HomeMy WebLinkAbout09 Geologic Assessment for Twana WayDonna Frostholm
From: Richard Rathvon <rich@ rathvonconsulting.com >
Sent: Thursday, March 13, 2025 12:29 PM
To: Donna Frostholm
Cc: 'Terry McHugh'
Subject: Geologic hazard assessment for Twana Way
Attachments: Geologic Hazard Letter for Twana Way.pdf
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Donna,
I had understood previously — perhaps incorrectly — that a letter from our Geotech specialist was sufficient,
which has already been submitted to your office.
For additional information, attached is a copy of the geologic hazard assessment for Twana Way.
Please let me know if you have any questions or require further information.
Regards,
Rich
STRATUM GROUP
PO Box 2546, Bellingham, Washington 98227
Phone: (360) 714-9409
February 25, 2025
Richard Rathvon
20 Liberty Knoll
Colts Neck, NJ 07722
rrathvon@gmail.com
Re: Geologic Hazard Assessment for Twana Way Improvements
Twana Way
Quilcene, WA
Dear Richard Rathvon:
This letter provides a summary of our road and slope stability assessment completed in February
2025. It is our understanding that you are proposing to improve Twana Way to allow
construction vehicle access to your property at 660 Twana Way.
Based on our field investigation, it is our opinion that road widening will be required in several
places in order to accommodate large trucks and/or other construction equipment. In some
locations, road widening can be accomplished by expanding the travelled roadway into the
existing shoulder areas (e.g. Figure 1). In other areas, road widening will require excavation into
existing cut slopes (e.g. Figure 2).
Stratum Group assessed all cut slopes where excavation is anticipated. The observed cut slopes
are underlain by dense, well drained sand and gravel (Figure 3). It is our opinion that excavation
of these existing cut slopes can be accomplished without increasing the potential for landslides
and without decreasing the stability of the roadway and adjacent areas as long as the
recommendations of this letter are followed. A temporary increase in minor soil raveling should
be expected in some areas due to removal of vegetation and soil disturbance.
In addition to road widening, regrading of the road may be required to lessen the steepness of the
roadway and also to repair holes and ruts. Regrading of the road will not increase the potential
for landslides or erosion along Twana Way or adjacent areas as long as the recommendations of
this report are followed.
Stratum Group
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February 25, 2025
Twana Way
Geologic Hazard Assessment
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Figure 3. Sandy soils that typify the road cuts along Twana Way.
Recommendations:
1. Where possible, road widening should be completed by utilizing existing shoulder areas.
Excavating existing cut slopes will be required in several areas. Road widening should
not involve creating or expanding any fill slopes.
2. New or expanded road cuts up to 6 feet high can exceed 1:1 in steepness as long as the
road cut is underlain by compact, well drained sand. Cut slopes exceeding 6 feet in height
should be 1:1 or gentler. If steeper cuts are required, Stratum Group should be contacted
to assess the stability before excavating. If clay rich soils or groundwater seepage are
encountered during excavation, Stratum Group should be contacted to assess to inspect
the cut slope.
3. Excavated material should be end hauled.
4. Construction should be completed using best management practices including temporary
erosion and sediment control (TESC). Soil and vegetation disturbance should be limited
to the proposed excavation and construction areas.
Stratum Group
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February 25, 2025
Twana Way
Geologic Hazard Assessment
Stratum Group appreciates the opportunity to be of service to you. Should you have any
questions regarding this assessment please contact our office at (360) 714-9409.
Sincerely yours,
Stratum Group "I Waste
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Enginee2aGeoff Malick, L.E.G., M.Sc. Se
Licensed Engineering Geologist Geoffrey Malick
Statement of Limitation and Indemnity
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This document has been prepared by Stratum Group for the exclusive use and benefit of the
client. No other party is entitled to rely on any of the conclusions, data, opinions, or any other
information contained in this document. This document represents Stratum Group's best
professional judgment based on the information available at the time of its completion and as
appropriate for the project scope of work. It is not possible to fully anticipate all future risks or
future site evolution. Services performed in developing the content of this document have been
conducted in a manner consistent with that level and skill ordinarily exercised by members of the
geology profession currently practicing under similar conditions.
The client shall understand that the subject property includes geologic hazard areas, and the
client has elected to develop and/or reside at this location. The client shall accept that there are
inherent risks associated with geologic hazard areas and assume sole responsibility for its future
consequences, both as detailed herein and unknown. The client shall accept that is not possible to
entirely eliminate all risk associated with geologic hazards. Stratum Group Inc, its staff and
owners, shall be indemnified and held harmless from the consequences of development and
residence at the subject property. Furthermore, no warranty, expressed or implied, is made.
Stratum Group
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