There may be coverage here, depending on certain things.

First, the insured has to be liable for the leak so that he legally has to pay for the clean up. We cannot answer questions about legal liability so you may want to check with an attorney in your area to see if the insured is liable for the clean up based on the circumstances of his using a nonowned trailer and possible poor maintenance by the trailer owner.

Second, the BAP will pay for clean up expenses under the covered pollution cost or expense insuring agreement only if there is bodily injury or property damage caused by the same accident. So, presuming that there is no bodily injury due to this pollution spill, there has to be some property damage here and not just a clean up charge.

Third, if the insured is legally liable for the spill and there is some property damage, the wording on the broadened pollution liability endorsement has to be reviewed. There is a standard broadened pollution liability endorsement from the Insurance Services Office (ISO) that applies to the garage form which may be of some help to you for comparison purposes. That endorsement changes the pollution exclusion on the liability coverage form so that paragraph a. of the exclusion, pertaining to a leak of pollutants contained in any property in the course of transit by the insured, applies only to liability assumed under a contract or agreement. The way you describe the incident, the trailer was still in the course of transit since it was not yet returned to the owner at the time of the leak. So, paragraph a. of the pollution exclusion would not apply to a claim for bodily injury or property damage in this instance if your endorsement is worded the same as the ISO endorsement.

The ISO endorsement also revises the definition of covered pollution cost or expense to include the type of claim that you describe, that is, a leak of pollutants from property in the course of transit by the insured.

The bottom line is that the insured can have coverage for this claim, but he has to be liable for the spill, there has to be some property damage involved and not just clean up expenses, and the wording of your broadened pollution liability endorsement has to be similar to the standard ISO endorsement.