Water Well Journal

April 2015

Water Well Journal

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This article is the sixth in a six-part series that will detail each of the 11 sections of the ANSI/NGWA Water Well Construction Standard. T he purpose of this article is to highlight key aspects of the stan- dard in respect to well perform- ance testing and the data to be recorded in the well completion report. Well Disinfection with Chlorine Well disinfection using chlorine is so familiar to us, as it has been used since what seems like forever. It also seems so easy that "anyone can do it." So why the specific points in the Well Construction Standard Section 9? The scope of the standard—and this application of chlorination—is well con- struction, rather than remediating prob- lems in existing wells. The function of new well chlorination (beyond "I need this well to pass the test") is to neutral- ize bacteria that may be introduced dur- ing the construction and not removed during well development. In new construction, any excessive casualness about chlorination can cause problems: • Just dumping hypochlorite or pellets down a well casing (1) misses pock- ets of material not properly devel- oped out that harbor undesirable bacteria, (2) doesn't properly treat the entire casing and can begin pre- mature steel casing corrosion, and (3) provides opportunity for concen- trated chlorine to lodge in rock frac- tures, especially permeable aquifer zones, or in the bottom of the well. • Just dumping hypochlorite is seldom conducted, considering the necessary dose. The concept can't be "If a gal- lon is good, two gallons is better" or "Throw some pellets in that and let's go." Actually, pH adjustment and calcu- lating dosage by volume are crucial to effectiveness. When dissolved in water, hypochlorites disassociate into hypochlorous acid and hypochlorite ion. Hypochlorous acid is the biocidal frac- tion, while hypochlorite oxidizes avail- able reduced metals such as iron. Lower pH and proper dosage favors hypochlor- ous acid. However, a too-low pH results in off-gassing of Cl 2 , which is both potentially hazardous and reduces the effectiveness of the disinfection. So, following the dosing charts for both chlorine and pH adjustment are both really important. Mixing solution through the well is also really important, as is removing sediment and deposits that consume chlorine (chlorine demand). This means complete development (Section 6) is important to effective well disinfection. In well construction and development, it is recommended avoiding use of any ad- ditives that potentially promote bacterial growth. The National Ground Water Associa- tion recommends well chlorination should be performed by a qualified pro- fessional. This is also the position of various U.S. states, most of which set some standard for qualifications. The need to closely manage disinfection dosage and to apply it properly should make it apparent why well disinfection is not for amateurs. Water Sampling and Analysis Sampling a well for water quality is important for determining the suitability of the well for the purpose for which it was drilled. As such, water samples are often collected for analyses during and after well construction. In summary, the sampling section of the ANSI/NGWA standard covers sam- ple collection, when and how often, sampling protocol, quality control, and identification (labeling). The standard focuses on how to ensure the collected sample is a true representative of the "source water quality intercepted by the well." Sampling can occur during and after well construction. Many resource management agencies also sample the various water-bearing zones extensively —including parameters to help assess the age of the water, and so forth. Some wells are "zone" sampled in order to de- termine the most appropriate zones of the aquifer to screen to meet the stated water quality objective. There are two types of analytical tests: field tests and laboratory tests. Field tests are those analyses that occur at the well site using properly cal- ibrated equipments in accordance with procedures prescribed by the manufac- turer. Field test results should be timely recorded. Samples destined for laboratory tests should be properly labeled. Such labeled samples are collected using appropriate containers and transported to the labora- tory using appropriate preservation and sometimes within specific time limits. The analytical results of the sampling can be valuable in determining what treatment or water blending regime are required to make the water suitable for its intended purpose. Given the potential implications, it is very important the water sampling and analyses follow the proper protocol and be defensible. For example, wells used for public water supplies must be sampled by certified operators. Many regulatory agencies or professional associations have established standard methods for the analyses of water. Also, there are certification programs for the laboratories involved in water quality analyses. It is advisable to use appropri- ately certified laboratories for analyzing the samples. Some sampling programs may have legal implications; it's not unusual to have completed chain of Go to the NGWA Bookstore to purchase your copy of the ANSI/NGWA-01-14 Water Well Construction Standard. It encompasses municipal, residential, agricultural, monitoring, and industrial water production wells. Topics covered include: well site selection; casing and casing installation; well screens, filter pack, and formation stabilizer; grouting; plumbness and alignment; well development; testing for performance; data recording; disinfection with chlorine; water sampling and analysis; and permanent well and test-hole decommissioning. Go to the bookstore at www.NGWA.org. 20 April 2015 WWJ waterwelljournal.com

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