cross-sectional diagram of barrier-well impact on seawater intrusion

Key Issue

  • Pumping reductions needed to prevent seawater intrusion could force the construction of an expensive alternative supply. Therefore, the District wanted to confirm the accuracy of the analysis.

Solutions

  • Todd Groundwater conducted a rigorous and detailed assessment of seawater intrusion prevention criteria and analytical methodologies and found them to be of high quality.
  • Due to the lack of expected correlations between pumping, water levels and water quality, an adaptive approach was recommended so that management measures can be adjusted to reflect findings from ongoing monitoring.

Peer Review of Seawater Intrusion Prevention Strategies

Santa Cruz County, California

A comprehensive peer review of the analyses and modeling used to establish criteria for prevention of seawater intrusion

The Soquel Creek Water District (District) located along Monterey Bay in Santa Cruz County, California is challenged with managing inland pumping to prevent seawater intrusion. Groundwater provides 100% of the water supply for the Soquel-Aptos Area underlying the District. In addition to the District, groundwater is pumped by other water purveyors and private parties.

map of the Soquel area on Monterey Bay

Currently, coastal groundwater levels are below estimated elevations needed to protect the Soquel-Aptos area from seawater intrusion, therefore creating a state of overdraft. The District retained a consulting firm to help establish management measures that the District can use to mitigate seawater intrusion. Subsequently, the District retained Todd Groundwater to assess the technical accuracy and soundness of the management measures.

The criteria used to direct the management measures include:

  1. the protective groundwater elevations necessary to prevent seawater intrusion,
  2. the amount of groundwater outflow to the ocean that would be associated with maintaining protective groundwater elevations,
  3. the overall sustainable yield of the basin given the outflow requirements, and
  4. the amount of the sustainable yield available for use by District.

Todd Groundwater found that the biggest challenge for managing groundwater resources in the Soquel-Aptos basin is not weakness in technical analysis but a lack of actual correlations between pumping, water levels and water quality. Data for those variables often do not exhibit the patterns expected from the physical laws governing groundwater flow. As a practical matter, this circumstance underscores the need for an adaptive management approach. The time frame for achieving protective groundwater elevations is long enough that pumping rates and other management measures can be adjusted to reflect ongoing results from monitoring.

Contact Todd Groundwater

We understand groundwater protection. Let us assist you in understanding and protecting your groundwater. For more information, contact Todd Groundwater