Groundwater Modeling of Aquifer Storage & Recovery (ASR) Projects
Groundwater modeling of proposed aquifer storage and recovery (ASR) applications may be required related to water rights issues of injury, either based on diminution of water availability, degradation in water quality, or both. Groundwater modeling of proposed ASR operations can address these water rights issues. When the recovery of recharged water is at a remote location from the recharge location(s), recovery of the groundwater may affect other users in the receiving aquifer. Likewise, because in many instances non-native water is being recharged into receiving aquifers with a different water chemistry, it has to be demonstrated that the recharge doesn’t result in water quality degradation, as UIC regulations require an anti-degradation of the existing potable aquifer system.
For example, the magnitude and direction of groundwater flow from a recharge mound, coupled with the subsequent recovery of recharged water at remote locations, can affect other users because the recovery is outside the area of influence of an injection well or RIB. Therefore, even though the recharge is supplementing the aquifer with additional non-native water, the recovery is depleting an area of the aquifer that has not benefited from the recharge.
To address this issue, LWS uses the transient numerical groundwater model MODFLOW to support proposed ASR projects using either RIBs or injection wells by evaluating the proposed recharge and recovery operations. Groundwater modeling is an effective means to demonstrate that there will not be injury to other users from the proposed ASR operations.
Simulation of groundwater recharge
Injection and recovery lines
Groundwater modeling can be very useful in demonstrating the hydraulics of recharge and recovery, both related to the efficiency for the operator of the project and to show the project won’t injure other users. But groundwater hydraulics is not the only factor that has the potential to cause injury. Water quality changes due to (1) differences in water chemistry between the source water and the aquifer, as well as (2) water quality chemical incompatibility, is also an issue. Numerical transient groundwater modeling, MT3DMS with MODFLOW, can evaluate water quality changes that may result from an ASR project, based on the type of constituents of concern that may be in the source water, e.g. conservative versus non-conservative ions, radionuclides, etc. Transient groundwater models can be used relative to assessing the fate and transport of constituents introduced into the aquifer from recharge operations to demonstrate that the recharge and recovery of water does not negatively affect the quality in adjacent wells so they can continue to divert their legally- and physically-available water supplies.
Geochemical modeling can also be conducted to evaluate the chemical compatibility of aquifer water, the geologic matrix, and a non-native source water [see LWS blog, Aquifer Storage and Recovery Through Injection Wells and Rapid Infiltration Basins]. A common model used for geochemical modeling is PHREEQC, developed by the U.S. Geological Survey. Geochemical modeling allows an initial analysis of chemical compatibility, as introduction of non-native water into an aquifer can result in unintended negative consequences, such as oxidation and precipitation of constituents that can clog well screens and aquifer pore space.
For more information on the common methods of achieving aquifer storage and the subsequent recovery of the water have a look at our previous blog. For more information on the permitting requirements and/or modeling of ASR operations, please contact LWS by email or give us a call.
Phone: 303-350-4090
Bruce A. Lytle, P.E. bruce@lytlewater.com
