Water Well Journal
Issue link: http://read.dmtmag.com/i/543740
is also good at producing fouling through accumulations of naturally ac- quired minerals and biology from the source aquifer that become intensified by conditions within the well. The standing column of water in the well can be visualized as a mixture of dissolved minerals, suspended particu- late matter, and biological components that will naturally react to the well environment and conditions within the structure. In a traditional, regularly operated well, this concentrated environment is regularly flushed from the well, reduc- ing the potential for fouling. However, in idle wells the issues are much more dramatic—culminating in blockages that can ultimately result in lost capacity, degradation of water quality, delayed use of the well, and un- planned and unbudgeted well system maintenance. A well system can become mechani- cally impacted by formation materials moving into the well structure, physi- cally blocking water flow. Wells may become obstructed by minerals falling out of solution and forming mineral scales, and can become biologically fouled due to bacterial presence and the resultant biofilm development. Physical corrosion and deterioration of well com- ponents and even structural failure can occur in idle wells and those without adequate maintenance schedules. Early recognition of problems and fouling within a well is important. Signs something is amiss may include discol- oration of produced water, taste and odor issues, positive coliform tests, high bacteria counts, failure to maintain chlo- rine residuals, corrosion, and accumula- tion of mineral scale both within the well as well as outside of the well. This can coincide with production losses, de- clining pump efficiency, or an increase in energy costs due to an overworked pump. Accumulating over time All wells will passively accumulate sediments and mineral deposits over time, resulting in scale and blockage within the filter pack and well. High total suspended solids and total dis- solved solids levels and the presence of crystalline material can indicate an influx of formation sediments toward the well. The movement of sediment and fines into the well and near-well formation increases the congestion within the borehole. These materials can become entrained in biological accumulations, further escalating any fouling that is occurring and impacting flow. Iron may be evaluated in multiple forms and can indicate high levels of background iron as well as dynamic iron problems within the well. For example, in wells exhibiting elevated levels of iron and oxidative conditions, possible corrosion of the well structure and interaction with resident bacterial populations should be investigated. The well water chemistry in these wells will be influenced by, and in turn have an effect on, any low-carbon steel, galvanized high strength low alloy, or similar less-noble well components that have a tendency to shed iron into the system. If the well is experiencing high iron, testing for iron and manganese related bacteria is important. Iron and man- ganese bacteria are naturally occurring bacteria found in a variety of aquatic en- vironments, including aquifers. These bacteria use iron and manganese as en- ergy sources and will accumulate oxi- dized iron and manganese in the stalks they produce. The soft, biologically mo- bilized iron is often shed during cycling of the well, resulting in surges of red water and spikes in total iron readings. Established populations of bacteria within a well can cause problems since they are known to produce biofilm or slime that can foul the water-producing zones of the well and near-well forma- tion areas. The lower portions of the well and surrounding gravel pack in the well an- nulus can become significantly fouled with anaerobic bacteria—organisms that thrive in no-oxygen environments. Anaerobic bacteria are often responsible for taste and odor problems in potable wells, and established populations of these bacteria can be problematic in all wells since they are slime formers and tend to harbor other species of bacteria, such as coliforms. The tendency for these organisms to inhabit deeper areas within the well and borehole can make it very difficult to effectively disinfect and clean affected wells, and presents a challenge for any rehabilitation efforts. Identification and measurement of anaerobic bacterial growth is essential since they are responsible for many taste and odor problems and can signal significant fouling in wells, especially idled wells. Sulfate-reducing bacteria are a form of anaerobic bacteria often identified in fouled or stagnant well sys- tems where low flow anoxic conditions typically occur. Well specific Depending on the age, historical use, and maintenance and the role it plays, responding to idled conditions is well specific. The response should be devel- oped based on the condition and identi- fied problems. Procedures should be planned for ahead of time, allowing it to be placed in the budget and schedule. Vigilance is vital. Idled wells require more proactive testing and monitoring, and require more frequent maintenance than active wells. Wells benefit from maintaining an active pumping schedule and a routine IDLED WELLS from page 25 waterwelljournal.com 26 August 2015 WWJ Microscopic evaluation (400x magnifica- tion) of debris present in discharge water from a seasonally idled well at startup. Heavy corrosion on a pump from an out-of-service well. Photo courtesy of Ned Marks, Terrane Resources