In 2002, the City and County of San Francisco began a Dental Mercury Reduction Program (DMRP).  The impetus for the program was that San Francisco's Southeast Water Pollution Control Plant was issued a revised NPDES discharge permit with new lower limits for mercury.  In the 2002 revision of this permit, the allowable effluent discharge level for mercury was reduced from 210 n/l to 87 n/l.  The permit also required that the City implement a mercury source reduction program.  All sources of mercury were targeted for reduction, including dental amalgam that can contain 40% to 50% mercury.