Four miles is a pretty big oil spill. There were always many uncertainties on how solidly was the Macondo well sealed and it may well be the case that it was wrong sealed in fact.
Today it has been reported in several media that a four mile sheen was spotted on September 17th and that US coastguard (NOAA) is investigating.
The relevant NOAA report #8510 is available (after some reports of not being able to access it). It reads:
Mystery Sheen in Lease Block MC-252, September 2012Gulf of Mexico off LA. 2012-Sep-17This hotline is being started for new reports of sheen of unknown origin in and near lease block Mississippi Canyon 252. This incident is likely related to reports in August 2011 (See incident #8345, Aug2011). Although the source of these sheens may be the wrecked BP Macondo Well, this relationship has not been established at this time. Activities include daily overflights sponsored by BP, with USCG or NOAA observers on board intermitently. BP is sending a vessel to the area with an ROV to investigate the potential source.Note: Documents are posted chronologically and early reports likely contain factual errors. These errors may be corrected in a later report.
Spill, potential spill, or other: Oil SpillCause of incident: Mystery SpillProducts of concern: Crude Oil Likely (sheen)Latitude (approximate): 28° 44.50' NorthLongitude (approximate): 88° 22.50' WestNOAA’s Office of Response and Restoration (OR&R) provides science-based solutions to protect and restore the nation’s natural resources from coastal environmental hazards. OR&R serves the nation by providing expertise and a suite of products and services critical for making science-based response decisions that prevent further harm, restore natural resources, and promote effective planning for future incidents.
Sources: EneNews, CNN, Daily Kos, the Examiner, NOLA.