Water Well Journal

January 2017

Water Well Journal

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

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Page 20 of 63

D espite the long held view aquifers are pristine water sources, a diverse and large group of bacteria inhabiting ground- water are now being analyzed to better understand the many varied influences they have on wells and the quality of water being produced. Efforts to monitor bacteria in ground- water wells have primarily been in regard to water quality. But a deeper knowledge of these bacterial communi- ties is more available than ever—and can serve as a valuable resource in as- sessing maintenance requirements that protect the increasingly important asset that is a groundwater well. Breaking with Tradition In large part, our view of bacteria in water wells continues to be in the con- text of water quality, the origins of which go back to the human need for clean, safe drinking water. Rightfully so, our first priority has been to manage the health risks posed by bacteria in our water supplies. The industry standard for determining drink- ing water's sanitary quality comes from regulatory actions put in place by the U.S. Environmental Protection Agency, which rely on a small group of bacteria called coliforms. A group of closely re- lated bacteria, coliforms have become the poster child for bacterial water qual- ity, earning the role of indicator organ- isms due to their similarities to a variety of other pathogenic microbes. While the primary goal may be safety, production of clean and aestheti- cally pleasing water also remains a chief goal of any water producer. A number of bacteria within water supplies are known for their undesirable effects on water quality—negatively impacting taste, odor, and visual appearances. A well-known member of this group of nuisance organisms are sulfate-reduc- ing bacteria. SRBs are a form of anaero- bic bacteria often identified in fouled or stagnant well systems. They are identi- fied through a presence-absence test— but their presence is readily identifiable by the distinctive hydrogen sulfide gas produced by the bacteria and the rotten- egg odor the gas is known for. While removing bacteria responsible for impacting water quality from both a safety and aesthetic viewpoint is cer- tainly valid, it does not ensure a well will be a good producer. Nor does it give any indication of a well's need of maintenance. To this end, the examina- tion of bacterial communities within wells from a performance perspective should also be used to help guide rou- tine maintenance and extend the opera- tional life spans of wells. The Roles of Biofilm Within the industry, "biofouling" has come to encompass a number of known tactics bacteria use to adversely affect water systems. Perhaps the most influ- ential fouling mechanism is the forma- tion of biofilm. Biofilm is a naturally occurring expression of bacteria result- ing from the extrusion of a slimy extra- cellular polymeric substance (EPS). The EPS matrix covers the cells and consists of polysaccharides, proteins, and nucleic acids used by the bacteria. Bacteria discharge this slime as a means of attaching themselves to a smooth sur- face for propagation, nutrient capture, growth, and can even facilitate com- munication between the encompassed microbes. Biofilms are not as rare as one might think and can actually be beneficial in some applications. They are used and can be specifically engineered for water and wastewater filtration and remedia- tion of contaminated soils and water— they even make up dental plaque. Unfortunately, the aspects of biofilm that make it advantageous for bacteria are also extremely detrimental to well systems. As the biofilm matrix grows, it can physically restrict flow paths— specifically within the producing zones of a well where screened, perforated, or slotted openings are found often in con- junction with surrounding gravel pack. Filling in the spaces in between these areas can rapidly decrease production and result in increased drawdowns. More advanced biofilm growth can also result in the stratification of differ- ent layers within the biofilm matrix, which not only increases the relative density and fouling potential of the biofilm, but also reduces oxygen levels in the deeper layers where anaerobic bacteria can thrive. This layering effect not only impedes disinfection efforts, but has also been shown to harbor more harmful organisms, such as coliforms thriving in anoxic environments. Additionally, as biofilms mature, cells from the colony are known to leave the matrix to spread and colonize new surfaces. Dispersion of these cells enables fouling to migrate into different zones throughout the well environment and beyond—including the pump, dis- tribution system, and treatment facilities where new biofilms can be established. Fortunately, a number of tools are available to help monitor biofilm growth before it reaches problematic levels. A common approach is to gener- ally quantify the total bacterial load within the well, with the notion greater population sizes reflect a greater poten- tial for biofilm formation. Periodic monitoring of population sizes in con- junction with well performance can also allow for correlations to be made and acceptable operational limits to be set. Various quantification techniques are available which fluctuate greatly in cost and accuracy. Of those methods, adeno- sine triphosphate (ATP) analysis is a simple test which can quickly and accu- rately quantify a biological load in a water sample—it measures the amount of ATP, a molecule found universally MICROBIOLOGY continues on page 20 (Left) Sample bottle with turbid water. Knowing Well Microbiology Knowledge of biofouling mechanisms can help drive maintenance of well systems. By Eric Duderstadt Twitter @WaterWellJournl WWJ January 2017 19

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