Developing Salt and Nutrient Management Plans

A key element of the Recycled Water Policy adopted by the California Water Resources Control Board is developing salt and nutrient management plans for every groundwater basin by 2014. A two-year extension to 2016 is possible if substantial progress is being made).

The plans are intended to protect groundwater from accumulating salt and nutrient concentrations that would degrade the quality of groundwater and limit its beneficial uses.

As local stakeholders start to meet on salt and nutrient plans, Peter Quinlan, Dudek’s lead hydrogeologist, offers the following considerations:

Infiltrating Rainwater Challenge

Rainwater is the cheapest method to improve basin water quality compared to energy intensive and expensive desalination. Desalination also creates brine disposal issues.

Flood control systems, however, are set up to efficiently move “big water” out of basins rather than capture it. While the value of retaining rainwater is recognized, the ability to do so in urban areas is constrained by lack of land to allow for storm water diversion, retention, and infiltration while avoiding flooding or damaging riparian habitat. The challenge is to develop an environmental friendly plan to capture and infiltrate rainwater that doesn’t use a lot of energy, create brine or flood habitat.

Stakeholder groups in urban areas may have to be creative because they are constrained by existing development and environmental concerns about riparian corridors. One potential avenue could be public-private partnerships to facilitate temporary seasonal spreading of stormwater flow onto vacant or pasture land, or gravel pits as a means of addressing the lack of open space suitable for infiltration in urban areas.

Consider Integrating Watershed Models and Stream Flow

Locating infiltration opportunities for a salt and nutrient plan will require integrating surface water models with a basin’s groundwater modeling. Most water agencies have large groundwater models that provide a good understanding of how pumping can affect water levels.

However, these models do not integrate surface water flows and infiltration, or model the migration of salts from one area to another. This analysis requires an integrated surface water–groundwater model with a water quality component. The existing models may not provide sufficient detail for such an analysis.

In addition, Dudek hydrogeologists’ experience in reviewing and preparing surface water models shows that infiltration is often intentionally neglected to make flood control management plans conservative. Integrating infiltration with recharge to groundwater can give a clearer picture of how the watershed and groundwater basin can be made to work.

Develop a Flexible Plan

Stakeholder groups can leverage the salt and nutrient management planning to develop models flexible enough to evaluate other basin issues, such as climate change, flooding, recharge over a multi-decade period, and groundwater pumping. One example of developing a flexible plan is to allow for a range of salinity goals so targets can be relaxed during drought and tightened during wet years.