Pasadena Water and Power
Raymond Groundwater
Basin Update
Municipal Services Committee
January 13, 2026
Item #2
Pasadena Water and Power
Raymond Basin Aquifer
Local Groundwater Basin
2 • 40-square mile groundwater basin
o North - San Gabriel mountains
o East - Cities of Arcadia & Sierra Madre
o West - San Rafael Hills
o South - Huntington Drive
• Sub-areas
o Monk Hill (Western unit, Pasadena holds water rights) o Pasadena (Western unit, Pasadena holds water rights)
o Santa Anita (Eastern unit)
• First and oldest adjudicated groundwater basin
in the state
o 10-member Board represents 15 agencies
o Enforces adjudication since 1944 to maintain and protect the supply of groundwater in the Raymond Basin area
o Pasadena is the largest water rights holder in the basin (42%)
Pasadena Water and Power
Stabilizing Groundwater Levels
3 • Groundwater levels decreased over time
• Taking action to stabilize groundwater levels
o Reduced decreed pumping
o Pasadena Sub-area
Starting 2009, reduced decreed pumping
(reduction held at 30% per year since 2014)
75,000 AF cumulative savings through FY25
o Monk Hill Subarea
In 2024, reduced decreed pumping by 24% per
year
3,700 AF cumulative savings through FY25
• Improving Forecasting: Hydraulic
Groundwater Model
o Performing 3-D numerical model for characterizing
groundwater behavior
o Performing multiple scenarios including storage
programs
Actual water levels
stabilizing due to
RBMB Actions
1910-1911
Pasadena Water and Power
Augmenting Groundwater Storage
4 • Continued active capture and recharge at
Arroyo Seco and Eaton spreading basins
• Regional partnerships and programs to
leverage imported supplies
o Proactively capturing surplus State Water Project
supplies for local groundwater replenishment
Metropolitan In-Lieu program (Cyclic Cost
Offset Program)
o Working with Metropolitan on additional programs
• Groundwater augmentation projects
o Arroyo Seco Canyon project
o Devil’s Gate Pump Back project
o Water Reuse project/partnerships
Pasadena Water and Power
Ensuring a Resilient System
5 New Production Wells Monk Hill Treatment
(Completed 2011)
Wadsworth Treatment
(Completed 2024)
Proposed Sunset
Complex Project
Pasadena Water and Power
Need for Enhanced Groundwater Basin/In-Region
Storage
6 • Climate extremes and weather whiplash
o More extreme drought and flood cycles impacting
both local precipitation and imported supplies
• Emergencies
o Wildfires, seismic events, natural disasters
• Increasing costs
o Imported water and other costs
Pasadena Water and Power
• Metropolitan programs
o Metropolitan Cyclic Cost Offset Program (in-
lieu program) potentially available this
calendar year
o Continuing to work with Metropolitan and
regional partners on additional groundwater
augmentation programs
• Legislation/Funding
o Potential new legislation
o Proposition 4: Safe Drinking Water, Wildfire
Prevention, Drought Preparedness, and
Clean Air Bond Act of 2024
o Other
7 X,000 AF
+X,000 AF Cyclic for Future Uses
Additional Upcoming Opportunities
Pasadena Water and Power
8