Geochemical Processes During Managed Aquifer Recharge With Desalinated Seawater

Abstract

We study geochemical processes along the variably‐saturated zone during managed aquifer recharge (MAR) with reverse‐osmosis desalinated seawater (DSW). The DSW, post‐treated at the desalination plant by calcite dissolution (remineralization) to meet the Israeli water quality standards, is recharged into the Israeli Coastal Aquifer through an infiltration pond. Water quality monitoring during two MAR events using suction cups and wells inside the pond indicates that cation exchange is the dominant subsurface reaction, driven by the high Ca2+ concentration in the post‐treated DSW. Stable isotope analysis shows that the shallow groundwater composition is similar to the recharged DSW, except for enrichment of Mg2+, Na+, Ca2+, and HCO3–. A calibrated variably‐saturated reactive transport model is used to predict the geochemical evolution during 50 years of MAR for two water quality scenarios: (i) post‐treated DSW (current practice) and (ii) soft DSW (lacking the remineralization post‐treatment process). The latter scenario was aimed to test soil‐aquifer‐treatment (SAT) as an alternative post‐treatment technique. Both scenarios provide an enrichment of ∼2.5 mg L−1 in Mg2+ due to cation exchange, compared to practically zero Mg2+ currently found in the Israeli DSW. Simulations of the alternative SAT scenario provide Ca2+ and HCO3– remineralization due to calcite dissolution at levels that meet the Israeli standard for DSW. The simulated calcite content reduction in the sediments below the infiltration pond after 50 years of MAR was low (<1%). Our findings suggest that remineralization using SAT for DSW is a potentially sustainable practice at MAR sites overlying calcareous sandy aquifers.

Using Desalinated Water for Irrigation: Its Effect on Field Scale Water Flow and Contaminant Transport under Cropped Conditions

“…The shift from natural freshwater to desalinated seawater has promoted research on different downstream effects of this change, including public health (e.g., lack of magnesium in drinking water, [7][8][9]); isotope characteristics of reclaimed wastewater [10]; use of desalinated seawater for…”

Managed aquifer recharge with reverse-osmosis desalinated seawater: modeling the spreading in groundwater using stable water isotopes

“…Stable water isotopes 18 O and 2 H are excellent tracers for water generated by seawater reverse-osmosis (SWRO) desalination. The lack of fractionation during the reverse-osmosis process, in contrast with various isotopefractionation processes occurring in natural, fresh water (Al-Basheer et al, 2017;Gat, 1996;Kloppmann et al, 2008a, b), is the cause of the distinct difference in isotope composition between reverse-osmosis DSW and groundwater (GW) originating from natural, fresh water (Ganot et al, 2018;Kloppmann et al, 2018;Negev et al, 2017). For example, the advantage of using 18 O and 2 H as a quantitative tool for tracing treated wastewater (originating from DSW) that mixes with GW was recently demonstrated by comparing the mixing ratios of chloride, carbamazepine and water isotopes in the soil aquifer treatment (SAT) site at the Shafdan MAR system, Israel (Negev et al, 2017).…”

Managed aquifer recharge with reverse-osmosis desalinated seawater: modeling the spreading in groundwater using stable water isotopes

“…In Israel, for example, DSW reached 80% of the domestic and industrial fresh water supply in 2017 (Israel Water Authority, 2017). This growing use of DSW affects downstream water systems such as reservoirs (Ronen-Eliraz et al, 2017;Negev et al, 2017;Stuyfzand et al, 2017;Ganot et al, 2017Ganot et al, , 2018, wastewater treatment plants (Lahav et al, 2010;Negev et al, 2017) and agricultural irrigation (Lahav et al, 2010;Yermiyahu et al, 2007). One direct way by which DSW use affects the water budget is Managed Aquifer Recharge (MAR).…”