BY ROGER E. MACHMEIER, PH.D., P.E.
PROFESSOR EMERITUS, UNIVERSITY OF MINNESOTA

Why an inspection?

The purpose of an inspection is to evaluate the present and future performance of an existing onsite sewage treatment system. It is likely that an inspection cannot show the true present condition of all parts of the system. The inspection certificate might state that the onsite sewage treatment system has been inspected and found to be in "satisfactory working condition" and apparently not in violation of any local sanitary codes. The definition of "satisfactory working condition" must be clearly defined and understood by all concerned parties. The provisions of the local sanitary code must be thoroughly known by the inspector.

The toilets may flush, all the drains may work with no back up, but the inside-the-house conditions say little about the condition of the onsite sewage treatment system. There may be no evidence of sewage surfacing in the area of the drainfield, but this doesn't mean that the drainfield is not full and at maximum capacity. A greater daily water use may cause a sewage back up or surfacing on the lawn.

The fact that the septic system appears to be in working condition at the present time is definitely not a warranty or guarantee that the system will continue to function properly for any given period of time in the future. This point must be carefully and fully explained to all interested parties. The average daily capacity of the system has been established by previous construction procedures and previous maintenance of the septic system. The average daily water use and future maintenance cannot be controlled by the person who inspects and issues a certificate of inspection of the system.

Inspection is for whom?

There are a number of parties vitally interested in the results of an inspection of the onsite sewage treatment system. They are the buyer, the seller, the real estate agent, the lending agency, and the local unit of government. They all have slightly different interests. The seller wants a clean bill of health for the sewage treatment system since "We never had a problem with it!" The prospective buyer wants the house but "Never wants to have a problem with the sewage system!" The lender wants the deal to go through as quickly and as smoothly as possible with no future problems. The real estate agent is interested in a commission as soon as possible. The local unit of government wants to know if the onsite system is up to the current standards and is not a public nuisance or health hazard. The inspector must prepare a report that will provide some answer to all the questions that might be raised.

An educational program about the operation of an onsite sewage treatment system along with inspection procedures and results is clearly needed. Some of the interested parties likely are not familiar with the operation and maintenance of an onsite sewage treatment system. The prospective owner certainly should be. And if the system doesn't work, that education will begin in a hurry.

"Bury it and forget it" is unfortunately too common a practice with onsite sewage treatment systems. The onsite professional should know that without frequent cleaning of the septic tank, solids will wash out of the tank into the drainfield. The amount of solids in the drainfield may range from negligible to nearly full. Certainly a drainfield with only a few solids will perform better and longer than a drainfield that is nearly full of solids. "The toilet still flushes good!" is a common evaluation of the onsite sewage treatment system. But, the prospective buyer wants to know for how long and the inspector is expected to provide that information.

Can any drainfield handle any amount of waste water that may be discharged into it? Absolutely not! Every soil absorption system has a maximum capacity, which when exceeded will result in a problem. Sewage will either back up in the basement or surface at the soil absorption unit. Which one happens depends on the relative elevation of the house and the drainfield.

What was the estimated water use of the present owners? What is the estimated water use of the prospective purchasers? What will happen to the system if the water use increases by double or more? Seller, buyer, lender, and agent had all better be well informed on what the amount of waste water means to the operation of an onsite sewage treatment system. It is the inspector's duty to clearly inform them, preferably in writing, so there is less chance of a misunderstanding.

Some questions that may need answers are:

• How thoroughly can the system be inspected without doing harm?
• What time of the year is the inspection being conducted?
• Has it been dry or has there been a prolonged wet spell?
• What would a new onsite sewage treatment system cost?
• Is there room on the lot for a new system?
• If the seller is sure that the present onsite system is adequate, would they be willing to put dollars in escrow as a guarantee?
• What will happen to the onsite system if the buyer moves in and uses extra large volumes of water?
• Could a water meter be installed for a period of time before the seller moves out?

The projected performance of the onsite system could be related to this water use. If the buyer is not willing to be restricted to such use, other provisions will need to be made.

As an example, let's say that two people have occupied the house now up for sale for 15 years. The onsite system is likely treating at least 150 gallons per day. The septic tank has been cleaned regularly and the present occupants have never had any sewage back up or surfacing. The buyers are a family of six &emdash; mom and dad, and four teenagers. The odds are very good that this family will use considerably more water than 150 gallons per day. Will the existing system handle more than 150 gallons per day? If so, how much more? How can one predict? If the system backs up or surfaces soon after the new family moves in, whose fault is it? Does the seller have the responsibility to provide an onsite system large enough for the water use of any buyer?

Serious questions that need to be answered to predict the capacity and life of an onsite sewage treatment system are:

1.How old is the onsite system? What month and year was it installed? (The month would tell something about possible soil moisture conditions and smearing during installation of the system.)

2.Is the sewage tank a septic tank or an aerobic tank? If aerobic, determine the name of the manufacturer.

3.What is the liquid volume of the septic tank?

4.How frequently have the solids been removed from the septic tank? What has been the cleaning schedule since the tank was new?

5.What type of tank cleaning procedure was used?

6.What was the average sewage flow in gallons per day?

• a.Water meter readings or;
• b.An estimate based on number and age of occupants, and number and type of water-using appliances.

7. What is the construction and layout of the drainfield?

• Seepage pit or pits
• Seepage bed
• Sewage treatment mound
• Drainfield trenches with distribution box
• Drainfield trenches with drop boxes

8. Has the drainfield ever been repaired or added to?

9. What is the size of the drainfield; i.e., area of drainfield rock?

10. Are there inspection pipes to measure the liquid level in the drainfield or parts of the drainfield?

11. What is the liquid level in the drainfield?

12. How much of the drainfield has liquid ponded in it?

13. How much sludge from the septic tank has washed out of the septic tank into the drainfield?

14. What is the predicted average capacity of the drainfield to treat septic tank effluent, measured in gallons per day, for the next 10 years or longer?

15. What assurances can the inspector give that the answers are correct and the predictions of future performance accurate?

16. Does the inspector have liability insurance in the remote event that the predictions are incorrect or misinterpreted?

General information needed:

• Date that the system was installed; age of the system.
• Permit issued by local unit of government; get a copy.
• As-built plans available? Get a copy.
• How many people used the system; ages. (This is important for predicting water use.)
• Was a garbage disposal used? Is one installed in the house?
• Estimate the average daily sewage flow by the residents.
• Was the laundry done in town at the laundromat?
• Water using appliances; water softener; iron filter; automatic washer; dishwasher; whirlpool bath; spa; etc.
• Septic tank cleaning frequency?
• Who did it?
• Are they reputable and do a good job?
• Is the house currently occupied?
• Do all the toilets flush and all the drains work? What information does this give?