HomeMy WebLinkAboutGEO2018-00047 Landslide Area 2 parcels - GEO General - 8/7/2018 Pn FZo i 8 -- 06ao (v
Evw'broteah Ev�,etvueerWw0, PLLc. RECEIVED
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615 W. Alder Street
August 7,2018
Dr.Brian Petersen
PO Box 3240
Belfair,Washington 98528
Reference: Geotechnical Site Assessment for Property Located at 200 E Cove View Drive,Belfair,
Washington(Parcels 12206-31-90081 and 12206-31-90082)
Dear Dr.Petersen,
Envirotech Engineering, PLLC has completed a site assessment of the general soils and surface
conditions for the referenced properties.This site assessment was partially based on a site visit performed
on July 31, 2018 in order to evaluate geological hazards, and identify the feasibility of constructing a
single family residential structure on each property. In addition, we reviewed and provided comments
concerning the Violation Order File:ENF 2018-00006 from Mason County.
The existing steep slopes near the project signal a potential landslide or erosion hazard area. The
referenced property is located within an area of geologic concern as delineated by the Mason County
Resource Ordinance. It appears that due to slopes exceeding 40% and located within an ancient landslide
formation, that Mason County will require a geotechnical report in conjunction with a permit for any new
development.
Recent and significant slope instability indicators on the property were not observed or discovered during
research. However, the property has landslide potential, and landslides have recently occurred near the
property. The earth movements near the property that have occurred are slight shifts, not disastrous, and
causes property damage such as foundation cracking, window/ door jarring, and drywall cracking.
Geotechnical design and recommendations would be available in the report in order to mitigate these
occurrences.
A complete geotechnical report will be able to identify everything needed for development, and comply
with the Mason County Ordinance.The following may be reasonably expected:
• Building setbacks will not be required for the upper elevations of the property, but will range
from 20 feet to 40 feet from the lower steeper descending slopes beyond the pad and service road,
• Setback encroachments are possible with appropriate mitigation,including deep foundations,
• Ordinary foundations may need to extend 6 to 8 feet closest to Cove View Drive. However pin
piles may otherwise be required. Pin pile foundations would be required closer to the service road
and beyond,
• Structures without permanent foundations such as concrete strip footing, may not require special
foundation provisions. However, this would be at the owners risk and subject to approval by
Mason County.
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• Roof drainage would require mitigation such as piping down to a location near the bottom of the
slope. Small roof areas may be allowed to have ordinary downspouts atop splash blocks,and,
• A geotechnical report would disallow the removal of vegetation except as needed for
construction, safety, and where slope grades allow. Limb cutting for view maintenance and other
options would be allowed.
• The property is within an erosion hazard area, and subsequently, the geotechnical report will
include an engineered erosion control plan for future development. There are no apparent earth
cuts or fill recently completed on the property. Earthwork associated with the site access has been
completed years prior,and sufficiently stabilized.
• It is our opinion that the recent vegetation removal has not caused additional slope stability
concerns. Also, we believe that the recent clearing has not disturbed the soils sufficiently where
sediments will erode from the property. This is due to the small amount of disturbed soils, the
establishing vegetation within the tree cutting area, and the natural vegetated flow path remaining
intact that is downslope from the tree clearing.
Thank you for the opportunity to work on this project. If you have any questions or need any further
assistance,please contact Michael Staten at 360-275-9374.
Sincerely,
Envirotech Engineering
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Michael Staten,P.E.
Project Director
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