A pungent odor at St. Croix’s Estate Richmond Power Plant that raised concerns among nearby residents Thursday was not propane gas but mercaptan, according to the V.I. Water and Power Authority.
Mercaptan is a harmless pungent-smelling gas, which has been described as having the stench of rotting cabbages or smelly socks. It is a substance used to odorize gaseous substances that are odorless and colorless (such as propane and natural gas), for easier detection.
Merlin Figueria, terminal manager for Island Project and Operating Services, an affiliate of VITOL that operates the propane storage facility, said in a statement from WAPA: “The displaced mercaptan vapors originated from the transfer of mercaptan from a mercaptan shipping tote into a smaller storage vessel in the mercaptan metering system at the LPG storage site.” He said the mercaptan metering system is designed with a carbon adsorption container, specifically designed to adsorb any mercaptan vapors displaced from the mercaptan metering system storage vessel before being released into the atmosphere. But the threshold for smelling mercaptan is extremely low and even a tiny amount is very smelly.
“We had already completed the transfer when the odor complaint came in and we will not do any more transfers or movement of the Mercaptan until we assess the situation and determine any improvements we can make to prevent a reoccurrence of this situation," Figueria said.
WAPA’s acting chief executive officer said WAPA wants to “ensure the public that there was no propane gas release or spilling of mercaptan.” Gregory Rhymer said, “What occurred was the escaping of mercaptan vapors in the transfer process.”
