SITUATION
In numerous major urban areas across the United States, crucial sewer trunk lines are situated in extensive drainage basins where substantial rainfall events can cause significant disruptions. These cities must carefully control sewer flow to address system capacity issues and prevent potential backups. San Antonio, Texas, the seventh largest city in the United States, is one such urban center grappling with the dual challenge of an aging and stressed infrastructure.
The San Antonio Water System (SAWS) serves a widely dispersed population exceeding 1.8 million individuals and over 411,000 wastewater customers scattered across the greater San Antonio area, encompassing Bexar County and parts of Medina and Atascosa counties. The EPA consent decree program identified essential pipelines in the metroplex requiring mandated repairs. Termed the SAWS Multiple Sewershed Package 2A project, this initiative involved rehabilitating six different sections totaling around 14,900 linear feet of existing pipe. Beyond employing cured-in-place pipe (CIPP) to rejuvenate aging pipes, the project encompassed repairs to gravity sewer mains ranging from 24 to 72 inches and the partial demolition, repair, and replacement of several large concrete structures at seven separate sites.
CHALLENGE
In and of itself, this project represented the most extensive CIPP undertaking in San Antonio's history. Nonetheless, SAWS recognized an opportunity to contemporaneously upgrade its flow management system with a new design. The project encountered substantial logistical challenges, with sections located beneath and traversing golf courses, city parks, floodplains, and residential neighborhoods. Additionally, the project engineer, CDS Muery, devised an innovative design involving metal flow plates that could be easily installed or removed to regulate flow management, replacing the troublesome mechanical gates within their respective structures.
Complicating matters were intricate bypass requirements. Initially, there was the simultaneous bypass of parallel 54- and 66-inch lines. While challenging on its own, midway through the project, a separate capacity project (involving the upsizing of existing lines or the installation of new pipeline) came online upstream, potentially adding 19 million gallons per day of additional flow. SAK stepped in and formulated a plan to accommodate these flows at no extra cost to SAWS, effectively managing the flow without complications.
SOLVED
Aside from the considerable scale of the CIPP rehabilitation project and the distinctive challenges encountered, this initiative marked the pioneering use of a flow-plate design for flow management and the initial implementation of such structures. The introduction of this innovative flow plate design revolutionized the approach to handling the substantial daily flow through San Antonio's sewer system, offering a more efficient solution.
The previous flow structures relied on mechanical gates that, over time, became inoperable and demanded extensive maintenance. These outdated gates were prone to freezing, leading to the breakage of their delicate stems used to raise and lower the gates. This impairment severely hindered SAWS's ability to redirect heavy flows to different pipelines or basins, rendering them unable to take lines out of service. Broken gates were often left unused, turning routine repairs into costly endeavors that required the lid to be pulled on the structure and lines to be bypassed.
The adoption of the flow plate design rendered all seven structures accessible for redirecting increased flows, significantly enhancing SAWS's capacity to manage overloaded lines. If individual pipelines needed isolation, SAWS teams could achieve that as well. Crucially, this investment in the new setup proved virtually maintenance-free. The flexibility of the flow plate design allowed SAWS to interchange plates across all structures, bringing about a substantial improvement and reduction in maintenance.
The success of the new flow plate design solution has prompted other U.S. metroplexes facing similar challenges to consider incorporating this technology. This marked the inaugural use of such technology for SAWS, and it appears likely that it won't be the last.
In addition to managing unexpected flows, SAK crews were entrusted with addressing four separate unplanned emergency projects:
A sewer collapse near an apartment complex along a Texas Department of Transportation right-of-way.
A substantial void on a 33-inch line within an easement.
A siphon located beneath the San Jacinto River.
A 24-inch line with voids requiring rehabilitation sooner than initially planned by SAWS.
