December 21, 2022

#03 | How to technically manage artificial aquifer recharge in water-stressed areas?

Author: Juan Antonio Barberá (CEHIUMA)

Manage aquifer recharge (MAR) techniques are demonstrated to be a promising water management strategy for generating alternative groundwater resources in water-stressed areas, as in the Mediterranean countries. However, their application is not always feasible since it is necessary to have a permeable geological formation (groundwater reservoir or aquifer) in which water intentionally infiltrates from surface.

A first step to deal with the MAR potentiality of a region is to conduct a preliminary geological characterization, by means of analyzing the typology of sediments or rocks acting as aquifer formations in subsurface. In those regions where outcropping lithologies are not porous or fractured, water won´t be able to flow through them, neither store, therefore, the possibilities for MAR are scarce. In case of existing aquifers, their dimensions (i.e. geometry) in depth will condition the amount of water that is able to accept.

To better assess the volume of sediment or rock hosting groundwater, hydrogeologists very often apply geophysical (use physical properties of substratum to know how lithologies are geometrically organized) methods or drill piezometers (pipes reaching the groundwater from surface) for getting reliable geological and hydrogeological information in depth. Another key issue will be to know the rhythm with the water shall be infiltrated through the aquifer. To that, specific test to quantify hydraulic properties, which are highly dependent on sediment/rock texture (e.g. grain size and packaging, porous volume, etc.), should be performed. Depending on the selected MAR facility (e.g. water infrastructure for water recharge as infiltration ponds, deep wells, etc.), clogging effects resulting in infiltration rate reduction can be a problematic issue engaging the performance of MAR operation.

Once physical acceptability of water is validated for MAR purposes, the chemical composition of native groundwater (water previously stored in the aquifer) and surface water to infiltrates must be analyzed in detail. A mid-long term hydrochemical characterization of native groundwater is recommended. Thus, the water types, chemical changes and the identification of hydrogeochemical processes occurring as the groundwater moves is of a broad interest to understand how and in which degree infiltration water shall impact on groundwater quality. If the first has lower quality (e.g. recycled waste water) than the second one, aquifers may induce water quality improvements favored by water-rock chemical interactions occurring naturally. Therefore, MAR techniques may have significant advantages in terms of water remediation.

Numerical models based on collected field data (aquifer hydraulic properties, chemical characteristics of native groundwater and infiltration water, etc.) may help to predict how infiltrated water will flow in the surroundings and in depth of MAR facility and chemically react in subsurface. However, during MAR operation, hydrogeologists and water operators will need to accurately monitor water infiltration processes, groundwater levels and the chemical composition of groundwater to verify that artificial recharge is effective in both quantity and quality aspects. An increasing of groundwater availability with acceptable water quality referred to quality thresholds imposed by national regulations for different water uses (drinking water, irrigation, etc.) will be the main goals of artificial recharge.