Water Well Journal

January 2017

Water Well Journal

Issue link: https://read.dmtmag.com/i/767379

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Page 28 of 63

The calculated treatment volume should be sufficient to flood the entire well, borehole, and near well aquifer. The standard recommendation for domestic wells is three to four times the standing well volume. The application of surging or agitation is recommended to effectively disperse the chemical solution throughout the treatment zone and continually bring new chemical in contact with the bacteria which are the target of disinfection. Surge blocks are effective in providing this activity and are proven to move fluids in and out of the well to accomplish the agitation required. In conjunction with agitation, sufficient contact time to allow the chlorine solution to effectively do its job is impor- tant. The rule of thumb used by our lab for water wells is a multiplier of the chlorine concentration and the hours of con- tact time to equal a minimum of 1000 contact units. There- fore, if you use 500 ppm of chlorine, you should allow a minimum contact time of at least two hours. Or if you use 100 ppm of chlorine, you should allow a minimum contact time of 10 hours. The Removal When the chlorination process is complete, the well should be pumped off from the bottom to assure effective removal of the chlorine solution and associated debris. It is recommended at a minimum the chlorine level be monitored to make certain the solution is removed. Measuring conductivity can be helpful as well to determine if and when evacuation of the solution is complete. Disposal of chlorine solutions is becoming a growing concern and many states have requirements for dechlorina- tion of these discharge fluids. However, most of the regulations are based on fluid volumes, and domestic wells may not provide regulated volumes to consider. Therefore, knowledge of your state's requirements will guide the need to treat disinfection fluid discharges. When required, there are products available to the industry based on standard chlorine neutralizing chemistries such as sodium bisulfite, sodium thiosulfate, and ascorbic acid. In summary, an effective well disinfection process should include: • Assessing the source of any noted issues that could be related to surface contamination • Assessing the need to potentially clean the well prior to disinfection • Selecting the appropriate chlorine product and concentra- tion required for your project • Evaluating the aquifer water pH and alkalinity to deter- mine the potential for a pH buffering additive • Dispersing the treatment volume of chlorine solution throughout the well, agitating the solution, and allowing an adequate contact time • Fully evacuating the well when completed, neutralizing the chlorine discharge fluids, and disposing of them in accordance with all laws and regulations • Placing the well back into active service and monitoring its performance. Effective water well disinfection is not a simple process and certainly not recommended for a well owner. Well disinfection requires a trained water well contractor who understands disinfection chemicals, their proper application procedures, and the rules and regulations under which to operate. That is what provides safe and successful results. Roger Miller is a senior consultant at Water Systems Engineering, specializing in water chemistry. He has worked over the past 40 years in research and develop- ment, analytical procedures, site assessment, and project oversight in the groundwater and water treatment indus- tries. He can be reached at rdmiller@h2osystems.com. DACUM Codes To help meet your professional needs, this article covers skills and competencies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: DOF-2, DOG-5, DOG-9, DOG-10, DOH-5, DOI-4 More information on DACUM and the charts are available at www.NGWA.org. WWJ Twitter @WaterWellJournl WWJ January 2017 27

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