The URL can be used to link to this page

Home My WebLink AboutBLD2013-00087 Geotechnical Report NORTHWESTERN TERRITORIES, INC. 717 SOUTH PEABODY STREET, PORT ANGELES,WA 98362 ' ■ , Engineers:Land 5uve+rcr3 :Geoicgists 111 Construction inspection :taateriais Testing X Phone(360)452-8491 1-800-654-5545 Fax 452-8498 jj: infoanti4u.com Jeffrey McGinty 19710 Twenty-Second Ave. NE Poulsbo, Washington 98370 March 4, 2013 ' Subject: Geotechnical Investigation of the McGinty Parcel at 110 North Bay Way, Port Ludlow, Washington 98365. Tax Parcel # 976800016 ' 1.0 Introduction ' Dear Mr. McGinty and Others Concerned, On February 18th, 2012, NTI Engineering and Land Surveying completed a geotechnical ' investigation of the property located at the above-mentioned address that lies within the Southwest Quarter of Section 29, Township 29N, Range 1 E near Oak Bay, Washington. ' The purpose of the reconnaissance investigation was to assess the capacity of the soil at the site to infiltrate stormwater and to determine if drywells or other infiltration facilities might be used to receive drainage from the site. 2.0 Background Information ' The soils at the project site have traditionally exhibited high moisture content year round. Drainage from the existing home is collected from multiple downspouts and conveyed through above-ground flexible non-perforated pipe to the northeastern side of ' the home and dispersed through approximately 90 feet of lawn and vegetation towards a low bluff. It is proposed that the existing double wide mobile home be removed from the parcel and replaced with a new approximately 3,900 square foot home, garage, and ' deck. 3.0 Site Description ' The parcel is located at 110 North Bay Way, approximately 10 miles northwest of Port Ludlow, Washington. Note the map of the parcel and its relationship to North Bay Way ' in Figure 1. F, LCL IV 1 L'1 JEFFERSON COUNTY DEPT.OF COMMUNITY DEVELOPMENT I 91UP-K.05 9/6W r;) 91e. Y'• ')-'.. . o SI y r ..iy... r_____ ------ 9/62u5(}" 9 r _f.{i.2 916t1XX4O r.49..... '', . 9/6,13(0).0 -- , %,......, 9/68/-11:0•3 „*..). • , . . \ ". - -- - ' --\ \ anst4 I ..... .y. y \P • . 1 --VIM I. 9?bei_v_r0•6 fi 1. . , \ .,- Z -- ', 91 , • t _ 1 _ N or 4111)16- \ -% ./' 91wy...,;022 9i68v_123 9/68aX)24 f' .9/ .r r'•?6 • I ^- •_4'S r� �n �,' 9168r.)Ci2ii �• , .� £ ammo .� FIGURE 1 - VICINITY MAP OF SITE I4.0 Site Geology& Mapping 4.1 Surficial Soil Types IThe Soil Conservation Service (SCS) Soil Survey classified the local soils as Alderwood gravelly loam (Amc). This soil unit is formed on terraces from reworked glacial till I sediments. Permeability is said to be moderate with a cemented layer formed in very compact glacial till at over 30 inches in depth. I The Coastal Zone Atlas of Washington (Department of Ecology) and other geologic mapping describe the parent rock in the vicinity of the property as Tertiary Sandstone (Ts). This unit is comprised of interbedded sandstone, shale, and mudstone, including I the Aldwell Formation of Eocene age and the Quimper Sandstone of Oligocene age. This unit was formed over 26 to 54 million years ago. IGeologic mapping of the site is included in the Appendix. I I I I I5.0 Site Observations I Field observations confirmed the presence of glacial till and Tertiary Sandstone. 5.1 Observation of the Bluff ISeveral outcrops along the shoreline of Oak Bay exposed medium stiff gravelly clay till at the upper face of a low bluff. The low bluff is approximately 18 feet in height above 1 the shoreline. This soil unit extends approximately 3 to 5 feet in depth beneath the surface, overlying moderately dense, orange-brown poorly weathered sandstone up to 2 feet in thickness. Very dense, gray, solid sandstone lies beneath the weathered Isandstone and likely extends to substantial depths. IProbing at various points within the site showed the presence of the same medium stiff gravelly clay till with a very thin cover of loamy silt. IAt the bluff below the site, groundwater was observed to be seeping through the face of the gravelly till and weathered brown sandstone. An outcrop of this exposure can be seen in Figure 2 below. The weathered sandstone was observed to be damp and highly I weathered from the subsurface groundwater seeping through its face with little cementation. I N,...-.AL. . 4F.',..,k,, 4;4111101."). .7.;0 ,-.0,.... ,,,, ;fp: •fr,,,t.glom wiii.via- 7,1" 41./. 44-i r . ', :-'1' ,.. -.;tii- ; .40'''',-,;e_4 ;1 leftale . - •Iiil -, 'IQ.fr- a sOtiO.,, - 4 NP.11.111* _iPfr . ' -,`„,""41VAIP-40011 a i • 111 "`teIN*, .. yy -,,, II r -.Till er �i A► ' i3 4, �� , .,4 ='OMpig • /� ' 4 i.. , —, .k 0.4S-i--74. AtAtt VIZ" i.16111- ild I I 444Z111 7jj,!��'• . , ; ' ~may " 4" .> ., . � , " * ' " • '0 ,4i trOvertilisitAlik. .,,_,Jrak.I • ` ,..r- , ar• . 4'titl,„....4." 4' 1 ilk rr FIGURE 2 —VIEW OF THE EXPOSED WEATHERED SANDSTONE AT THE BLUFF INorth of the site, another exposure of sandstone was observed. The exposure showed substantially less weathered orange-brown sandstone formations with moderate 1 induration. A view of the cemented, less weathered sandstone can be seen in Figure 3. 3 I I 1 •tom• `. v : < "" } �., /i/ 4. c �+ + 1 .a�� • I1 �. •-w.,. ,- , LL , . -. 'r :A : rift: ' ier j r �10 IFIGURE 3 —VIEW SHOWING CEMENTED SANDSTONE Below the orange-brown sandstone layer, very dense, solid, gray, sandstone was I generally observed along most of the bluff. Exposures of the sandstone showed stratified cobbles protruding from the face of the bluff. IAir' ` ,, ,t 1 �y I I 1 _ I . Vie!_. =,�;e �• . ,';•m� I ,tip .i-!' P... . 1 r FIGURE 4—VIEW SHOWING VERY DENSE UNWEATHERED SANDSTONE I I Probing of the shoreline over 5 feet away from the toe of the bluff suggests the gray sandstone underlies some of the sandy beach at shallow depths. A view of the Isandstone formation can be seen in Figure 4. 5.2 Test Pit Observations I During a preliminary drainage investigation on January 30, 2013, a single test pit was 9 dug on the downslope portion of the property using a post-hole digger to verify general I soil properties for stormwater management design. The upper 3 inches revealed medium dense, dark brown, moist, loamy silt. Beneath this soil unit dense, brown, saturated, silty clay with small amounts of sand and gravel was found to depths of over I18 inches. At 18 inches in depth ground water was actively seeping into the test pit. A view of the flooding test pit can be seen in Figure 5. 1 * i' . F �� --,4i1. I 1 y y 1 . " > I FIGURE 5 — VIEW OF DOWNSLOPE TEST PIT IA second test pit was excavated during the follow-up geotechnical investigation to assess soil conditions. This test pit was located further upslope at the property adjacent to the southwest corner of the existing house. The upper 2 inches revealed medium Idense, dark brown, moist, loamy silt. Beneath this soil unit medium stiff, brown, saturated, silty clay with gravel and sand was found to over 20 inches in depth. At 20 inches in depth ground water was actively seeping into the test pit. Probing indicated I increasingly stiff soil below the limits of the excavation. I I 1 I : , r - ,- ..t , 4' �"" ', ._ tea; ' , ' " ; 4P ItIN t's , ' • ' ,i . I .,4. ;l , • tio ..., c , ..., .. " ` ; } • . • • • r I z I • r r • r r •".•. I FIGURE 6 —VIEW OF UPSLOPE TEST PIT Observation of the site showed no change in topography or vegetation suggesting that I the entire site is underlain with the same moderately dense, poorly permeable glacial till and impermeable sandstone formations. I6.0 Recommendations The McGinty Parcel appears to be entirely underlain by clayey glacial till. The Iweathered material is poorly permeable with nearly impervious sandstone beneath and, hence, is not suitable for drywells. Under the circumstances, infiltration cannot be used and a drain pipe leading to the shoreline is recommended. I I I I I ' 7.0 Limitations The observations and conclusions of this report apply only to the subject property and they are not transferable to nearby or adjoining property. This report is the sole property of Mr. Jeffrey McGinty and may be used by others only with his permission. NTI Engineering and Land Surveying warrants that this report was diligently and conscientiously prepared in accordance with the practice of professional engineering and according to the principals of geologic science. No other warranty, either express or implied, is provided herewith. ' Please call on the undersigned engineer ifyou have questions about the contents of this 9 g ' report. Sincerely, rf -4 , o 74 3 •ks.Q77.61,0) 1 fUNAL Steve S. Luxton MSc, PE Trent T. Adams, E.I.T Senior Geotechnical Engineer Project Manager I 1 7 � APPENDIX I I I r. �' �r . iiiir ,_.. .._ .- _ moo ....� ,.+ V .. r I ,e''' //! r : I7. T 1 • 1 r ' • I4°.. 1 re I� I f • . • Y I I .. 1 tI I • 0 I I I I