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

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

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

Santa Ana River Channel Off-River Channel

 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

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

Test Period 1

Test Period 2

Pilot Study Results

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

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

Inlet Surface Flow and Pumping Rates

Phreatic Surface Depth (E vs W) Capture from Storage

Phreatic Surface Elevation (E-W transect)

` Phreatic Surface Elevation (N-S transect)

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)

Transmission Loss and Groundwater Recharge

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

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

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