Planning Hydrochemical Studies

The economical value of hydrochemical studies also has wider aspects, as they may reduce the number of new drillings needed or improve their location. The price of hydrochemical measurements is small compared to drilling expenses, but they should be minimized by careful planning and proper selection of the parameters measured at each stage of the study and proper selection of water sampling frequencies. These topics are discussed in section 18.2. 

Figure 4.21 depicts temperature profiles in a well close to the Mohawk River, New York. In May a temperature of 43° F is observed at the measured depth interval of 205-165 ft above sea level. The July profile looked totally different it showed 57° F at the top, 64° F at the center, and 52° F at the bottom. The January profile looks different again 56° F at the top, 68° F at the center, and 52° F at the bottom. The interpretation of these temperature profiles is discussed in section 4.8. For our present topic, the planning of hydrochemical studies, it is important to keep in mind that water strata are not necessarily uniform—if they vary in their temperature profiles, they may vary in other parameters as well. 

Planning of a hydrochemical study has to take into account the need to measure depth profiles and to select the proper time to do them. 

Having praised repeated measurements, we now discuss their incorporation into the planning of hydrochemical studies. A common rule of the thumb is that each water source should be studied four times to cover at least one hydrological cycle, including the four major seasons. This may be regarded as a minimum, because time-data series with only four points suffer from poor resolution. 

Planning of a hydrochemical study should include the question, will the data be expressed in contour maps If so, data have to be obtained with an adequate geographical coverage and adequate density of measured points. These requirements are necessary to ensure adequate resolution and to avoid white holes in the maps. 

Planning a hydrochemical study should include the question of whether the transect approach is desired. If so, the locations of the transect should be decided. Such a decision should take into account... 

Pollution detection and monitoring projects should be planned and conducted within the guidelines that were found useful for all hydrochemical studies (Chapter 7). To these should be added the requirement for specialized laboratories that analyze the specific compounds present in unusual wastes. 

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