Septic System Basics for Home Builders
When someone decides to build a house, they need to contact a homebuilder who has a reputation of building good quality houses within budget and who could provide solid advice regarding all aspects of the homebuilding process. As the client and homebuilder deliberate details about the house, particular attention are often given to kitchen and lighting features, storage space, façade design, counter-top material, backsplash color and bathroom fixtures, among others. However, household waste treatment features, like septic systems, are seldom discussed in great detail.
Often, the client would rely on advice and information given by homebuilders to come
up with decisions about their house. Ideally, details regarding the type of septic
system permitted in the property, additional expenses for soil and site characterization,
designating an area for possible septic system repair and the associated costs involved
in all of these should be included in the client-homebuilder discussions. For example,
if the land would require a very expensive septic system (say $10,000), it is best
if the builder can advise the client about this detail so it can be considered in
possibly making adjustments in house design to keep within budget.
This Fact Sheet will focus on the following key topics that are useful to homebuilders and their clients: 1) homebuilder responsibilities; 2) important site and soil properties; and 3) various permissible systems.
The homebuilder is the primary source of information and professional advice concerning any aspect of the house – including septic systems. In our opinion, the following are the septic system-related responsibilities of the home builder:
Inform the client about the process associated with the filing of permits and all steps involved until the system is installed.
Homebuilders are not expected to file the permits themselves, but they are expected to inform the client about the process of getting an installation permit and the amount of time that should be allocated to it. Ideally, the builder should be able to refer clients to a State-certified installer and a licensed soil profiler. In some cases, a percolation test (a test measuring the rate of downward water flow through the soil) may need to be done. It should also be noted that many municipalities in Oklahoma require a soil test report before issuing a building permit.
A list of State-certified installers can be found at:http://www.deq.state.ok.us/ECLSNew/CertInstallers/certInstallers.htm.
The list of licensed soil profilers could be accessed at http://www.deq.state.ok.us/ECLSNew/On-site/soilprofilers.htm or inquire from the local DEQ office.
Homebuilders should inform the client of the juncture in the homebuilding process when the septic system needs to be installed. This is critical so the client can prepare for the associated expense. Note: The septic system installer will take care of the installation permit application.
Inform clients on the probable types of systems that may be installed in the area,
as well as the cost and time needed for system installation.
There are six types of systems permitted in the State. The various types of systems
permitted in the State will be discussed later. Some systems rely heavily on gravity
and the soil to accomplish the dispersal and treatment of the wastewater, while others
require electricity and involve mechanical parts driven by complex electronics. All
of these systems require up-keep by homeowners and involve some expense when needing
periodic maintenance and repairs by professionals.
Cost for installation varies widely, depending upon the type of system, location and site properties. Homebuilders are advised to check with a local installer for the range of installation cost applicable for the area. Table 1 shows the estimated time required for installation of the various On-site Wastewater Treatment Systems (OWTS).
Table 1. Estimated time required for installation of various OWTS designed for a two-bedroom house that produced 200 gallons of wastewater per day.
|On-site Wastewater Treatment System||Installation Time|
|Conventional System||1-2 days|
|Shallow Extended Subsurface Absorption Field||1-2 days|
|Low Pressure Dosing System||1-2 days|
|Evapotranspiration/Absorption System||1-2 days|
|Lagoon System||2 days|
|Aerobic Treatment System||1 day|
Site and Soil Properties
Site and soil properties eventually determines the type of OWTS that can be installed in the area. The homebuilder should identify the location within the property best for the house, taking into consideration the requirements for OWTS installation.
Minimum Lot Size
The homebuilder needs to ascertain whether the property has enough space for both
the house and the OWTS. At least 10,000 square feet should be allocated for OWTS installation
in the general installation area. In addition, the area should be accessible to the
installers and the equipment needed in earth-working activities related to the installation.
If public water would be used in the house, the minimum size for a residential lot that needs an OWTS is one-half acre. If a drinking water well needs to be installed in the area, then a minimum lot size of three-fourths acre would be required.
Area for Repair
Apart from the area allocated for OWTS installation, enough area should be designated as “repair area.” This is the area where dispersal lines will be installed in case the first system installed would fail.
Soil Profile Evaluation
Only State-certified soil profilers can perform soil profile descriptions. However, it is ideal if the homebuilder can understand the soil profile description report so they can explain to the client the OWTS cost and installation timing implications of having certain types of soils in the area. Refer to Extension Fact Sheet PSS-2271, Soil-based Septic System Decisions in Oklahoma for more details.
Areas in the property where surface runoff would tend to pass through or could be collected should not be used as effluent dispersal site. Make sure the effluent dispersal area is not in a floodplain. In addition, the toe slope of a sloping area is not a good location for installation of the OWTS, because, aside from being an area that collects runoff, the water table also tends to be shallow underneath it.
Other Site Considerations
Slope: Sloping areas could still be used for installation of OWTS. However, installation of OWTS in relatively flat areas is easier for installers and would not require major earth work. As rule of thumb, areas with a slope greater than 10 percent are undesirable areas for the installation of OWTS.
Proximity to protected water body: Home builders should determine if the property is within the Water Body Protection area as described in the Oklahoma DEQ Rules. If the chosen effluent dispersal area is in Zone 1 (660 feet) or Zone 2 (1,320 feet) from a streambed, advanced systems with a nitrate-reduction component would be required. This means the homeowner is going to pay more for the OWTS. To determine whether the property is within a water body protection area, check with your local DEQ office or go to http://gis.deq.ok.gov/flexviewer/.
Subdivision restrictions/codes: If the property is in a housing subdivision, it best practice to double-check if the Subdivision Covenant Agreement has restrictions about septic systems or not (e.g. a provision stating that spray dispersal systems are not allowed).
Permissible Systems in Oklahoma
The conventional system is the most widely-used and least expensive type of on-site wastewater treatment system. It has two main components: 1) the septic tank and 2) the soil treatment area (STA). This is the preferred system in sites with deep, good soils (loamy sands, loam, clay loam, sandy clay) that meet STA size requirements. This system relies on the soil for wastewater treatment and on gravity for the distribution of wastewater throughout the STA. Well-maintained conventional systems could stay effective for more than 20 years.
Figure 1. Schematic illustration of a conventional septic system.
Low Pressure Dosing (LPD) System
The low pressure dosing system is similar to the conventional system except that it has a pump tank. It is used in sites with slight limitations related to soil texture, soil thickness and area size. For example, it is used in areas with coarse soils (coarse sand or loamy coarse sand) that do not meet the land area size requirement of a conventional system.
Pressure generated in the pump tank is used to evenly apply the effluent throughout the entire soil treatment area. Because of the even effluent dispersal, the use of the STA is maximized – compensating for soil- and site-related limitations.
Evapotranspiration/Absorption System (ET/A)
The ET/A system is another option for areas with fine-textured soils (high clay content). This system is a particularly good option in areas where evapotranspiration exceeds precipitation. This system requires one acre as the minimum lot size. In Oklahoma, this would be more suited in areas west of Interstate 35 (e.g. the panhandle) than in the southeast.
Aerobic Treatment System
The aerobic treatment system is currently very popular in Oklahoma. It is used in areas with major limitations regarding soil texture, soil thickness, slope and other site limitations. It has an aeration tank wherein the wastewater is bubbled with atmospheric air (has about 20 percent oxygen). The introduction of oxygen significantly enhances microbial activity, which in turn, improves wastewater treatment prior to land application. Effluent may be dispersed by subsurface drip lines or may be surface-applied by a spray irrigation system. Surface-applied effluent is pre-treated with bleach. This system will need a lot more maintenance than other systems.
Figure 2. Schematic illustration of an aerobic treatment system. Other variations of this system involve a single large tank divided into three compartments/smaller tanks namely: 1) the trash tank, 2) the aeration tank and 3) the pump tank.
Treatment lagoons are good alternatives in areas where evaporation exceeds total precipitation. It relies on evaporation as a mode of disposal of wastewater. This system uses an open pond as the storage/evaporative area and a septic tank for pre-treatment of wastewater. Lagoons are permitted on any type of soil that has a lot size of at least two and a half acres.
There are instances when none of the systems described earlier can be allowed or is practical. In these instances, an alternative OWTS is needed. For additional information concerning the types of alternative systems available and the application/approval process for alternative systems, please contact your local DEQ office or call 405-702-6100.
For more detailed discussions about the various OWTS permissible in Oklahoma, refer to Extension Fact Sheet PSS-2913, On-site Wastewater Treatment Systems Permitted in Oklahoma.
Sergio M. Abit Jr., PhD
Extension Specialist for On-site Wastewater Treatment Systems
Environmental Specialist, Oklahoma Department of Environmental Quality