The US Coast Guard issues a policy letter describing procedures for obtaining an Alternative Management System (AMS) determination of a foreign type-approved ballast water management system (BWMS).
Foreign approved systems in accordance with applicable IMO standards must be as effective as traditional ballast water exchange for the prevention of introductions of aquatic nuisance species, says the Coast Guard. Foreign manufacturers of type-approved BWMS can request a Coast Guard determination that the BWMS is an AMS for purposes of the federal regulation. Applicants are also required to apply for USCG type-approval. Use of an AMS will be allowed for up to five years after the vessel is required to comply with the federal ballast water discharge standards.
Click on CG-OES Policy Letter 12-01 (6/15/12) for full details: http://www.uscg.mil/hq/cg5/cg522/cg5224/docs/AMSPolicyLetter12-01.pdf