Mar 28, 2007

Testing Groundwater

When dealing with water treatment of private wells, there are a number of tests that may be needed. Groundwater can vary from one well to another based on various geologic and human-influenced factors.

Geological formations can influence the pH levels as well as levels of elements such as calcium, magnesium, potassium, sodium, chloride, iron, manganese, arsenic, radon and radium. Human-influenced contaminants typically include chlorine, volatile organics and other synthetics such as pesticides or herbicides. When dealing with water from a private well it is important to do some onsite testing to get a baseline of the water quality. Additional lab analysis may be required, especially for bacteria and volatile organics if there is reason to suspect their presence.


Onsite Testing

When determining treatment needs for a groundwater source, it is critical to determine the pH level because it can affect other treatment methods such as softening or disinfection. When water is exposed to the atmosphere, it has a tendency to take in carbon dioxide, which can react with water and, in turn, form carbonic acid and H+, lowering the pH level. Thus it is important to measure pH immediately after sample collection to ensure the most accurate reading. pH is typically determined by indicators or meters. Many use pH indicators to get a general idea of the pH level. Indicators are chemicals added to the solution, which produce a color change based on the pH level. Unfortunately, color is very subjective to individual interpretation and can lead to imprecise readings. A pH meter should then be considered if a more accurate measurement is needed. pH meters use a glass probe that produces a certain voltage based on the pH level of the solution being measured.

It is important to properly calibrate your pH meter to ensure high accuracy. Meters should be calibrated based on their usage. If used frequently, like in a laboratory setting, a meter should be calibrated more frequently than if it is used less often. It should be calibrated using at least two buffers, if not three. Buffer solutions are solutions with known pH levels, which are used to compare against when testing unknown samples. A buffer solution with a pH level of 7 is used along with one of 10 if the solution is suspected to be basic; or a buffer with a pH of 4 if the solution is suspected to be acidic. If you are unsure of the general pH level in the area you are working, you should calibrate using all three buffer solutions. To calibrate, place the probe alternately in two or three solutions until the meter obtains an accurate reading. Most modern meters will only need a single immersion to get an accurate reading. After the meter is calibrated, the probe should be rinsed using deionized or distilled water and blotted dry with a clean tissue to remove any residue that could interfere with the reading. It should then be immediately placed into the sample being tested. You may want to take a couple more samples to get an average pH level, as this can fluctuate.


Analyzing Conductivity

Another important analysis is conductivity, which is a good indication of mineral content. Conductivity is a measurement of a substance’s ability to conduct electricity. Conductivity is commonly run because it is a quick and inexpensive way to determine the ionic strength of the water. Conductivity can easily be measured with a meter. Pure waters tend to have lower conductivity levels than water that contains high salts, minerals, acids or bases. A high conductivity reading may indicate the need for additional analysis to detect common culprits such as chlorides, silica, sodium, phosphates and hardness minerals, depending on what other treatment equipment you may be considering. Conductivity is commonly used to estimate the total dissolved solids (TDS). Laboratories typically use a gravimetric method to determine TDS. This method is very time-consuming and costly, but it is the most accurate. Conductivity can be run on site for economical reasons and for more immediate results. Conductivity is measured in milli-siemens per centimeter or micro-siemens per centimeter, while TDS is measured in parts per million or milligrams per liter. A simple calculation is used to convert conductivity into TDS; however, because the calculation will vary based upon the calibration solution used, it is best to check with the manufacturer of the meter being used. Temperature also greatly affects the conductivity reading; e.g., an increase in temperature will increase the conductivity level. Some meters automatically compensate for the differences in temperatures and some do not, so check with the manufacturer if the unit has this feature.

Calibration of the meter or controller is essential in maintaining and ensuring a high level of accuracy. Calibration involves using a solution with a known concentration to ensure the meter is measuring accurately. Conductivity meters should also be calibrated based on how often they are used and at the levels of conductivity to which they are typically exposed. A good rule of thumb for calibrating TDS and conductivity meters is once per month for meters used on a daily basis. Calibration involves immersing the meter in the known calibration solution until the meter obtains an accurate reading.


Testing for Iron

Iron is another common problem in groundwater. There are three types of iron: ferric, ferrous and organically bound. Ferric iron readily precipitates and gives the water a reddish brown color that eventually settles out. Organic iron is bound to organics such as tannins or liginands, and also makes the water appeared discolored. Organically-bound iron is more difficult to remove. You can easily run a small sample of the water through a 0.45 micron filter using a syringe, and if the water is still discolored then you have an organic iron problem. Water containing ferrous iron—also called clear water iron—makes the water appear clear or colorless, but upon extended exposure to air, the iron will become oxidized, precipitate and settle. Ferrous iron is commonly found in deep wells where oxygen is lacking. To determine an accurate level you can run a benchtop analysis or colorimetric test for iron, or you can send it to a lab if certified analysis is required. There is also iron bacteria, which utilizes iron as a food source. A good indication of iron bacteria is the presence of a slimy reddish brown build-up typically found in the back of a toilet tank. Testing for iron bacteria can be done using a biological activity reaction test, also called the BART test. This test does not require a lab, microscope or incubator, but is an excellent way to confirm the presence of iron bacteria and give an activity level.


Closer Inspection

You should also take into account the appearance of the water if it has any distinct color. You can use a white styrofoam cup to visually inspect the water for color. The white cup makes any discoloration more noticeable, so it is a good idea to carry white cups in your testing kits. As discussed, iron can cause a reddish or brownish color but other colors may be noted. A blue-green color can indicate copper, which may also indicate low pH levels dissolving copper pipe and fittings. Dark brown or black discoloration can indicate the presence of manganese, which typically will deposit in sinks, showers and especially toilets. It’s important to inspect the toilet, including the back tank, for these mineral deposits and hard water stains that indicate levels of calcium and possibly magnesium. You also should test the water for odor by simply smelling the water for any unusual odors like rotten egg, musty or metallic smells. These can indicate the presence of contaminants like bacteria, hydrogen sulfide or other metals. When dealing with a private well it is a good idea to have the water tested for bacteria to ensure it is microbiologically safe before installing any equipment. You should have the analysis done by a competent laboratory. When dealing with groundwater, you may want to include preventative equipment to ensure continued disinfection, should bacteria suddenly contaminate the water.

When dealing with unknown water quality, as is the case with many groundwater sources, it is important to observe all the physical characteristics of the water, which can be helpful in determining testing needs as well as treatment options. When dealing with the unknown it is always better to do a little testing first than to have to go back and test after equipment is installed and is not functioning correctly. Physical inspection of the water is just as important as any other test that could be run, so do not forget to take note of any color, odor or taste in the water. These are the qualities that customers are most concerned about.


About the author

Marianne R. Metzger is accounting specialist for Accent Control Systems, Inc. Metzger is a member of the Editorial Advisory Board of Water Quality Products. She can be reached at 610.630.7640, ext. 145, or by e-mail at [email protected].