Why Pump Your Septic Tank?
Septic systems are simple units intended to treat domestic wastewater before it recharges groundwater.
2016 Fallby Joe Meek, Environmental Scientist, Montana Department of Environmental Quality and Adam Sigler, Extension Water Quality Specialist, Montana State University
“If it ain’t broke, I’m not gonna fix it.” These words of selfprofessed wisdom were uttered by a rural homeowner during one of our presentations about operating and maintaining septic systems, purposely loud enough for folks sitting around him to hear, which generated a nod of agreement from one and scowls of irritation from others. A lack of understanding of septic systems can lead to similar reactions from homeowners.
Septic system maintenance is not rocket science. The systems are simple mechanical and biological treatment units intended to treat domestic wastewater before it recharges groundwater. When properly maintained, systems work well for treating wastewater in areas with low density development. It is important that recharge from septic systems to the subsurface is as clean as the system can make it, since you and your neighbors may have a drinking water well which taps into that same groundwater.
A standard septic system typically consists of a septic tank and a drainfield. Septic system maintenance includes many operational factors, but this article will focus on pumping the tank.
The septic tank is a primary settling unit, similar to the early components in any large sewage treatment plant. Primary settling separates the floaters and sinkers from the wastewater stream to produce “effluent.” The latter receives additional treatment in the drainfield and then recharges groundwater.
Referring to floaters and sinkers in wastewater can cause the boys in a fourth grade class to break out in laughter, but in reality, the movement through the pipes to the septic tank tends to break it down so it doesn’t look exactly like what was flushed from the toilet bowl. Floaters are actually fats, oils, and grease that become a scum layer on the top of the septic tank contents. Sinkers are the heavier solids that fall to the bottom to become sludge. The clarified layer in the middle, with floaters and sinkers removed, is nutrient-rich effluent that is teeming with micro-organisms and is what moves into the drainfield for further treatment before recharging groundwater. Microbes work in the tank to break down the organic material in the solids that settle out, which helps reduce the volume of solids stored in the bottom of the tank. After time, however, material the microbes don’t break down starts to build up. This reduces the effective volume of the tank and results in more floaters and sinkers moving through the tank to the drainfield, and the movement of any solids into the drainfield is usually very harmful.
Septic tanks are designed to capture fats, oils, grease, and sludge specifically to keep these materials out of the drainfield since they will clog the drainfield and severely compromise final treatment. Often, a clogged drainfield may cause surfacing effluent in the yard or a backup of sewage into the house, which will be obvious to the homeowner and not much fun. If, however, the drainfield is situated in the coarse, rocky soils of many Montana valleys, it may not backup into the house or surface in the yard, but simply move into groundwater without being treated. That failure to treat may lead to groundwater contamination by pathogenic microorganisms, the same groundwater that is the source of drinking water for you or your neighbors.
Stories about septic system failure often include elements such as “…we had a whole house full of guests and then … the toilet started overflowing...” This can happen if a system is on the brink of failure and the increased wastewater load from more guests puts it over the top. This can be avoided by regularly scheduling maintenance rather than waiting for an emergency. Another common element is “…it happened in the middle of that crazy cold snap and it took us hours to find the access to the tank with the snow and the frozen ground…” or “…the pump truck struggled to get into position because the ground was so wet and soft…” These types of scenarios can be avoided by scheduling pumping during the summer or fall when the weather and wet conditions are not obstacles. It can also be very helpful to put a riser with a manhole on the portals to the tank so that they are accessible from the surface without digging. Regularly scheduled maintenance can help avoid emergencies and make sure a system is treating wastewater as well as possible. The recommended schedule for pumping depends on the size of the tank and the number of people using the system (Table 1).
The next time you hear someone say that they’ve never pumped their septic tank and aren’t about to start, think about the quality of the effluent his or her system is producing that is recharging groundwater, and thank your lucky stars if they are not your immediate neighbor on the upgradient side of your property. If they are that neighbor, talk with them and point them toward some educational information about septic systems.
For more information about septic systems, go to http://waterquality.montana.edu/well-ed/.