(GP/GT) for Additional Water Supply in the Lower Rio Grande

Areas or Application
The information developed in the Harden study was specifically focussed on a geographical area just to
the Northeast of Brownsville. However, as stated in that Study, water in the gravel zone increases in
mineralization from West to East, and the water quantity available from the gravel zone is dependent on
location. Reference to Figure 4 of the Study, a copy of which is enclosed, generally indicates the
following:
1. For IDS concentrations lesS than 5000 ppm, the well field would need to be located to the West
of the Southern Pacific Rail Line and FM 1847.
2. For IDS concentrations lesS than 3000 ppm, the well field would need to be located to the West
of the Missouri Pacific Rail Line and Highways 77 and 83.
Dennition or Gravel Zone
That zone within the alluvial deposits at a depth of approximately 180 feet below ground level and
typically containing coarse gravels of potential high water productivity.
WeI! Field Development
1. Based on available information, it is estimated that a 20-year sustainable yield of approximately
5 mgd can likely be developed from the gravel zone.
2. Pumping rates (yields) per well of 350 gpm are estimated, requiring an estimated lO wells for
a 5 mgd supply.
3. Wells should generally be spaced approximately 2000 to 2500 feet apart, making the length of
the well field about 4 to 5 miles. Well depths should approximate 220 feet.
4. The capital cost of the well field is estimated to be approximately $1,500,000, or about $150,000
per well. These estimates include all costs for the construction by a reputable, experienced
contractor of a production water well installation including pilot hole drilling, well construction,
testing, pumps, motors, foundation, engineering, appropriate bonds, and with well efficiency and
sand content guarantees. The estimated costs do not include property acquisition, prior test
drilling, power lines, electrical controls, pipelines, right-of-way, or any special costs to discharge
or dispose of mineralized water during construction or testing. To account for the fact that wells
for brackish, rather than fresh, water are being developed, the costs of the pumping equipment
incorporated into the well and well field costs presented above have been increased by 50%.
5. The next step in proceeding with a well field development of the gravel zone would be a test
drilling program. This work would include drilling approximately 5 (five) test holes, geophysical
logging, water sampling, water quality analysis, planning, inspection and evaluation. The
estimated cost for such a program would be approximately $300,000.