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Carrollton’s Infiltration and Inflow Rate Among Lowest in the Region

Post Date:02/19/2020 5:09 PM
In a recent assessment by the Trinity River Authority of Texas (TRA), Carrollton had one of the lowest infiltration and inflow rates of the 20 partner cities evaluated. This means that less groundwater and stormwater entered Carrollton’s sanitary sewer system than other communities in the Metroplex, resulting in less strain on the water treatment system and lower costs for Carrollton utility customers. 

The ranking by the TRA of the Central Regional Wastewater System reflects the City’s commitment to ensure only wastewater enters the sanitary sewer system to be treated, keeping wastewater rates low and preventing sanitary sewer overflows (SSO). SSOs can contaminate City waters, kill fish, cause serious water quality problems and economic loss, as well as result in property damage and public health impacts. 

“Carrollton’s vision is to be the City that families and businesses want to call home, and the prioritization of our citizens’ health and safety through investment in our infrastructure is an important part of progressing toward that vision,” Marc Guy, Assistant City Manager for Public Safety and Development Services, said.

Sanitary sewer systems collect and transport domestic, commercial, and industrial wastewater to treatment facilities. Infiltration is groundwater that enters the sanitary sewer system, and inflow is stormwater that enters the system. Both can overload the capacity of the pipes reducing the system’s ability to transport wastewater thereby increasing the cost to treat the total higher volume of water.

Stormwater should be entering the stormwater sewer system before being discharged into rivers, creeks, and ponds, but can enter the sanitary sewer instead through private and public defects within the collection system. Some sources of improper connections include driveway drains, window wells, and downspouts. Groundwater can also improperly enter the sanitary sewer system through cracks and leaks in sanitary sewer pipes and/or deteriorated manholes. 

Carrollton is committed to preventing improper connections from occurring through consistent maintenance of its 430 miles of public sanitary sewer lines and 5,947 manholes. That commitment is proven in the TRA’s Phase VI Infiltration and Inflow Assessment.

Infiltration & InflowAccording to the report, Carrollton’s ratio of the maximum daily flow to the average daily flow, or peaking factor (PF), was only 3.3 for a one-year storm peak compared to an average of 7 across the 20 cities evaluated. In addition to having the lowest PF for a one-year period, Carrollton also had the second lowest PF for a five-year storm peak of 4.8 in comparison to an average of 10.8.

To prevent improper connections from occurring and therefore allowing stormwater and groundwater to enter the sanitary sewer system, Carrollton’s Public Works Department conducts smoke testing on more than 100,000 linear feet of sewer lines each year to identify breaks and defects. Additionally, the City performs sanitary sewer system rehabilitations in several neighborhood subdivisions each year with priority placed on its design standards.

“By keeping infiltration and inflow to a minimum through preventative measures like smoke testing and sewer system rehabilitations, the City is protecting its residents from the public health impacts that can result from a sanitary sewer overflow, as well as being a good steward of its utility funds to keep costs low,” Public Works Director Jody Byerly said. “Though pipeline infrastructure, sanitary sewer systems, and wastewater aren’t top of mind for most residents, they are for us. Our crews are committed to keeping the community safe and functioning smoothly.”

In a residential municipal cost of service comparison of 20 cities in the DFW area, Carrollton currently holds the second lowest water and sewer rates.

For more information about the City’s sanitary sewer lines, visit To learn more about Carrollton’s utility services and billing procedures, visit or call 972-466-3000.
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