Environmental assessment - Phase 1 and 2

Does anyone have experience with environmental assessments? I'd like to talk to someone who has ideally conducted assessments. I am in DD on a company (asset sale, not real estate included) where environmental leaks can be a problem. Ideally, buyer is responsible for any leaks pre-close and seller is responsible for any leaks post-close. But, determining when leak occurred can be difficult. A Phase 2 environmental assessment could set a baseline, but it is cost prohibitive. So, I would like to talk with someone who has experience to understand if it is possible to identify rough timeline of leak if an assessment is required down the line. Thanks.