Skip to main content

NC State Extension

Monitoring Protocol for on-Site Systems

en Español / em Português

El inglés es el idioma de control de esta página. En la medida en que haya algún conflicto entre la traducción al inglés y la traducción, el inglés prevalece.

Al hacer clic en el enlace de traducción se activa un servicio de traducción gratuito para convertir la página al español. Al igual que con cualquier traducción por Internet, la conversión no es sensible al contexto y puede que no traduzca el texto en su significado original. NC State Extension no garantiza la exactitud del texto traducido. Por favor, tenga en cuenta que algunas aplicaciones y/o servicios pueden no funcionar como se espera cuando se traducen.


Inglês é o idioma de controle desta página. Na medida que haja algum conflito entre o texto original em Inglês e a tradução, o Inglês prevalece.

Ao clicar no link de tradução, um serviço gratuito de tradução será ativado para converter a página para o Português. Como em qualquer tradução pela internet, a conversão não é sensivel ao contexto e pode não ocorrer a tradução para o significado orginal. O serviço de Extensão da Carolina do Norte (NC State Extension) não garante a exatidão do texto traduzido. Por favor, observe que algumas funções ou serviços podem não funcionar como esperado após a tradução.


English is the controlling language of this page. To the extent there is any conflict between the English text and the translation, English controls.

Clicking on the translation link activates a free translation service to convert the page to Spanish. As with any Internet translation, the conversion is not context-sensitive and may not translate the text to its original meaning. NC State Extension does not guarantee the accuracy of the translated text. Please note that some applications and/or services may not function as expected when translated.

Collapse ▲

Anish Jantrania, Ph.D., P.E.

Technical Services Engineer

Division of On-site Sewage and Water Services

Virginia Department of Health


As relatively newer treatment and disposal systems for on-site wastewater management become available, the interest in monitoring the performance of these systems in the field is rising in the regulatory agencies. Wastewater treatment using aerobic treatment devices or media filter is not new from a scientific point of view. Scientific theories for aerobic and anaerobic treatment of wastewater are well tested, and are used extensively in large-scale wastewater treatment systems. Such theories are now employed for developing on-site wastewater treatment systems using the technologies such as media filtration with enhanced recirculation, flow-through or sequencing batch reactions with efficient air diffusing system, ultra-violate light disinfection system, etc. Unlike large scale wastewater treatment plants, small on-site systems currently are not required to have an on-going performance monitoring and reporting of effluent quality as a condition for their operating permits. At the same time, long-term field performance and the environmental impact from the use of many of the on-site systems are still not well established. An adequate monitoring protocol for on-site systems is needed of both short-term field evaluation of new system sand for long-term performance monitoring of such systems.

In the current regulatory frame-work for on-site systems, when someone proposes to use a wastewater treatment and/or disposal system that is not listed in the regulatory prescription, the very first question asked by the regulators is where is the data that shows the proposed system will work! Performance data collected from the treatment systems during the testing period under control conditions are not always accepted for obvious reasons. Moreover, the performance of disposal technology in any on-site system is somewhat dependent upon the site conditions and may vary from site to site. Hence, there is a need for developing a monitoring protocol that can allow the regulators or any third party evaluators to collect performance data from both the treatment and disposal system while being used in the real working conditions. This paper presents thoughts on how to develop a monitoring protocol, examples of monitoring performance of on- site systems, information that should be gathered form the monitoring, and how to interpret the information gathered form a monitoring protocol.


Regardless of what technology is used for on-site treatment and disposal of wastewater, the main objective for monitoring the performance of such technologies must be to determine if the proposed on-site system is operating in an environmentally sound manner without causing adverse public health impact. All the on- site systems, just like centralized large systems, will have some impact on the environment in which these systems area installed. The area that is impacted by the operation of on-site systems can be called the zone of influence or the design management zone.

The objectives for evaluating the performance of any on-site system should be to determine the boundary of such a zone of influence around the disposal system, to establish the limits for the pollutants at the boundary of the zone, and to collect samples necessary to determine if those limits are met.

For a conventional septic drainfield system, the most commonly used on-site system, the zone of influence is normally established by setting the separation distances (horizontal and vertical) from various components of the system (septic tank, drainfield, etc.) to a number of environmentally sensitive location, such as seasonally high groundwater, wells, stream, lake, etc. on the site. Such separation distances are presented in the regulations for on-site systems, and their values vary from state to state or sometimes even among the localities within a state.

Since the septic tanks are capable of achieving only primary level treatment, the effluent has high level of all three types of contaminants – organic (measured as biological oxygen demand – BOD5, and total suspended solids – TSS), nutrient (measured as total nitrogen TN and total phosphorus – TP), and bacteriological (measured as fecal coliform – FC). Complete removal of these contaminants is expected to be done by soil in a conventional drainfield system. Hence, there is a need for establishing a separation distances around and below the drainfield that allows for further treatment of septic tank effluent by soil.

The need for such separation distances depends on the quality of effluent that is discharged into the environment and on the type of disposal system used. Typically, higher the quality of effluent (i.e., lower level of pollutants discharged) and lower the loading rate associated with the sizing of disposal system (i.e., larger the disposal area), lesser the need for separation distances. Thus, establishment of the zone of influence should be based on the type of treatment and disposal system proposed for the evaluation as well as the pollutants that are of significant concerns from public health and environmental issues. Typically, bacteriological contaminants (FC) are of the primary concerns form the public health issues, while nutrient contaminants (such as Nitrate or TN or TP) are of the environmental concerns, specially when a surface or groundwater source is in the area nearby the on-site system.

I propose that the next generation of on-site systems (i.e., non- septic systems) have the zone of influence that is less than one foot vertically below the disposal system, no more than 25 feet from the edges of the disposal system, and zero feet above the disposal system primarily for the bacteriological contaminants (FC). Which is to say that no FC be detected out side this zone of influence regardless of the soil and site conditions in which an on-site is operating. The zone of influence for the nutrient contaminants should be based on the presence of either surface or groundwater that may be sensitive to nitrogen or phosphorus. Most of the times, the effect of nutrient pollutants from on-site systems can be adequately addressed by allowing for appropriate dilution area around the disposal system. It is now possible to limit or eliminate the discharge of any type of pollutants into environment using an appropriate on-site treatment and disposal system, thus minimizing the adverse impact out side the zone of influence.

The quality of effluent form septic tank is normally not an issue, and it is widely accepted at least among the regulators that the septic tanks treat wastewater to primary standards. However, when other types of treatment devices such as aerobic treatment units or media filters are proposed for use the effluent form those devices needs to be monitored to evaluate the treatment effectiveness of those devices. Monitoring protocols for the treatments devices should specify the frequency of sampling, type of sample (grab or composite), the parameters that the sample needs to be analyzed for (BOD5, TSS, TN, TP, FC, etc.), and finally the length of the monitoring period. Typically, a treatment device that is engineered and packaged using sound principles of wastewater treatment systems, will adequately operate within its design limitations, and on the long-term basis the effluent quality from a well designed system should meet the expected performance as long as it is adequately operated and maintained.

Monitoring the performance of on-site disposal systems is a bigger challenge than the monitoring the performance of non- conventional treatment systems. Getting a sample that represents the environmental impact from subsurface disposal of treated effluent is quite challenging. When to collect samples, how to collect samples, and how to interpret the results of the sample analysis are the basic issues needed to be considered. An effluent sample from a treatment device is easy to collect regardless of the time of year, but a sample underneath or around a subsurface disposal system is hard to collect during dry season. Soil moisture samples using devices such as suction lysimeter are normally collected to evaluate the movement of pollutants underneath and around the disposal system. Due to complexity of subsurface movement of water, it is hard to establish the “hydraulic connection” between the sampling location and the movement of effluent form the disposal system. Keep in mind, here we are talking about non-point source disposal system. There needs to be some balance between the efforts undertaken for sample collection and the risk that the subsurface disposal system poses on the environment.

The Virginia Department of Health (VDH) has developed monitoring protocols for evaluating the performance of a proprietary single pass peat filtration system (Bord-na-Mona Puraflo System) and a proprietary sequencing batch reactor system (Aquarobic Filterbed System). Both of these systems are designed to pre-treat wastewater at a higher level than a septic tank (better than secondary standards), and are designed to dispose the treated effluent in areas that are typically not suitable for the disposal of septic tank effluent. These systems in Virginia are given an experimental status during the period of evaluation, which is 36 months. During this period, performance of twenty- four systems will be monitored based on the protocol developed with the inputs from the companies, and cost of such monitoring will be absorbed by the companies.

The private companies are working with local universities for sample collection and analysis. The state is looking at the effluent data from the treatment units to determine the level of treatment achieved prior to disposal, and the subsurface water sample data underneath (about one foot below) and around the disposal system to determine the movement of pollutants within the zone of influence. This is a very costly proposition for the companies and it appears, at least to me, that there may be a better way to offer the use of such alternative on-site systems to the citizens on a large scale. We need a utility company that takes responsibility for the adequate operation of all on-site systems and that reports to the regulatory agency on a regular basis whatever information is needed to make sure that these systems are not causing any harm to the environment or to the public health. However, until such a company or companies are formed, long-term monitoring of all the on-site systems will be quite a challenge.

Besides the large scale monitoring of two experimental systems in Virginia, the staff of VDH is also involved in several small- scale demonstration and evaluation projects. Monitoring protocols have been developed for evaluating performance of a filterbed system installed in fill material that receives effluent from a sequencing batch reactor system (Weldon Dean Project), a small shallow gravel-less trench that receives effluent from media filters (Easter Shore and Ivanhoe Projects), and an evapo-transpiration system (Charles City County Project). Detailed information on these projects is given during the presentation of this paper. The basis objective for all these projects is the same – to evaluate the environmental and public health impact form on-site systems that are installed on soil and site conditions not suitable for a conventional drainfield system. The first three quarters’ results from Weldon Dean’s project showed no indication of fecal coliform at a foot below the filterbed effluent disposal system that is installed in an area with fill material and less than two feet depth to shale. Monitoring of other projects will start later this year and will continue for the next couple of years. those who want to get more information on these projects may contact the author.

Although quite challenging, I think a monitoring protocol can be developed for any on-site treatment and disposal system to clearly understand the impact of such a system on the environment and public health. the cost of monitoring is quite high, and one must consider the cost-benefit ratio for such an effort. With the sampling tools currently available, I believe that any on- site system when located in an environmentally sensitive area can be adequately monitored and operated in a manner to minimize or eliminate the risk of causing adverse impact on the environment and protect public health.


Tools that allow for easy and adequate access to various points within the treatment and disposal system scheme of an on-site system for collecting samples are very important part of the monitoring program. such tools should be incorporated during the installation of the system that needs to be monitored. A list of monitoring tools used in the above mentioned projects include: a water meter to record the flow data; a sampling port or a faucet to collect effluent sample from a treatment device; a groundwater sampling well to collect free-water samples underneath or around the disposal area; a suction lysimeter to collect soil moisture samples when fee-water is not present in the disposal area; a tension-meter to measure the soil moisture potential (i.e., wetness indicator); and a remote data sensor to automatically record the depth of free-water in an evapo-transpiration beds and store the data on site. There are quite a few other tools available in the market that can easily be used for monitoring the performance of on-site systems.

With the advances in control system, it is now possible to monitor the performance of pumps and other mechanically devices used for on-site treatment of wastewater. Telephone lines can be used for transferring data from field to a central location on a routine basis or whenever necessary. Flow data can be recorded on-site and can be monitored from a distance location using advanced control systems. With the use of appropriate sensors, it is possible to remotely monitor some of the qualitative parameters such as dissolved oxygen, turbidity, pH, etc., in the effluent prior to discharge, when needed. Such parameters can indicate the overall performance of the treatment system and allow the operators to optimize the site visits for maintenance purposes. Since the on-site systems are typically scattered over a large area, advances in remote monitoring is quite valuable for those who want to develop an operation and maintenance infrastructure for these systems. When the performance of an on- site system is closely monitored, it’s maintenance becomes quite cost-effective. An appropriate on-site system that is professionally operated and well maintained can protect public health and environment on a permanent basis.


A well- prepared and executed monitoring protocol will generate tremendous amount of information about the performance of an on- site system. For example, a monitoring program that collects quarterly samples from 24 sites for three years will have 288 data point for each parameter observed. It is important that the information gathered from a monitoring protocol reveal meaningful information about the performance of the system and it’s impact on the environment. It is practically impossible to predict how a three-year monitoring scheme will work before starting the project. Hence, instead of waiting for three years and then looking at the information, it is wise to review the information on an annual or semi-annual basis and adjust the monitoring scheme to add or remove the parameters that are monitored. The frequency os sample collection for a particular parameter can be adjusted based on the variability in the results of that parameters. For example, if the BOD5 values for the effluent from a media filter are less than 10 mg/l for all the sites in the first year, collecting quarterly samples in the next two years may not be necessary, and the sampling frequency can be reduced to either once or twice a year. On the other hand, if the results indicate more variability than expected, then the sampling frequency may need to be increased. Thus, meaningful flexibility in data collection during the monitoring period is necessary.

Information gathered from a monitoring protocol is generally used to determine if the on-site system met the expected performance standard. Regulators are quite often interested in pass/fail criteria of the monitoring protocol. A system that meets the expected standards is typically considered for “approval” by the regulatory agencies. However, this approach has a draw back! Performance monitoring of any wastewater system during a three – year period (typically used by VDH) would indicate only how the system would function during its initial phase (also called “design life”). Just because monitoring results from a media filter or an aerobic treatment unit indicate acceptable performance during a three year period, the performance of such units on a long-term (permanent) basis should not be taken for granted.

On-site wastewater systems, just like large-scale wastewater systems, should be monitored on a regular basis, if they are to be used as an alternative to large-scale system. The frequency and intensity of monitoring of on-site systems, however, can be different compared to large-scale systems, and it should be based primarily on the complexity of the system and the sensitivity of the environment in which the eon-site system is operated. Typically, concepts of risk analysis should be used to determine the need for the level of monitoring necessary for on- site systems. Currently, the operation of septic systems is not at all monitored by the regulatory agencies. but, as the environmental impact from such systems are debated and as the use of alternative systems become wide-spread, performance monitoring of on-site systems is expected to become a routine exercise within the regulatory agencies.

Information from any short-term monitoring program should be used mainly to determine the treatment effectiveness of the on-site systems (effluent quality and variability), operability of the treatment system, operation and maintenance requirement of the treatment system, the zone of influence of the disposal system, i.e., detectable environmental impact from various types of pollutants that are discharged into the disposal systems, and the frequency at which the on-site system will need to be monitored on a permanent basis. Based on such information, the use of on- site system monitored on a permanent basis. Based on such information, the use of on-site system should be regulated for the area where it’s operation is practical and it’s impacts on environment and public health is minimized. A well developed and properly executed monitoring protocol can generate valuable information that can be used for cost-effective and widespread implementation of on-site wastewater systems in any state.


Monitoring of on-site systems is a relatively new concept that is gaining momentum as non-conventional treatment and disposal systems are developed and proposed for use in areas that are not suitable for septic systems. Currently, monitoring protocols are developed for field evaluation of such alternative systems only on a short-term basis. However, long-term monitoring of on-site systems should be considered by the regulatory agencies, if the on-site systems are to be used as a true and equivalent option to a centralized wastewater system. With the monitoring tools currently available, it is possible to monitor the performance of a large number of scattered on-site systems using remote monitoring techniques. An adequately monitored on-site system can be operated and maintained by professional wastewater operators in a cost-effective manner. A permanent operation, maintenance, and monitoring infrastructure (utility) is needed for all on-site systems in order to protect public health and environment fro the operation of such systems. When such a utility is established, an on-site system can be made available to all the citizens who don’t have access to a centralized wastewater system.

Please address any questions to Dr. David Lindbo.

Page Last Updated: 9 years ago
Was the information on this page helpful? Yes check No close