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3.1.8. Wilson Creek III (EX‐3)

A synopsis of the infiltration testing completed at the Wilson Creek III is shown on Figure 9.
The site in the eastern portion of the Gateway Subbasin. Based on the lithologic log of
exploratory boring EX‐3 located about 900 feet to the east, the site is underlain by
permeable sand and gravel deposits. Only a few minor silt layers were observed in the
vadose zone. Depth to water in EX‐3 was 202 feet‐bgs in 2014.

Results of infiltration testing indicate that the site is highly suitable for recharge. The
average infiltration rate from constant‐head testing is 52 feet/day (based on relatively
stabilized rates observed after 10 days of testing). It is possible that rates may be
overestimated due to the proximity of the test basin to a large‐diameter conveyance pipe
along the east side of 2nd St, set in a gravel‐filled trench. Because the basin drained within a
couple of hours, an infiltration rate from the falling‐head test could not be calculated.

A full‐scale basin initial infiltration rate is predicted at 26.0 feet/day, and a full‐scale long‐
term infiltration rate is predicted at 13.0 feet/day.

Pilot‐scale infiltration testing involving installation of monitoring wells north and south of
the Chicken Hill Fault is recommended, if the size of a potential full‐scale recharge project is
significantly larger than the test basin. Monitoring of water levels in the nearby YVWD
production well located south of the test site may preclude the need for a monitoring well
south of the Chicken Hill Fault if the well is not actively pumped during pilot testing.

3.1.9. Oak Glen Creek Basins (Excavated) (EX‐2)

A synopsis of the infiltration testing completed at the Oak Glen Creek Basins (excavated) is
shown on Figure 10. 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 indicate that the site is highly suitable for recharge. The
average infiltration rate from constant‐head testing is 21.0 feet/day (based on stabilized
rates observed after one day of testing), which is verified by measured infiltration rates from
the falling‐head test (19.7 feet/day). An apparent decline in infiltration rate was observed
from Day 9 through Day 11 of testing. This is believed to be related to a pressure drop in the
fire hydrant, which resulted in pond water levels gradually dropping over this period as well.

A full‐scale basin initial infiltration rate is predicted at 10.5 feet/day, and a full‐scale long‐
term infiltration rate is predicted at 5.2 feet/day. This rate assumes historically accumulated
silt/clay in the upper 3 feet of the basin is removed, and a basin maintenance plan is
established.

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 17 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 36 of 137