WHAT IS THE RECOMMENDED SETBACK DISTANCE OF SEPTIC TANK SYSTEMS FROM DRINKING WATER WELLS?

Human contact with sewage is a serious public health risk. Drinking water contaminated with sewage can cause health problems such as diarrhea, nausea, cramps, dysentery and hepatitis. Exposure to sewer gases can also cause discomfort and illness. For at-risk areas, connecting to an adequate public sewer system is generally the best alternative for disposing of domestic sewage from private residences. Where access to a public sewer system is unfeasible or too expensive, proper sitting and design of an onsite sewage system is critical to avoid its premature failure.

A septic tank system consists of three major components: the septic tank, a distribution device and an absorption field.

A septic tank system consists of three major components: the septic tank, a distribution device and an absorption field. A septic tank is a large, watertight, corrosion-resistant, buried container that receives raw sewage from the plumbing drains of the home. In it, solids are separated out of the raw sewage and are partially digested by anaerobic (oxygen-lacking) bacteria. The septic tank must be large enough to allow retention of the raw sewage and some decomposition for at least 48 hours. Solids that are not digested either float to the top to form a scum layer or settle to the bottom of the tank as sludge. Depending on tank size and sewage volume, the sludge and scum must be pumped out at least every 2 to 5 years to allow bacterial digestion to continue in the tank.

Otherwise, raw sewage may flow directly through the tank and into the absorption field, causing its failure. After primary treatment in the septic tank, the liquid effluent flows through the distribution device, which ensures that equal quantities of effluent go to each pipe in the absorption field. The absorption field is a subsurface leaching area within the soil that receives the liquid effluent from the distribution device and distributes it over a specified area where it is allowed to seep into the soil. The filtering action of the soil, combined with further bacterial action, removes disease organisms and treats the harmful material in the effluent, completing the treatment process so that the water is recycled to the surface or groundwater source.

In many situations, an existing system that is failing may not be "repairable." Thus a completely new system may be needed. Misuse of individual sewage systems results not only in water quality problems and nuisance conditions, but also in costly repairs to rehabilitate a failing system. Failing systems include both those that you can see and smell and those that seep effluent, or waste liquids, into groundwater supplies before the soil can properly remove disease-causing pathogens.

When considering options for selecting the location for a new water well, contractors and property owners should also consider the likelihood of having to replace the on site waste disposal system in the future, and where that system would have to be located. This area should then be eliminated from consideration as a possible site for the well. Planning for the future in this way could prevent major headaches and expense down the road.

Setback standards for wells and septic tank systems vary widely from state to state, but most range from 50 to 100 feet. Setback distances may increase when special limiting factors exist, such as the presence of limestone, karst or fractured bedrock in the soil formation. Contact your local health department for the particular setback regulations in your community and your state.