Managed Aquifer Recharge Geochemical Evaluations in Basalts

The Pacific Northwest (PNW) has been at the forefront of using MAR as a successful component of its overall water supply strategy. SSP&A has provided consulting services to municipalities since the 2000s to identify and understand changes in water and mineral chemistry that can occur during managed aquifer recovery (MAR) projects such as aquifer storage and recovery (ASR), which involve the injection of surface water into Columbia River Basalts (CRB).

SSP&A has designed sampling and analysis plans to determine groundwater and basalt chemistry, performed geochemical reactive transport modeling to predict the types and consequences of chemical reactions during ASR operations, and identified mitigation measures in cases where chemical incompatibilities between recharge water and basalt have been identified.

An example of a MAR geochemical evaluation is a project performed for the Tualatin Valley Water District, Oregon, which involved the injection a new source of water (consisting of treated Willamette River surface water) into its existing ASR system. SSP&A used site-specific geochemical data to calibrate a kinetic-based reactive transport model and used the model to simulate time-dependent chemical reactions between recharge water and the primary and secondary basalt minerals and glass in the CRB. SSP&A evaluated the effects of different treatment plant options on the concentrations of inorganic constituents and trihalomethanes compounds both in the ASR aquifer as well as the potential for mineral precipitation or corrosion in the distribution system. SSP&A was able to demonstrate little potential for deleterious changes in water quality by the introduction of the proposed treated water. Some mineral precipitation and/or corrosion could occur, but use of a new source water was not found to affect ASR operations or necessitate additional maintenance. SSP&A submitted a report on behalf of the water district as part of its permitting process.

Other municipal clients include:

• City of Kennewick, WA
• The Dalles, OR
• City of Stayton, OR
• City of Prineville, OR
• City of Cornelius, OR
• City of Walla Walla, WA
• City of West Richland, WA
• City of Salem, OR
• City of Fossil, OR