Hydraulic gradient, from wells

FIGURE 3.15 Determination of hydraulic gradient from wells. (After Freeze and Cherry,... 

The figure illustration shows occurrence of clogging by plotting data from an observation well (OW) and compare that to the production well (PW). In this case the production well shows a decreased specific capacity while the observation well shows a steady level versus time. The only explanation is then that the resistance for water to enter the production well is increasing. The increased resistance will lower the drawdown inside the well, while the groundwater table outside the well is kept constant. This will increase the hydraulic gradient (the driving force) between the well and the aquifer and hence maintain a constant flow rate. 

Two hydraulic head gradients determined from wells or piezometers are shown in Figure 3.15. Piezometers are basically pipes or wells put in the ground which are... 

Reinjection of coproduced groundwater through the use of wells is commonly used to return the water to the same aquifer and to set up hydraulic barriers in an effort to contain the plume. Injection wells are commonly used in conjunction with withdrawal systems to enhance the recovery of hydrocarbons. Injecting water at appropriate locations will create a pressure ridge to increase the hydraulic gradient effectively toward the withdrawal point. Normally, the water pumped from the recovery wells is used as the injection water and is injected, without treatment. This method provides an economical way of handling the produced water, as well as being beneficial to the recovery effort. 

Fig. 4.11 Determining flow gradient. The drop of water table between wells I and II is Ah — 412.6 — 411.8 = 0.8 m the distance (read from a map) is 0.76 km. Hence the hydraulic gradient is 0.8m/0.76km= l.Om/km.

Within the radius of influence downstream of the well, the hydraulic gradient of the aquifer is sloping away from the well, but maintains the same sign in contrast, the pumping of the well tends to cause water to flow in the opposite direction, toward the well, and thus the gradient sign is reversed ... 

A municipal well pumping 1200 m3/day is located 100 m from a major river. Aquifer transmissivity is 800 m2/day, aquifer thickness is 30 m, and the background hydraulic gradient (i.e., in the absence of the well) is 0.002 toward the river. 

Analysis of the RFT-data combined with detailed sequence stratigraphic studies were performed to obtain representative pore-pressure gradients from top to base of the individual permeable sands. Fig. 7 shows the interpreted pressure gradients for the Juras-sic-Triassic sequences within hydraulic compartment I based on RFT data from wells 10-1 and 10-2. Figs. 8 and 10 illustrate the same for hydraulic compartment II (based on wells 7-1, 7-2 and 7-4) and hydraulic compartment III (based on wells 7-3 and 7-5) respectively. 

It is well known that the EK process relies on several interacting mechanisms, including (1) advection resulting from electro-osmotic flow and externally applied hydraulic gradients, (2) diffusion of the acid front to the cathode, and (3) the migration of cations and anions toward the respective electrode. The electrolysis of water is the dominant and most important electron transfer reaction that occurs at the electrodes during the EK process. 

An example of induced infiltration brought about by overpumping. The original hydraulic gradient over much of the area has been reversed so that pollutants can travel in the opposite direction, namely, towards the well. Additionally, the aquifer has become influent (i.e. water drains from the river into the aquifer) instead of effluent as it was originally. 

Within the radius of influence downstream of the well, the hydraulic gradient of the aquifer is sloping away from the well, but maintains the same sign ... 

FIGURE 8.9 Hydraulic gradient necessary to initiate blob mobilization at for nonwetting NAPLs with various interfacial tensions, (gr cm/s ), in different soil types. (From Wilson, J. L. and S. H. Conrad. 1984. In Proceedings of the Nationcd Water Well Association Conference on Petroleum Hydrocarbons and Organic Chemicals in Groundwater, Houston, TX, Nov. 5-7, 1984, pp. 274—298. With permission.)... 

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