Water Well Journal
Issue link: http://read.dmtmag.com/i/440561
20 January 2015 WWJ waterwelljournal.com mulation of high concentrations of dissolved byproducts. This congested or crowded environment can prevent the complete dissolution of the mineral deposits. It is because of this crowding principle that the proper choice of both the acid and the concentration used is necessary for a successful cleaning. It is the same principle requiring a minimum of a pH of 3 be maintained during pump-out of the cleaning solution to ensure removal of the dissolved products. The most common mineral acids used in water well reha- bilitation are hydrochloric acid, phosphoric acid, and sulfamic acid. Organic Acids Organic acids are organic compounds with acidic proper- ties. In general, organic acids are weak acids and, unlike the strong mineral acids discussed already, do not dissociate completely in water. The most common organic acids used in well cleaning are acetic acid, citric acid, and oxalic acid. Organic acids, like oxalic acid or acetic acid, have been used for oil and gas well stimulation treatments. These acids are much less reactive with metals than strong mineral acids such as hydrochloric acid. Citric acid and oxalic acid, com- monly used for rust removal of hand tools, are often used in well remediation because they can dissolve and combine with iron oxide without damaging the base metal the way stronger mineral acids do. The neutralized forms of many organic acids can provide a significant carbon source (food) for bacteria. As such, it is important organic acids not be allowed to neutralize down- hole and they be fully flushed from the borehole environment to prevent future biofouling effects. Acid Selection and Use The choice of acid employed for well cleaning should be based on the identified fouling, the construction and integrity of the well, and the means in which it is employed down- hole—not availability or price. Similarly, the strength used and the time applied should also be balanced with the well and the fouling present. Not all acids are created equal. Whether the acid is mineral or organic, concentrated or diluted, the grade and reactivity are all important factors to consider during well maintenance. Each chemical has a different effective strength, weight, and other properties that define its use and compatibility with other products. Phosphoric acid, for example, is available in multiple con- centrations, forms, and trade names, each having different advantages and disadvantages. This acid is also less corrosive toward steel, especially stainless steels, in comparison to other acids. In addition to evaluating the NSF approval, take time to evaluate the selected chemicals and be sure they are appropri- ate for the job at hand. With your chemicals selected, secure the necessary material safety data sheets to have on-site during the application and use of the products. Proper well cleaning typically involves the usage of multi- ple chemicals coupled with some means of mechanical agita- tion. When choosing chemicals: • Select a chemical that targets the fouling mechanism • Make sure the products are NSF Standard 60 certified for potable well use • Ensure the products are compatible with each other and the well construction. Always use a chemically clean form of acid, and when necessary, use an approved inhibitor to reduce the harmful effects of corrosion. Calculate the proper dosage based on the well design and the manufacturer's recommendations for the type of problem and degree of impaction identified. One mistake often made is SCHNIEDERS from page 19 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-1, DOF-2, DOF-6, DOG-2, DOG-3, DOG-4, DOG-7 More information on DACUM and the charts are available at www.NGWA.org. It's important to have an on-site safety shower for use in washing off of chemical splashes or spills on personnel during well cleaning.