Chapter 12: Your Septic System

This section contributed by Tim Roark, Gallatin County Department of Environmental Health.

Septic systems are designed to break down and neutralize contaminants before they enter groundwater or surface water systems. A properly designed, installed and maintained system is an essential link in maintaining water quality in the Gallatin Watershed.

How Your System Works

The typical septic system consists of:

1. septic tank, which separates, stores and begins to treat solid wastes
2. distribution system, which is generally a series of perforated drainpipes
3. drain field, or soil absorption system

The soil absorption system receives effluent from the septic tank and filters and treats it by natural biochemical means before it enters the groundwater.

Siting Septic Systems/Permitting

Because of its dependence on natural filtering and treatment, soil is the most important part of a septic system. Chemical processes and naturally occurring microbes in soil break down contaminants, while pathogens eventually perish in the inhospitable environment. If soils are too wet (hydric soils), oxygen is not available for organisms that break down waste. Gravelly soils allow water to pass through to surface or groundwater too quickly, before breakdown of contaminants is complete. Clay soils may impede the rate at which water is filtered. In combination with household chemicals like water softeners, these soils can cause a system to fail. The Gallatin Watershed has many areas of both hydric and gravelly soils, meaning that septic system design is not a “one size fits all’ proposition. The design of a system is based on soil and site characteristics, including depth to groundwater. Depending on where you live, soil and site characteristics may determine that a more sophisticated septic system is required. The design and sizing of any septic system in Gallatin County requires approval of the County Sanitarian. All septic systems are inspected to insure that they are properly installed. State and county regulations require that all soil absorption systems be located at least 100 feet from the 100-year flood plain and 100 feet from any surface water, as well as being located at least 100 feet from any existing well or spring.

Typical Absorption Field

Signs your septic system may be failing:

• Sewerage backup in drains or toilets
• Sluggish drains
• Mushy ground or greener grass around septic system
• Outdoor odors
• Nitrates or bacteria in your drinking water
• Algae blooms in ponds adjacent to your home

Common Causes of Septic System Failure

While many things can interfere with the operation of your septic system, by far the most important step you can take to prevent problems is to properly maintain your system. Your system requires two things to operate efficiently:

Proper bacterial action - the system is designed to accept normal household waste that contains the organisms necessary to promote digestion. Bacteria-killing products, like paint thinner, chemical drain cleaners, some water softening salts, paints, oils, acids and pesticides will destroy or inhibit the ability of your septic system to break down household waste.

Periodic pumping - sludge is the accumulation of solid material that cannot be further broken down by bacterial action and must be periodically pumped out. Failure to pump the system allows solids to overflow into the distribution system thereby clogging the drainfield. This not only can force a costly replacement of the system but may also result in sewage surfacing on the ground. While the frequency of pumping depends on the use of the system, the frequency of garbage disposal use, and the number of people using the system, generally a standard tank of 1,000 gallon capacity used by a family of four people should be pumped about every three years. Additives should not be added to your system to dissolve sludge. Several commercial septic pumping businesses operate in Gallatin County.

Septic system failure can also result from:

• Overloading. Avoid putting too much water into the system at one time; wash clothes at off-peak times, for example, rather than when the shower or sinks are being used.
• Pouring decay-resistant materials into the system. Grease, sanitary napkins and other solids will fill the tank faster than expected.
• Tree roots. Roots can clog or destroy the absorption system.
• Compacting soil over the drainfield. Driving vehicles over the drainfield should be avoided.
• Age of the system. Septic systems are designed for an operational life of 20 to 30 years. If you have an aging system, it may be time to inspect and replace your system.

Knowing When to Pump Your Tank

If you are unsure whether you need to pump, locate your access or inspection ports and determine the following:

• Scum is less than 3 inches from the bottom of the baffle or top of outlet tee.
• Sludge is less than 12 inches from the bottom of the outlet tee.
• If the sludge and scum together take up more than half of the tank.

Source: NRCS
Colored areas show general soil types in the valley that may have some limitations for septic due to higher water. The county sanitarian determines the appropriate system for your soil type after more detailed site analysis.

Information

MSU Extension Service - septic system guides; Montguides 9401, 9403
(406) 994-3451

MDEQ - design standards for septic systems, circular WQB
(406) 444-4969

Resources

NRCS - soil maps
(406) 587-6988

Permitting

Gallatin City - County Department of Health -septic permits
(406) 582-3120

MDEQ
(406) 444-4969

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