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Generally, a site with favorable long‐term recharge potential requires a combination of high
surface infiltration rates and available land to construct a reasonable‐sized recharge facility.
A pilot‐scale infiltration test is recommended if the size of a full‐scale recharge project is
significantly larger (e.g., 1 acre or more) than the field‐scale test infiltration basin. Pilot
testing will generally require excavation of a recharge basin commensurate in size with the
intended full‐scale recharge basin, conveyance and metering of test water sufficient to fill
and maintain a constant‐head, and accurate measurement of pond water levels. The pilot‐
scale infiltration test should be implemented over at least a 2 to 3‐month period to identify
potential site vadose zone storage capacity constraints, particularly if there are nearby
geologic faults or hydraulic barriers. Installation of monitoring wells on both sides of a
mapped fault or barrier is recommended to confirm groundwater levels beneath the site
and the hydraulic connection across the fault/barrier during pilot recharge testing.

3.1.1. Tennessee Street Basin

A synopsis of the infiltration testing completed at the Tennessee Street Basin is shown on
Figure 2. As shown on Figure 1, the site is located northwest of the Western Heights
Subbasin, the northwestern boundary for which generally coincides with the Western
Heights Fault. Despite its upgradient location relative to the Western Heights Subbasin and
Western Heights Fault, the site is favorably located if recharge water can migrate below
regional clay layers in the Western Heights Subbasin and replenish aquifers that support
local groundwater production. No exploratory borings were drilled in 2014 near this site,
and depth to groundwater is unknown.

Results of infiltration testing indicate that the site is suitable for recharge. The average
infiltration rate from constant‐head testing is 10.8 feet/day (based on stabilized rates
observed after 9 days of testing), which is verified by measured infiltration rates from the
falling‐head test (9.5 to 11.1 feet/day).

A full‐scale basin initial infiltration rate is predicted at 5.4 feet/day, and a full‐scale long‐
term infiltration rate is predicted at 2.7 feet/day.

Pilot‐scale infiltration testing involving installation of monitoring wells north and south of
the Western Heights Fault is recommended, if the size of a potential full‐scale recharge
project is significantly larger than the existing storm detention basin.

3.1.2. Dunlap Channel

A synopsis of the infiltration testing completed at the Dunlap Channel is shown on Figure 3.
As shown on the Figure 1, the site in the Western Heights Subbasin along the margins of a
pumping depression centered approximately one mile east of the site. As shown on the
cross section in the upper right corner of Figure 2 (modified from Geoscience 2014b), the
site is underlain by thick and regionally extensive clay layers in the vadose zone. A nested
USGS monitoring well (Dunlap Well) indicates that depth to groundwater in the area is
about 400 feet‐bgs.

Infiltration Testing at Eleven
Investigation Sites in the Yucaipa
Basin, Yucaipa Valley, CA 13 TODD GROUNDWATER

Yucaipa Sustainable Groundwater Management Agency - January 23, 2019 - Page 32 of 137