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Central Valley Flood Protection Board Meeting

Central Valley Flood Protection Board Meeting. Evaluation of Groundwater Impacts from the Upper Yuba River South Levee Repair Activities Christian Petersen, P.G., C.Hg. 2/26/10. Topics. Project Overview Physical Setting Evaluation Methods Evaluation Results Conclusions. Project Overview.

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Central Valley Flood Protection Board Meeting

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  1. Central Valley Flood Protection Board Meeting Evaluation of Groundwater Impacts from the Upper Yuba River South Levee Repair ActivitiesChristian Petersen, P.G., C.Hg. 2/26/10

  2. Topics • Project Overview • Physical Setting • Evaluation Methods • Evaluation Results • Conclusions

  3. Project Overview Levee Location • Designed for 200 year protection • 16,700 ft Levee Length • 15,000 ft Slurry Wall – 47 to 80 ft Deep • 1,500 ft Seepage Berm – NE End

  4. Project Overview Study Objectives • Characterize local groundwater conditions • Develop and inventory of existing wells in the project area • Assess groundwater impacts resulting from levee repairs Questions Addressed • Will slurry wall reduce groundwater recharge? • Will slurry wall cut off flow to my well? • Will slurry wall cause groundwater to rise into root zones?

  5. Physical Setting • Groundwater basin boundaries • Groundwater surface and flow • Conceptual understanding of aquifer system

  6. Basin Boundaries • Groundwater Basin • Groundwater Surface • Groundwater Flow Direction • Basin Recharge and Discharge

  7. Groundwater Surface and Flow Local Groundwater Flow Direction

  8. Conceptual Understanding of Aquifer System It is Important to Accurately Characterize the Local Groundwater Conditions to Asses Impacts Scenario #1 Scenario #2

  9. Evaluation Methods • Compile and review well logs and soil borings in project area • Assess the thickness and lateral continuity of confining units • Theis equation to estimate well effects near slurry wall • Hydrus 2D Model used to assess impacts to shallow root zone

  10. Identified Wells in the Area Well Inventory • 2-mile buffer from levee • 695 logs from DWR • 227 logs used in analysis

  11. Geologic Profile Locations Geologic Profile Locations

  12. Geologic Profile Along Levee Alignment Geologic profiles show discontinuous shallow confining layers

  13. Relative Permeability Along Levee Alignment Geologic profiles show discontinuous shallow confining layers

  14. Relative Permeability at Cross Section E-E’ Geologic profiles show discontinuous shallow confining layers

  15. Cone of Depression Cone of Depression Slurry Wall in Levee Well Well Evaluation Results Illustration of Potential Slurry Wall Interference with Shallow Well Pumping Plan View Profile View

  16. Evaluation Results 400 Feet Wide Approximately 13 Wells in the yellow area (1 to 3 ft of drawdown) – Being Verified 1,000 Feet Wide Approximately 8 Wells in the orange area (up to 5 feet of drawdown) – Being Verified

  17. Conclusions 1) Based on GW flow pattern, discontinuous confining layers, and evidence from historic groundwater levels, the proposed slurry wall will not reduce groundwater recharge. 2) The slurry wall will not cut off flow to a well, but if a well is very close to the levee, it may experience up to 5 feet of additional drawdown. 3) The slurry wall will not cause groundwater to rise into root zones, however shallow groundwater has historically impacted orchards adjacent to the Goldfields. The levee repair project will neither improve or significantly compound this existing natural condition.

  18. Vertical Connectivity of Aquifers Multi-level monitoring wells show high degree of connection between shallow and deeper zones within the aquifer

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