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HomeMy WebLinkAboutStormwater Reports - COM Engineering / Geo-Tech Reports - 4/26/1996 MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Wwhing "584 DATE: April 26, 1996 INTER-DEPARTMENTAL COMMUNICATIONS TO: Mike Byrne, General Services Director FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. SUB.r: Stormwater/GeoTech Report Reviews NAME: Belfair Post Office Mike, Imrich Halvy of the Halvy Corporation delivered a set of Stormwater Plans and a copy of a Geotechnical Engineering Study for the proposed Post Office located in Belfair Washington. The Stormwater Site Plan appears acceptable, but supporting calculations have not been submitted. I expect to be in contact with Joe Maw, the stormwater engineer for this project and will request a copy of his calculations. I have informed Mr. Maw and Mr. Halvy that an Operation and Maintenance Covenant will be required to be created, recorded, and a copy of the recorded instrument delivered to Public Works before the completed facilities are allowed to be finalized. The Geotechnical Engineering Study(attached)was prepared to investigate soil properties and concerns regarding the construction of retaining walls along the back and sides of the proposed post office. The geotechnical report reveals substantial quantities of groundwater flow, creating concerns regarding drainage from behind the proposed retaining walls. The engineer recommends specific soil gradation requirements for the backfill material, which should be strictly adhered to. Public Works has not received any soil gradation reports or lab analysis of the native materials in the"ACE" gravel pit, but personal observations of the site lead me to believe that the material does not conform to the specification recommended in the geologist's report. Public Works raises no objections to the proposal, but supports the recommendations made by the geotechnical engineering consultant, and feels the recommendations contained in the report should be incorporated into the project as permit conditions. n A. Tahja encl: Geotechr&al Engineering Study AT:at File: H:\WP\STRMWTR\REVIEWS\BLFR-PO.IDC on stormwater requirements; he can be reached at (360) 427-9670 extension 461. This review is typical for commercial development in Mason County and are part of the review for this type of building permit . If you have additional questions, please contact me at Community Development at (360) 427-9670 ext . 365 . Sincerely, Allan Borden Senior Planner J. KEITH CROSS, P.E. Geotechnical Engineering Consultant (206) 820-0951 9210 NE 134th Street, Kirkland,Washington 98034-1876 March 19, 1996 Imrich Halvy Halvy Corporation 14249-R Ambaum Boulevard SW Burien, Washington 98166 Report for Preliminary Subsurface Exploration and Geotechnical Engineering Studies, Retaining Wall Design Considerations, Proposed Post Office, Belfair, Washington Project No. 3063-001 This report summarizes the results of our preliminary subsurface exploration and geotechnical engineering studies at the above referenced site. The scope of our services was outlined in our proposal to you dated February 22, 1996. As outlined in our proposal, our services to this project are limited to a general review of the site ground conditions, the provision of general site development recommendations, and specific recommendations and design considerations for the proposed retaining walls. Verbal Authorization to proceed with our study was received from Imrich Halvy on February 27, 1996, and followed by written authorization received on February 28, 1996. The fieldwork portion of our study was undertaken and completed on February 27, 1996. The site is located on a frontage road just to the north and east of the northeast corner of State Route 3 and Cokelet Lane in Belfair, Washington, and directly east of the existing Kitsap Bank and McDonald's properties. The proposed post office building is to be located in the east-central portion of the property with paved parking and driveway areas provided on the north, south and west sides of the building. We understand that the proposed building is to be cut into the existing slope and have a finished floor elevation between about 188 and 192 feet. The required cut slopes are to be supported by retaining walls which, depending upon final design, will have maximum heights ranging from six to twelve feet. Based on the parking lot elevations shown on the site plan provided, moderate to substantial re-grading will be required to complete development as desired. p CEYZ -Z 3- �,�soN c,%,R00 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 2 Subsurface Exploration Program The subsurface conditions of the site were evaluated by excavating and logging soils exposed in a series of eight exploration pits across the general development area; six along the retaining wall line and two at the western edge of the proposed building. The exploration pit locations are shown on the attached Site Plan, Figure 1 of this report. Additionally, a reconnaissance of the site and adjacent areas and a review of information in our files was completed. The exploration pits were excavated using a rubber-tired backhoe to a maximum depth of 12 feet. Soils exposed in the exploration pits were examined and logged by the engineering geologist. The exposed soils were examined and the difficulty of excavation evaluated as an indication of the relative soil density. The soil strata encountered are shown on the attached Exploration Pit Logs, Figures 2 through 4. The soil strata shown on the logs were observed at spot locations across the site. Actual subsoil conditions and thicknesses may vary between pits or as exposed in excavations. Elevations referenced in this report are based on topography shown on the site plan provided by Imrich Halvy. The drawing is untitled and identified only as "Version 1.0" with an issue date of April 15, 1994, and a plotted date of November 15, 1995. It should be noted that this drawing has an indicated scale of 1"=20'-0", however, the drawing was received in a reduced condition and appears to have an actual scale closer to one inch equals between 32 and 37 feet. This drawing was used as a base for the attached Figure 1. Site and Subsurface Conditions This site and the adjacent properties to the north were cleared and grubbed prior to our site work. Overall the site appears to be minimally modified topographically due to this previous site work. Based on the soils exposed in our exploration pits there appears to have been little filling associated with the previous site clearing and grubbing operations. In general it appears that the property sloped gently to moderately downward to the west prior to the grading. From the street on the west side of the property to the property high point near the northeast corner there is a maximum topographic rise of about 30 feet. Along the line of the retaining wall elevations range from about 190 to 204 feet. J. KEITH CROSS, P.E. 9210 NE 134'Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 3 Soil Conservation Service maps of the area indicate that the site is underlain by Alderwood gravelly sandy loam and Everett gravelly loamy sand. Alderwood soils are derived from a glacial till parent material. The Everett soils are developed from outwash parent materials and generally occur in outwash channels between ridges of Alderwood soils. Alderwood-type soils (glacial till) appear to be exposed in road and development slope cuts to the north and south of the project site. Alluvial, Everett-type soils appear to underlie the site and adjacent areas. Native soils exposed in the exploration pits consist primarily of gravelly sand to sand with a varying amount of gravel and a minor amount of silt. When first encountered the native soils are loose. They rapidly become medium dense and further increase in density with increasing depth. Soil coloration varies from brown to tan to gray-brown in the upper sections, becoming grayer with depth. Ground water flows were encountered in six of the eight explorations. Only in pits 4 and 5 was no ground water observed. Depths to ground water and flow descriptions are shown on the exploration pit logs. It should be anticipated that the observed ground water levels may vary up or down seasonally, and during periods of increased or prolonged rainfall, or dry weather. CONCLUSIONS AND RECOMMENDATIONS Based on the results of our subsurface exploration program, review of existing site conditions, and our understanding of the proposed development, it is our opinion that the site is generally suitable for the type of construction proposed. Site dewatering and control of ground water flows through the site may present a major geotechnical concern during site preparation and grading. Long-termed control of the ground water will be required for maintenance of the retaining wall design loads and satisfactory performance of the wall. Additional geotechnical concerns is the use of the on-site saturated soils for structural fill. Subsequent recommendations address these concerns and should be considered in site planning and development. From a geotechnical perspective, the ground water conditions in the north parking lot area appear to be a significant challenge to development of this site. We would make several suggestions related to ways to deal with this condition. First, would be to raise the grade of the parking lot north of the building to minimize the required excavation into the water bearing sands and J. KEITH CROSS, P.E. 9210 NE 134'Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 4 gravels. It would appear that this might require moving the entrance to the building away from the north side to the northerly portion of the west side in order to maximize the parking lot grade. Secondly, a staged excavation is suggested for the north parking lot area to draw down the water table prior to final excavation for the retaining wall construction. It is our opinion that this could be done by excavating a broad Swale centered in the north parking lot. As soon as equipment could be mobilized, 3 horizontal to 1 vertical (3H to 11,/) maximum slopes should be excavated from the north and east property lines. The base of this slope should extend several feet below parking lot grade. The soils excavated from this area are probably initially too wet to compact. However, if they are stockpiled, it is likely that they will drain sufficiently in a couple of weeks to months to be used as a source of material for structural fill. Observation of this area should be made by an experienced geotechnical engineer to evaluate the dewatering effort for construction sequencing of the retaining wall cuts. It will be desirable to place a permanent drain in the base of the cut to minimize the potential for the ground water to rise beneath the parking lot and create subgrade support problems. Observation of ground water conditions on adjacent properties to the east should be made to assess if adverse conditions have developed from this dewatering effort. Recommendations Site Preparation and Grading If site grading and preparation are undertaken during the normally drier portions of the year it is anticipated that storm water will influence earthwork operations to only a minor degree. However, in that we have no evidence as to the dry weather elevation of the ground water, we recommend that the contractor be prepared to deal with potentially moderate to heavy ground water flows in cut slopes and excavations. If site work is undertaken during wet weather, the near surface sands and siltier soils may become over-saturated and temporarily unworkable. If the site work is undertaken during wet weather the contractor should be fully prepared to deal with soil and water problems normally encountered in these materials during wet weather work including the filtering of runoff, as needed to prevent siltation. Dealing with ground water issues and wet weather earthwork may cause delays in construction sequencing, and/or may involve additional costs to implement non-typical dewatering measures and/or import of all weather fill materials. J. KEITH CROSS, P.E. 9210 NE 134'Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 5 At present the site is generally free of debris and vegetation and no additional stripping is anticipated to be required prior to the placing of fill. It is recommended that prior to the placement of any fill, the exposed subgrade should be proof rolled and compacted using a vibratory roller developing a dynamic rating of at least 25,000 pounds. Compaction of the stripped subgrade should be continued until field density tests show that a minimum compaction of 95% of the maximum dry density, as determined by ASTM method D-1557, has been achieved in all building and pavement areas. Any soft or weaving areas disclosed during proof rolling should be excavated and replaced with compacted structural fill. As part of the site preparation the exploration pit locations should be re-excavated and the backfill compacted as outlined below. Areas which are to be filled to bring the building or pavement grades up to the desired elevation should be filled with compacted granular material free from roots, trash or other deleterious materials. It is anticipated that fill will be obtained from the on site cuts. It is anticipated that these soils will be satisfactory for use during dry weather or when not overly wet with ground water. During wet weather or if overly wet with ground water, the site soils may not be suitable for use as fill. These soils are sufficiently fine grained, such that with the addition of small quantities of water they may become overly saturated and are difficult or impossible to compact to the desired density. If the excavated soils are stockpiled and allowed to drain, they may become compactable. We recommend that materials used as structural fill (fill placed under buildings or pavements) during periods of wet weather consist of free draining sand and gravel with not more than 5.0% fines, material passing a U.S. No. 200 sieve. All structural fill should be placed in layers approximately 8 inches in loose thickness, conditioned to a moisture content suitable for compaction, and compacted to 95% of the maximum dry density as determined by ASTM D-1557. Field density tests should be made at a frequency adequate to assure that the required compaction is achieved. It should be anticipated that ground water will be encountered in cuts and/or excavations reaching elevations similar to those reached in our exploration pits. We anticipate that prior to making the proposed retaining wall cuts, dewatering of the cut area will be required. Due to the potential ground water considerations and in-washing and caving observed in the exploration pits J. KEITH CROSS, P.E. 9210 NE 134'Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 6 we recommend that temporary cut slopes for the dewatering swale be planned at 3H to 1 V or flatter. At the time of construction, re-examination of the soil and ground water conditions exposed in the cuts by the geotechnical engineer may allow steeper temporary slopes. Depending upon the final site and building grades and overall design it is possible that ground water may create potential problems after construction. However, to preclude the possible build- up of ground water or storm runoff in the soils adjacent to the building, it is recommended that a four inch diameter perforated, rigid pipe be placed, perforations down, around the outside of the building foundation at the footing subgrade elevation. All of the drainage system should be bedded in pea gravel and designed to carry any accumulated water away from the structures to the storm drainage system. Roof drainage should not be connected to the footing drains. Foundation backfill in unpaved areas and all landscaping should be sloped away from the building for a distance of at least ten feet. Specific drainage recommendations for the retaining walls are provided in the following section. Concrete Cantilever Retaining and Subsurface Wall Foundations It is recommended that foundations for all retaining structures and subsurface walls be designed to bear on the medium dense to very dense insitu native soils or on properly placed and compacted structural fill. Foundations should have a minimum embedment of 18 inches below the lowest adjacent finished grade and have a minimum footing width of no less than 18 inches regardless of the resulting bearing pressure. Foundations should be designed in accordance with Uniform Building Code requirements, as modified by local codes and regulations, in effect at the time of construction for structures within seismic zone 3 as defined by the Uniform Building Code. It is recommended that all foundation excavations be inspected, prior to placing concrete, to verify that the bearing surface has been properly cleaned and prepared. Bearing surfaces should be firm and free of disturbed, sloughed or water-softened soil prior to concrete placement. We recommend that, following excavation of the foundation areas to the subgrade elevation, the J. KEITH CROSS, P.E. 9210 PEE 134"Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 7 exposed subgrade be recompacted to assure a firm bearing surface without pockets of loose material. For foundations designed and constructed as outlined above the following allowable soil bearing pressures may be used. Material Allowable Soil Bearing Pressure, psf Structural fill, placed and compacted as outlined above 2500 Medium dense to dense insitu native soil 2500 Very dense insitu native soil 4000 We estimate that total settlement for foundations designed and constructed as outlined above will be an inch or less, with differential settlement between similarly loaded foundations potentially approaching the total settlement. It is anticipated that most settlements will occur as the foundations are loaded. Failure to properly place structural fill or prepare the subgrade areas may increase settlement. Pressures on Subgrade Walls The parking lot retaining walls and foundation retaining walls are anticipated to retain the exterior slopes around the site. For non-fixed (cantilever) walls, an active soil condition may be assumed, and an equivalent fluid pressure of 35 pounds per cubic foot (pcf) should be used in design. Fixed walls should assume an at-rest soil condition, and an equivalent fluid pressure of 45 pounds per cubic foot (pcf) should be used in design. These values assume the presence of the soils encountered in our explorations or a structural fill as described above, and a freely drained condition behind the wall. The above values do not take into account hydrostatic pressures, sloping ground behind the wall or surcharges due to equipment loads. For a uniformly distributed load behind the wall, a corresponding uniformly distributed pressure equal to 30 or 50 percent of the surcharge should be added to the lateral soil pressure for a yielding or fixed wall conditions respectively. For the recommended 3H to 1V slope above the wall, an active earth pressure of 42 pcf and an at rest earth pressure of 55 pcf should be used in design in lieu of the above pressures for level ground. J. KEITH CROSS, P.E. 9210 NE 134" Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 8 Earthquake loadings are expected to increase the lateral pressures indicated above. Seed and Whitman discuss a procedure for determination of lateral loading following an approach suggested by Mononobe and Okabe. As input to the Mononobe-Okabe evaluation, I used a friction angle of 35 degrees for the backfill soils, a horizontal earthquake acceleration of 0.20g, a vertical earthquake acceleration of 0.10g, and a slope inclination of up to 3H to 1 V. Based on this input and some assumptions on wall friction, an earthquake loading lateral earth pressure of 50 pcf (equivalent fluid pressure), for level ground surface, and 70 pcf, for a 3H to 1V ground surface, was determined. This loading replaces the static "active" pressures indicated above, for the dynamic condition. The application of this loading depends on the wall type chosen. If a cantilever wall is selected, the earthquake loading should be applied as an inverted triangular loading. If a braced wall is selected, the earthquake loading should be rectangularized. Resistance to sliding could be developed by either base friction or passive pressure or a combination thereof. A base friction coefficient of 0.5 is considered appropriate for the expected foundation support soils. An ultimate passive equivalent fluid pressure of 350 pcf is considered available for the intact native sand soils or structural fill, where level ground exists at the base of the wall. Appropriate safety factors should be applied to the recommended base friction and passive pressure values. Compaction within one-half of the wall embedment height behind the wall should be performed with light equipment such that the wall is not adversely stressed. The maintenance of a dewatered/drained condition behind all retaining structures is required for the above values to be valid. The following drain system and backfill requirements are recommended. Retaining Wall Drainage A longitudinal subdrain with a minimum diameter of 4 inches should be constructed at the footing elevation behind the walls. This drain should be constructed of a 4 inch diameter perforated pipe laid, perforations down, bedded in an eighteen inch envelope of free-draining sand and gravel. This system should be sloped to drain and the water disposed of in the storm drainage system. J. KEITH CROSS, P.E. 9210 NE 13,e Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 9 Clean-outs should be provided at bends and convenient intervals, so that the drainage system can be maintained in a well-functioning condition. Flexible plastic piping (such as ADS) should not be used behind the wall. Roof and parking area drainage systems should not be connected to the wall subdrain system, but may utilize the same tight-line outfall well away from the wall. All wall backfill over the gravel envelope should consist of clean, free-draining, well-graded sand and gravel containing less than 2.0% fines (material passing a U.S. No. 200 sieve). This material should extend out from the rear wall face a minimum of eighteen inches. The free-draining backfill should be placed to the surface in paved areas or to within eighteen inches of the surface in non-paved areas. Backfill should be compacted as recommended above for fills. In non- paved areas, the final eighteen inches of backfill should consist of topsoil or native materials firmly tamped into place. Construction Considerations As previously noted, due to the potential ground water flows, caving and in-washing of materials, we recommend that as a preliminary guideline for temporary cuts slopes be initially planned at 3H to 1 V or flatter. Steeper slopes may be approved by the geotechnical engineer following inspection of the soil and water conditions encountered at the time of construction. Temporary cuts of 1 H to 1 V are expected to be appropriate in the dewatered slope state. Temporary slopes or excavations should be benched as required by safety regulations in effect at the time of construction. These temporary slope recommendations are for native soils and fill materials, flatter slopes may be required in wet weather or if soil conditions other than those previously described are encountered. The contractor should be aware that slope height, slope inclination, and excavation depths (including utility trench excavations) should in no case exceed those specified in local, state, or federal safety regulations; e.g., OSHA Health and Safety Standards for Excavations, 29 CFR Part 1926, or successor regulations. Such regulations are strictly enforced and, if not followed, the owner, the contractor, or the earthwork or utility subcontractors could be liable for substantial penalties. The contractor should be made responsible for the stability of all excavations and slopes during construction because he is continually on site and can observe the J. KEITH CROSS, P.E. 9210 NE 134'Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 10 stability of the exposed soils. In addition, the contractor should be prepared to shore any unstable slope area and provide shoring as required by local, state, or federal laws or codes. In no case should excavated soils be placed on the slope or stockpiled within 20 feet of the top of any existing or excavated slope, rock wall or retaining structure. Failure to comply with these guidelines may lead to destabilization of the slope. The site soils may be easily eroded by channelized water or sheet flow storm runoff. Therefore, it is recommended that all site preparation and excavation work be completed during the normally drier portion of the year. During periods of heavy rainfall, ditching should be used to divert water away from stripped areas and visqueen should be used to cover the slopes and soil stock piles to aid in preventing excessive surface erosion. This covering also aids in preventing infiltration of water into the unprotected soils. All disturbed soil areas and slopes should be replanted with fast-growing, deep-rooted grass, shrubs and other ground cover as soon after final grading as possible. If the vegetation is not fully established prior to the on set of wet weather, the slopes should be covered with visqueen to aid in preventing excessive erosion and water infiltration. Unsupported permanent cut slopes on this lot should generally be no steeper than 2H to 1V. It should be anticipated that there could be a number of additional site development or construction problems, particularly, if the earthwork has not been completed and the site properly protected at the onset of wet weather. It is recommended that the architect, structural engineer or their representative make periodic inspections of all excavations and slopes to provide early recognition and recommendations to correct potential construction problems. Pavement Concepts The sand and gravel subgrade at the site is expected to provide a generally desirable subgrade for pavement support. Once proof-rolled as recommended above, an estimated CBR value of 20 is expected for the native subgrade or structural fill constructed from the on-site soils. In a drained condition this is likely to provide commonly accepted levels of performance for the 6-inch basecourse and 3-inch asphaltic concrete pavement discussed. A thinner pavement of 2 inches J. KEITH CROSS, P.E. 9210 NE 134'Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 11 of asphaltic concrete surfacing over a 4 to 5 inch crushed rock basecourse is likely to provide similar performance levels in areas of automobile parking and light trafficking only. REPORT LIMITATIONS This report has been prepared for the exclusive use of the Halvy Corporation and their agents for use in planning of the referenced development. The conclusions and recommendations in this report are based on our interpretation of site conditions as they presently exist, anticipated future construction activities, and the expectation that the exploratory efforts adequately define the subsurface conditions throughout the area of the retaining wall and adjacent paved areas. This report is not intended to address geotechnical or design considerations for the building. The recommendations contained in this report should not be expanded for use in the design of the building without our review unless specifically stated in the report. The soil conditions described in this report and the conclusions and recommendations contained in this report are provided for this specific site only and should not be expanded for use on adjacent properties without additional exploration and review of those sites by our firm. The data and report should be provided to prospective contractors for their bidding or estimating purposes, but the report conclusions and interpretations should not be constru3d as a warranty of the subsurface conditions. There are possible variations in subsurface conditions. In the event that the scope or location of the project should change or subsurface conditions different from those encountered during this study be observed or suspected, we should be advised. At that time a review of the changed conditions will be made, and alternative or remedial recommendations given as required. NOTE: Although we have explored subsurface conditions as part of this study, we have not conducted analytical laboratory testing of any samples obtained, have not evaluated the site for the potential presence of contaminated soil, and have not evaluated or addressed ground water conditions or concerns except as noted in this report. The owner and the contractor should make themselves aware of and become familiar with applicable local, state, and federal safety regulations, including current OSSA excavation and trench safety standards. Construction site safety generally is the sole responsibility of the J. KEITH CROSS, P.E. 9210 NE 134'Street, Kirkland,Washington 98034-1876 Report to Halvy Corporation Project No. 3063-001 March 19, 1996 Page 12 contractor. The contractor shall also be solely responsible for the means, method, techniques, sequences, and operations of construction operations. The firm, J. Keith Cross, P.E. (including consultants) is providing the preceding information and recommendations solely as a service to Halvy Corporation. Under no circumstances should the provision of this information or recommendations be construed to mean that the firm, J. Keith Cross, P.E. (including consultants) is assuming responsibility for construction site safety or the contractor's activities; such responsibility is not implied and should not be inferred. Within the limitations of scope, schedule, and budget for this work, it is warranted that the work has been done in accordance with generally accepted practices followed in this area at the time this is report was made. No other warranty, expressed or implied is made. Should you have any questions or concerns which have not been addressed, or if we may be of additional assistance, please call. Sincerely �y EITH WAS H1`t`c�ScS' ti 1 I t! i J. Keith Cross, P.E. 784 sroNAL EXPIRFS10/9/ " J. KEITH CROSS, P.E. 9210 NE 134"street, Kirkland,Washington 98034-1876 Halvy Corporation/Report-Retaining Wall Design Considerations, Proposed Belfair Post Office February 19, 1996 Project No. 3063-001 EXPLORATION PIT LOGS EXPLORATION PIT 1 Approximate Elevation: 192+/-feet Depth-Feet Soil 0.0 - 1.5 Gray-brown, loose, gravelly SAND with some silt, wet. (Fill) Trace of old root zone. 1.5 - 4.0 Brown, loose to medium dense, silty, gravelly SAND,wet. 4.0 - 10.0 Gray-brown to gray, medium dense becoming very dense, gravelly SAND with trace to some silt,wet. -Seepage to moderate water flow surface to 18 inches. Heavy to very heavy water flow below 4.5 feet. -Moderate to heavy in-washing in seepage zones. EXPLORATION PIT 2 Approximate Elevation: 202+/-feet Depth-Feet Soil 0.0 - 1.0 Brown, loose, gravelly SAND mixed with clearing debris,wet. 1.0 - 4.0 Gray-brown, loose to medium dense, gravelly SAND with trace to some silt, wet. 4.0 - 9.0 Gray, dense to very dense, gravelly SAND with some interbeds of clean sand, silty sand, and gray to tan silt, wet. 9.0 - 11.0 Gray,very dense, gravelly SAND to SAND and GRAVEL, wet. -Seepage to moderate water flow surface to one foot. Heavy water flow at four to five feet. Unable to determine water flow conditions below 6.5 feet due to flooding and caving of excavation. -Heavy in-washing in seepage zones. -Massive caving below three feet. -Faint odor of decomposing organics. Figure 2 Halvy Corporation/Report-Retaining Wall Design Considerations, Proposed Belfair Post Office February 19, 1996 Project No. 3063-001 EXPLORATION PIT 3 Approximate Elevation: 200+/-feet Depth-Feet Soil 0.0 - 3.0 Brown to gray-brown, loose to medium dense, SAND with some gravel to gravelly, trace silt., very moist. 3.0 - 9.0 Gray, medium dense to dense, gravelly SAND to SAND with some gravel, very moist to wet. 9.0 - 12.0 Gray, dense, SAND with some gravel and interbeds of silty sand, and silt, wet. -Heavy water flow below five feet. -Massive caving five to nine feet. EXPLORATION PIT 4 Approximate Elevation: 201+/-feet Depth-Feet Soil 0.0 - 2.0 Brown to tan, loose to medium dense, SAND with some gravel,very moist. 2.0 - 11.0 Gray, medium dense becoming very dense, gravelly SAND, moist.. -No ground water observed. EXPLORATION PIT 5 Approximate Elevation: 190+/-feet Depth-Feet Soil 0.0 - 0.5 Dark brown, loose, gravelly TOPSOIL. 0.5 - 2.0 Brown to tan, loose to dense, gravelly SAND, moist. 2.0 - 10.5 Gray, dense to very dense, gravelly SAND, moist to very moist. -No ground water observed. FIGURE 3 Halvy Corporation/Report-Retaining Wall Design Considerations, Proposed Belfair Post Office February 19, 1996 Project No. 3063-001 EXPLORATION PIT 6 Approximate Elevation: 191+/-feet Depth-Feet Soil 0.0 - 0.5 Dark brown, loose, gravelly TOPSOIL. 0.5 - 5.0 Brown to tan, loose to medium dense, gravelly SAND, moist. 5.0 - 12.0 Gray, dense to very dense, gravelly SAND with scattered interbeds of fine gravel and sand,wet. -Moderate to heavy water flow below five feet. -Moderate caving below five feet. EXPLORATION PIT 7 Approximate Elevation: 201+/-feet Depth-FeetSoil 0.0-1.5Dark brown, loose, gravelly, sandy TOPSOIL, moist. 1.5-3.513rown to tan, medium dense, gravelly SAND, moist. 3.5-12.OGray, medium dense to very dense, gravelly SAND, moist to wet. -Heavy water flow at 10.5 feet. EXPLORATION PIT 8 Approximate Elevation: 192+/-feet Depth-FeetSoil 0.0-10.013rown to tan grading to gray, loose becoming very dense, gravelly SAND, moist to wet. -Moderate to heavy water flow below 4.5 feet. Figure 4