Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 295

COD (mg/g) T-N (mg/g)

25

2

19.6

1.54

20

1.5

15

1

10

0.5 0.38

3.6

5

0 0

Inside sand cap Outside sand cap Inside sand cap Outside sand cap

T-S (mg/g) T-P (mg/g)

0.6 0.6

0.51

0.47

0.5

0.5

0.37

0.4

0.4

0.3 0.3

0.2 0.2

0.1

0.1

0.04

0

0

Inside sand cap Outside sand cap Inside sand cap Outside sand cap

FIGURE 8.16
Effects of a sand cap (Port of Kanda, the Ministry of Land, Infrastructure and Transport, Japan). COD, chemical
oxygen demand, T-N, T-S, and T-P, total nitrogen, total sulides, and total phosphorous, respectively.

8.5.3 Removal of Contaminated Sediments by Dredging

8.5.3.1 Dredging

Dredging has historically been used (a) for beach reclamation, (b) to remove bottom
sediments to deepen channels, waterways, and harbors and ports, (c) for maintenance of
desired water depths for sea routes, and (d) to obtain materials for reclamation. Regardless
of the type of equipment used (cutter wheels, augers, bucket wheels, pumping, suction
hopper, self-propelled, automatic, etc.), dredging is a very invasive and destructive proce-
dure. When used for removal of contaminated sediments, total disruption of the bottom
ecosystem occurs. To return the benthic layer to full functionality, replacement of the food
supply for benthic organisms is necessary. Removal of the irst trophic level in the food
chain will have severe consequences on the higher trophic levels. In that regard, planning
for dredge removal of the contaminated bottom layer must include restoration of the func-
tionality of the benthic layer.

8.5.3.2 Treatment of Dredged Sediments

Two options are available for disposal of dredged contaminated sediments: (1) disposal in
a secure landill and (2) treatment of the contaminated sediments and reuse of the treated
sediments. Option (1) is not an option that has many proponents. Treatment of contaminated