Private Well & Septic Service

Onsite Systems Distribution in the County

The Department of Environmental Protection (DEP) estimates that approximately 17,500 properties in the county use an onsite well for their water supply.  Approximately 20,000 properties use a septic system for wastewater disposal.  Most of these onsite systems are found in large-lot residential and rural-zoned areas.  As shown on the following maps, areas served by onsite systems tend towards the western and northern parts of the county.  However, numerous onsite systems still serve properties within the existing public water and sewer service areas, including locations where public water and sewer mains are available for service.

Onsite Systems Testing & Permitting

When a property owner has a well or septic system installed for use on the land, the owner wants assurance that they will function adequately and provide service for a reasonable length of time. The testing and permitting requirements established by the County's On-Site Systems Regulations ensure that when wells and septic systems are installed that purpose is accomplished.

In Montgomery County, the Department of Permitting Services (DPS), acting on behalf of the Maryland Department of the Environment (MDE), has the responsibility of testing for and permitting wells and septic systems. (Note that in other Maryland jurisdictions, the local Health Department often carries out this function.) 

The discussions below on the testing and permitting processes for wells and septic systems provide only general background information. The DPS Zoning Division webpage has well and septic system testing and permitting requirements and application forms. The DPS Well and Septic Section may be reached by phone locally at “311,” or from outside the county at 240-777-0311. 

Water Supply Well Requirements

In most areas of the County, groundwater is reasonably plentiful provided you drill deep enough to find it. As a result, DPS does not usually require testing before it issues a permit for drilling a water supply well. However, the agency does need to approve an on-site system plan before issuing a permit.

Flow testing is required after drilling and before a building permit is issued to ensure that the well can pump an adequate flow of water. The state's minimum flow requirement for approving a new well for use is 1 gallon per minute (GPM).  Keep in mind that though allowed, 1 GPM is a low flow rate that requires spacing out typical high-volume water uses, such as bathing and washing clothes and dishes, throughout the day.  A well producing 1 GPM water flow would produce approximately 1440 gallons of water per day.  DPS staff can advise well permit applicants about special requirements, including the areas of the County where prior testing is required for a permit (call 240-777-0311).

The MDE Water and Science Administration's Water Supply Program requires some multiple-unit residential projects and nonresidential projects using groundwater wells to apply for and obtain a water appropriation and use permit. Contact the MDE Water Supply Program. 

• Download a copy of the  MDE water appropriation and use permit
• Find additional information on how to apply for the water appropriation and use permit

Septic System Requirements

Before any formal testing occurs, the Department of Permitting Services needs to review and approve a layout plan for the site showing proposed testing locations. Following this step, testing for new septic systems occurs in two stages—a water table test and a percolation test. 

Water Table Testing

The first test, the water table test, determines the depth to the groundwater, the fully saturated soil under the property. The unsaturated soil between the bottom of the drainfield trench and the top of the water table provides area for treating the wastewater effluent. If a depth of at least approximately four feet-between these is not maintained, untreated wastewater effluent might enter the water table and could contaminate ground water and from there, water wells or streams and ponds. The level of the water table fluctuates throughout the year. Note that this test is conducted only in the late winter to early spring when the water table is known to be at its highest level. If low rainfall conditions have occurred throughout the preceding year, the DPS Well and Septic Section may choose to shorten the usual testing period. 

Illustration of Groundwater and the Water Table

Illustration Source: U.S. Geological Survey

Percolation Testing

The second test, the percolation test, determines how quickly wastewater effluent will move downward through the soil. You need to complete and satisfy water table testing before moving on to percolation or "perc" testing. If the flow rate though the soil is too fast, the effluent won't stay in the soil long enough for adequate treatment, again allowing untreated wastewater into the water table. If the flow rate is too slow, the soil won't accept and distribute effluent flows from the drainfield quickly enough. Eventually the septic system will back up to the yard above the system or into the user's building. As expected, either situation can create a public health problem.

Area Requirements 

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 for 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 and need to be down grade (lower in elevation) than other nearby wells. In addition, County onsite systems regulations establish other septic system setbacks for site features like steep slopes, stream buffers, and buildings.

Exceptions for Onsite Systems Use in Public Service Areas

Where properties are planned for public water and sewer service, the County’s expectation is that owners will pursue service from public systems if an onsite well and/or septic system fails or if new development or redevelopment is proposed. However, not all properties within the County’s planned public service areas have direct access to existing water and sewer mains. Onsite work for public service for some properties may involve restrictive complications or excessive cost. An onsite system failure may present public and/or environmental health concerns that require expedited relief. A property owner may request the temporary use of an onsite well and/or septic system in these circumstances. Where properties are designated as water and sewer categories W-1, W-3, S-1, or S-3, the Department of Permitting Services (DPS) will require an exception from the Department of Environmental Protection (DEP) that allows for the use of either a new or a replacement onsite system.

A property owner or the owner’s designated representative may request a category 1 or 3 onsite system exception from DEP using this linked application: MS Word version or Acrobat PDF version. Please follow the instructions on the form for completing and submitting the application. 

An applicant may find it helpful to discuss their specific case with DEP staff before applying for an exception.  Please do not hesitate to contact either of the following staff members for information or with questions:

• George Dizelos at 240-777-7755 or George.Dizelos@MontgomeryCountyMD.gov
• Alan Soukup at 240-777-7716 or Alan.Soukup@MontgomeryCountyMD.gov

DEP does not charge a fee for an onsite systems exception request.

Note that a DEP exception approval does not guarantee DPS permitting of an onsite well or septic system. If DPS does issue a permit for a new or replacement onsite system under these conditions, DPS will likely issue an “interim” permit for the onsite system.   Interim permits require that owners of properties abandon the onsite system and connect to public service within a year of the time that public service becomes available. Please refer to DPS Zoning Division for additional information about onsite system permitting issues; scroll down the page to the section titled "Well and Septic".