Septic Systems

When your property uses a septic system for wastewater disposal, you become your own sanitary utility. You own and operate the facilities, maintain them, and must replace them when necessary. Your wastewater disposal system is the septic system buried under your yard. The septic system treats wastewater that flows from your home or business and disperses partially treated effluent for final treatment as it percolates through the soil. The ability of a septic system to adequately and safely treat and dispose of sewage depends on the soil and rock conditions under your property and on how well you maintain and operate the systems.

Area Requirements for Septic Systems

Septic System with Septic Tank and Drainfields
Source: Thomas H. Miller (MCES)

Under current standards, a septic system for a new building lot must have an initial drainfield and enough area for three reserve or back-up drainfields. These back-up fields are built and put into service only as the drainfield currently in use fails. A typical single-family house needs an area of at least 10,000 square feet (slightly less than one-quarter acre) for the initial and reserve drainfields.

Properties in the Patuxent River watershed, with water supply reservoirs for the Washington Suburban Sanitary Commission, must reserve an additional 70 percent of treatment area. That means a single-family house that needs to reserve 10,000 square feet elsewhere in the County would need to set aside 17,000 square feet (slightly less than two-fifths acre) in the Patuxent River watershed.

Septic systems may not be located closer than 100 feet to any existing or proposed well. In addition, County onsite systems regulations establish other septic system setbacks for site features like steep slopes, stream buffers, and buildings.

Septic Systems

Two-Cell Septic Tank Cross-Section
Source: Thomas H. Miller (MCES)

A modern septic system includes two main parts. Wastewater from a building first enters the septic tank that separates wastewater solids and liquids. The liquid or effluent from the septic tank flows into the drainfield that discharges the effluent into the ground where aerobic bacteria in the soil provide further treatment. A contractor needs to pump wastewater solids out of the tank usually once every two to five years.

Septic Tank

A septic system typically includes a septic tank connected directly to your building. Current regulations require two-chamber septic tanks that hold up to twice the daily maximum expected flow from the user. The tank design allows sewage solids to separate from liquids and settle to the bottom of the tank. Every two to five years, a contractor needs to remove the solids from the tank, a process referred to as “pumping the tank”.

Until late 2016, the State had required all new and replacement septic tanks to utilize Best Available Technology (BAT) to promote better removal of nitrogen from wastewater. Reducing nitrogen from wastewater benefits environmental restoration efforts for the Chesapeake Bay and its tributaries. This requirement subsequently was removed from areas of the state located outside of Chesapeake Bay and Atlantic coast critical areas. Montgomery County does not include any state-designated critical areas. Local permitting authorities such as the County’s Department of Permitting Services (DPS) retain the discretion to require BAT septic systems on a case-by-case basis.

Drainfields and Other Effluent Discharge Features

The liquid from the upper level of the septic tank flows into an underground drainfield—a network of gravel and sand-filled trenches that use pipes to distribute the effluent across a broad area into the ground. Bacteria in the soil below the drainfield provide the final step in the treatment process as the effluent percolates down through the soil and finally into the water table.

Most septic systems in use in the County are deep-trench systems, in which drainfield trenches about two feet deep are buried at least two feet under the soil surface.

Also in use are shallow-trench systems, also referred to as shallow tile systems. In these systems the side of the trenches are lined so that effluent only drains downward, not out side-to-side. A shallow trench system typically requires more initial and reserve area than a deep-trench system designed for the same capacity.

An alternative to the deep- and shallow-trench systems is the sand-mound system, where a sand drainfield is artificially elevated above the natural soil surface to overcome a shallow water table or a marginal percolation rate in deeper soils.

Sand Mound Septic System Cross-Section
Source: Glen Hills Area Sanitary Study (DEP), 2015

One alternative or innovative type of septic system in use in the County is a shallow drip dosing system. These systems are installed just under the surface of the yard and pump effluent into a network of small pipes. The pipes have small holes that discharge the effluent into the soil. This type of alternative system is used only to relieve a failed septic system and cannot be used for construction of new buildings or expansion of existing buildings.

Shallow Drip Dosing Septic System
Source: U.S. EPA

Older on-site systems use several varieties of discharge methods, such as seepage lagoons, dry wells, and seepage pits. These older systems may continue to serve only existing structures provided they continue to function adequately. Under the County's current on-site system regulations, new construction (a new structure or a significant expansion of an existing structure) may use only deep-trench or shallow-trench and sand-mound septic systems.

Septic System with Seepage Pit Discharge
Source: Glen Hills Area Sanitary Study (DEP), 2015

Septic Systems Maintenance

Just as public sanitary utilities must monitor and maintain their wastewater disposal systems, a property owner needs to perform periodic maintenance and inspection of private onsite septic systems. This helps to ensure the maximum life of the systems, to reduce replacement and repair costs, and to protect the health of users and the environment. (See Onsite well maintenance.)

The primary maintenance responsibility for septic system owners involves pumping accumulated wastewater solids from the septic tank. Property owners hire a certified septic contractor to pump out the septic tank once in every two to five years. The County Department of Permitting Services (311/240-777-0311) can provide information on certified contractors. The frequency of pumping will depend on the intensity of use of the septic system. A household with six residents will need to pump out the septic tank more frequently than a household of two residents. When the contractor comes to service the septic tank, the owner should also have an inspection of the septic system performed, as is feasible.

Ideally, the septic tank lid (or lids) is clearly visible at the surface of the yard (see the following illustration). However, in many cases, the lid for the pump out port (or ports) may not be visible at the surface of the yard, especially if the tank has not been pumped out for many years.

For older septic tanks, the tank lid may be buried at the level of the top of the tank. In these cases, there is no "riser" that extends the opening to the level of the yard. A septic contractor may be able to add a riser to the septic tank to make future pump-outs easier. The following image, enlarged from the preceding sand mound system, shows a septic tank with risers that raise the lids to ground level.

Enlargement of the Sand Mound Septic System Cross-Section
Source: Glen Hills Area Sanitary Study (DEP), 2015

Opened Septic Tank Pump Out Port - Visible at Surface of the Yard

Illustration Source: DEP

One hint to the location of a septic tank is to find the sewage outfall pipe from your house, if visible in the basement. The septic tank is likely in a direct, straight line outside the house at that point. An owner can also gently probe or tap the ground in the yard using a metal pole. In most locations you will hear a solid thump as the pole taps the ground. If the pole hits the septic tank lid, there will be more of a hollow thump. Gently dig in this location to see if you can uncover the lid. If these procedures do not locate the septic tank, the pumping contractor may be able to find the tank for you.

Septic System Maintenance Resources

The County’s Department of Permitting Services (DPS), Well and Septic Section, has prepared useful brochures about well and septic system maintenance.

The University of Maryland Extension has prepared several useful documents that address these subjects. Anyone who uses or contemplates using a septic system should review and pay attention to the tips, recommendations, and sound advice in the following document:

Septic Records and Maintenance Guidelines (PDF, 381K) : Proper design, installation, and maintenance of your septic system will maximize your system's life. It will prevent failures that can be unsightly, foul-smelling, and threatening to your family's health. Good maintenance reduces the risk of contaminating your well water and may save you from costly repairs or system replacement. Septic tank inspection may be required by lenders when you sell or refinance your home. The repair of a failing system is usually a cost to the seller. So, ignoring your septic system will not save money in the long term!