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SMGA Basin Boundary Modification Plan

Background – Sustainable Groundwater Management Act

The City of Corona (City) relies on local groundwater basins for a significant source of its water supply. Recognizing the importance of groundwater to communities like Corona, the state legislature enacted the Sustainable Groundwater Management Act of 2014 (SGMA). SGMA provides local water agencies with important new groundwater management tools not previously available for the purpose of achieving sustainable groundwater use.

In order to implement SGMA, the California Department of Water Resources (DWR) has prioritized all of the Designated Groundwater Basins in California as high, medium, low, or very low. In accordance with SGMA, DWR requires the formation of Groundwater Sustainability Agencies (GSAs) that cover the entire basin for all medium and high priority Groundwater Basins. A GSA can be a single agency, or a group of agencies coordinating the sustainable planning and management of the basin.

In 2008, the City adopted a Groundwater Management Plan (GWMP) for portions of two DWR-designated groundwater basins from which the City relies on for water supply: the Temescal Subbasin of the Upper Santa Ana Valley Groundwater Basin (No. 8-2.09) and a hydraulically distinct northwestern portion of the Elsinore Basin (No. 8-4), referred to locally as the Bedford-Coldwater area. DWR has designated the Temescal Subbasin and the Elsinore Basin as medium priority and high priority, respectively. Corona has been actively managing groundwater resources in the Temescal Subbasin for decades. The City, in coordination with Elsinore Valley Municipal Water District (EVMWD) and Temescal Valley Water District (TVWD), also manages groundwater in the Bedford-Coldwater area. Groundwater in the remainder of the Elsinore Basin (southeast of the Bedford-Coldwater area) is managed by EVMWD as described in its 2005 GWMP.

Basin Boundary Modifications

Successful groundwater management relies on accurate delineation of groundwater basins. DWR has defined and designated 515 groundwater basins and subbasins in California. However, DWR and SGMA recognize that some of the groundwater basin designations are imperfect and, in some cases, could better support sustainable management with revised boundaries. SGMA includes a process for modifying groundwater basin boundaries from the current official delineations in DWR Bulletin 118. This process allows local agencies to request Basin boundary modifications from DWR, and provides opportunities for public and agency input. In November 2015, DWR finalized regulations for requesting modifications for basin boundaries and initiated a 90-day basin boundary modification period on January 1, 2016.

Proposed Boundary Modifications

The northwestern portion of the current Elsinore Basin from which Corona pumps groundwater is within the Temescal Wash watershed, and is locally referred to as the Bedford-Coldwater area. The City of Corona is coordinating closely with TVWD (formerly Lee Lake Water District) and EVMWD to explore a potential basin boundary modification request from DWR to create a new groundwater basin covering the Bedford-Coldwater area. This boundary modification request would also include realignment of the existing Elsinore Basin boundaries to match the alluvium of the Elsinore Valley and Temescal Wash areas, as mapped by the United States Geological Survey (USGS). The City, TVWD, and EVWMD are submitting a combined request for boundary modifications, as required DWR.

The basin boundary modification request will document the benefits and need for the Elsinore Basin boundary modifications and creation of the new Bedford-Coldwater Basin:

  • The Elsinore Basin and proposed new Bedford-Coldwater Basin boundaries would be modified to align with the alluvial deposits as mapped by the USGS, a change that would result in better correlation between the description in DWR Bulletin 118 and the mapped extent of the basins.
  • Groundwater within the Bedford-Coldwater area is hydraulically connected to the remainder of the Elsinore Basin primarily beneath a narrow channel (referred to as Temescal Canyon) of Temescal Wash, and to a limited extent through shallow upland alluvial material. This limited connection provides a natural break for a basin boundary.
  • The proposed new boundary between the Bedford-Coldwater Basin and the Elsinore Basin is located across this channel, generally separating two regional groundwater flow regimes.
    • Groundwater flow north of this boundary is primarily towards the northwest and the center of the proposed Bedford-Coldwater Basin.
    • Although some groundwater inflow occurs across this boundary from the south, most of the groundwater in the remainder of the Elsinore Basin flows southeast toward the basin center.
    • The canyon contains shallow bedrock and thin alluvial sediments, which restrict the volume of subsurface inflow across the boundary.
    • Recharge within the Bedford-Coldwater area primarily occurs from runoff in adjacent hills east and west of the area rather than from the small amounts of inflow from the south.
  • The Elsinore Basin south of the Bedford-Coldwater area is within the service area of the EVMWD, but the Bedford-Coldwater area is outside of EVMWD.
  • The City and TVWD service areas cover almost all of the Bedford-Coldwater area; those portions outside of these service areas are not within the service area of any local water agency. The agencies will coordinate with Riverside County for these currently unmanaged areas as required under SGMA.
  • Corona, in coordination with EVMWD and TVWD, has long been responsible for managing groundwater conditions in the Bedford-Coldwater area. For example, the City has executed legal agreements with EVMWD for the managed withdrawals from the Coldwater area.
  • Creation of this new basin would allow the City to continue to coordinate with the other agencies overlying the Bedford-Coldwater area separate from activities in the Elsinore Basin. This arrangement would facilitate activities for sustainable management of the groundwater within the Bedford-Coldwater area.

Recognizing the hydrogeologic and jurisdictional conditions in the Bedford-Coldwater area that are distinct from the remainder of the Elsinore Basin, Corona, TVWD, and EVMWD believe that more effective sustainable groundwater management will be achieved if Bedford-Coldwater is a separate groundwater basin. The modified basin boundaries of the new Bedford-Coldwater Basin and the re-aligned Elsinore Basin will be more consistent with both the hydrogeologic conceptual model and historical and ongoing management of these shared groundwater resources. A map that shows the current and proposed basin boundaries can be accessed here.

Public Notification and Consulation

The City is also closely coordinating with EVMWD and TVWD to prepare the required combined boundary modification request package. The City of Corona has notified and is coordinating with all other affected public water systems regarding this basin boundary modification request. The City is also submitting to DWR a notification of intent to pursue a basin boundary modification creating the new Bedford-Coldwater Groundwater Basin and modifying external boundaries to better match the extent of alluvial sediments.

The City of Corona and EVMWD have adopted resolutions and submitted a coordinated basin boundary modification request to DWR. That package was deemed complete by DWR on April 8, 2016. The public may provide information to support or oppose the proposed boundary modification request by submitting written notice to DWR within 30 days of the completed package. Public input must include the name, address, and electronic mail address along with a clear statement of the basis for the support or opposition to the proposed boundary modification. The public comment period closes May 7, 2016.

For additional information or to request notifications on the proposed Basin Boundary Modification, please email or submit in writing to the following address:

City of Corona
Department of Water and Power
Attn: Mr. Tom Moody
755 Public Safety Way
Corona, CA 92880