 with methemoglobine- mia (blue baby syndrome), a condition that affects infants, and with stomach cancer. The quality of effluent from the aerobic treatment unit appears to be significantly better than that of the septic tank, but there are several other factors to consider when choosing which to use. The REGULATIONS AND PROCESSES Figure 2.2 Typical aerobic treatment unit. aerobic units are considerably more expensive. They require more maintenance. They require electricity to operate. They malfunction occasionally and at those times, produce very poor quality effluent. The higher quality effluent is necessary if you have a site where effluent must be discharged to a watercourse (to do this a federal permit is required). Also, aerobic effluent is preferred where the effluent is to be reused, because it is less likely to cause odor prob- lems. For example, aerobic treatment before discharge to an above- ground sand filter or to the land surface can reduce or eliminate potential complaints from the neighbors. Most state and local governments do not allow credit for aerobic units in terms of reductions in disposal field size or in clearance to the ground water table. If credit is allowed, and if you need that credit, it may be cheaper to use an aerobic unit than to choose an expensive alternative to the standard drain field. THE DISPOSAL PROCESS Unlike municipal sewage treatment systems, problems which develop with an individual onsite system are the immediate prob- ONSITE WASTEWATER DISPOSAL lem of the homeowner. Also, unlike municipal systems, individual systems are designed to function with minimal maintenance for many years. The time during which half of the installed septic sys- tems have failed in particular areas of the country varies from around 25 years to over 60 years. Many disposal systems fail within three years as a result of improper design or installation. If the system works properly for more than three years, subsequent failure is more likely to be due to improper use or lack of maintenance. A pro