Tunnel Project Helps Meet San Antonio Growth

By Jeff Griffin, Senior Editor | March 2009 Vol. 64 No. 3

The population of the city of San Antonio has quietly grown to make this pleasant south Texas city the second largest city in the state and seventh largest in the U.S. With a population of more than 1.3 million, San Antonio ranks just behind Houston and ahead of Dallas in population.

Providing clean drinking water and reliable sanitary sewer services is among the responsibilities of the San Antonio Water System (SAWS) a city owned utility. SAWS operates and maintains a water and wastewater infrastructure that includes 10,000 miles of pipe, including 4,800 miles of sanitary sewer mains.

As it is for any large city, ensuring residents and businesses have the water and sewer services they need is a continuing challenge, and SAWS utilizes a multi-year capital improvement program to identify facility and equipment requirements for sustaining, restoring and modernizing facilities and infrastructure and to prioritize and schedule projects.

SAWS reports the overall funding split for the 2009 water delivery and wastewater collection and treatment program is 74 percent repairs and replacements and 26 percent additional capacity to support new growth and development. Among major projects under way in San Antonio are significant improvements to the city's sanitary sewer system.

A good example is the nearly completed Western Watershed Sewer Relief Line W 04 project, said Andrea Beymer, P.E., SAWS project engineer. The $19.8 million project included the construction of approximately 11,250 linear feet of 66 inch and 60 inch diameter sanitary sewer mains to replace the existing 42 inch main in a highly urbanized area of San Antonio. The old pipe was abandoned.

Engineering for the W 04 segment was done by Weston Solutions Inc., San Antonio. General contractor was BRH Garver Construction, Houston.

As designed by Weston, the improvements of the project would include 1,832 linear feet of 60 inch and 9,422 linear feet of 66 inch FRPM (fiberglass reinforced plastic mortar) pipe, with the depth of the interceptor ranging from 10 to 55 feet below ground surface. The project also encompassed the design of six lateral connections to the rerouted collection system including 1,341 linear feet of 8 inch; 659 linear feet of 15 and 18 inch; 459 linear feet of 24 and 36 inch; and 34 linear feet of 48 and 54 inch pipes.

Open cut construction was used wherever possible, but because surface improvements limited access in many areas, depth requirements for the new pipe, rocky subsurface conditions in many areas, nearly half the construction was completed by tunneling.