Attachment 23UPP GEOTECHNOLOGY
Engineering Geology • Geotechnical Engineering
Mr. Dan Ross
233 West Main Street
Los Gatos, CA 95030
C2 E.ARTH INC
31May2017
Document Id. 15068C-01L2
Serial No. 18049
SUBJECT: SUPPLEMENTAL GEOTECHN ICAL INFORMATION
TREE REMOVAL
Dear Mr. Ross:
ROSS PROPERTY
339 AND 34 1 BELLA VISTA AVENUE
LOS GATOS, CALIFORNIA
As you requested, we are pleased to provide our professional op inion s related to the removal of
unhealthy trees on your property at 339 and 341 Bella Vista Avenue in Los Gatos, California.
Based on our r eview of an arborist report by Deborah E lli s, MS that you provided to us, we
understand that most of the trees on the site are not in good condition as a result of crowding and
being shaded for many seasons. We understand that Ms. Ellis has recommended removal of five
trees and possible removal of five add it iona l trees. We further understand that one of the Town
Council members has asked for our opinion on whether the removal of trees on the property will
destabilize the site s lopes.
We previously conducted an updated geologic and geotechnical study for the proposed
residential development of your property and presented the results of that study in our Updated
Geologic and Geotechn ica l Study report dated 25 June 20 15 (Document Id. I 5068C-O 1R1 ).
Add iti onall y, we presented our opinions related to s lope stability with r espect to the proposed
development in our Supplemental Geotechnica l Information letter dated 13 April 2016
(Document Id. l 5068C-O I Ll ).
Based on our assessment, the site is underlain at depth by supportive alluvium comprised of
medium dense to very dense sandy and si lt y gravel. The alluvium is mantled by a layer of non-
supportive colluvium comprised of loose to medium dense gravelly clayey sand to sandy clayey
grave l that is up to about 3 Yi feet thick. As discussed in our report and supplemental letter, our
studies have not revealed evidence of current or historic s lope instability at the site.
A lthough the root-structure of healthy trees and vegetation generally adds to the stabi lity of
hillsides, trees in poor condition can act to destabilize s lopes. Wind loads and other pressures
acting on trees can result in lateral and/or uplift forces that can be transferred to the soil, reducing
the overall stability of the slope. Furthermore, trees that do fall over during storms and have their
root-mass uplifted or exposed, can create localized over-steepened areas on the s lope and areas
where water can collect and pond, further reducing the overall slope stability.
In our opinion , the recommended removal of trees trees from the slopes on this site will not act
to destabilize the s lope and may result in increasing the overall s lope stab ilit y. Holes or
Copyri ght -C2Ea rth, In c. !.ATTACHMENT ? 3
Proiect Narie Ross
31 May 2017
Document Id 15068C-C1 L2
Page 2 of 2
UPP GEOTECHNOLOGY --------
C2 E: filH ,, .
depressions r esulting from the r emoval of the trees and their roots s hould be backfilled m
accordance w ith the earth work section of our report.
Followin g the removal of the tree s and backfilling of any depressions, we recommend re -
vegetating disturbed areas by hydro seeding the slope with native grass and wi ld-flower seeds
prior to the on set of the next rainy season. After hydroseeding, erosion control b la n kets should be
in sta ll ed and maintained over the s lope until vegetation/ground cover is well established. We
recommend using an erosion contro l blanket w ith a minimum 2 -year desi gn life that is des ig ned
for steep s lopes, such as Western Excelsior CS-3, or an equivalent.
We appreciate the opportunity to continue to assist yo u with your project.
Sincere ly yo urs,
Upp Geotechn o logy
~ision of C2Earth. Inc.
cf 1:1!.~e r, Principal
Certifi ed Engin eering Geolog ist 2314
Certified Hydrogeologi st 882 =~~~~
Distributi on: Addressee (v ia e-mail to danros s@ 3 141 oan.com)
ll1is document is protected under Federal Co pyright Laws . Unauth ori ze d use or co pying of th is doc ument by anyone other th a n the clien t(s) is
strictly prohibited. Conta c t C2Ear th , In c. for "APPUCJ\llON TO US E."
Co p)T ight -C2Ea rth, In c.