If you own a home with a private sewer system and the system fails the Title 5 inspection because of the leach field, it will require a new one. The next step is a Perc Test to determine the location, size, and type of system needed to replace the old system.
"Perc" test is short for a Percolation Test. The purpose of the Perc Test is to allow the fluid's safe distribution to dissipate into the ground preventing it from entering any water supply. To that end, it must also be placed over 100' from you and your neighbors well/water supply.
The Perc Test will require coordination between a Civil Engineer who will evaluate the soil, perform the test, and ultimately design the system, a Board of Health member serving that particular town to witness the test, and an excavator to dig the holes.
The first part of the test is to dig a deep hole(s) approx 10'. The BOH member will determine how many holes they will require. At that point, the Engineer will "read the soil" and record the soil type(s) and locate the seasonal high watermark. The BOH member and Engineer will determine if the leach field will be placed 2 or 4' above the seasonal high watermark depending on the soil and other code factors. That also will set the location for the actual "Perc Test".
They then dig a small hole large enough to hold 12' of water in that location, pour water into it, and "soak the hole" Once it is soaked, they will time the water as it absorbs back into the soil recording the results per inch. The Engineer will use this information and the soil type to determine the size and type of the leach field or leach pits needed to replace the old system.