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based on local groundwater levels, does not appear to represent a subsurface barrier to
groundwater flow. Based on the lithologic log of exploratory boring EX‐1 located on the
berm 450 feet to the southwest, the site is underlain by coarse‐grained deposits; however,
shallow fine‐grained (clay) deposits create perched conditions beneath the basins during
recharge and limit surface infiltration rates. Such conditions were observed both during
pilot‐scale infiltration test by the USGS in 1970 and during field‐scale testing. Depth to water
in PZ‐1 (constructed in EX‐1) was 272 feet‐bgs in 2014.

Results of infiltration testing confirm that the site is suitable for recharge. The average
infiltration rate from constant‐head testing is 7.4 feet/day (based on relatively stabilized
rates observed after 11 days of testing), which is verified by measured infiltration rates from
the falling‐head test (5.5 to 7.4 feet/day). The “high” infiltration rate (based on an
infiltrating area of the basin bottom only) matches the final infiltration rate achieved by the
USGS in 1970 of about 9 feet/day. The USGS‐reported rate and rates from field‐scale testing
are considered representative of a “clean” basin.

A full‐scale basin initial infiltration rate is predicted at 3.7 feet/day, and a full‐scale long‐
term infiltration rate is predicted at 1.8 feet/day.

If site recharge goals are expected to exceed the operational capacity of the basins based on
predicted long‐term rates, the removal of the upper approximately 3 feet of sediment in
each of the basins prior to resumption of active recharge is recommended. Pilot‐scale
testing is not recommended at this site.

3.1.7. City of Yucaipa at California Street (EX‐5)

A synopsis of the infiltration testing completed at the Wildwood Creek at California Street is
shown on Figure 8. The site in the eastern portion of the Calimesa Subbasin with no nearby
geologic faults. Based on the lithologic log of exploratory boring EX‐5, located about 100
feet to the southeast, the site is underlain by generally permeable sand and gravel deposits.
Only a few minor clay layers were observed in the vadose zone. Depth to water in EX‐5 was
342 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 16.0 feet/day (based on stabilized
rates observed after 4 days of testing), which is verified by measured infiltration rates from
the falling‐head test (14.5 to 16.8 feet/day).

A full‐scale basin initial infiltration rate is predicted at 8.0 feet/day, and a full‐scale long‐
term infiltration rate is predicted at 4.0 feet/day.

Pilot‐scale infiltration testing is recommended, assuming a full‐scale recharge basin would
include the majority of the land parcel. No new monitoring wells are needed. However,
monitoring of water levels in the nested USGS Equestrian well, located just east of California
Street and north of Avenue G, is recommended during pilot testing.

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 16 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 35 of 137