At approximately 0830 hrs. on 07/08/09, OSC Ullock rec'd NRC Report #910930, and a call from MS DEQ informing him of a 4800 gallon release of 15% Sodium Hypochlorite (RQ 10# @ 15%) at the Mississippi Power Daniel Plant located in Moss Point, MS. OSC Ullock in coordination with the R4 TEL, deployed to the scene to assist MS DEQ with clean up oversight, documentation and additional EPCRA compliance requirements. This is the second significant Sodium Hypochlorite spill from this AST within a year. This spill was caused by a combination of human error and faulty hardware associated with the 5000 gallon AST sight glass. The hose clamp attaching the sight glass tube to the AST bottom nipple became corroded and failed, causing the subsequent release of concentrated bleach to escape into the unsecured, secondary containment. The secondary containment drain valve had been inadvertently left opened by the facility chemist during routine rounds conducted during the previous 24hrs. The concentrated bleach travelled in a wide swath, overland-West, approximately 600' into a stromwater drain located upon Mississippi Power property. Clean crews hired by MS Power were directed by MS DEQ and EPA on where to focus clean up operations which include the use of a vac truck and the manual application of pelletized citric acid to lower pH in impacted soil. Response complete.