Basically, the Valero Refinery had a number of contractors, so it may have been shut down for some sort of work... It is near the Bonne Carre Spillway...
They're called "shutdowns" or "turnarounds". If the work was at an existing unit, and if it wasn't "new construction" (building a "new" unit), then this would be regular maintenance which is performed on a consistent basis.
Some units have annual turnarounds while others can go several years without needing to be shut down for maintenance or repair. It depends on the individual unit and what it does. Sometimes when something in a unit goes wrong you have emergency shutdowns and it's a scramble to get the unit serviced and back on line as quickly as possible.
Many times you'll find two units that perform the same function and the company will schedule even/odd year maintenance so that production isn't stopped during maintenance time. Alternately one unit may operate "full bore" full time all the time and the other may work at 1/2 rate or less all the time and only "full bore" during maintenance of the other unit. There's less wear on that unit and you go longer between maintenance on that one.
It varies from refinery to refinery and from company to company.