What are Septic Perc Rates, Septic Layouts & Septic Asbuilts?

What are Septic Perc Rates Septic Layouts & Septic Asbuilts

Today we are going to cover septic systems. We’re going to talk about septic layouts, percolation rates, and septic as-built. These pertain to purchasing land and affect the build process in different ways.

Percolation Rates

If you’re looking to buy a piece of land that’s never had anything built on it, you want to find out if a perc test has ever been completed. The percolation rate measures in inches per minute the time in which it takes for liquid to recess into the ground. The septic engineer will drill a hole to fill with water. The time it takes for the water to recede and soak into the ground is your percolation rate. The faster the water level drops, the better the percolation rate. The minutes means that the septic system can be smaller because the smaller system will leach the same amount as a larger system with a higher perc rate. Those are the basics of percolation rates.

Alternate Perc Rate Labeling

There’s one other method that can be used to label a perc rate. Let’s say a piece of property has been subdivided from the other legal lots, and the surrounding lots have been developed. That particular property that you’re buying may not have a previously recorded perc test. With the County of San Diego, often you can contact them during the septic layout process and explain that the surrounding properties, with similar soils, have had perc tests completed. The County will look at what the perc rates were on the adjoining properties around yours, and they’ll use the worst-case perc rate for your property. Say one lot was 40 minutes and another was 20 minutes, they will label your lot as the 40 minute and allow you to move forward without having to pay for a percolation test.

Percolation tests may cost about $3,500, so it may or may not make sense depending on the system that you’re putting in. Regardless, this is one option to avoid needing a perc test.

Types of Septic Systems

Now, there are different septic system types such as standard systems, seepage pits, and there’s an alternative septic system which is used in the event of potentially high groundwater. Let’s say the perc test identifies that the groundwater is not very far below the surface. There must be a separation between the groundwater and the effluent that exits the septic system. In this case, an alternative system is required and can significantly affect the cost. Alternative systems cost a lot more than standard septic systems.

Costs Between Septic Layouts

A standard system typically costs between $10,000 to $15,000. An alternative system can cost somewhere between $30,000 to $45,000 depending on the amount of square footage that you’re required to have for that alternative system. The percolation rate affects the size and once we know what that is, we can draw up what we call a Septic Layout. Now, this pertains to property that has not been developed. The septic layout design can occur while your plans are being processed for permits at the County or City, but the layout must be completed to get a permit issued to build. You will pull the permit at the same time as the septic permit if the septic layout is not approved before pulling the permit.

The Process

The process to get a septic layout is essential to begin before you start working on the building permit. The septic layout is drawn on an 11 x 17 sheet of paper. It is a small site plan that identifies anything that can impact a septic system such as property boundaries, easements, location of the home, and any areas that have or need grading. The septic system cannot go in an area that has been impacted by grading. The County or City wants the septic to sit in the natural soils. After identifying where the house pad location is, which requires grading, then we’re going to draw where the primary septic system goes and where the reserve area goes. Standard and alternative systems require one hundred percent reserve area. Keep in mind, however, that standard systems typically take up a lot more space than alternative systems.

Submitting the Layout

Once the septic layout is drawn, it is then submitted to the Department of Environmental Health. If they want some changes made, they will recommend alterations, if they like the original layout, they will approve it. The biggest impact on the size of the system is the number of bedrooms. Bathrooms do not matter, neither does the size of the home, but the number of bedrooms will determine the size of the septic system, such as length of leach lines and tank size. A four-bedroom home requires more leach lines than a three-bedroom home.

Occasionally when the lot is approved for a three-bedroom, they’ll let a four-bedroom go. They might say, “Yeah, well, you’re a three-bedroom at this perc rate with a hundred lineal feet of leach lines,” Even though the lot was initially perc tested for a three-bedroom home, if there’s no problem build a one-bedroom home, they will allow it, but that doesn’t always occur if you’re limited on space. So, if you run out of space for your primary septic system and your reserve, then this may not be an option. The lot could be limited to a two or three-bedroom house, or some of the ADUs that we’re building because the lot is limited to one-bedroom due to the available space on the lot. It is important to remember that adding an extra bedroom requires an extra leach field.

The As-Built

A septic as-built is different from a layout. The septic layout refers to what will be installed. An as-built refers to what currently, or previously, exists on this property. The septic contractor or general contractor is responsible to draw up a septic as-built that identifies what has been installed. Often, it’s the same as the septic layout, but sometimes something unforeseen may come up, such as hitting rock, and you must move the system, or maybe one line is made longer than what was originally shown on the layout. The exact lineal footage of each leach line in the leach field is drawn on the plan as-built. So, the plans drawn as it was built, that’s what an as-built is. The layout is prior to the work actually being done.

Sometimes, a property exists that had a previous home, which may have been torn down or burned down. When you’re buying land that had a prior home on the property, you can pull up the septic as-built from the county records to see what is currently installed and where it was installed on the property. This helps future owners as it should identify the location of the septic tank, tightline, and where the entire leach field is. Particularly with older properties, the as-built is not always exact, but it gives a starting point on where to find that system.

All right, so that is septic systems, perc tests, the difference between septic layouts and as-builts. If you have more questions, you can visit our website at www.freemansconstruction.com. You can download a ton of information on buying land, building custom homes, remodeling homes, and building ADUs. Thank you for your time and have a great rest of your day.

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