Page 250 - _ 180314 Special Yucaipa GSA Packet

Infiltration Testing for Thirteen Sites in Yucaipa Basin Area 02-Feb-2018

Question 2:
In addition, has this approach been utilized elsewhere by Geoscience?

Response to Question 2:
We have conducted testing using a similar Infiltrometer approach; however it was not integrated
into a container as proposed for your project. The testing used a 20 ft x 20 ft square
Infiltrometer constructed of sheet steel and was keyed into the ground in a similar fashion as the
proposed units. A slightly deeper ponded water height was used in this testing and the design
worked very well yielding good data. This work was done for Rancho California Water District as
part of the Upper VDC recharge project. With multiple sites and the possibility of security
breaches, enclosing the infiltrometer was deemed prudent this

Question 3:
Is there a significant impact to having no side wall infiltration?

Response to Question 3:
As the water is ponded in an excavated basin, flow is induced horizontally into the banks of the
pond, which will result in an initial higher percolation rate due to lateral percolation. With the
containerized Infiltrometer approach, lateral percolation will be less as the Infiltrometer will be
keyed into the underlying material.

There is a benefit to minimizing the lateral percolation that occurs from side wall infiltration as
our goal in this testing is to obtain accurate estimates of the saturated vertical hydraulic
conductivity at each site. If lateral percolation is much higher relative to vertical percolation at a
given site, then there is a potential to overestimate percolation rates.

Question 4:
Is there a benefit to excavating down a certain depth to remove the top layer of soil (e.g. the
proposed test basin of 30x30x5), that is, is it more representative to an actual basin?

Response to Question 4:
The depth of the alluvial channel fill may be as much as 60 feet. The materials are a mixture of
silt, sand, and gravel which are generally stratified. In some cases removing material to five feet
would put the footprint in more permeable materials. In others, we would need to remove up to
15 feet of materials. In others, gravel and sand is at ground surface. For the purposes of
determining an overall vertical infiltration rate for long-term recharge, removing five feet of
materials will likely not result in a significant improvement in the overall infiltration rate.

Question 5:
If the containers are metal is there a possibility of metals leaching out?

Response to Question 5:
We would apply a water-tight coating--similar to a bed-liner--to the internal surfaces in the
container that contact water. Given that water is chlorinated and contains oxygen, we do not see
a risk of leaching metals out of any steel surfaces that may inferentially become exposed to
water.

GEOSCIENCE Support Services, Inc. San Bernardino Valley MWD
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Yucaipa Groundwater Sustainability Agency - March 14, 2018 - Page 222 of 226