You hear this term thrown around a lot by Real Estate Agents, but what does it really mean?The purpose of the testing is to determine if the soils on a particular lot are suitable for an onlot septic system. If you see a lot that advertises "Lot passed perc," it doesn't necessarily mean that the lot is suitable for a septic system; there is much more to it.
First, know what you are getting yourself into when agreeing to have the testing done and pay for it, it can be costly, up to about $1200. First, application must be made to the local township; the applications are available from your local Sewage Enforcement Officer (SEO), or the Department of Environmental Protection (DEP). The township will typically have their own fees ranging from about $150-$300, to be submitted with the application. You will need to have some idea of how many bedrooms your new construction will have; it can always be changed at a later date, but that will cost you a few more bucks.
Once the township is in receipt of your application and fee, you're are ready to proceed with the first phase of the testing. You will need to contract an excavator who will typically call the SEO to schedule a "test pit," or "probe." The cost for the excavator will be in the range of $250-$300. The excavator will locate an area on the lot that is somewhat flat, and in a preferred location (typically they shoot for the rear of the lot). He then will dig a three foot deep pit for the SEO to jump into and evaluate the soils. He will look for indicators of the seasonal water table and determine how many inches of usable soil you have. The minimum for a standard above ground (sand mound), on lot septic system is 20" from the surface down. There are alternate systems that can be used if you have less than 20", but that tends to be a bit more costly in some cases. If the first pit fails, they will usually continue around the lot, digging two or three more pits for evaluation. You are not charged an additional fee for the extra pits.
Once the SEO determines that you have 20+" of usable soil, he will allow you to proceed with the perc test, not on that particular day, but at a later date. There is a fair amount of preparation that goes into conducting a perc test. In most cases the person or company you hire to do the test pit, will also schedule and conduct the perc test. The perc test will run between $250-$300. First they will go to the site and dig six perc holes, about 20" deep, in a 20'x40' area, within 10' feet of the test pit. They will put a measuring device into each hole. Then they will pump about 50 gallons of water from their truck to the site, into a 50 gallon barrel. Once that is done they can begin the pre-soak. They will fill the holes with water, and come back 24 hours later to conduct the perc test.
The next day, when they return (with more water), they will do a couple of more presoaks, and make a determination, based on how fast the water is soaking into the soil, of whether the testing will be done in 10 minute or 30 minute intervals. Then they fill the holes with 20" of water, and wait the allotted time, and take a measurement to determine how much the water has dropped, through absorption, into the soil. That measurement is then recorded on forms provided by the DEP. The field technician will repeat the soaking and recording until the ground is saturated and the measurement has not dropped more than a 1/4 inch over four readings. They will then calculate the results using a formula to determine if it passes, and to determine the size of the absorbtion area (sand mound). He or she, will then stake out that area, determine the slope of the area, take measurements to the corners and sidelines of the lot, and to the nearest well (which should be 100+" away). All of this information is then taken back to the office to be used to design the septic system, on paper. The sewage enforcement officer is present just to observe and make sure the test is done properly.
Once the design is complete, it is submitted to the township for review. The SEO will go to the site, with the design and make a determination that everything is correct. Only then will a septic permit be issued. Keep in mind that just because a lot advertises "passed perc," that does not mean that you will be issued a permit. I advise all my buyers to have that permit in hand before closing on the lot. Many people get as far as the perc and stop, believing that that is all they need; not true. The best advise I can give you is find a reputable company to do the testing, there are several out there, and go all the way...don't stop at the perc.