In 2011, we were asked what a hydraulic load test is and what kind of information it might provide. At about the same time, the National Association of Wastewater Technicians (NAWT) education committee took up the task of writing a draft standard that could be used to define the test.

This work was done as a result of questions that arose over a test we have long talked about as a part of system inspections. The concept was incorporated into the NAWT inspection program for point-of-sale real estate inspections where the level of inspections is gauged at an operational level. In our view, this level of inspection ensures that all pieces of the system are in place, are in good condition, and are operating the way they were intended.

What about vacant homes?

A number of questions started to arise around inspecting vacant houses and evaluating the systems, sometimes after yearlong vacancies. Due to the economy and the number of foreclosures, such systems have made up a large share of those inspected during the last couple of years. Given the responses over the past year, it is hard to think everyone conducting inspections will reach a consensus on what the hydraulic load test should be, much less uniformly incorporate the information into a set of requirements.

However, in the spirit of keeping the discussion current, and to the extent that the procedures discussed can help some service providers and others conducting inspections, we will discuss two types of tests at the operational level and highlight some outstanding issues. We would suggest readers either respond through Onsite Installer magazine or go to www.nawt.org and join the discussion.

Operation test

An operation test is conducted only on systems that are currently being used. The test as we have used it for inspections is designed first of all to make sure all of the connections in the system are taking the wastewater from the house to the tank.

To that end, we recommend that the toilets be flushed and all spigots run to verify that their outputs flow into the treatment tank. This may or may not involve the use of dyes to verify the connections. If all the water is delivered to the tank, the rest of the test can proceed; if not, there is some additional locating work to be done to identify where the water is going.

To conduct the rest of the test, water should be introduced into the tank at 3 to 4 gpm for 20 to 30 minutes. This amounts to one spigot opened, or the water can be delivered using a water meter on the end of a hose. The water level is then observed in the tank. If the level does not rise and the water moves to the next system component, the system is operating as it should.

If water backs up and the level of water rises in the tank; then further investigation is needed to determine why it is backing up, because there should be no backups in a properly operating system. Once the operation test has been performed, the tank can be pumped out to determine whether it is in sound condition and watertight.

Hydraulic load test

The following excerpts explaining the use of the hydraulic load test are taken from the draft procedure:

A hydraulic load test should be performed when, during the course of a point-of-sale inspection, building or remodel permit application, or system evaluation for maintenance contract considerations, the following findings occur:

The structure has been vacant for more than seven days.

The pretreatment tank has been pumped and cleaned in the past 30 days.

Previously diverted or new graywater sources have been introduced to the system.

There has been any type of soil treatment area remediation within the past 30 days (e.g. chemical additives, soil fracturing, root removal).

Initial inspection reveals that, for whatever reason, the pretreatment tank's liquid level is below the outlet pipe. (The reason for this is that if the tank is leaking, then the soil around the tank is providing additional infiltration area to the field.)

Repairs to the soil treatment area have been made (e.g. crushed outlet line, fouled or damaged distribution box).

A seepage pit has received less than the average daily flow during the previous 24 hours.

The inspector learns of any significant changes to the use of the system (e.g. increased occupancy, vacations, or other changes that may affect the system).

A note here: We do not like to see seepage pits as a part of standards because we feel those systems should be considered failing and unacceptable. However, the fact is there are still lots of these systems out there in different parts of the country.

A hydraulic load test should not be performed if these conditions are present:

The soil treatment area has been in use less than six months (new systems have no biomat to control effluent flow).

There are any signs of soil treatment area failure (e.g. fully saturated trenches or beds based on inspection port observation, surfacing effluent, hydrophilic vegetation at the surface).

Test basics

The test itself involves introducing a specified volume of water downstream from the septic tank to the soil treatment unit. The evaluation includes observing whether water flows back into the tank, surfaces in the yard, or is accepted by the soil.

The first two findings clearly indicate problems with the system. The water is usually introduced using a hose from an outside sillcock connected to a water meter to determine the amount of water delivered at the outlet of the septic tank.

One major area of discussion and disagreement about the test is what volume of water should be added. We hear a variety of opinions on this issue. Some suggest using the average daily flow. Others say to open up all the faucets in the house and let them run for an hour.

Before a hydraulic load test is performed, based on ponding in the soil treatment area, the inspector should determine if there has been heavy use that has been normal in the operation of the system, such as many laundry loads in a single day. If there has been heavy use in the last 24 hours, the inspector should suspend the inspection and load test and return the following day to observe the soil treatment area again, to determine if the ponding has subsided.

Alternate procedure: Instead of a hydraulic load test, the soil treatment area can be reinspected if the inspector verifies that the structure has been either fully occupied (maximum design) for one week, or has been partially occupied full-time for 30 days. In either case, the installation of inspection ports for monitoring is required.

Review the procedure

The complete recommended procedure for performing a hydraulic load test is available at www.nawt.org. We would appreciate feedback on it. We also want to hear from those who have run tests similar to this about where they have been conducted, why, and the results. In future articles, we will report on the comments and give our take on them.