San Antonio Water System Brackish Groundwater Desalination (BGD) Program

Challenge

To reduce dependency on the Edwards Aquifer, the main water supply source for nearly 1.6 million in San Antonio, Texas, officials with the San Antonio Water System (SAWS) approved a unique brackish groundwater desalination program as part of its overall 2012 water management plan. Located in the southern Bexar County region, this previously untapped water source of brackish groundwater, will both diversify and meet regional water needs over the next 50 years. Once treated, the brackish groundwater will augment current surface water sources with production of 30 million gallons per day (mgd).

Approach

As the CMAR firm for the project, Parsons Environment & Infrastructure Group, Inc. and its joint venture partner constructed the first portion of this critical brackish groundwater desalination (BGD) program. Projected to cost $119 million, the project includes: a 12-mgd reverse-osmosis membrane water treatment plant, 12 raw water production wells, raw and finished water conveyance, residual conveyance, a new deep injection well, a chemical treatment system, supervisory and data acquisition controls, and a new administration building.

Using a unique milestone constructability review and cost-estimate process, Parsons collaborated with designers to adapt alternative construction methods, resulting in substantial cost savings. The permit team—consisting of experts from SAWS, Parsons, and its JV Partner, worked quickly to obtain needed environmental and construction permits and avoid delays.

To address complex soil conditions that can lead to borehole instability, a construction method that uses polymer slurry for the drilled pier foundations kept the borehole stable for the entire depth of the excavation. Reinforcing steel was then placed into the slurry, and concrete injected from a pump beginning at the bottom of the excavation.

Creating individual work packages for the early critical-path scopes which involve coordinating multiple complex tasks—which included integrating smaller subcontract firm participation and an accelerated work schedule, but also provided more and greater opportunities for local firms to participate in the project.

A significant factor in any project is its safety program — which is designed to be proactive and interactive in order to achieve a safety goal of zero incidents. The SAWS project safety program includes: daily “Take 5” meetings, weekly safety meetings, monthly mass safety meetings, and a host of safety-related items resulting in a record of zero lost time to date, not only meeting the target milestones, but has also exceeding all quality standards.

Results

SAWS’ BGD plant generates approximately 6 million gallons of water per day, or 13,440 acre-feet per year, from the Wilcox Aquifer. The project’s (SMBE/SWBE) program maximizes participation and promotes equal opportunity and has exceeded SAWS’ goal of awarding 17% to SMBEs/SWBEs; with at 36.4%.