4.3 Water Resources
above MSL and 12 percent below MSL. Turbidity plumes are calculated to be localized within about 100
to 300 feet of the discharge point, and may be visible up to 3,000 feet down current under maximum
current speeds when the finest grain sands are pumped. Both are consistent with the measurements from
Agua Hedionda Lagoon and Oceanside Harbor beach replenishment projects with sediments less than 10
percent silt/clays. Construction would occur at the South Oceanside receiver sites for approximately 30
days and at the North Carlsbad receiver site for 20 days. Depending upon the type of dredge, there may
be continuous turbidity or periodic episodes. However, due to the localized nature of the impact, the grain
size of the material (average 92 percent sand), and the presence of training dikes which would help reduce
turbidity, there would be no significant impacts to water quality at these two receiver sites.
South Carlsbad (North and South), Batiquitos, Leucadia, Moonlight Beach
All these receiver sites would receive material from the SO-7 borrow site. Percent of fine grain material
(less than 63 m) would be three percent or less which is equal to the natural condition in the Oceanside
Littoral Cell above MSL. Turbidity plumes are calculated to be localized within 100 feet of the discharge
location, but may extend 1,000 feet down current under maximum current speeds. The average plume
distance, and the conservative maximum plume distance, are both within the range of turbidity plumes
detected during the Agua Hedionda Lagoon replenishment project involving sediments with less than 10
percent silt/clays. Construction at any given receiver site would occur over 10 to 15 days and may be
either relatively continuous or episodic, depending upon the type of dredge. Again, due to the localized
nature of the impact, the grain size of the material (97 percent sand) which is equal to the natural condition,
and the presence of training dikes which would help control and reduce turbidity, there would be no
significant impacts to water quality at these series of receiver sites.
Cardiff
Cardiff would be the only site to receive material from borrow site SO-6. Material from this borrow site
would 97 percent sand, also similar to the existing condition in the Oceanside Littoral Cell above MSL.
Localized turbidity plumes are calculated to be less than 200 feet from the point of discharge, with a
maximumvisible plume under the greatest current conditions of 1,500 feet down current. Construction with
training dikes would occur over an estimated 11-day period. As with the other sites, the localized nature
of the short-term impact and the use of training dikes would ensure no significant impact.
Regional Beach Sand Project EIR/EA
Page 4.3-3
99-69\SANDAG EIREA 4.1 to 4.13.wpd 7/17/00
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