By John Nolte, GISP, GIS Manager, Denver Water

Denver Water is committed to delivering a safe, reliable water supply to its customers. The water provided to homes and businesses is lead-free, but lead can get into the water as it moves through customer-owned, lead-containing household fixtures, plumbing, and water service lines—the pipe that brings water into the home from the main in the street.

In 2020, Denver Water launched its unprecedented Lead Reduction Program. The program was approved in December 2019 by the Environmental Protection Agency and the Colorado Department of Public Health and Environment.

This program contains several regulatory requirements, including the identification, inventory, and removal of an estimated 64,000 to 84,000 lead service lines, a task that will take 15 years to complete. In addition, Denver Water will be conducting a comprehensive communications program and distributing pitcher filters and replacement filters certified to remove lead to every customer who has or may have a lead service line. The filters are to be used until six months after the lead service line is replaced.

Denver Water's Lead Reduction Program is a massive undertaking. The company serves more than 1.5 million people in a 335-square-mile service area with more than 3,000 miles of pipelines, 23 pump stations, 30 underground reservoirs, and more than 320,000 taps.

Denver Water maintains extensive customer usage and billing records. However, information on service lines is incomplete because the utility does not own any part of these lines. The work of identifying the location of these lines and the materials they are made of required extensive research and analysis. The goal was to develop a probability matrix designed to fill data gaps and build an initial inventory.

Tasked with developing the inventory, Denver Water's GIS team began with tap locations pulled from the utility's customer billing database. The team then added research results from hand-written records kept by one utility employee who had previously replaced many lead lines. Those records were augmented with information from construction permits issued by the City and County of Denver, including when the permit was issued and the type of work it covered.

GIS staff worked with a consultant to build the initial inventory using Esri ArcGIS Desktop. Denver Water staff migrated the lead data to ArcGIS Pro as they progressed with the project.

These combined sources of information resulted in fewer than 1,000 locations of lead service lines. With many historic homes in the Denver Water service area, the team had to analyze additional data sources to get a more accurate inventory depiction.

Corona Environmental Consulting helped build the inventory by updating the geodatabase with existing data, such as tap date and year the parcel's home or building was built. The consultants also added results of previous water quality tests at customer taps. The GIS team used the new data in ArcGIS Desktop to sort locations into categories, describing the certainty or likelihood of a lead service line.

The resultant data was added to an ArcGIS Pro project and developed into a lead service line inventory map used by decision-makers to plan line removals.

Denver Water's initial inventory identified more than 80,000 lead lines serving about 120,000 distinct customers, including multifamily buildings with one service line for multiple customer dwellings.

The team members added more data to further refine the results. They analyzed attributes for discrepancies in material type. Additional data included water quality data and information about line material from Denver Water's universal metering program, which began installing meters in 1987 at locations that did not previously have them.

The additional data narrowed the projected maximum number of lead service lines to about 64,000 locations. The team successfully reduced projected inventory locations from the high-end range. This move is expected to save Denver Water's Lead Reduction Program more than $50 million over the program's 15-year life-span, based on the cost of replacing lines and supplying customers with water filters.

To remove all the projected lines within 15 years, Denver Water will need to replace approximately 4,500 service lines per year and distribute water filters to residents who live at properties enrolled in the program. 

The distribution of filters to all customers presented another challenge because Denver Water's customer account and billing system tracks customer accounts generally based on property ownership.

This creates a challenge for multifamily properties served by a lead service line where there are multiple tenants who do not have a direct customer relationship with Denver Water. To ensure that the filters are sent to residents who live at these locations, Denver Water needed to identify and categorize customers in its billing system associated with each lead service line, such as homeowner, property owner or manager, or tenant. To do this, the team added more data, including US Postal Service addresses and information from the City and County of Denver. The GIS team used ArcGIS Pro to analyze an additional 30,000 addresses in suburban water districts served by Denver Water by contract.

Once identified, addresses in Denver and the suburban areas were added to the inventory, and a public-facing web map was developed in ArcGIS Online using ArcGIS Web AppBuilder. This map informs customers whether they are included in the program and whether their service line is categorized as known lead, likely lead, unlikely lead, or nonlead. The team also created an ArcGIS StoryMaps story to teach website visitors how to use the map.

In addition to the map, the inventory data supports a prioritization model that includes demographic information to plan replacement work.

Contractors doing the replacement work are using mobile applications to update the program's database, inventory, customer billing information, and GIS. These applications include ArcGIS Survey123 and ArcGIS Collector. The GIS team will use information about replacement work to update the public-facing map every six months, recategorizing the homes that have had their lead service lines replaced.