4.3 Water Resources
slated to receive sand under Alternative 1 are not proposed for sand replenishment under Alternative 2.
As no construction would occur at these sites, even short-term impacts to water quality would not occur.
Borrow Sites
As under Alternative 1, given the predominantly sandy nature of the borrow site sediments, and the mixing
and diluting capacities ofthe coastal environment, any increases in nutrients are anticipated to be short-term
and not of sufficient concentrations to result in plankton blooms that could cause red tides. The mixing and
diluting capacity of waters at the borrow sites are considered sufficient to avoid changes in pH as a result
of dredging activities. No violation of the California Ocean Plan objective would occur from dredging any
of the borrow sites.
The potential for turbidity impacts associated with dredging at the borrow sites is also addressed in detail
in Appendix D. Modification of dredge and/or disposal operations, as necessary, to adhere to the
RWQCB conditions will help ensure no significant impacts to water quality resulting from the alternative.
Localized increases in turbidity would not result in significant impacts to water quality at any of the borrow
sites. This conclusion is based on the relatively localized nature of the expected turbidity plumes for the
majority of the dredge period, and rapid diluting capacity of the open ocean. The larger turbidity plumes
associated with use of a hopper dredge would occur in pulses and not represent a continuous impact at the
borrow site, and the continuous turbidity plumes associated withuse ofa cutterhead dredge would be highly
localized. Because silty sands occur in a shallow and non-uniform overburden at the SO-9 site, there is
the potential for more extensive turbidity plumes to develop, however, they should be of short duration if
they occurred.
Water quality monitoring will be required as part of the RWQCB 401 Certification Order which also sets
conditions on proposed operations. If monitoring indicates that suspended particulate concentrations
outside the zone of initial dilution exceeds RWQCB conditions, the dredging operation will be
modified/suspended and appropriate measures taken to ensure compliance.
Mitigation Measures for Alternative 2a
As no significant impacts would occur, no mitigation measures would be necessary. Some monitoring
would be required consistent with the RWQCB permit.
Regional Beach Sand Project EIR/EA
Page 4.3-9
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