PERMFILE108821

• Permit No: M1980047
• IBM Index Class Name: Permit File
• Section_Exhibit Name: EXHIBIT G WATER INFORMATION
• Media Type: D
• Archive: No

. The degradation of the stream is well illustrated by comparison
of the characteristics of Middle Fork just below the falls
(Station 551) with Parachute Creek just below Grand Valley
(Station 555) (Table G-7). This portion of Parachute Creek,
approximately 15 miles long, is flanked by the town of Grand
Valley and several irrigating ranches.
There are two primary causes of this degradation. The first
is that, as the water gets farther away from its source it
accumulates soluble salts from the stream bed and from natural
runoff. The second cause is the large amount of irrigation in
the lower reaches of the stream. Irrigation not only diminishes
the amount of water in the creek (which tends to increase the
concentration of salts in water which enters below the diversion
point), but also contributes a high amount of turbidity and soluble
salts as part of the return flow.
• Analyses of water samples to date have shown that levels of lead
and mercury appear to be quite low in Parachute Creek and its
tributaries (Wilber, 1973). The biological oxygen demand (B.O.D.)
(a measure of overall stream pollution) is low throughout most
of the lower reaches of Parachute Creek. Some upper portions of
the stream system (at the upstream end of Middle Fork and Davis
Gulch on the plateau) are often polluted with domestic animal
wastes (Flickinger, et.al., 1973).
On the basis of average annual flow data, the ratio (or dilution
factor) of flow in the Colorado River to flow leaving the project'
site is approximately 4000:1. This means, for example, that if
a pollutant with a concentration of 1,000 mg/1 were to leave the
site, its concentration in the Colorado River would be .25 mg/1.
Dilution factors for various seasons between the Colorado River
and the project site are presented in Table G-8 (Metcalf & Eddy,
1975) .

G-16