Our study reveals that many facilities established written rules guiding routine CEMS operation and maintenance, a notable improvement from 1999 when very few power plants had any written rules (Zhu et al., 2000). But the comprehensiveness of the rules varies significantly. For example, one facility had only two pages of rules: (1) ‘‘Key Elements of CEMS Operational Quality Control Rules’’ (one page); (2) ‘‘CEMS Operational Safety Rules’’ (one page). Another facility developed a relatively comprehensive set of rules, including: (1) Monthly Report of CEMS Operations Quality; (2) CEMS Quality Control Records; (3) CEMS Operation Records; (4) CEMS Operation Daily Report; (5) CEMS Maintenance and Management Rules (established by the facility’s parent company); (6) Methods for Handling Abnormal CEMS Data; (7) Daily CEMS Operating and Management Requirements (established by the CEMS’s third-party operator). There did not appear to be any guidance or standards for the written rules that guide CEMS operators in operating and maintaining the CEMS.