WSP07180

• File Number: 8043
• Description: Section D General Studies-Salinity
• State: CO
• Date: 6/1/1971
• Author: WaterPowerResources
• Title: Improving Municipal Water Supplies in Colorado by Desalting
• Water Supply Pro - Doc Type: Report/Study

Section 1

SUMMARY

This study examined the technical and economic feasibility of applying
desalting technology to the problem of improving municipal water supplies for
six selected communities in Colorado. The six communities, in their order of
size J are La Junta, Lamar, Brighton, Ft. Morgan, Las Animas J and Ft. Lupton-.
The water quality goal established for this study was to produce potable water
with a total hardness below 200 mg/l, with total dissolved solids less than
1000 mg/l, and no United states Public Health Service (USPHS) rejection stan-
dards exceeded.

Preliminary estimates of desalting costs and benefits were made for each
of the candidate communities. The Office of Saline Water "Desalting Cost Cal-
culating Procedures" manual (OSW Il&D No. 555) was used to estimate the cost of
desalting for each of the systems considered for application. Generally, the
membrane processes (electrodialysis and reverse osmosis) appear to provide the
best desalting cost economics for these communities. A potential improvement
in the cost of applying membrane desalting plants appears possible through
coupling to ion-exchange equipment for the removal of hardness ions prior to
further desalination. Such coupled systems appear attractive for providing sig-
nificantly increased product water yield with accompanying reduction in brine
volumes and their associated disposal costs. A preliminary cost estimate was
made for an all ion-eXChange system for treatment of the feedwater for one of
the communities (La Junta). The results indicate unit water costs somewhat low-
er than for any of the other processes considered. In summary, it is feasible
to desalt the available feedwater for each candidate community to the target
quality goal by the application of one or more of the processes considered.
The specific process yielding the indicated lowest unit cost of water is strong-
ly dependent on the specific composition and degree of salinity of the feed-
. water. Water costs for the candidate communities, including feedwater supply,
desalting processing, product water distribution and brine disposal range from
a low of 63 cents per 1000 gallons to a high of 119 cents per 1000 gallons.

The economic feasibility of desalting hinges upon the economic impact of
the improved water on the subject communities. The economic impact for any
community is derived from the quantifiable ben~fits to the community over a
20-year period. Benefits in any single year are calculated based on the dif-
ferences in overall expenditures in the community for the cases with and with-
out improved water. Computed benefits for the year 1970 in the cities studied
ranged from $100,800 to $464,800, while 1990 benefits were from $158,000 to
$647,300.

It should be pointed out that the benefits itemized here reflect only the
tangible benefits resulting from desalting. Intangible benefits accruing to
these communities as a result of improved water include quality of life, en-
vironmental, and economic development benefits.

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