Environmental Impact Statement - Sonoma Land Trust

California Department of Fish and Game
U.S. Fish and Wildlife Service
Section 3.3. Water Quality
The water quality analysis also relies on other sections in this EIS/EIR, especially
Section 3.1 Geology, Soils, and Paleontology, Section 3.2 Surface-Water
Hydrology and Tidal Hydraulics, and Section 3.9 Hazardous Substances and
Waste.
Impact Mechanisms
Exceedance of Water Quality Objectives due to Dredged
Material Placement Activities
The primary water quality concern associated with placement of dredged material
is the potential for formation of acid-sulfate soils. During the drying process,
sulfides formed under anaerobic conditions while submerged are oxidized to
sulfate, which then forms sulfuric acid on contact with water from runoff or rain.
The acidic conditions and low pH (less than 5.5) can adversely affect aquatic life
and wetland vegetation.
Other water quality issues associated with wetlands created withplacement of
dredged material include:
• turbidity may increase over the short term during dredging;
• increasing concentrations of sulfide, ammonia, and phosphorus in brackish
water and freshwater environments to levels exceeding those permitted by
water quality objectives, both in drainage water from recently placed dredged
material and in leached runoff after placement; and
• increasing concentrations of heavy metals in drainage water after placement
of dredged material as a result of the conversion of soil chemistry from
anaerobic (reducing) to aerobic (oxidizing) conditions, which increases the
dissolved, readily soluble concentration of many heavy metals.
Dredged material could contain contaminants and other chemical constituents
that pose a threat to water quality. There are several upland and aquatic pathways
by which contaminants can threaten water quality in a wetland environment. The
contaminant pathways are:
• effluent discharge;
• runoff;
• leachate runoff;
• seepage by soluble diffusion and soluble convection through tidal pumping
and capillary action; and
• bioturbation, which includes the physical and biological activities that occur
at or near the sediment surface that cause the sediment to become mixed.
These pathways also indicate the biotic resources potentially affected by the
mobilization and accumulation of toxic contaminants. Water quality degradation
could occur initially in surface water that comes into contact with levees or
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
3.3-11
April 2012