Initial Design/Septic Replacement
Life Expectancy
Conventional septic systems do not last forever and can fail due to a number of different reasons. A common reason for failure is plain and simple old age. The components that make up the system deteriorate over time to the point of physical failure. Other common sources of failure include organic overloading and hydraulic overloading.
Years of use gradually tip the ratio of organic material added to the system and the microorganism’s ability to break them down, making the system ineffective. This process is known as progressive failure. A biological clogging layer referred to as a biomat develops in the leaching trenches. The biomat is an anerobic growth that slows the drainage of water out of the trenches. Conventional septic systems are designed to follow this path of progressive failure. These systems are sized so that the system is large enough so that by the time the biomat has grown to encompass the entire system, the septic system has reached the end of its useful life.
Hydraulic loading refers to the volume of water that is directed through a septic system. The size of the system and type of the underlying soil in the drain field have a finite ability to move water. If more water enters the system than it can handle, the system may become hydraulically overloaded and fail. Hydraulic overloading can occur when more wastewater is generated in the house than the system is designed to handle. Other sources of hydraulic overloading include groundwater inundation or surface water intrusion. Changes in the land use in the vicinity of the septic system over time can contribute to groundwater and/or surface water problems.
It is generally recommended that the septic tank be pumped out and solids removed for off site disposal every 3-5 years, depending on usage. The routine pumping out of the septic tank will contribute to getting the longest life expectancy out of the septic system. If the septic tank is not periodically pumped out, solids will fill up the tank and then flow out to the soil absorption field causing failure.
It is important to have a properly functioning septic system so that the contaminants in the wastewater are treated prior to the water draining into the groundwater and nearby surface water. The contaminants in the wastewater are quickly filtered out as the water passes through dry porous soil. However, if the contaminants reach the groundwater table, they can migrate considerable distances and potentially contaminate other environmental resources including surface water or drinking water supplies.
First Step in Replacing a Septic System
Selecting a Design Professional is the first step in the process of installing a septic system. This is true for both replacement septic systems and those serving new houses. The New York State Department of Health Design Guidelines outline all aspects of designing a septic system. Its important in the process of selecting a Design Professional to keep in mind when you hire an engineer or architect, the product you get is a result of that individual’s opinion & experience. Although all septic systems follow the same general guidelines for implementation, it is increasingly more important to have a properly trained, experienced, and well-versed designer on the more challenging sites. In particular, sites where the conditions are not suitable for the placement of a conventional septic system.
Site Characterization
The Design Professional conducts a site evaluation which includes witnessing deep test holes excavated up to 6-feet deep and conducts soil percolation tests. Subsurface soil conditions are evaluated to identify the depth to a limiting condition that is a seasonal high groundwater table or bedrock. The soil percolation tests provide information about the soils ability to drain water. The following log form is used during completion of the soil percolation tests.
NYSDOH
An original stamped property survey is very useful to the design professional conducting the site characterization.
Upon completion of the site characterization activities, the designer will layout the placement of the septic system components. That is, the septic tank, distribution box, and dispersal field. The septic system components must meet vertical and horizontal separation distances to receptors such as surface water, groundwater and/or bedrock. Required separation distances are found on Table 2 of the NYSDOH Design Guidelines entitled “Required Separation Distances from Wastewater Treatment System Components”.
These separation distances have been established so that the septic tank effluent dispersed into the ground has the time needed to adequately degrade as it drains through the soil prior to reaching a receptor which could be a drinking water well, surface water, dwelling, property line or drainage ditch. Separation distances have been established to provide a reasonable factor of safety.
Septic designs for new construction that do not meet these separation distance requirements must have an approved Specific Waiver.
Replacement system sites should to the best extent possible meet new construction standards or have components in-place to mitigate the limited separation distances required by new construction. Because the separation distances have been established to ensure that the water reaching receptors has undergone adequate treatment.
The DOH uses the following form to review a septic design.
The NYSDOH provides the following suggested guidance for evaluating septic systems that are not properly functioning.
Evaluating and Correcting System Failure
The NYSDOH Table recommends the use of an ETU as a possible solution to correct the failure of a soil based septic system.
