4.3 Water Resources
Solana Beach, Del Mar, Torrey Pines
All three receiver sites would utilize material from the SO-5 borrow site. The average silt/clay content of
the sediment layers is 5 percent at this borrow site. Turbidity plumes are calculated to extend about 300
feet from the discharge point on average, but may extend up to 1,500 feet down current under maximum
current speeds. This would be consistent with the range of turbidity plumes detected during the Agua
Hedionda Lagoon replenishment project involving sediments with less than 10 percent silt/clays.
Construction would occur at these three sites for approximately 13, 16 and 20 days, respectively, and
turbidity levels may vary over this time depending upon the type of the dredge. There would be no
significant water quality at these locations giventhe high sand content (95 percent) and use of training dikes.
Mission Beach
The sands at MB-1 have an extremely low silt/clay content of 1 percent. Turbidity plumes at this receiver
site are calculated at less than 100 feet on average and less than 350 feet under maximum downcurrent
conditions. Construction may occur over an 11-day period either as a continuous event or periodic,
depending on the dredge type. Given the very high sand content and very localized nature of the effect,
as well as use of training dikes, there would be no significant impacts.
Imperial Beach
Borrow site SS-1 also has a high sand content of 99 percent and turbidity plumes are estimated to extend
an average of 200 feet but possibly up to 600 feet under maximum current speeds. The duration of this
elevated condition would be on the order of 12 days. Given the very high sand content and very localized
and short-term nature of the effect, as well as use of training dikes, there would be no significant impacts.
Borrow Sites
Dredging at all of the borrow sites was evaluated for potential to exceed the criteria established in the
California Ocean Plan for bacteria, dissolved oxygen, contaminates and sulfides, turbidity, nutrients, and
pH. All of the borrow sites would be of sufficient distance from wastewater outfalls to avoid bacterial
exposure. Sandy sediments such as those in the borrow sites would have low organic carbon and
contaminant concentrations, which have the least potential to degrade oxygen concentrations, and they are
located in coastal waters, which remain well oxygenated due to mixing from currents, surge, and tidal
Page 4.3-4
Regional Beach Sand Project EIR/EA
99-69\SANDAG EIREA 4.1 to 4.13.wpd 7/17/00
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