A septic tank is an underground box constructed of reinforced concrete or plastic. It must be installed at least ten feet from a building foundation, so repairs or pumping do not weaken the building. Since the tank holds wastewater, it must be installed at least fifty feet from a residential or private drinking water well (wells serving several buildings or more than 25 people requuire larger isolation distances).

Most solids fallout of the wastewater and remain in the septic tank. Bacteria breaks them down into sludge but never eliminates them completely; periodic cleaning is needed. A small amount of sludge is stirred up from the bottom by incoming wastewater; it then moves into the disposal field. This happens even with the best maintenance program. Over time, the sludge clogs the soil in the field and reduces its ability to absorb water. If the field is undersized or already overloaded with water, even a small amount of sludge will have a great effect. All systems eventually fail.

• Diagram of a Septic Tank

This reduces the sludge available to move into the field. Regard it as an investment, like paying a utility bill. It is best to pump every 1-3 years. Pumping reduces the sludge and the potential for problems.The frequency of pumping depends on the amount of sewage produced. In cases where the disposal field has a limited capacity (high groundwater, poorly drained soils, small absorption area) or where more wastewater is produced (large families, homes with garbage disposals/grinders), it is critical to pump more often. Ask a licensed septic tank pumper to evaluate your septic system and recommend a pumping schedule. Do not, under any circumstances, attempt to empty or repair the tank yourself. Dangerous gases are one result of the septic process, gases which can kill.

• Septic Tanks 101