My Well Results

 After a delay because the lab was very busy and running behind on processing samples and prepping data, the Virginia Tech Extension Virginia Household Water Quality Program finally emailed the water test results from the water clinic.This is what I saw when I opened my attachment:

I was "Present" for Coliform bacteria, though everything else looked good. Oh my. The results meeting that evening listed the results for the 86 samples taken as:

I noticed in the electronic version of the presentation that the coliform PRESENT rate for Prince William County was nearly double what had been the previous four years. That in itself is suspicious, but not particularly meaningful since the distribution of households changes. However, my well tested positive with an MPN of 1.01/100 mg/L indicating that there is a very small amount of bacteria (about 1 per 100 ml of water).This could be an accidental cross contamination  or it could be in the source water, plumbing or on the faucet. I have no water treatment devices in my house so that was out. I wondered if the high percentage of homes with coliform PRESENT might be due to careless sampling because the instruction was virtual.

Normally, if my well had tested positive for coliform bacteria I would simply jump right to fixing the problem: methodically shock chlorinate the well (according to the procedure from VA Tech), repack the soil around the well pipe to flow away from the well and check and disinfect the well cap and replace as necessary. That is a lot of work for contamination that may have happened in taking or processing the sample. Standard protocol if a well tests PRESENT for coliform is:

1. Retest using proper sampling procedure and verify that E coli is tested for.
2. If the sample still tests positive for total coliform then treat the system with chlorine
3. Retest the water after the chlorine has left the system in about two to three weeks (make sure that the water tests negative for chlorine).
4. If your well water still tests positive for total coliform: Carefully check the well and water system for points of contamination. Make sure you have a sound and secure sanitary well cap and that the soil around the well is packed to drain water away from the well.
5. Then treat the well and plumbing system again making sure to disinfect any treatment equipment, replace filters, with chlorine for 12-24 hours to disinfect system (the 12-24 hours is essential). Then flush the chlorine from the system- not to your septic system. Make sure that this is done correctly.
6. Retest the water after the chlorine has left the system in about two weeks. If coliform bacteria is “ABSENT” you’re done. If not, then it is time to install a long term disinfection system. (UV light or continuous chlorination)

Usually, if the MPN is above 50-100 I would skip retesting.  However, a few months ago I had replaced the well pump, the wiring, the pressure tank, pressure switch and gauge and the well cap. This was a preplanned replacement and in two and a half hours the new pump was in the well with a couple of cups of high-test calcium hypochlorite to disinfect it, and new well cap in place. After that I waited for 24 hours for the well to settle and the chlorine to disinfect the well and then spent several days flushing the well. About three weeks later I had done a bacteria test to make sure that the well was free of bacteria and had even done a second confirmation testing in the middle of July after a series of rain storms. Both times my well tested absent of Coliform bacteria. So, this test result was very unexpected. Though I hate to think that I was the source of human error, taking a sample at 5:30 am I certainly could have been. The lab, too, could have been the source of cross contamination.

There could be other sources of minor Coliform contamination. From Penn State Extension we also know “Time of year and weather conditions can affect the occurrence and amount of coliform bacteria in wells. ....Since coliform bacteria like to live near the surface of the earth and prefer warm temperatures, it is reasonable that bacteria would be more likely to occur in groundwater wells during warmer, wetter weather conditions when surface water is recharging groundwater aquifers. Thus, the highest number of bacteria will be found by testing your well shortly after several weeks of rainy weather, while the fewest bacteria will be found when testing during dry, cold conditions in the winter. These variations in bacteria with season and weather conditions need to be considered when testing your water supply for bacteria.”

This failed test had been taken during a week that we had a several days of rain at the beginning of September. Our geology is fractured rock with very little overburden...still 1.01 MPN spoke more of accidental cross contamination. Since it had rained about two inches in the previous 48 hours, I went out and got a sample bottle from a certified laboratory and carefully took another sample.

The next day I had my results. Absent with MPN < 1. Still I was not happy, though I had chlorinated my well after the equipment was installed I had not disinfected the inside of the well cap and that nagged at me. Just to be sure,  after the next rain when the unseasonably cold of the past couple of weeks had passed, I took one more sample. Once more Absent with MPN < 1. I’m done. The well is fine and it only cost me $240 in testing in the past few months to know and accept that.