As Orange County;s groundwater authority, the Orange County Water District (OCWD; the District) performs many functions to protect and replenish the groundwater basin. Among these activities, OCWD recharges water via spreading grounds and prevents seawater intrusion through the use of injection wells. Due to the concentration of production wells operated by various retail water producers within a relatively small geographic area of OCWD's jurisdiction, there is a groundwater depression in the central portion of the basin near the cities of Santa Ana and Costa Mesa. This results in groundwater gradients from all directions that cause water to flow towards the depressed water table. The gradients include those related to seawater intrusion.

In addition to the threat of seawater intrusion, the lower water table causes increased pumping and increased water production costs due to added energy requirements. It also reduces pressure within the groundwater aquifers caused by the lower water tables and might contribute to the upwelling of colored water from deeper portions of the basin.

OCWD has plans to address this local groundwater depression through a Mid-Basin Injection (MBI) program. When the Groundwater Replenishment System (GWRS) pipeline was constructed to transport purified water from Fountain Valley to Anaheim, several turnout locations were constructed to readily serve future MBI wells. The MBI wells will be similar in function to those preventing seawater intrusion, but will have a dedicated purpose of replenishing groundwater supplies into the principal aquifer, which will help reduce flow gradients, producer pumping costs and potential for colored water upwelling.

A Demonstration MBI well project was studied for feasibility in 2008 by the District and a project plan was developed in 2009 by DDB Engineering, Inc. The site for this well is located at the northwest intersection of Edinger Avenue and the Santa Ana River in Fountain Valley. The site is owned by the County of Orange which has leased the land to the District for the demonstration project. The purpose of the demonstration well is to pilot the MBI technologies and operational strategies, and to monitor the water quality impacts resulting from the introduction of GWRS water directly into the principal aquifer.

The well began injection operations in April 2015. Several months of testing and monitoring of the well's injection impact are needed in order to gather hydrogeologic, water quality, and operational information to support the required permitting and construction of subsequent MBI wells. The District is currently in discussions with the City of Santa Ana and engineering firms to design and construct four additional MBI wells in Santa Ana's Centennial Park, located southeast of the demonstration site.

The District will initially utilize the Demonstration MBI well conservatively to properly prepare the surrounding geology for long-term injection activities. Initial injection rates are being limited to 2 million gallons per day so that District staff can determine the specific mounding and decay rates of the site. Over the next several months, the injection rate will be increased until the maximum sustainable rate is determined. The Demonstration MBI project was self-funded by OCWD as a capital improvement project.