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sediments to about 3 feet in depth have a significant negative impact on infiltration rates.
The average infiltration rate from constant‐head testing is 5.6 feet/day (based on stabilized
rates observed after one day of testing), which is verified by measured infiltration rates from
the falling‐head test (5.2 to 6.6 feet/day).

For the bermed test, full‐scale initial and long‐term infiltration rates of 2.8 feet/day are
predicted, as the existing basin is currently clogged. The estimated long‐term infiltration
rate is similar to the infiltration rate of 3.2 feet/day measured for the middle basin during
pilot‐scale testing of the Oak Glen Creek Basins in 2017‐2018 (City of Yucaipa et al., 2018).

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

3.1.12. Oak Glen Creek at Western Heights (EX‐9)

A synopsis of the infiltration testing completed at the Oak Glen Creek Basins at Western
Heights is shown on Figure 13. The site in the center of the Western Heights Subbasin.
Based on the lithologic log of exploratory boring EX‐9 located along the northern channel
bank about 550 feet to the northwest, the site is generally underlain by permeable sand and
gravel deposits. Fine‐grained deposits were identified in EX‐9 from 15 to 25 feet‐bgs
(approximately 0 to 10 feet below the channel bottom); however, fine‐grained material
observed during excavation of the test basin indicated significant fine‐grained sediment load
from natural stormflows. Depth to water in EX‐9 was measured at 347 feet‐bgs in 2014.

Results of infiltration testing indicate that the site is not suitable for recharge. The average
infiltration rate from constant‐head testing is 1.4 feet/day (based on stabilized rates
observed almost immediately after the start of testing), which is verified by measured
infiltration rates from two falling‐head tests (1.5 to 1.6 feet/day).

Full‐scale basin initial and long‐term infiltration rates are predicted to be less than 0.7 and
0.4 feet/day, respectively. Low infiltration rates appear to be associated with fine‐grained
geologic deposits and associated with sediment loads from stormflows. Development of a
recharge facility and any additional investigations are not recommended at this site.

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 19 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 38 of 137