From “Army engineers clean up graffiti along L.A. River” — LATimes (Dec 28, 2009) by Andrew Blankstein:
…The whitewash is part of a program the Army Corps of Engineers began in September to cover or erase graffiti along 100 miles of the county’s sprawling flood-control system, which includes the downtown area as well as the San Fernando and San Gabriel valleys and the southern end of the county.
Using $837,000 in federal stimulus money, the corps awarded a one-year contract to San Fernando-based BJD Resourcing to remove the tags in rivers, channels and creeks. In some areas, crews have used high-pressure water to spray off the toxic paint used in tagging. Hazardous-material crews would dam and capture all the paint and water runoff to keep it out of the riverbed. For the most part, however, the work is being done using waterway-safe paint, said Sgt. Maj. Jeffrey E. Koontz of the corps.
Motorized paint sprayers, — using 63,000 gallons of paint in a typical day — are the tool of choice. In three months, the corps has covered about 13 square miles of walls, banks and bridge abutments, equivalent to painting the entire city of Downey.