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09.23.1968-Dames & Moore-Mead Geo Eval.pdfREPORT OF GEOLOGIC EVALUATION ME, ADOWDALE AREA EDMONDS , WASHINGTON for the CITY OF EDMONDS �0 N5 1 I Nliz i_N L_: 'R'' IN I4 E APF i`-1.: >_, I ...-, V,,.;i .:. 1'..,...;. ri 1. L. IA 1800 WESTLAKE AVENUE NORTH - SEATTL_L_, WASHINGTON 98109 (206) 284-8160 • TELEX: 3-2415 PARTNERS JOSLPH LAAv10NT. JR. - DONALD E, NELSON ASSOCIATE: RODE€? A. L.OVNlE CHIEF ENGINEER: ALLY.AN DER A. HIG HTON September 23, 1968 City of Edmonds City Hall Edmonds, Washington 98020 Attention: Mr. Leif Larsen Gentlemen: We submit herewith eight copies of our "Report of Geologic Evaluation, Meadowdale Area, Edmonds, Washington," for the City of Edmonds. The scope of our work was derived in discussions between Mr. Leif Larsen, Mr. James Reid of Reid, Middleton & Associates, and the writer. We were first requested to consider an overall investigation of the area in order to specifically evaluate the feasibility of sewer construction and the requirements for procedures to enhance this feasibility. It was our suggestion, however, to approach the problem first from a geologic standpoint which would not involve complex investigative methods or the expenditure of large amounts of money. Your acceptance of this idea is grafitying, and we trust that this report will. serve your needs. More detailed investigation is recom- mended herein, however, as being essential to the ultimate development of this area to its highest and best use. We appreciate the opportunity to work with you on this problem. Please call upon us if we may answer questions or be of additional service. Yours very truly, DAMES & MOOR.E By gel�, DEN-WSB:jm Donald E. Nelson cc: Reid, Middleton & Associates (2) 324 Main Street Edmonds, Washington 98020 Attention: Mr. James Reid REPORT OF GEOLOGIC EVALUATION MEADOWDALE AREA EDMONDS, WASHINGTON for the CITY OF EDMONDS INTRODUCTION GENERAL We present in this report the results of our geologic evaluation of the Meadowdale area in Edmonds, Washington, for the City of Edmonds. This area is located in the extreme northwest corner of the city and was annexed to the city by Ordinance No. 1.004 dated July 16, 1963° The general topography of the area consists of a rolling upland surface and a steep to moderately steep broken slope down to the level of Puget Sound to the west. Several steep -sided gullies extend to the Sound westward across the area. Drainage is generally well developed. The area use presently is low—density residential with higher density areas to the south and cast. The mainline trackage of the Great Northern Railway parallels the western boundary of the area along the narrow beach, SCOPE The purpose of our evaluation is to investigate the overall stability of the area from a geologic standpoint and to form a preliminary opinion regarding the feasibility of installing a sanitary sewer system. Specifically, the scope of our work includes a general geologic reconnaissance of the area and a review of available information in regard to stability problems. Our work is intended to be largely preliminary in character; no detailed subsurface information by deep -drilling methods has been obtained, Our report includes the following information; -2- 1) 2.- 1) A discussion of the geological history of the general area. 2) A generalized description of subsurface soil and groundwater conditions. 3) An evaluation of the general geologic features of the area, with particular regard to areas of recent instability. 4) A discussion of probable reasons for the instability. 5). Comments relative to the possible stabilization of these areas. 6) A conclusion relating to the feasibility of sewer construction. 7) A recommendation for further study. It is intended this report be used as a guide to planning. More detailed conclusions and recommendations will require further study involving explora- tion. It is hoped, however, that this report will. satisfy the present need for information relative to the approximate extent of existing and likely future problems. PHYSIOGRAPHY AND GEOLOGY The general topography of the area can be considered in terms of ;four separate terrain elements. These. are: (1) the rolling upland surface; (2) the moderately steep to steep escarpment just below the upland area; (3) the wide irregular slope between the base of the escarpment. and Puget :Sound; and (4) the steep -sided ravines which are incised in the upland surface. The undeveloped portion of the area, approximately one-half the total area, is moderately to heavily wooded with both coniferous and deciduous trees and thick underbrush. The soils in this general area are almost entirely of glacial origin and were deposited during complex cycles of glacial advance and retreat. The Puget Sound lowland is known to have been invaded by continental ice B during at least three different periods. The origin of the continental ice was the mountain ranges of western Canada and Vancouver island. The major portion of the soils exposed in this vicinity are related to the last advance of ice. This occurred during recent geologic timers, less than 15,000 years ago, when a finger of continental ice (referred to as the Puget Glacial Lobe) advanced into the Puget Sound lowland. In its early stages of advance into the Puget. Sound lowland, the glacier acted as an ice dam in the Admiralty Inlet area, resulting in a lake -like environment in most of the Puget lowland, The lake was fed by both meltwater from the advancing ice from the glacier and from streams flowing into the area from the surrounding highlands. During this period of time, the silts and clays which underlie the area of investigation were deposited„ As the ice front advanced farther south into the lowland, the outwash deposits of sand and sandy gravel which overlie the silt and clay were deposited. During the period of time when the glacier was advancing across the area, the glacial till was deposited immediately in front of the advancing ice sheet and subsequently overridden by the ice. The glacier is thought to have occupied the area for approximately 2,000 year's, and during this time reached a maximum thickness of some 5,000 feet. After the ice receded from. the area for the last time, approximately 13,000 years ago, it. Left a rolling surface° Meltwater from the retreating ice front flowed from the rolling upland surface into the Puget Sound basin creating the large gullies or gulches which trend generally east -west through the area of investigation. Subsequent to the disappearance of the ice, the present erosion cycle began. This primarily consists of additional erosion by water flowing from the upland surface to Puget Sound and modification. of the coastline by wave erosion. _4 -- The 4a, The escarpment which forms the boundary between the upland surface and the moderately steep irregular slope down to the level of Puget Sound is the result of an ancient landslide �Jhich involved primarily the movement of large blocks of earth. SOIL CONDITIONS The rolling upland surface is generally underlain by a thin to moderately thick formation of glacial. till. The glacial till is the. youngest deposit in the area and is an unsorted mixture of silt, sand, and graver The material was deposited immediately in front of the advancing ice and was subsequently overridden by the ice. This process consolidated the material and resulted in a very compact deposit. This material is moderately permeable when weathered and essentially impermeable in an unweathered form; only the upper few feet are significantly weathered. Physically, the mixture is similar in appearance to a weak, light --gray concrete and is referred to locally as "hardpan." This material is very resistant to erosion and forms a resistant capping over the more easily erodible older soils. A typical exposure of the glacial till occurs near the intersection of North Meadowdale Road and 65th Avenue West. Underlying the glacial till is a thick deposit of sand and sandy gravel. This advance outwash material was deposited by meltwater flowing from the advancing ice front and, like the overlying glacial till, was consolidated by a great weight of ice. The formation is sufficiently permeable to allow water to percolate into the ground quite readily, and surface drainage is characteristically good where the outwash formation is exposed. The outwash formation comprises the moderately west sloping upland surface between North Meadowdale Road and Meadowdale Beach Road. In addition, the formation comprises the upper one-third to one-half of the escarpment and the major portion of the steep -sided gully walls. Clear exposures of this deposit can be seen in the vicinity of the area under development immediately west of the intersection of 164th Street S. W. and .72nd Avenue West. Underlying the outwash formation is a deposit of finely laminated to massive gray and blue -gray salt and clay. This deposit of silt and clay comprises the lower two-thirds to one-half of the escarpment. Its lower limit is not known, but it probably extends to or below the Level of Paget Sound. This material was deposited in a lake -like environment some distance in front of the advancing ice and, like the overlying materials, has been consolidated by the weight of the glacial, ice. This material is firm and is somewhat resistant to erosion. It is essentially impermeable and, in areas where this formation is exposed, surface water tends to run off rather than percolate into the ground. Because of the essentially impermeable character of the clay and silt and the high permeability of the overlying formation. of sand and gravel, a zone of seepage or springs generally marksthe contact between the two formations. During periods of dry weather, the contact can be identified on the North Meadowdale Road by a wet area in the roadway at a point approxi- mately midway between 68th Avenue West and 75th Place West. The majority of the water wells in the upland area producing moderate quantities of water are probably terminated near the base of this sand and gravel formation above the clay. In one area, till -like material was found exposed below the silt. and clay formation but appears to be discontinuous. The extreme northern portion of the area, in general that. area north of 158th Avenue West, is an ancient tilted fault block which probably predates the massive slide which left the still -visible, escarpment which crosses the entire area. The fault block underwent enough downward displace- ment so that the contact between the outwash formation and the underlying clay was not exposed in the northern portion by the later sliding; this contact becomes clearly defined toward the south. Indications are that a vertical displacement of at least 80 feet occurred when this fault block broke off from the main land mass at a time probably immediately following glacial retreat. RECENT HISTORY OF AREA Several sources were examined in an attempt to obtain dates of known earth movement and the resulting damage. These sources included the Great Northexn Railway Company, Snohomish County Engineering Division, and many long-time residents of the area. It was found that available informa- tion for the period prior to 1940 is sparse. The Great Northern Railroad has records of earth movement on or adjacent to their right -of --way dating back. to 1945. The records indicate that no major damage has been incurred by the railroad as a result of these movements. The damage has primarily been in the form of debris which has moved down to and over the tracks. The railroad company has installed a bulkhead adjacent to and on the uphill side of the tracks along the major portion of the rail line through the area. In addition., the railroad has installed slide -warning devices along these sections. We understand that in 1947, an area immediately south of Haines Wharf experienced movement which caused a moderate amount of damage to homes 7® and roads in the area. it is our understanding that the affected area was approximately 800 feet in a north -south direction and extended from above the railroad tracks to a point immediately east of 75th Place West. An examination of the existing roadway indicates that a small amount of movement has taken place since 1947° A Washington State Department of Highway's geologist, Mr. Arthur Ritchie, studied the area after this period of move- ment and recommended the construction of a perimeter ditch in the undisturbed clay layer immediately below the clay -sand contact.. This ditch was to serve as an interceptor and to prevent the wager emerging near the bottom of the sand formation from saturating the finer grained soils downhill. It is our understanding that a problem developed in obtaining the required easements, and the project was abandoned in its early stage with only a few hundred feet of ditch completed, It appears since that. time that little or no maintenance of the ditch has been accomplished. We understand the area immediately east of the 1947 movement and extending to the base of the escarpment was regraded at one time with the intent of developing a mobile park but because of zoning restrictions was not developed. The eastern portion of this area is now very poorly drained with ponded water. In late 1955 and early 1956, movement occurred north in the inter- section of North Meadowdale road and 75th Place West. The movement damaged many of the homes in the area and resulted in the destruction of at least two homes. We understand this movement occurred after several days of heavy rains combined with a 10 --inch snowfall, As in the case following the slide in 1947, another program to install the interceptor ditch north of the North, Meadowdale Road was initiated, It is our understanding that easements were .• g obtained; but construction difficulties halted the work in its early stage with., again, only a small portion of the work completed. It is our understanding that since the movements in 1955-1956, only minor movements have occurred in the area and that most of these problems involved relatively minor sloughing of the steep escarpment. The ancient movements which have occurred in the area appear to be currently stable. These very large-scale massive landslides were far greater in extent than the more recent movements and have probably been inactive for a long period of time. The Great Northern Railroad Company has placed a protecting riprap wall along the Puget. Sound side of their trackage and have thus eliminated damaging erosion by wave action, This has added to the general stability of the area, and the now stable shoreline probably decreases substantially the risk of reactivation of the major older landslides.'', The recent more serious slides appear to have occurred almost entirely within the formation of silt: and clay. It is probable that at least a portion of these soils had been disturbed by earlier movements. GENERATE CONCLUSIONS It is our opinion that it is not only feasible to install sanitary sewers in the area, but that such an installation would be of benefit, Groundwater has been a major factor in the instability of the area; reduction of the volume of water to the area will decrease risks of future damaging earth movements. It should be recognized, however, that at least in certain areas, the maintenance cost of the system would probably be high; unless substantial other work to improve stability is accomplished, the area will remain subject to occasional small landslides and reactivation of older move- ments. Sanitary sewers would reduce the water available to the clay soils; the installation of a complete storm sewer system, local surface grading, ditching, and the possible use of horizontal subsurface drains would substantially further reduce groundwater problems resulting in stability improvement, It is our opinion that such procedures would reduce the risk of damaging landslide activity to a satisfactory level, except at certain critical locations which we believe would be revealed by further investiga- tion. The risk of future landslides can never be eliminated completely, however, except by procedures which would not appear to be warranted by current property values. If these risks were unacceptable relative to sewer construction, then they would certainly seem unacceptable from the standpoint of residential construction. Therefore, if the city considers the area safe for maintenance of dwellings, it would seem inconsistent not to permit sewer construction - particularly as sewers can be of benefit. CALYSES OF INSTABILITY The recent slides have generally involved a downhill movement or slumping of blocks of clay as a result of gravity and groundwater seepage forces. Groundwater will also tend to increase the weight of any mass tending to slide and will decrease the ability of that mass to resist sliding by softening the soil along seepage zones and impending failure surfaces. A small-scale slump low on the hillside which might otherwise result only in small local damage will, tend to relieve restraint from soils uphill; the uphill soils are thus placed in, tension and will yield laterally or even begin sliding as well. Tension cracks which open up at the ground surface may tend to collect water, further aggravating the situation. A progressive series of such movements results in the kind of irregularly terraced surface characteristic of much of the subject area. -1 -0 - Defining the underlying "cause" of the instability of the area is difficult. At the risk of over -s tion, we suggest that the basic problem is the steepness of the area; these same soils would be stable on. a flatter overall slope. Each slide movement tends to create such a flatter slope and illustrates nature's way of correcting the instability. Other factors are involved, however, and groundwater appears to be a major contribution to instability, Removal of all ground and surface water would probably eliminate all risk of sliding, except perhaps during an extreme earthquake catastrophe or a storm which could result in extensive toe erosion. While it is not feasible to eliminate either all groundwater or all risk of future problems, it would be, in our opinion, feasible to control ground and surface water conditions to a far greater extent then has thus far been attempted and to therefore reduce the. risk of serious problems to a substantially lower level. If no such control work is accomplished, it would be our recommendation that new residential construction in much of the area be prohibited. WATER CONTROL The present sewage disposal is handled by septic tanks, and the elimination of these systems would reduce the amount of water presently allowed to percolate into the soil. Rased on a daily average consumption of 100 gallons of water per day per capita and total. discharge through the septic systems, the septic systems could be contributing as much as 20 percent of the total water percolating into the ground. This is based on the assumption of an average yearly rainfall of 30 inches and a runoff factor of 50 percent. The installation of a complete storm sewer system would significantly OW ff _11- further 11- further reduce the amount of water percolating into the soil. Tt is our understanding that the residential area located in the adjoining upland area does not have either sanitary or storm sewer systems, Because of the established drainage patterns and their topographic position to one another, the lower lying areas will receive at least a portion of the discharge from these systems either in the form of surface or groundwater, To further stabilize the Meadowdale area, therefore, control work is also required outside the limits of the benefiting locations. It is our understanding that in approximately 1944, the area started to obtain their domestic water service from the Alderwood Water District. Prior to this time, the major portion of the area residents obtained their water from small water systems supplied by the springs emerg- ing near the base of the sand and gravel formation. We understand that since that time, at least a portion of these systems are no longer maintained and that much of this water is permitted access back into the ground. This problem should prove easily solvable. In addition, we believe that the installation of the perimeter interceptor ditch as earlier proposed is a very essential part of the program of stabilization. As open ditch might, however, prove inferior to a well- designed subsurface drain. We believe that this interceptor, in effect, could consist of a series of separate systems which could take advantage of the local terrain. Once the system is installed, a program of maintenance should be initiated to insure the proper functioning of the systems At the same time, the areas near the base of the escarpment which are poorly drained should be regraded or otherwise drained to avoid ponding of water. A study should be made to evaluate the feasibility of the installa- tion of a horizontal drain system to facilitate the removal of the water from -12 - the lower saturatedortion of the sand p an and gravel formation. Horizontal drains involve the drilling of near -horizontal holes into the slope and installing a slotted plastic casing. The slot size in the casing is determined by the grain sizes of the material into which the installation is to be made. The water thus collected would be directed into a storm system and out of the area. Much of the foregoing may encounter legal difficulties; property acquisition or easements may be required; financing of various features may prove to be complex. We advise, however, that such steps are essential not only to maintain property values but to maintain the security of the persons who occupy the area. FUTURE STUDIES This evaluation has been intended to be general in nature; detailed recommendations for stabilization procedures should be based on further study. The need for some deep drilling to obtain subsurface soil and groundwater information is clearly indicated. It would probably be inefficient to try to establish a complete control program based only on .surface observation. Sewer construction will be an important first step, however, and should not be delayed. Provision should be made for continuous `monitering of the functioning of all sewers to locate leaks or breaks. Existing ditches and drains should be well maintained,and the system expanded where this would obviously be of benefit. The more sophisticated and expensive elements of the control procedures such as deep interceptors and .horizontal drains should be delayed pending further study, however. Respectfully submitted, DAMES & MOORE y r yV September 23, 1968 Donald E. Nelson � w � w d � r/?e vv\ \\\\\\� /a II (��s�nu-• � , �'lll 1'ii�I�1ra II 1 , Isi k CY r ❑ Orb a I r� \r I I w� Lu r� I� q\VIII co LL w Ss tl,� Iii I� it I 2 0 � �a U a Lai a U) ...___._......._ z w h IIII u u � II om LU e� �' o ill I I,IN _ ©� \m I'II I � r a III I v�10 a � w � w d � r/?e vv\ \\\\\\� /a II (��s�nu-• � , �'lll 1'ii�I�1ra II 1 , Isi k CY r ❑ Orb a \\ w� Lu o co LL w o a w� Lu o co LL \ 2 0 � �a U a Lai a U) 0 z w u LU e� � I PARTNERS .JOSEPH LAMONT, JR. • DONALD E, NELSC)N ASSOCIATE: ROGER A. LOWE CHIEF ENGINEERALEXANDER A. F41GHTON October 1, 1968 City of Edmonds Edmonds, Washington 98020 Attention: Mr. Leif Larson Gentlemen: 11 Proposal Soils Investigation Meadowdale Area Edmonds, Washington, for the City of Edmonds INTRODUCTION We are pleased to present herein our proposal for a soils investigation of the Meadowdale area in the northwest portion of Edmonds. This area is that which exhibits a record of instability over relatively recent years and which was the subject of a geologic evaluation recently accomplished by our firm. The results of that evaluation were presented in a report dated September 23, 1968. The purpose of our geologic evaluation was to investigate the overall stability of the area from a geologic standpoint and to form an opinion regarding the feasibility of installing a sanitary sewer system. In that report, we concluded that sanitary sewers would be not only feasible but would be an important step in stabilizing this area, presuming; that general stabilization is to be a long-range objective of the city. In that report, we also recommended that additional studies of a more detailed nature be accomplished to permit evaluation of other procedures which would benefit the area. It was pointed out, however, that because of the topographic and groundwater problems, the risk of future problems of some magnitude could not be completely eliminated. The area which would be the subject of our soils investigation is that which extends from the Meadowdale Country CLub;.access road south to approximately 165th Street S. W., and from the shoreline east to about 72nd Avenue West, Only relatively minor indications of stability problems exist outside this area; such problems could probably be handled satisfactorily on a property -by -property basis and meed not, in our opinion, be of overall concern to the city at the present time. El r?i'. 0%, L". 'GALS LAKI �_I'I'Y i ---------------------- 1800 WESTLAKE AVENUE NORTH SEATTLE;WASHINGTON 98109 (206) --B4-8160 TELEX: PARTNERS .JOSEPH LAMONT, JR. • DONALD E, NELSC)N ASSOCIATE: ROGER A. LOWE CHIEF ENGINEERALEXANDER A. F41GHTON October 1, 1968 City of Edmonds Edmonds, Washington 98020 Attention: Mr. Leif Larson Gentlemen: 11 Proposal Soils Investigation Meadowdale Area Edmonds, Washington, for the City of Edmonds INTRODUCTION We are pleased to present herein our proposal for a soils investigation of the Meadowdale area in the northwest portion of Edmonds. This area is that which exhibits a record of instability over relatively recent years and which was the subject of a geologic evaluation recently accomplished by our firm. The results of that evaluation were presented in a report dated September 23, 1968. The purpose of our geologic evaluation was to investigate the overall stability of the area from a geologic standpoint and to form an opinion regarding the feasibility of installing a sanitary sewer system. In that report, we concluded that sanitary sewers would be not only feasible but would be an important step in stabilizing this area, presuming; that general stabilization is to be a long-range objective of the city. In that report, we also recommended that additional studies of a more detailed nature be accomplished to permit evaluation of other procedures which would benefit the area. It was pointed out, however, that because of the topographic and groundwater problems, the risk of future problems of some magnitude could not be completely eliminated. The area which would be the subject of our soils investigation is that which extends from the Meadowdale Country CLub;.access road south to approximately 165th Street S. W., and from the shoreline east to about 72nd Avenue West, Only relatively minor indications of stability problems exist outside this area; such problems could probably be handled satisfactorily on a property -by -property basis and meed not, in our opinion, be of overall concern to the city at the present time. El GAMES e_ rA00RF=_ City of Edmonds October 1, 1968 Page -2- SCOPE The purpose of the soils investigation would be to develop detailed recommendations for stability improvement measures, principal among which would be surface and subsurface drainage. Specifically, our work would include the following: 1) Nine exploratory borings to depths averaging about 75 feet. 2) Laboratory tests on undisturbed samples obtained from the borings. 3) Development of detailed information on groundwater by piezometer installation. 4) Detailed recommendations for horizontal drains projecting' into the hillside to tap major sources of subsurface seepage. 5) Recommendations for subsurface interceptor drains and/or ditches which would serve the purpose of intercepting sources of groundwater located at shallow depth. 6) Recommendations for local surface drainage to minimize the amount of surface water which can gain access to critical areas. 7) Mathematical evaluation of the existing stability of the area and an estimate of stability improvement as a result of improved drainage. 8) A discussion of additional procedures beyond ground and surface water control which might be considered to further improve stability. 9) As a separate item, the possible installation of recorders in one or more key borings to measure earth deformations. METHODS The nine borings would be drilled using truck -mounted, power - operated drilling equipment under the continuous supervision of an engineering geologist from our staff. Three of the borings would be located on higher ground above the critical areas principally to provide information relative to the need for horizontal drains or interceptors in the upper bluff area. Three borings would be drilled within the critical areas subject to recent earth movement to evaluate soil 7 W City of Edmonds October 1, 1968 Page -3- stratification and groundwater patterns in these areas. Two borings would be located at intermediate locations near the toe of the upper bluff. The remaining boring would be drilled in the north portion of the area to evaluate conditions within the tilted fault block discussed in our recent report. Undisturbed samples would be obtained from the borings at frequent intervals using a specially designed Dames & Moore soil sampler. The samples would be tested in our Seattle laboratory to evaluate soil shearing strength, field moisture and density, and perhaps other pertinent parameters as well. Several piezometers would be installed to evaluate groundwater conditions at various levels in key borings. These devices would be permanent and would permit later observation of changes in groundwater conditions. Not each boring would be tested in this manner because of the relatively high cost of this procedure. An Earth Deformation Recorder is recommended for one or more of the three borings located in obvious recent slide areas to more specifically examine any tendency toward current movements and to permit mapping of future movements. To provide a permanent means to record movements, a slotted casing would be installed in the borings which would permit measurement of changes in the alignment of the casing using an electronic recorder. This procedure would locate the depth and magnitude of earth movements which are occurring within the soil mass penetrated by the casing. The casing would be left in the ground as a permanent feature, and capped, to permit periodic measurements of deformations in the ground over a long period of time. Because this information is not at this time considered vital to the development of the basic recommendations which are the objective of this study, this item is not presented herein as an integral part of the proposal. In the fee schedule which follows, we detail this as a separate item which can, if desired, be added to the basic scope of our work. The principal.advantage of establishing recorders would be to better understand the mechanism of movement and to therefore more confidently evaluate the general effect which the drainage improvement will have on the area. It is anticipated, however, that our basic recom- mendations would not be significantly influenced by the results of the recorder installation. The results of our field and laboratory work would be analyzed to develop our recommendations. To evaluate stability, we would make use of a computer program available for this type of situation wherein the soil characteristics, the geometry of the area, groundwater conditions, and other parameters would be analyzed in a number of ways to investigate City of Edmonds October 1, 1968 Page -4- mathematical 4- mathematical interrelationships. The end result would be a factor of safety (a measure of risk) against future sliding. By varying the parameters relative to groundwater, it will be possible to estimate the effect of drainage improvement on, the area and therefore the reduction, of risk of future problems (increase in factor of safety). The results of our studies, including a summary of all field and laboratory data would be submitted in a comprehensive written report. This report would discuss our findings in some detail and would present specific recommendations 'for the number and locations of horizontal drains, together with a cost estimate for installation of such drains; the locations of ditches required to handle surface water where it tends to pond in critical areas; and recommendations for localized improvements, where necessary, on individual properties. A complete design and costing of these features would not be included as part of our work. Our report would include a location plan of the borings and a graphical log of each boring. Earth deformation data, if obtained, would also be presented graphically. SCHEDULE It would be possible to begin our work within approximately three weeks following your authorization to proceed. The drilling would require several additional weeks to complete, and the total study would require about three months from the date of your authorization. Actually, because of seasonal groundwater variations, it would be desirable to accomplish the principal portion of our work during the most critical time of the year, perhaps in late winter following the period of most severe winter rains. This would permit observation of conditions during that period which is of maximum concern to the objective of this study. On this basis, if authorization were to be given this fall, we would suggest delaying the field work for a brief period so that drilling would be accomplished in the period roughly between mid-January and mid-March. The results of our study would therefore be available in April or May, in time for summer construction of at least those features which can be accomplished without those delays which may result from property and easement complications. FEE We propose to base our fee on our standard Schedule of Charges, a copy of which is attached. This will provide a flexible method for fee determination consistent with the relatively uncertain requirements in the extent of the field work. The boring depths, for instance, cannot be determinelprecisely at this time, and the required depths of the borings U'S City of Edmonds October 1, 1968 Page -5- would depend on the conditions actually encountered. Based on our standard schedule, we estimate that our fee would be approximately $13,000. This, however, would not include the cost of installing earth deformation recorders at one or more of the critical locations of recent sliding. Each installation of this type would result in a fee increase of about $1,500, with a fee of about $200 for each set of subsequent readings, including interpretation. We anticipate that approximately three sets of readings would be desirable over each winter season following completion of the installation, or more frequently if serious movement should develop at such a location. Piezometer readings would also be desirable following completion of our basic study. Occasional billings for these readings, and perhaps other consultation as well, should be anticipated in addition to the basic amount. SUMMARY The pfoposed soils investigation would be generally supplementary to the geologic evaluation already accomplished. It would be possible to proceed with much of the work required to improve drainage for this area without accomplishing this soils investigation. Recent slides and the results of the geologic evaluation indicate that the area is only marginally stable, representing a fairly high risk of future problems. On this basis, almost any procedure to eliminate water from the area would undoubtedly result in stability improvement, even though such procedures are not designed with the benefit of comprehensive subsurface data. On the basis of the foregoing, it would be possible to delay the soils.investigation proposed herein and to complete certain elements of drainage for the area (such as sanitary and storm sewers, shallow surface ditching, and tapping of major springs) without delay. It might be found that such procedures would be of sufficient advantage to satisfactorily improve the area without further work. We doubt that this would be the case, but in view of the substantial cost involved in going beyond this, the city might consider it appropriate to try these measures before proceeding further. The "preliminary" work would not be wasted. The principal omission from this work would be interceptor and horizontal drains which could be added to the system at any time. We also suggest that the city consider organizing a meeting of the affected property owners to discuss the various aspects of this work and the risks which they are willing to accept in maintaining their own properties. In the past, only certain property owners have been affected by movements; all property owners within the subject area sustain some Brisk of future problems, however. Some face less risk than others. Since City of Edmonds October 1, 1968 Page -6- many of the properties within the area will be involved both in the investigative studies and in the corrective work, it might be wise to inform the property owners of the present estimate of the situation. if we can be of any help in this regard, please contact us. DEN:jm Attachment 3 Copies Submitted Yours very truly, DAMES & MOORE By Donald E. Nelson I 1 OLV STREeT LEVEI, " N klz�< IOLUe