Environmental Statement - Maersk Oil

Balloch Field Development Environmental Statement
Section 3 Baseline Environment
Total organic matter (TOM) ranged between 3.8 % (station 2) and 7.5 % (station 4) (Fugro, 2010).
TOM levels at the majority of stations were higher than typical background levels found at 95 % of the
stations in the CNS (4.48 %) (UKOOA, 2001).
3.5.3. SEDIMENT CONTAMINANTS
A summary of contaminant levels typically found in surface sediments of the North Sea is given in
Table 3‐7. Across the North Sea, quantities of total hydrocarbons in sediments tend to show an
increase from the SNS to the NNS, with background hydrocarbon concentrations being generally
higher in fine sediments (muds and silts) than in coarser sediments (sands and gravels) due to their
greater surface area and adsorptive capacity. Nevertheless, it should be noted that drilling activity
and hence the input of oil derived contaminants has been considerably more intensive in the
northern and central sectors compared to the SNS and consequently this would add to the higher
levels recorded further north (CEFAS, 2001).
For PAHs it is thought the same is true, with concentrations higher in the NNS relative to the SNS and
total PAH concentration ranging between 0.02 µg/kg and 74.7 µg/kg at oil and gas locations.
Table 3‐7 Contaminant levels typically found in surface sediments of the North Sea (Sheahan et al., 2001).
Location
Oil and Gas
Installations
THC
(µg/g)
10‐450
PAH
(µg/g)
0.02‐
74.7
PCB
(µg/kg)
Nickel
(µg/g)
Copper
(µg/g)
Zinc
(µg/g)
Cadmium
(µg/g)
Mercury
(µg/g)
1,917 17.79 17.45 129.74 0.85 0.36
Estuaries ‐ 0.2‐28 6.8‐19.1 ‐ ‐ ‐ ‐ ‐
Coast ‐ ‐ 2 ‐ ‐ ‐ ‐ ‐
Offshore 17‐120 0.2‐2.7 5000 m
Nickel 17.79 15.36 9.18 9.5
Copper 17.45 7.25 8.96 3.96
Zinc 129.74 38.5 21.43 20.87
Cadmium 0.85 5.56 0.2 0.43
Mercury 0.36 0.22 0.33 0.16
Lead 57.52 16.34 11.7 12.12
Total Hydrocarbon Concentrations
The stations surveyed by Fugro (2010) had relatively low levels of THCs. Levels varied from 2.8 µg/g
dry weight to 6.6 µg/g at stations 4 and 6 respectively. These levels were higher than the
concentrations recorded previously for the Donan field environmental survey (Fugro, 2005), but
comparable to the published UKOOA (2001) mean background concentration of 9.51 µg/g.
Carbon Preference Index (CPI)
The Carbon Preference Index (CPI) is used to assess the relative contribution of petrogenic and
biogenic sources in hydrocarbon samples and is determined by calculating the ratio of the sum of
odd‐ to the sum of even‐carbon n‐alkanes. The range of n‐alkanes from nC21‐36 is of particular interest
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