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

III-34
1. Group 1 through Group 4 waters contain levels of boron in excess of 1.4 ppm which will cause severe
problems for fruits, plants and other growing things, but waters containing boron levels up to 45 ppm
can be consumed by humans with no problems. Because only potable water for human consumption, as
opposed to irrigation water, is under consideration herein, the impact of the presence of boron is ignored.
However, if boron reduction is required, both EDR and RO could reduce same by having the feedwater
pH raised to 8.5 - 9.5.
2. As regards silica (SiO,), the content of same in the Group 1 through 3 waters is such as to significantly
limit the level of recovery of product water much more for the RO process than for the EDR process.
The Group 4 waters contain much lower levels of (SiO,), and for such waters its presence is not as
adverse. Because high levels of product water recovery are essential to minimize brine disposal. most
probably via injection wells. the impact of (SiD,) in most of the ground waters under consideration is to
give a substantial comparative advantage to EDR.
3. The presence of calcium and bicarbonate in each "Group" of water at the "mean levels" indicated in the
analyses can, to some extent, negatively impact both the RO and EDR processes. For RQ, the presence
of such levels of these constituents requires the feeding of sulfuric acid to the feedwater in order to
control the level of CaCo, scaling in the RO brine. In the case of Elm, with such levels of these
constituents in the feedwater, their impact is to necessitate an increase in electrical power in order to
maintain higher water recovery levels.
In summ3Q', both Alternatives A and B should be eliminated from further consideration on the grounds of technie.
feasibility, whereas Alternative C and D, namely EDR and RO, should be carried forward to Step 2. As regards rank,
EDR appears to have an advantage over RO, primarily because of the impact of Si0 2 •
Energy Forms
At the outset it should be noted that both the EDR and RQ processes use electrical power as their energy source.
Accordingly, in evaluating the comparative technical feasibility associated with the three energy forms, namely E(B),
E(G), and E(P), the two important criteria are (a) the magnitude of the source of energy insofar as its ability to power
a sizable EDR or RQ plant and (b) the state of the technology associated with the transformation of each energy form
into electrical power utilizing commercially available equipment. As regards the magnitude of the sources, this
information is presented earlier in the Section under the heading Order-of-Magnitude Projected Quantity Ranges, and the
evaluation for each form is presented as follows:
lliID - Based on the above mentioned projections, the quantities available from lliID are more than adequate,
although higher temperatures would be more desirable. As regards the status of the technology, our one
source of available literature(l) suggests that both the Kalina Cycle System 12 and the Cascade Rankine
Cycle may be on the verge of commercial utilization for geothermal power generation, but that there are
still some unknowns.
E.(Q) - Again, based on the above mentioned projections, the quantities of entrained natural gas are more than
adequate. As regards the state of the technology, the use of gas turbine generators such as those built
by Stewart & Stevenson is very well established to provide an efficient conversion to electrical power.