3.1 Geology and Soils
beach nourishment, and the layer is thick enough (1 to 11 feet) for efficient and economical dredging.
There is no silt overburden at this borrow site.
SO-6
Site SO-6 is located offshore of San Elijo Lagoon. The project dredge area covers approximately 29
acres in 60 to 80 feet of water of the approximately 225 acres investigated. The results of the grain-size
analysis indicate that most, if not all, of the sediment within SO-6 is acceptable for beach replenishment
purposes. A single, wedge-shaped layer of fine-grained sand with a low content of silt overlies shale
bedrock within the site. This wedge of material measures less than 5 feet thick along the nearshore
boundary and uniformly increases toward the offshore boundary to a maximum of 14 feet in thickness.
There is no silt overburden at this borrow site.
SO-5
Site SO-5 is located offshore of San Dieguito Lagoon. The area investigated was about 225 acres and the
proposed project dredge area has a surface area of approximately 127 acres. The dredge area would be
located between 50 and 80 feet of water. A majority of the site contains suitable sand for beach
nourishment. The thickness of the sand layer is 1 to 22 feet. The predominant sediment within Site SO-5
is gray to olive-gray fine-grained sand with 3 percent silt content. The site contains a single, homogenous,
wedge-shaped layer of fine-grained sand. There is no silt overburden at this borrow site.
MB-1
Site MB-1 is located offshore of Mission Beach and north of the San Diego River. The area investigated
was over 500 acres, but the proposed project dredge area covers approximately 19 acres at 65 to 75 feet
of water. The majority of the site contains fine- to coarse-grained that is suitable for beach replenishment.
The site contains a very thick layer of medium- to coarse-grained sand covering the entire area and varying
in thickness from 15 to 45 feet. There is no silt overburden at this borrow site. Of all the proposed borrow
sites, this site contains the largest overall volume of suitable sand for beach replenishment.
Regional Beach Sand Project EIR/EA
Page 3.1-11
99-69\SANDAG EIREA 3.4.wpd 7/17/00
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