The USAF Occupational and Environmental Health Laboratory conducted an on site wastewater treatment plant evaluation survey at Otis Air National Guard Base from 16-21 Mar 84. The survey was requested because the base is negotiating a National Pollutant Discharge Elimination System (NPDES) permit with the State of Massachusetts, Division of Water Pollution Control. Data was needed to show the current operating efficiency of the plant. Specific concerns of the base were disinfection of the effluent and plant removal of nutrients such as nitrogen and phosphorus. Results of the survey indicate that the plant is able to meet current effluent limitation except for total coliform bacteria. However, future limitation which will include forms of nitrogen may not be met during the winter months when low temperatures adversely affects oxidation of nitrogen. Recommendations were made to: (1) provide a contact chlorination tank for adequate disinfection; and (2) consider methods to increase the organic content of wastewater reaching the trickling filter.