumentation and check that all units are collecting and/or outputting valid data. 6. Proceed with DGM data collection activities. One member of the team will be responsible for maintain- ing the field documentation record. Note, this does not nec- essarily mean that person is responsible for creating each document; individual documents may be produced by any member of the field investigation team. Field documentation includes, at a minimum, the checklists and forms included with this SOP and other relevant SOPs. These documents are delivered to the Field Lead at the end of each production day. Each page of the field documentation will be dated, sequen- tially numbered, and identified by the project name/number; all entries will be signed by the Field Lead. At a minimum, the following information should be recorded as field documentation: • Unit area for data set identification; • Time survey started; • Time survey completed; • Names of geophysical investigation team members; • All QC and instrument function tests; • Weather conditions; and • File names for the digitally recorded data. At the end of the day, • All equipment is returned to storage, and the batteries are placed on charge. • The completed survey areas are recorded in the field documentation. • The GNSS positional track maps and field documen- tation are accessible for periodic verification by the QC Geoscientist. Before any data collection session, the TEM system should be tested in an area free from both surface and subsurface metallic objects. By doing so, the data analyst will be better able to perform drift/leveling corrections on the EMI data and establish true background noise levels, thus enhancing the ability to recognize targets that are only slightly detect- able above background (i.e., deeper and/or smaller targets). If possible, each data collection session should begin and end at the same location in the metal-free area. A fewer number of longer time-of-collection data sets are generally more desirable than a greater number of shorter time-of-collection data sets. C.7.2 Full Coverage (Grid) Geophysical Survey One hundred percent of the work scope accessible areas will be geophysically surveyed with the TEM, integrated with RTK GNSS. The field investigation team can use several methods to ensure full coverage. A few methods include (i) establishing markers in the field to delineate data collection lanes using flags, ropes, painted lines, or cones; (ii) using the heads-up data track display on the data acquisition computer; and (iii) using swath light-bar guidance systems. The idea is to gain comprehensive coverage at maximum productivity by eliminating data gaps and overlap. If conditions allow, two or more data collection schemes acquiring data in alternate directions and orientations can be beneficial. C.7.3 Real-Time Geophysical Surveys Real-time geophysical data are collected in either a designed pattern or a meandering path fashion. The geophysical data in this case are interpreted in real time in the investigation area. During this operation it is not necessary to record sen- sor data. This mode of operation is not currently practical with the TEM system because the DGM operator cannot sufficiently monitor and interpret the TEM sensor readings in real time. Therefore, geophysical data are digitally logged for subsequent analysis; if geophysical anomalies believed to represent buried utilities or other cultural features of inter- est are encountered during the survey, the geophysical inves- tigation team will document the presence of such features in the project field documentation and record their coordi- nate position.

113 C.7.4 Partial Coverage Geophysical Surveys For partial coverage DGM, digital geophysical data are col- lected in either a designed pattern or a meandering path fash- ion. Data sets are collected in the same manner as for full coverage digital grid surveys with the only exception being that 100% coverage is not required. C.7.5 Obstacles and Deviation from Lane Orientation/Spacing Deviation from geophysical survey lane spacing and orienta- tion will be determined and documented in the field. The Site Geoscientist will be responsible for determining whether an area is considered inaccessible due to site conditions. All inac- cessible areas will be photographed and/or sketched in the field documentation and denoted as to their source. Examples of typical obstructions include manmade immovable structures; unsafe terrain/conditions; and cultural objects such as cars, power lines, signs, and fences. Reasonable attempts are to be made to have parked vehicles and other potentially moveable obstacles moved. The Field Lead will designate one member of the field investigation team to document deviation from standard lane setup due to terrain, slope, or other conditions that make the area impassable. The following steps are rec- ommended for performing lane deviation documentation: • Deviations will be tied to an individual data set. If devia- tion is necessary, a sketch and/or photograph of the data set boundary will be denoted with the cause of the devia- tion. Data gaps caused by deviations from line path and not obstacles should be filled in with a subsequent data collection set if possible. • Obstacles may cause inaccessibility and result in additional sources of lane orientation and/or spacing deviations that should be documented. Remove obstacles from the inves- tigation area if possible. C.7.6 Daily Data Management A few files are generated by the geophysical and positioning systems for the acquired data at each investigation area of a project site. These data are stored on the field computer and are converted to standard importable numerical text files by the operator. At the end of daily field activities, the data col- lected by the field investigation team will be uploaded to a designated data management computer. The following file types are generated for each survey: • Geophysical data file with signal intensity and RTK GNSS positioning coordinates (.tem, .Data.csv, and .AcqParams .csv); • Digital photo files (.jpg) relevant to data acquisition/ interpretation; and • TEM DGM QC checklist at the end of this appendix. C.8 Quality Control (QC) and Quality Assurance (QA) This section outlines the quality control function through discussion of generalized field procedures and testing to document the execution and completion of a subsurface tar- get detection project using TDEMI digital geophysical map- ping. The Project/Site Geoscientist, in collaboration with the QC Geoscientist, is responsible for the maintenance of this procedure. C.8.1 Response, Detectability, and Interpretability Utilities and other metallic targets of interest are detectable and interpretable based on the anomalous response (ampli- tude, shape, size, etc.) exhibited by the source above back- ground levels. The anomalous response of the source varies based on the site conditions and the target’s electrical prop- erties. Target properties influencing anomalous responses include, but are not limited to depth of burial, size, orienta- tion, and material properties. C.8.2 Equipment Functionality and QC Tests The geophysical service provider will perform QC tests tai- lored to the project’s specifications to ensure both instrument functionality and consistency of measurements from the instru- ment in question. A number of QC tests are instrument spe- cific, while others are universal. A daily checklist will be filled out by the field investigation team, and all QC tests will be recorded in the Project/Site Geoscientist’s field documenta- tion. The forms are located at the end of this appendix. The suite of tests is instrument specific and may include some or all of the items listed in Table C.1. Table C.1. QC Tests Test # Test Description Equipment Frequency 1 Equipment warm-up TEM Daily 2 Cable/port setup check TEM/GNSS Daily 3 Cable shake test TEM/GNSS Daily 4 Static repeatability TEM Twice daily 5 Latency (chain) test TEM/GNSS By data set 6 Geodetic equipment functionality GNSS By data set

114 C.8.2.1 Equipment Warm-Up ApplicAbility TEM procedure Minimize sensor drift due to thermal stabilization. Most instru- ments require several minutes to acclimate to current weather conditions (temperature, humidity, etc.) and stabilize readings before data collection can take place. While the equipment is on and in a static position, monitor readings until the readings sta- bilize with predictable constant response decay curves (typically 5–15 minutes depending on ambient temperature). Frequency Beginning of each day and after equipment has been shut down for more than 1 hour if air temperatures are below 50°F C.8.2.2 Cable Port Setup Check ApplicAbility TEM/GNSS procedure Before production mapping or QC testing, data operators ensure accurate cable-to-computer port connections from the geophysical sensors and positioning instrumentation. The field team does this by introducing a piece of metal directly beneath each sensor of the array, one at a time, while viewing the detec- tion response curves for each coil on the acquisition software (EM3D) display monitor. Frequency Beginning of each day or after the system is disconnected or shut down during a day’s operation C.8.2.3 Vibration Test (Cable Shake) ApplicAbility TEM/GNSS procedure Identify and replace shorting cables and broken pins on con- nectors. With the instrument held in a static position and collecting data, shake all cables to test for shorts and broken pin-outs. An assistant can help by observing any changes in instrument response. If shorts are found, the cable should be immediately repaired or replaced. After repair, cables need to be rigorously tested before use. Frequency Beginning of each day C.8.2.4 Static Repeatability (Instrument Functionality) ApplicAbility TEM procedure Quantify instrument background readings and electronic drift, locate potential interference spikes in the time domain, and determine response and repeatability of the instrument to a standard test jig designed by the geophysical service pro- vider. Improper instrument function, the presence of local sources of ambient noise (such as electromagnetic transmis- sions from high-voltage electrical lines), and instability in the earth’s magnetic field (as during a magnetic storm) are all potential causes of inconsistent, nonrepeatable readings. To aid in the repeatability of the spike test, the DGM operator will use a spike test jig to ensure the test item is in the same posi- tion relative to the sensor(s) for all tests. For this test, 1 minute of static background data must be collected after instrument warm-up, followed by a 1-minute spike test followed by a second, 1-minute collection of static background data. The DGM operator must review the read- ings to confirm their stability before continuing with the geo- physical survey. To aid in the repeatability of the spike test, the DGM operator will use a spike test jig to ensure the test item is in the same position relative to the sensor(s) for all tests. Frequency Minimum twice daily C.8.2.5 Latency (Chain) Test ApplicAbility TEM/GNSS procedure Document lag/latency, repeatability of response amplitude, and positional accuracy. This test will be performed at the beginning and/or end of each data set in an area relatively clear of anomalous response. The test line will be well marked, with the chain drawn completely straight to facilitate con- sistency for each section of the test. The chain should be approximately 10 ft in length so that it can be passed over in nonoverlapping segments. The test requires that the TEM DGM operator traverse over a chain (laid flat and straight) in opposing perpendicular directions at the beginning and/or end of each data session. For chain tests performed twice dur- ing the same data collection set, the chain should be placed at differing locations outside of the data session coverage area if possible. Such test(s) will allow the data analyst to monitor instrument latency over a sustained period of time. The end- points of the chain, at all test locations, should be surveyed

115 with the site position instrumentation and in the project- specific coordinate system. Those chain endpoint positions should be included in the project location survey file. Frequency At least once per data set C.8.2.6 Geodetic Accuracy and Functionality ApplicAbility GNSS procedure At the beginning of each day, a known survey point will have the position recorded and compared to the known position to ensure it is within the tolerance of the naviga- tion system. The position will be checked against the known coordinates in the field before survey activities commence. All surveyed points will be tied into the project network of checkpoints. Frequency Daily TDEMI DGM Field QC Form Field Operator TEM QC Tests Date: Project: Field Team: Test # Test Description Frequency Completed? Notes 1 Equipment Warm-up Daily yes / no 2 Cable/Port Setup Check Daily yes / no 3 Cable Shake Daily yes / no 4 Static Repeatability Minimum: 2 Daily yes / no 5 Latency (Chain) Test Per Data Set yes / no yes / no yes / no yes / no yes / no yes / no yes / no yes / no 6 Geodetic Accuracy Daily yes / no