TM 5-813-8
APPENDIX A
SAMPLE PROBLEMS
A-1. Sample source and process selection. A facility has been proposed near El Paso, Texas. The final facility population
is set at 100 full-time resident personnel. Use TM 5813-1 to obtain water consumption per day. The calculation is as
follows:
100 Persons X 150 gallons X (Capacity)
day Person
(Factor)
The nearest flowing river is the Rio Grande, which is 100 miles from the proposed site. Surface water in shallow lakes is
also available. Investigations at one location indicate that the lake is much saltier than seawater. A groundwater literature
review indicates that several brackish water aquifiers exist in the area.
The assumed site data are summarized below:
1-Surface lake water is more saline than sea water.
2-River water is more than 100 miles away.
3-Available brackish water is only slightly saline.
4-Solar energy is available.
5-Pond evaporation of brine would be about 0.7 multiplied by net pan evaporation (86 inches per year) = 60 inches
per year.
6-Power lines are remote. A natural gas supply is available at the proposed site. Electricity for the facility could be
produced by natural gas engines.
Saline Lake Water
The use of table 4-1 indicates that Rule 1 will apply to this water source (see fig. A-1, Sample use of table 4-1).
Rule 1 states that water saltier than sea water is probably not economical for desalination. A total dissolved solids
determination should be run on the lake water to verify excessive salinity.
Assume that the laboratory analyses recommended in table 4-1 were performed and the following was obtained:
Saline lake water
Total dissolved solids 70,000 milligrams per liter
Now use table 4-2 where Rule 1 is applicable. Rule 1 states that if this water must be used, thermal distillation is the only
possible process. (See fig. A-2, Sample use of table 4-2). Since alternate brackish water sources are available, this
water source is rejected.
Brackish Groundwater
The use of table 4-1 indicates that Rule 6 or Rule 7 will apply to this water source (see fig. A-1).
Rule 6 states that the most economical method to obtain drinking water from brackish water is through reverse
osmosis, regardless of how electricity is to be generated. Analyses of total dissolved solids, calcium, sulfate, carbonate,
pH, bacterial count, silt density index, turbidity, and low-level oil and grease (less than 1 milligram per liter), as well as the
other tests called for in Appendix B, should be performed on test-well water sample.
Rule 7 states that electrodialysis reversal should be investigated for slightly saline water, regardless of electric or
steam costs. A total dissolved solids determination, full ionic breakdown, bacterial count, turbidity, and the other tests
listed in Appendix B should be done on these test-well samples.
In one area of the site assume that a 230-foot-deep test well is drilled and that the laboratory analyses recommended
in table 4-1, Rule 6, were performed and the following data shown in figure A-3 were obtained:
The following data were extracted from the laboratory analysis and bacterial plate count:
230-foot-deep well
total dissolved solids 5,000 milligrams per liter
++
Ca 150 milligrams per liter
=
SO 4 300 milligrams per liter
=
CO 3 milligrams per liter
HCO 3 172 milligrams per liter
A-1
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