HomeMy WebLinkAboutGeo-Tech Compliance Report for BLD2007-00053 - BLD Engineering / Geo-tech Reports - 9/25/2006 MARTIG ENGINEERING
P.O. Box 11850
Olympia, WA 98508-1850 RE__C E I V E D
(360) 754-9687
Fax (360) 705-0789 JAN 11 7IjU t
September 25, 2006 426 W. `CuAk S1,
Mason County
Department of Community Development
426 W. Cedar
P.O. Box 578
Shelton, WA 98584
Attn.- Land Use Planner
Re: Geotechnical Compliance Report for:
* Owner: Kevin E. & Juanita C. Lea (360) 275-4109
41 NE Jolly Roger Lane
Belfair, WA 98528
• Property Site Address: 41 NE Jolly Roger Ln
Bellfair, WA; 98528
• Tax Parcel No: 1233&54-00029;
• County Reference Numbers: SWG 2006 00690
• Section 31, T 23 N, R 01 W;
• NEW GEOTECHNICAL REPORT for New Garage
with new Septic System for bathroom within garage.
Planning:
I, Kenneth W. Martig, Jr., PE, of Martig Engineering have completed my own
engineering investigations regarding the Geotechnical Report requirements associated
with the above referenced property, as required by the County.
The proposed action at this site is to construct a new Garage( for the existing
Residence) with a new Septic System for the new bathroom within the garage.
As a result of our investigations, we can affirm that all potential Landslide Hazards can
be overcome in such a manner as to prevent harm to property and public health &
safety and that no significant Environmental Impacts will result if this project is
permitted as outlined within this Geotechnical Report and its attachments.
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REPORT SUMMARY
We have determined that all slopes upon the subject property are quite stable. None of
the normal causes that create slope instability are present at this site, and none will be
induced if the proposed new Garage, with new Septic System, are constructed in
accordance with County Standards and the provisions outlined within this Report.
The submitted Septic System Design for the new garage has been assigned the County
designation SWG 2006 00690.
The new Garage will serve the existing Residence on the property.
GEO-TECHNICAL REPORT
1. Geology, Soils, Groundwater, Landslides:
This site was found to be stable. No landslides were found on or near this site.
The USGS Belfair Quadrangle Map confirms the slopes found by the topographic
survey prepared for the planning of the new garage. The Attachment 3 Elevation
View (Measured Section A-A) shows the Topography and the nature of the slopes
within the Site. The six pages of 35-mm Photographs, Attachment 4, show the Site,
its slopes, and the Septic soils test holes..
The Mason County Soils Survey shows the site soils to be Everett gravelly loamy
sand with slopes from 15 to 30%. These soils are excessively drained with the
upper 12" to 36" being loose before weak cementing becomes apparent. Gravel and
sand are being extracted from nearby commercial sites.
When undisturbed, the upper layer of unconsolidated granular soil infiltrates
precipitation readily, producing essentially no runoff. The proposed Septic System
Drainfield is located within this undisturbed upper soil, between the garage location
and slope break where no grading has occurred.
No signs of groundwater impact are apparent on this site, and no measurable offsite
surface water runoff is tributary to the property.
No visual signs associated with landslide activity were found.
2. Site Plan and Important Geologic Features:
The Attachment 2 Site Plan Map shows how the proposed new garage and Septic
Drainfield will be situated upon the property.
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The Attachment 3 Elevation View, Section A-A, shows the existing ground slopes.
The six pages of photographs, Attachment 4, show the important features of the
site.
3. Location of Soil Exploration Holes/Probes:
The partial excavation for placing the new garage shows a 12-foot cut-bank. The
two Septic Drainfield soils test holes show the upper 5-feet of soil. Further, the older
Driveway and Admiral Drive stable slopes demonstrate the nature of the soil slopes.
Given these exposed soils, no additional soils test borings or test pits were required
to confirm the conditions and type of soils at this property.
4. Cross Sections Showing Slope Disturbances:
The Attachment 3 Elevation View, Section A-A, shows the measured ground slopes
that exist to the west and east of the proposed garage.
The partially completed excavation for the garage shows the nature of the soil at the
garage location. These westerly and northerly cut slopes vary in height from 0' to
12'. They will be stabilized by using a combination of rock retaining walls and
reinforced concrete garage walls. The architectural drawings will show the final
configuration of these.
In any case, the stabilization of these cut slopes is simple, since no saturation of the
soil is possible at this location_ Further, unconfined soil cut slopes have a measured
stable angle of repose of 1:1, and the older existing 6-foot high rock wall, shown on
photo Page 1 of 6, remains stable at a near vertical slope.
5. Slope Stability Discussions:
All Site slopes are presently stable. The measured natural angle of repose for these
soils is 1:1, but we recommend that constructed open soil slopes be no steeper than
1.5-feet Horizontal to 1.0-foot Vertical (and protected against erosion).
The cut slopes necessary to construct the new Garage can be easily stabilized
using either rock retaining walls (see Attachment 3 Detail) or reinforced concrete
walls. No ground saturation is possible at this site.
Normally, either surface water runoff or the emergence of groundwater along
steeper slopes, are the primary cause(s) of slope instability. Given the site soils and
ground slopes, no runoff or saturation of surface soil problems are possible at this
site. No groundwater surfaces along the property slopes. Therefore, this site is very
stable against the primary causes of slope instability.
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6. Drainage, Septic, Water, Placement:
Drainage at this site is not a problem, due to the ability of the soils to infiltrate
precipitation rapidly and the fact that no offsite runoff is tributary to the Site. Roof
drainage should disbursed into the ground south of the garage.
An existing Residence exists at the site with existing water and an onsite Septic
System.
The new garage will receive water from the existing house connection. A small new
Septic System will be constructed for the garage, SWG 2006 00690.
7. Clearing & Grading Plan:
Initial Clearing and Grading has been completed, as shown on the Attachment 2
Site Plan and on the Attachment 3 Elevation View.
Additional excavation & grading is required to construct the Garage, including:
excavating several feet more to the north, installing retaining walls; installation of
the garage footings; and the installation of the Septic System..
8. Erosion Control Plan:
Since no runoff currently exists and no offsite runoff is tributary to the site, no
special erosion control plan is necessary.
The driveway and parking pad will be covered with several inches of crushed rock_.
All ground surfaces, where large portions of bare earth remain (outside the Garage
and driveway/parking areas), shall be covered with 3" to 4" of loose straw/hay or
coarse beauty-bark to prevent erosion.
The remaining Understory vegetation should remain undisturbed as much as
practical when installing the remaining improvements.
The roof drain downspouts should directed south of the garage.
A row of staked straw bales or a silt fence shall be placed as shown on the
Attachment 2 Site Plan to prevent erosion until all construction is completed and
Revegetation/Landscaping is accomplished.
9. On-Site & Off-Site Impacts:
In summary, no adverse environmental impacts or landslide triggers will result,
either on-site or off-site, if the Garage improvements are permitted as guided by the
other Mason County Permits and as presented within this Geotechnical Report and
its attachments.
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10. Final Development Conditions:
No special "Development Conditions" are necessary.
The normally required Mason County Permits, including the provisions outlined
within this Geotechnical Report, are sufficient for the safe implementation of the
requested Garage Improvements.
This completes our Geotechnical Report for the proposed Garage construction.
I, Kenneth W. Martig, Jr., PE, of Martig Engineering have completed the required
Geotechnical Report as documented within this letter Report and its attachments. I am
familiar with this site, having visited and inspected the site and its surrounds. As
documented, potential landslide hazards have been overcome and no significant
environmental impacts to the public or property will result if this proposal is permitted
as discussed above.
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1. Vicinity Map o
2. Site Plan z
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3_ Elevation View, Section A-A
4. Six Pages of 35-mm Photographs A% s
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EXPIRES 1-9- (� ..._.�
THESE PLANS MUST BE
ON TIME 100 SITE
FOR INSPECTION
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ATTACHMENT 4 (Photos)
Page 1 of 6: Looking north along the existing Driveway
into the site. These photos show the excavated slope
holding stable at a 1:1 slope. The lower photo shows
an old rock retaining wall standing stable at a
slope of 4.0-feet Vertical to 1.0-foot Horizontal.
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Page 2 of 6: Looking north at the partially completed
excavation for the new garage_ The slopes have unraveled
to a stable slope of 1:1. The upper photo shows the excavated
soil piled north of the excavation, causing the cut slope to
appear higher than the actual 7-foot cut at the north center
location of the proposed garage. The deepest cut is 12-feet
at the northwest corner of the excavation, lower photo.
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Page 3 of 6: Looking west along the north
edge of the partial excavation. The upper
F .. photo shows the stable Jolly Roger roadbed
with existing Fir trees. The lower photo
shows the pile of excavated soil north of the
excavation. Again, the unraveled slopes are
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stable at 1:1. When permits are secured for
construction of the garage, the excavated area
will expand several feet more to the no- rth.
The north and west edges of the excavation
will be stabilized using either concrete garage
ha walls or a rock retaining wall (or combinations
thereof).
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Page 4 of 6- Looking north at the Septic Drainfield location.
The soils test holes are 5-feet deep, with roots and usable
soils to 4-feet of depth.
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