Environmental Impact Statement - Sonoma Land Trust

California Department of Fish and Game
U.S. Fish and Wildlife Service
Section 3.3. Water Quality
resultant concentration of methylmercury is dependent on numerous variables:
salinity, pH, vegetation, sulfur concentration, dissolved organic carbon, oxidation
/reduction, and seasonal variations in each of the identified variables.
Current information suggests that tidal wetlands do not contribute to methyl
mercury production in the same manner as freshwater wetlands. In a study of the
Hamilton Wetland Restoration Project, the USACE (2007) tentatively concluded
that “marsh restoration does not provide evidence for increased bioavailability”.
This conclusion is supported by the work done by Slotton et al. studying
methylmercury concentrations in biota (biosentinel fish). Methylmercury
concentrations in the Napa Sonoma Marshes, including the fully-restored Pond
2A, were among the lowest in the entire study area. The study area extended
from the Petaluma River east to the upper watersheds of the Sacramento/San
Joaquin Delta (Slotton et al. 2006).
Preliminary information suggests that methylation is less likely to occur in
permanently flooded environments, and more likely to occur under sequential
drying and flooding conditions (Best et al. 2005). This finding is supported by
information collected by Slotton et al., which also indicated that infrequent
flooding of typically dry lands could lead to short-duration (seasonal) increases
in methylmercury concentrations in biota (Slotton et al. 2006). These findings
suggest that at least during the transition of the site to tidal marsh, production of
methyl mercury would be low. Furthermore, in the study of restored marshes
around San Pablo Bay, researchers found that methyl mercury production was
lower in vegetated sediments than in bare sediments (Best et al. 2005), which is
consistent with the USACE and Slotton et al. (2006) findings regarding methyl
mercury production in brackish to salty tidal marshes.
Thresholds of Significance
Criteria used for determining the significance of an impact on water quality are
based on the State CEQA Guidelines and professional standards and practices.
Impacts were considered significant if an alternative would:
• violate any water quality standards or waste discharge requirements,
• substantially degrade surface water and/or groundwater quality,
• contaminate a public water supply,
• substantially increase suspended solids and turbidity in receiving waters, or
• discharge contaminants into the waters of the United States.
Impacts and Mitigation Measures
No-Action Alternative
Under the No-Action Alternative, the proposed wetland restoration site would
remain in its present condition. Prior to transfer of the property to CDFG,
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
3.3-13
April 2012