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Home My WebLink AboutGEOtech Assessment BLD2003-01120 - BLD Engineering / Geo-tech Reports - 8/8/2004 h • I OC MASON COUNTY S u PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER NN Shelton,Washington 98584 DATE:_ Aug. 8'', 2004 INTER-DEPARTMENTAL COMMUNICATIONS TO: Tammi Clark, DCD- Planner FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. WO#PLG-04 SUBJ: Geo-Tech Assessment Review NAME: Janicek Cabin g Cushman BLD2003-01120 Tammi, The geotechnical assessment prepared for the Dale Janicek vacation cabin constructed at 30 N Deer Court, has been received and reviewed by Public Works. The report appears to satisfactorily address County requirements for geotechnical assessments. The assessment's author indicates that, in his opinion, the completed development of the property will not cause stability problems for either the subject property or neighboring properties, and that a more detailed investigation(report) is not warranted. From the contents of the assessment, I recommend accepting the report as satisfying the County's requirement(s) for stability investigation and geotechnical reporting. Recommendations contained in the assessment should be incorporated into the site's development and made conditions for permit issuance. Adequate erosion and sediment control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. In summary, the geotechnical assessment appears acceptable, and stability issues may be considered to have been adequately investigated and addressed. 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. Si erely, l Al n A. Tahja File: H:\WP\GEO\Assessments\Janicek.doc } �/o 9 LAKE CU SHMAN N0. 14 SECTION 4 a 5. TWP. 22 N., RGE. 4 W., W.M. MASON COUNTY, WASHINGTON X 0 {� 4 +, N s� n� SCALE t 1"- OO' .y " vs i Ali , �I� ! UNPI_.4TTF0 �F,Y�.� ', -. // , '.y , � ♦♦ "ten ,wnvd� �i� .v vr� Ap t r'• l{� '`�� j 1 z ,'` Yob AWN" Lml •j-1 `S '��iy ' s\'nr.y:Art. n•r'r!L♦'Yf I rs d jawN° n �+ 4 J7 0 i p, ♦z � ♦♦ 1� rr b9� p SHEET 2 OF 3 SHEETS Aug 02 U4 U9: 2sa DHLE JANICEK 7892500 p. l August 2, 2004 To: Mason County Department of Community Development Planning Division Fax: 360/427/7798 Re. Lot 52 Division 14 Lake Cushman Parcel No:422055000052 Project Description. cabinAhed ATT. Mr. Scott Longanecker I received notice from LCMC that a Geological Assessment was not received and am sending a fax copy to you and will also put a hard copy in the mail today. I am truly sorry that this was not taken care of in a timely manner. I am also sending you a copy of the Wetland delineration, this will be in the mail in a couple of days. Thank you for your understanding in this mailer. Dale Janicek This fax contains a total of six pages. Aug' 02 04 09: 29a DALE JANICEK 7892500 P. 2 TE E C A';UA TIEARRAENA IRONNIhNTA1. CONSULTING, INC. Rcsroi-Y e Coimrucr 16 Junuary 2004 Mr. Dale Jank;ck- 4286 Brothers Avenue Juneau, Alaska 99801 SUBJECT-- (JE-OLOGIC ASSESSMENT— MASON COUNTY Location: Lol 952 Lake Cushman North 30 r)ccr Court. Division 14 Parcel Number: 422 055 000 052 Mason County Case Number: BLD2003-01120 FILE: C:\Documcnts andSettings\ChrMiltn\MyDocumcntq\A"I'LrC\PROJECTS\GEOTf.(-.I I & MAR[Nro,\G*I'ECH-MASON-CO\CEOLOC,IC, ASSESSM ENTS\Jgknecek\GA-Ldoe Dear Mr.and Mrs.Janicek., At your request Agua Tierra Environmental Consulting, Inc.(ATEQ conducted a Geologic Assessment (GA)for the above mentioned subject property. 11 is within a location governed by Mason County Resource Ordinance 17.0 1.100—Landslide Hazard Areas. This determination was issued in a letter from Mason County staff dated August 23.2003 following,a review of your permit application for a previously constructed cabin on the site. 1.0 INTRODUC.'TION Per Mason County Ordinance, a site is considered a landslide ha.?.Hrd due to presence of one or more of the following characteristics: • Geomorphic indications of past slope instability; • Artificial oversteepened or tinenginecred slopes(cuts or fills)-, 0 Slopes containing soli or potentially liquefiable soils- ft Slopes ovurstuepened/unstable as result oi'strcam or wave erosion; 0 Slopes greater than 15 percent(8.5 degrees)ANI)potentially containing a slippage plain and groundwater discharge; or 0 Slcjljcs greater than 40 percent(21.8 degrees)with 10 or more feet ol"vertical relief(excluding bcdrt-x:k). Development proposed within 300 feet of a landslide hazard arcs is required to have either a Geologic Assessment(GA), or a more rigorous Geotechnical ((GR),or both(MCO 17.01A 00-F.1)depending on site conditions, study result~,and the,opinion of County staffreviewing the project and any slope evaluation reports submitted. Based on the County's requirement,and H1.your written consent, we conducted this GA for thusi1c. Our findings and recommendations follow. 1711VERS FISH H-AL41 IAJ`* 10 WETLANDS WAI LH�.HEDS MARINE SHLIHELI I N.FR AGUATIESRA ENVIRONMENTAL CONSULTING, INC, 506 Edison Supat SF. - SOW I OU-QIYMDiO,Waahingtnn 98601 T.- (W)l 7,54-3755- F:13601754-3431 -&Mail; itoevououstierra.nat Hug Ui' U4 UU: eSa DHLE JHnICEK 7892500 p. 3 1.1 EXISTING LANDUSE The property is approximately 1 Mere in size and is partially developed for recreational landuse. A small cabin shed! is located in the lower portion of the lot, and is the subject of the unpaved driveway lead,,from the Decr Court cul de sac to the cabin. The rernainder ofthermit and this l t isr with a mixed age and species forest. covered 1.2 PROPOSED LA.NDUSh: Additional development work on the site is not currently planned nor the subject of this GA. The existing cabin shed is the subject of this work and permitting is currently being performed in an "atler-the-litct" sequence. Site improvements include a 14 by 16 foot cabin- a sloping unpaved driveway access entering, at the crest of the lot on Deer Court,an on-site septic system and utility lines. 1.3 FI.ELD WORK Fieldwork was perl'ormed on January 30, 2004 by ATEC7s btoteclinical engineer, Henry Gertjc, P.E. Field observations included a traverse by titiot ofthe property and vi,,iral inspection of landlurms and human development in the surrounding area. Basic slope geometric measurements were made. Observations were made ofexposcd geologic features on site and within the vicinity. Observations were made to identify geomorphic landforms and indicators, ifany,ofactive slope processes. Z-0 EXISTING PROPERTY DESCRIPTION The site is approximately I acre in size, irregular in chaps,and has its longest axis oriented north-south_ The northern end ofthe i)roperty meets the cul do sac of Dcer Court_ The southern ix:irtion of tilt; lot includes a shoreline area along Lake Standstill. There is approximately 20 to 25 feet ol'clevation change across the property_ Beginning at Deer Court, there is an unpaved driveway,approximately 15 iix.t in width and i 00 feet in length with a downward gradient of about IS percent. The driveway ends in front ofthe cabin shed. Adjacent to the; driveway, is a 2H toI V slope,with an incomplete low masonry block landscaping wall at the base,2 teet in height and 20 feet in length. Beyond the cabin, is a lower flat area including a wetland and lake front. During the time of the field visit, the lake appeared to be at a seasonal high as indicated by inundation of shoreline vegetation_ The minimum distance from the shoreline to the edge of the cabin was approximately 55 to 60 feet. The cabin is a single story structure wnstructcd vn a cast on gmde concrete :slab_ The soil supporting the structure is a till consiatinb ofnative suit excavated on the upper portion ofthe lot. The fill in this area is about 3 to 4 feet in thickness and extcnds approximately 12 feet beyond the cabin shed. Thu cabin shed eXllibitti no indicators of settlement or displacement There are no gutters on the structure. On adjacent properti(:. ,other older cabins and homes are pm-sent. including: I} Westerly, a 2-story home on Lot 56.approximately 130 feet distant from the subject cabin is at approximately the same elevation; 2) Northerly,a 2-I/2 story log home,greater than 10 year~ in age, approximately 100 feet distant from the subject cabin is approximately 10 feet higher in elevation; 3) Easterly, a 2-story framed house, unknown age, approximately 240 feet distant from the subject cabin is approximately 20 feet higher in elevation_ 2.1 VEGETATION ION 1'hc site is covered by a mixed age and species forest. The larger t -c;s include Douglas Firs from 4 to 10 Aug 02 04 09: 30a DALE JANICEK 7892500 p. 4 inches in diameter and cedars from 6 to 10 inches in diameter. Alders dominate the disturbecl areas. ranging from 1 to 4 inches in diameter. Alders on the fill area are estimated at approximately 6 years in age, The shoreline area is vegetated by larger alders and willows. Native brush vegetation is present in all areas not disrurbed by earthwork, with the exception of the upper driveway area where scoter broom is becoming established, The subject lot and surrounding lots are approximately 30 percent modified by earthwork. 2.2 SETBACKS Mason County Planning Depariment required wetland bufTers on the site. The presence aPslope rates greater than 40 pment activated the requirement I'or the GA. County ordinance prescribes a minimum 50- foot setback from the toe or cress of any such slope. Observed site conditions are snfticiintly stable for[Ile subject structure to not require any modification to its location. 23 SLOPE GF.OMETRY I TOPOGRAPHY The natur-di topography of the subject lot and surrounding land area is moderately sloping, averaging 21-1 to I V or Icss(50%). 'Ille slope area is further chairacteriz"]as terraced and rolling with individual hilts ranging from 20 to 30 feet in height. Sinuous hollows, 6 to S feet in depth separate the rolling hills. 2.4 GEOLOGY One geologic soil unit(glacial till) is exposed in numerous shallow excavations in the vicinity of the situ_ The USCS Soil Survey for Mason County identifies this material as Hoodsport Series gravelly sandy loam. 'Phis material is compact, coarse to tine Sand,with Clayey Silt,coarac to finc gravel and occasional cobbles. Nearby water well logs indicate that glacial till or advance outwaah is present to depths of 40 feet or more,overlying basalt bedrock. A second geological soil unit is believed to be present in the shoreline area of Standstill Lake, alluvium, with organics. The USCS Soil Survey for Mason County identifies this material as McMurray Series, peat. 2.5 EXPRESSIONS OF PAST SLOPE INSTABILITY There were no indications of past or recent slope instabilities on the site, neighboring home silcs, or nearby slope areas, 2.6 RUNOFF, EVIDENCE OF SE F:PAGE,OR EROSION Runoff generally flows from north to south, from the entrance towards Standstill Lake_ There is ni> evidence of flow concentration, seepage or erosion on the lot. Pondinb was not evident in the area surrounding the cabin, in higher areas, nor in the forested area between the lake front wetland and the cabin. 3.0 CONCLUSIONS Taken together, the broad presence of glacially overridden soil, and moderate, low height slopes on and around the property imply that the risk of slope instability is low, Further evidence of long term soil stability is found in the vertical trees surrounding the site, as well as the presence of established homes surrounding the subject developed lot. There are no expressions of soil instability or erosion- Thu he cabin is constructed on shallow fill of miknown density. it appears that grading;of the lot predates the construction of the cabin shed by several years,though this has not been verified by ATE(', Thou is no evidcncc of settlement of either the fill or the underlying soils. The cabin shed exhibits no signs of distortion or strain. There are some small potential risks to this very small and light structure, including HUg U2 U4 U9 : 30a DALE JANICEK 7892500 10, 5 fill tire settlement. potential scour along the slab and frost heave- failure motion could caux a hearing failure through the fi11 if the base of the fill rests on very soft alluvial or organic material. Again, there is no clear evidence for this,and the risk appears low, i ra l is not eroding, nor creating Disturbed arc-as are m—vegetating naturally, mainly with native trees and shrubs, ncentr�rted n,nuf( Grading of the lot appears stable, Disturbed so 4.0 RECOMMENDATIONS No further slope stability investigations are recotnnrcnded forth's site lrcrtair,ing to the current state of land use. The owner may wish to investigate Soils beneath the fill near the cahin :shed to assess risk of future settlement. Any future strictures planned for construction on this site should be the subject ofa geotcchnical report. The cdgc of the cabin concrete slab bs>ttom is exposed above the soil surface, This edge should be insulated and protected fi`om erosion, by covering the perimeter soils with lightweight insulating material, such as polystyrene_ We recommend that roof drains be installed and discharged downgradicnt of t consistent with Mason County stormwater requirements_ he cabin in a manner Mulch or compost the exposed inorganic soils around the house in cut/fill areas to assist in the regrowth of native plants and reduce rainfall impact erosion. Scotch broom in the upper I0T is an invasive species that should be removed as soon as possible to protect tl,e emerging native brush. 5.0 STANDARD DISCLOSURE STATEMENT This report is based on a limited reconnaissance inspection of the existing liite conditions. No scientific measurements or calculations were performed_ The findings and report are limited to the nornial standard of care for an investigation without benefit of a subsurface testing and laboratory prog m . Recommendationsra provided here are intended to be at a general level. More detailed design work ,r,ay be needed_ if construction is planned rind/or implemented using these documents as a reference, no warranty is made by ATFC concerning conformity of the construction to the amclusions and recommendations of this report unless The plans are prepared and/or reviewed, and the construction work inspected by a represcntative ol'A rEC_ Within the limitations of the scope and hudgct, our services have been executed in accordance with generally accepted professional practieas_ 1n addition,conditions may change at the site due to human influences, floods, groundwater regime changes, or other factors. This warranty is in lieu of all others, either expressed or implied. The content of this report is client and site specific and valid for 6 months from the date of fieldwork. Hug ue u-t ua: uua DFILE JFINICEK 7892500 p. 6 • ti Thank you for this opportunity to be of asaislunce. Jma- ,ki Sincerely; ro Christian Fromuth, M.Sc.,C.)✓_ 46 - lydrologist/Geomorphologist * 29378 XL tom' Henry Gertje. PE, M.Sc.,C.F. EXPIRES 10/5/ o s- Cycoteclinical Engineer