* Sept synthetic trades at $2.20/bbl above WTI
* Sept WCS trades at $24/bbl below WTI
CALGARY, Alberta, Aug 28 (Reuters) - Canadian lightsynthetic crude prices edged lower on Wednesday after supply wasboosted by the completion of maintenance on a coker atSyncrude's oil sands project in northern Alberta.
Canadian Oil Sands, the largest shareholder inSyncrude, said on Tuesday the turnaround of coker 8-1, whichstarted in June and was originally expected to last 50 days, hadbeen finished and the unit was back in operation.
Light synthetic crude from the oil sands for Septemberdelivery was last trading at $2.20 per barrel above the WestTexas Intermediate benchmark, according to Shorcan Energybrokers.
That compares with a settlement price of $2.25 per barrelabove WTI on Tuesday.
Trading volumes were thin, however, as the Canadian crudemarket is currently outside the nearly three-week "window" - theperiod starting on the first of each month until pipelinenominations are due - in which the bulk of trading takes place.
Royal Dutch Shell Plc has started plannedmaintenance at its 100,000 barrel-per-day Scotford, Alberta,refinery, although the company said there was no material impacton production.
The refinery runs light synthetic crude that has been minedand upgraded at Shell's Athabasca oil sands project.
Western Canada Select heavy blend for September deliverylast traded at $24 per barrel below WTI, unchanged fromTuesday's settlement.