A UST must be permanently closed if:
- It has been temporarily closed for more than six months and does not meet Maryland performance standards for new or upgraded USTs; or
- It has been temporarily closed for more than 12 months and does meet Maryland standards for new or upgraded USTs.
At least 30 days prior to closing the UST, the owner/operator must notify the MDE in writing of the intent to close the UST, and confirm the planned closure with the MDE at least 48 hours in advance. The owner/operator must also initiate and complete a site assessment by measuring for a release where contamination is most likely to be present. If contaminated soils, contaminated groundwater, or free product as liquid or vapor is discovered during the site assessment, the owner/operator must immediately begin corrective action. When a tank has been permanently closed, it must be emptied, cleaned, and either removed from the ground or, with MDE approval, left in the ground and filled with an inert solid material.