At most of the 21 Butler County towns on our map, the logs reach bedrock at a median of 12 to 20 feet, then keep going: town median well depths run from 105 feet around Harrisville to 184 around Portersville.
From 105 feet at Harrisville to 184
Portersville (184 feet), Callery and Harmony (175 each), and Evans City and Zelienople (170 each) have the deepest town medians in the logs. Harrisville (105), Slippery Rock (120) and Saxonburg (126) have the shallowest. The USGS county record of 324 wells puts its middle half between 76 and 193 feet.
Median yields range from 6 gallons a minute around Harmony and Zelienople, 9 around Evans City and 10 around Callery, Mars and Valencia, up to 20 around Chicora, Harrisville, Karns City, Petrolia, Saxonburg, Slippery Rock and West Liberty. A deep well with a modest yield needs the submersible pump and the pressure tank matched to it, and depth is one of the things behind the price of a new well.
Allegheny and Glenshaw, close to the surface
Only two rock units are mapped at the 21 town centers: the Allegheny Formation at 13 and the Glenshaw Formation at eight, among them Callery, Evans City, Mars, Prospect and Valencia. Depth to bedrock in the logs is a median 12 feet around Butler, Cherry Valley, East Butler, Eau Claire and Saxonburg, and 14 to 20 around all the rest except West Liberty (25), Harrisville (33) and Slippery Rock (35).
Around Butler itself, the logs reach rock at a median 12 feet against a median well depth of 158. Before a new well, the logs nearest the property are the best preview of that pattern; on an older well, a well inspection is the place to start, and pump repair comes from the same crew.
Public systems at 12 of 21 towns
Twelve of the 21 towns sit inside a public system on EPA's map. Pennsylvania American Water's Butler system, serving 43,286 people from Oneida Reservoir, Thorn Run Reservoir and the Allegheny River, covers Butler, Connoquenessing, East Butler and Saxonburg. Harmony's system draws its own surface water, and Chicora, Mars and Slippery Rock pump groundwater. Evans City, Petrolia, Valencia and Zelienople are on purchased water.
The other 10, Portersville and Prospect among them, have no system on that map, which doesn't mean no home there is connected; a home on a public line gets its report from the utility. The Butler County treatment page covers what these systems do to their water.
Source: Water quality: USGS National Water Information System results for Butler County wells, served through the Water Quality Portal, sampled between 1926 and 1997, retrieved 2026-09-14. Each well counts once, as the median of its samples. The 0.3 mg/L iron and 0.05 mg/L manganese marks are EPA secondary standards, which are aesthetic limits, not health limits. Well depth: USGS groundwater site inventory for Butler County, 324 wells with a recorded depth, retrieved 2026-09-14.
