HomeMy WebLinkAboutGeoTech Report for BLD2002-00577 - BLD Engineering / Geo-tech Reports - 7/30/2002 MASON COUNTY
PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER
Shelton,Washington 98584
DATE: July 301h, 2002
INTER-DEPARTMENTAL COMMUNICATIONS
TO: Rick Mraz, DCD - Planner
FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. WO# PLG-02
SUBJ: Geo-Tech Report Review NAME: Whitman Garage 9 310 NE Riverside PI
BLD2002-00577
Rick,
The geotechnical report prepared for the proposed Dann Whitman garage to be constructed at
310 NE Riverside Place, Belfair, has been received and reviewed by Public Works.
The report conforms to accepted standards of engineering/geotechnical principles and practices
and appears in compliance with requirements of DCD for geotechnical reporting.
Please feel free to contact me at County extension 461 if you have any questions regarding these
comments, or if you feel any features need further discussion or attention.
s. cerely,
L
Alan A. Tahj
File: H:\WP\GEO\REVIEWS\Whitman.doc
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RECEIVED
MARTIG ENGINEERING JUL 2 5 2002
P.O. Box 11850
Olympia, WA 98508-1850
(360) 754-9687 MCCD - PLANNING
July 22, 2002
Mason County
Department of Community Development
426 W. Cedar
P.O. Box 578
Shelton, WA 98584
Attn: Rick Mraz, Land Use Planner
Re: GEO-TECHNICAL REPORT for:
Property Owner- Dann Whitman;
Parcel Address- 310 NE Riverside PL
Belfair, WA 98528
Phone Number- 360 275-6398
Tax Parcel Number- #12320-10-03350
Proposed Project- New Garage (unattached)
Response to Mason County Letter Dated 5/22/2002 from Rick Mraz
Dear Mr. Mraz:
Martig Engineering has completed a full Geo-Technical Report for the above
referenced Whitman project. All potential Landslide Hazards can be overcome in such
a manner as to prevent harm to property and no significant Environmental Impacts will
result if this project is permitted as outlined within this letter and its attachments.
PROPOSED PROJECT
Dann Whitman proposes to build a new Garage (unattached) near his existing single-
family residence, at the above referenced property.
The Vicinity Map (Attach: #1) shows directions to the Property. The proposed location
of the new garage is shown on the Whitman Property Site Plan (Attach: #2). The
attached Photos numbered 1 thru 4, inclusive, show this site (#1 looking NW from the
NW corner of the residence, #2 looking south across the garage site toward the
residence, #3 looking north across the site, & #4 looking west across the site).
1
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GEO-TECHNICAL REPORT
The following discussion summarizes our: Site Investigations, Research of Site
Conditions; Analyses; and Conclusions, allowing this Geo-Technical Report to be
completed for the above referenced site.
1. Geology, Soils, Groundwater, Landslides:
This site does not show up on the Coastal Atlas Maps or on any other Slope
Instability map. No landslides or other signs of slope instability could be found.
The Mason County Soils Survey identifies the soils as Everett Gravelly, Loamy,
Sand and indicates slopes of 15 to 30%. These soils are well draining and
consistent with the R.J. Carson Geologic Conditions Map (Attach: #5) and the
Water Supply Bulletin No. 18 Geologic Map (Attach: #6). This Everett soil series is
an excessively drained pale-brown granular soil at the surface with a substratum
that stands in bank formation at this site.
We found no evidence of slides or slope instability during our site inspection visit
nor did we find any using DNR stereo Aerial Photographs, both past, 5/9176, and
present, 5/18/97. A 1" = 1000' scale copy of the 5/18/97 DNR Photo (Attach: #4)
shows the stable site.
Due to the macro-nature of the existing topographic maps (contour intervals no less
than 20-feet developed when forest cover was present), maps do not properly show
that the developed portion of the Whitman property is actually situated on top of a
stable flat plateau (looking like a small hill with its top cut off).
This plateau drains in all directions and has no tributary off-site runoff to it. Only the
precipitation falling directly on it introduces water into the plateau soils. Since the
surface rapidly infiltrates precipitation, no surface water flow can exist. Even the
roof drains from the existing 30-year old residence do not need any formal drainage
system, nor will the proposed new garage.
Given the plateau geologic conditions, we did not expect to find, nor did our site
inspection encounter, any horizontal subsurface groundwater interflow that could
cause slope instability on any of the plateau slopes, not even the westerly slope
toward the Union River.
It is important to emphasize that no groundwater interflow occurs thru any
unconsolidated soil formations that could erode, even if disturbed, and that NO
NEW CLEARING OR MEASURABLE NEW GRADING will occur anyway. The
existing cleared site and flat grade, shown on the site plan and in the photos, will
allow the new garage to be constructed as proposed.
2
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2. Site Plan of Important Geologic Features:
Two Geologic Maps are presented (Attach: #5 & #6). The 1" + 1000' scale USGS
Quad Topographic Map (Attach: #3) and attached 35mm Photos numbered #5 & #6
show the geologic features as discussed above (Photo #5 being three photographs
looking north along the west plateau slope and #6 being two photographs looking
south along a roadway cut in the east plateau slope.
3. Location of Soil Exploration Holes/Probes-
The Everett Series soils formation that exists at the site is exposed as a cut-slope
on the north and easterly edges of the bench plateau (the ground siting upon which
the existing stable 30-year old residence and proposed new garage are situated).
Given these exposed soils, no additional soils test borings or test pits were required
to confirm the conditions and type of the site soils (see attached 35mm Photos
numbered #6). These soils are also visible by the driveway cuts to the south.
4. Cross Sections showing slope disturbances:
No new excavations or grading will be necessary to construct the new garage as
proposed. The driveway to this site exists. In any case, the siting of the new garage
is safely set back from all plateau slopes (see Attach: #2). NO DISTURBANCE TO
ANY SLOPE/BANK will occur.
Section A-A shown on the USGS Quad Topographic Map (see Attach: #3) shows
the cross section thru the proposed new garage. Note that the actual ground line,
plateau, is not as broad as existing maps show, due to the macro-nature of the
elevation contours.
5. Slope Stability Discussions:
As discussed within this report, the proposed activity will not create significant
environmental impacts and no landslide hazard will be induced when the new
garage is constructed. The site is safely set back from all plateau slopes so no
activity will disturb them in any way. The site, in its existing condition, is already
cleared and graded flat to accommodate the new garage without further clearing or
grading. An existing driveway leads to the site.
6. Drainage, Septics, Water, Placement:
This proposal is for a new garage. It is an outbuilding for the existing 30-year old
residence that already has water & septic. The roof drains for the new garage do
not pose a problem since the Everett Series soils infiltrate very rapidly. The roof
runoff can either drain directly to the ground with no gutters, or gutter downspouts
can be piped into a drain rock filled hole, 10-feet away from the structure, for safe
infiltration into the surrounding soils.
3
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7. Clearing & Grading Plan:
No new clearing or grading is necessary or proposed.
8. Erosion Control Plan:
During construction, since no new grading will be necessary, special erosion control
measures will not be needed. Since the driveway and yard areas will remain intact,
only rainfall falling directly upon the new garage footprint will be present. This small
amount of runoff will readily infiltrate into the flat plateau Everett Series soils (no
offsite runoff is tributary to the new garage footprint).
After construction, any disturbed soil should be planted with grass seed and
covered with mulch or simply covered with 3 to 4 inches of loose straw.
9. On-Site & Off-Site Impacts:
In summary, no adverse environmental impacts nor landslide triggers will result if
this proposed development is permitted as presented within this Geo-Technical
Report.
10. Final development Conditions:
Existing site conditions will be maintained and no new clearing or grading is
necessary. Therefore, no special conditions are necessary for this proposed new
garage.
I, Kenneth W. Martig, Jr., PE, of Martig Engineering have completed the required Geo-
Technical Report as document within this letter 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 will result if this proposal is permitted as discussed above.
Certified by.-
Kenneth W. Martig, Jr., PE
1 ti
Attachments: #1- Vicinity Map
#2- Whitman Property Site Plan
#3- USGS Topography Map (with Cross Section A-A) GIS�F`sS/pNT E`'a\
#4- DNR Aerial Photo Map (5/18/97)
#5- R.J. Carson Soils "Drainage Orientation"
#6- 1965 Water Supply Bulletin #18 (Geologic Map) EXPIRES 1-9- U ,
# - Four Pages of 35mm photographs (photos 1 thru 6)
4
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