Septic System 101: Operation and Maintenence

Septic systems

Ravalli County has more than 13,000 septic systems in its 2,814 square-mile watershed, and about 3,000 of these systems have been installed since 2000.  Since then, county and state regulations have required new systems to have safety features like above-ground access points for pumping, easy-to-clean effluent filters, and drain fields appropriate to the soil type and ground water level. These regulations not only ensure that systems will work well now, but also make it more likely that they will function properly well into the future.

Since permitting for waste water treatment systems didn’t begin in the county until 1972, many substandard and inadequate septic systems exist within the valley which pose serious threats to drinking water. Local septic pumpers all have stories of such non-functioning septic systems, including tanks made out of wood, car bodies, and 55-gallon drums, some of which drain right into the ground.  Such systems allow nutrient- and bacteria-rich effluent to leach directly into ground water.

Any septic system installed prior to 1972 is grandfathered in, so if it fails, the property owner is guaranteed a replacement.  The new system, however, must be permitted through current Ravalli County Subsurface Wastewater Treatment and Disposal Regulations. Any system that was installed with a valid permit in or after 1972 may also be replaced according to current regulations.

But any post-1972 system that doesn’t have a permit is considered illegal and may have to be abandoned if it cannot be brought into compliance with current standards.

Septic tanks

            A septic system, or on-site wastewater treatment system, includes an underground septic tank and a drain field. Septic tanks installed in Montana must be made of non-corrosive materials, and in Ravalli County almost all new tanks are concrete.         

The size of a septic tank must be at least 1,000 gallons and is determined by the number of bedrooms in the home it serves. Tanks are either one or two compartments and must be water tight.

Raw waste from bathrooms, kitchens and laundry rooms flows into the septic tank where the solids separate from the liquid. Light solids, such as soap suds and fat, float to the top and form a scum layer.  The scum layer remains on top and gradually thickens until the tank is pumped. The liquid waste goes into the drain field, while the heavier solids settle to the bottom of the tank where they are gradually decomposed by bacteria. Some non-decomposed solids remain in the tank forming a sludge layer that eventually must be pumped out.

Two-compartment tanks do a better job of settling solids and are required under certain circumstances. A tee, or baffle, at the tank’s inlet pipe slows the incoming waste and reduces disturbance of the settled sludge. A tee or baffle at the outlet keeps the solids and scum in the tank. Modern tanks have removable effluent filters in the outlet tees for extra protection in keeping solids out of the drain field.

Drain fields

            Further treatment of wastewater occurs in the soil beneath the drain field. The drain field consists of long, underground perforated pipes or infiltrator chambers connected to the septic tank via a distribution box. The network of pipes is usually laid in parallel trenches two feet wide and no deeper than 36 inches. Liquid waste, or effluent, flows out of the tank and is evenly distributed into the soil through the pipes. The soil below the drain field provides the final treatment and disposal of septic tank effluent. After the effluent has passed into the soil, most of it percolates downward and outward, eventually entering the ground water. A small portion is taken up by plants though their roots, and some evaporates through the soil.

            Soil filters effluent as it passes through the pore spaces. Chemical and biological processes treat the effluent before it reaches the ground water or a restrictive layer, such as hardpan, bedrock or clay. Such processes work best when the soil is somewhat dry and permeable and contains plenty of oxygen for several feet below the drain field. The size and type of drain field depends on the estimated daily wastewater flow and soil conditions.

Tips for using your septic system

            Even a properly designed and installed septic system cannot treat waste water if the tank is not used and maintained properly.  Here are a few tips for installing and using your septic system:

• Make an accurate diagram showing the location of your tank and drain field so damaging activities and tree planting can be avoided in the drainfield area.
• Keep a record of pumping, inspection and other maintenance, including the date and contact information of installers and pumpers.
• To simplify tank access for inspection and maintenance, install a watertight concrete riser over the septic tank.
• Leave the area above the drain field undisturbed, with only a grass cover. Roots from nearby trees or shrubs may clog and damage your drain lines.
• Keep automobiles and heavy equipment off the drain field.
• Do not plan any building additions, pools, driveways or other construction work near the septic tank, drain field or replacement drain field area.
• Do not put too much water into the septic tank. (See below)
• Do not flush non-biodegradable materials such as plastics, disposable diapers, sanitary napkins and applicators – they will rapidly fill up the tank and clog the system.
• Restrict the use of your kitchen garbage disposal – it increases the amount of solids in the tank, making them slower to decompose.
• Do not pour grease or cooking oils down the sink drain because they can solidify and clog the soil absorption field.
• Don’t allow paints, motor oil, pesticides, fertilizers or disinfectants to get into your septic system. They can pass directly through the system and contaminate ground water. These chemicals can also kill the microorganisms which decompose wastes and can damage the soil in the drain field.
• Do not use caustic drain openers for a clogged drain.  Instead, use boiling water or a drain snake on clogs.  Clean your toilet, sinks, shower and tubs with a mild detergent, borax or baking soda rather than the stronger and potentially system-damaging commercial bathroom cleansers.
• Finally, have your septic tank pumped regularly – every three to five years is a good general recommendation.

Water overload occurs when the drain field is flooded with more water than it can effectively absorb, reducing the system’s ability to drain wastes and filter sewage before it reaches the ground water. It also increases the risk that effluent will pool on the ground surface and run off into surface water or down nearby water well casings.

Typical indoor water use is about 50 gallons per day for each person in the family. Water-saving devices such as low-flow shower heads, faucet aerators, toilet dams or low-flow toilets can greatly reduce water flow into the system. Strategies such as taking short showers, spreading out laundry loads over the week and never allowing rainwater from downspouts to enter the system will also help.

Most of the information in this article came from the Montana State University Extension Service publication “Septic Tank and Drainfield Operation and Maintenance.”  Next week we will discuss septic tank inspection, evaluation and trouble-shooting.

Septic tank inspection, evaluation and trouble-shooting

Last week we discussed how septic systems work and gave tips on their operation and maintenance. This week, with the help of a Montana State University Extension Service Fact Sheet by Michael Vogel, we will discuss septic tank inspection and trouble-shooting.

We recommend conducting a septic system evaluation whenever a property is placed on the market and certainly before a sale is completed. Such an evaluation protects both the buyer and seller, and most importantly, ensures that the wastewater treatment system is functioning properly and will continue to do so. It also protects the buyer from potentially high costs of system repair or replacement soon after the sale.

For the seller and Realtor, a septic system evaluation will minimize the possibility of unknowingly selling a house with a defective or failing system, and could help avoid possible lawsuits that might arise as a result. Likewise, a properly functioning septic system can also be a good selling point and enhance the value of a property.

What’s involved in a septic evaluation?

            At a minimum, an evaluation should examine the following things:

• The location, age, size and original design of the septic system.
• The soil conditions, drainage, seasonal water table and flooding possibilities on the site where the septic system is located.
• The history of the system if records are available, including the date the system was last pumped.
• The condition of the plumbing fixtures and their layout to determine whether structural changes have been made to the plumbing that would increase the flow to the septic system above its capacity. Added components that could affect the system, for example, are water softeners, extra sinks, bathrooms or wash machine lines. Slow-flushing toilets and slow drains may indicate a failing system.
• The sludge level in the tank if it has not been recently pumped.
• The condition of the drain field.  Look for evidence of liquid waste reaching the soil surface, draining toward nearby surface water, or clogging the soil beneath the field. (This usually requires digging up a small portion of the field.)

What is meant by septic system failure?

A septic system should effectively accept liquid wastes from your house and prevent biological and nutrient contaminants from getting into nearby wells or surface waters. Anytime these things do not happen, the system is failing.

By far, the most common reason for early failure is improper maintenance by homeowners and renters. When a system is poorly maintained and not pumped out on a regular basis, sludge builds up inside the tank and flows into the drain field, clogging it beyond repair.

Clogged or failed drain fields must be replaced, which can be very costly. 

One sure way for a drain field to fail is having solids pass through the tank. Modern systems are required to have inlet tees to direct the solids downward and removable effluent filters to prevent solids from passing into the drain field. These amenities, along with regular pumping of the tank, can ensure a properly functioning drain field for many decades.

How to know when to pump the tank?

The frequency with which a homeowner needs to pump a tank depends on several variables:  (1) The size of the tank, (2) the number of people in the household contributing to the volume of waste water, (3) the volume of solids in the waste water, and (4) the use of a garbage disposal. (The use of a kitchen garbage disposal can increase the amount of solids in a septic tank by as much as 50 percent.)  If you are unsure about when to have the tank pumped, you can measure the level of solids on a yearly basis.

The primary maintenance point in a septic system is the septic tank, and inspection is accomplished by measuring the scum depth and sludge depth in the tank each year. The tank should be pumped if the sludge depth layer has built up to within 18 inches of the tank outlet or if the scum layer thickens to within three inches of the bottom of the outlet baffle or sanitary tee.

Measuring the scum and sludge depths in a septic tank can be done by a homeowner, but the task is not pleasant. The best solution for most people is to have the tank pumped by a certified contractor on a routine basis. In addition to removing the solids from your tank, a reputable septic pumper can also help determine whether the system is functioning properly and the frequency with which the tank should be pumped.

Are septic additives necessary?

            Many commercial additives are currently on the market which claim to accelerate the digestion of solids, break up scum, and generally lengthen the time between pumping. In general, such additives fall in two categories: (1) chemical, including inorganic and organic compounds, and (2) biological, including yeast, bacteria and enzymes.

            Chemical additives, such as caustic hydroxides and sulfuric acid, should never be added to a septic system. Such products will destroy the bacterial population in the septic tank, change the permeability characteristics of the soil absorption area and may cause groundwater contamination.

            Many biological additives are touted to restore the bacterial balance in a septic tank on a monthly basis as part of a routine maintenance program. This is not necessary because these bacteria already reside in human feces.

            There are special instances when the use of a biological additive may be warranted, such as when occupants of a home take antibiotics and other prescription medications. However, it should be noted that research is still needed in this area.

            Claims made on the effectiveness of additives to either eliminate pumping of a septic tank or restore the permeability of the soil absorption system are unsubstantiated. No product will allow a homeowner to escape a regular septic tank pumping and maintenance schedule.

            In general, the Ravalli County Environmental Health Department does not recommend the use of septic system additives. We do recommend evaluating and familiarizing yourself with your septic system and getting your tanks pumped and maintained regularly.

In order to help citizens understand more clearly many of the environmental health issues in Ravalli County and the role of the Environmental Health Department in addressing these issues, our department will run a series of weekly  articles titled “Environmental Health Talk.” 

In this ongoing series we hope to help raise the community’s awareness of issues such as air and water quality and give readers useful tips on topics like recycling, collecting and disposing of hazardous materials and maintaining septic systems, just to name a few.  To this end, we welcome pubic comment.  If there’s an environmental health issue you’d like us to address, write call or email the department: RCEH, c/o “EnviroHealth Talk,” 215 South 4^th St, Suite D, Hamilton  MT  59840. Phone: 375-6571. Email: rdaniel@ravallicounty.mt.gov

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