Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
1
Introduction
1.1 General
The German submarine U-864 was sunk outside Fedje in the county of Hordaland, Norway
09. February 1945. The submarine was torpedoed midship by a British submarine, broke in
two and sank. The wreck is located at 150m water depth. Both wreck sections are standing on
the seabed on their keels, with a list of 24 and 15 degrees for forward and aft section
respectively. The aft wreck section is situated on a relatively flat terrain and the forward
section in a relatively steep slope with its bow pointing upwards.
U-864 is assumed to have had 67 tons of liquid mercury (Hg) onboard, stored in 1857 carbon
steel cans in compartments inside its keel. There are two different types of Hg cans. Due to
the number of Hg cans combined with the available space in the keel compartments, it is
assumed that most of the compartments have been utilized for Hg storage.
When torpedoed, the mid section of the submarine was blown up, and a substantial number of
the stored Hg cans was destroyed. This led to significant Hg pollution of the seabed below.
The number of Hg cans that have corroded and started to leak mercury in the seabed is not
known.
It is assumed that there still are intact Hg cans inside the keel compartments of both wreck
sections, but the number of Hg cans and their condition is not known.
Kystverket has performed three offshore survey campaigns on the wreck site, phase 1 in 2005
and phase 2 in 2006 and phase 3A in January 2013. Both wreck sections were drained for oil
products between outer and inner hull in March 2013.
The authorities have decided to further evaluate two different methods of Hg pollution
abatement:
 Seal-in the polluted area, utilizing sand with special characteristics.
 Retrieve the Hg cans from the keel section and seal-in the polluted area (ref. above)
1.2
Purpose
The aim of phase 3B operation is to provide the NCA with information to identify different
risks and gain information on the feasibility of salvaging Hg canisters from the wreck of the
U-864. This is to be achieved by using the identified visible keel, which was identified during
phase 3A, as an entry area to attempt to inspect any Hg canisters, and to recover any canisters
which are identified during the operation.
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
There will also be some additional information gathering based on the results from
the survey 3A.
2 Process and delivery specifications
General
2.1
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All equipment shall have the capacity to operate in Hs<3
Surface platform shall be equipped with a heave compensated crane
Deck space on surface vessel must be organized in a clean and dirty zone, and Bidder
shall me able to handle possible Hg contamination on equipment.
Any substances (sea growth/sea bed) brought on deck during operation, shall be
collected and deposited in accordance with regulations
2.2 Preparatory work
The following list contains a number of special equipment required to perform the offshore
work. The list shall not be regarded as complete.
 Tool(s) to gain access to keel compartments
 Tool(s) for removal of intact Hg cans.
 Retrieval basket(s) for Hg cans. The basket to be sealed off (watertight), in order to
eliminate the possibility of Hg pollution during handling and retrieval through the
water column.
 Tool(s) for seabed sampling
Function testing and non field depended subsea operations, shall be performed prior to
mobilization and be documented.
2.3 Mobilization on site completed
Preliminary study completed
All equipment needed for the start of the operation is in place at the location of the wreck,
function tested on board the vessel and prepared for the operation.
All personnel shall be informed regarding the risk for Hg contamination from subsea
equipment and items recovered.
Supervisors and personnel operating equipment on the seabed shall be informed that the
operation is to be performed on a war grave site, and that special ethical guidelines shall be
respected.
Equipment needed for later stages is prepared and will be available according to planned time
schedule.
2.4 Inspection of keel aft section of U-864
During the operation 3A in January 2013, the keel was observed by ROV on the aft section at
starboard side. The NCA estimates that 2-3 meters of the keel is accessible and this area
should provide an opportunity to drill/cut holes in the keel compartments, in which a camera
can observe if any Hg canisters are stored inside. If any Hg canisters are observed in a
condition that retrieval is possible, , the steel plate covering the compartment is to be removed
and the Hg canisters shall be retrieved to the surfaced in a watertight basket with no risk of
Hg escaping in the water column or at the surface.
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
The accessibility might be hampered by debris that’s located close to the keel
compartments. Target 8 consist of debris from the wintergarten and may be relocated if
deemed necessary to establish working space for the ROV. The removal of sediments is to be
kept to a minimum.
During sampling of steel from inner hull in March 2013, the aft section moved further
towards port when oil/air leaked out of the hull. The position of the aft section has to be
monitored during keel inspection.
The keel is welded onto the inner hull with steel covers of 5 mm thick steel. The steel covers
are held in place by recessed screws.
Any retrieved mercury during keel inspection is to be disposed in accordance with relevant
regulations. Some Hg might be kept by the NCA for analyzing purposes.
Figure 2.1: Visible keel observed on ROV
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
Target 8
Visible keel
Figure 2.2: Overview of aft section U-864
Visible keel
Figure 2.3: Debries U-864
Target 8
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
Figure 2.4: Keel compartment from U-534 on display in Birkenhead, UK
Figure 2.5: Assed keel area on ship drawings
2.5
Assessment of positions on bow/aft section for securing and stabilizing
Tools shall be on board and ready to cut/clean positions on the inner hull of both wreck
sections, to assess the feasibility of fastening equipment to sections to stabilize them.
The positions are to be decided by PURCHASER on a later time.
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
2.6 Sediment sampling
A total of 10 – ten – sediment samples is to be gathered in the upper northwest corner of the
polluted area. The positions for sampling are to be decided by the PURCHASER on a later
time.
To be able to do tests in the laboratory on capping design, a substantial amount of sediments
from the wreck area is needed.
It is expected that about 50 litres of mixed bulk sediment is needed. The sediments for the
capping design tests can be sampled with Van Veen grab or similar. Samples should be taken
from areas with high mercury concentration. The high mercury concentration has to be
confirmed with sediment analyses, preferably on board the vessel.
2.7
Assessments on damage/condition of the buried keel compartments
(Option)
There exists subsea technology which is developed to detect/classify objects in the seabed,
which are buried and not visible, by using acoustics signals or similar technology.
The Offer should include a presentation of such technology and the feasibility on using this
equipment to assess the extent of damage to the keel on both wreck sections.
If the feasibility is considered good, these measurements will commence as the first
operational step after the mobilization.
3 Environmental monitoring
The Offer shall include environmental monitoring.
The environmental monitoring and sampling is suggested to be done with a separate smaller
vessel with respect to both cost and mobility. The vessel should have capacity to measure
salinity, temperature and turbidity profiles in the whole water column during water sampling
(preferably using a water sampling rosette with an attached CDT-probe). Further, the vessel
should be able to perform water sampling through the whole water column with a documented
vertical precision of at least +/- 2 m.
3.1 Turbidity measurements
Turbidity measurements shall be done during the operations.
Turbidity is a robust and well tested method to indirect monitor the concentration of particles
in the water column. Turbidity sensors can be placed stationary on buoys at several depths,
used as a profiling instrument deployed to record vertical turbidity profiles from the smaller
survey vessel, or mobile on a ROV to monitor the operation. Turbidity monitoring should be
done with online and real time access to the data.
It is suggested that 8 turbidity stations (OV1 to OV8) are used and that they are located as
suggested in Figure 3.1.
It is recommended to change the position of OV8 to southeast, because the main current is
northwest (NIVA, 2006).
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
Figure 3.1: Location of turbidity stations
The turbidity sensors should be placed at two depths. Suggested depths are 3 m and 10 m
above the seabed at positions OV1 to OV8 (see Figure 3.1).
3.2 Sediment traps
To document the overall impact of the operation, sediment traps located 3 m above the seabed
and one higher up in water column (10 m above the seabed) shall be used at positions OV1 to
OV8 (see Figure 1 above).
An example of a sediment trap is illustrated in Figure 3.2. The traps must be moored to the
sea bottom with weight and buoys must be used to achieve buoyancy.
Preferably the sediment traps should be placed at a water depth corresponding to the depth at
the wreck location or deeper. This because it is anticipated that stirred up sediments will have
relatively little upward momentum.
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
Figure 3.2: Illustration of a sediment trap
3.3 Water samples
There shall be taken water samples during the operations
For monitoring of mercury in the water column during the measure, it is proposed that the
water sampling is carried out in transects which includes the main current. Samples shall be
taken in the four main directions (northeast, northwest, southwest and southeast), as shown in
Figure 3.3.
10
0
0
10
m
0
10
m
10
0
m
Figure 3.4: Proposed locations for water sampling
m
Contract 2013/2567 – Keel inspection U-864
Annex A – Process and delivery specifications
Suggested distance for stations is 100 and 200 m from the wreck in every direction. The water
samples are proposed taken at 3 and 10 m above the bottom and at maximum turbidity as
identified during the sampling. The frequency of the water sampling should be a minimum of
two samples pr. day but preferably more often if time is available. This gives 8 sampling
points and 16 samples per day in total.
Water samples can be analysed quickly if they are analysed in a laboratory in the vessel. This
has been done with success by NIVA in 2006. From a water sample is on board the vessel it
takes relatively short time before the result is available (detection limit ca. 0.2 ηg / l).
3.4 Currents measurements
Currents shall be measured with at least one acoustic doppler profiler placed close to the
working area, but not in conflict with the operation at the wreck. The currents shall be
measured online during the whole operation.
Figure 3.4: Currents measurements
The current measurements have to reach minimum 30 m above the seabed.
The purpose of the current measurements is to assist the interpretation of turbidity data and
data from sediment traps. In addition, these data will be important as a basis for the design of
erosion protection measures on the cap as well as for the assessment of potential advection of
water in the capping layers as a result of pressure differences caused by water currents. It
would be preferable to base this part of the capping design on a water current measured, if
possible, over a year. Therefore, the current profiler shall be left in the water after the main
cruise to record over the next year.