Steady critical discharge rates from vertical and horizontal wells in fresh–saline aquifers with sharp interfaces

Abstract

In this study, the critical (or maximum) discharge rates before saline water enters a well were determined for vertical and horizontal wells in a freshwater aquifer which is separated from a static saline aquifer by a sharp interface. Flow around the well was solved by integration of a point sink solution along the well axis, and both the critical discharge rate and critical interface rise were determined through a comparison of the heads and vertical gradients at the saline-fresh water interface. The rates were determined for vertical and horizontal wells with various lengths and depths for different aquifer salinities. Results were generalized by drawing dimensionless type curves. The results showed that the dimensionless total critical discharge rates are higher for the longer horizontal wells and longer vertical wells with a certain bottom depth, and they almost linearly decrease with well depth at rates of 0.7-0.9. For the dimensionless well length of 0.2, the dimensionless total discharge rate of a horizontal well is about 0.1 more than that of a vertical well with the same length and well-top depth. Also, the critical discharge rates per unit length of well are inversely proportional to well length and remarkably higher for shallower wells. Additionally, the critical pumping rate is proportional to the salinity difference of the aquifers. These results were confirmed by comparison to existing solutions for vertical wells with dimensionless lengths of 0.2, 0.5 and 0.6, and for critical interface rises in the range of 0.75-0.9.

Mitigation of saltwater intrusion by ‘integrated fresh-keeper’ wells combined with high recovery reverse osmosis

“…Replenishment of already deteriorated water is expensive and sometimes ineffective, and prevention is hampered by the need to provide enough substitutes of chemically suitable water. Therefore, this issue has attracted much attention over the last decades, and several countermeasures have been proposed: (1) reducing pumping (Sherif et al 2012), (2) changing extraction arrays (Cai et al 2015), (3) enhanced natural and/or artificial recharge (Sophiya and Syed 2013), (4) direct reuse of treated wastewater or via artificial recharge (Ouelhazi et al 2014), (5) water transfer from other regions, (6) building subsurface physical barriers (Sugio et al 1987), (7) installing hydraulic barriers with/without injection wells (Hendizadeh et al 2016) which are sometimes supported by desalination plants (Payal 2014;Javadi et al 2015), (8) integrated fresh-keeper (IFK) wells (Grakist et al 2002;Kooiman et al 2004;Stuyfzand and Raat 2010;Zuurbier et al 2016), or (9) stand-alone BWRO or seawater reverse osmosis (SWRO) plants; the former with better feedwater quality has several advantages over SWRO leading to lower operational costs and less environmental problems (Stein et al 2016). Nevertheless, most of these actions are hampered by specific limitations reducing their wide applicability.…”