Unexpected contamination can make this prerequisite expensive. For example, a Phase I ESA in Colorado can cost $1,000–$3,000, while a Phase II ESA in the same state can cost $10,000 and up. If the Phase II ESA finds that your site is contaminated, you are required to remediate the site to local, state or federal standards, whichever is most stringent. Though dependent on the extent and type of contamination, remediation has the potential to be very costly and time-consuming.