The Development of an Alternative Water Supply for
the Lower Rio Grande Valley

Kevin J. Spencer, P.G.
R.W. Harden and Associates, Inc.,
and
Joseph W. (Bill) Norris, P.E.
NRS Consulting Engineers

Abstract:
The lower Rio Grande Valley is one of the fastest growing regions of Texas and is experiencing critical water supply shortages from a sustained drought and a failure of Mexico to repay over one million acre-feet of water debt. The planning process for development of a drought resistant water supply that is not dependent on flows in the Rio Grande has been ongoing for over 20 years, but the time to place conceptual plans into action has arrived.

Much of the lower Rio Grande Valley sits above vast brackish groundwater reserves from the Rio Grande Alluvium and the underlying Gulf Coast aquifer. These resources have been unused principally due to the cost of treatment. Regionalization and considerable improvements to the reverse osmosis treatment process have resulted in large reductions in the cost of treatment. Faced with increasing demands and coupled with innovative engineering and construction management techniques, the Southmost Regional Water Authority has undertaken the construction of a regional brackish groundwater treatment facility that will initially provide a treated water supply of eight million gallons per day, approximately 40% of the supply to communities in southeastern Cameron County. The raw water source is from the Rio Grande Alluvium, which is a gravel and sand aquifer that occurs between 150 and 350 feet below the base of the Rio Grande. Deposited by outwash from the Rio Grande and its associated tributaries, the Alluvium is composed of complexly interbedded fluvial and deltaic deposits of sand, silt, clay, and gravel. The Alluvium generally parallels the Rio Grande, and is present from about 60 miles northwest of Brownsville to the Gulf of Mexico. Along the length of the Rio Grande, the deposits are thinnest in the northwest portion (upstream), and accumulate in downstream areas near the river. In the area of the well field, these deposits average about 350 feet thick and overlie the Pleistocene Beaumont and Lissie Formations.

The process of proving up the groundwater reserves initially began with drilling and geophysically logging 10 test holes, completing four test wells, groundwater sampling and aquifer testing. A groundwater model was developed from the test drilling effort as well as from numerous well logs, water quality data, and pumping tests from irrigation wells drilled in the 1950's, TWDB drilling, and other projects conducted by our firms. Upon demonstration that there was a high probability the supply could be developed, a pilot production well and seven piezometers were utilized to conduct a 28-day, 800 gallon per minute pumping and recovery test that was used to evaluate aquifer boundaries and interconnectedness. The groundwater model was refined and numerous sensitivity analyses performed to complete the aquifer evaluation.

Currently, the treatment plant and well field are under construction and are scheduled to be on line by the end of 2003.

 

Kevin J. Spencer, P.G. holds a Bachelors and a Master of Science degrees from Baylor University and has been working in the groundwater hydrology industry in Austin since 1991. After working in the lignite mining and environmental fields for seven years with Hall Southwest Corporation and enduring two corporate buyouts, he decided there must be a better way to make a living. For the past five years, Kevin has worked with R.W. Harden and Associates, Inc. in Austin in the groundwater supply industry with a smattering of lignite mining work for old time's sake. During his time with R.W. Harden, he has performed numerous groundwater availability studies, well field evaluations, and assessments of impacts from groundwater pumpage.

Joseph W. (Bill) Norris, P.E. is a registered engineer in Texas with a BSCE from Texas A&M University and a MSCE from the University of Texas at Arlington. He has over 25 years experience in the water resources area. He has been developing the desalination of water for the Rio Grande Valley since 1985 through pilot plant studies to full scale projects for several entities. Major projects include the Harlingen Wastewater Recovery and Reuse Facility and the Southmost Regional Water Authority Brackish Treatment Facility.