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Sanitary Sewer Infrastructure Monitoring and I/I Reduction Program

Solution Overview

Dallas Water Utilities has implemented a comprehensive infrastructure monitoring and maintenance program focused on sanitary sewer evaluation studies, point repairs and pipe replacement, and closed-circuit television (CCTV) inspection of large diameter pipes along major waterways.[2] This approach addresses the critical need to reduce inflow and infiltration (I/I) in the city's aging wastewater collection system while maintaining regulatory compliance with the Texas Commission on Environmental Quality's Sanitary Sewer Overflow Initiative.[3] The initiative serves approximately 1,300,000 customers across Dallas and surrounding communities through a network spanning over 4,000 miles of sanitary sewer pipe.[3]

Technical Components

The monitoring system was built on historical data from 52 permanent flow meters that evaluate the wastewater collection system's ability to convey dry- and wet-weather flows, with an additional 28 monitoring locations recommended to further isolate the location of large inflow and infiltration contributions, bringing the total to 80 flow meters.[5] The model was calibrated to within 5% of dry-weather flows and within 10% of wet-weather flows for 80 meters.[5] Services provided under the inspection agreement include internal pipe inspection via close circuit television, high velocity sewer cleaning, robotic television inspection, sonar, and sewer corrective repair services.[3] The non-destructive pipe analysis agreement surveys, inspects, assesses, and monitors city pipelines for pressure, leaks or gas pockets, internal wall condition, testing and assessment of the pipe's external wall, and condition of pre-stressed concrete cylinder pipe for broken wires and bars.[6] This innovative approach allows the pipeline to remain in service and intact, eliminating the need to excavate and cut a section of system piping for evaluation.[6] Freese and Nichols created a hydraulic modeling and planning team that developed a CIP Prioritization Tool with capabilities for future updates, all while using off-the-shelf software.[5]

Implementation Details

The City of Dallas authorized a three-year service price agreement for televised sewer inspection, maintenance, and repair services with Acme Utility Inspection Services, Inc. for an estimated amount of $5,590,222.00.[3] The fiscal allocation for FY 2025 totals $1,552,770.00, with $1,399,950.00 from Dallas Water Utilities Fund and $152,820.00 from Stormwater Drainage Management Fund.[3] The service price agreement is financed through the Dallas Water Utilities Fund ($5,040,070.00) and Stormwater Drainage Management Fund ($550,152.00), subject to annual appropriations.[3] Additionally, the City Council approved a five-year service price agreement on October 8, 2024, for non-destructive pipe analysis and internal leak surveying services with Pure Technologies U.S., Inc. for an estimated amount of $21,577,920.00.[6] The fiscal allocation for the Dallas Water Utilities Fund is $4,315,584.00 for FY 2025, $4,315,584.00 for FY 2026, and $12,946,752.00 for future years.[6] The service price agreement will be used by Dallas Water Utilities to augment the in-house maintenance program and help ensure the proper operation of the sanitary sewer system.[3] The project addressed population growth, regulatory compliance, aging infrastructure and organizational challenges plus new development and redevelopment areas within the City of Dallas and 11 wholesale wastewater customers.[5] Prompted by the Texas Commission on Environmental Quality's Sanitary Sewer Overflow Initiative, Dallas had a primary need for an updated wastewater collection system master plan every 10 years.[5]

Benefits and Impacts

The City of Dallas spent over $300 million on the SSO Initiative since 2001, including $100 million on cleaning and inspection and $200 million on rehabilitation.[8] Dallas cleaned and inspected over 3,800 miles (95%) of its 4,000-mile wastewater collection system as part of the SSO Initiative.[8] The cleaning and inspection program identified over 100,000 structural defects in the wastewater collection system.[8] Dallas repaired over 70,000 defects in its wastewater collection system as part of the WWCS Rehabilitation Program.[8] Identified damage is reported to Dallas Water Utilities, which allows them to plan and coordinate the replacement and/or rehabilitation of identified pipeline segments prior to it reaching critical failure status.[6] The non-destructive underground leak detection surveying and condition assessment services allow Dallas Water Utilities to monitor the condition of critical arterial pipelines, reducing the likelihood of catastrophic failures, service interruptions, and large-scale water-loss events.[6] The new CIP Prioritization Tool provides Dallas with a 25-year master plan based on extensive data and the ability to update priorities as conditions change.[5] The City of Dallas Comprehensive Wastewater Collection System Assessment Update was recognized with an Engineering Excellence Gold Medal from ACEC Texas and advanced to the American Council of Engineering Companies' national competition.[5]

Climate Adaptation Relevance

The reduction of I/I will reduce wet weather sanitary sewer overflows and help improve the resilience of wastewater treatment plants, lift stations, and the overall collection system during major storm events.[2] Improvements made to the collection system will help to prevent vulnerable communities with aging and undersized infrastructure from experiencing sanitary sewer overflows.[2] On August 21 and 22, 2022, the greater Dallas area experienced a 1,000-year storm event with some parts of the metropolitan area, including at the Southside WWTP, receiving more than 15 inches of rain in a 24-hour period.[7] This extreme weather event demonstrated the critical importance of maintaining resilient wastewater infrastructure, as similar record rains in May 2015 delivered almost 17 inches in the Fort Worth-Dallas area and set in motion perilous riverbank damage that exposed critical wastewater pipelines.[1]

Business Analysis

The service price agreement will assist Dallas Water Utilities with maintaining the regulatory requirements of the Texas Commission on Environmental Quality Sanitary Sewer Overflow Initiative.[3] Wastewater Operations is responsible for collecting, transporting, controlling the discharge of, and treating domestic and industrial wastes; and maintaining treatment plants and pipelines in the wastewater system.[4] The City will continue to invest in its collection system to reduce the overall I/I.[2] The investment can be in the form of sanitary sewer evaluation studies, point repairs and pipe replacement, and closed-circuit television (CCTV) inspection of large diameter pipes along major waterways.[2] The multi-year financial commitment demonstrates a sustained municipal investment model, with funding structured across multiple fiscal years and drawing from dedicated utility and stormwater management funds to ensure program continuity.[3][6]

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