The first objective of a regulator is to protect the public health and the environment, but he has a secondary objective to do everything possible to help the property owner use his property as desired.
Threats to public health from on-site wastewater systems are the spread of many contagious diseases and toxic chemicals. People may come into direct contact with wastewater on the soil surface, drink contaminated water or germs can be spread by insects or other animals to food or water consumed by people. Nitrates and artificial chemicals are potential public health problems, if they travel to the ground water or to surface water that is used as a source of drinking water.
Two types of environmental threats from on-site systems are nonpoint source pollution and environmental impacts. A malfunctioning system may contribute significant quantities of raw sewage and bacteria to surface and ground water (NC Guidance Manual). "Unfortunately septic tank systems are the most frequently reported source of ground water contamination" (Duncan, 1994). On-Site systems can contribute nitrogen and phosphorous to surface waters causing eutrophication; an overgrowth of algae, plants, and bacteria. Part of a stream may become anaerobic, no oxygen in the water, from on-site systems. Eutrophication and anaerobic streams can cause fish kills and damage other animals and plants. Bacteria from on-site systems near shellfish waters has been blamed for damaging or destroying the shellfish area (NC Guidance Manual).
It has been estimated that only 32 percent of the total land area of this country has soil that will properly treat and dispose of wastewater (EPA Design Manual). About 40 percent of the land area of North Carolina may be unsuitable for conventional on-site wastewater systems (Considering the Alternatives). "Based on regulations that existed in the 1970's, Goode (1974) estimated that 50% of the State of Virginia land area did not have soil suitable for conventional septic tank-soil absorption systems. with the 1994 proposed Regulations, land area in Virginia with suitable soils for conventional drainfields will be greatly lessened" (Duncan 1994). Approximately 74% of Florida s soil have severe to very severe limitations for conventional "septic tank" systems by SCS criteria (Sherman, 1997).
Over 50 percent of population of North Carolina (Considering the Alternatives) and about 25 percent of the population of the United States use on-site systems to treat their wastewater (EPA Design Manual). In the last few years, about 50,000 (new and repair) systems per year are installed in North Carolina and approximately 500,000 systems per year are installed in the US (Considering the Alternatives).
In the past on-site systems were regarded as temporary systems designed to keep raw sewage away from direct contact with people until a centralized sewerage system could be extended to the area (Considering the Alternatives). On-Site systems have been considered second rate, temporary, and failure prone. Therefore, sometimes they are not well received by the public. This attitude "contributed to poorly designed, poorly constructed, an inadequately maintained onsite systems" (EPA Design Manual). Today a properly sited, designed, installed, and maintained "septic tank" system can last the lifetime of the house, building or building site (Considering the Alternatives).
Most on-site wastewater systems use a septic tank to provide some pre-treatment, but most of the treatment of the effluent occurs in the soil. In effect, treatment, but most of the treatment of effluent occurs in the soil. In effect, "the site becomes a biological, physical, and chemical treatment facility for wastewater as well as a porous medium through which to dispose treated wastewater" (Otis, 1994). "Wastewater treatment in the soil can be broken down into three different types of processes: physical, chemical, and biological. Physical processes include soil filtration, sedimentation in the soil profile, dispersion, and dilution. Chemical processes involve cation exchange, absorption, organic residue complex formation, and precipitation. Biological processes consist of biological oxidation, nitrification, denitrification and plant uptake, interaction, immobilization, and pediation" (NC Guidance Manual).
With a thorough site evaluation; the proper choice of conventional, modified, alternative, or innovative systems; and proper installation, inspection, and maintenance on-site systems can treat wastewater without endangering humans or polluting the environment (NC Guidance Manual). the steps in developing a site in NC while protecting public health, the environment and the owner using the property as desired are: preliminary information, soil/site evaluation, design, installation and inspection, and maintenance.
The property owner or applicant must make an application to the
local health department, have the property lines marked and make
the site accessible. The application must contain at least the
following information:
"The most critical element in onsite wastewater treatment system
design is the evaluation of the site on which the system is to be
constructed". The site evaluation needs to provide sufficient
information to determine if the site can support an onsite
wastewater treatment and disposal system, what system design
concept to use, and what design parameters to follow (Otis,
1994). The components of a soil/site evaluation are:
The system design must be compatible with the daily flow, the
wastewater characteristics, and the soil/site conditions.
"Proper construction of the onsite wastewater treatment and
disposal system is crucial to the successful system performance.
Since most onsite systems are designed to utilize soil in its
native state, native conditions must be preserved. A frequent
cause of system failure is poor construction practices which
damage the soil (U.S. EPA, 1985). Once damaged, native
conditions can seldom be restored" (Otis, 1994). therefore, it
is
essential that onsite systems are properly constructed and
inspected. The components of a good installation and inspection
are:
Most systems have no operation and maintenance requirements, except for that performed by the homeowner. In North Carolina low pressure pipe systems, systems with more than one pump or siphon, systems with a daily flow greater than 3,000 gallons, aerobic treatment units, and other types of pretreatment require a management entity. The certified operator must inspect, maintain the system, and report to the local health department at the frequency specified. At the review frequency specified in the rules an agent of the state must determine if the system is in compliance of the Operating Permit.
Given appropriate soil and site conditions, septic tank systems are the most cost-effective for wastewater management because of their simplicity, treatment efficiency, stability, and low cost (Considering the Alternatives). With that said, more must be done to insure the protection of public health and the environment. Attention must be paid to the environmental impacts of on-site systems such as: density of development, impact in nutrient sensitive areas, water quality, etc. Researchers and industry must strive to develop better technologies. Efforts are technologies. More emphasis will have to be placed on operation and maintenance.
| System Type | Min. Soil Depth | Soil Cover | Trench depth | Trench
width Actual/Design | Trench Spacing | Example | |
|---|---|---|---|---|---|---|---|
| convent | 30" | 6" | 18" | 36"/36 " | 9' oc | n/a | 240 ln. ft. |
| Idp 10" ID | 30" | 6" | 18" | 12"/30" | 7.5 ' oc | n/a | 288 ln. ft. |
| 8" ID | 28" | 6" | 16" | 12"/24" | 6' oc | n/a | 360 ln. ft. |
| ppbps | 42" | 6" | 30" | 24"/n/a< /td> | 8' oc | 50 | 120 ln. ft. |
| lpp | 24" | 4" | 12" | 8+"/n/a | 5' oc | n/a | 280 ln. ft. |
| fill conv | 18"/12"w | 6" | 18" | 36"/36" | 9' oc | n/a | 400 ln. ft. |
| lpp | 18"/12"w | 4" | 12" | 8+"/n /a | 5' oc | n/a | 480 ln. ft. |
| drip anaerobic aerobic | 18" | 6" | 6" | 1-2"/-- | 2' oc | n/a | 1353
& 720 ln. ft. |
| chambers infiltrator | 36" | 12" | 24" | 36"/48" | 9' oc | 25 | 180 ln. ft. |
| envirocham | 36" | 12" | 24" | 36"/48" | 9' oc | 25 | 180 ln. ft. |
| biodiffuser | 36" | 12" | 24" | 36"/48" | 9' oc | 25 | 180 ln. ft. |
| cultec 75 | 30" | 6" | 18" | 30"/42" | 7.5' oc | 14 | 206 ln. ft. |
| 100 | 30" | 6" | 18" | 36"/48" | 9' oc | 25 | 180 ln. ft. |
| 125 | 36" | 6" | 24" | 30"/42" | 7.5' oc | 14 | 206 ln. ft. |
| C1 | 27" | 6" | 15" | 12"/12" | 5' oc | n/a | 720 ln. ft. |
| C2 | 27" | 6" | 15" | 24"/24" | 6' oc | n/a | 360 ln. ft. |
| C3 | 27" | 6" | 15" | 36"/36" | 9' oc | n/a | 240 ln. ft. |
| C4 | 27" | 6" | 15" | 48"/n/a | bed | n/a | -- |
| houch drainage 20003 tri | 35" | 6" | 23" | 24"/36" | 7.5' oc | n/a | 240 ln. ft. |
| 2012 tri | 18" | 6" | 24" | 30"/50" | 9' oc | 28 | 173 ln. ft. |
| 2012 hor | 30" | 6" | 18" | 36"/48" | 9' oc | 25 | 180 ln. ft. |
Minimum soil depth is based on a level site, natural soil for cover. the example is based on a daily flow of 360 gpd, with LTAR of .5 gal./day/ft.sq.
This page
(http://plymouth.ces.state.nc.us/septic/98lynn.html)
created by
Vera MacConnell,
Research Technician, I
on November 20, 1998.
Last Updated on 3/29/05 by Roland O.
Coburn, Research Tech. I
Please address any questions to Dr. David Lindbo, Assistant Professor/Extension Specialist.