11.7 Evaluation of Water Quality Data
Much of the focus of Section 11 is on presenting the important chemical parameters of, and dissolved constituents in, groundwater; the ways that those parameters and constituents are measured; basic calculations for and graphical representations of water quality data; as well as the processes that link the water chemistry to geologic settings. A common reason why groundwater samples are collected and analyzed for chemical constituents is to evaluate whether the water quality is acceptable for the intended use of the water. In most areas, groundwater designated for a municipal water supply (i.e., for drinking and household use) must meet specific water quality standards (e.g., the National Primary Drinking Water Regulations promulgated by the U.S. Environmental Protection Agency5) or be treated to comply with those standards before water is distributed to consumers. Groundwater developed for other uses may require much different standards. For example, water for livestock or irrigation can contain higher concentrations of many constituents, as livestock and plants can typically tolerate higher concentrations of various ions. Water is also required for most industrial processes (e.g., power generation, manufacturing, mining), and different industrial uses require different minimum water quality – in some cases the use may require very pure water with low salinity, while others can use high salinity water with no problem.
When performing water quality evaluations, it is very important to understand the requirements of the anticipated use before developing sampling and analysis program. All relevant regulations should be determined so that the correct laboratory analyses can be chosen. Proper sampling protocols must be established, and the laboratory should be contacted in advance so that proper sample containers are used, acceptable hold times (i.e., the time between sample collection and delivery to the laboratory) are not exceeded, and laboratory transmission protocols (e.g., samples kept on ice) are followed. All laboratory results should be checked for charge balance.