WSP07539

• File Number: 8281.300
• Description: Colorado River Studies and Investigations - Colorado River Consumptive Uses and Losses Report
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 10/1/1991
• Title: Consumptive Uses and Losses in the Arizona Portion of the Upper Colorado River Basin for the Water Year 1990
• Water Supply Pro - Doc Type: Report/Study

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Consumptive Uses and Losses

6

Indian Mfairs (BIA), the Water Operations and Maintenance Department of the
Navajo Nation (Navajo WOM), and some privately developed community water
systems.

Table 1 shows the number of population served by community water systems
operating on the reservation during 1990. All of the communities obtain their
water supply from ground water.

Table I.-Populations served by community water systems during 1990

Operator or system

Percent of
population served

Number of population
served

NTUA
BIA
Navajo WOM
Private

55
31
12
~

14,110
7,955
3,080
515

Total

100

25,660

NTUA Water Systems.-The cities and surrounding communities of Red Mesa,
Oak Springs, Red Valley, Red Valley South, Sweetwater, Chinle, Tsaile, Rough
Rock, Nazlini, Cottonwood, Round Rock, Rock Point, Wheatfields, Lukachukai,
Kayenta, Chilchinbeto, Dennehotso, Shonto, Inscription House, and Kaibeto
derive most of their domestic water supply from wells operated by the NTUA.
Well pumping records are available. According to these records, the total
water pumped for 1990 was 1,620 acre-feet with an uncertainty estimated to be
7 percent of this value or :t110 acre-feet. This quantity constitutes about
4 percent of the total water use in the study area.

The NTUA manages the raw waste water; portions of which flow to individual
septic tanks, some to evaporation ponds, and some, such as for the cities of
Chinle and Kayenta, flow to wastewater treatment plants. Very little water,
if any, is returned to the ground-water system through leakage from the
evaporation ponds, but there are losses from the main collection system.
Effiuent from the Chinle and Kayenta waste water treatment plants is
metered. Under normal conditions, the effiuent returns to the Colorado
River system and is subtracted from the pumping totals to determine a
net consumptive use. For 1990, Chinle's treatment plant effiuent was
240 (:t10) acre-feet, and Kayenta's effiuent was 330 (:t10) acre-feet.
A:n estimated uncertainty of 3 percent was used for the effiuent of these two
plants. The total effiuent of 570 acre-feet is subtracted from the NTUA
Pumping total of 1,620 acre-feet to arrive at a net consumptive use of
1,050 (:t70) acre-feet.