saving 650 gallons of water by not eating a quarter-pound hamburger. Lot Evaluation How much land is necessary in order to accommodate a house and a properly functioning septic system? This is not only a ques- tion for public officials and land use planners, it's a question for the rural homeowner and prospective rural homeowner. The answer, despite many local and state positions, is not, "Enough land to contain a normal-size house with garage and a standard drain field plus replacement, and to provide for all property line setback requirements." If this were true, one-eighth acre would be sufficient. It is now apparent that, in general, the potential for ground water contamination by nitrogen is the critical limiting factor. Nitrogen, in the form of nitrate, is not filtered out by the soil and can travel great distances through the soil to contaminate ground water. The maxi- mum safe level for nitrate-nitrogen in drinking water is 10 mg/L. Septic tanks can discharge concentrations 10 times that. Nitrate con- tamination problems caused by septic tanks are not common in isolated and sparsely settled areas, but are increasingly common in densely settled areas such as subdivisions and mobile home parks. It may take several years to several decades for nitrate concentra- tions to reach unhealthy levels, but once they do, it is very unlikely that the contamination will be cleaned up. Two popular solutions to this problem are to extend public water supplies and drill deeper wells-and continue to pollute the ground water for users downstream. The answer to the original question of how much land is needed is, unfortunately, "it depends." Bacteria and viruses can migrate many hundreds of feet in the ground water from below a drain field to a water supply well. Nitrates can flow virtually anywhere. There is no absolutely safe and practical setback distance or lot size. The best you can do is be aware of the factors contributing to problems and consider them when looking for a suitable homesite. 236 ONSITE WASTEWATER DISPOS