Draft EIS_072312.pdf - Middle Fork American River Project ...

20120723-4002 FERC PDF (Unofficial) 07/23/2012
• Alkalinity concentrations were lower than 20 mg/L at numerous locations in
the project vicinity due to naturally low concentrations in the granitic
watershed. The EPA standard for the protection of freshwater aquatic life is
that alkalinity as CaCO3 should be at or above 20 mg/L except where natural
concentrations are less.
PCWA conducted a screening level assessment of methylmercury concentration in
fish tissues, with a total of 154 sport fish and crayfish captured and analyzed from
sampling conducted between 2007 and 2009 at French Meadows reservoir, Hell Hole
reservoir, Middle Fork interbay, Ralston afterbay, and the Middle Fork American River
at Otter Creek. Methylmercury concentrations in the sampled fish and crayfish were
compared to the California’s Office of Environmental Health Hazard Assessment
(OEHHA) screening guidelines for methylmercury of 0.08 milligrams per kilogram
(mg/kg). Methylmercury concentrations in at least one fish or crayfish from each
location exceeded the OEHHA screening value of 0.08 mg/kg. In addition, about
55 percent of the fish analyzed from all the sample sites combined had methylmercury
concentrations that exceeded the screening value. The highest concentrations (up to
2.31 mg/kg) were measured in fish from Hell Hole reservoir, where the largest fish were
caught, and 75 percent of the sampled fish weighed between 1 and 5 pounds. For
crayfish, 15 of the 24 crayfish analyzed from Hell Hole and French Meadows reservoirs
exceeded the screening value of 0.08 mg/kg, with the highest concentrations also
associated with Hell Hole reservoir (up to 0.264 mg/kg).
Aquatic Biological Communities
The project’s eight river reaches, four reservoirs, and three small diversion pools
(see figure 1) provide habitat for a variety of aquatic invertebrates and fish communities.
Riparian habitat, wetlands, amphibians, and reptiles are addressed in section 3.3.3,
Terrestrial Resources. Special-status aquatic species are described separately at the end
of this affected environment subsection.
The streams and rivers associated with the project support diverse communities of
benthic macroinvertebrates. The status and health of benthic macroinvertebrate
communities were measured at 21 representative study sites and overall there was no
observable difference in the index of biotic integrity or the individual benthic
macroinvertebrate metrics at the study sites related to project operations or facilities,
except at the study sites at the top of the peaking reach immediately below Ralston
afterbay dam and immediately below Oxbow powerhouse. At these sites, there were
fewer EPT (taxa found in the orders: Ephemeroptera [mayflies], Plecoptera [stoneflies],
and Trichoptera [caddisflies]) that are intolerant of disturbance, more high-tolerance
individuals, and lower taxa richness compared with the adjacent sites on bypassed
reaches (Rubicon and Middle Fork American Rivers) and comparison sites (North Fork
American and North Fork of the Middle Fork American Rivers).
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