Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2

• Description: Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2
• State: CO
• Date: 3/1/2005
• Title: Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2
• Water Supply Pro - Doc Type: Publication

Las Vegas Valley
Las Ve
-Muddy River
Wash
captions go here
water of 500 mg/L. Nevada's standard
for TDS is 1,000 mg/L. TDS of water
in Boulder Basin increased 11 percent
from 2000 to 2004, to 1,021 mg/L. Water
entering the water treatment facility is
drawn from lower elevations in the lake
where it is not as susceptible to the effects
of evaporation, but TDS of water entering
the water treatment plant increased nine
percent during that period of time, to
635 mg/L. Some Las Vegas residents find
the drinking water unpalatable due to high
concentrations of TDS. Increasing TDS
concentrations because of the drought
have only intensified and spread this
dissatisfaction with the taste.
The increase in bromide and TOC are
more of a concern from a drinking water
treatment perspective. For example,
when drinking water is disinfected with
ozone and bromide is present, bromate is
produced. Higher bromide concentrations
and an elevated ozone dose results in the
production of more bromate. The bromide
concentration has increased 36 percent,
from 0.068 mg/L to 0.106 mg/L, in
Boulder Basin, while the concentration
of bromide entering the water treatment
plant has increased 40 percent. Bromate in
drinking water is regulated by EPA under
the Disinfection By- Products Rule. Water
treatment processes have been modified
to ensure the bromate concentration in the
drinking water does not exceed the EPA
standard of 0.01 mg/L. According to the
2004 Consumer Confidence Report (CCR)
for the Las Vegas Valley Water District,
the bromate concentration in drinking
Virgin. River
' Grand
Canyon
i
Hoover Dam
water averaged 0.006 mg/L.
TOC is a precursor in the formation of
trihalomethanes (THMs), which are also
regulated under EPA's Disinfection By-
Products Rule. THMs are formed when
TOC comes in contact with chlorine.
Chlorine is used as a disinfectant in Las
Vegas and many other drinking water
supplies. Similar to bromate, higher TOC
concentrations and elevated chlorine
doses result in production of more
THMs in the drinking water supply.
TOC in Boulder Basin increased from
2.9 mg/L to 3.8 mg/L from 2000 to 2004
(up 24 percent), while TOC in the water
entering the treatment plant increased
28 percent (3.6 mg/L). The EPA limit for
THMs is 0.08 mg/L. The concentration
of THMs in Las Vegas drinking water
averaged 0.052 mg/L according to the
2004 CCR. An increase in either of
these disinfection by- products requires
additional drinking water treatment
processes to prevent their formation.
Into the Future
The 2000 to 2004 drought in the Colorado
River watershed significantly impacted
water quality in Lake Mead and the
domestic water supply for Southern
Nevada. Although these issues will
continue and intensify for the duration
of the drought, the Southern Nevada
Water Authority will make changes to
water treatment processes as necessary to
continue to protect the quality of Southern
Nevada's domestic water supply.
For additional information, contact J. C. Davis at
jc.davis @lvvwd.com.
4.5
0.11
1020
•= 1200
o� 1000
x
0.10
e
E
-..ice ��
4.0°«
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averaged 0.052 mg/L according to the
2004 CCR. An increase in either of
these disinfection by- products requires
additional drinking water treatment
processes to prevent their formation.
Into the Future
The 2000 to 2004 drought in the Colorado
River watershed significantly impacted
water quality in Lake Mead and the
domestic water supply for Southern
Nevada. Although these issues will
continue and intensify for the duration
of the drought, the Southern Nevada
Water Authority will make changes to
water treatment processes as necessary to
continue to protect the quality of Southern
Nevada's domestic water supply.
For additional information, contact J. C. Davis at
jc.davis @lvvwd.com.
Average concentrations of bromide, total organic carbon, and total dissolved solids (calculated from
specific conductance) in Boulder Basin of Lake Mead, 2000 - 2004.
March /April 2005 • Southwest Hydrology • 27
4.5
0.11
1020
•= 1200
o� 1000
x
0.10
e
E
4.0°«
p
0
1180
c 980
\
=
0.09
ti
3.5
a
CD 960
0
cc
H
c
0.08
�
a
1160
'c 940
v
am
m
-3.0 cQ
v
0.07
920
1140
900
2.5
0.06
2000 2001 2002 2003 2004
Average concentrations of bromide, total organic carbon, and total dissolved solids (calculated from
specific conductance) in Boulder Basin of Lake Mead, 2000 - 2004.
March /April 2005 • Southwest Hydrology • 27