Water Well Journal
Issue link: http://read.dmtmag.com/i/617280
I nfluence, stressors, contamination, vulnerability . . . all key watchwords that cause the well owner, consultant, and contractor anxiety. So we ask: What changes can we look for in our wells to understand pos- sible impactions? While the sudden onset of discolor- ation or odor can indicate influence, there are often subtle clues in the pro- duced water that indicate changes in the well, aquifer, or area of recharge that could impact the well. Some changes in water chemistry and microbiology are seasonal, and regular monitoring will in- dicate this. Others however, may reflect more dynamic influences which require action. A few of the common water chem- istry parameters useful in evaluating well health include pH, total dissolved solids, conductivity, oxidation reduction potential, hardness, iron, manganese, and microbial presence. While not a conclusive list nor presented to substi- tute a full chemical and biological testing, the following parameters are helpful in evaluating problems before they become significant. pH This abbreviation for "power (or potency) of hydrogen" represents an expression of the hydrogen (acid) ions in solution. It is a logarithmic represen- tation in which the acid-alkaline level of water is written 0 to 14, with 14 being the most basic (alkaline). Conversely, any number below 7.0 is considered acidic. The natural groundwater pH varies greatly across North America, with wells registering values as low as 4.5 and others as high as 9.0. Groundwater pH is typically considered a very stable value with only minor fluctuations. Changes of 1.0 or more may indicate an influence is occurring on the well. Total Dissolved Solids and Conductivity TDS is a measure of the combined total of inorganic and organic sub- stances present in a liquid in molecular or ionized form. TDS is not considered a pollutant, but is used as a cursory indi- cation of drinking water quality. The two accepted methods of meas- uring TDS are gravimetric and electrical conductance. The gravimetric method is the most accurate; however, it is also the most expensive and time consuming. Electrical conductance (conductivity) is the measure of the ability of water to pass an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chlo- rides, nitrates, sulfates, and phosphate anions (ions that carry a negative charge) or sodium, magnesium, calcium, iron, and aluminum cations (ions that carry a positive charge). Conductivity is also affected by temperature—the warmer the water, the higher the con- ductivity. For this reason, conductivity is reported at 25°C. TDS and conductivity are relatively stable parameters in hard rock aquifers. In alluvial aquifers, these parameters generally increase during periods of heavy recharge. Regardless of the aquifer, fluctuations of more than 200 points in either TDS or conductivity would be considered abnormal and may indicate that influence on the well or aquifer is occurring. For example, a flooded well may exhibit a TDS or con- ductivity reading that is two to three times the normal value. Oxidation Reduction Potential ORP is the measure of the tendency of a solution to gain or lose electrons when it is subjected to change—be it chemical, biological, or mechanical. Positive readings are more oxidative while negative readings are said to be more reductive. Water with a higher or more positive ORP will have a greater tendency to gain electrons from the new entity, therefore oxidizing the new species. For example, the oxidation of iron when it enters a water of high ORP. Although it is relatively easy to take a reading, many factors limit its inter- pretation, and as such, field measure- ments seldom correlate with calculated values. Nevertheless, ORP has proven useful as an indicator of change in a system rather than the calculation of absolute values. ORP results are read in millivolts (mV). ORP levels fluctuate with well activ- ity, and as such, the well's use or inac- tivity should be considered. Changes in ORP can indicate corrosion is occurring, microbial populations are increasing, or chemical influence is occurring. For ex- ample, when chlorine is present, ORP levels generally increase significantly. As such, abnormal spikes in ORP can indicate backflow of treated water into the well is occurring. Hardness This is a term used to include all or most of the multivalent ions that can SCHNIEDERS continues on page 24 (Left) There are multiple methods of evaluating the microbial community within the well, useful means of identi- fying problems early. Twitter @WaterWellJournl WWJ January 2016 23 Six helpful parameters to evaluate problems before they become significant. By Michael J. Schnieders, PG, PH-GW TRACKING WELL HEALTH