7046 ‎(2)‎

• UCREFRP Catalog Number: 7046
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Final Report\
• USFW Year: 1992.
• Copyright Material: NO

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constitute a hazard in the marine environment, and levels less than 0.2 mg/l present minimal risk of
deleterious effects (Van der Leeden et aL 1990). ERI (1986) reported 0.55 and 1.28 mg/l aluminum
in the Dolores and San Miguel rivers, respectively, compared to 6.2 - 57 mg/l and 2.8 - 5.0 mg/l in the
respective rivers in 1991 (Table 42).

Cadmium may reach the aquatic environment through atmospheric fallout and in emuents from
pigments, plastics, alloys, and other manufacturing operations as well as from municipal emuents
(EP A 198Od). Total cadmium in the Dolores River in 1991 ranged from <0.01 - 0.015 mg/l. Based
on the range of water hardness in the Dolores River in 1990-1991, a maximum 1 hour average
concentration of 0.005 - 0.047 mg/l is not to be exceeded more than once every 3 years on average
(EPA 1986). Concentrations in the Dolores River never exceeded the upper EPA limit, although
cadmium was analyzed only during the last two trips. Cadmium in the Dolores and San Miguel rivers
reported by ERI (1986) was similarly low compared to levels recorded in 1991 (Table 42). Smith
(1977) reported cadmium levels as high as 2.0 mg/l in the San Miguel River in 1977 (Table 42).

Silver is usually found in extremely low concentrations in the aquatic environment because of its
low crustal abundance and its limited mobility in water (EPA 198Oe). Silver in the Dolores River
never exceeded <0.01 mg/l in 1991. For preservation of freshwater aquatic life, total silver should
never exceed 0.007 - 0.182 (based on hardness) at any time (EPA 1986). ERI (1986) also found low
levels of silver in the Dolores and San Miguel rivers in 1986 (Table 42).

4.3.2.10 Oil and Grease. Oil and grease in the Dolores River were less than 0.5 mg/l, with the
exception of slightly higher concentrations detected during Trip 6. Because of a 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 (EPA 1986). No numerical criteria
has been established by the EP A

4.3.2.11 TSS. Total suspended solids (TSS) ranged from 14 to 18,600 mg/l on Trips 1 and 5,
respectively. High TSS were usually associated with turbidity from runoff of high intensity storms.
High levels of TSS may affect fish and fISh food populations in four ways (EIFAC 1969): 1) reduced
growth rate and resistance to diseases that may lead to death; 2) impeded development of fish eggs
and larvae; 3) altered movements and migrations and; 4) reduced abundance of food. 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.

4.3.2.12 Sulfate. Sulfate was measured only on Trips 5 and 6, and ranged from 100 - 424 mg SOJl
on the Dolores River, and 76.5 - 88 mg/l on the San Miguel River. Sulfate levels in the San Miguel
River in 1991 were substantially lower than reported by ERI in 1986 (Table 42). No EP A criteria
exist for sulfates.

4.3.2.13 Salinity. Salinity of the Dolores River in 1990-1991 was generally at or below 1 part per
thousand (ppt), with the exception of Reach IV where the Dolores River traversed Paradox Valley.
This persisted to the confluence of the San Miguel, where dilution from increased flow reduced 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.

4.3.2.14 Specific. Conductance. Conductance of the Dolores River ranged from 154 to 7500
umbos/em. Highest conductivities were observed during Trip 1 in Reach IV and were probably

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