TM 5-813-8
pH 8.5
Bacterial count 0/100 milliter (membrane filter technique)
Silt density index 1
Turbidity less than 0.01 nephelometric turbidity unit
Oil and grease less than 1 milligrams per liter
In table 4-2, Rule 7 is applicable (see fig. A-2). Rule 7 states that reverse osmosis processes should be investigated.
The low level of silt density index precludes the necessity of an alum jar test.
Use table 4-3 showing that Rule 8 applies (see fig. A-4). Rule 8 states that hollow fine-fiber reverse osmosis
specifications should be prepared. No specific pretreatment process is necessary.
In another area of the site a 500-foot test well was drilled. The driller's report indicated that this water had a slight
saline taste. Table 4-1, Rule 7 applies (see fig. A-1).
Rule 7 states that electrodialysis reversal should be investigated for slightly saline water, regard- less of electric or
steam costs. The recommended laboratory analyses are: total dissolved solids, a full ionic breakdown, bacterial count,
turbidity, and the other tests for electrodialysis-reversal feed waters listed in Appendix B.
Assume that the laboratory analyses of this water sample give the following data shown in figure A-5.
The following data were extracted from the laboratory analysis and bacterial plate counts:
500-foot-deep well
total dissolved solids 1,000 milligrams per liter
++
Ca 100 milligrams per liter as CaCO3
++
Mg 7 milligrams per liter
=
SO 4 240 milligrams per liter
=
CO 3 0 milligrams per liter
-
HCO 3 21 milligrams per liter
-
Cl 389 milligrams per liter
+
Na 326 milligrams per liter
Bacterial count 0/100 milliliter (membrane filter technique)
Turbidity less than 0.01 nephelometric turbidity unit
Table 4-2, Rule 8 applies (see fig. A-2). Rule 8 states that electrodialysis reversal should be investigated. The low
level of turbidity precludes the use of an alum jar test. The low salinity of this sample indicates this to be a superior quality
brackish water source.
Application of the preliminary process selection information with table 4-3 results in two possible final process
selections. Both Rule 9 and Rule 10 are applicable to this water source. (See fig. A-4)
Rule 9 states that low-pressure high-rate reverse osmosis specifications should be prepared, with antiscalants to be
recommended.
Rule 10 states that electrodialysis-reversal specifications should be prepared.
A final decision should be based on the probability of the total dissolved solids fluctuating by more than approximately
15 percent.
Assume a fourth water source was also investigated at this same site. A shallow 32-foot test well was drilled. A
preliminary inspection indicated this water was slightly saline and foul tasting with a strong rotten egg smell.
Use of table 4-1 indicates that Rule 6 and Rule 7 may apply (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,
low-level oil and grease (below 1 milligram per liter), and any other tests called for in Appendix B should be performed on
test-well water samples.
Rule 7 states that for slightly saline water electrodialysis reversal is the most economical method to obtain potable
water from brackish water. Analysis of total dissolved solids, a full ionic breakdown, bacterial count, turbidity, and any
other tests called for in Appendix B should be performed.
The laboratory analyses of this water sample give the following data shown in figure A-6:
A-6
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