The following guidance assumes the AOSE conducting the inspection is familiar with the construction requirements found in Part IV of the Regulations (12 VAC 5-610-10 et. sec). What follows are recommendations on developing a practical approach to inspecting onsite sewage disposal. In general there are two steps in the process. First establish that the major components are in place and second assure that the components are installed in a way that will achieve and continue to operate as intended. The goal is to have a system that is placed in operation that will not contaminate ground or surface water for the foreseeable future. Ideally the system will be installed in strict accordance with the permit. In the real world "discrepancies" occur.
How important are discrepancies and what action should an AOSE take? It depends largely on the discrepancy. Moving a septic tank and effluent line from the east side of a house to the west side is usually of little significance. When the relocated septic tank encroaches on the set back distance to the homeowner's or a neighbor's well, the discrepancy takes on added significance. As a general rule there are three items which are difficult or impossible to correct and most everything else can be brought into compliance with the Regulations.
The following three items are perhaps the most critical because they are the most difficult to fix and may not always lend themselves to a simple correction.
Location. The drainfield is supposed to be installed exactly where it is shown on the permit. Soil characteristics can change rapidly and a system located just a short distance from the area specified can require an entirely different design or be in unsuitable soils. Having said that, some flexibility is necessary in almost every instance. As a rule, if the system is located within 10 feet of the area specified and there are no significant changes in the soil characteristics and the system does not encroach on any setback distances, it is safe to conclude the system was located in accordance with the permit.
When the permitted location for a system is not suitable to the homeowner, the correct practice is to apply for a new permit. The theory is that it is best to find out if a site meets the Regulations before installing a system. Theory and reality don't always coincide. If a system has been substantially relocated and the builder/installer/homeowner is lucky, the soils will be suitable and the system design acceptable as installed or readily modifiable into an acceptable design. In this instance, a full site evaluation should be done and documented and submitted to the local health department with a new application and fee. This will make the specific system legal. The Department does not condone moving a drainfield without first modifying the existing permit or obtaining a new one. Enforcement action may be taken against the contractor (or other party as deemed appropriate) to assure future permit compliance.
If the builder/installer/homeowner relocated the system and the soils are unsuitable there is no obligation on the part of the AOSE or the Department to approve a system that does not comply with Regulations. In fact doing so may increase the liability exposure of either or both the AOSE and the Department. The better solution is to modify the system design or location such that it meets the regulations. This is a tough call to make but as the AOSE of record you are being asked to certify that a system was installed substantially in accordance with the Regulations and the design and location you specified. Determining what modifications may be necessary is difficult to discuss in abstract. Each case is different and what is appropriate in one instance may be completely inappropriate in another situation. The functional principle is the modifications must suffice to bring the system into compliance with the regulations and not just into compliance as fully as possible. The permit issued by the Department, regardless of whether the site evaluation was completed by the Department or an AOSE, was issued for a system that fully complied with the regulations and the homeowner deserves no less.
Depth. Installing a system at the wrong depth will likely mean that the perc rate used to design the system is not the same as the perc rate where the system was installed. Since systems are usually designed to be installed in the horizon with the fastest rate, changing the depth frequently means the system is undersized for the soils at the new installation depth. It may also mean that the system encroaches on a limiting factor in the soil. Correcting this error may be as simple as reevaluating the site to be sure the new installation depth complies with the regulations and submitting that information to the Department with your final inspection report. On the other hand it may mean additional absorption area is required or pretreatment is required or the system must be reinstalled. As a general rule systems are installed deeper than designed in order to get gravity fall from the house. Systems installed too deep tend to create more conflicts than systems installed too shallow because they encroach on a limiting factor. Once again, the functional principle is the permit revisions must bring the system into compliance with the regulations and not just into compliance as fully as possible.
Contour. The problems with a system installed off contour are both significant and often subtle. Generally, little can be done other than reinstall the system in a new location on contour.
When a discrepancy between the permit and the installation is discovered during an inspection the first determination should be does the installation fully comply with the regulations. Another way to answer this question is would you, the AOSE that recommended this site, have been willing to certify the system as meeting the Regulations to the health department as it is installed? If the answer is yes the next question is does the system substantially comply with the permit. If you as the inspecting AOSE decide that the system substantially complies with the Regulations, at a minimum an as built drawing (to scale) needs to be completed and filed with the health department. If the installation does not substantially comply with the Regulations, a new application and fee along with a complete AOSE site evaluation package needs to be completed and filed with the department.
Most of the remaining elements of the inspection lend themselves to ready corrections, if they are not correct at the time of inspection.
Septic Tank (see 12 VAC 5-610-810) - The tank must be constructed of an approved material. Concrete tanks are by far the most common but other materials have been approved (see GMPs #40, #55, #76, #77). The tank should be properly bedded, and if it is not a concrete tank it should be properly anchored to prevent floating, if located in soils subject to periodic saturation. The tank needs to be of the proper size and should be water tight. The inlet and outlet tees need to comply with the Regulations (see 12 VAC 5-610-810.C.3). When inspecting concrete tanks the exterior surfaces should be smooth free of spalling and with no rewire, rebar, or aggregate showing.
Gravity Conveyance System (12 VAC 5-610-850 through 890) - Gravity conveyance systems are the simplest and most commonly encountered conveyance system. Confirm that the proper material has bee used (1500 lb per foot crush strength) and that over disturbed soils (as would be encountered exiting a septic tank) the pipe is properly supported.
Distribution Box (12 VAC 5-610-930.C) - The distribution box is one of the more critical elements of the system. Distribution boxes are commonly either concrete or plastic. Plastic boxes always have a plastic weir (usually a plastic insert with an eccentric hole that can be rotated). Concrete boxes may have either plastic or concrete weirs (or dams). Distribution boxes should at a minimum be set on undisturbed soil, and preferably should be bedded on a gravel or concrete pad. The inlet should be an inch above the outlets and the outlets should be timed to provide equal distribution. When using concrete weirs be sure the concrete is firmly bonded to the box and that the cross sectional area of flow is equal (not just the elevation). As a rule, the plastic weir inserts are preferable. Distribution boxes must also be watertight.
Header Ditch (12 VAC 5-610-930.D) - When inspecting the header ditch make sure the pipe material is correct, there is at least 2 inches of fall per 100 feet, assure that there are no significant humps or dips, and that the joints are watertight. The materials need to be properly bedded. This is usually most important with semi-rigid pipe which may not maintain a 1500 lb per foot crush strength unless properly bedded. Check with the manufacturers recommendation if in doubt. The header line is to terminate two feet into the absorption trench.
Absorption Trenches (12 VAC 5-610-930.E) - Gravel trenches should be installed at the proper depth, on contour, with the minimum center-to-center separation distance specified on the permit. Check to be sure there is adequate gravel (13": six inches below, approx. 5" to cover pipe and 2 inches over pipe) and that the gravel is clean and free of fines. Excessive fines (a judgment call) reportedly can lead to premature failure. The percolation piping should have three holes, placed in 130 degree arc, facing down with line or spot opposite the center hole facing up and the piping should have a grade of 2-4 inches per 100 feet (be sure the grade is in the proper direction).