General Contact Number: (530) 621-5567

Environmental Health

Water Well Disinfection

Before disinfection, read through all instructions and call this office at 530-621-5300 if you have any questions.

Examine well head for missing bolts, open holes, casing cracks, etc. Take all steps necessary to completely seal off possible contamination entrance points. A screened, sanitary well vent is recommended. If a rope hole exists, tie off the pump rope under the sanitary well cap on an inverted eye bolt. Check surrounding area to make sure drainage is sloped away from the well.

Add chlorine (household liquid bleach) to the well at an opening (normally covered) dedicated for this purpose. The chlorine is added between the casing and the center pump drop pipe. If no accessible opening exists, contact a professional pump contractor/well driller for retrofit.

Amount of chlorine to use = 1 quart bleach to every 100 gallons of water:
(Depth of well - static level) x 1.5 gallons per foot = gallons of water in the well

Wait for 30 minutes, then surge the well (to mix) by opening and closing nearest faucet/hose bib. Repeat the surging 3-5 times, pausing between surges to minimize stress on the pump.

Starting with the closest faucet/hose bib to the well, one at a time, open every tap in the water piping system until the chlorine odor is detected, then shut off tap and open the next. Continue throughout the system (both inside and outside faucet/hose bibs) until all piping/plumbing has been in contact with the chlorine, including flushing toilets, running showers, etc.

Let stand overnight or at least 12-24 hours.

After the recommended holding period, the chlorine can be flushed out of the system by opening taps until the odor is not detectable. To minimize impact on a septic system from the additional water, flushing should be done first at an outside hose bib, directing the flushed water away from the septic area. When the chlorine odor appears almost gone, then flush the inside plumbing to rid the entire system of chlorine.

 Resampling for coliform bacteria should be done after the chlorine is completely absent from the water supply to verify that the water is bacteriologically safe to drink.

 NOTE: It is possible that creeks and rivers flowing from the fire-affected areas may have elevated levels of heavy metals, including Aluminum, Antimony, Arsenic, Cadmium, Selenium, Lead as well as Poly Aromatic Hydrocarbons (PAH’s). Property owners who have private wells and live near creeks or rivers should consider testing for the presence of these heavy metals and PAH’s in their well water. Residents in these areas should drink bottled water until well water is tested and confirmed free of contamination. 

Image of Well diagram


  •  For flooded wells, flush water at the wellhead until it appears clear before chlorinating.  
  •  For stubborn contamination problems, the well may need to be chlorinated by inserting a sprayer which recirculates the chlorinated water by spraying from the top down for a pre-determined period of time.  
  •  If a storage tank is connected to the system, add chlorine to the tank after chlorinating the well, and before moving the chlorine through the system. (One gallon bleach per 1000 gallons storage capacity).  
  •  It is recommended that a well be chlorinated annually, and after repairs are done to the well or the plumbing system.