7729

• UCREFRP Catalog Number: 7729
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Annual Summary Report - 1990\
• USFW Year: 1991.
• Copyright Material: NO

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Based on the Dolores River water hardness, the EP A has determined that freshwater species should
not be affected unacceptably if the I-hour average concentration does not exceed 0.124 - 1.36 mg
lead !L (depending on water hardness) more than once every three years on the average (EP A 1986).
Based on this criteria, lead levels in the Dolores River do not appear to be problematic.

EP A criteria for zinc specifies that concentrations should not exceed 0.421 - 2.012 mgIL (again, based
on water hardness in the Dolores River) at any time (EP A 1986). Like lead, zinc concentrations in
the Dolores River appear to be at an acceptable level.

Oil and Grease

All values for concentrations of oil and grease in the Dolores River were less than 0.5 mgIL. Because
of the wide range of compounds included in the category of oil, it is impossible to establish
meaningful 96-hour LCSO values for oil and grease without specifying the product involved (EP A
1986). No numerical criteria has been established by the EP A

TSS

Total suspended solids (TSS) ranged from 14 to 9,050 mg/L on Trips 1 and 2, respectively. Base flow
levels during Trip 1 were much lower than those of the following two trips. High TSS levels were
generally associated with turbidity from runoff of high intensity storm events that occurred during
Trips 2 and 3. High levels of TSS may effect fish and fish food populations in four ways (EIF AC
1969): 1) by acting directly on the fish swimming in the water in which solids are suspended, and
either killing them or reducing their growth rate, resistance to disease, etc,; 2) by preventing the
successful development of fish eggs and larvae; 3) by modifying natural movements and migrations
of fish, and; 4) by reducing the abundance of food available to the fish. Given the high tolerance
to turbidity of native fish species in the Dolores River, it is difficult to postulate any adverse effects
of current TSS levels without historical data.

Salinity

Salinity levels measured afield in the Dolores River were generally at or below 1 part per thousand
(ppt) concentrations, with the exception of Reach IV. The Dolores River traverses the Paradox
Valley within this reach and picks up a significant salt load which persists to the confluence of the
San Migue~ where dilution from increased flows reduce the concentration of salts. Highest salinity
reading were recorded during Trip 1, when flows were lowest During this trip salinity increased from
less than 1 ppt to 7 ppt in a 7.2 mile reach, from RM 75.4 to RM 68.2. This extreme salinity gradient
was not observed during other trips when flows were higher.

Specific Conductance

Conductivities measured afield in the Dolores River ranged from 375 to 7500 umbos. Highest
conductivities were observed during Trip 1 in Reach IV and were assumed to be related to saline
groundwater inflow in the Paradox Valley area.

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