Nearly 700,000 Virginians depend on septic tanks and other wastewater treatment systems for treatment of household wastes. The Joint Subcommittee Report HJR 7 1987 reported that sixty percent of Virginia's residential septic “systems and drainfields are operating improperly. With the demand for rural and suburban development increasing, a viable alternative to septic systems and drainfields is needed. One proposed alternative is single family package treatment systems. One vital concern is that a majority of these systems discharge directly into surface waters. Thus, the objective of this study was to evaluate the performance of aerated package treatment systems (APTS). Five APTS located in southwest Virginia were chosen. Each site was visited three times during 1990 and 1991, and various parameters were monitored from the primary settling chamber, aeration chamber, and effluent. Systems were sampled in the morning, afternoon, and night. Also, two dye studies were conducted to evaluate hydraulic displacement. The results indicated that overall field performance was poor due to unreliable maintenance by homeowners, an ineffective chlorinator/dechlorinator system, inadequate biological treatment, and mechanical malfunctions. Eighty-one percent and 62% of the effluent samples were found to have five day Biochemical Oxygen Demand (BOD,) and total suspended solid (SS) concentrations exceeding 30 mg/L, respectively. Effluent dissolved oxygen values were less than 5 mg/L, the state's standard for small package treatment systems. Sixty-four percent of the effluent samples were found to contain more than 200 fecal coliforms/100 mL. In five instances where disinfection was evident, chlorine residuals were detected in the effluent, which also violates state standards. / Master of Science