The Role of Groundwater Models in Well Project Planning

The Role of Groundwater Models in Well Project Planning
A case study on the role of groundwater models in the Pure Water Oceanside project

The Issue

Groundwater models are key to successful well planning and project execution as demonstrated in Geoscience’s successful groundwater model supporting the City of Oceanside’s Pure Water project.

Groundwater modeling and well siting, design, and construction are not mutually exclusive. Accurate modeling supports well project planning and provides a better understanding of the geohydrologic conditions in an aquifer leading to more effective well designs and promoting groundwater project success.

Unfortunately, developing and using reliable groundwater models to help design and configure well projects is an often neglected, yet vital, part of the process. In fact, groundwater modeling and well siting, design, and configuration are often treated as separate projects with no relation to one another.

Case Study

The City of Oceanside (City) is responsible for providing water treatment and delivery services, and wastewater collection and treatment for the City’s domestic, commercial, and irrigation customers. To help provide more than 31 million gallons of water per day to city residents, the City operates the Robert A. Weese Direct Water Filtration Plant, Mission Basin Groundwater Purification Facility (MBGPF) for brackish groundwater treatment, and the San Luis Rey Water Reclamation Facility (SLRWRF) for wastewater treatment and recycled water production. The current desalter facility has additional capacity to develop groundwater, that can be used to further augment water supplies.

To increase water supply, and improve supply sustainability, the City began the Pure Water Oceanside project—an indirect potable reuse (IPR) project to recharge the Mission Groundwater Basin using advanced treated recycled water from SLRWRF. The advanced treated recycled water would supplement natural recharge in the groundwater basin and be extracted by down-gradient wells to enhance the City’s potable water supply, improve supply reliability, and reduce dependence on imported water.

To implement the project and better understand conditions in the Mission Groundwater Basin, the City investigated groundwater replenishment reuse projects and completed extensive hydrogeologic investigations in 2017 and 2018.

The investigations included several steps:

Compile and review data
Update and calibrate the Mission Basin Groundwater Model
Run modeling scenarios to evaluate potential recharge/extraction locations
Based on modeling results drill exploratory boreholes and conduct lithologic sampling to better understand hydrogeologic conditions in areas of interest
Refine and recalibrate the groundwater model based on information gained through exploratory investigations
Use the recalibrated model to simulate recharge operations to determine project feasibility and confirm injection and extraction locations.

The groundwater modeling was key to the investigation and verified the City could achieve long-term sustainable groundwater production levels by redistributing recycled water injection, and groundwater extraction wells.

Idea in Brief

Groundwater modeling is key to water agency managers’ ability to identify potential project locations and detect key areas where additional information may be required. Field investigations can then be planned to maximize hydrogeologic understanding and minimize data costs. Follow-up investigations designed for model refinement enhance the ability of groundwater models to simulate local project effects. This approach was used by the City of Oceanside when implementing the Pure Water Oceanside project, a planned aquifer recharge project using advanced treated water from the City’s wastewater treatment plant, and groundwater desalter. As a result of the approach, the City was able to effectively identify injection and production well locations, and simulate facility operations to help identify the optimal project layout and design.

Map showing production wells and proposed injection wells siting based on groundwater modeling.

Key for map showing details of groundwater model informed well siting

Groundwater Modeling Informed Injection Well Siting

As illustrated above, the updated and refined groundwater model was used to run scenarios that predicted future facility operation and helped identify optimal injection well sites to recharge the aquifer with recycled water.

Results

Currently, the City is installing both new injection and production wells in Mission Basin to help meet future demand and increase current production capacity to the existing desalter facility. The use of groundwater modeling and simulations in conjunction with field investigations provided the City with a clear path forward, enhanced insight for well siting, project design, and long-term groundwater management.

Key take-aways…

Groundwater models can help plan future projects and forecast how those projects well affect basin management.
Groundwater modeling helps with project permitting from agencies such as the Regional Board and Division of Drinking Water.
A groundwater model can help move a project forward during the planning and design phases.
A groundwater model improves chances of ultimate project success and mitigates risks.

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