Quantifying Contaminant Transport with On-Line Monitoring
Quantifying Contaminant Transport with On-Line Monitoring Anita Nybakk (NGI, Trondheim, Norway) Gijs Breedveld (NGI, Oslo, Norway) Marianne Kvennås (NGI, Trondheim, Norway) Randi Skirstad Grini (NGI, Trondheim, Norway)
Monitoring sediment remediation The last 5-10 years NGI has been monitoring several sediment remediation projects along the Norwegian coast. The monitoring has consisted of laboratory analysis: • Sediment samples • Sediment traps • Water samples • Passive sampler • Diffusion chambers And real-time analysis: • On-line measurements of current velocity and direction • On-line measurements of turbidity
Turbidity Cloudiness of a fluid Quantified by measuring the scattering of light The light is spread mainly by particles in the water Different types of sediments were expected to give different turbidity to suspended material rate How much will the ratio of turbidity to suspended material vary between different types of sediments?
Monitoring with real-time analysis Estimate the transport of pollutants out of the remediation area Continuous data set The laboratory analysis can be used to calibrate the continuous data set from the real-time analysis.
Monitoring with real-time analysis Make sure that the remediation is done within the permit Limits for turbidity and current velocities are determined on the basis of • • •
concentrations of pollutants in the sediments measurements of the current in the area experience from other similar projects.
Aim of this project Better basis for deciding turbidity limit Improve the quality of data used to estimate transport of polluted sediments in remediation projects
Why is this necessary?
Why? • Simplify the decision procedure for turbidity limits • If the limits are too high, there will be a higher transport of polluted sediment than desired. • If the limits are too low, the contractors might not be able to work as fast as they would otherwise.
Experiments Three 2 m high columns filled with sea water Wet sediments were added and homogenized with the water Water samples were drawn from the columns Turbidity was measured and the water samples were filtered for suspended material
Turbidity versus time 500 100 450 90 80 400
Turbiditet Turbiditet (NTU) (NTU)
70 350 60 300
Stamsund Stamsund Gjerdsvika Gjerdsvika Ramstadlandet Ramstadlandet Roald Roald Fosnavåg Fosnavåg
50 250 40 200 30 150 20 100 10 50 0 0
500
1000
0 0
500
1000
1500
2000
1500 Tid (min) 2500 Tid (min)
2000 3000
3500
2500 4000
3000 4500
5000
The three stages of sedimentation 500 450 400
Turbidity (NTU)
350 300 Stamsund Gjerdsvika
250
Ramstadlandet 200
Roald Fosnavåg
150 100 50 0 0
500
1000
1500
2000
2500 3000 Time (min)
3500
4000
4500
5000
Results The assumption that coarser sediment types sediment faster than finer sediment types does not count. Turbidity from shell sand stays higher for a long time The sedimentation can be divided into 3 stages • Fast stage • Slow stage • Very slow stage
Turbidity versus suspended material 450 70 400 60 350
Turbidity (NTU) Turbidity (NTU)
50 300
Fosnavåg Stamsund Roald Ramstadlandet Gjerdsvika Roald Ramstadlandet Gjerdsvika
250 40 200 30
Stamsund Fosnavåg
150 20 100 10 50 00 00
5010
100
20 150
30 200 25040 300 50 350 Suspended material (mg) Suspended material (mg)
60 400
450 70
500
Sediment fractions and concentrations
Summary Sedimentation rate differ from sediment to sediment, and it is hard to predict the sediment rate by measuring the grain size. Turbidity – suspended material ratio do not vary much from sediment to sediment in the area of interest. The fraction with highest concentration of pollutions vary from sediment to sediment, and from pollutant to pollutant. To decide limits of turbidity one need to run sedimentation tests and fraction analysis in the lab.
Monitoring sediment remediation The last 5-10 years NGI has been monitoring several sediment remediation projects along the Norwegian coast. The monitoring has consisted of laboratory analysis: • Sediment samples • Sediment traps • Water samples • Passive sampler • Diffusion chambers And real-time analysis: • On-line measurements of current velocity and direction • On-line measurements of turbidity
Turbidity Cloudiness of a fluid Quantified by measuring the scattering of light The light is spread mainly by particles in the water Different types of sediments were expected to give different turbidity to suspended material rate How much will the ratio of turbidity to suspended material vary between different types of sediments?
Monitoring with real-time analysis Estimate the transport of pollutants out of the remediation area Continuous data set The laboratory analysis can be used to calibrate the continuous data set from the real-time analysis.
Monitoring with real-time analysis Make sure that the remediation is done within the permit Limits for turbidity and current velocities are determined on the basis of • • •
concentrations of pollutants in the sediments measurements of the current in the area experience from other similar projects.
Aim of this project Better basis for deciding turbidity limit Improve the quality of data used to estimate transport of polluted sediments in remediation projects
Why is this necessary?
Why? • Simplify the decision procedure for turbidity limits • If the limits are too high, there will be a higher transport of polluted sediment than desired. • If the limits are too low, the contractors might not be able to work as fast as they would otherwise.
Experiments Three 2 m high columns filled with sea water Wet sediments were added and homogenized with the water Water samples were drawn from the columns Turbidity was measured and the water samples were filtered for suspended material
Turbidity versus time 500 100 450 90 80 400
Turbiditet Turbiditet (NTU) (NTU)
70 350 60 300
Stamsund Stamsund Gjerdsvika Gjerdsvika Ramstadlandet Ramstadlandet Roald Roald Fosnavåg Fosnavåg
50 250 40 200 30 150 20 100 10 50 0 0
500
1000
0 0
500
1000
1500
2000
1500 Tid (min) 2500 Tid (min)
2000 3000
3500
2500 4000
3000 4500
5000
The three stages of sedimentation 500 450 400
Turbidity (NTU)
350 300 Stamsund Gjerdsvika
250
Ramstadlandet 200
Roald Fosnavåg
150 100 50 0 0
500
1000
1500
2000
2500 3000 Time (min)
3500
4000
4500
5000
Results The assumption that coarser sediment types sediment faster than finer sediment types does not count. Turbidity from shell sand stays higher for a long time The sedimentation can be divided into 3 stages • Fast stage • Slow stage • Very slow stage
Turbidity versus suspended material 450 70 400 60 350
Turbidity (NTU) Turbidity (NTU)
50 300
Fosnavåg Stamsund Roald Ramstadlandet Gjerdsvika Roald Ramstadlandet Gjerdsvika
250 40 200 30
Stamsund Fosnavåg
150 20 100 10 50 00 00
5010
100
20 150
30 200 25040 300 50 350 Suspended material (mg) Suspended material (mg)
60 400
450 70
500
Sediment fractions and concentrations
Summary Sedimentation rate differ from sediment to sediment, and it is hard to predict the sediment rate by measuring the grain size. Turbidity – suspended material ratio do not vary much from sediment to sediment in the area of interest. The fraction with highest concentration of pollutions vary from sediment to sediment, and from pollutant to pollutant. To decide limits of turbidity one need to run sedimentation tests and fraction analysis in the lab.
