1. Dredging and disposal of sediments in Finland Dr. Jani Salminen

2. Outline Why are we concerned about dredging and disposal of sediments?
How do we manage environmental protection in the context of dredging and disposal of sediments in Finland?
Site history and investigations prior to dredging
Guidelines instructing the permissions given for dredging and disposal of sediments
Choice of disposal site
Minimization of environmental impacts at dredging and disposal sites

3. Why are we concerned about dredging and disposal of sediments?
”Wild” practices resulted in unsuccessful cases
No limit values for pollutants in disposed sediments
No requirements for disposal sites
Case Kuuva,
in Turku archipelago

4. Case Kuuva disposal site
= angry citizens, fishermen, summer cottage owners etc.
= very bad reputation of dredging & disposal ?

5. National guidelines for dredging and disposal of sediments
First given in 2004, revised in 2015
Not legally binding but in practise quite strictly obeyed
Is applied to marine and inland water sediments
Only for large projects (>500 m3) that need a permission from the environmental authority
Given by the Ministry of Environment
Used by water constructors like cities and the Finnish traffic agency, consultants, authorities
There are numerous small dredgings by private
summer cottage owners (operated by small
businesses). They inform the local authority, which
decided whether a permission is needed or not
       

6. National guidelines
Gives instructions on when and how to investigate the site where dredging will be done
Sites are often impacted by polluting activities (harbours, water traffic (anti-fouling agents like tributyltin TBT), industry, shipyards, waste water treatment plants and so on
Site history needs to be known
It is likely that there are high concentrations of pollutants ( ) in the sediments that will be dredged
To avoid pollution of the water environment, these concentrations need to be known
Sediments samples have to be taken and analysed to do this
For presumably non-contaminated sediments and sandy sediments no sampling and analyses are required
Underwater cultural heritage needs to be investigated, evaluated and potentiallyprotected in collaboration with National Board of Antiquities
       

7. Several samples need to be taken
Figure: Jyrki Hämäläinen GTK
Photo: KVVY
Photo: Jyrki Hämäläinen GTK

8. More samples are required when the site has a high risk for pollution and no earlier data on pollution in the sediments exist
Number of individual sampling spots and subsamples in a composite sample at a dredging site with high risks of pollution and no previous data on pollution in the sediments
Minimun number of sampling spots
Minimun number of subsamples in a composite sample
Dredging area (1000 m2)
Number of sampling spots and subsamples in a composite sample at a dredging site with low risk of pollution or with good existing datasets on pollution distribution
Minimun number of sampling spots
Minimun number of subsamples in a composite sample
Dredging area (1000 m2)

9. Several contaminants need to be analyzed
Pollutant
Cannot be disposed to open water
No disposal limitations due to pollution
Can potentially be disposed to open water depending on the suitability of the disposal site
Oil
Organotins

10. Placement of the sediments
Three options:
At the see/lake at a disposal site which has a permission by an authority
For sediments with relatively low concentrations of pollutants ( )
At the shore behind a semi-(im)permeable barrier
Often used for moderately polluted sediments ( )
At land
Most expensive, hard to find place for muddy/clayey sediments
For polluted sediments ( )
Water quality monitoring
Rainfall
Water flow through the barrier
Water flow through disposed sediment
Sea/lake/river
Disposed sediment
Construted semipermeable barrier

11. Open-water disposal sites need to meet criteria to get a permission
Assessment is based on geological and biological properties
Geology, seafloor type, topology, water flow conditions
Disposed sediments need to stay where they are placed!
Impacted area needs to be estimated
Nature conservation areas
Fishing areas
Fish reproduction areas
Recreational areas

12. Conditions given in permissions for dredging and disposal sites
For dreding sites: During the operating and for some time thereafter
Time limitations (spring/summer, windy days)
Fish populations, physical & chemical parameters (turbidity, nutrients, contaminants)
For disposal sites: Long-term monitoring during the operational period (several years… few decades)
How much sediments have been disposed
How well do the sediments stay where they have been put (soundings, sampling)
Water quality in the surrounding areas
Limiting the spread-out of the fine particles upon disposal (weather conditions)

13. Environmental protection measures during dredging
SILT CURTAIN
Photo:
Photo: Kainuun Sanomat
USE OF ENVIRONMENTAL DREDGE HEAD, NAVIGATOR, STOPPING THE WORK WHEN THE CONDITIONS ARE WINDY
SILT CURTAIN
Photo: Sukellustyö Perlant
Photo: National Traffic Agency

14. Thank you for your attention! jani.salminen@ymparisto.fi