1. The Orange County Water District Riverbed Filtration Pilot Project Jason Keller 1, Michael Milczarek 1, Greg Woodside 2, Adam Hutchinson 2, Robert Rice 1 1 GeoSystems Analysis, Inc 2 Orange County Water District

2. Orange County Water District  Recharges groundwater basin using Santa Ana River (SAR) water and other sources of water Over 1,000 acres of surface spreading basins Average recharge of 200,000 acre-ft/year  SAR flow comprised of tertiary-treated effluent and stormwater  SAR water quality: Total Suspended Solids (TSS) varies from 5 to 400 mg/l Total Organic Carbon (TOC) typically 5 to 10 mg/l  Spreading basin performance declines in exponential fashion due to clogging. OCWD wants to:  Improve basin performance  Increase total recharge volumes

3. Riverbed Filtration System Pilot Project Objectives  Evaluate riverbed filtration technology to treat SAR water  Design pilot scale riverbed filtration system Want to induce recharge (create more recharge into river) Want low tech, low cost (shallow drainfield)  Construct pilot project in SAR off-river channel Evaluate potential long-term performance Monitor: – Clogging rates – Influence on groundwater system – Shallow water level response – Increased recharge rates with filtered water

4. Santa Ana River Channel Off-River Channel

5.  Design for 10 cfs (4,500 gpm)  Monitoring system to evaluate riverbed filtration system performance 13 Monitoring Wells and piezometers Temperature at 1 ft, 6 ft, and 10 ft bgs in selected wells Stream flow gaging → Flow in – Flow out = GW recharge and drain capture (transmission loss)  Bi-weekly samples of raw source and riverbed filtration treated water collected and analyzed for water quality  Percolation testing using raw water and riverbed filtration treated water to evaluate percolation decay Pilot Project Design

6. Initial Conceptual Subsurface Model Santa Ana River Off-River Channel 0 10 30 Sand/Gravel Desilted water to recharge basins feet bgs

7. Test Period 1

8. Test Period 2

10. Pilot Study Results

11. Water Quality  Riverbed filtration significantly improved water quality Reduced TSS and turbidity by >99% and 96% Decreased TOC, TKN, iron, and manganese by 50% or greater Riverbed filtered water quality significantly better than other treatment technologies evaluated – Cloth filter, flocculation-sedimentation, dissolved air flotation, ballasted sedimentation

12. Percolation Decay  Percolation rates 50% of initial percolation within: Raw water ~ 7 hours Riverbed filtered water ~ 58 hours  Air entrapment during early period of riverbed filtration column

13. Inlet Surface Flow and Pumping Rates

14. Phreatic Surface Depth (E vs W) Capture from Storage

15. Phreatic Surface Elevation (E-W transect)

16. ` Phreatic Surface Elevation (N-S transect)

17. Pumping and Phreatic Surface Data Summary  Phreatic levels and pumping capacity very responsive to surface water flows  East side of drain system less productive than west side Water from west supplying east laterals  Unsaturated zone especially in east side Reduced K, potential for air entrapment  Strong hydraulic gradient to north  Maximum Pumping Capacity Test Period 1 (w/out L-berms) = 1,350 gpm Test Period 2 (w/ L-berms) = 2,000 gpm 30% - 40% of target collection rate (4,500 gpm)  Potential clogging observed (phreatic surface deeper after pumping than prior to pumping)

18. Transmission Loss and Groundwater Recharge

19. Conclusions  Riverbed filtration significantly improves water quality and percolation performance  System performance dependent on surface water flow rates and depth Maximum pumping capacity of: – 1,350 to 2,000 gpm – 30% - 40% of target collection rate Lower than expected groundwater elevations Unsaturated zone and strong south-to-north gradient reduced system efficiency  Drainfield east of the collection vault was less productive than west of the collection vault  Drain system induces recharge during pumping and most of water collected from induced recharge

20. Future Studies  Effective surface water and groundwater depths Need to maximize groundwater elevations (reduce unsaturated zone)  Surface clogging may have contributed to a reduction in induced recharge Longer term study required to evaluate surface clogging influences Treatment options (to control clogging)  System optimization  System expansion planned

21. THANK YOU!