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HomeMy WebLinkAboutSEPA EPIC-ND-34 - BENAROYA COMPANY - PARKWAY PLAZA WEST GRADINGPARKWAY PLAZA WEST BENAROYA GRADING EPIGND -34 TO: FILE • MEMORANDUM CITY of TU a W ILA PLANNING DEPARTMENT FROM: Kj el l Stoknes, Responsible Official SUBJECT: Benaroya Application for grading and cutting hillside DATE: .August 197( This memorandum is intended to be a chronology of events leading up to the issuance of a grading and cut permit for Benaroya for the cutting of the hillside east of Interstate 5 and west of Southcenter Parkway for approximately 15,000 cubic yards of excavation. 1. The application for fill was received on.)Ju1y 16, 1976. 2. Due to inadequate information on the proposed hillside cutting, additional information was requested for that portion of the application. Th'e fill application for the lower portion was processed, the environ- mental questionnaire accepted and a negative declaration made. Following this the grading permit for only the lowland portion was issued. 3. On July 20, 1976, a Dames & Moore Report on consultation for the pro - posed cut was submitted to the City of Tukwila. This was to support the environmental questionnaire submitted on July 16, 1976. Additional information includ d a slope of 14 to 1, 3 cross sections'of the slope cut, • • proposed drainage system, restoration plan, and a cost estimate for the excavation. 4. July 22, 1976, in a meeting between Gary Crutchfield, Fred Satterstrom, Al .Pieper with Bob Sandwick and Jim Bucky of the Benaroya Company additional information was requested. That was affirmation of the . railroad that the minimum turning radius for the railroad required the cutting of the hill, copy of the soils report by Dames & Moore dated 28,June 1976 plus an additional ansite analysis by Dames & Moore. They were also informed that they would have to appear before the City Council and application for a waiver to resolution #489 to allow the staff to process this excavation permit. 5. An additional inspection report from Dames $ Moore dated July 26, 1976 was submitted. This was analysed by the Public Works Director and he felt it was adequate and that the soils would be stable. Subject was reviewed by the City Council during their study meeting on this date and tabled until their next regular meeting of 2 August 1976. 6. City Council considered the matter at a regular City Council meeting and after considerable deliberation authorized the staff to process the permit. 2- Ah,gvs+ -2(0. 7. I signed the environmental questionnaire as a result of all the information before me and concluded that it would have a negative environmental impact. 8. 5 August 1976 grading permit authorized and'issued allowing the cut of the hillside to begin per plans with certain stipulations. 0 Memorandum File 4 August 1976 Page 2 It is my feeling that there has been adequate public awareness on this matter and that an adequately thorough review of the environmental affects has been made and that a negative declaration was in order. Pursuant to these things the grading permit may be issued on August 5, 1976. KS /cw ki KjelT Stoknes Resp nsible Official • CITY OF TUKWILA CE(tTIFICATJON BY APPLICANT: - I hereby certify that the information furnished nett is environmental checklist sheet is true and accurate to the best y Project Name: Signature and Title Parkway Plaza West Project. Address: 17500 Southcenter Parkway, Tukwila. . � '767 BELOW THIS LINE FOR CITY USE ONLY ACTION .BY OTHER' DEPARTMENTS: 1. Date of Review: Building . by: Planning - by: Engineering 4 r —36 by: ..Police by Fire by:, Agency review of environmental checklist determined that ' ';.The project is exempt by definition. The project has no significant: environmental impact and application should be processed without further consideration of environmental affect: The project has. significant environmental impact and a complete environ -,: L mental impact. statement must be . prepared prior to further action for perm More specific information is needed to determine impact. • • July 16, 1976 Date . =Check one. ( +) or • ( +) or (I ( +) or ( -) ( +) or (-) Signatur and._Title•of Responsible Official 3. Applicant was notified of decision on: by Date Date Staff Person • by Letter, phone In accordance with Washington State Environmental Policy Act and City of Tukwila Ordinance No. .759. ( +) Means recommend a full environmental impact statement be'done. Means recommend a full environmental . impact statement not•be done. f5 ° 17/2A .V f7 ' pise y c:74/ 7%26/? z . 4/26, ''` G� � ' ,peg-. 5/8.7 41)1 e2/26 • • CITY OF TUKWILA ENVIRONMENTAL QUESTIONNAIRE This questionnaire must be completed by all persons applying for a permit from the city of Tukwila., unless it is determined by the Responsible Official that an environmental assessment or full impact statement is required. Other forms have been developed for single- family home applications and legislation proposals. BACKGROUND DATA: 1. Name of applicant: Jack A. Benaroya Company 2. Address and phone of Applicant: 5950 Sixth Avenue South, Seattle, WA 98188. .762-4750 3. . Project name: Parkway Plaza West 4. Project location: 17500 Southcenter Parkway; Tukwila, WA 98188 . Naturs and brief description of proposal: Cutting, grading and filling site (approximately 12 acres) G,J; vttcq nti- e1S��Q Estimated completion date: August 15, 1976 Do you have any plans for future expansion, if yes please explain: Development.of retail buildings 8.' `:hat other governmental permits are required prior to completion of this project? (a) Rezone, conditional use, substantial development, etc. - YES NO'X W YES NO X (b) King County Hydrolics Permit .. . (c) Building' permit - YES : .NO X (d) Puget Sound Air Pollution Control Permit YES • NO X (e) Sewer hook up permit YES • .NO X • (f) Sign permit YES NO X (g) Water hook up permit YES- NO X (h) Storm water system permit (connection to* existing) YES x NO • (i) Curb cut permit YES X .NO (j) Electrical permit (State of Washington) YES NO x (k) Plumbing permit (King County) YES NO X (1.) Other 9. Do you know of any plans by others which may affect the property covered by your proposal? If yes, explain: No 10. Agency requiring checklist: City of Tukwila, De ar_tmen 11. Accepted by agency on: •`2//o 2�i t • by: st (to be filled in by city p P of check .• ENVIRONMENTAL IMPACTS (Explanations of all "yes" and "maybe" answers are required.) Yes Maybe y Earth. Will the proposal result in: (a) Unstable earth conditions or in •any changes in geologic sub - structures: (b) .Disruptions, displacements or overcovering of the soils: (c) Change in topography or ground surface relief features? (d) The destruction, covering, or modification of any unique g.2ologic or physical features? Any increase in Wind or water erosion of soils, either on or off the site? • Changes in deposition or erosion of beach sands, or in changes in siltation, deposition, or erosion which may modify the channel of a river or stream or the bed. of 'the ocean . or any bay, inlet or lake? .Explanation: ( (f) Air. Will the proposal result in: (a). Air emissions or deterioration of ambient air quality? (b) The creation of objectionable odors? (c) Alteration of air movement, moisture or temperature, or in any change in climate, either locally or regionally? Explanation: X X • -1- X Water. Will the •posal result in: (a) Changes in currents, or the course or direction of water movements, in either marine X or fresh waters? ---~ b Changes in absorption rates, /04y4„,0 s ( ) patterns, or the r''` �� , ce Pie .7A5 p � ����r��.y� � amount of surface water run - 4.v�, , off? S y�7 cd.- - • . %a- - Yes layb e No (c) Alterations to the course or flow of flood waters? (d) Change in the amount of surface water in any watercourse? (e) Discharge into surface waters, GG'' or in any alteration of sur -5 face_ water quality, including 7/4,i,* temperature or turbidity? Alteration of the direction or rate of flow of ground waters? Change in the quantity of . ground waters, either through direct additions or withdrawals, or through interception of an acquifer by cuts or excavations? (h) Deterioration in ground water quality, either through direct injection, or through the seep- age of leachate, phosphates, detergents, waterborne virus or bacteria, or other substances :into the ground waters? Reduction in the amount of water otherwise available for public water. supplies ?'. (1) Explanation: X Flora. Will the proposal result in: (a) Change in the diversity of species, or numbers of any species of flora (including trees, shrubs, grass, crops, micro -flora and aquatic plants)? (b) Reduction of the numbers of any unique, rare or endangered species of flora? (c) Introduction of new species of flora into an area, or in a bar- rier to the normal replenishment of existing species? Explanation: Fauna.' Will the proposal result in: (a) Changes in the diversity of species, or numbers of any species of fauna (birds, land animals including rep - tiles, fish and shellfish, benthic organisms, insects, or micro-fauna)? ) Reduction of the numbers of any unique, rare or endangered species of fauna? ( Introduction of new species of fauna Into an area, or result in a.barrier to the migration or movement of fauna? (d) Deterioration to existing wildlife habitat? .4' vnf • Explanation: Noise. Will the proposal ing noise levels? Explanation: es Maybe increase exist Light and Glare. Will the proposal produce new light or glare? Explanation::' Land Use. Will. the proposal result in the alteration of the present or planned land. use of an area? Explanation: Natural Resources. Will the proposal re- sult In: . . ja) Increase in the rate of use of any natural resource? (b) Depletion of any nonrenewable nat- kne,4;ei ural resource? .7.ese lc 04244- , fa Explanation:.. Yes Maybe No • Risk of Upset. Does the proposal involve a risk of an explosion or the release of hazardous substances (including, but not limited to, oil, pesticides, chemicals or radiation) in the event of an accident or . upset conditions? Explanation: Population. Will the proposal alter the location, distribution, density, or growth rate of the human population of an area? . Explanation: X • Housing. Will the proposal affect existing housing availability, or create a demand for additional housing? Explanation: • Transportation /Circulation. Will the pro- ae, posal result in: (a) Generation of add itional vehicular movement? (b) Effects on existing parking facilities, or demand for new parking? (c) Impact upon existing trans)orrt,ation systems? apize 4 i&1- 4e , ?7`0� f . (d) Alterations to p esent patterns of circulation or movement of people and /or goods? (e) Alterations to waterborne or air traffic? Yes Maybe Explanation: Local Services.. Will the proposal have an effect upon, or result in a need for new . services in any of the following areas: (a) Fire protection? W✓? (b) Police protection? /y ; dc (c) Schools? (d) Parks? (e) Maintenance of public facilities, including roads? • Other 'governmental services? play) Mvi , (f) Explanation: X• X Energy. Will the proposal result in: (a) (b) Use of substantial amounts of fuel or energy? Demand upon existing sources of energy, or require the development of new sources of.energy? Explanation: Utilities. Wi11'the proposal result in a need for new systems, or alterations to the follow- ing utilities: (a) Power or natural gas? (b) .Communications systems? (c) Water? (d) Sewer or septic tanks? (e) Storm water drainage? (f) Solid waste and disposal? Explanation; Yes Maybe X X- • -.X Human Health. 'Will the proposal result i n the • creation of any health hazard or potential health hazard (excluding mental health)? Explanation: Aesthetics. Will the proposal result in the f>es G2 lbe S'.. . obstruction of any scenic vista or view open Pose) s, s to sh to the public, or will the proposal result 1 'in the creation of an aesthetically offensive 14140 �' / site open to public view? .. Explanation: 111 V Yes Maybe Recreation. Will the proposal result in an impact upon the quality or quantity . of ex- isting recreational opportunities? Explanation: Archeological /Historical. Will the proposal result in an alteration of a significant archeological or historical site? *Explanation: .Revenue. Will the proposal cause a signifi- can ncrease in city revenues? � 44 6 pa -cam cue . Explanation : 10 • tQ ' 444 ,44"4.--j -ei -2,. .. -' X Employment. Will the proposal create a significant amount of new jobs? . Explanation: j2;,,eEf- A- 1 • X. O. Jack/A. Benaroya Company 5950 Sixth Avenue South, Seattle, WA 98108 (206) 762 4750 .I: August 2, 1976 Mr. Kjell Stoknes Planning Director City of Tukwila Tukwila, WA 98188 AUG ilECEIVED III 02 1916 OW OF TUKWILA Re: Application for permit to grade' for railroad right -of -way This letter is intended to support our application for permit to cut and grade a portion of a ridge west of Southcenter Parkway and to support our request for a waiver by the City Council of the provisions of Resolution No. 489. The requested grading permit is required in connection with the relocation of the railroad crossing and trackage across Southcenter Parkway which re- location was presented to the City Council at the Committee of the Whole meeting on May 10, 1976 and the authorizing ordinance adopted by the Tukwila City Council at its regular meeting on May 17,1976. At the meeting on May 10, 1976, Mr. Robert Fehnel of the Benaroya Company presented the rail- road's plan showing the existing rail and crossing and the proposed location and crossing as it cut across the edge of the ridge. A copy of this plan is attached hereto as Exhibit A. While we believe that the presentation to the Council and the adoption of the crossing was a recognition that the relocation necessarily required a cut in the corner of the southerly slope and was in fact a waiver of Reso- lution 489, we also believe that an analysis of the criteria established by the City Council for waivers under Resolution 489 have been satisfied, as follows: 1. Is the proposed action.,consistent with presently merging Land Use Policy Plan? Yes: The natural environment element of the City's Land Use Policy Plan considered by the City Council with motion of intent to adopt on February 2, 1976, establishes certain recommended objectives and policies, which are generally to promote the maintenance of natural vegetation on slopes and specifically to discourage development on slopes in excess of 20% and in areas where the stability of slopes may be questionable only after a quali- fied professional can demonstrate that slopes will be stable even after site modification. These and the other guidelines being considered for the Tukwila Land Use Policy Plan to be adopted by the City recognizes that while the main- tenance of natural vegetation and land form is desirable there will in fact INDUSTRIAL PARKS /WAREHOUSES /OFFICE BUILDINGS /SHOPPING CENTERS AND SPECIALIZED MERCHANDISE MARTS. • • Mr. Kjell Stoknes Page Two August 2, 1976 be instances where cuts in slopes are required, specifically, that in areas where there is question as to the stability of slopes that development will be allowed if a qualified professional can demonstrate that the slopes will be stable after site modification. The action which the Benaroya Company intends to take is not strictly a development and is required only as the result of the relocation of a public utility, the relocation of which will maintain the railroad right -of -way in an area which will be more effectively screened from public view and more aesthetically pleasing. 2. Does the proposed action represent a unique condition which is insignificant in scale and to which no other apparent alternatives are reasonable? Yes. The proposed action is a unique condition in that it is required as the result of relocating an existing industrial railroad track and crossing over Southcenter Parkway to its originally intended location. It is generally agreed that the existing location of the track and crossing is objectionable both with respect to pedestrian and vehicular traffic and its aesthetic aspects. It is further unique in that it does not involve the cutting of a major slope, but rather the cutting and grading of the "nose" of a steep ridge. The proposed action is relatively insignificant in scale when placed in con- text with the entire hillside along I -505. The area of cut and grading will not be visible from the north. A vehicle driving south along Southcenter Parkway will observe the cut only as it draws parallel to it. The cut will be screened in part by vegetation already in place as well as the landscaping which will be accomplished as part of the proposed work. The cut and grading will be visible only along South 180th and Southcenter Parkway south of the proposed work. Any visual impact as noted above will be reduced by the re- seeding of the slope and the planting of trees. A site plan of the proposed cut and the area along Southcenter Parkway is attached hereto as Exhibit B. The location of the track and the necessity for the cut have been established by the minimum radius required by the railroad in order to safely move large rail cars on the track. In order to minimize the impact of the cut and grading, the elevation of the railroad bed has been established at the highest possible elevation acceptable to the railroad for operation of the track. A number of alternatives to the proposed work have been considered. Among those alternatives have been a slope cut similar to the proposed action but at a ratio of 1:1 rather than 1:1 -1/4. Dames & Moore in their investigation did not believe that a slope cut on a 1:1 ratio was appropriate in this in- stance:. Further, the overall area of a 1:1 cut would be substantially greater than the 1:1 -1/4 which is shown on our application. Another alternative which has been considered is the building of a retaining wall or tiered re- taining walls. A single retaining wall would extend between 60 and 70 feet in elevation and require a thickness of at least 48 ". The additional Mr. Kjell Stoknes Page Three August 2, 1976 engineering, substantial increase in cost and the unsighliness as well as the hazards of a wall of such height render this alternative unfeasible. The other alternative involving retaining walls involves two tiers of walls, each of which would extend at least 30' in height. While from an engineering standpoint such tiered retaining walls would be more acceptable than a single wall, the hazard, the unsightliness and cost makes such an alternative unfeasible. A further alternative which has been suggested is that the curvature of the rail begin its curvature at a point easterly of Southcenter Parkway. Such an alternative is substantially different from the right -of -way configuration previously approved by railroads and the City Council. The area of Southcenter Parkway to be crossed was designed for a crossing at the site previously approved with proper bedding in place and is not designed for crossing at a more southerly location. Relocating the point of curvature would also place the track west of Southcenter Parkway in an area of worse soil condition. In addition to substantial impact on the useability of property both west and east of Southcenter Parkway, such alternative would further involve expenditure of substantial sums to change the configuration of the building already under construction east of Southcenter Parkway. 3. If the request for waiver involves grading or excavation in areas identified as having potential and natural limitations for development, are mitigating measures provided? Yes. In order to minimize the impact and assure the stability of the final configuration of the slope, the Jack A. Benaroya Company engaged Dames & Moore, a recognized and respected soils engineering firm, which has confirmed that the soil of the slope is relatively intact glacially consolidated soil and exhibits good engineering properties. Copies of the reports by Dames & Moore on the proposed slope cut are attached hereto as Exhibits C and D. In order to assure that the slope cut is in fact undertaken as shown on our application and to provide adjustments as may be required during slope cut operations, the Jack A. Benaroya Company is engaging, at its expense, the services of Dames & Moore to maintain a constant onsite inspection of the work and who will be available to City staff. 4. Do Resolution No. 489 requirements impose a special hardship to the site for which a waiver of the provisions would not necessitate a major policy commitment prior to the adoption of the Land Use Policy Plan? Yes. The granting of a waiver for the Jack A. Benaroya Company's appli= cation for grading is not a major precedent which would constitute a policy commitment by the City of Tukwila or impair the objectives and policies to be adopted by the City Council. The proposed action as noted above represents a unique condition and can be distinguished from the development of the site requiring major significant slope excavation. The particular slope here in- volved isaa narrow ridge extending out toward Southcenter Parkway and will be limited in visual impact. The denial of a waiver of this application would constitute a special hard- ship to the applicant in that it has proceeded based on prior approval of • • Mr. Kjell Stoknes Page Four August 2, 1976 the relocation of the railroad and the work undertaken under foundation permit upon a building within the existing railroad right -of -way. The ap- plicant has incurred substantial cost and has entered into agreements and commitments which, if the waiver is denied, would cause substantial and irreversible economic loss. The Jack A. Benaroya Company would not undertake the realignment of the slope unless it were considered necessary and is concerned with respect to the aesthetic impact of such a cut. The work to be performed on the slope includes a substantial allowance for landscaping, including immediate netting and reseeding and planting of trees at the earliest possible date. The sub- stantial investment of the Jack A. Benaroya Company along Southcenter Park- way necessarily requires that the Benaroya Company assure that the cut area will blend into the natural vegetation as quickly as possible. The City has been provided with a bond in the amount of $26,000.00 to assure that the Benaroya Company will accomplish the work and the required landscaping. Favorable action by the City upon our application and request for waiver is urged. The Jack A. Benaroya Company has no objection to waiver conditioned upon the presence on site during the work of a soils engineer acceptable to the staff at Benaroya's cost, together with a bond for a period of one year to assure the landscaping phase. Robert D. Sandwick House Counsel t r.D •.. COQ • r Fy "A /w Ti; 1—fr■ y -R.I.,. Z7 t.4 l0.-54? CaO 11 "T NP' Itt 1 11 14.07.3 JA PC 0 WMSE 1 it I L • d s 1 eau FY, -�- plIJI k• g v?•..i r -. 10.sv fi v 4 8 • r•M<«_ 96 'INC? tat b'3�� ' ^-•tea `" "l rosie •s �-' ° v? trt 4 v • • Vr•'1 PNJJ "Paw osni • tg o 4 ;0 • , 00/ - ft/ .77r.2.51 ANCHORAGE ATLANTA ' BETHESDA BILLINGS 'BOCA RATON BOSTON CHICAGO • CINCINNATI CRANFORD' ,DENVER, FAIRBANKS HONOLULU WHITE HOUSTON L05 ANGELES NEW ORLEANS NEW YORK PHOENIX PORTLAND SALT LAKE CITY SAN FRANCISCO SANTA BARBARA SEATTLE SYRACUSE WASHINGTON, D. C• PLAINS • • ®A6 ES CONSULTANTS IN THE ENVIRONMENTAL AND APPLIED EARTH SCIENCES BEIRUT MELBOURNE CALGARY PERTH JAKARTA SINGAPORE JOHANNESBURG SYDNEY LAGOS TEHRAN LONDON TOKYO MADRID TORONTO VANCOUVER, B.C. SUITE 500, NORTHGATE EXECUTIVE CENTER • 155 N. E.100TH STREET • SEATTLE,WASHINGTON 98125• (206) 523-0560 CABLE: DAMEMORE TWX: 910-444-2021 July 26, 1976 Jack A. Benaroya Company 5950 Sixth Avenue South Seattle, Washington 98106 Attention: Mr. Jim Bakke Gentlemen: Report of Inspection Proposed Cut for Railroad Realignment Giovanneli Property Tukwila, Washington INTRODUCTION At the request of Mr. Jim Bakke, we have made a brief reconnaissance of a hillside cut area on the Giovanneli Property. The cut involves the. removal •of material from the nose of a ridge to form the right -of -way for a. realigned railroad spur. We recently developed preliminary comments-and recommendations concerning the proposed cut, based on the results of borings performed at nearby locations and our general knowledge of the area. These comments and recommendations were given to you in a letter dated July 20, 1976. In this letter we recommended a tentative design slope of 1.25:1 (horizontal to vertical) with 10 -foot wide benches at approximate 40 -foot intervals in elevation. This recommendation was made with the understanding that we would provide inspection during the excavation and that a program of erosion protection would be carried out, • consisting of initial seeding with grasses followed by planting with deep- rooted vegetation. Reseeding of exposed soil is -to be accomplished as soon as possible following excavation. • We understand that the City of Tukwila has expressed concern over cutting the ridge, in view of previous experiences in the vicinity of the Tukwila Interchange, where cuts of moderate steepness have initiated large -scale earth movements. On July 21, 1976, an engineer from our staff inspected soil exposures in limited.areas at the base of the ridge where grading and clearing had been initiated. The purpose of this inspection was to con- firm the existence of intact, glacially consolidated soils as assumed in our EXHIBIT D P I ES 0 LVICDOI:1? Jack A. Benaroya Company July 26, 1976 Page 2 letter of July 20, 1976, to determine the geological relationship of the exposed soils to the nearby surroundings, and to identify any conditions which might affect the stability of the slope. SITE CONDITIONS The-soil exposures examined during this site visit consist of an initial cut extending from approximately Elevation 30 at the base of the ridge up to Elevation 50 to 55, and a small cleared area on the side of the ridge south and west of this cut lying at approximately Elevation 60. The soils exposed in the cut consist of very dense to hard silty sands and sandy silts in the upper portion cfthe cut, grading to very dense medium sands near the toe of the ridge:. The lower sand contains little or no fines. All of these soils have been preconsolidated under the weight of glacial ice. The excavation was started by undercutting the .bank such that, at the time of our inspection, the upper part of the slope was overhanging the base. As a result of this oversteepening, a significant amount of the sandy material had sloughed down from the exposed cut face. .The...small.cleared. area, at approximately Elevation 60, exposes the contact between a very dense silty fine sand and an underlying hard silt stratum. The silty sand just above the contact was slightly damp; however, no trace of seepage could be found in a close examination of the general area. The near - surface portion of the silt, which was exposed in this cleared area, is jointed. The joint surfaces are oxidized to a °dark brown and reddish brown color. Seepage was noted,at the.toe of the from a layer of clean, medium sand. at or below Elevation 30. No other of . the ridge within the area of the DISCUSSION AND RECOMMENDATIONS ridge at several locations, emanating All of the seepage areas occurred seepage was noted in a reconnaissance proposed cut. The results of our inspection, together with previous explorations upslope from the proposed cut area, indicate that the materials within the area affected by the cut are of a different geologic sequence than the relatively unstable, highly 'fractured silt deposits of Vashon Age which lie to the north. The hard silt stratum at the site consists of a pre - 'Vashon deposit similar to that encountered in the adjacent borrow areas to the south. This stratum is relatively intact and exhibits good engineering properties. We understand that the proposed railroad alignment will lie at approximately Elevation 22 in the vicinity of the cut, well below the level of seepage '1 • ®0%NMES 0 ffifil OORE Jack. A. Benaroya Company July 26, 1976 Page 3 noted during our inspection. We therefore recommend the following measures and procedures to provide control of ground water and maintain stability of the slope during the excavation. 1. The initial operation should consist of excavating a shallow trench or a series of trenches down the slope within the planned cut area to allow an early examination of soil conditions and stratification. This could be accomplished in conjunction with access and clearing work; a bulldozer cut would be satisfactory. 2. We strongly recommend that excavation bf the ridge to rough grade proceed from the top of the•ridge downward, rather than cutting from the toe. 3..• The benches should be cut as the excavation progresses. The actual location of benches across the cut should be determined in the field, based on conditions encountered as the face of the •cut slope is approached during excavation. The 40 -foot vertical interval for benches is intended as a guideline; closer spacing may be dictated by field conditions. The benches should be cut at a reverse slope, graded to carry slope runoff to the north edge of the cut. From this point the water should be carried downslope in closed pipes or protective channels and routed into the planned roadbed drainage system. 4. Seepage will be encountered as the excavation approaches the toe of the proposed cut. At this point test pits should,be excavated to the level of the railroad alignment to allow evaluation of seepage conditions and the most suitable means of controlling these conditions. This control could be accomplished by . construction of an interceptor drain below the level of the roadbed or by the installation of horizontal drains at the toe of the cut. Alternative means may be feasible for the control of seepage, depending on the conditions which are encountered during construction. Any trenching or excavation which extends below the level of seepage along the face of the cut should be accomplished in a series of horizontal stages so that at any given time the maximum length of open excavation is 25 feet. A possible method of seepage control is schematically-illustrated on Plate 1.. 5. Regardless of the method of seepage control, we recommend that the lowest portion of the cut face be buttressed with a layer of angular free - draining rock extending up to the level at which seepage is noted during excavation. The rock should be DAUM ES 8 PACICOIRE Jack A. Benaroya Company July 26, 1976 Page .4 separated from the slope face by a graded filter blanket or a layer of manufactured filter cloth. Quarry spalls or crushed rock at least 4 inches in average minimum dimension is desired for the buttress. A suggested buttress configuration is shown schematically on. Plate 1, together with the interceptor drain. 6. As described in our letter of July 20, 1976, we recommend that protection against erosion from surface runoff and seepage be acomplished through a phased program of seeding and planting implemented in conjunction with or immediately following- excavation. We recommend that all phases of the excavation be observed by a competent soils engineer or geologist, who would provide recommendations for bench locations, adjustments to the design slope angle, or other measures as indicated by observed soil and ground water conditions. We further recommend that the completed slope be inspected on a monthly basis during the first winter season to check for uncontrolled seepage, erosion, or other indications of instability which might require attention. We appreciate the opportunity to assist you on this project and look :forward to 'working with you during-the grading operations. Please .contact us if you have any questions concerning this report or if we could be of further assistance. Yours very truly, DAMES & MOORE By h./ --` Jack K. Tuttle Partner JKT:WJG:ss 4 copies submitted 4368- 024 -05 stloo• s sswwr O/Y . . GOHi_'Gy A'O? 339 5'SUci �o f'�Oi1&fa_Si)771 "j/1bW3HDS" -,Cy /1.,•/wb rzi ,yd LLB yrP.1 bea'rrd'!fe A...xi ea/9 aft cda'9 xV- IWW/v/be 4.2 1,17 9/v re a t "d- aea -I.a11.77 57/ BFTHESC•• NEw ORLEANS ' • BILLINGS NEW YORK BOCA PATON PHOENIX BOSTC, PO PTLANO CHICAGO • SALT LAKE CITT CINCI4NAT. 5•N FRANCISCO CRANFORD SANTA BARBARA DENVER SEATTLE :tAIRBANrS S■PACUSE HONOLULU v.ASHINGTON.D. C. WHITEtP.LAINS pampa ES A®®12 E CONSULTANTS IN THE ENVIRONMENTAL AND APPLIED EARTH SCIENCES B{IRUT MELBOURNE CALGARY PERTH JAKARTA SINGAPORE JOHANNESBURG STONEY• LAGOS TEHRAN IONOON TOKYO MAORID TORONTO VANCOv,ER, B.C. SUITE 500, NORTHGATE EXECUTIVE CENTER • 155 N. E. 1007!^ STREET SEATTLE,WASHINGTON 98■25 • 1206) 523 -0560 CABLE: DAMEMORE TWX: 910-444 -2021 July 20, 1976 Jack A. Benaroya Company 5950 Sixth Avenue South Seattle, Washington 98108 Attention: Mr. Robert Fehnel Gentlemen: Report of Consultation Proposed Cut for Railroad Realignment Giovanelli Property Tukwila, Washington INTRODUCTION The results of our consultation regarding the stability of a proposed cut are presented in this letter. The cut involves the removal of material from the "nose" of a steep ridge, in order to form the right -of -way for a realigned railroad spur to be placed across the Giovanelli Property. . Our work was authorized verbally by Mr. Fehnel on July 19, 1976. We have previously performed several investigations for the Benaroya Company in the general site area, including an investigation for that portion of the realignment through the Giovanelli Property which crosses the low -lying swamp area adjacent to Southcenter Parkway. The results of this investigation were presented in our report dated June 28, 1976. In addition, Dames & Moore has gained extensive knowledge of the hillside area during investigations for the borrow area which lies immediately t� the south, and observations which were made during the operational life of this borrow area. The proposed cut will extend horizontally into the existing ridge a maximum distance on the order of 100 to 125 feet, with a maximum cut height of roughly 135 feet. The cut will intersect the ridge for a distance of approximately 150 feet along the railroad alignment. EXHINC.' •. DAPiES 8 M® ®0E Jack A. Benaroya Company July 20, 1976 Page 2 SITE CONDITIONS Based on information in our files, we anticipate that the ridge is composed primarily of dense, glacial deposits ranging from an unsorted mixture of gravel, sand, and silt (glacial till) to sorted, stratified deposits of silt and sand. Generally, the silt soils are found in the lower portions of the hillside. These. glacial soils have generally been consolidated by the weight of overlying ice and consequently exhibit high strength. All of the soils are susceptible to erosion; the silts are also subject to surficial softening, particularly under the influence of surface runoff and ground water seepage. We anticipate that localized zones of groundwater may be encountered within the limits of the excavation, particularly at contacts between silt layers and overlying more coarse sandy layers. DISCUSSIQN AND RECOMMENDATIONS On the basis of our present knowledge of site conditions we anticipate that a limited cut across the "nose" of the ridge will remain stable at a slope _. steeper than the 1.75:1 ('horizontal to vertical) inclination which we have previously recommended for adjacent sites. This steeper inclination is primarily a result of the existing configuration of the ridge, the limited extent of the cut, and the distance which separates the top of the proposed cut from the freeway right -of -way. The ridge in question has apparently remained historically stable at its present steep inclination (approximately 1.4:1). We would anticipate that any failure which might occur in the intact preconsolidated soils to be limited to shallow sloughing which would not involve large volumes of material and would not endanger freeway right -of -way. For planning purposes, we recommend that the cut be designed with a slope of 1.25:1, with 10 -foot wide,reverse- sloped benches incorporated into the slope . configuration at intervals of no more than 40 feet in elevation change. This will result in an overall slope which will approximate the existing natural slope. To confirm the soil conditions which exist within the cut area, we -recommend that the initial earthwork consist of bulldozing a trench or strip down the ridge. This.cut must extend through the surface soils and expose the underlying deposits. This trench should be carefully examined by a soils engineer or geologist from our office to determine the type and sequence of'the exposed soils. A further inspection should be made prior to shaping the •tnal configuration of the slope, to confirm the stratification which exists at the cut face. The information gained from these inspections will be used to make adjustments,-as necessary, in slope inclination, to check the need for special drainage provisions, and to provide for any appropriate changes in the location of benches. DAWIES 8 !MOORE • Jack A. Benaroya Company July 20, 1976 Page 3 Because of the erodibility of slope materials, it will be important to provide means of controlling seepage and runoff from the slope face. Seepage from the slope will be intercepted by the benches and carried to the northern edge of the cut. From this point the water should be carried downslope in closed pipes or protective channels such as half sections of corrugated metal pipe. We understand the water will be routed into a ditch along the railroad alignment for final disposal in a manhole located adjacent to Southcenter Parkway. To further protect against erosion from surface runoff and seepage, we recommend that slopes and benches be seeded or planted to provide an adequate ground cover. This could be accomplished in two phases. The first phase would consist of seeding with appropriate mixed grasses immediately after excavation to provide protection during the first winter. This seeding can probably best be accomplished by hydroseeding or with the use of jute mats. The second phase would consist of long -term protection gained by the planting of deep- rooted vegetation such as red alder or scotch broom. We believe the foregoing information will serve your present needs. We look forward to working with you during the grading of the cut slope. Please contact us if you have any questions concerning this report, or if we can be of further assistance. Yours very truly, DAMES & MOORE By A4r6 Jack K. Tuttle. Partner JKT:WJG:ss 4 copies submitted 4368 - 023 -05