Wastewater, Earthmoving, Erosion Control


Soil Percolation & Training


Percolation testing involves investigating the soils at a particular location and determining the site’s suitability for the disposal of wastewater or stormwater. A percolation test is always required for any new septic system (“individual wastewater disposal system” or “IWDS”), and is almost always required for earthmoving and erosion control (“One Start”) permit applications.

Why are percolation tests required?

Percolation tests provide critical information for the sizing of septic systems and stormwater “ponding basins” because those types of systems rely on the ability of soil to absorb water. If a percolation rate is just guessed at, or a contractor fails to notice restrictive soil conditions, the final result may be a system that fails 6 months after it is built, or a system that is built larger and more costly than necessary. Although the cost of a percolation test may seem like an unpleasant expenditure, it is far less than the cost of replacing a failed leaching field, or the construction of an over sized stormwater infiltration system.

How to obtain a percolation test

Starting in July 2007, DEQ began requiring that all percolation tests must be performed by qualified individuals. A qualified percolation tester is a person who has attended training provided by DEQ and passed an examination proving their knowledge of percolation testing procedures and basic soils information. If you are paying for a percolation test, make sure the tester has been authorized by DEQ first – they can show you a numbered certificate if you ask. For most single-family homes, only one percolation test pit is required. For other types of projects, three or more percolation test pits are required in order to obtain good results. Additionally, in certain types of soils a “deep observation pit” may need to be dug, in order for the percolation tester to obtain enough information to make their final design recommendations.

How can one become certified to perform percolation tests?

In order to be allowed to perform percolation tests for submittal with DEQ permit applications, one must first be able to show DEQ their ability to perform the test according to established procedures, and they must be able to pass an examination proving they fully understand the procedures and requirements. DEQ occasionally conducts workshops, which for the most part has resulted in the authorization of most companies and individuals advertising percolation testing services in the CNMI (as of September 26, 2007). Future workshops may be conducted as more requests are received for training, or as refreshers for those already certified. Call the DEQ Wastewater Earthmoving & erosion control Branch for more information regarding future workshop schedules. Self-study is also a way to obtain certification. The DEQ Reference Manual is available for free download by clicking the following link: CNMI Percolation Testing Manual and contains enough information, including a sample exam, to prepare for the exam. Depending on availability of staff, an interested person can schedule an examination at DEQ which would include taking the written examination with a passing grade pf 70 and above, as well as demonstrating proficiency at the actual test procedures.