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Dry cleaning facilities that use perchloroethylene as a cleaning solvent are called perc dry cleaners.  Perchloroethylene is a known human carcinogen and perc dry cleaners are subject to SCAQMD Rule 1421 – Control of Perchloroethylene Emissions from Dry Cleaning Systems (PDF, 52kb).  An industry-wide risk assessment was performed for the perc dry cleaners.  Perchloroethylene usage limits to ensure cancer risks less than 25 in a million were established using emission estimates, dispersion modeling, and risk assessment procedures approved by the Governing Board in 2007.  The procedures are briefly described next, but a more detailed discussion of the methods and results is available in the Health Risk Assessment for Perc Dry Cleaners (PDF, 989kb).

The three key variables necessary to estimate cancer risks from perc dry cleaners are: 

• Perchloroethylene usage, usually expressed as gallons per month or gallons per year; 

• Distance to the nearest residential and commercial receptor, which are always assumed to be directly downwind of the facility; and 

• Location of the perc dry cleaner, which is necessary for determining the appropriate meteorological site. 

For facilities without reported receptor distances, staff calculated the distance from the facility to the nearest census block centroids which were obtained from a database developed for CARB’s Hot Spots Analysis and Reporting Program (HARP) modeling system.  According to Rule 1421 the use of perchloroethylene as a cleaning solvent will be discontinued by December 31, 2020.  Effects of the future phase out of perchloroethylene are evident in the decreasing number of permitted perc dry cleaners as shown in Figure 1 and trends of ambient perchloroethylene concentrations in the South Coast Air Basin illustrated in Figure 2.

Figure 1.  Recent Trends in Perc Dry Cleaning Facilities

Figure 2.  Recent Trends in Ambient Perchloroethylene Concentrations