Mar 21 2011 geotech letter.pdfirmrr//%ar° o,
imm�ioui Iui�
ROBINSON
NOBLE RECEIVED
MAR 2) 12011
DEVEIJOPMENT
March 21, 2011d�L�'
Ms. Diana Clay
Clay Enterprises
2002 - 196t1 Street SW
Lynnwood, WA 98036
Supplemental Letter
Response to Review Comments
Edmonds, Washington
File No. 2592-001 A
Dear Ms. Clay:
This supplemental letter provides additional comments to address the concerns from the City
of Edmonds as specified in their letter, dated December 21, 2010. We have previously
prepared a Geotechnical Evaluation Report, dated May 10, 2010. We have also been provided
a letter, dated March 18, 2011 and a Tree Replacement Plan, dated June 21, 2010 both
prepared by Burrus Design Group.
The City has requested additional clarification regarding ECDC 24.40.240.C. The code states the
following:
23.40.240.C.1 For alterations to frequently flooded areas, wetlands, and fish and wildlife habitat
conservation areas, the following minimum performance standards shall be met for the restoration
of a critical area; provided, that if the violator can demonstrate that greater functional and habitat
values can be obtained, these standards may be modified:
a. The historic structural and functional values shall be restored, including water quality and
habitat functions;
b. The historic soil types and configuration shall be replicated.
17625 -1301h Avenue Northeast, Suite 102 ® Woodinville Washington 98072 W Phone: 425-488-0599 ® Fax: 425-488-2330
www.robinson-noble.com
Supplemental Letter
Response to Review Comments
March 21, 2011
File No. 2592-001A
Page 2
c. The critical area and buffers shall be replanted with native vegetation that replicates the
vegetation historically found on the site in species types, sizes, and densities. The historic
functions and values should be replicated at the location of the alteration; and
d. Information demonstrating compliance with the requirements in ECDC 23.40.130,
Mitigation plan requirements, shall be submitted to the city planning division.
23.40.240.C.2. For alterations to flood and geological hazards, the following minimum performance
standards shall be met for the restoration of a critical area; provided, that if the violator can
demonstrate that greater safety can be obtained, these standards may be modified:
a. The hazard shall be reduced to a level equal to, or less than, the predevelopment hazard;
b. Any risk of personal injury resulting from the alteration shall be eliminated or minimized;
and
c. The hazard area and buffers shall be replanted with native vegetation sufficient to minimize
the hazard.
Our response for the above comments are provided as outlined below.
23.40.240.C.1.a - Refer to Kerr Mitigation Plan, dated March 18, 2011, prepared by Burrus
Design Group. The goals and objectives are identified on Page 1 of their report.
23.40.240.C.1.b — The soil type and the configuration was not altered.
23.40.240.C.1.c - Refer to Kerr Mitigation Plan, dated March 18, 2011, prepared by Burrus
Design Group, specifically pages 2 through 4.
23.40.240.C.1.d - Refer to Kerr Mitigation Plan, prepared by Burrus Design Group, dated
March 18, 2011.
23.40.240.C.2.a — It is our opinion the hazard of the trees falling down during a wind storm has
reduced by cutting the trees. The trees need to be removed from the slope as soon as
possible. The tree stumps will be left in place and some new trees are being planted to
Robinson Noble, Inc.
Supplemental Letter
Response to Review Comments
March 21, 2011
File No. 2592-001 A
Page 3
supplement the revegetation plan. Burrus Design Group has recommended a size and
procedure to removing the trees with as minimal disturbance as possible. We do not
recommend the trees be pulled down the slope, causing erosion issues in areas that are
undisturbed. In our opinion it is better to pull the trees uphill to the end of the paved roadway.
Vegetation disturbed from removal of the trees should be properly protected with erosion
control methods. In our opinion the hazard after the project is complete has reduced to a level
equal to, or less than, the predevelopment hazard.
Also, previous improvements to the site have improved the long-term performance of the slope
by dewatering and removing some overburden. It appears that these previous improvements
have helped in reducing shallow surface failures.
23.40.240.C.2.b — Since the weight of the trees will be removed during the tree replacement
process, it is our opinion there will not be any change to the stability of the slope. The risk of
shallow slides will be similar to the pre -tree cutting condition. As the new tree root structure
becomes established and since the tree trunks are being left in-place, eventually these
additional trees will create a better condition for the slope. Since there is no significant change
to the stability of the slope, in our opinion there is minimal additional risk of personal injury
resulting from the alterations.
23.40.240.C.2.c — Since the cut tree stumps will be left in place, we recommend augmenting
the new tree plants with species that will allow for better root structure. New species of plants
should have ample growing time to establish root systems. The better root structure will
improve the stability of the site therefore reducing shallow slough events.
Our comments above are in agreement with recommendations made in our original
geotechnical report and all the supplemental reports. The maintenance plan will help control
trees from growing to a hazardous condition, falling over and starting a landslide.
Robinson Noble, Inc.
Supplemental Letter
Response toReview Comments
March 21'3O11
File No. 2592-001A
Page
We hope this letter meets with your needs at this time. If there are any questions concerning
this letter or if we can provide additional services, please call.
Sincerely,
Rick B. PovveU, PE
Principal Engineer
11111011��
o
RobinsonThree Copies Submitted
Noble, Inc.