My Well Test Results

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:

 

Coliform bacteria was found present. Total coliform bacteria is called an indicator bacteria. They are  found on the ground surface and in surface water, generally do not cause disease. They are indicators of the possible presence of disease bacteria, and if found, point to the need for additional testing  for E. coli ,which was not found. Total coliform (and E. coli bacteria) results also include “MPN”, or “most probable number”, which is a statistical estimation of how many bacteria were found in 100 mL of sample. This number can range from < 1 (Absent)  to greater than  2,419, which is represented as “>2419” or “too numerous to count”. The MPN can give an idea of the extent of contamination of a water supply, but, ideally, no bacteria should be present. My MPN was 1.01.

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, a result of all the rain,  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.

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)

If the MPN is above 50-100 I would skip retesting and 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.

Though I hate to think that I was the source of human error, taking a sample at 4:30 am I certainly could have been. The aerator or  lab, too, could have been the source of cross contamination.

There could be other sources of minor Coliform contamination and these are beginning to worry me. 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 two week period where we had several days of rain. Our geology is fractured rock with very little overburden...still 1.01 MPN spoke more of accidental cross contamination, but this is the second time in 4 years that I got this result. I always worry that with a fractured rock system we a susceptible to contamination. Over the weekend I went out and got a sample bottle from a certified laboratory and will carefully clean the spouts and take  another sample this week. If it is positive, I will chlorinate this month, if negative, I will think about it, maybe test the well for coliform bacteria quarterly and track it more closely. It is, after all, my family’s water supply.