Television Inspection/ SewerScanning
Internal television is typically performed as a result ofinformation collected during manhole inspections and smoke testing, customercomplaints, excessive infiltration or in association with a preventativemaintenance program. The purpose of this type of inspection is todetermine:
• Structural condition
• Location of structural defects
•Identify size and material of construction
• Locate service laterals
•Locate obstructions and sources of infiltration
CCTV uses a televisioncamera mounted on a remote-controlled, self-propelled robotic device that isconnected to a video monitor, typically located in a van. The robotic system isinserted in a manhole and placed in the sewer for inspection. Once inside thesewer, the remote control device moves through the pipe. As it moves, anoperator watching the video monitor stops the camera at any type of defect orpipe condition change to get a more detailed inspection. The inspector typicallyuses the camera’s 360-degree articulating lens to get detailed information atall points of concern. This information is electronically recorded on VCR tapes,CDs or DVDs; however, CDs and DVDs are becoming more prominent because of theirease of use. An electronic footage counter is connected to the camera andenables the operator and engineers reviewing the data to know where the problemsare located within the sewer.
Historically, individual cities,television companies and engineering companies have had their own protocols forcoding defects identified during television inspections. This lack of uniformityin coding preferences led to problems when comparing collected videoinformation. However, the NASSCO Pipeline Assessment Certification Program(PACP) coding system was recently established to help bring uniformity to theprocess and remove subjectiveness currently inherent to the diverseguidelines.
Until recently, traditional CCTV (on a crawler) was the bestway to evaluate sewers from 6 to 72 in. in diameter, where flow depths are lessthan 30 percent of the pipe’s diameter. However, there is a new technology thatcan provide more complete, accurate and understandable data for sewers from 6 to30 in. Sewer scanning evaluation technology (SSET) is an alternative to CCTV,shifting the responsibility of rating the structural integrity of the sewer fromthe camera operator to the engineer.
SSET provides the frontal image thatCCTV provides, but it also provides a 360-degree scanned visual image of theinterior surface of the pipe wall. The data can then be analyzed in the officewith the assurance that no important defect is overlooked. The system alsorecords inclination, thus providing sag locations and potential locations forsedimentation buildup.
The 360-degree scan enables the entire surface ofthe pipe wall to be observed in plain view, giving the engineer the capabilityto measure the opening of the joint. In addition, this view enables the engineerand owner to develop a baseline condition of the sewer and the ability tocompare the degradation of the pipe wall over a period of time. The side scanalso permits a much faster review of the information. For example, 300 ft ofsewer might take five minutes to review as opposed to the 15 or 20 minutes itwould take to review the same line of traditional televised information.
Figure 5 shows approximately 100 lf of sewer on one screen. The informationis reviewed similar to reading a sentence or a paragraph. The upstream portionof the sewer is located on the left side of the first line. The data is reviewedfrom left to right. The data from the right side of the first line matches up tothe left side of the second line. This process continues until you reach thebottom of the screen. Red lines are overlaying cracks. Light blue circlesidentify locations of good laterals, with dark blue indicating a problem withthe lateral. The pink line identifies root intrusion. Finally, the gold linesidentify joints that have excessive separation. Using the cursor to clickanywhere on the screen will provide either a closer side scan view at thatlocation and/or the traditional CCTV frontal looking view. Both the CCTV-typeview and side scan view can also be reviewed concurrently. Pricing for SSET iscompetitive with traditional CCTV and can be imported into most GISdatabases
Advanced Technologies for SewerSurvey
As advances in electronics continue to improve, so will thetechniques used to collect information on the condition of sanitary sewers. Twoof the lesser-known technologies include sonar and laser scanning. Sonar is usedto identify problems below the flow line of a sewer and lasers are used toevaluate sewers above the flow line. Sonar units emit a sound wave that travelsuntil it hits a solid object (pipe wall or debris line) and returns back to theunit. The sound wave outlines the shape of whatever it bounces off. Theinformation can be used to identify things such as the level of debris in asiphon (Figure 6) or if the invert of a pipe is loosing structural integrity.
Currently, most the sonar units generate two-dimensional information.However, new technology is coming out that can actually generatethree-dimensional drawings of the sewer. By moving to the third dimension,engineers can generate a 3-D model of the entire pipe and get a betterunderstanding of the pipe’s condition.
Laser scanning is a relatively newtechnique used to evaluate sewers. The technology has only been applied tosewers for the last two years and works by emitting up to a million points at atime. These laser points enable the pipe and any other attribute within the pipeto be outlined and a 3-D model to be constructed. The advantage of thistechnology is that accurate measurements are generated without the presence oflight. While this technology is beneficial for all pipe sizes, it is probablythe most beneficial for the evaluation of large diameter sewers. On a 12-ftdiameter pipe, a change of less than .0125 in. can be seen. This is importantbecause currently the primary way to inspect large diameter pipe is by havingpersonnel walk in the sewers.
Evaluating the condition of a largediameter sewer by walking poses many challenges. These challenges include theneed for a large amount of manpower, safety concerns for people walking in thesewer, as well as the traffic safety personnel on the top of the manholes, theneed for extensive lighting and the inability to identify if the pipe ischanging shape. In general, when walking a sewer there is no chance fordeveloping baseline information on the shape and condition of the pipe unlesssome gross defect is observed.
By having this type of baseline information and watching how or if a largediameter pipe changes over time, municipalities can potentially predictimpending failure before it happens. Knowing and addressing a possible largediameter sewer collapse before it happens could save sewer districts tens ofmillions of dollars. Figure 7 is one example of how laser information can bepresented to a municipality as a wire mesh grid shape. In this particularexample, the blue indicates where the pipe is in its original shape and the pipechanges color as it moves out of its designed shape. Red indicates where thepipe is most out of round.
Note that many of the capabilities discussedin this article are relatively new. There are also a number of othertechnologies that are in the design and developmental stages. While the oldermethodologies used to collect information regarding sewer infrastructure stillprovide accurate data, there are many new and exciting ways to provide theengineers and owners with information that will enable them to make not onlyeasier but better decisions with regard to the condition and repair of theirwastewater infrastructure.
Field Data Management
Fieldinvestigation produces enormous amounts of data. Moderate to larger scale SSESprojects are capable of generating data at a rate that can quickly overwhelmeven the most experienced project manager. The ability to rapidly input data,conduct ongoing quality assurance checks and publish final forms, tables andreports from a single set of data and a single program was the prime drivingforce in development of the SSES database. The key to any SSEM program is datamanagement.
An excellent paper on the topic has been presented byauthors Halfaway, Pyzoha, et. al.(http://gis.esri.com/library/userconf/proc00/professional/papers/PAP158/p158.htm)based on the work done for the City of Columbus, Ohio, Department of PublicUtilities, Division of Sewerage and Drainage (DOSD) as part of EngineeringAgreement No. CT-16376 A.
Approximately 70 MB of SSES data for theproject was stored as a collection of tables (or relations), where each tablecontains a set of records. The SSES database was developed using MS-AccessRelational Database Management System (RDBMS).
Two primary keys are employedwithin the database to link the numerous tables and queries associated withmanhole and TV inspection work:
• MH ID — a unique number assigned to eachmanhole structure during initial data entry;
• Line ID — a unique numberassigned to each main line and lateral connected to a manhole structure.
The assignment of the identifiers generated an early coordination effortfor the project team. The final product needed to have the key identifiers to bethe assigned manhole and pipe segment numbers created by the DOSD system ofidentification. A link was created between the database assigned identifier andthe City numbering system. Links to digital photo files are maintained byautomatic “update queries” in the database and photo files are assigned propernames either on the local hard drive, CD or server being employed for filestorage. CAD drawings of manholes (corbel/frame cross-section and plan viewdrawings) are stored directly in the database for viewing or report generationpurposes. Smoke test drawings are generated directly from the map of the sewersystem, including a “smoke leak” layer and are copied directly into thedatabase.
The ability to manage, manipulate and correlate a 70-MBdatabase, which expands to a 500-MB file with nearly 7,600 digital photos,reports and other images are included, would be virtually impossible without theuse of a database management system. In addition, the open architecture anddesign of the database allowed the SSES information to be readily referenced,queried, updated and manipulated as the larger GIS project began to beundertaken.
The SSES database enables users to query and view data inthree categories:
• 1) manhole inspection;
• 2) TV inspection; and
•3) smoke testing.
Figure 8 shows the main database interface form. Using predefined queries andreports, users can quickly and easily create and print SSES reports for manytopics. The user can navigate through the SSES data using various queries andforms implemented within the database environment. The following list representsa sample of the reports available from the SSES database:
Reports based ongeneral inspections:
• Detailed inventories of main lines and laterals
•Collection system summaries
• Repair reports including
manhole walls,manhole frames and capped/inactive lines
• Manhole cover inflow reports
Reports based on TV-inspections:
• Defect reports including
leakingmains, leaking manholes, roots, broken pipes and cracked pipes
The GIS interface is usedto present the SSES data in its spatial context and to present the spatialrelationships among various map features. The GIS interface was developed usingArcView and Avenue programming language. The main function of the GIS interfaceis to enable the user to visualize the sewer system characteristics on the mapand to query the system. The GIS interface allows users to point at map features(e.g. manholes or sewer lines) and retrieve SSES information from the database.It also allows users to run a set of pre-defined queries or build their ownqueries and to display query results or reports.
A useful feature of theGIS interface is to present and analyze the spatial relationships among mapfeatures. Examples of these relationships include adjacency (i.e. manholes in aspecific area), connectivity (i.e. sewer lines connected to specific manholes),and containment (i.e. manholes or sewer lines contained in a specific area). Animportant function of the GIS interface is to produce graphics on the screen oron paper that convey the results of analysis to engineers who make decisionsabout maintenance and improvement work. Graphical representation of the sewersystem characteristics (e.g. I/I sources) can be generated and thus allow systemusers to visualize and understand the SSES data and the analysis of potentialevents.
Each sub-sewershed is represented as a separate view (Figure 9). Each viewcontains a number of map themes that the user can choose to display or hide. Asub-sewershed view contains themes for the base map, manholes, sanitary sewerlines, storm sewer lines, street names, right of way, positive smoke testingresults and TV inspected lines, among others. The map interface retains all thestandard functionality provided by ArcView. In addition, customized toolsprovide quick access to key information like manhole depth, images of manholesand sewer lines, inspection reports and links to orthophotos.
The GISinterface communicates with the SSES database via the Open Database Connectivity(ODBC) standard. An important step during system configuration is to create anODBC connection to enable communication between the SSES database and theArcView project. The use of the ODBC standard enables databases developed usingother ODBC-compliant RDBMSs to be incorporated into the system in the future.
The GIS interface serves as the link between the SSES database and theproject area maps. Early versions of the GIS were designed to permit theconstant, ongoing editing of SSES database and AutoCAD map files that isnecessary during data collection and review procedures. Design of the ArcViewViews, collection of field data, review and processing of field data and qualitycontrol checks all occurred simultaneously, thereby limiting the ability to planeach step in advance. The design of the initial GIS interface was based on usingthe SSES database and AutoCAD mapping procedures already in place for non-GISrelated work on SSES projects.
With aging infrastructureand shrinking budgets, owners and engineers need to advocate and support apro-active and cost-effective approach to SSEM. Fortunately, with the advancesin computer technology, more accurate means of collecting and storing sewersystem information are available. By having better information readilyavailable, engineers and owners have the capability to make better designs andfiscal decisions that ultimately would help lift the sanitary sewer systeminfrastructure from the bottom of the heap, from the existing D- grade to onethat is hopefully an A+.