Page 36 - Yucaipa Sustainable Groundwater Management Agency - Yucaipa SGMA

115 feet‐bgs, similar to water levels east of the fault in the Calimesa Subbasin, and 300 feet
higher than in the Western Heights Subbasin, indicating that the hydraulic connection
between the site and Western Heights Subbasin is likely poor.

Results of infiltration testing indicate that the site is suitable for recharge. The average
infiltration rate from constant‐head testing is 12.7 feet/day (based on relatively stabilized
rates observed after 12 days of testing), which is generally verified by measured infiltration
rates from the falling‐head test (9.8 to 11.5 feet/day).

A full‐scale basin initial infiltration rate is predicted at 6.4 feet/day, and a full‐scale long‐
term infiltration rate is predicted at 3.2 feet/day.

Pilot‐scale infiltration testing involving installation of monitoring wells west and east of the
Chicken Hills Fault is recommended, if the size of a potential full‐scale recharge project is
significantly larger than the existing storm drainage area.

3.1.5. Wildwood Creek at California Street (EX‐5)

A synopsis of the infiltration testing completed at the Wildwood Creek at California Street is
shown on Figure 6. 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 400 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 YRP‐ EX‐5 was
342 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 3.5 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 (2.4 to 3.1 feet/day).

Full‐scale basin initial and long‐term infiltration rates are predicted to be less than 1.7 and
0.9 feet/day, respectively. Low infiltration rates appear to be due to a clayey silt layer, the
top of which occurs at a depth of 10 to 12 feet below the channel floor. Dry soil conditions
were observed below the clayey silt layer at the end of testing. The fine‐grained material
may be associated with sediment load from natural stormflows.

Surficial coarse‐grained sands and gravels on the surface of Wildwood Creek at California
Street appear to have limited thickness and are underlain by a fine‐grained matrix that
significantly limits infiltration. Development of a recharge facility and additional
investigations are not recommended at this site.

3.1.6. Wilson Creek Basins

A synopsis of the infiltration testing completed at the Wilson Creek Basins is shown on
Figure 7. As shown on Figure 1, the site is located in the upgradient portion of the Basin in
the center of the Gateway Subbasin. The Chicken Hill Fault is located north of the site, but

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 15 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 34 of 137