Gulf Coast Aquifer: Not Relevant for Purposes of Joint Planning
GMA 13 Technical Memorandum 16-07, Draft 1
William R. Hutchison, Ph.D., P.E., P.G.
March 29, 2016
Introduction
The Texas Water Development Board, in its July 2013 document, Explanatory Report for
Submittal of Desired Future Conditions to the Texas Water Development Board, offers thefollowing guidance regarding documentation for aquifers that are to be classified not relevant for
purposes of joint planning:
Districts in a groundwater management area may, as part of the process foradopting and submitting desired future conditions, propose classification of aportion or portions of a relevant aquifer as non-relevant (31 Texas Administrative
Code 356.31 (b)). This proposed classification of an aquifer may be made if thedistricts determine that aquifer characteristics, groundwater demands, and current
groundwater uses do not warrant adoption of a desired future condition.
The districts must submit to the TWDB the following documentation for the portionof the aquifer proposed to be classified as non-relevant:
1. A description, location, and/or map of the aquifer or portion of theaquifer;
2. A summary of aquifer characteristics, groundwater demands, andcurrent groundwater uses, including the total estimated recoverable
storage as provided by the TWDB, that support the conclusion thatdesired future conditions in adjacent or hydraulically connected
relevant aquifer(s) will not be affected; and3. An explanation of why the aquifer or portion of the aquifer is nonrelevant for joint planning purposes.
This technical memorandum provides the required documentation to classify the Gulf Coast
Aquifer as not relevant for purposes of joint planning.
Aquifer Description and Location
As described in George and others (2011):
The Gulf Coast Aquifer is a major aquifer paralleling the Gulf of Mexico
coastline from the Louisiana border to the border of Mexico. It consists ofseveral aquifers, including the Jasper, Evangeline, and Chicot aquifers, which
are composed of discontinuous sand, silt, clay, and gravel beds. The maximum
total sand thickness of the Gulf Coast Aquifer ranges from 700 feet in the south
to 1,300 feet in the north. Freshwater saturated thickness averages about 1,000feet. Water quality varies with depth and locality: it is generally good in the1Gulf Coast Aquifer: Not Relevant for Purposes of Joint Planning
GMA 13 Technical Memorandum 16-07, Draft 1
William R. Hutchison, Ph.D., P.E., P.G.
March 29, 2016
central and northeastern parts of the aquifer, where the water contains lessthan 500 milligrams per liter of total dissolved solids, but declines to the south,
where it typically contains 1,000 to more than 10,000 milligrams per liter oftotal dissolved solids and where the productivity of the aquifer decreases. Highlevels of radionuclides, thought mainly to be naturally occurring, are found insome wells in Harris County in the outcrop and in South Texas. The aquifer isused for municipal, industrial, and irrigation purposes. In Harris, Galveston,Fort Bend, Jasper, and Wharton counties, water level declines of as much as
350 feet have led to land subsidence. The regional water planning groups, intheir 2006 Regional Water Plans, recommended several water management
strategies that use the Gulf Coast Aquifer, including drilling more wells,
pumping more water from existing wells, temporary overdrafting, constructing
new or expanded treatment plants, desalinating brackish groundwater,developing conjunctive use projects, and reallocating supplies.
Figure 1 (taken from Wade and Bradley, 2013) shows the limited extent of the Gulf Coast Aquifer
in GMA 13. Note that it occurs only in a small portion of Gonzales and Zapata counties.

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Gulf Coast Aquifer: Not Relevant for Purposes of Joint Planning
GMA 13 Technical Memorandum 16-07, Draft 1William R. Hutchison, Ph.D., P.E., P.G.
March 29, 2016

Figure 1. Location of Gulf Coast Aquifer in GMA 13
Aquifer Characteristics
The Jasper Aquifer is the relevant formation within the Gulf Coast Aquifer system in GMA 13.
Previous studies (i.e. Chowdhury and others, 2004, pg. 36) note that hydraulic conductivity in theJasper is about 1 ft/day.

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Gulf Coast Aquifer: Not Relevant for Purposes of Joint Planning
GMA 13 Technical Memorandum 16-07, Draft 1
William R. Hutchison, Ph.D., P.E., P.G.
March 29, 2016
Groundwater Demands and Current Groundwater Uses
The Texas Water Development Board pumping database shows 2012 groundwater pumping for
the Trinity Aquifer as follows:Gonzales: 60 AF/yr
Zavala: 0 AF/yr

Total Estimated Recoverable Storage
Wade and others (2013) documented the total estimated recoverable storage for the Trinity Aquifer
in GMA 13 as follows:

Total storage is given in the first column. The recoverable storage is assumed to be between 25
and 75 percent of the total storage.
Explanation of Non-RelevanceDue to its limited areal extent and generally low use, the Gulf Coast Aquifer is classified as not
relevant for purposes of joint planning in Groundwater Management Area 13.
References
Chowdhury, A.H., Wade, S., Mace, R.E., Ridgeway, C., 2004. Groundwater Availability Modelof the Central Gulf Coast Aquifer System: Numerical Simulations through 1999. Texas Water
Development Board, Groundwater Availability Modeling Section, September 27, 2004, 114p.
George, P.G., Mace, R.E., and Petrossian, R., 2011. Aquifers of Texas. Texas Water Development
Board Report 380, July 2011, 182p.
Wade, S., and Bradley, R., 2013. GAM Task 13-036: Total Estimated Recoverable Storage forAquifers in Groundwater Management Area 13. Texas Water Development Board, GroundwaterResources Division, July 8, 2013, 30p.

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