Ground water recharge protection and enhancement: a regional approach for augmenting local supply

1. Ground water recharge protection and enhancement:a regional approach for augmenting local supply A. T. Fisher Earth and Planetary Sciences Department and the Institute for Geophysics and Planetary Physics University of California, Santa Cruz, CA M. Cloud Water Resources Division Santa Cruz County Soquel Creek Water District 30 April 2008 Soquel, CA

2. Presentation Overview* • Modes of ground water recharge • Highlights from previous assessments of ASR potential • Opportunities to enhance and monitor recharge • Limitations within the SqCWD based on aquifer characteristics, distribution of wells and demand • Options and remaining questions * Comments offered at the request of Laura Brown, not intended to replace or replicate numerous high-quality studies completed by SqCWD staff and contractors

3. Some forms of ground water recharge and management Ground water recharge Natural recharge Managed recharge Regional precipitation Streambed Irrigation Surface recharge Well recharge • Identify locations and quantify • Protect and enhance • Confined aquifer wells • Water table wells • Vadose zone wells • Stream bank filtration • Spreading basin/trench Single purpose (injection) or Dual purpose (ASR)

4. Many kinds of "enhanced" recharge Harkins Slough MAR project

5. Highlights from previous assessment of potential for ASR by SqCWD • • Use existing Purisima extraction wells, estimate injection capacity from pumping capacity, limited testing • • perhaps 3.9k–5.6k gpm [~6k–9k af-ft/yr] (L&S, 1999) • • more like 1.2k–2.8k gpm [~2k–4k af-ft/yr] (DW, 2004) • • Not all existing Purisima wells have high capacity (5/11 are better) • • Water quality from SC diversion probably OK, modest treatment needed • • Existing infrastructure may be incompatible (partly compatible): well completion, pumps, piping, valves and controls, etc. • • ASR often works best with dedicated wells, requires maintenance to avoid clogging, maintain injection and recovery capacity

6. Exposure of aquifers across SqCWD

7. Exposure of aquifers across SqCWD Better for surface recharge? Better for subsurface recharge?

8. What are some options for the SqCWD? • • Different options in areas in which Purisima and Aromas aquifers are dominant sources for ground water, outcrop, etc. • • Where Purisima is main aquifer: • • limited transmissive properties will limit potential for ASR - maybe distributed injection recharge? • • maybe still worth mapping and assessing streambed recharge, baseline information, opportunities to enhance in ephemeral streams? • • Where Aromas is main aquifer: • • map streambed recharge, limit sedimentation and enhance streambed properties and flow where possible • • options for managed recharge through spreading basins, trenches, or vadoze zone wells? • • In any case, where will the excess water originate? • • Desal when supply exceeds need? • • Recycled water • • Temporary surface storage of excess surface flows • • Permitting, water rights, water quality will all remain issues (DBP, ECs)

9. ASR alternative: distributed injection recharge? • • Network of small-capacity wells (confined, unconfined, vadose) and/or other systems that can be used to distribute recharge along a path, rather than trying to force it in within the limited aquifer area surrounding one or a few wells. • • Earlier studies suggest that limit using current wells and ASR might be ≤1500 ac-ft/yr. Potential alternative: • • array of 16-18 small-capacity injection wells, each capable of 250-300 gpm, with 8-10 operating at a time (~1500 ac-ft/yr) • • design for injection, cycle periodically with occasional production to avoid clogging - primary purpose is injection, not recovery • • locate injection sites either (1) upgradient from current production wells, or (2) near coast in effort to create higher water levels and avoid intrusion • • Recovery efficiency? • • would depend on goals, might be 60-80% if upgradient from production wells, maybe <50% if closer to coast • • Goal would emphasize long-term augmentation of natural recharge, rather than storage (different from ASR)

10. Opportunities to enhance ground water recharge and storage • Identify and protect regional recharge areas (limit urbanization, use pervious pavement, etc.) • Reduce high sediment loads in streams where recharge occurs (maintain high streambed hydraulic conductivity) • Eliminate "dry gaps" in losing streams by maintaining flows along critical stretches (remain connected to aquifer). • Supplement natural recharge with managed recharge - look for creative recharge sources (excess storm flows, tertiary treated water, etc.). Being done in many CA basins! • Explore use of temporary holding facilities that allow management of water quality (reduce sediment loads, remove nutrients) prior to recharge. • Develop agreements that facilitate conjunctive use on a regional basis (requires political will, infrastructure, funding, permits, water rights, cooperative spirit)