Groundwater basins account for nearly 70% of Orange County’s water supply. The 125-acre Burris Basin holds water diverted from the Santa Ana River equal to the need for nearly 300,000 households each year. Water from here is then pumped through a 5-mile long, 66-inch pipeline for recharge at the Santiago Basins. This project replaced the aging pump system with vertical turbine pumps installed in a circular wetwell, with new electrical and mechanical equipment and a 50-foot-deep intake pipe installed on the slope of a new embankment. This CalGeo 2017 Large Project of the Year was built in two phases to allow continued pumping, and protect the sensitive habitat.
Orange County Water District
- Geotechnical Engineering
- Geotechnical Testing
Saving potable water for 300,000 households – because when it rains, it doesn’t always pour.
The Leighton Solution.
Phase I included building an earthen coffer dam around the site of the new pump station. The coffer dam involved placement of 27 feet of engineered fill (130,000 cy of soil) and cuts to 32 feet which provided a dry interior for phase 2 construction. Compaction grouting was performed on top of the earthen embankment to reduce inflow of water. The target zone of grouting was the sand layer located 5 to 15 feet below the embankment.
Phase 2 finished construction of the new 10,000 SF storm water pump station and intake pipe installed on the slope of the embankment, connecting the new pumps to the intake invert. The new pump station is a large structure with an overall height of 100 feet and a wet well 70 feet in diameter.
Leighton is the geotechnical engineer of record for the project. Addressing the earthen berm construction, we advanced two borings and three Cone Penetration Tests (CPTs) to depths of 60 to 75 feet.
Slope stability analyses was performed to evaluate stability of temporary and permanent slopes considering the effects of water levels in the basin. Recommendations were developed for material for construction of the slopes and embankment, foundation of the new pump stations, lateral earth pressures for the wetwell design, and riprap for slope protection.
During construction of the cofferdam, Leighton provided quality control testing of the compaction grouting which included observation of grout pressure, grout return, and quantity of grout. Over 100,000 gallons of grout were injected over a period of two months.
After completion of Phase I Grading, five additional hollow-stem auger borings were advanced from the top of the earthen embankment to depths ranging from 32 to 47 feet to further characterize the embankment materials and the underlying soils. A supplemental report was provided for final grading design for the pump station.
During Phase II, Leighton provided observation and sampling of compacted fill, import fill for moisture content and relative compaction, rebar placement for foundation, concrete and grout sampling and testing. Observed and tested aggregate base placement over the subgrade for the Intake Inlet Structure 96” pipe and 66” discharge pipe.