The SJB Consulting Group has over 25 years experience with the investigation and design of on-site residential and commercial wastewater (septic) systems. From conducting the field investigation to developing the final design package, our team of dedicated professionals works with both our client and the regulatory agency to ensure that the project meshes with your development plan and provides the necessary treatment to protect our surface and groundwater resources.
IN A NUTSHELL…On-site wastewater (septic) systems are designed to properly treat and dispose of domestic or commercial wastewater and are required for any parcel that is not connected to a community sewer system. There are a variety of different types of systems that may be used to mitigate adverse site conditions located on a specific parcel. Adverse site conditions may consist of any (or all) of the following: high groundwater (seasonal or permanent), shallow soil depth, limited area, nearby stream or seasonal drainage, etc.
The development of on-site wastewater systems is a phased process involving the property owner (or buyer), county regulatory agency and our design team. The various phases of system investigation and design are:
Conceptual Site Development
Soil Profile Analysis
Percolation testing (when required)
Topographical Survey
Design Development
Once the system has been designed, it is submitted to the county for review and approval-at which point a permit may be obtained and the system installed.
SYSTEM INVESTIGATION
Conceptual Site Development-The first phase of the investigation process is perhaps the most important. It is at this point that the property owner (or buyer) and a member of our design team meet and discuss the overall development objectives (i.e. the size and location of the dwelling, the location of the garage, pool, driveway and well (if appropriate). In addition, the number of bedrooms in the dwelling should be decided at this time. Septic systems are designed based upon the number of bedrooms-having this information going into the field investigation is helpful to ensure that an adequate area is located for the system.
The second step in the investigation process is the soil profile analysis. This test requires the use of a backhoe to excavate test pits. County staff and a member of our design team carefully assess the various soil horizons encountered in the test holes to determine soil texture, soil structure, apparent permeability and depth to seasonal or permanent groundwater.
The soil profile analysis is definitely the most significant aspect of this entire testing process. The proper interpretation of the soil characteristics (color, texture, mineralization, etc.) requires years of specialized experience in the local area.
With the soil profile analysis successfully completed, a determination may be made as to the type of septic system required. If the site is suitable for a standard system, the county may develop a design and ready an installation permit for issuance. If however, the site requires an engineered system, then the project must proceed with the following steps.
SYSTEM DESIGN
Once the field data has been collected and appropriate authorization given, your design team commences with the design development. The design process starts with a topographic survey and the creation of a topo map in AutoCad that establishes the relationship between the ground topography, our test locations, property corners and other items of concern (streams, cut banks, etc.). This map is used to develop the disposal field configuration and to assist in the design calculations. The completed design documents depict the significant portions of the parcel, the system configuration and detailed drawings of all significant system components.
SYSTEM TYPES
Generally speaking, there are three different types of on-site septic systems-each suitable for use in different soil and topographic conditions. Additional system components (curtain drain, capping fill, etc.) are often added to these basic system types to mitigate site specific conditions.
Standard System
A standard system relies on gravity to direct the flow of wastewater. Sewage flows from the dwelling into a septic tank. After primary treatment in the tank, the wastewater flows into gravel filled disposal trenches for final treatment and dissipation into the soil.
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Pressure Dose System
Pressure dosed systems are perhaps the "simplest" of the engineered systems. By introducing a pump system into the second compartment of the septic tank, the wastewater is pressurized to the disposal field. This pressurization provides better distribution and better treatment in the soil. In areas of limited soil depth, sand may also be added to the trenches to "pre-treat" the wastewater prior to dissipation into the soil (sand filled pressure dosed system). At times, a disposal bed (at grade bed) is more appropriate than trenches. At grade beds function on the same principle as pressure dosed systems, but are constructed on the ground surface and require less soil depth than trench systems.
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Pre-treatment Systems
Sites with severe site conditions (high groundwater, very shallow soils) require a pre-treatment unit to provide additional treatment before disposal into the soil. Pre-treatment systems come in many different forms, from site built systems like mounds and sand filters to pre-fabricated units like the textile and aerobic systems. Most of these systems function in a similar manner by providing a surface matrix (either sand or a textile fabric) to support bacterial growth. This bacterial growth digests the contaminants in the wastewater.
Drip Irrigation
Drip irrigation is a newer technology that is gaining momentum as the preferred choice for the disposal of wastewater. The philosophy behind subsurface drip irrigation is wastewater recycling. By re-using the wastewater, in this case for irrigation of lawn and landscape plantings, we can help to reduce the pressure on our ground and surface water resources.
A drip irrigation disposal field (dripfield) is composed of a network of small diameter drip irrigation tubing that is buried 6 - 8 inches deep. The tubing is equipped with pores spaced about every 24 inches. Because of the shallow depth and the close spacing of the pores, the wastewater can be used to irrigate a lawn or other landscape plants. In addition, the nutrients in the wastewater act as fertilizer for the plants. For additional information on subsurface drip irrigation, see our Links page for the Geoflow website.
Once the field data has been collected and appropriate authorization given, your design team commences with the design development. The design process starts with a topographic survey and the creation of a topo map in AutoCad that establishes the relationship between the ground topography, our test locations, property corners and other items of concern (streams, cut banks, etc.). This map is used to develop the disposal field configuration and to assist in the design calculations. The completed design documents depict the significant portions of the parcel, the system configuration and detailed drawings of all significant system components.
