Groundwater Monitoring

Ammonia levels can reach several mg/L in groundwater systems, especially those located in agricultural areas. The ammonia levels can change seasonally and need to be monitored. The ammonia will react with chlorine to form chloramines, creating an uncontrolled chloraminated water. The uncontrolled chloramination can cause taste and odor issues and possible nitrification problems in the distribution system. The standard salicylate method can be used to determine ammonia levels in the unchlorinated water.

Ammonia in groundwater can be destroyed by taking the water through breakpoint chlorination. Free chlorine is added to the water to convert all the ammonia into chloramines. The further addition of free chlorine converts or "breaks" the chloramines down into nitrogen gas and other volatile species leaving only free chlorine as the residual disinfectant. The standard DPD Free Chlorine method can be used to determine when the desired free chlorine residual is reached. Free chlorine also causes iron and manganese to form insoluble precipitates, which can be removed by filtration but may interfere with DPD chemistry. Use the Indophenol No-interference Method 10241 to measure free chlorine residual when iron or manganese is present.

Test for total chlorine to determine total disinfectant residual levels. The total chlorine concentration is required by most regulatory agencies for compliance reporting purposes. Use the total chlorine concentration for calculating the CT credits and optimizing the treatment process. Select the DPD Total Chlorine method that adequately covers the expected chlorine concentration range and gives the test sensitivity and concentration resolution desired. The method required may change depending upon the sampling point within the treatment system. The titration methods are easily adapted to meet the test ranges required in treatment process.

Iron is present in most ground waters and is considered a secondary contaminant with maximum contaminant level (MCL) = 0.3 mg/L. The level of naturally occurring iron in a groundwater remains nearly constant and is usually present as ferrous iron (soluble form). When the ferrous iron reaches the surface it is oxidized by air to the ferric form giving the characteristic red water color and precipitating to give the red rust-colored stains on equipment and plumbing fixtures. Iron can also occur as the result of corrosion of well pipes or as the result of iron-reducing bacteria. Any sudden change in the iron concentration may indicate pipe or equipment corrosion, the presence of iron reducing bacteria or changes to the aquifer itself from seismic events, well infiltration or new drilling or fracturing activities in close proximity of the groundwater source. Use FerroVer Iron method for the routine checking for the presence of iron. The TPTZ method may be used for low level iron testing.

Manganese is present in most ground waters especially when iron is present, and is considered a secondary contaminant with maximum contaminant level (MCL) = 0.05 mg/L. At concentration levels above the MCL, it causes black stains on plumbing fixtures, laundry and other items in contact with the water. Use the extremely sensitive PAN method to determine manganese levels.

The pH of groundwater varies widely throughout the various regions of the world. Monitor the pH of the groundwater to determine the pH adjustments that are required to give the optimum pH range for chlorine disinfection. While the pH of groundwater remains essentially constant, monitoring of the pH is also a surrogate method to quickly detect any intentional or unintentional events that have occurred to the groundwater source, especially if it is under influence of surface water (GWUDI).

Toxic hydrogen sulfide is produced by the anaerobic decomposition of organic material and sulfate reducing bacteria. It is characterized by a very noticeable rotten-egg odor. It is mainly found in groundwater supplies. It contributes to the chlorine demand of a raw water source and is easily removed by aeration or by the addition of chlorine.

Chlorine demand is a measure of the amount of chlorine consumed by a source water after a fixed time at a fixed pH and temperature. Organic materials, ferrous iron, reduced manganese, sulfide and ammonia are examples of species that consume chlorine during the disinfection process. A high chlorine demand suggests that disinfection by-products may form if the demand is due to organics, such as natural organic matter (NOM). Chloramines may be formed when ammonia is present and sulfides produced by sulfate reducing bacteria will add to the chlorine demand. The chlorine demand test can be modified to use the specific conditions of your source water or to investigate the demand from alternative groundwater sources.

Nitrate is a regulated contaminant with 10 mg/L maximum contaminant level (MCL) often found in agricultural areas due to the use of fertilizers. Monitor your sources for nitrate because treatment is difficult and may require RO filtration.

Monitor your sources for nitrite as it may be present in the source and gets oxidized during treatment to produce nitrate.

Mainly, groundwater facilities aim to remove dissolved metals and/or TOC with pre-oxidation, ion-exchange, or membrane treatment. However, some utilities may employ chemical treatment with coagulants. If your water source requires additional treatment with coagulants to remove colloidal particles, you can use advanced monitoring and optimization tools available from Hach.