Bacteria and UV disinfection for Pennsylvania wells
A coliform-positive test on a Pennsylvania well usually means one thing: surface water is getting in. The lasting fix is two moves, close the pathway and disinfect continuously, and an ultraviolet (UV) system is the standard second half. This page explains the result, the technology, and what a contractor should check before quoting; the quote itself is free for homeowners statewide, from the Lancaster, York, and Berks corridor out.
Why bacteria is the Pennsylvania well problem
Total coliform shows up in 35 percent of tested Pennsylvania wells and E. coli in 15 percent, per Penn State Extension, the highest-occurrence health-related failure in the state. The cause is structural. Pennsylvania sets no statewide well construction standards, per the Pennsylvania DEP, so hundreds of thousands of wells were drilled with whatever casing depth, grouting, and cap the driller chose. Wells with shallow or ungrouted casings, buried well caps, or pits collect surface runoff, and every rainstorm re-inoculates the water. Coliform itself is an indicator group; its presence says the barrier between surface and aquifer has failed. E. coli present is the more serious line: it indicates fecal contamination, and drinking untreated water carrying it can cause gastrointestinal illness, per Penn State Extension.
Reading your result
- Total coliform absent, E. coli absent: passing. Retest annually; this is the one test Penn State Extension recommends every year for every well.
- Total coliform present, E. coli absent: the well is open to surface influence. Confirm with a retest, walk the wellhead, and plan continuous disinfection.
- E. coli present: use boiled or bottled water for drinking and cooking now, then retest and treat. Do not wait on this one.
Shock chlorination: the stopgap, not the fix
Shock chlorination, dosing the well and plumbing with chlorine and flushing it through, is cheap and sometimes appropriate: after a new pump, a repair, or a one-time contamination event with a known cause. What it cannot do is stay in the water. If the entry pathway is still open, the next positive is a matter of weeks, which is exactly the cycle many corridor well owners know by heart: shock, pass, fail again by fall. The full comparison, including the narrow cases where chlorination alone is the right call, is in the UV system vs shock chlorination guide.
How a UV system actually works
A point-of-entry UV system sits where the water line enters the house. Water passes a quartz sleeve surrounding a UV-C lamp, and the light dose inactivates bacteria, viruses, and protozoa by disrupting their DNA; systems certified under NSF/ANSI 55 Class A are rated for exactly this disinfection duty. No chemicals enter the water, nothing changes the taste, and operating cost is a lamp change roughly once a year plus a small electric draw.
The engineering caveats decide whether it works in practice. The lamp only treats water it can shine through, so sediment prefiltration (typically five micron) is standard, and water high in iron, manganese, or hardness needs those addressed upstream or the sleeve fouls; that is how a bacteria problem becomes a whole-house treatment train on many Pennsylvania reports. Sizing is by peak flow, so the unit keeps its dose when two showers and the washer run at once.
What a UV quote should cover
- Inspect the wellhead: cap, casing height, grade, and any pit, because treating the symptom without the pathway wastes your money.
- Read the full lab report, not just the bacteria line: iron, hardness, and turbidity change the system design.
- Size the UV unit to measured peak flow and specify NSF/ANSI 55 certified equipment.
- Arrange a post-installation retest through a DEP-accredited lab so the fix is proven on paper, the same paper that failed you in the first place.
Bacteria pressure is statewide, and the agricultural corridor sees it constantly; the Lancaster and York county pages carry the local groundwater context. Whatever county you are in, start from the result: the Pennsylvania well test guide covers every band on the report, and the quote form takes the numbers from there.