By Emily Constantine Mercurio
Our nation’s sewers are under critical examination now more than any other time in history. The act of collecting sewage and stormwater, transporting it to the treatment system, and processing waste is no doubt a feat of science and engineering that we take for granted in the developed world.
Sewer infrastructure is a critical public asset whose importance in modern life cannot be overestimated, and to keep things running properly takes round-the-clock maintenance and operations. It’s only when the system fails or floods that we fully appreciate our dependence on it.
At last count, there are at least 16,000 publicly owned wastewater treatment systems (also called Publicly Owned Treatment Works, or POTWs) in the United States, providing sewer service for more than 245 million people. Additionally, about 860 communities have combined sewer systems (CSS) that serve about 40 million people.
These CSS capture both sewage and stormwater before the combined mixture is treated and either reused, recycled or discharged to the environment. In wet weather events, untreated waste and stormwater can escape capture due to overfilled combined storm sewers, known as combined sewer overflow (CSO). These CSO events can spill sewage into rivers and streams, creating a major source of water pollution across the country.
To make matters even more complicated, the effects of climate change and increased rainfall in some areas have created new challenges to our nation’s sewer infrastructure.
Additionally, federal and state regulations like those for municipal separate storm sewer systems (MS4) that discharge untreated runoff into the environment have added new demands of our publicly owned entities that manage these systems.
The impact of sewer overflow is especially felt in the eastern United States where the combination of aging infrastructure and increasingly frequent and severe rainfall events have presented significant challenges in the capture, handling and treatment of sewage.
With some eastern cities receiving record rainfall in the past few years, it’s now more important than ever to understand our sewer infrastructure, including: where it is, who is responsible for it, when it was installed, how it is networked, and what are its defining characteristics. These data are essential for performing maintenance, for planning growth, and for undertaking new construction projects. The need for better understanding, visualizations, and communication of sewer data assets is a perfect use case for Geographic Information Systems.
The Case for Mapping Sewer Networks
There are many moving parts to a sewer network. Representing each manhole, sewer line, pump station, inlet, and outlet within a unified map requires expertise in the art and science of mapping. Spatial data from a breadth of sources like engineering drawings, as-builts, CAD datasets, spreadsheets, field surveys, sewer cameras, flow meters, and aerial imaging have traditionally been the go-to datasets for constraining the topology, attributes, and capacities of sewer networks. Additionally, new kinds of data procured from emerging geospatially-enabled technologies like subsurface robotic pipe inspections and simultaneous localization and mapping (SLAM) provide a glimpse of where sewer map data will come from in the future. For POTWs and their stakeholders, information from both old and new sources can synergistically come together in a GIS as part of a greater asset management program.
Creating a unified map of sewer infrastructure from many data sources requires time and effort to construct proper geospatial data topology, correct directionality, and accurate attributes. These undertakings are greatly supported by the development of data models, workflows, tool sets, metadata, and documentation that will make it easier for workers to maintain sewer data now and in the future. The added bonus of developing these data for use in a GIS is a highly valuable and functional data asset that can be used to inform operational and business processes at every level of the organization.
An organization’s data represents the outcomes of some of the mostly costly investments and operational endeavors undertaken by that entity. When big or important projects are completed, it is the data collected during the work that lives on after staff turnover and retirements. With respect to mapping sewers, many POTWs already have much of the data they need to put into a mapping system, whether it be in a CAD file, on paper, or living in a spreadsheet. GIS liberates these data so that it becomes a living product and enables them to be leveraged in powerful ways and across multiple operational areas.
Implementing a sewer GIS increases the return on investment of data, creates a platform for data sharing across other systems, and sets the stage for innovation and efficiency improvements.
While creating and maintaining a sewer GIS might sound like a big-ticket item, modern mapping tools are making it more cost effective than ever before. Competitively priced software licensing, open-source GIS technologies, cloud computing, and in-browser processing can lower the costs of geospatial application development. Further, establishing geospatial data pipelines and application programming interfaces (APIs) can reduce the time needed to condition data before they are ingested into mapping systems and across multiple software platforms.
Taking sewer GIS to the next level with network tracing
One of the most exciting applications of a sewer GIS is the capability to perform network tracing. These traces can show the locations and direction of wastewater flow from any point within the system and are commonly performed by POTW engineering personnel. The ability to perform a sewer network trace within a GIS is valuable for several reasons.
The trace helps operators and engineers better visualize the contributing sources to main sewers that collect wastewater from the many lateral and branch sewers that service buildings, businesses, and homes. Enabling this capability in a GIS environment makes it more accessible to other personnel, and especially those working on site. Allowing POTW easier access to network tracing through a GIS helps teams across the organization stay informed on what addresses are connected to which sewer mains, facilitating better communication and collaboration on maintenance and expansion projects.
The network trace can operate upstream to locate which buildings might be contributing to problems downstream. From any manhole or service location, the sources of industrial or commercial waste violations or exceedances can be better identified through upstream sewer tracing. The ability to query any point along the sewer network and constrain the sewershed from that point saves time and resources of field personnel when diagnosing problems and finding solutions.
Sewer systems are vital, publicly funded resources yet most people know very little about the way their homes and businesses connect to this system. Inviting the public to view a unified and continuous map that represents their sewer network is a great learning resource and facilitates increased awareness and familiarity with the work of the POTW.
Once such example is the Flush-It web application. This app allows the public to interact with an engaging map that shows the path their flush takes on its way to the treatment facility. The tool was built on open source geospatial technology and uses a unified, topologically correct sewer data set as the backbone of the network trace. Applications like these are also great for educating students on the importance of science and engineering on daily life.
The process of building a GIS of networked sewer map from a set of historic and disparate set of data sources might seem daunting for many POTWs, but the benefits of doing so profoundly outweigh the headaches.
This type of mapping system saves time and money in the long run by ensuring that the best and most current data are shared across multiple operational units and opens up new pathways for innovation and outreach.
As cities continue facing the complications of aging infrastructure and a changing climate, there is no better time than the present to modernize sewer data and use this amazing data resource to both protect communities and equip them with the information needed to tackle future challenges.
Emily Constantine Mercurio is the CEO and co-founder of CivicMapper. Emily grew up in Pennsylvania’s coal country, and at a young age became interested in geoscience, maps, and the interplay of nature and human activity. Her career has centered on creating innovative, data-driven, and tangible solutions to support decisions at the intersection of our natural and built environments. She leverages more than 25 years of experience with Earth science data and geospatial technologies for leading the development of CivicMapper’s products and services. Emily has a Ph.D. in Geology and is a licensed professional geologist.
