that an intrinsic oil spill countermeasure process previously described as "clay-oil flocculation" (Bragg & Yang 1993 a & b) was occurring at the coastal sites impacted by the SEA EMPRESS incident.
This interaction between the mineral fines and the oil :
・ Minimised the contact of oil directly with the substrate, thereby reducing the adhesion of the oil to the shoreline.
・ Prevented the re-coalescence of oil droplets, thereby promoting the dispersion of oil within the surf zone.
Recent studies with samples collected from previous spill sites (e,g., Arrow 1970 ; Metula 1974 ; BIOS test spill, 1981 ; Fred Bouchard 1993) have demonstrated the almost universal ability of the different crude and refined oil types to flocculate in the presence of seawater and mineral fines under various environmental con-ditions (Owens et al. 1994 ; Bragg and Owens 1995) . The finding that clay-oil flocculation was taking place in Carmarthen Bay beach sediments, resulted in a modification of the planned operational response. The oiled cobble zone at the eastern end of Amroth beach (a site of high amenity value) was subjected to "surf washing". The technique is essentially a matter of using an excavator while the water is at low tide to move material from the oiled zone at the high water mark towards the middle of the intertidal zone. As the tide rises, the energy imparted in the surf zone is then sufficient to remove the Forties emulsion from the oiled cobbles. The mineral fines in the waters of the surf zone are believed to act as surface active agents to promote the removal of the oil from the substratum and to allow dispersion of the oil into the surf zone. We estimated that half of the oil being released from the cobble was dispersed (stabilised by the mineral fines). The other half was released as a broken surface slick (weathered emulsion, in appearance like tea leaves floating on the sea surface).
Over 4 days, the cobbles from the high water mark were moved down the beach at low water. The oiling of the cobbles was reduced at each tidal cycle so that by the 5th day there was no longer significant oiling in the cobble zone at the eastern half of Amroth beach. Boulders at the western end of Amroth were not subjected to surf washing since they were greater than 30 cm in diameter, were not moved by the energy in the surf zone and hence were not subjected to the same degree physical energy. This area was therefore treated with dispersants at a later date.
The success of the surf washing on Amroth beach meant that other beaches were also subjected to surf washing as a final polishing process.
High Energy Environment : Dispersant treatment
As the Easter vacation approached there was increasing pressure from the local councils to cleanup the high amenity value areas of Carmarthen Bay, in time for the arrival of the tourists. Over the last 2 weeks of March, particular attention was given to cleaning up the holiday resort of Tenby. Type ? dispersants were shown to be effective at cleaning both the natural and man-made surfaces contaminated with oil.
Carmarthen Bay is a shallow-water bay important for both fisheries and the ecology of the area. Therefore, it was important to monitor the impact of the dispersant operation in terms of raising the levels of dispersed oil in the bay. NETCEN monitored the concentration of dispersed oil in the bay generated by each application of dis-persant prior to the high tide. The dispersed oil concentrations were found to be relatively low (3 ppm as a maximumand more typically <1 ppm) and also very localised (typically affecting areas of around 20m diameter).
In April and May dispersant application has been extended to Saundersfoot, the westrn end of Amroth, Marros. Lydstep, Manobier, Freshwater West, Monkstone. The Glen, and Swallow Tree. Monitoring at each of these sites showed that the dispersant application had a negligible effect in terms of raising the levels of dispersed oil in the water column. This monitoring allowed the JRC to proceed with the cleanup of high amenity areas with confidence that the localised operations were not having a major impact on the surrounding marine environment.
Low-energy environment - Potential for Bioremediation
The low-energy environment refers mainly to the coastline within Milford Haven itself. As with the high-energy coastline, the first stage of bulk oil removal was largely completed by the start of March. The techniques used most extensively within Milford Haven have beenbulk removal of contaminated sand and sea water flushing.
