Short answer
It can happen, though a fence post doesn't cause one. Oley and Exeter sit on limestone and dolomite, and Berks County's planning documents say parts of Oley have many surface depressions and sinkholes. DCNR says stormwater and leaking water lines speed sinkholes up. For a fence, that means keeping downspouts and runoff away from the post line, checking DCNR's PaGEODE map before a long run, and watching for posts that drop or lean after heavy rain.
Why this valley is sinkhole country
The joint natural resources plan for Oley, Alsace and Ruscombmanor describes Ordovician dolomite and limestone running through central Oley, and Cambrian dolomite and limestone along the township's east and northeast edges. It says the Cambrian limestone "has many surface depressions and sinkholes." The same plan notes that Oley has more Class I farm soils than any other municipality in Berks County, so this is good ground that needs some respect.
Statewide, about 7 percent of Pennsylvania sits on sinkhole-prone karst, and state surveys have mapped swaths of it in Berks, Montgomery, Chester and Lehigh counties. Exeter Township knows this well. A sinkhole opened in front of the Lowe's at Exeter Commons in summer 2010, about a year after the center opened, and a later one swallowed part of the parking lot.
What actually triggers a sinkhole
The Department of Conservation and Natural Resources explains that sinkholes form where water dissolves limestone and dolostone underground, and that concentrated stormwater and poorly maintained water lines speed the process up. A fence post with a bag or two of concrete is a small, light load and doesn't cause one. What can matter is the water around it:
- Downspouts or sump lines that discharge right at the fence line
- A swale or low spot where runoff collects along the fence
- A leaking irrigation line, water service or pool line near the posts
- Regrading that sends more water toward one corner of the yard than before
Warning signs along a fence line
| What you see | What it may mean |
|---|---|
| A post that has dropped or tilted after heavy rain | Soil washing out from beneath the footing |
| A new circular dip or crack in the lawn near a post | Possible subsidence; keep people and pets off it |
| Puddles that used to sit and now vanish fast | Water finding a path underground |
| A gate that suddenly sags or won't latch | Movement at the hinge post |
Not every leaning post is a sinkhole. Frost heave and rot cause plenty of them. But in Oley or Exeter, a post that drops straight down rather than leaning over is worth a closer look. DCNR's Bureau of Geological Survey takes questions at 717-702-2017, and for anything near a house, driveway or utility line, call a geotechnical engineer before you fill or repair it.
How we plan a fence on karst ground
- We look up the lot in DCNR's PaGEODE viewer, which maps known karst features, before we lay out a long run.
- We ask where downspouts, sump lines and septic components are, and we keep posts out of the path of concentrated runoff.
- If a post hole opens into a void or soft pocket, we stop, move the post and span the gap with the rail or panel rather than pouring concrete into a hole we can't see the bottom of.
- We favor materials that tolerate small adjustments, like split rail, post-and-board and aluminum, on lines that cross known depressions.
Permits still apply
Exeter Township requires a zoning permit for permanent fences, with a to-scale lot map showing the fence location and lot-line dimensions (§390-83A). If you know of a sinkhole or depression on the lot, mark it on that map. We haven't verified Oley Township's fence rules from its code, so we confirm them with the township for each job. If your property has a history of sinkholes, mention it when you book the estimate.
Common questions
Does my homeowners insurance cover sinkhole damage to a fence?
Coverage for sinkholes and earth movement varies a lot between policies. Read your policy or ask your agent. We can document the damage for your claim.
Should I fill a hole that opened under a fence post myself?
Not without advice. DCNR's guidance and a geotechnical engineer can tell you how to repair a sinkhole properly. Dumping soil or concrete into it can hide a problem that keeps growing.
Is the Exeter Commons sinkhole near homes?
Exeter Commons is a shopping center. It shows the ground in the township is prone to sinkholes, not that a given yard will get one. PaGEODE shows mapped features near your address.