On November 19, 2010, during mixing of activated sodium persulfate (ASP) solution for pilot testing of in-situ chemical oxidation (ISCO) injection, approximately 2-3 gallons of ASP was released from the equipment.
The release occurred while mixing the ASP solution by means of circulating the contents of two 500-gallon trailer mounted tanks placed next to each other on a closed-circuit/low pressure mixing and injection trailer equipped with built-in secondary containment. The ASP solution consisted of 20 percent (by weight) powder sodium persulfate mixed with water and activated by liquid sodium hydroxide. The breach in the system occurred while the two tanks were circulating under high flow/low pressure. The connection between the transfer hose and the elbow fitting connecting to the top of Tank #2 came loose and the solution was released. The emergency shutoff switch was quickly triggered by the authorized personnel overseeing the operations and the discharge was stopped. The operators in close proximity of the mixing tanks were wearing the required personal protective equipment (PPE) yet were not exposed to the solution. The majority of the solution lost (approximately 6-8 gallons) drained into the built-in secondary containment pan of the trailer. A portion of the solution (approximately 2-3 gallons) was released beyond the boundary of the secondary containment and onto the surface of the site. The released ASP solution was immediately contained and isolated using litter, then slightly diluted with water, and collected with a 3-gallon portable shop-vac. None of the site workers were exposed or injured during this event.
The lesson learnedhere surrounds equipment inspections prior to operation. The hose disconnected from the fitting most likely due to the hose clamp not being fully tightened. The system was low pressure (but high volume). Simply because the system was low pressure doesn’t necessarily mean that the fittings “don’t not be fully tight”. The mass of the solution and the force imposed by the movement of high volumes (mass) adds stress to fittings and will additively increase the stress on joints and fittings; therefore, everything should be tightened to the appropriate manufactures specifications. Remember, the failure of a system occurs at the weakest link of a chain.
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