Sewer condition assessment - GIS database without introducing processing errors

Sewer condition assessment - GIS database without introducing processing errors

BJ Raval, AICP
GIS Southwest Inc.
8601 North Black Canyon Highway, Suite 215
Phoenix, Arizona 85021

John G. Malone II, P.E.
URS Corporation
7720 North 16 th Street, Suite 100
Phoenix, Arizona 85020

Abstract
The City of Phoenix (COP) has begun a program to investigate and evaluate the COP™s wastewater collection system. The COP divided their system into four groups. These include the Unlined Concrete Sewer System, Large Diameter Sewer System, Small Diameter Sewer System, and Lined Concrete Sewer System. In 1999, the COP hired GIS Southwest/URS to investigate and evaluate the condition of the Large Diameter Sewer System, consisting of approximately 1.37 million feet of 15-inch through 42-inch pipe not included in the Unlined Concrete Sewer System. Due to the pending Sanitary Sewer Overflow policy and Capacity, Management Operation, and Maintenance (CMOM) requirements, the COP needed a system to manage the large amount of data this study would produce. The system would store the information gathered by the Closed Circuit Television (CCTV) investigations and the subsequent Capital Improvement Program data in a controllable format. The COP chose the COP Water Department Geographic Information System (GIS) database. Historically, study results are stored in the GIS database. This information is gathered and printed electronically and hand-entered into the GIS database, resulting in many errors. GIS Southwest/URS has used an automated system for an electronic collection of data and a inhands-offlS transfer into the COP™s GIS.

Introduction
Sanitary Sewer Evaluation Studies (SSES) have been completed by both large and small communities across the county. SSES have historically required the capture, management, and evaluation of a large amount of data. These data are generally stored on a database such as GIS. Historically, the information is captured by CCTV and passed to the Engineer or evaluator using a hard copy, paper format. The Engineer, or evaluator, would hand enter the data into a GIS- compatible database.

Technology changes in database management have allowed the capture of the information including: defect type, location, severity, and a still photo while in the field and directly transfer to the GIS database. This allows the direct transfer of data without the tedious hand entering of the data into the database. The use of a GIS database allows for the integration of traffic data, environmental data, contour data, and physical features into the evaluation. These features can be overlaid onto a single map using ARCINFO TM .

To our knowledge, and through our national SSES group located in Virginia Beach, Virginia, this is the first project being completed using the seamless and paperless transfer of information in the United States.

Project Scope
The Large Diameter Sewer Condition Assessment and Inspection Program includes a detailed analysis of the 15-inch through 42-inch pipe including the following task items:

Provide a CCTV inspection of all the pipes which are within the size requirements;
Provide manhole observations as the CCTV inspections were completed;
Place all inspection data onto the COP Water Department GIS including defect locations, defect types, and photographs of the defects;
Provide an assessment of all the pipes including defect scoring and impact factor scoring onto the COP Water Department GIS; and
Provide a Capital Improvement Program (CIP) based upon the information listed above.

The COP™s expectation of this project was to meet the Condition Assessment and Rehabilitation requirements of the pending EPA Collection System Regulation CMOM section. These expectations included:

CCTV Inspection
Rating System for Pipe Defects and Establish Priorities for Rehabilitation and Repair
Identify and Repair the Imminent Failure Locations
Prepare Long-Term Rehabilitation and Repair Program including priorities
Prepare Capital Improvement Program including costs and schedule of repairs

City of Phoenix Database Preparation
The COP Water Engineering and GIS Department had to provide a database of the sewer system prior to the award of the project. The process of extracting the desired data from the COP Water Department Geographic Information System (GIS) required several steps to achieve the correct format. The first step was to use ArcInfo and ArcEdit, which is the platform that the data currently reside in, to query the database for sewer pipe 15-inch to 42-inch of non-concrete pipe material, such as Vitrified Clay Pipe (VCP) and Ductile Iron Pipe (DIP). A coverage was created by doing a iogetld on the sewer lines that met this criterion. The data in this coverage had to go through a clean-up process for the following reasons: (1) the COP GIS information is stored in a quarter section by quarter section, or what is termed as a tile by tile basis, and (2) to assure for the highest accuracy possible based on COP GIS current records. Because of the tiled data format, the pipeline segments had to be snapped together across tile (quarter section) boundaries, and lines needed to be un-split in order to remove unnecessary breaks in lines or pseudo-nodes. For quality assurance, flow direction was checked, pipe material in question was re-verified, and missing pipelines were added.

The next steps in the process involved much data manipulation. The information or the attribution data about the manholes, inverts, stationing, etc., is contained on the nodes (at the ends of each line segment) and not on the line segment itself. For the purposes of the project, the consultant needed this information on the line segment. Therefore, the information had to be transferred from the nodes to the lines (arcs) by relating the two through their common unique identifier, the arc number. At that point, the COP GIS Department chose to compare the GIS coverage and its associated data to a Sewer Flow Modeling database that is maintained in the COP Wastewater Engineering Division.

The Flow Modeling database not only contains the information that the COP GIS Department maintains in the GIS, but also additional information such as slope and basin designation for each sewer pipe. In order to compare two databases, the COP GIS Department used the ArcView TM platform. The GIS coverage that the COP GIS Department created was converted to an ArcView shapefile and the Flow Modeling database, maintained in Fox Pro and imported to Microsoft Access, was imported into ArcView as a database file. Before a comparison could be done, a couple of obstacles had to be overcome. The two databases did not have a common field that could be compared, and the quarter section numbering system was not the same between the two tables. It was decided the GIS fields would be manipulated to fit the schema of the Flow Modeling database. This was done by creating a look-up table in ArcView that would be used to match the GIS quarter section numbers to that of the Flow Model. Once the quarter section numbering systems matched, the fields in the GIS database table were manipulated to create the primary key field that would be used as the common field. Next, the Flow Model table was joined to the GIS table to create one table containing their combined information. By joining the tables, the COP GIS Department discovered some records did not match up or, in other words, discrepancies were found. Some examples of these were missing manholes, pipe segments, attribution, etc., which was caused because the pipe was in an area that had not been converted to GIS or updated. Several hours of research on these unmatched sewer pipe segments and updates to both the GIS data and the Flow Modeling data were done until a 100% match was achieved.

The pipe segments that needed to be added to the GIS database were edited and added in ArcEdit and then re-converted to an ArcView shapefile. The final shapefile of the combined databases of sewer lines 15-inch to 42-inch made of non-concrete pipe was then delivered to URS, along with other shapefiles containing pertinent COP data, such as city limits and street information.

Database Management and Use

Establish Database Design
GIS Southwest, Inc. (GISSW) had the task of bringing data from a variety of sources together into a coherent database structure. The goals of the database were several. First, the database must be compatible with the COP GIS database. The COP database was provided at the beginning of the project. Second, the database must incorporate the field data collected by Hoffman Southwest, Inc. (ProPipe). The ProPipe data was collected into a Microsoft Access database running behind an application called Flexidata TM which is produced and distributed by PearPoint, Inc. Third, the database must incorporate manhole inspection data collected in the field outside of the Flexidata application. To this end, GISSW designed a manhole inspection database including an input form. This database was designed based on input from the other team members in terms of the data that were needed and in terms of integration with the final database. Fourth, the database had to be dynamic in nature to accommodate the evolving needs of the project and had to provide the flexibility to incorporate analysis parameters such as pipe defect scoring and impact analysis factors. Finally, the database had to provide a useful and efficient tool for this project, as well as for the COP to conduct future analysis.

PearPoint Flexidata TM Conversion Requirements
The initial database provided by the COP was an ArcView shapefile containing sewer lines from 15-inch to 42-inch in diameter within the COP. This database contained information about each line segment including upstream and downstream manhole numbers, pipe age, pipe slope, pipe length, pipe diameter, and others.

The Flexidata database was provided on a periodic basis by ProPipe as data came in from the field. Generally, data were transferred to GISSW on a weekly basis. The Flexidata database is a Microsoft Access database comprised of numerous related tables. Each week, the data collected during the previous week were sent to GISSW via e-mail. GISSW then processed the weekly data using a group of Avenue scripts to conduct QA/QC and to append the weekly data to the project database. The data contained within the structure of the Flexidata database had to be parsed to pull out the specific data items that were needed for this project. Of twelve tables contained in the Flexidata database, data from only five tables are being used for this project.

The manhole inspection database was designed to collect and store data about the condition of manholes in the system, the flow direction through the manhole and grit depth. The team collectively identified the data items needed to provide the proper information about each manhole for future analysis to facilitate repair and rehab needs. In order to enable incorporation of the manhole inspection data into the main database, GISSW designed an input form that the field crews could use and data entry personnel could subsequently use to populate the database.

Each of the pieces described above keyed on the upstream and downstream manhole numbers as the link to the GIS database. The pipe segments throughout the database structure are identified by their upstream and downstream manhole. The manholes are uniquely identified by an eight- digit number, comprised of the quarter section map number and the assigned manhole number within that quarter section.

The final step in the database design/data conversion tasks was to incorporate all the pertinent data into the GIS database originally provided by the COP. This was accomplished with an Avenue script that joins the Access database tables to the ArcView attribute table using the upstream and downstream manhole numbers as the key fields for the join. The resulting database enables GIS functionality to visualize and analyze the data. The user is then able to click on individual defects along a line segment to get information about that defect and see a picture of the defect as captured by the CCTV team. The user can identify patterns of defect type and severity, can get pipe segment score and impact factors, and can see manhole condition. The user is also able to conduct spatial analysis using GIS tools to determine the relationships between the various factors.

Data Flow
ProPipe provided the CCTV inspection and manhole observations for the project. The CCTV inspections were saved using PearPoint Flexidata software. The manhole observations are used to eliminate the majority of manholes that may require further inspection. GISSW obtained the raw data for the CCTV inspections from ProPipe and applied the information as a theme to the COP Water Department GIS database. The COP distributed a copy of the database at the beginning of the project with the knowledge that all adjustments to the database will be made at the conclusion of the project. GISSW added the scoring based upon the field generated defect coding and defect severity.

URS reviewed all CCTV tapes generated by ProPipe and made adjustments in the database as required. URS returned the database, with the modifications, to GISSW to include on the COP GIS database.

GISSW assigned the impact factors, using GIS. The line segments would be sorted for debris/grit defects and pipe defects. The debris/grit pipe segment list was used to determine debris problem areas. The pipe segment list was used to compile a CIP for the repairs/rehabilitation of the system.

Procedure for Correcting GIS from Field Data
The largest difficulty discovered during the completion of this project was the inconsistencies between the COP database and the real world. These inconsistencies include different manholes found during the CCTV operation and not included in the database and large deviations in the segment footage. The database footage is the result of as-built drawings. The team reviewed all footage differences larger than 10 feet. This is what was considered a significant deviation. The causes of the inconsistencies include as-built drawing errors, additional manholes constructed but not as-built, relocations of pipe segments not as-built, and errors obtained during the edge matching process.

The project team and the COP established the following procedural flow chart to handle new features located during the CCTV investigation.

Rating System
URS established a rating system for the defects that are generally found in the COP sewer system. The defect types and classifications are based upon a combination of PearPoint Flexidata Observation Codes, COP Procedures, the UK Water Industry Manual of Sewer Condition Classification, and prior experience of the project team with the COP Sewer System. The rating system is shown in Table 1.

Table 1: Rating System

The scoring has been broken into two categories. These include debris/grit defects and pipe defects. The pipe defects includes all defects except Debris, Grease and Obstruction. The pipe defects are used to establish the CIP for rehabilitation/repair of the system. The grit/debris defects have been used to analyze the capacity of the system, and to determine debris removal costs and requirements.

Impact factors have also been assigned to each pipe segment. The impact factors are a combination of a traffic factor, environmental factor, railroad factor, and age factor. The traffic factor is based on the pipe crossing a roadway with a certain 1999 Average Daily Traffic (ADT). The environmental factor is based on the pipe segment crossing a wash, irrigation canal, or drainage facility. The railroad factor is based on the pipe crossing a railroad track. The age factor is based on the joint material used at the time of construction. The newer joint material and construction method is more adept in keeping roots and groundwater out of the system. The total impact factor is a combination of the impact factors and is multiplied by the raw pipe score to determine and impact factor score. The impact factor score is used to determine the order that the pipe segments will be rehabilitated/repaired. The impact factors are listed in Table 2.

Table 2: Impact Factors

The impact factors are automatically assigned to the pipe segments using GIS. The traffic coverage was obtained from Maricopa Associations of Governments (MAG) in GIS format. The railroads, washes, canals, and drainage ditches are geographic features. The year constructed was obtained from the COP database.

Overview of Scoring System and GIS Layering
The automatic scoring system allows for immediate recall of data using the GIS. Data gathered and stored in the GIS can be manipulated and used to determine construction requirements for the present and may help determine future construction requirements. For example, a Capital Improvement Program is being developed for rehabilitation and repair of the existing segments where defects have been identified. The GIS is helping to provide slope and flow information from the database received from the COP. The raw scoring of the segments based on the defects is providing the locations of the repairs, and the final scores with the impact factors show the proposed order or necessity of repair. The GIS also provides data on the adjacent segments, which may not be in the initial repair group but should be rehabilitated in conjunction with these segments in order to save money in the long run. The slope and flow information will provide data to show which line segments may be at or near capacity and may need replaced instead of rehabilitated.

Results
The major results of using GIS for a Sanitary Sewer Evaluation Study are:

Less opportunity for data entry and processing errors and provided project tracking capabilities;
Almost immediate accumulation and management of the data;
Automated source for data manipulation and queries;
User friendly software for storage and review of the data;
Seamless data integration into COP™s GIS;
Spatial visualization of sewer system condition and problem areas; and
Use of spatial analysis tools to provide a more complete picture of cause and effect relationships and the various condition parameters on the resource factors.

Lessons Learned
We found several problems during the project. These problems include:

Map number errors: The COP map numbers, which are being used by the CCTV field operators, do not match the manhole numbers in the database.
Tracking actual pipes length CCTV™d. The 15-inch to 42-inch sanitary sewer system has never been cleaned since it was constructed. It was assumed that these pipes would be self- cleaning and that maintenance requirements would be minimal. During the CCTV process, it was found that significant debris occurred in segments that would not allow the CCTV tractor to get by. This resulted in a number of segments which were televised at two or more times and the footage and database information would either be overwritten or would have to be added together in a final database format.
Data lost (misplaced) in transfer.
Incorrect data entered by the CCTV operators.
Phoenix Sanitary Sewer System is dynamic. New manholes and pipe segments are constantly being added to the system. The model and the database lag behind due to the timing between construction and submittal of the as-built plans.

The use of GIS allowed for the tracking and correlation of these data.

Conclusion
GISSW/URS is proposing this technology on all SSES projects. Even if the municipality does not have GIS capabilities with their sanitary sewer system presently, the data will be managed and stored in a format that will allow for this in the future. The proposed CMOM regulations specify the use of a maps and information management for the sewer system. Also, CMOM specifies the requirements of CCTV inspection, a rating system to establish repair/rehabilitation priorities, and a Capital Improvement Program based upon the rating system. The use of GIS is a natural way to collect, store and manage the data required for the CMOM regulations.

Acknowledgements
City of Phoenix Ś Paul Kinshella, P.E., Greg Ramon, P.E., Terry Dorschied
Hoffman Southwest, Inc. (ProPipe)
PearPoint