Credit: Photos: Woolpert
A Woolpert surveyor takes measurements and determines pipe sizes on a section of the sanitary sewer system in Alexandria's Old Town historic district. Attribute data was collected for both pipes and manholes—approximately 20 attributes per structure.
This surveyor determines flow direction and gathers as many attributes as possible on a curb inlet without a manhole. Data collection was sometimes a challenge for nonstandard historic structures in the city.
Locating structures, collecting attributes, and determining structure connectivity in the oldest and most congested areas of Alexandria presented several challenges.
Surveyors found more structures than anticipated. After the project got under way, surveyors began finding 30% more structures than estimated. Because inventory data had to be collected for 30% more structures, the project was in danger of going over budget. Woolpert worked with the city on a solution, which redirected surveyors to capture all sanitary and combined structures, and all storm structures in the public right of way, but not storm structures on privately owned parcels. This solution allowed the project to stay within budget.
Surveyors had to adapt the data collection effort along the way. Data collection sometimes was difficult for nonstandard historic structures:Instead of finding curb inlets downtown, surveyors sometimes found chiseled curb holes for accommodating stormwater. In some cases, surveyors could not access these structures, which meant fewer attributes were collected for these features.Surveyors working in the combined sewer area could not always discern immediately whether a line was a separate sanitary, separate storm, or combined sewer line.Within the pilot area, surveyors began finding additional structures, such as catch basins with and without hoods, which had to be incorporated into the geodatabase design. Because these hoods, which prevent bottles, cans, trash, and other debris from entering the combined system, could not be removed, surveyors could not collect certain attributes for catch basins. Woolpert adapted the geodatabase design and inventory effort to include these structures, documenting in the database whether a hood was present, missing, or broken so that city maintenance staff could address these issues.
The highly populated area, and the density of utilities, made collecting data and establishing connectivity challenging. Alexandria, and Old Town in particular, is known for its narrow streets with the right of way and historic buildings located right at the sidewalk's edge. This former industrial area has been reborn with dense residential development, which city planners say enhances the city's character. “Alexandria has prime real estate,” said Baker, “but that presents challenges in terms of utilities.”
Over the years, for example, city crews had to install utilities in the tightest of spaces; Woolpert surveyors routinely found 20 to 30 utility structures or lines—conventional, unconventional, historic, and abandoned—at a single intersection. And since Alexandria grew by annexation, it inherited infrastructure from other communities dating back to the 1940s. Woolpert surveyors spent time in the field learning how different infrastructure systems had been installed and connected over time, and verifying whether the right structures were connected to the right pipes.
Cars often remain parked on Alexandria's streets, blocking manholes and making data collection impossible. If inventory data could not be collected for certain structures, proper connectivity could not be established. When surveyors noted other discrepancies in the field, issues were documented on a project-specific ArcIMS Conflict Resolution Web site. Woolpert surveyors uploaded preliminary utility data as it was collected in the field so city staff could track, investigate, and resolve conflicts. This Web site allows users to post data, automatically generate maps, use a redline tool, perform queries through SQL commands, turn map layers on and off as needed, and generate reports by geographic area or structure type to aid in conflict resolutions.
City staff will decide how to prioritize and resolve these conflicts, either by sending out another field crew, performing dye tests, or doing something more invasive.What's Ahead
As the project nears completion, one of the next steps will be to create an asset management/work order management system. Ultimately, the city also wants to collect vertical data as needed throughout the city for modeling applications.
“As we learned in the past, this mapping data is simply a snapshot in time,” said Baker. “Redevelopment will continue to change the landscape in Alexandria. It's the city's responsibility to keep this information current so that it always has value. We are developing a process to ensure that any updates received by developers or generated by a work order management system are added to the geodatabase.”
The infrastructure GIS also is a starting platform for incorporating condition-assessment data and information from the city's infiltration/inflow, sanitary sewer overflow, and NPDES permitting projects. Ultimately, the city envisions the infrastructure GIS available as a desktop application for everyone.
— Salva is a civil engineer and project manager for the sewer mapping program, DOT and environmental services, with the city of Alexandria; Cobb is the survey manager for Woolpert's Portsmouth, Va., office and Woolpert's project manager for the city's sewer mapping program.