WorldWide Drilling Resource®

Notes from the Groundwater Guy by Thomas E. Ballard, P.G., C.H.G. Southeast Hydrogeology, PLLC Chlorine: Fact and Fiction Despite the fact chlorine is probably the most widely used chemical in the water well industry, it is likely the most misunder- stood. Most commonly used for disinfection of wells, chlorine is often used for other pur- poses, where it is much less effective or even harmful to the well. I have attended classes and webinars with so-called experts who have advocated chlorine for treating biofilm and dissolving mineral incrustations where, in actuality, chlorine is completely ineffective at these applications. Chlorine is most effective as a biocide against free-swimming bacteria (as opposed to biofilms attached to the well). However, to be used for this purpose, one must understand a bit about the chemistry of chlorine and chlorine compounds. When we talk chlorine, we are usually talking about compounds which contain chlorine. Chlorine itself is an element in the form of Cl 2 , whereas chlorine compounds are those chemicals which contain the active chlorine. In well drilling, there are two commonly used chlorine compounds: Sodium hypochlorite is common bleach that comes in liquid form and is often used for disinfection in well drilling and construction. There are several challenges in using sodium hypochlorite: it has a short shelf life of about six months; it is very caustic and can corrode wells; and, it is pH (acidity) sensitive, meaning it is most effective within a narrow pH range. The short shelf life means the available chlorine in the bleach you are using can vary widely and result in uncertain dis- infection effects. Calcium hypochlorite has about 65%-70% available chlorine, comes in a solid, and has a shelf life of about a year. Calcium hypochlorite should be mixed at the surface then applied, because pellets and granules may not dissolve com- pletely when just dropped into the well. With any of the chlorine compounds, the target compound you want to form for disinfection purposes is hypochlorous acid (HOCl). However, due to variables such as pH, temperature, water chemistry, hardness, and alkalinity, the amount of hypochlorous acid produced can vary. For example, hypochlorous acid is most stable at a pH of about five, yet most chlorine compounds will want to move the pH out of this optimal range, making the chlorine less effective. For this reason, when using sodium or calcium hypochlorite, it is important to also use a buffering com- pound to stabilize the pH, or use a chlo- rine product which is pre-combined with a pH buffer. This will hold the pH in the proper range for most effective disinfec- tion results. Tom Tom Ballard may be contacted via e-mail to michele@ 36 APRIL 2020 WorldWide Drilling Resource ® Congratulat ions to: James Torlish & Sons Armonk, NY Winner for March! Time for a Little Fun! March Puzzle Solution: Drill King International Flomatic Corporation Win a prize! Send your completed puzzle to: WWDR PO Box 660 Bonifay, FL 32425 or fax to: 850-547-0329 Can you identify which ads in this issue these two photos came from? WTR June Issue Deadlines! Space Reservation: April 25 th Display & Classified Ad Copy: May 1 st