What is a site assessment?

In the past, many people simply did a "perc test" and with that they looked up the length of field required in a table supplied by the Health Department. Like many things these days a better understanding of the science behind the onsite sewage industry has altered our approach to the design of onsite sewage systems.

However, we know that many designers and planners do not do a proper perc test. In fact if the perc rate is in the order of 10 - 20 minutes, it will normally take 12 - 18 hours to do a perc test. If you leave the site and come back, you often find that you have " missed " the readings.

When CSSI started in this business like others we did the perc test. However we did the perc test according to the proper protocol. However, when Kelly was lying on the ground for almost two hours with a flashlight at 10:30 pm waiting to start the perc test when the water level passes the 6" mark. It was obvious that most people would not do this. People often skip or shorten the presoak period or the first complete drawdown phase of the test. The net result is that the perc test results are very often optimistic.

Now we do a site assessment rather than a perc test. We look at many factors, starting with determining the design sewage flow for the proposed system. To do this we have the client complete our Owner Declaration Form.

We then look at the site and consider some or all of the following: location of wells, fresh water supplies, breakout points, perimeter drains, property lines. We look at the vegetation and soils, equipment access, surface and groundwater intrusion, rock, distance of site from sand, gravel and topsoil supplies.

When we have completed the site assessment we have an understanding of what the constraints are and how severe they are. It may be an easy site or a challenging one.

The perc test has been banned as an unreliable test in many jurisdictions.

The permeameter test, in our view, is a more reliable and more repeatable test. Since we can do the permeameter test quickly, we run more tests. In the past people typically did two or three perc tests. We tend to do six or seven permeameter tests.