A septic system must fit the soil, site and proposed home. Learn what testing can show, what still requires approval and which questions to ask before you buy.
A septic system is not simply a tank placed somewhere on the property. It is an onsite wastewater-treatment system that must fit the soil, slope, home size, well locations, property boundaries and current county requirements.
The tank receives wastewater and separates solids from liquid before the liquid moves to the dispersal area.
The dispersal area allows treated effluent to enter suitable soil through trenches or another approved design.
Testing helps determine the soil conditions, limiting layers and the type and size of system that may be considered.
A second suitable area is commonly protected for future replacement of the dispersal field.
The phrase is commonly used for the field investigation performed to evaluate whether the soil can accept and treat wastewater. Depending on the county and the site, the process may involve test holes, soil-profile observations, percolation testing, seasonal information or other technical review.
The county Environmental Health department should explain which procedure applies. A local septic designer, engineer, geologist, soil professional or licensed contractor may perform or coordinate the work, depending on the project and local requirements.
Before ordering new testing, ask Environmental Health whether the parcel already has septic records, an old perc test, an approved layout, a prior permit or nearby information. Old records may not satisfy current rules, but they can help you understand what has already been investigated.
A favorable soil evaluation is valuable, but a complete septic approval usually considers more than the test result. The proposed number of bedrooms, anticipated wastewater flow, tank size, system type, primary and reserve areas, setbacks, access for construction and maintenance, and the locations of wells, buildings and property lines may all matter.
Septic should therefore be reviewed together with Lesson 104: Understanding Property Maps, Lesson 105: Power, Water, Septic & Internet and Lesson 106: Zoning & Allowed Uses.
The primary area is where the initial dispersal field is installed. The reserve area is kept available in case the original field eventually needs replacement. Buyers sometimes focus only on whether one system can fit today, but the reserve area can be just as important.
Protect both areas. A future house, garage, pool, driveway, grading plan or well location can interfere with the approved primary or reserve area. Before choosing a building location, understand where the septic components and replacement area may need to go.
A conventional system generally uses a septic tank and gravity-fed dispersal trenches in suitable soil. It is often the simplest option when the parcel has appropriate soil, slope, depth and space.
When conventional criteria are not met, a site may require a specialized design, such as pressure distribution, a raised or shallow system, supplemental treatment or another approved approach. These systems can add design, installation, electrical, monitoring and maintenance requirements.
An engineered system is not automatically a reason to reject a property. It simply means the buyer should understand the design, expected cost, operation and ongoing maintenance before proceeding.
Some city lots and developed areas connect to public or community sewer and may not require a private septic system. See Lesson 105.
Ask for prior permits, soil tests, approved layouts, failures, repairs, well records and correspondence associated with the APN.
Show the likely home, driveway, well and accessory-building locations so the septic evaluation reflects the actual plan.
Ask whether it is conventional or engineered, how large it must be, where the primary and reserve areas are, and what maintenance may be required.
Request site-specific estimates for testing, design, permits, excavation, equipment, installation and any required electrical or monitoring components.
When septic feasibility is important, consider an appropriate investigation period or contingency with guidance from your real estate and legal professionals.
It is encouraging information, but soil and site conditions can change over short distances. Your parcel should be evaluated on its own facts.
No. A large parcel can still have steep slopes, shallow soil, drainage issues, wells, easements or other constraints. Usable area matters more than total acreage.
Yes, as background information. Ask the county whether it remains acceptable under current standards or whether new testing is required.
When septic is essential to the intended use, a site-specific estimate can help you compare the property with your total budget.
Everything in Land University is based on what I've learned over many years of buying, selling, developing and researching land in Northern California.
My goal is to help you understand the questions to ask and the issues to investigate before buying land. Every property is different, laws change and city or county requirements can vary.
I'm not an attorney, licensed land surveyor, engineer or city or county official. These lessons are practical education based on my experience, not legal, engineering, surveying or tax advice.
Please verify important information with the appropriate city or county departments and consult an attorney, licensed surveyor, engineer, CPA or other qualified professional when needed.
— Ken Grisham
The home site, well, driveway and septic areas should be considered together—not one at a time.
A parcel may have plenty of acreage and still require careful planning to fit the primary and reserve areas around the other improvements.
Send the APN, county and any existing perc, septic, soil or well information you have.
Ask a Land QuestionUse what you learned to review current opportunities, or ask a property-specific question before you make a decision.