For insurance contracts, the limitation period begins when when the material facts on which [the claim] is based have been discovered or ought to have been discovered by the Plaintiffs by the exercise of reasonable diligence. The Plaintiffs in this case were seeking indemnification for a major remediation project resulting from contaminated soil. The material facts are that they had a major environmental catastrophe on their hands, and this was not known until the 1998 investigation despite a persistent oil-smell in their basement dating from the mid-1980's. On the evidence, the Plaintiffs were reasonably diligent in handling this problem and therefore their claim was timely and not barred by contract or statute. Based on principles of interpretation involving insurance contracts, the plaintiffs were covered despite ambiguity in the contract.