Water Well Journal

May 2015

Water Well Journal

Issue link: http://read.dmtmag.com/i/498253

Contents of this Issue

Navigation

Page 25 of 91

24 May 2015 WWJ waterwelljournal.com tory standpoint, analytical terminology, advances in testing capabilities, and a lack of clear understanding of wells aids in this confusion. All too often the prob- lems stem from poor communication. Following guidelines With regards to maintenance and op- erational issues, water testing is gener- ally targeted at identifying the potential for mineral scale formation, the likeli- hood of corrosion, and an evaluation of the microbial community. While the focus and parameters are different for regulatory purposes, regulatory and maintenance testing generally use the same methods for analyses of a water sample. Laboratory testing procedures for water samples are performed according to the guidelines set forth in Standard Methods for the Examination of Water and Wastewater as established by the American Public Health Association, the American Water Works Association, and the Water Environment Federation. In general, these methods are approved by both the EPA and AWWA for the reporting of water and wastewater data. Regulatory testing requires specific collection methods, the use of special containers and preservatives, and has strict limits with regard to holding times prior to testing. Maintenance testing generally has different procedures for sample collection and submittal, par- tially reflective of the well or problems being encountered. In evaluating the water chemistry from a well for maintenance, the pri- mary concern is for scale formation or corrosion. Useful parameters for evalua- tion include pH, alkalinity, total dis- solved solids, hardness level, calcium, magnesium, iron, manganese, and the oxidation-reduction potential. Calculation of the Langelier Satura- tion Index and the Ryznar Stability Index incorporate many of these parameters and are valuable indicators of the potential for scale development or corrosion. In evaluating a water sample for maintenance, the biological testing is conducted in an effort to understand the biofouling potential. Our industry uses the term "bacteria test" to account for a wide range of tests, but generally it is used to indicate the required total col- iform occurrence test. Coliform tests are a means of evaluating for the presence or absence of coliform organisms, a large group of bacteria generally used as an indication of contamination. A well can be heavily biofouled and still remain coliform free. When conducting biological analy- ses, it is advised you first quantify the population. This is done to see whether or not the microbial community falls within a normal range. Traditionally, the heterotrophic plate count (HPC) has been used. However, studies now indi- cate this method is not as useful, as less than 5% of the known bacterial species are culturalable on the media used. The adenosine triphosphate (ATP) test is a more accurate assessment, quantifying all living species—both aerobic and anaerobic—within a sample. Once you've identified the size of the bacterial population, it is recom- mended you have the lab assess the anaerobic population. Anaerobic bacte- ria are a collective group of bacteria that do not require oxygen for survival. Testing for anaerobic growth is useful in identifying areas of heavy fouling as well as the development of environ- ments for more problematic organisms such as sulfate-reducing bacteria (SRBs). SRBs are the easiest to identify from a water sample, as a very distinctive hydrogen-sulfide gas is produced by the bacteria. Hydrogen sulfide gas has a distinctive rotten-egg odor, which diminishes the aesthetic quality of produced well water. Sulfate-reducing bacteria are common inhabitants in groundwater systems, often noticeable after prolonged periods of inactivity or in severely fouled wells suffering pro- duction problems. In addition to the evaluation of anaerobic growth and the presence of SRBs, testing for the presence of iron bacteria is recommended. Iron-oxidiz- ing bacteria are common problems in wells, especially those in alluvial aquifer settings or wells with low car- bon steel completions. Often misidenti- fied as iron-reducing bacteria, iron oxidizers are more readily identifiable by the iron-laden stalks they shed dur- ing their life cycle. Simple microscopic evaluation is useful in identifying the presence of iron bacteria and assessing their relative rate of occurrence within a sample. SCHNIEDERS from page 23 Multiple biological testing methods are advised to better understand problems occurring downhole. Comparing deposit samples with water analysis can help determine the extent of a problem occurring downhole.

Articles in this issue

Links on this page

Archives of this issue

view archives of Water Well Journal - May 2015