Achieving the Triple-Bottom Line: Microtunneled Intake Pump Station at Granger Lake

Abstract

The Brazos River Authority (BRA) currently owns and operates a raw water intake structure, pump station, pipeline, and water treatment plant on and near the U.S. Army Corps of Engineers' (USACE) Granger Lake in east Williamson County, Texas. The existing intake structure and pipeline do not have adequate capacity to meet the projected demands of the East Williamson County Regional Water System (EWCRWS) and they are having operational problems with the pool elevation and sedimentation of the upper reaches of the lake. BRA hired Freese and Nichols to provide final design and construction management for the project which was funded by the Texas Water Development Board. The following facilities were included in the design of the new transmission system: ≤ A new raw water intake pump station with an ultimate pumping capacity of 54 MGD and an initial capacity of 15 MGD ≤ A 4-mile, 48-inch raw water transmission pipeline to BRA's existing East Williamson County Water Treatment Plant ≤ The recreation mitigation plan agreed upon between the USACE and the BRA The available footprint for the pump station was small and required an innovative design to reduce the impact on the UASCE Park. The final design called for a 40-foot circular sump constructed using tunnel liner plate to a depth of 70 feet. Two 54-inch intakes were constructed into the lake using microtunneling equipment to allow the sump to remain dry while tapping into the lake and minimize the disturbance in the lake. The pump station includes six pump slots with three vertical turbine pumps installed initially. This paper will conclude with a discussion how the pump station project will meet the triple bottom line of reducing environmental, social and economic impacts.