Septic Perc - A Real Estate Industry Misconception

Septic “Perc”- aka Percolation Test, for septic development in Sonoma County

Whether a lender, real estate agent, buyer, underwriter, or seller, the statement that a property has an existing “perc” is tossed around everywhere in Sonoma County’s real estate industry. This is a big misconception, and an alarming one.

The word “perc” is slang for a septic system development related Percolation Test. A percolation test does not guarantee septic development potential for a property. Rather, it indicates the permeability (ability for water to pass through) of the soil in the tested area. The results of a percolation test in Sonoma County provide one critical design parameter for septic system design calculations and plans and in no way does it illustrate a number of bedroom potential. Again, it only indicates if the soil tested will pass water (and ultimately sewage) quickly or slowly and gives a Soil Application Rate to the person designing the septic system. A good rule of thumb: If the percolation test rates are fast, the septic system will be smaller in size than if the rates were slow.

So, if a “perc” does not guarantee if a property can have a septic system, then how can an interested party get a guarantee? The answer is simple, a guarantee can be provided by obtaining a septic system construction permit or a vesting certificate from the County of Sonoma. Septic permits and vesting certificates are valid for three years after issuance, and if not renewed will expire.

To reach a guarantee, by obtaining a permit or vesting certificate, takes several steps, one of which is a “perc”. A soil investigation with a County representative is the first step, followed conventionally by a percolation test, and a septic system design is the final step necessary to submit for a guaranteeing County entitlement. In some cases where the property is flat (less than 5% ground slope in the tested area) or in other rare conditions, there is a wet weather groundwater test that is also required to submit for a County septic permit or vesting certificate.

Unfortunately, going through the steps to obtain a guarantee will take anywhere from 4 months to over a year! This is way too long of a wait period to endure during a typical escrow. But there’s a hybrid approach to serving buyers and sellers that can be done in a number of days and still provide high levels of confidence and septic development insight.

Now, the good news is that not all real estate transactions need a guarantee, but rather a strong indication that septic suitable conditions and area exist at the subject property. This can typically be achieved by exploring the site’s soils with an excavator. This step is referred to as a soil investigation, or if performed with the County present, is called a Pre-Perc Site Evaluation. Preliminary sizing of a septic system can also be performed by a consultant such as BC Engineering Group to help in determining if the site’s septic area will be big enough to support the ultimate residential uses, for example number of bedrooms or homes desired on the site.

BC Engineering Group strongly encourages our clients to have a soil investigation done with our staff and an excavator before taking ownership of any property that will need septic system work to meet the client’s goals. Just by looking at the property and the sub-surface soils, we can confidently forecast whether the septic potential for the property is strong, marginal, or weak. If the confidence level for septic conditions is strong, clients can move forward with their transactions self-assured. If marginal or weak, we typically recommend that our clients perform additional steps in determining the septic development potential, such as taking the other steps as referenced in the fourth paragraph.

So, next time you hear that a property has an existing “perc” or you think about making such a statement yourself, remember that it only means that soil testing was done at the subject property to determine how fast water/sewage will move in the soil, not how big the septic system will be or how many bedrooms it will support.

To get more information on this topic, or to schedule septic development inspection work, please contact the professionals at BC Engineering Group at 707-542-4321 or online at www.bcengineeringgroup.com