The Bay of Plenty Regional Council has sent Mobil Oil a $691,766clean-up bill for the efforts so far following the oil spill in Tauranga Harbour on April 27.

Clean-up operations re-focussed on the Tauranga Bridge Marina this week, says council's on scene commander Adrian Heays.

'A minor amount of oil remobilised at Bridge Marina last week, so we have reactivated clean-up efforts with prop washing and booms, recovering oil from the water, waterline scraping and solvent cleaning of dry marina structures.

'We've been wiping down the pier surface and using divers to clean difficult surfaces under water,” says Adrian.

Pile cleaning continues at the port, with a final washing off to contain and remove any oil that may be trapped in pockets in rocks under the wharf.

At Maungatapu and Motuopuhi Island, Mobil staff and local hapu are checking shorelines regularly and a remediation plan is being developed for oiled seawalls and jetties.

The clean-up will continue until all areas have reached an acceptable end state, rather than an end date. Final costs for the regional council will not be known until then.

'Once we get to the point that transferable oil is largely removed from the affected areas we can terminate the response phase of the clean-up. Independent environmental monitoring will continue, and it's expected Mobil will lead the affected parties through an appropriate recovery and mitigation process,” says Adrian.

Clean-up operations have finished at the worst affected area, Matakana, and at Rangiwaea Island, Pilot Bay and Sandy Bay.

About 1.5 tonnes of oil is estimated to have leaked into the harbour during the spill.

Early results from initial sampling on April 29 (two days after the oil spill) showed levels of oil-related pollutants in shellfish at Maungatapu Bay were higher than baseline levels on that date.

All other monitoring sites, including the Port, Bridge Marina, town reach and Motuopuhi Island, had results within typical average levels for Tauranga Harbour.

'This suggests initial impacts of the oil spill on shellfish were localised, affecting only heavily-oiled shoreline areas. Current contaminant levels and longer term oil spill impacts on shellfish can't be assessed until at least six weeks of sampling has been completed at the end of June,” says Adrian.