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Pre and Post-Installation Issues: Inspection Protocol

John P. Williams, Regional Soil Specialist
Wilmington Regional Office, On-Site Wastewater Section, Division of Environmental DENR
127 Cardinal Drive Extension, Wilmington, NC 28405.

The objective of this presentation is to discuss inspection protocol for the installation of an on-site wastewater system. North Carolina Laws and Rules for Sewage Treatment and Disposal Systems sets forth right criteria for the approval of a site to receive on-site wastewater effluent. This presentation will explain the steps that must be taken to ensure that the treatment and disposal system is constructed out of quality materials and performs as it is designed. These steps include: 1)Basic principles of on-site systems, 2)Responsibilities of the builder, septic system contractor, and regulator, 3)Pre-construction conference, 4)Installation inspection, and 5)Issuance of completion approval.

Basic principles of on-site systems.

The five principles of on-site wastewater design are outlined in On-Site Wastewater Management – Guidance Manual. The first principle states that all on-site systems should be designed so that sewage is treated and disposed of to minimize the pollutants and prevent contamination of ground water and surface water. The second principle states that on-site systems should be designed and installed to maximize the aerobic treatment of the sewage. The third principle sates that effluent should be applied to the soil only in appropriate sites and in a constructed treatment and disposal field. The fourth principle states that treatment and disposal field trenches should be as long and narrow as possible to maximize soil contact and disposal area. The fifth principle states that the treatment and disposal field trenches should be level across the bottom and be level along their entire length to distribute the effluent as evenly as possible. These five principles point out the relationship between choosing the appropriate site and properly constructing the on-site wastewater system. A properly constructed system on a poor site will not function properly. Likewise, an improperly constructed system on the best site will not function properly either.


Although a contractor will install the on-site system and a regulator will approve the installation, there are many people who have responsibility for various aspects of system design and installation. It is the responsibility of the homeowner or businessman to accurately represent what is going to be built at the site. The regulator must know what areas are available for the on-site system at any give site. The homeowner must be forthcoming with the actual home location, the presence of decks and porches, swimming pools, outdoor buildings, etc. These features can not be located within the on-site system or repair area. In some cases, minimum horizontal setbacks must be maintained from these features. A business owner must also clearly indicate what areas are to be used for parking, outdoor dumpsters, unloading zones, etc. Anyone proposing to build must be clear about the use of the facility, how much and what type of wastewater will be generated. Knowing this information in advance will allow the regulator to design the system properly to eliminate problems later.

The on-site wastewater system contractor has a responsibility to use the best quality materials and to install the system as designed. If the contractor can not install the system as designed, the regulator should be notified immediately. Use of poor materials or installing a system contrary to the design will result in a failed inspection or a shortened system life. Neither of which are fair to the individual purchasing the on- site system.

The regulator has the responsibility to design the best system for the site making sure that all system options have been considered. The regulator must also inspect the system installation and determine that it was installed in accordance with the design plan, meets all appropriate regulations, and is constructed out of high quality materials. Failure to perform this task adequately may result in premature failure of the system.

Preconstruction conference.

Preconstruction conferences are tools that can be used to ensure that the five principles of on-site systems are met. Preconstruction conferences can be used at any site and should be used when dealing with a complex site, limited space for system installation, or an unusual system requirement. The preconstruction conference should be attended by all necessary parties. That list may include the regulator, on-site system contractor, builder, certified operator, licensed soil scientist, professional engineer, innovative product representative, etc. A preconstruction conference should be held prior to the construction of the building if the building location is critical for proper wastewater system performance. the conference should be held prior to on-site wastewater system construction if the system location is critical or is system components are unique.

Installation inspection.

The installation inspection will determine if quality materials have been used and if the system was constructed in compliance with the permit and all conditions of the permit. A system installation inspection should be thorough and logical. The regulator should start at one end of the system and check through to the other end. Numerous inspection forms have been devised to eliminate error in this process. North Carolina has devised a form that can also be used as the operation permit itself (see Figure 1). This form is especially useful when a system inspection takes more than one day or more than one person as one might encounter with a system that pumps sewage effluent off- site. Each person involved can initial and date the part of the inspection that they have completed. Specifically, the steps of system inspection are as follows: 1)Check to see if the permit matches the site. The best permit is of no use if the system is being installed on the wrong lot. 2)Make sure that the system is located where it was entended to be. The permit should contain X and Y coordinates from a known horizontal benchmark so that there is no mistake in system location. Use of a 100 or 200 foot measuring tape and compass will eliminate errors in measuring the coordinates. 3)Determine if all minimum horizontal setbacks are met. A perfectly constructed trench is of no use if it is too close to a property line or a well. Again, a tape measure will be needed to verify compliance. 4)Check the septic tank. The regulator must determine that the septic tank is properly constructed of high quality concrete of the appropriate strength, is sealed properly, and will function as designed without leaks. The outlet must be lower than the inlet, the vent must be cleared so that it will work properly, the sanitary tee must be in place and the tank halves arranged so that the baffle will perform as designed. Tools for this task include a rebound hammer, metal detector, manhole hook, and shovel. If a pump tanks is involved, it must be determined that it is compliance with the regulations and that the pump and floats will perform as designed. State approved non-concrete tanks are becoming more prevalent and should meet manufacturer’s specifications. 5)Check the distribution system. Make sure that the appropriate type of distribution (serial, distribution box, drop box, pressure manifold, etc.) has been used and it will work as designed. Unequal distribution will shorten the life of any system. 6)Chick the trenches. The trenches must be constructed at the proper grade and with aggregate of the proper size and cleanliness to ensure long system life. The pipe in the nitrification trench should be in the center of the ditch, at the appropriate grade, and oriented with the holes facing down. The trenches should be parallel to each other and minimum spacing must be maintained so that sewage effluent is not concentrated in one area which may lead to a hydraulic failure and surfacing of effluent. The trenches must be installed at the proper depth as indicated by the permit. No adjustments in trench bottom depth or location should be accepted without prior approval by the regulator. A laser level, shovel, and rock probe are necessary to accomplish this task. If an innovative product has been utilized in the trenches instead of rock, all conditions of approval and manufacturer’s requirements for the product must be met. 7)The repair area must be preserved. North Carolina requires that a repair area with acceptable soil be set aside for the future replacement of an on-site system. This area must be free from structures or driveways. 8)Check to see that all conditions of the permit have been met. Conditions may include the use of geotextile fabric in the trenches, grading and shading of the field, erection of a traffic barrier to protect the system, etc.

Issue of completion approval.

At the time that the system inspection is complete and all conditions have been met, the completion approval can be released. At that time a detailed record should be made that reflects the actual as-built plan of the structures and the on- site system. This information will be essential if a repair must be made to this system in the future. Once released, the completion approval allows the system to be placed into use and the structure to be occupied. Unfortunately, when a system goes out of sight, it typically goes out of mind as well. Therefore, the completion approval should never be released until every concern is satisfied. This will help ensure that the user will get a high quality, long lasting system that will protect public health.


Arnold, J.A., D.L. Osmond, M.T. Hoover, A.R. Rubin, D.E. Line, S.W. Coffey, and J. Spooner. 1996. On-Site Wastewater Management – Guidance Manual. North Carolina Cooperative Extension Service and North Carolina Department of Environment, Health, and Natural Resources. Raleigh, NC. North Carolina Administrative Code, Title 15A Subchapter 18A Rules 1901-.1968. Rules Effective July 1, 1982, Rules Amended Effective January 20, 1997.