This report presents the results of an extensive evaluation of the hot-side electrostatic precipitator (ESP) on the San Juan power plant Unit 1, near Farmington, New Mexico. There is interest in the San Juan precipitator because it is one of the few hot-side precipitators in the US utility industry that is performing satisfactorily. The evaluation included particle removal efficiency measurements and an analysis of installation and operating costs. Particle mass and trace element concentrations as a function of particle size were measured at the inlet and outlet of the precipitator to determine the size dependent removal efficiency. Overall particle collection efficiency was 99.74 percent and emissions were 0.018 lb/10/sup 6/ Btu during normal full-load operation. Collection efficiency was lowest (99 percent) for particles in the size range of one micrometer diameter. The plume was visible during testing; the measured opacity varied from 2 to 6.5 percent (normalized to a 20 ft pathlength). Approximately 10 percent of the total particle emissions was caused by particle reentrainment during rapping. The capital cost for the precipitator installation was $54.38 per gross kW (1979 dollars). The operating and maintenance costs were 0.298 mills/kWh. The major precipitator operating problem was malfunctioning of the fly ashmore » removal system. Reliability (defined as 1 minus the fraction of power generation lost due to precipitator malfunction) was 99.6 percent. 25 references, 44 figures, 30 tables.« less