Establishing Hydraulic Interconnections

5 Establishing Hydraulic Interconnections 6.5.1 Direct Proofs for Hydraulic Interconnections 

If dyes injected into one well are then found in an adjacent well, this directly proves hydraulic interconnections and the direction of groundwater flow. Fungal spores, salt, and various radioactive isotopes have been used to trace groundwater flow. A drop in the water table as a result of pumping in an adjacent well is another direct proof of hydraulic interconnections. 

The drawback of these methods is that they can be traced over small distances, on the order of tens to hundreds meters, and even that requires substantial effort. For greater distances, other indirect tracing methods are 

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2 Water Level Gradient A Necessary Condition for Determining Flow Direction, but Not a Sufficient One 

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The level water reaches in an artesian well reflects its pressure, called the piezometric, or confined, water head (Fig 2.6). In boreholes drilled at altitudes that are lower than the piezometric head, water will reach the surface in a jet (or wellhead pressure) with a pressure that is proportional to the difference between the altitude of the wellhead and the piezometric head. The piezometric head is slightly lower than the water level in the relevant phreatic section of the system due to the flow resistance of the aquifer. Confined aquifers often underlay a phreatic aquifer, as shown in Fig. 2.7. The nature of such groundwater systems may be revealed by data measured in boreholes and wells. The water levels in wells 1 and 2 of Fig. 2.7 did not rise after the water was encountered, and both wells reached a phreatic aquifer. Well 3 is artesian, and the drillers account should include the depth in which the water was struck and the depth and nature of the aquiclude. The hydraulic interconnection between well 1 and well 3 may be established by... 

Monitoring of contaminants is somewhat like troubleshooting, but each contamination case study also has a scientific aspect, because each pollution case serves as a large-scale tracing experiment. The tracing of pollutants complements the methods presented in section 6.5, which is devoted to the establishment of hydraulic interconnections, the basic premise that underlies most groundwater models. 

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