Use Risk-Based Asset Prioritization to Develop Accurate Capital Budgets

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March 31, 2020 | Matthew Grewe

This story is featured in the March edition of AWWA's Opflow Journal

North Charleston Sewer District (NCSD) was founded in 1972 to provide wastewater service for customers in an area approximately 60 mi2 in three different South Carolina counties, including six municipalities. The district currently has about 31,000 customers and manages approximately 480 miles of a gravity collection system, 35 miles of force mains, and 11 miles of identified lateral connections. In total, the linear asset network is 520–530 miles.

As for vertical assets, NCSD has 60 pump stations, making it unique in a coastal pain area with little topology. This creates an average of one pump station per square mile, as the trunk interceptors—installed in the late 1960s and early 1970s—are at the area’s lowest topology points, between the Ashley and Cooper rivers. These interceptors are 42, 54, 60, and 66 inches in diameter. Piping infrastructure ranges from 4 to 78 inches, with the largest pipelines inside the 32-mgd Felix C. Davis Wastewater Treatment Plant (WWTP), and the gravity collection system includes more than 11,000 manholes.

From mapping to advanced analysis

To help manage its infrastructure, NCSD standardized on Esri’s ArcGIS database as its “data of record” in 2001. With a mature geographic information system (GIS), the district had most of its infrastructure's descriptive information readily at hand. Although initially the GIS was used as a historical reference tool, it has become a daily driver for many components of the district’s infrastructure management toolset.

Internally, NCSD integrated Innovyze’s InfoAsset Planner asset repair and capital project prioritization software for a risk-based asset prioritization and prescriptive maintenance planning tool. NCSD’s project planning software works within the GIS database, using work order and inspection reports from Lucity, a computer maintenance management system (CMMS). NCSD’s open-platform software avoids database duplication yet allows data to be shared, in turn maximizing decision making through the organization.

A focused capital planning program

NCSD started using the asset repair and capital project prioritization software in 2013 for its capital planning program, which led the district to create its Capital Projects Division. The division is headed by a capital projects director and includes engineers, GIS staff, inspectors, and wastewater collection system and pump station staff.

The Capital Projects Division developed a five-year capital plan that allowed the district to proactively review maintenance requests and schedule asset renewal and/or replacement (R&R) within NCSD’s wastewater transmission and collection system. The challenge was to determine what assets to service and when.
The average age of pipes in NCSD’s underground network is about 41 years.

According to AWWA’s 2019 State of the Water Industry report, R&R of aging water and wastewater assets was the top challenge identified by surveyed utilities, with financing capital improvements as the second most important issue.

This is a common challenge on the East Coast of the United States. Parts of the city of North Charleston date back to the 1600s. There were infrastructure booms just before World War II, right after, and again in the 1980s that have sustained the area. Up until the 1950s, most of the pipe network was vitrified clay pipe (VCP). From then until the 1970s, it was a mix of concrete pipe and VCP. Then, starting in the mid- to late 1970s, polyvinyl chloride (PVC) was used. Force mains are ductile-iron or cast-iron pipe. The largest material in the system is VCP, followed by reinforced concrete pipe. There are even some problem pipes called “Orangeburg” pipe, which is papier-mâché reinforced by tar, leftover from the World War II era.

To ensure it could efficiently and effectively inspect these assets, as well as budget and plan for ongoing capital improvements, NCSD used in-house resources to complete an asset repair and capital project prioritization methodology. The district onboarded its asset repair and capital project prioritization software to help address the R&R of its aging wastewater transmission and collection system. Using internal and external inspection records, as well as data from the recommended capital planning efforts, NCSD began to substantiate the work that needed to be done to specific assets so the R&R budget could be justified and defended.

Developing a prioritization framework

NCSD’s typical process involves incorporating preloaded inspections, with geospatial information, from the district’s closed-circuit television (CCTV) database into the asset repair and capital project prioritization software. In addition, lateral, mainline, and manhole inspections are processed in the asset repair and capital project prioritization software. These geospatial inspections allow for a geo-referenced rehabilitation plan to be developed.

In the asset repair and capital project prioritization software, NCSD catalogs condition assessments from the CCTV data and creates asset risk scores, provides R&R recommendations, and assigns risk scores. NCSD uses this framework to prioritize the riskiest assets so intermediate inspections can be scheduled to understand impacts to deteriorating assets. This allows NCSD to maintain a realistic multiyear capital plan.

The information used to score assets is based on risk determined by the following factors:

  • A Consequence of Failure (proximity to buildings, railroads, water, critical facilities, and roads; pipe diameter; and population density
  • Likelihood of Failure (Proximity to acidic soils, installation date, material, age, and pipe diameter.)

A risk summary illustrates the length of pipe and the percentage of total length by risk category.

NCSD is confident with such an assessment because of the maturity of its GIS. The unweighted factors are analyzed to produce a 5 × 5 bi-directional risk matrix, which is used to visualize pipe length and percent of total pipe length at each critical stage, as shown in the figure above.

The rehabilitation plan generated by the asset repair and capital project prioritization software is funneled into and processed through NCSD’s Rehabilitation of Lines Program and capital budget so proper funds are allocated accordingly each year by asset. What began as a simple analysis has grown to consider real-world scenarios. The program is completed for all pipelines, manholes, and laterals.

Recently, NCSD received rehabilitation work bids that were within 3 percent of the actual contract price awarded and the budgeted dollar amount identified by the district’s asset repair and capital project prioritization software. At a minimum, the software’s cost tables are updated every six months to keep up with current market prices. The capital planning software will then generate recommendations that help NCSD project its budgeted requirements and fiscal goals into the future.

NCSD also connects its CMMS to the risk model and planning software via an exchange module. There are approximately 11,000 pipes in the CMMS database, and more than 95 percent of the CMMS work orders are leveraged in the risk analysis tool, which generates a Likelihood of Failure scenario based on the history of work orders against a pipe. 

Asset management expansion

NCSD’s asset management program is still evolving, as a lot of the assets on the list require inspection in hard-to-reach areas, such as along a pond easement behind residential buildings. Access for inspection equipment and vehicles is limited. The goal is to look at the cost plan tables used in evaluating these assets, especially if the contractor is charging per mile of pipe.

Currently, NCSD manually exports the R&R recommendations from the asset repair and capital project prioritization software and then imports them into the CMMS. NCSD needs to use the application programming interface to the CMMS provided in the asset repair and capital project prioritization soft-ware. Improving the frequency and seamlessness of this data transfer is a key project NCSD expects to implement in the near future. NCSD also plans to expand its program to other asset classes, including pump stations and treatment plant assets.

Sound Stewardship

NCSD is in great standing with state and federal environmental governing bodies, partially because of the sound stewardship of the district’s assets and the leadership of its Capital Projects Division staff. The district’s culture of effective, prioritized asset management starts with the integrity, accuracy, and detail of the data in its GIS. This up-front effort drives most of NCSD’s analysis and allows its representatives to speak confidently about the location, attributes, and condition of the district’s wastewater transmission and collection system assets.




Matthew Grewe

Matthew Grewe

Regional Sales Manager, Americas


Matthew Grewe is an experienced engineer and Regional Sales Manager at Innovyze. He serves utilities in the American Southeast, always ensuring that they have the right tools for effective management of their water and wastewater systems.

Phillip Sexton, PE

Phillip Sexton, PE

Capital Projects Director at North Charleston Sewer District


Phillip Sexton is the Capital Projects Director at North Charleston Sewer District (NCSD)

David Dellenbach, GISP

David Dellenbach, GISP

Asset Management Specialist at North Charleston Sewer District


David Dellenbach is the Asset Management Specialist at North Charleston Sewer District