Page 39 - Yucaipa Sustainable Groundwater Management Agency - Yucaipa SGMA

If site recharge goals are expected to exceed the operational capacity of the basins, we
recommend the removal of the upper 3 feet of sediment in each of the basins prior to
future active recharge. Pilot‐scale testing is not critical at this site.

3.1.10. Wildwood Creek Basins (EX‐4)

A synopsis of the infiltration testing completed at the Wildwood Creek Basins is shown on
Figure 11. The site is located in the Oak Glen Creek Subbasin upgradient of the South Mesa
barrier and aquifers in the Calimesa Subbasin relied upon for groundwater production. The
site is underlain by highly permeable deposits that should allow for uninhibited vertical
migration of recharge water to the underlying water table. Available vadose zone storage
may be limited by the existing depth to water (104 feet‐bgs in MW‐3 [constructed in EX‐4] in
2014) located about 140 feet to the east. The degree to which recharge water can flow
across the South Mesa Barrier into the Calimesa Subbasin is a critical knowledge gap that
requires further investigation and/or evaluation.

Results of infiltration testing indicate that the site is highly suitable for recharge. The
average infiltration rate from constant‐head testing is 39.0 feet/day (based on stabilized
rates observed after 9 days of testing), which is generally verified by measured infiltration
rates from the falling‐head test (28.3 to 31.2 feet/day). Lower rates from the falling‐head
test are likely due to less driving head from declining water levels.

A full‐scale basin initial infiltration rate is predicted at 19.5 feet/day, and a full‐scale long‐
term infiltration rate is predicted at 9.8 feet/day.

Pilot‐scale infiltration testing is recommended to identify potential site vadose zone storage
capacity constraints due to associated recharge mounding, which may be exacerbated by
the South Mesa Barrier. Installation of a monitoring well west of the South Mesa Barrier and
monitoring of water levels in the new monitoring well and MW‐3 during pilot testing is
recommended to better understand the subsurface flow dynamics across the South Mesa
Barrier.

3.1.11. Oak Glen Creek Basins (Bermed) (EX‐2)

A synopsis of the infiltration testing completed at the Oak Glen Creek Basins (bermed) is
shown on Figure 12. This site is unique, in that native material was used to create shallow
berms to test the infiltration through undisturbed sediment at the ground surface. The site
is favorably located upgradient of major production wells in the Gateway and Wilson Creek
subbasins. Water levels indicate that recharging at this location will likely benefit aquifers on
both sides of the Chicken Hill Fault. Based on the lithologic log of exploratory boring EX‐2
located about 200 feet to the east, the site is underlain by coarse‐grained deposits that
allow for uninhibited vertical migration of recharge water to the underlying water table,
which is at 302 ft‐bgs in 2014).

Results of infiltration testing, combined with the results from the excavated test basin (see
section 3.1.9), indicate that while the site is highly suitable for recharge, accumulated

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 18 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 37 of 137