Buying land: why you need a perc test contingency

Buying raw land without a perc test contingency is one of the easiest ways to end up with a lot you cannot build on the way you planned. A good contingency gives you time to verify that the property can support the septic system you need, that the local permitting office will approve it, and that the cost and timing still fit your budget and closing date. (epa.gov)

If the property is not served by public sewer, the local permitting agency usually has to evaluate the site and soils before a septic system can be approved. Because septic design depends on things like soil type, lot size, slope, weather, local rules, and setbacks, a land deal that looks simple on paper can turn complicated fast. (epa.gov)

A perc contingency is really a buildability contingency

People still say “perc test,” but many places now use a broader soil and site review instead of the old bucket-and-hole idea. Orange County, North Carolina says “perc test” is an antiquated term and says its older method was replaced in the mid-1970s with a comprehensive soil and site evaluation. Clallam County, Washington says that today, instead of a simple perc test, a soils profile evaluation and official site registration are required. (orangecountync.gov)

That matters for buyers because the real question is not just whether water drains through soil. The real question is whether the county or health department will sign off on a septic area for the house size and layout you want, with the required setbacks and any reserve area the rules call for. In other words, your contingency should protect the buildable use you are buying, not just the test itself. (epa.gov)

A smart contingency also protects you from vague seller language. A listing may say a lot has been “perked,” but Orange County warns buyers to be cautious about that claim unless a valid permit has actually been issued by the health department. That is a big difference. A casual statement from a seller is not the same as current approval from the office that regulates septic permits. (orangecountync.gov)

What can go wrong without one

First, the soil may not work for a standard system. Montgomery County, Maryland explains that if the water moves through the soil too fast, wastewater may not stay in the soil long enough for proper treatment. If the flow is too slow, the soil may not accept the wastewater fast enough, which can cause backups into the yard or building. (montgomerycountymd.gov)

Second, the water table can be the problem even when the surface looks dry. Montgomery County says the unsaturated soil between the bottom of the drainfield trench and the top of the water table provides treatment area, and if there is not at least about 4 feet of separation, untreated wastewater may reach groundwater and then water wells or streams and ponds. Clallam County also notes that a seasonal water table can limit development and may need wet-season observation. (montgomerycountymd.gov)

Third, the lot may simply be too constrained. Clallam County says some sites do not have deep enough soils, some have a shallow water table, and some do not have room for required setbacks, which can prevent septic permit approval. Montgomery County says a new building lot there must have an initial drainfield plus enough area for up to three reserve drainfields, and a typical single-family house needs at least 10,000 square feet for the initial and reserve fields. (clallamcountywa.gov)

That is why a perc contingency is not just a technical detail. It is protection against buying land that may be legally owned but practically unbuildable for your plan. Clallam County says soils evaluation for land division is meant to prevent the creation of lots that later turn out to be effectively “unbuildable.” (clallamcountywa.gov)

What to put in the contingency

Every state and contract form is different, so have your agent or attorney tailor the language to the property and local practice. Based on how official agencies handle septic approvals, a strong land contingency usually covers these points. (epa.gov)

1. Approval standard. Say exactly what has to happen for the contingency to be satisfied: a passing soil evaluation, an approved site registration, an improvement permit, or another named local approval. Do not rely on the words “percs” or “suitable soils” alone. (orangecountync.gov)
2. Enough time for the real process. Build in time for plan review, site visits, test-hole work, weather delays, and any wet-season requirements. In some places, water table work can only happen during a declared wet season. (assets.montgomerycountymd.gov)
3. The house and use you actually want. Tie the contingency to the planned bedroom count, footprint, and likely house location. Orange County says septic sizing is based on bedroom count, and a permit for a 3-bedroom home may need to be replaced if you want a 4- or 5-bedroom home. (orangecountync.gov)
4. Who pays for testing and design. Decide up front whether the buyer or seller pays for the evaluator, designer, excavator, county fees, and any redesign if the first layout does not work. (assets.montgomerycountymd.gov)
5. What happens if only an alternative system works. EPA says there are many conventional and alternative septic system types, and the right choice depends on site conditions and local rules. Your contingency should say whether you can walk away if only a costlier or higher-maintenance system is available. (epa.gov)
6. Clear exit and refund language. The contract should say what notice is required, when earnest money is returned, and whether you can extend the contingency if the county schedule or season causes delay. That is contract drafting, not a septic rule, but it is what makes the septic review useful in real life. (assets.montgomerycountymd.gov)

If you want help organizing the steps, start with What is a perc test?, Perc test vs. soil evaluation: what's the difference?, and The septic permit process, step by step. Those guides make it easier to match the contract language to the local process.

Timing matters more than buyers expect

A common mistake is giving the contingency too little time. Montgomery County’s testing guideline says water table testing must be done in a declared wet season, typically February 1 through April 15, and percolation tests must be supported by water table tests unless county staff already has enough data on record. It also says wet-season soils may only be tested during a declared wet season. (assets.montgomerycountymd.gov)

That means a land deal signed in late spring or summer may run into a calendar problem, not just a paperwork problem. Clallam County says a soils evaluation can be done any time of year, but if there is disagreement or uncertainty about a seasonal water table, the decision may be delayed until the site is observed through the winter months. (clallamcountywa.gov)

Old approvals can create timing traps too. Orange County says improvement permits and construction authorizations are valid for 5 years, and it is possible in some cases to get an improvement permit with no expiration if the application includes a plat with detailed site information. But the same county also says buyers should be cautious about claims that land has been “perked” unless a valid permit has been issued. (orangecountync.gov)

If you are early in the search, it helps to search your city, county or ZIP and read the local page before you make an offer. It is also smart to review When to schedule a perc test (and seasonal limits) so your contract dates line up with the season your county actually uses.

A pass is not the same as a permit

Even when a site looks promising, do not treat a favorable soils report as the same thing as final build approval. Clallam County says approval of an official site registration does not constitute approval of a future building or septic permit, and it does not grandfather the property for a specific system type in the future. (clallamcountywa.gov)

That point matters because your plans can change, rules can change, and the usable septic area can change. Clallam County says re-evaluation may be needed if conditions change, and grading, filling, logging, or excess stormwater can alter the original findings. (clallamcountywa.gov)

Orange County gives a practical example of why details matter: if a property has a permit for a 3-bedroom home and you want a 4- or 5-bedroom home, you need a new improvement permit and construction authorization to increase the septic system size. The county also says a typical 4-bedroom system and repair area will need about one-quarter to one-third of an acre of acceptable soil. (orangecountync.gov)

So if the seller says the lot already passed once, ask better questions. Passed for what bedroom count? Under what permit? On what date? Under current rules? Those are the questions that a good contingency gives you time to answer. (orangecountync.gov)

Costs and who does the work

Testing costs vary a lot by county, and they are not limited to one fee. In Cape May County, New Jersey, the published fee list shows $125 for a residential septic application and $125 for witnessing soil boring and a perc test. In Santa Clara County, California, the 2026 environmental health fee schedule lists $705 for site evaluation, $1,205 for a perc test performed by others for up to 6 holes, $3,014 for a perc test performed by county staff for up to 6 holes, and $200 for each additional hole on the same site visit. (capemaycountynj.gov)

Those examples are not national averages. They show why your contingency should address budget, not just pass or fail. One county may require a modest application fee, while another may involve multiple review, field, or wet-weather charges before you even get to system design. Santa Clara County’s same schedule also lists $754 for wet weather water testing or deep boring. (files.santaclaracounty.gov)

The work itself may also require licensed professionals. Montgomery County’s guideline says the test plan preparer must be registered with the Maryland State Board of On-Site Wastewater Professionals, and it says that, effective January 1, 2023, the law requires an individual who provides an on-site wastewater service to be licensed by that board. In short, a buyer often needs more than a shovel and a free afternoon. (assets.montgomerycountymd.gov)

For a fuller budget picture, see Failed a perc test? Your options. If poor soil means an alternative design is possible, the cost and maintenance picture can change quickly.

If the site is marginal or the test fails

A failed or marginal result does not always mean the deal is dead. EPA says there are many conventional and alternative septic systems, and some are designed for high groundwater, shallow soil, small lots, or other difficult site conditions. But EPA also says system choice depends on factors like soil type, lot size, weather, proximity to sensitive water bodies, and local regulations. (epa.gov)

That means the next question is not simply, “Can anything be built here?” It is, “Can the site support a legal system that fits the house, budget, maintenance level, and financing plan?” Before you waive or shorten any contingency, confirm the current rules with the county health, environmental health, or permitting office for the property. You can also browse /states for state-by-state pages if you are comparing rules across multiple areas. (epa.gov)

Frequently asked questions

Is a perc test the same as a septic permit?

No. In many places, the old idea of a simple perc test has been replaced by a broader soil and site review. Clallam County says site registration is typically the first step toward a septic permit, not the permit itself, and Orange County says a valid permit is what matters when someone claims land has been “perked.” (clallamcountywa.gov)

How long should a perc test contingency last?

There is no one national number. The right time period depends on local review steps and seasonality. For example, Montgomery County says water table testing is typically done during the declared wet season from February 1 through April 15, and some wet-season soils may only be tested during that period. (assets.montgomerycountymd.gov)

Can I rely on an old permit or old test result?

Maybe, but only after checking the current status with the local office. Orange County says improvement permits and construction authorizations are valid for 5 years, while Clallam County says an approved official site registration is not the same as approval for a future building or septic permit and may need re-evaluation if conditions change. (orangecountync.gov)

Who usually regulates perc tests and septic site approvals?

Usually the county or local permitting agency does. EPA says that under most regulatory programs, the local permitting agency conducts the site assessment to decide whether soils can provide adequate treatment and to apply setback rules. (epa.gov)