Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 294

sediment particles, but also reduces the lux of contaminants into the water column
above.
A sand cap can provide a new sand beach and tidal lats that will serve as a habitat
for various kinds of organisms, from bacteria in pore spaces to macro-benthos such as
bivalves, sea cucumber, and seaweed. These organisms consume a large amount of nutri-
ents. When sand is obtained from regions distant from the capping site, organisms and
small animals may exist in the transported sand that are not native to the capping site.
This is especially true when the source of the sand is land-based. Newly created sand
cap beaches can function as physical puriication units, i.e., iltration, through the action
of waves and tides. Removal of suspended solids from the seawater and decomposition
of organic matter adhering to the suspended solids by microorganisms in the pores are
additional beneits obtained in sand capping.
For sand capping to be robust and successful in providing the necessary isolation capa-
bility, the following must be accounted for in the design and construction of the cap:

a. Nature and type of currents, waves, lood, etc., that would cause drifting of
the sand during and after emplacement. The record shows that hurricanes and
typhoons are capable of dramatically altering the near-shore bottom conditions.

b. Possible movement of some benthic organisms through the sand cap.

c. Disruption of the food chain.

Table 8.6 shows a sampling of some recent major sand capping projects. The beneits
from sand capping are shown in Figure 8.16. Data reported by the Port of Kanda, Ministry
of Land, Infrastructure and Transport, Japan, for COD, T-N, T-S, and T-P following sand
capping indicate environmental beneits such as less COD, less sulide, and a lesser amount
of nutrients in the sand cap, in comparison to that of the surrounding silty seabed. From
the viewpoint of biological diversity, there is every indication that the sand cap is better
than the surrounding silty seabed.

TABLE 8.6
Puriication Projects Using Sand Caps

Construction
Methods Project Location Contaminants Site Conditions Cap Design Reference

Kihama Inner
Lake, Japan

Nutrients 3700 m 2 Fine sand, 5 and

20 cm

Akanoi Bay, Nutrients 20,000 m 2 Fine sand, 20 cm

Denny Way,
Washington

PAHs, PCBs 1.2 ha near shore

with depths from
0.6 to 18.3 m

Average of
80 cm of sandy
sediment

Barge
spreading

Sumeri, 1995

Simpson Tacoma,
Washington

Creosote,
PAHs, dioxins

6.8 ha near shore
with varying
depths

1.2 to 6.1 m of
sandy sediment

Hydraulic
pipeline with
“sandbox”

Sumeri, 1995

Hamilton Harbor
Ontario

PAHs, metals,
nutrients

10,000 m 2 portion
of large,
industrial harbor

0.5 m sand Tremie tube Zeman and

Patterson,
1996

Eitrheim Bay,
Norway

Metals 100,000 m 2 Geotextile and

gabions

Deployed
from barge

Instanes,
1994