Household Sewage Treatment System Site Evaluation, Soil Evaluation, Installation Inspection, and Operation and Maintenance Checklists

 The following is how we did these evaluations in a county in Southern Ohio. There are specific rules for states as these septic systems are regulated by states and also must comply with county rules.

 

Site and Soil Evaluation

1)        Initial Contact: If it is a new build, make sure there is a property address, a copy of the land deed to scan for deed restrictions, and floor plans for the house, if applicable. Propose a site evaluation with a soil evaluation by the county health department registered sanitarian or a registered soil scientist.

2)        Visit site and determine areas to excavate the soil to evaluate it, either then and there with an excavator to dig, or a soil probe, or place flags for the soil evaluation to be done in the future. Evaluate site for the suitability of the soils for a soil absorption system with leaching trenches and chambers, which is the preferred system type due to both cost and low maintenance. If soil is unsuitable due to a high seasonal water table or some other restriction, another type of approved system should be considered. These include mound systems, sand-lined systems, peat pod systems, drip systems, spray systems, and Anua Aerocel systems. Soil evaluation includes determining for each soil layer its grain size: usually sand, silt, or clay, its clay content, its fragment content, its grade, whether it is friable or firm, and its color, (including colors of redoximorphic features) from the Munsell Color chart. It is also important to determine whether the soil has been disturbed and to what depth. Assuming a gravity leach system, continue as follows:

3)        Evaluate the site for footage along contour for the main leach field and the replacement area for a future leach field if the current one ever fails.

4)        Evaluate the site for isolation distances: > 50ft from a private water system well (all components), >50ft from a perennial stream, pond, or wetland (all components), distances from rights-of-way and easements can vary from about 10’ to 25’ or more, and >10ft from property lines, which often need to be determined or verified in the field.

 

System Design

5)        If there is room and there are good contours for the main and replacement areas, then proceed with septic system design. Doing this requires calculating several metrics based on the soil evaluation. The main means of this is using what is called a Tyler chart (developed by Jerry Tyler at the University of Wisconsin at Madison) where estimates of soil infiltration loading rate (ILR) and hydraulic linear loading rate (HLLR) are obtained from the soil characteristics. These loading rates estimate the movement of the sewage effluent through the soil pores and the biological oxygen demand that would be present in the soil. The first calculation is simply the Daily Design Flow (DDF). This is based on the number of bedrooms and is estimated at 120 gallons per day of flow per bedroom. The minimum sized system would be a one or two-bedroom system at 240 gal/day DDF. These are conservative estimates. Under sizing a septic system is riskier than over sizing one. The ILR and HLLR calculations determine the size of the leaching area required in lineal feet assuming the most commonly used leaching chambers 24 inches wide and 8 or 12 inches tall. The calculations determine how many leach lines there should be and how long they should be, adding in “resting” footage that can be conserved or available for high use times. The slope of the site is also factored into the calculations since slopes have better drainage. Trench depth is dependent on the soil characteristics. A restriction, or ‘limiting condition’, such as a seasonal perched water table shows what are known as concentrations and depletions which indicate respectively oxidation and reducing conditions. They are also known as redoximorphic features. Oxidation occurs when the water table drops lower and the soil there dries out and reduction occurs when the soil becomes saturated over time. Concentrations are typically reddish or yellowish iron oxides and some black manganese oxides. Depletions are typically gleyed soil, a greenish-gray very indicative of saturating conditions. The gleyed soil is a restricting layer as are clays that often occur lower in a soil profile. There should be a minimum of 12 inches of soil between the bottom of the trenches and the restricting layer. This is for the sewage effluent to percolate through before it reaches saturated conditions. Loams, silt loams, and sandy loams are the preferred soil types for leach fields due to sufficient permeability to allow the effluent to penetrate the soil and remain oxygenated enough for treatment to continue. Leach fields utilize the aerobic bacteria in the soil for decomposition of the particles in the effluent. Aerobic bacteria consume oxygen. Oxygen is present in higher amounts closer to the ground surface and deeper soils are more likely to be saturated or partly saturated. Sand-lined systems work well due to the high permeability of the sand combined with the effluent flow rate. The depth to the restricting soil layer is known as the vertical separation distance (VSP). The method used to evaluate suitability based on depth is the ability to keep at least 12 inches of soil from the bottom of the leaching trench to the restricting layer and at least 2 inches of soil to cover the chambers.

6)        When the system is designed, it is drawn out roughly to scale and given to the installer who then tweaks it a little or not for the ‘design layout’ which goes back to the regulator (in our case the local county health department) for approval to issue the permit. The drawings should depict roads, structures, system components, isolation distances, property lines, ponds, streams, a water well if present, and a diversion drain, often recommended to divert excess water away from the leach field. Permits are issued when fees are remitted. An installation permit is issued, and an operation permit is issued. The installation permit is good for one year but can be extended for six months upon reasonable request. The operation permit expires in 10 years when the septic must be inspected again with agreed fees remitted at that time.

 

System Installation

7)        When the system is installed, the regulator inspects that installation, noting tank(s) type, manufacturer, size, materials used, length of leach lines, degree of smearing on trench walls if present (which should be raked out) which can impede percolation, amount of drop to the leach field (should be a minimum of 1/4" per foot), the inspection ports, how level the leach lines are, and whether any are wet. Sometimes lines can be rerouted around the water, and since the excavator is there, it can be done quickly. Then the system is approved for backfill. The installer then provides an “as-built” to show in picture form the final system configuration. The system is then approved and finalized. Approval may be mailed or preferably emailed with all documents pertaining to the system and fact sheets specific to that system to the owner. 

 

Operation and Maintenance

8)        Operation & maintenance (O&M) inspections of the system are done first with a 12-month inspection. Here the regulator goes out to check the system for possible issues. Typically, the regulator looks into the outlet compartment of the tank to check the outlet filter, making sure it is not clogged or to note whether it should be cleaned. The inlet compartment may also be inspected to determine sludge level is high enough to warrant pumping. Each inspection port is examined to see if there is sitting water, which there should not be, although there can be some at a low level. The distribution box and/or drop boxes are opened and examined to determine if the pipe levels are still good and whether any pipes have moved causing some leach lines to be bypassed. Water levels are noted to determine if there are any clogs. Any running water in drop boxes or even into the tanks should be accounted for as it could have resulted from a leaky appliance such as a toilet. The leach field is examined to see if any water is surfacing. If there is a problem – such as the boxes or tank being covered, pipe movement, water in ports, or water surfacing, then the installer is called in to fix. This is important since the installers are legally required through their bonding to essentially warrant the system for 18 months.

9)        A 10-year inspection is required in some states, and this may include older existing systems as well. These older systems are more likely to have some of the issues noted above. 10-year inspections also require estimating the solids level in the inlet compartment where the solids abide and decompose. If this sludge level is high, it is recommended that the tank be pumped out. Many of these older systems and newer ones as well have pre-treatment components such as aerators, UV lights, and chlorinators, and lift station pumps where there is no topographical drop or a rise to the leach field. Aerators are motors that oxygenate the effluent so that it is partially treated before it enters the leach field. Lift stations are usually ½ hp pumps that pump the effluent through 2-inch pipes up to the leaching area. These too can pump too hard, causing the effluent to bypass some leach lines. Unfortunately, aerators and pumps have short life spans and must be repaired and/or replaced at the owner’s expense. Often when they stop working, they are not repaired or replaced due to costs. UV lights have even shorter life spans but cost less. This ends up resulting in issues where the landowner does not want to pay or cannot afford to pay for repairs and replacements. Sometimes they are eligible for grants, full or partial, if they apply. It is recommended that the required 10-year inspections are done by a service provider as they are equipped to fix issues with the system. They could also pump it out while they are there. Otherwise, the local health department can do the inspection and provide guidance for what needs to be done.

 

     There are quite a few different kinds of septic systems based mainly on the limitations of the site for soil absorption of septage effluent. In many places, the soil is unsuitable to absorb effluent, typically due to the depth of saturation, whether it is an apparent or seasonal water table. In such places there are types of systems including mound systems, low-pressure drip systems, sand-lined systems, peat pod systems, systems with synthetic leaching components, and spray systems where the treated effluent is sprayed on a time schedule. Some of these systems will work well for decades but the ones with mechanical components: aerators, UV lights, chlorinators, lift pumps or other pumps, and spray heads will likely need to be maintained with considerable expense to the owner. Some of these systems are quite expensive to install as well. Some of the older systems may discharge to a stream, ravine, or ditch after minimal or even no treatment. To determine if that is the case one may conduct a dye test by putting dye down a sink or in the tank then running the water for a time to see if the dye shows up in the outfall water.