A Trial Capping Project for Contaminated Dredged Material from ...
A Trial Capping Project for Contaminated Dredged Material from the Port of Tyne, UK – A Learning Experience!
Chris Vivian, Silvana Birchenough, Jon Rees and Andy Birchenough - The Centre for Environment, Fisheries & Aquaculture Science (Cefas), Lowestoft, UK Trial Cap – Post Sand cap
Port of Tyne – The Problem • In 2003, 160 000 m3 contaminated sediment identified as needing removal to facilitate efficient port functioning. • Sediments at the Port of Tyne were contaminated with TBT, heavy metals including Cd, Cu, Hg, Pb and Zn and PAHs. • Metals mainly from historic mining sources in the Tyne catchment, TBT from dry docks and PAHs from industry. • There are limited solutions for the removal and disposal of the material that are both environmentally sound and economically viable in this highly urban estuary. • Trial capping project for 60,000m3 (=94,000t) sediment from 3 wharves was agreed.
Dredging Sites – Tyne Estuary Swan Hunter (Tyneside) Ltd Slipway Ends
b a
A&P (Tyne) Ltd Wallsend Dry Docks
d
Newcastle City Council Neptune Quay
c
Objectives of the Trial The sea-disposal and capping trial was designed to meet the following objectives set by the licensing authority:
• No loss of contaminated material during transport to the capping site; • Minimal loss of contaminated material during the dredging operation; • Minimal contaminant loss to the water column by shortterm monitoring during the placement and capping operation; • Minimal disturbance of contaminated material during the placement of the cap material; • Placement of adequate thickness of capping material over the whole volume of the deposited contaminated material; • Long-term maintenance of the integrity and efficacy of the cap assured by monitoring and cap maintenance when required;
Work plan • Characterisation of material: ¾ Chemical – TBT/DBT, metals, PCBs, PAHs, ∑ HCs, TOC, elutriate test ¾ Physical – PSA, % dry matter, geotechnical analysis
• Dredging method – backhoe with lid • Selection of capping area – within existing Souter Point disposal site • Type of disposal – split hopper barge • Cap design – level bottom capping with 1.5 m cap made up of 135,000t silt and sand • Monitoring plan
Capping Trial Disposal Site Capping trial disposal site
Dredge site
• • • • •
Souter Point disposal site is about 4 miles off the NE coast. Maximum depth is approximately 48 m. Relatively weak tides – max 20 cm/s springs and 10 cm/s neaps. Ebb and flow tides predominantly in a near north-south direction with a residual flow to the south. Capping trial disposal site - CDM targeted at 200 x 200 m box with cap intended to cover 300 x 300 m box.
Monitoring/Assessment Seabed topography Sediment structure Benthic biota Sediment quality Water quality AGDS
Microbial
Trace organics
PSA Sidescan
Water analysis
Epifauna SPI
Multibeam
Meiofauna Contaminants
Photograph
Macrofauna Sub-bottom Profiler
Dredging & Split Hopper Barge
Placement of CDM and capping material CDM Placement: • 160 barge loads between 13th Dec 2004 and 20th Mar 2005 • Only 1 barge load outside target zone – by 20 metres • Period prolonged due to adverse weather • Contributed to spread of thin layers of CDM • Dumped CDM settled rapidly – 35 minutes to settle out • Only low water column SPM levels reached site boundary Capping material placement: • After 100,000 m3 silt deposited by 11th April 2005, multibeam survey found it had been widely dispersed - ~70% lost outside target area • Silt deposition suspended and 90,000 m3 sand deposited • DEFRA /CEFAS agreed that a 0.6m sand cap was adequate after sediment re-suspension modelling • Multibeam surveys not useful for defining limit of area needing capping due to limited resolution but adequate for cap thickness • However, SPI was very effective at detecting thin layers of CDM
Cap Thickness
Total sand and silt cap
East West section through cap
North south section through cap
Risk Assessment of Cap Facts about the cap
•
Cap thickness – median 0.2 – 0.25 m (max 1.0 m) – but ? up to 0.45m allowing for errors in bathymetric data Cap thickness significantly
Chris Vivian, Silvana Birchenough, Jon Rees and Andy Birchenough - The Centre for Environment, Fisheries & Aquaculture Science (Cefas), Lowestoft, UK Trial Cap – Post Sand cap
Port of Tyne – The Problem • In 2003, 160 000 m3 contaminated sediment identified as needing removal to facilitate efficient port functioning. • Sediments at the Port of Tyne were contaminated with TBT, heavy metals including Cd, Cu, Hg, Pb and Zn and PAHs. • Metals mainly from historic mining sources in the Tyne catchment, TBT from dry docks and PAHs from industry. • There are limited solutions for the removal and disposal of the material that are both environmentally sound and economically viable in this highly urban estuary. • Trial capping project for 60,000m3 (=94,000t) sediment from 3 wharves was agreed.
Dredging Sites – Tyne Estuary Swan Hunter (Tyneside) Ltd Slipway Ends
b a
A&P (Tyne) Ltd Wallsend Dry Docks
d
Newcastle City Council Neptune Quay
c
Objectives of the Trial The sea-disposal and capping trial was designed to meet the following objectives set by the licensing authority:
• No loss of contaminated material during transport to the capping site; • Minimal loss of contaminated material during the dredging operation; • Minimal contaminant loss to the water column by shortterm monitoring during the placement and capping operation; • Minimal disturbance of contaminated material during the placement of the cap material; • Placement of adequate thickness of capping material over the whole volume of the deposited contaminated material; • Long-term maintenance of the integrity and efficacy of the cap assured by monitoring and cap maintenance when required;
Work plan • Characterisation of material: ¾ Chemical – TBT/DBT, metals, PCBs, PAHs, ∑ HCs, TOC, elutriate test ¾ Physical – PSA, % dry matter, geotechnical analysis
• Dredging method – backhoe with lid • Selection of capping area – within existing Souter Point disposal site • Type of disposal – split hopper barge • Cap design – level bottom capping with 1.5 m cap made up of 135,000t silt and sand • Monitoring plan
Capping Trial Disposal Site Capping trial disposal site
Dredge site
• • • • •
Souter Point disposal site is about 4 miles off the NE coast. Maximum depth is approximately 48 m. Relatively weak tides – max 20 cm/s springs and 10 cm/s neaps. Ebb and flow tides predominantly in a near north-south direction with a residual flow to the south. Capping trial disposal site - CDM targeted at 200 x 200 m box with cap intended to cover 300 x 300 m box.
Monitoring/Assessment Seabed topography Sediment structure Benthic biota Sediment quality Water quality AGDS
Microbial
Trace organics
PSA Sidescan
Water analysis
Epifauna SPI
Multibeam
Meiofauna Contaminants
Photograph
Macrofauna Sub-bottom Profiler
Dredging & Split Hopper Barge
Placement of CDM and capping material CDM Placement: • 160 barge loads between 13th Dec 2004 and 20th Mar 2005 • Only 1 barge load outside target zone – by 20 metres • Period prolonged due to adverse weather • Contributed to spread of thin layers of CDM • Dumped CDM settled rapidly – 35 minutes to settle out • Only low water column SPM levels reached site boundary Capping material placement: • After 100,000 m3 silt deposited by 11th April 2005, multibeam survey found it had been widely dispersed - ~70% lost outside target area • Silt deposition suspended and 90,000 m3 sand deposited • DEFRA /CEFAS agreed that a 0.6m sand cap was adequate after sediment re-suspension modelling • Multibeam surveys not useful for defining limit of area needing capping due to limited resolution but adequate for cap thickness • However, SPI was very effective at detecting thin layers of CDM
Cap Thickness
Total sand and silt cap
East West section through cap
North south section through cap
Risk Assessment of Cap Facts about the cap
•
Cap thickness – median 0.2 – 0.25 m (max 1.0 m) – but ? up to 0.45m allowing for errors in bathymetric data Cap thickness significantly
