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HomeMy WebLinkAboutT-3453 i z GEOTECHNICAL ENGINEERING STUDY AND ABANDONED MINE ASSESSMENT North 405 Upper and Lower Sites Renton, Washington Project No. T-3453 i ,z x Terra Associates Inc. � 0 yc � L 4 Y R i>'itaayo c1a�, `' i 1: S i i t Prepared for: Opus Northwest, LLC Bellevue, Washington of, �o 00, December 17, 1997 am M mom i 1 ........................ ........................ t ..........._............. t TERRA ASSOCIATES, Inc. Consultants in Geotechnical Engineering, Geology and Environmental Earth Sciences December 17, 1997 Project No. T-3453 Mr. Harry DeMarre Opus Northwest, LLC 200— 112th Avenue NE, Suite 205 Bellevue, Washington 98004 Subject: Geotechnical Engineering Study and Abandoned Mine Assessment North 405 Upper and Lower Sites Renton, Washington References: i Report, Aerial Photograph Interpretation, Monster Road, prepared by Golder Associates, Inc., Reference No. 973-1212, dated November 26, 1997 2. Report, Preliminary Abandoned Mine Assessment,prepared by Golder Associates, Inc., Reference No. 973-1212, dated August 22, 1997 3. Preliminary Geotechnical Study, Oaksdale Business Park, prepared by Terra Associates,Inc., Project No. T-3453, dated February 15, 1997 Dear Harry: As requested, we have completed a geotechnical engineering study and abandoned mine assessment for the above subject project. Our work was conducted in accordance with your instructions and authorization. The results of our study indicate that previous mining for coal did occur on the site predominantly in the western portion of Parcel A, the upper site. This coal mining activity extracted a shallow coal seam from a depth of about 10 to 14 feet below existing surface grade using strip mining techniques. However, there is also evidence that mine prospects or tunnels were advanced northeastward across the site at a depth below this upper mined out coal seam. These mine prospects appear to extend beyond the extent of the surface mining operations and, therefore, would impact the extreme northwest corner of the proposed building construction and the west portion of the upper west parking lot. Fortunately, the prospects are relatively shallow and limited in nature (less than 25 feet deep) and measures to mitigate the potential for surface collapse can readily be implemented concurrent with site grading activities. I 12525 Willows Road, Suite 101, Kirkland, Washington 98034 • Phone (425) 821-7777 Mr. Harry DeMarre December 17, 1997 Detailed discussion and recommendations regarding the above issue, along with geotechnical engineering recommendations for design and construction, are summarized in the attached report. We trust the information presented is sufficient to meet your current needs. If you have any questions or require additional informati 11. fl� J. S� Sincerely your d� TERRA AS T " T odore J. Sc Principal Enggirinne—ee ' TJS:ts tea 6,qW 9$ Project No. T-3453 Page No. 17 TABLE OF CONTENTS Page 1.0 Project Description 1 2.0 Site Conditions 2 2.1 Surface 2 2.2 Subsurface 3 2.3 Groundwater 4 3.0 Geologic Hazards 4 3.1 Coal Mines 4 3.2 Steep Slopes 5 3.3 Seismic 6 4.0 Discussion and Recommendations 6 4.1 General 6 4.2 Site Preparation and Grading 6 4.3 Slopes and Embankments 8 4.4 Excavations 8 4.5 Foundations 9 4.6 Slab-on-grade 9 4.7 Retaining Walls 10 4.8 Rockeries 10 4.9 Drainage 10 4.10 Utilities 11 4.11 Pavements 11 5.0 Additional Services 11 6.0 Limitations 12 Figures Vicinity Map Figure 1 Exploration Location Plan Figure 2 General Slope Fill Detail Figure 3 Retaining Wall Drainage Detail Figure 4 Reinforced Fill/Rockery Cross-section Figure 5 Appendix Field Exploration and Laboratory Testing Appendix A Golder Associates, Inc. Reports Appendix B Geotechnical Engineering Study and Abandoned Mine Assessment North 405 Upper and Lower Sites Renton, Washington 1.0 PROJECT DESCRIPTION The project will consist of developing the sites with office warehouse type structures. The structures will have a clear span height of about 27 feet and will be constructed using precast concrete tilt up wall panels. Perimeter wall loads are expected in the range of three to five kips per lineal foot with interior isolated columns supporting the roof structure loaded to about 100 kips. Based on drawings prepared by AHBL, dated October 22, 1997, the structure on the upper site will have its finish floor constructed at Elev. 72. The structure on the lower site will have its finish floor constructed at Elev. 55. Significant grading will be required at this site in order to establish these finish floor elevations, as well as the perimeter parking and drive access routes. For the upper site, excavations or cuts into the existing south hillside approaching a depth of 25 feet will be required to establish the parking and access grade along the south side of the structure. The drawings by AHBL show that the lower six to eight feet of this cut will be vertical with a backslope graded at an inclination of 2:1 (Horizontal:Vertical). Fill material, ranging in depth from 8 to about 12 feet will be required to establish desired building grade in the north-central portion of the structure and north parking lot area. Off the north perimeter of the parking area,the fill is shown sloped at a gradient of 2:1. The lower site will have its finish floor established at an elevation of 55. This will require excavations in excess of 60 feet below existing grade into the adjacent eastern hillside. This cut is shown on the drawings prepared by AHBL to be laid back at a finish inclination of 1:1 along the east perimeter of the structure. Along the western and northern margins of the structure, fill material approaching a depth of 20 feet will be required to establish the adjacent parking and drive access grades. A stormwater biofiltration swale will be constructed along the west perimeter of the upper site, north of the lower site. The biofiltration swale will have its center line grade established at Elev. 58 at the north end and Elev. 54 at the south end. Along the Swale centerline, a maximum excavation depth of about 30 feet will be required to establish this swale grade. An eight to ten-foot high rockery is shown along the east perimeter of the swale, supporting the vertical break in grade adjacent the east parking lot area. An alternative building layout is also proposed for the upper site. This layout for Cascade Airgas, while having a different building footprint, would require similar grading as that shown on the October 22, 1997 drawings by AHBL. The recommendations contained in the following sections of this report are based upon the above design features. Should actual features vary or if changes are made, we should be informed and requested to review them in order to supplement or amend our recommendations as required. December 17, 1997 Project No. T-3453 2.0 SITE CONDITIONS 2.1 Surface The site is bounded to the east and southeast by Monster Road and a METRO sewer treatment facility. Warehouse facilities bound the site to the north. The Burlington Northern Railroad right-of-way bounds the site to the southwest. An approximately 2-1/4 acre parcel owned by METRO extends northwest of Monster Road and bounds the southern part of the subject property. A 15-foot wide water easement and 60-foot wide railroad easement run along the eastern and western parts of the northern property line, respectively. The site is situated on a hill surrounded by the Green River valley floor. Most of the eastern portion of the site (Parcel 3) is open with nearly flat to gently sloping ground extending to the east and north. These slopes steepen to a gradient of approximately 3:1 at the southern margin of Parcel 3 and lead off of the site toward the hill's peak on the adjacent METRO property. The northern margin of the site slopes downward toward the neighboring warehouse facility properties at an overall inclination of approximately 2:1. This slope continues westward into Parcel 4B where it turns southward and runs toward the Burlington Northern right-of-way at the site's southwestern margin. The slope's height ranges from approximately 40 feet at the northeastern corner of the site to 100 feet within Parcel 4B. In the vicinity of Test Pit TP-1, we observed a north-south trending, approximately 30-foot wide mine adit that formed an excavated trough extending down the face of the slope toward the northern property line. We also noted an approximately six foot square opening in the ground east of the adit that was partially obscured by berry brambles. The opening appeared to be a mine exploratory or ventilation shaft. The approximate locations of these features are shown on Figure 2. The southern part of the site contains southwest-facing slopes standing at grades of up to 3:1. Relatively level areas are located adjacent to the top of a near-vertical 30 to 40-foot high cut made for construction of the adjacent railroad. The cutslope appeared to expose weathered sandstone and did not show any seeps, springs, or significant signs of instability. Portions of the cut were draped with chain-link fencing to provide protection against rockfall. A flat, marshy area is situated between the railroad spur and Burlington Northern line within the northwestern corner of the site. At the time of our January 22, 1997 site visit, standing water covered most of this low-lying area. Minor standing water was also noted at the eastern part of the site. No signs of recent surface water runoff or erosion were noted during our visit. Vegetation at the site consisted of wild grasses and berry bramble within the open, eastern part of the site. Mature coniferous and deciduous trees, and occasional blackberry brambles covered the western sloped areas. Page No. 2 December 17, 1997 Project No. T-3453 2.2 Subsurface We explored subsurface conditions at the site by excavating five test pits at the upper site and three test pits at the lower site on January 22, 1997. The results of our exploration, along with preliminary conclusions regarding site development, were presented in a report dated February 15, 1997. Subsequent this report, Golder Associates, Inc. was retained to complete a more detailed study to assess the coal mine hazard at the site. The ensuing site exploration undertaken by Golder Associates,Inc. included the excavation of several test trenches which extended to depths of 14 to 18 feet below existing site grade for lineal distances ranging from 50 to over 400 feet. The results of their study and preliminary conclusions were presented in reports dated August 22 and November 26, 1997. These reports are attached in Appendix B. Following the Golder Associates, Inc. studies, on December 11 through December 15, 1997, we drilled three additional soil test borings on the upper site. These borings were performed to further assess the coal mine hazards at the site and to evaluate the excavation characteristics of the underlying rock formations. The locations of the explorations completed by Golder Associates, Inc. and Terra Associates, Inc. are shown on the attached Exploration Plan, Figure 2. The following provides a general summary of the conditions observed. Near-surface soils at the site to depths of 1 to 2.5 feet were shown to consist of fill or topsoil composed of an organic sandy to clayey silt to silty sand. Underlying these near-surface soils, layers of weathered sandstone, clay, and silt, of the Renton formation were encountered. The weathered sandstone was generally noted to be in a medium dense to dense condition with the clay and silt strata noted to be stiff to hard. Very dense glacial till or till-like soils were also observed along the south portion of the upper site at Test Pits TP- 2 and TP-3. These till or till-like soils were composed of a silty fine sand with gravel and contained occasional cobbles and clasts of highly weathered sandstone. Below depths of approximately 10 to 15 feet, at Test Trench No. 6 and Test Boring B-2, slightly weathered to unweathered sandstone was observed. Underlying the south slopes, large boulders were also noted overlying the Renton formation sandstone at Test Trench No. 2 and Test Boring B-3. As described in the attached Golder Associates, Inc. report, the area west of the upper site and north of the lower site has been subject to previous grading activity from coal mining. The coal, which was shown to reside at a relatively shallow depth of about 10 to 14 feet below, was extracted by strip mining with the area then reclaimed following coal removal. Site exploration revealed coal mine spoils composed of silty sands, clays, coal fragments, extended to depths of 10 to 18 feet below existing surface grades. Detailed descriptions of soil conditions encountered are summarized on the test pit and test boring logs attached in Appendix A. A narrative description of conditions observed at the test trenches excavated by Golder Associates, Inc. is included with their reports attached in Appendix B. Page No. 3 December 17, 1997 Project No. T-3453 2.3 Groundwater We observed groundwater seepage of varying intensity at Test Pits TP-1 through TP-8 with the exception of Test Pit TP-5. These test pits were excavated in January of 1997. No indication of groundwater seepage was observed at the test trenches excavated by Golder Associates, Inc. in August of this year. We observed groundwater seepage at depths varying from two to ten feet below existing surface grades. The seepage was occurring from more pervious soil zones or the weathered rock horizon overlying relatively impervious strata of unweathered sandstone or siltstone. As demonstrated by this study, groundwater seepage levels will fluctuate on a seasonal and annual basis. Higher levels of groundwater seepage would be expected during the wet winter season with seepage levels diminishing or becoming absent in the dry summer months. 3.0 GEOLOGIC HAZARDS 3.1 Coal Mines There is both surficial evidence and evidence in the literature that indicates that coal mining activity occurred on and adjacent the subject site. We provided a preliminary evaluation of this activity in our referenced February 15, 1997 report. Golder Associates, Inc. was retained to perform a more detailed assessment of the possibility for abandoned mines to exist on the property. The results of their studies were summarized in two reports dated August 22, 1997 and November 26, 1997, both of which are attached in Appendix B. The results of the Golder Associates, Inc. studies indicate that mining activity on the site primarily occurred within the western portion of the upper site. The mining that occurred removed a relatively shallow coal seam residing approximately 10 to 14 feet below existing surface grades using surface mining techniques. Once the coal was extracted, the area was reclaimed with the excavated spoils. Test Trench No. 3, which was a 400-foot excavation north to south across the site, delineated the approximate eastern extent of these surface mining activities. The location of Test Trench No. 3 was surveyed in the field and is shown on attached Figure 2. At Test Trench No. 1, a mine opening was observed at a depth of about 8 to 14 feet below existing surface grades. As reported by Golder Associates, Inc., this trench probably encountered the remnants of the 207-foot long Black River Mine slope. However, Golder Associates, Inc. indicated that the slope was mined in an easterly direction below the elevation of the upper coal seam as encountered at Test Trenches No. 3, 7, and 8. Therefore, it was speculated that there was a potential for a second lower seam to exist at the site. Golder Associates, Inc. recommended further investigation at the site by drilling to determine whether a deeper coal seam than the one that was observed in these trenches existed. On December 11 through December 15, 1997, Terra Associates, Inc. followed Golder Associates, Inc.'s recommendations and drilled three additional soil test borings at the site. Boring B-2 was drilled to a depth of 59 feet specifically to determine if there was a second lower coal seam which could have economically been extracted by driving a tunnel from west to east across the site. The result of our additional exploration revealed no such second lower seam. However, at Test Boring B-1, which was drilled in the area of Test Trench No. 4 and the existing sink holes, we observed what appears to be remnants of a mine tunnel in the form of timber and coal debris. This material was encountered at a depth of approximately 20 feet or at roughly site Elev. 50. Page No. 4 December 17, 1997 Project No. T-3453 The mine opening observed at Test Trench No. 1 was at approximately site Elev. 54. We believe that the opening observed at Test Trench No. I and conditions observed at Test Boring B-2 represent shallow prospects which were terminated when it was determined that a minable coal resource farther eastward into the site was not available. Subsidence observed in the vicinity of Test Trench No. 4 is likely related to the collapse of this shallow mine working. Based on the results of the Golder Associates, Inc. studies and our subsequent exploration, we conclude that there are undocumented mine workings which extend from the southwest to the northeast along the western portion of the upper site. These workings are likely abandoned prospects and exist at a relatively shallow depth of 20 to 25 feet below existing site grade (Elev. 45 to 55). There is a risk that these relatively shallow tunnels could collapse, resulting in surface sink holes if not mitigated. This risk would be present along the parking and drive areas west of the structure on the upper site as well as the extreme northwest corner of the structure. Proposed grading, particularly in the central and southern portions of this area of the site will require excavations of 14 to 30 feet below existing surface grades. These excavation depths are equivalent to or extend below previously mined depths at the site as indicated by our studies. It is likely that any mine workings in this area will be uncovered and reworked by the planned grading. The exception to this occurs in the area of the existing sink holes near Test Trench No. 4 as shown on the Exploration Location Plan, Figure 2. Here, minimal grading of less than two feet below existing surface grade will be required to establish desired construction elevation. To mitigate the risk posed by undocumented mine workings below this area of the site, we recommend that this area also be overexcavated to a minimum depth of 20 feet below current site grade with grade then restored with suitably compacted structural fill as described in a subsequent section of this report. Alternatively, deep dynamic compaction (DDC) can be used to consolidate the soils and collapse any undocumented mine workings. DDC consists of dropping a heavy weight generally on the order of six to ten tons using a large crane from a height of about 30 to 50 feet. The weight is dropped at the same location five to ten times to consolidate loose fills at depth. Given the expected shallow workings, which may be present in this area, the energy delivered by the DDC would also be expected to collapse any undocumented workings. Specific details for application of DDC at the site can be provided if this option is selected. 3.2 Steep Slopes As indicated by our exploration, the site is primarily underlain by competent soils and weathered block. Existing slopes on the site, which range in inclination from near-vertical adjacent the railroad cut to the southwest, to gradients of 2:1 south of the upper site, were noted to be in a stable condition with no indication of previous or current landslides or slope instability. The near-vertical cut at the southwestern portion of the site was faced with chain-link fencing to contain material falling or eroding off of the near-vertical cut. In our opinion, provided recommendations contained in the following sections of this report are followed, site grading as proposed resulting in cut slopes varying from 1:1 to 2:1 would remain stable and would not impact the current site stability or that of adjacent properties. Page No. 5 December 17, 1997 Project No. T-3453 3.3 Seismic The Puget Sound area falls within Seismic Zone 3 as classified by the Uniform Building Code (UBC). Based on the soil conditions encountered and the local geology, from Table 16J of the UBC, a site coefficient of 1.0 should be used in design of the buildings. With the competent nature of the native soil and rock which underlies the site, there would be no risk for soil liquefaction related impacts to the structures or associated utilities. 4.0 DISCUSSION AND RECOMMENDATIONS 4.1 General Based on the results of our study, it is our opinion that there are no geotechnical constraints which would preclude development of the sites as proposed. However, mitigation to eliminate the hazard associated with previous mining activity as discussed in the coal mine hazard section of this report will be required within the western portion of the upper site. It is recommended that this mitigation work occur concurrent with the start of site grading activities. Extensive excavations will be required at both sites to achieve desired construction grades. Initial soils excavated from the sites to depths of 10 to 15 feet will consist of layers of silty sands, clays, silts, and weathered sandstone. It is also likely that large boulders or fragments of intact bedrock will be encountered at excavation depths of 10 to 15 feet below current side grade. Below 15 to 20 feet, hard sandstone, associated with the Tukwila formation, will be encountered. The soils contain a significant amount of fines and will not likely be suitable for use as structural fill during wet weather conditions. Therefore, we recommend that mass grading activities at the site only be contemplated during the drier summer months(June through October). In addition, the grading contractor should be prepared to use hard rock excavating techniques, such as ripper claws and hard formation teeth, to achieve the desired construction elevations. For the lower site, which will require excavations of 60 feet below existing grade, blasting to facilitate excavation of the hard Tukwila sandstone formation may need to be considered. The following sections of this report provide detailed recommendations pertaining to the above issues, as well as other geotechnical design considerations. These recommendations should be incorporated into the final design drawings and construction specifications. 4.2 Site Preparation and Grading To prepare the sites for construction, prior to excavation and placement of fill material, it will be necessary to strip the organic surface layers. On the existing south and western slopes, surface stripping depths of four to six inches should be expected to remove the organic topsoil. Along the lower flatter portions of the sites, site explorations indicate surface stripping depths of one to two feet will be required. These soils will not be suitable for use as structural fill, but can be used in nonstructural landscaping areas. Page No. 6 December 17, 1997 Project No. T-3453 Concurrent with site excavations, mitigation work to eliminate the potential risks associated with undocumented mine workings in the western portion of the upper site should be undertaken. As described previously, proposed grading activity in the central and south portions of this area of the site should extend to a depth equivalent to or below the depth of the mine workings as identified by our study. However,within the north portion of this area of the site, additional excavation approaching 20 feet below existing grade should be planned. The approximate limits where this overexcavation is recommended for the purpose of mitigating the mine hazard is shown on the Exploration Location Plan, Figure 2. Once excavated, uncovering suspected mine workings or competent bedrock material, the grade can be restored using structural fill. As described earlier, an alternative to this overexcavation and refill procedure would be the use of DDC. Prior to placing fill materials, stripped subgrades should be proofrolled with heavy construction equipment to determine if any isolated soft and yielding areas are present. If such areas are found, and they cannot be stabilized and placed by compaction, the affected soils should be overexcavated to firm bearing and replaced with structural fill. Similar proofrolling should be performed on native subgrades, which will provide direct support for building or pavement construction. The soils at the site contain a significant amount of fines and, in our opinion, would not be suitable for use as structural fill during wet weather conditions. Therefore, we strongly suggest that grading activity only be contemplated during the drier summer months (June through October). In addition, given the fines content of the soil and the presence of weathered bedrock fragments of siltstone and sandstone, a sheeps foot compactor should be used to compact the structural fills. If grading activities are planned during the wet weather season, or if they are initiated in dry weather and extend into the winter, you should be prepared to import a relatively clean fee-draining pit run sand and gravel for use as structural fill. Imported material for wet weather grading purposes should meet the following requirements. U.S. Standard Sieve Size Percent Passing 3 inches 100 No. 4 75 maximum No. 200 5 As an alternative to importing wet weather structural fill, consideration could be given to amending native soils which are unstable due to excessive moisture using Portland cement or kiln dust. These additives, when mixed uniformly with the soil, reduce the soils' moisture content and generally produce a workable and compactable material. When compacted, the cement or kiln dust continues to hydrate with the soil, improving its strength and decreasing its compressibility. If necessary, soil amendment of this nature can also be considered for utility trench backfill soils. Page No. 7 December 17, 1997 Project No. T-3453 Structural fills should be placed in uniform loose lifts not exceeding eight inches and then compacted to a minimum of 95 percent of the soils' maximum dry density as determined by ASTM Test Designation D-698 (Standard Proctor). The moisture content of the soil at the time of compaction should be in the range of plus or minus two percent of the soils' optimum moisture, as determined by this same method. In nonstructural areas, and for utility trench backfill below a depth of four feet, the degree of relative compaction can be reduced to 90 percent. 4.3 Slopes and Embankments Fill embankments should be graded with a finish slope inclination of no steeper than 2:1. Fill material used to construct the embankment should be placed and compacted as a structural fill, as described in the preceding section. Where the fill will be placed on existing slope gradients, in excess of 20 percent, it should be keyed and benched into the native subgrade as shown on attached Figure 3. Finish slope surface should be firmly compacted, trackwalked, and appropriately vegetated to reduce or prevent erosion. Surface water runoff should not be allowed to flow in an uncontrolled fashion over the crest of the slope or on the slope face. If surface water is not directed away from the slope, it should be controlled in a swale and either tightlined in a closed conduit down the slope face or in an appropriately lined channel. Finish cut slopes exposing competent bedrock of the Tukwila or Renton formation can be laid back at finish inclinations of 1:1 to 2:1. For near-surface stability considerations, where the slope gradient exceeds 2:1, we recommend the slope surface be covered with a permanent erosion control and stabilization geosynthetic material. We recommend using a material, such as Enkamat S or equivalent, which is staked to the slope surface in accordance with the manufacturer's recommendations. Once this material is placed, the slope surface should be hydroseeded with a hydroseed mix appropriate for the slope inclination. 4.4 Excavations All site excavations must be completed in accordance with local, state, or federal requirements. Based on the current Occupational Safety and Health Administration (OSHA) regulations, near-surface materials and existing disturbed mine spoils would be categorized as a Group C soil. Accordingly, excavations within this material which extend to a depth of greater than four feet should be laid back at an minimum inclination of 1.5:1. In our opinion, temporary excavations which extend into the weathered bedrock and unweathered bedrock can be laid back at minimum slope inclinations of 1:1 to 1/2:1, respectively. The above information is provided solely for the benefit of the owner and other members of the project design team. It should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project general contractor. Page No. 8 December 17, 1997 Project No. T-3453 4.5 Foundations The building may be supported on conventional spread foundations bearing on competent native soils or on structural fills placed above competent native soils. Foundation subgrades should be prepared as recommended in the Site Preparation and Grading section of this report. Perimeter foundations exposed to the weather should be at a minimum depth of 1.5 feet below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. We recommend designing foundations obtaining support on competent native soils for a net allowable bearing capacity of 4,000 psf. Foundations bearing on structural fill should be proportioned for an allowable bearing of 2,500 psf. For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity can be used. With the expected building loads and these bearing stresses applied, the estimated total settlements fall in the range of one-half to one inch, of which 1/4 to 3/4 inches would be differential in nature. The greatest magnitude of differential settlement would occur at the transition from native bearing soils to structural fill. If required, foundations spanning this transition can be stiffened to resist this bending. For designing foundations to resist lateral loads, a base friction coefficient of .4 can be used. Passive earth pressures acting on the side of the footing can also be considered. We recommend calculating this later resistance using an equivalent fluid weight of 350 pcf. We recommend not including the upper 12 inches of soil in this computation because they can be affected by weather or disturbed by future grading activity. This value assumes the foundation will be constructed neat against competent native soil or backfilled with structural fill as described in the Site Preparation and Grading section of this report. The passive value recommended includes a safety factor of 1.5. 4.6 Slab-on-grade Slabs-on-grade may be supported on the subgrade prepared as recommended in the Site Preparation and Grading section of this report. Immediately below the floor slab, we recommend placing a four-inch thick capillary break layer of clean, free-draining sand or gravel that has less than three percent passing the No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. Moisture can still be transmitted through the floor slab by vapor transmission. This can be particularly troublesome for floor covering adhesives. To guard against this occurrence where necessary, a durable plastic membrane should be placed on the capillary break layer. The membrane should be covered with two inches of clean, moist sand to guard against damage during construction and to aid in curing of the concrete. Page No. 9 December 17, 1997 Project No. T-3453 4.7 Retaining Walls The magnitude of earth pressure development on lower-level or retaining walls will partly depend on the quality of the wall backfill. We recommend placing and compacting wall backfill as structural fill. To guard against hydrostatic pressure development, wall drainage must also be installed. A typical recommended wall drainage detail is shown on Figure 4. With wall backfill placed and compacted as recommended and drainage properly installed, we recommend designing unrestrained walls for an active earth pressure equivalent to a fluid weighing 35 pef. For retrained walls, an additional uniform lateral pressure of 100 psf should be added. These values assume a horizontal backfill condition and that no other surcharge loading, such as traffic or sloping embankments, will act on the wall. If such conditions will exist, then the imposed loading must be included in the wall design. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Valued for these parameters are provided in the Foundations section of this report. 4.8 Rockeries Excavations along the south and east perimeters of the upper and lower sites, respectively, should expose dense Renton or Tukwila sandstone. These conditions would be suitable to face with rockery construction to a maximum height of eight feet. Rockeries should be constructed by an experienced rockery contractor in accordance with the Association of Rockery Contractors guidelines. The excavation along the east perimeter of the biofiltration swale is expected to encounter disturbed mine spoils along its northern portion. These soils will not be suitable to face with rockery construction. The fill should be removed and replaced with structural fill that is reinforced with geogrid. A general reinforced fill/rockery section is shown on attached Figure 5. 4.9 Drainage Final exterior grades should promote free and positive drainage away from the site at all times. Water must not be allowed to pond or collect adjacent foundations or within the immediate building area. We recommend providing a gradient of at least three percent for a minimum distance of ten feet from the building perimeter, except in paved locations. In paved locations, a minimum gradient of one percent should be provided unless provisions are included for collection and disposal of surface water adjacent the structure. Surface water must not be allowed to flow uncontrolled over the crest of the site slopes and embankments. Surface water should be directed away from the slope crests to a point of collection and controlled discharge. If site grades do not allow for directing surface water away from the slopes, then water should be collected and tightlined down the slope face in a controlled manner. Page No. 10 December 17, 1997 Project No. T-3453 Subsurface We recommend installing perimeter foundation drains below landscaped areas adjacent to the structures. Where pavement extends to the structure perimeter and positive slope is provided away from the building, we do not believe foundation drains are necessary. Drains, where installed, must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. 4.10 Utilities Utility pipes should be bedded and backfilled in accordance with American Public Works Association(APWA)or City of Renton specifications. At minimum, trench backfill should be placed and compacted as structural fill as described in the Site Preparation and Grading section of this report. As noted, soils excavated on-site should be suitable for use as backfill material during dry weather. However, at the time of our study, the soils' moisture content appeared to be above optimum. Therefore, drying back or other means to condition the material may be necessary to facilitate proper compaction. If"utility construction takes place during the winter, it may be necessary to import suitable wet weather fill or amend native soils for utility trench backfilling. 4.11 Pavements As a,means to prepare a stable subgrade and pavement base, we recommend using a soil cement application. The soil cement, or cement treated base (CTB), can be constructed using the native soils observed below the organic surface layer. We recommend scarifying the top 12 inches of the subgrade and then blending in Type 1 Portland Cement at a rate of 60 pounds per square yard of surface area. The cement should be blended uniformly with the soils, with the mixture also moisture conditioned as necessary. The soil cement moisture should be within—1 to +3 percent of optimum as determined by ATSM Test Designation D-698 (Standard Proctor) prior to compaction. Once blended and conditioned, the soil cement should be compacted to a minimum of 95 percent of its maximum dry density as determined by this ASTM standard. Traffic at the facility will mainly consist of cars and light trucks with only occasional heavy traffic in the form of tractor-trailer rigs and trash removal vehicles. We recommend that the pavement section constructed over the 12 inches of CTB consist of two inches of asphalt concrete (AC). The AC should meet WSDOT specifications for Class B mix. 5.0 ADDITIONAL SERVICES Terra Associates, Inc. should review the final design and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and incorporated into project design. We should also provide geotechnical services during construction in order to observe compliance with the design concepts, specifications, and recommendations. This will also allow for design changes if subsurface conditions differ from those anticipated prior to the start of construction. Page No. 11 December 17, 1997 Project No. T-3453 6.0 LIMITATIONS We prepared this report in accordance with generally accepted geotechnical engineering practices. This report is the property of Terra Associates, Inc. and is intended for specific application to the North 405 Upper and Lower Sites project. This report is for the exclusive use of Opus Northwest, LLC and their authorized representatives. No other warranty, expressed or implied, is made. The analyses and recommendations presented in this report are based upon data obtained from the test pits and test borings excavated on-site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. Page No. 12 a .. .1 A I I I •> + • c i , s� ��$� S r l24 ST s�.a art 9 Oti Pam• Ta FS CfB i V IL 3 n' _. . --`� `; i:• ^'s, .�N r�4pQY _ i , s �(1 -.R+•y►tN ¢ p E�. �` i.. � � � 9 - � �' ,Z6td 'r_`� Ll s i n bbb }■ _ Oa S S! n �fAI s u„Tx n s + . 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(-`T..• R£1rT1M" ._ r TT r Z6 OR s ' 1r 4o. 00 29TH ST ITS s rBe �. �s, 5 _} 30 Sr,_ '< h Z �"{'s er MlfBtfO ` S 3M Y - 1 Sr00 .. .Zm7 5 ,e YE7IMQS sn. 1 r - - ST ,. ST S- 172NO PC -CORPORA _ �'_ tN - - �- < ST BLVD SN $t - r v v.WRY/r T-�T x `JBTH A J` Nei PLW �� ST a FP A78TH t1ST - s ^imu f TR[ ^ S _ ,:� x+.,yt�•xA,,�. -,a4., �+.. � i v LA REFERENCE: THE THOMAS GUIDE, KING COUNTY, WASHINGTON, PAGES 655 AND 656, 1998 EDITION. VICINITY MAP TERRA NORTH 405 UPPER AND LOWER SITES RENTON, WASHINGTON .. .•: ASSOCIATES Geotechnical Consultants Proj. No.3453 Date DEC. 1997 1 Figure 1 ! I EXISTING BUILDING I ! a 1.000'' __- ------ .��'- / •vlve Rr.s OF - ` �,` PARCEL .I \`'\� 1 '��• s •r� l--- -- - 'tip,nn.,r: _ •—� , ! +' I' t' `\\.���\y\•.�, •;.1�tt /'-�- •'li�;'!� �"1•,_-..`„_` \ ,1, t /' / I., I_`'. "fir •� �' '� � / /' % ,, / . -mow � ^-� i j i / l:: 'r � 7EDFM Wi -s.-- ` ; ; .C- �' APPROXIMATE SCALE -- \� `: �- �, 51'a^ !;t ' '� "i• —"'--�- .Q_Q,a�, I;f� /` - t— 0 150 0 150 300 feet CONTOUR INTERVAL: 2 feet j'-�• `�4lul �� ��%i%/� ` `;iiil�i,i �,i z i,-�, 't-e _ ''p i,; �'`� PARC.EL-'A,�/' /• f' --__-'-'-- ' I \, /• /,, {1 �\�t'48/U®.j 1�',l��\ 1„ d .�.-. \ b� / / t,0/O.iovY�6 � rR� \.:\��" ;�/>,;,. t;;i,;;,{ ,,;• {; \ =="- \\ `� ! ! ® TEST PITS BY TERRA ASSOCIATES (1/97) `•` �\\`` \\. V. ��,�`\ - %///,, 1 fllii,�, :nC,7,�•':,'.y„ :ice' h '\ � ``` 1 � ,Is \ �.li , /' ./jj// ; fr r id, �'�lil :�: '` \\ _�� _ , '• t B ,t t I' '� /�'. � \ \ ,, ��,,�/ ,,,,,t , ,,•,�,{,,, ;:;,,,:r=-,^•_ , •_ �r,�„ h � TEST TRENCH BY GOLDER ASSOCIATES (8/97) 9 \ \ \ / �/ ,///,/ Is s'i:;i nN ¢,!,r n n -_ `- �•.�` i t \\ t', �• I \ ./ l TEST BORINGS BY TERRA ASSOCIATES (12/97) -0 �t , , /��/rn/�,/ji/sir/� 1,�;t n!ri 1 n V ��.:\,•. \ ��, a \� , \ \, f J t.w i ~//%/✓/ ',I it n � 8 � Jf_1 �` t ,`qb\ V\` ` `` /'•, !' � I •.arras:. A li �i �\�. „ ', jit. r.�; r m�.r.oweown Jt: '-I. Z i / I ;;� „� � ;�;���e �,a..m�� _I;! ; REFERENCE: .1I-� ' / SITE PLAN PROVIDED BY GOLDER ASSOCIATES lhj,,,`;, ,;l`,� �\ ! i JOB No. 9731212, PLATE 4, DATED 11/97. ,.p `�\♦ ♦ 1 r rr�' ;t Mil',::;N,..t`} ,'l':\'. ,' ,r 9 \r �,.h ;/ r,.;,,Ill7rfiitV'a`` tC;\`?\\• � �`. �� by�� r'g-' •'\\` `� -.•�:': ,. � `'v?tF;_::�,+r=�`:;•?•: ,�,, .�'\�••�-.�f,'tgrti.:tit`'ii» �' NN EXPLORATION LOCATION PLAN TERRA NORTH 405 UPPER AND LOWER SITES V RENTON, WASHINGTON �1,, � •. .•. ASSOCIATES •' '••• Geotechnical Consultants Proj. No.3453 Date DEC. 1997 Figure 2 SLOPE TO DRAIN NEW STRUCTURAL FILL I MAXIMUM SLOPE GRADIENT: 2:1(H:V) — 2 - EXISTING _ - GRADE TYPICAL BENCH - - MAY REQUIRE SUBDRAIN IF SEEPAGE -1,1 AT D . E CONDITIONS ARE INDICATED GRADE AFTER THE REMOVAL OF : . . TOPSOIL AND OTHER LOOSE SOILS KEY CUT AND TOE DRAIN - 4" DIAMETER PERFORATED PIPE ENVELOPED IN 1 cu.ft. 1/2" DRAINAGE GRAVEL . NOT TO SCALE NOTES: 1. SLOPE SHOULD BE STRIPPED OF TOPSOIL AND UNSUITABLE SOILS PRIOR TO PLACING ANY FILL. 2. "BENCHES' SHOULD BE A MINIMUM OF 6 FEET WIDE. 3. "KEY' SHOULD BE MINIMUM 2 FEET DEEP AND 6 FEET WIDE, EXTENDING THE FULL LENGTH OF THE SLOPE FACE. 4. FINAL SLOPE FACE SHOULD BE DENSIFIED BY COMPACTION. 5. PLANT OR HYDROSEED SLOPE FACE TO REDUCE EROSION POTENTIAL. 6. ALL STRUCTURAL FILL SHOULD BE COMPACTED TO 95% OF SOILS MAXIMUM DRY DENSITY PER ASTM D-698 (STANDARD PROCTOR). GENERAL SLOPE FILL DETAIL N®r. TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON otechnical Consultants Proj. No.3453 Date DEC. 1997 Figure 3 12" MINIMUM WIDE FREE—DRAINING GRAVEL SLOPE TO DRAIN 12" 17 EXCAVATED SLOPE _ - (SEE REPORT FOR APPROPRIATE ii INCLINATIONS) COMPACTED STRUCTURAL BACKFILL < 127 OVER THE PIPE 4" DIAMETER PVC 3 BELOW THE PIPE PERFORATED PIPE NOT TO SCALE RETAINING WALL DRAINAGE DETAIL TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. 3453 Date DEC. 1997 Figure 4 Swale for surface drainage control Miraft 5XT Geogrid or equivalent ';reinforcement approved by Geotechnical Engineer (see reinforcing schedule below) 1.5 to 2.5' L 1 o 1.5' 6 . ... Compacted Structural Fill per �, C WSDOT 2-03.3(14)B and 1.5' . Crushed rock filter.. 1.5' material, between 2 and 4 inch size. 1 0' H/3 18 In min \, \ ��i✓i \i \\, \i i`� i'�>Y :\., \i:\`., < Grade at Rockery face Firm undisturbed 3 in. min soil to be verified Keyway12 In. by Soil Engineer min. 4 in. minimum diameter drain pipe surrounded by gravel meeting WSDOT Keyway should be sloped 9-03.12(2) specifications down towards the face being protected GEOGRID REINFORCING SCHEDULE Rockery Height No. of Grid Layers Grid Length (L) 4' 2 4' 6' 3 5' 8' 4 6.5' NOT TO SCALE NOTE: Penetrations through geogrid for installation of guardrail can be made. Grid should be exposed and cut cleanly and not ripped, torn or pulled by action of drilling auger. Cut dimension should not exceed 12 inches. REINFORCED FILL/ROCKERY CROSS-SECTION gorGeotechnical TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Consultants Proj. No.3453 Date DEC. 1997 1 Figure. 5 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING North 405 Upper and Lower Sites Renton,Washington We explored subsurface soil conditions at the site by excavating eight test pits using a rubber-tired back hoe on January 22, 1997. Subsequent this exploration, additional test pits were excavated in August 1997 by Golder Associates, Inc. under a subcontract with our firm. Following their exploration on December 11 through December 15, 1997 in accordance with Golder Associates, Inc.'s recommendations, we advanced three soil test borings using a truck mounted drill rig. Test pits excavated at the site, both by Terra Associates, Inc. and Golder Associates, Inc. extended to depths of 10 to 18 feet below existing surface grades. Test borings were drilled to depths of 16 to 59 feet below existing grade. The approximate location of the field explorations are shown on attached Figure 2. Logs for Test Pits TP-1 through TP-8 and Test Borings B-1 through B-3 are presented on Figures A-2 through A-10. A description of soil conditions encountered at the test trenches excavated by Golder Associates, Inc. is summarized in narrative format in their reports attached in Appendix B. Engineering geologists from Terra Associates, Inc. and Golder Associates, Inc. conducted the field explorations and classified soil conditions encountered. Our representative maintained a log of each test pit, obtained representative soil samples, and observed other site features pertinent to the proposed construction. All soil samples were visually classified in accordance with Unified Soil Classification System (USCS) described on Figure A-L Representative soil samples obtained from Test Pits TP-1 through TP-8 and Borings B-1 through B-3 were placed in closed containers and taken to our laboratory for further examination and testing. The moisture content of each sample was measured and is reported on the test borings and test pit logs. Atterburg limits evaluating the plasticity characteristics of two representative samples were also performed. These test results are also recorded on the test pit logs opposite the samples on which they were performed. Grain size analyses were also performed on three of the samples,the results of which are shown on Figures A-11 and A-12. MAJOR DIVISIONS LETTER TYPICAL DESCRIPTION SYMBOL Clean GW Well-graded gravels, gravel-sand mixtures, little or no GRAVELS Gravels fines. C (less than GP Poorly-graded gravels, gravel-sand mixtures, little or O N More than 5% fines) no fines. U) 'Y) 50% of coarse Silty gravels, gravel-sand-silt mixtures, non-plastic � 0 .L m fraction is Gravels GMfines. W larger than No. with fines CU•— 4 sieve Z E GC Clayey gravels, gravel-sand-clay mixtures, plastic fines. 0 0 N Clean SW Well-graded sands, gravelly sands, little or no fines. o SANDS Sands � Z (less than Poorly-graded sands or gravelly sands, little or no c C More than 5% fines) SP fines. co Oa 50% of coarse o fraction is SM Silty sands, sand-silt mixtures, non-plastic fines. U smaller than Sands No. 4 sieve with fines SC Clayey sands, sand-clay mixtures, plastic fines. GO Inorganic silts, rock flour, clayey silts with slight _J •f-o SILTS AND CLAYS ML plasticity. 0 CL Inorganic clays of low to medium plasticity, (lean clay). E o a) Liquid limit is less than 50% o Z. OL Organic silts and organic clays of low plasticity. Z Lea) Q C a)CU M H Inorganic silts, elastic. `m SILTS AND CLAYS CH Inorganic clays of high plasticity, fat clays. Z 0 (nn Liquid limit is greater than 50% OH Organic clays of high plasticity. HIGHLY ORGANIC SOILS PT Peat. DEFINITION OF TERMS AND SYMBOLS w Standard Penetration 2 OUTSIDE DIAMETER SPLIT Q Density Resistance in Blows/Foot I SPOON SAMPLER X Very loose 0-4 2.4" INSIDE DIAMETER RING SAMPLER `o Loose 4-10 OR SHELBY TUBE SAMPLER Medium dense 10-30 z Dense 30-50 1 WATER LEVEL (DATE) < Very dense >50 Tr TORVANE READINGS, tsf Standard Penetration Pp PENETROMETER READING, tsf gConsistency Resistance in Blows/Foot DID DRY DENSITY, pounds per cubic foot U Very soft 0-2 LL LIQUID LIMIT, percent `o Soft 2-4 F. Medium stiff 4-8 PI PLASTIC INDEX J Fn Very stiff stiff 1g13 N STANDARD PENETRATION, blows per foot Hard >32 UNIFIED SOIL CLASSIFICATION SYSTEM TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-1 Test Pit No. TP-1 Logged by: KPR Date: 1/22/97 Depth USCS/ Graph Soil Description W 0 OL TOPSOIL/FILL: Dark brown organic sandy SILT,very soft, moist. 1 CH Light gray-brown, mottled CLAY, fractured with original laminated structure,stiff(qu=1.5tsf), moist, medium plasticity. 37.1 5 Light gray, mottled silty CLAY with siltstone and coal inclusions, CL stiff(qu=1.5 tsf),fractured texture, moist, low plasticity. 35.5 Black COAL,fractured, moist,very soft. _ 10 Gray very fine grained SANDSTONE, widely-spacedfractures, '/ ' hi hl weathered soft moist. Test pit terminated at 12 feet. Light and moderate perched groundwater seepage observed at 2 feet and 15 10 feet respectively. No caving. Test Pit No. TP-2 Logged by: KPR Date: 1/22/97 Depth USCS/ W Gra h Soil Description OL SM TOPSOIL/FILL: Dark brown organic silty sand with few gravel inclusions and occasional buried wood, loose, moist. 33.9 ML Brown, mottled sandy SILT with clay, stiff(qu=2.0 tsf), moist, 28 1 low plasticity. 5 Gray-brown silty very fine SAND with gravel,occasional cobbles, and clasts of highly weathered sandstone,very dense, moist. SM (Glacial Till) 10 16.0 Test pit terminated at 11 feet. Very light perched groundwater seepage at 4 feet. No caving. 15 TEST PIT LOGS TERRA 405 NORTH UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-2 Test Pit No. TP-3 Logged by: KPR Dater 1/22/97 Depth USCS/ Graph Soil Description W OL TOPSOIL: Dark brown organic clayey silt,very soft, saturated. 1 CL Gray, mottled silty CLAY, fractured, stiff(qu=1.0 tsf), moist, low to medium plasticity. 35.6 5 Brown to blue-gray, mottled clayey SILT with occasional organic fibers, laminated, very stiff to hard (qu=3.0 tsf), moist, medium LL=59 MHI plasticity. 45.6 PL=35 PI=24 1 Gray, mottled silty fine SAND with few gravel inclusions, occasional 10 SM I cobbles and rare 24 inch boulders, dense, wet to saturated. (Till-like) 24.2 Test pit terminated at 12 feet. Ponded water at surface. Moderate groundwater seepage at 8 feet. No caving. 15 Test Pit No. TP-4 Logged by: KPR Date: 1/22/97 Depth GSCS/a Soil Description W 0 PT TOP OIL. SM Red-brown (oxidized) silty fine SAND, medium dense, moist, 17.2 com-pletely weathered sandstone). ag Light gray to orange(oxidized layers) fine SAND with silt, dense, �F,; 5 moist becoming saturated at 8 feet(completely weathered 13.9 sandstone). "SP-SM 10 1 -= Gray to orange (oxidized zones) highly weathered SILTSTONE, 19.1 soft bedding structure occasional fractures moist. Test pit terminated at 13 feet. 15 Heavy perched groundwater seepage at 8 feet. No caving. TEST PIT LOGS TERRA 405 NORTH UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-3 Test Pit No. TP-5 Logged by: KPR Date: 1/22/97 Depth USCS/ Graph Soil Description W 0 A A pT A TOPSOIL: Dark brown organic sandy silt,wet. Tan to orange (oxidized) silty fine SAND with trace gravel, medium 23.2 dense to 4 feet becoming dense, moist to wet. (completely SM weathered sandstone). 5 • • • Brown to orange-brown (oxidized stains)SANDSTONE, highly • • • • • • weathered, bedding structure,thin coaly seams,very fine grained, 10 . . soft, moist. 19.8 Test pit terminated at 11 feet. No groundwater seepage or caving observed. 15 Test Pit No. TP-6 Logged by: KPR Date: 1/22/97 Depth GSa Sh Soil Description W 0 (0 to 8 inches TOPSOIL) Brown silty very fine to medium SAND with clasts of sandstone, 31.4 SM 4 foot boulder at 4 feet, disturbed texture, dense, moist 5 becoming saturated at 6 feet. _ Yellow-tan fine-grained SANDSTONE, massive, highly weathered, 15.6 .. . . . . . . soft, moist. 10 Test pit terminated at 9.5 feet. Moderate perched groundwater seepage observed at 6 feet. No caving. 15 TEST PIT LOGS TERRA 405 NORTH UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 I Date DEC. 1997 1 Figure A-4 Test Pit No. TP-7 Logged by: KPR Date: 1/22/97 Depth USCS/ Graph Soil Description W 0 OL FILL: Dark brown organic silt with clay, soft, moist, low plasticity. �r�r MH Gray, mottled clayey SILT fractured,very stiff, (qu=2.25 tsf), LL=60 moist, medium plasticity. 28.3 PL=41 5 PI=19 Brown-gray, mottled sandy SILT,very fine sand, medium dense, non-plastic, wet to saturated. 1 MLI 26.9 - IT 10 -__--== Dark aray SILTSTONEfractured,moderately weathered. moist. Test pit terminated at 10.5 feet. Perched moderate groundwater seepage at 8 feet. No caving. 15 Test Pit No. TP-8 Logged by: K.PR Date: 1/22/97 Depth GsaS/ h Soil Description W 0 FILL: Dark brown organic silt with clay,soft, moist, low plasticity. OL 21.1 t- becoming mottled CLAY,fractured,thin laminae, stiff(qu=2.0 tsf), medium plasticity. 25.7 5 s ery fine to medium SAND with gravel, clasts of weathered one and occasional 2 foot boulders,dense,saturated 15.8 moist at 7 feet. 10 Test pit terminated at 10 feet. Very light groundwater seepage and caving observed at 6 feet. 15 TEST PIT LOGS TERRA 405 NORTH UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-5 Boring No. B-1 Logged by: ABK Date: 12/15/97 Approximate Elev. Consistency/ a (N) Moisture Soil Description Relative Depth E Blows/ Content Density (ft.) ft. N Note: Drill pad cut 2 feet below existing grade. FILL: Brown silt,scattered wood pieces and organics, moist. Very Soft 2 5 FILL: Gray, gray-brown and rust-mottled silt, scattered wood and organics,with 8 laminations of sandy silt, increasingly Loose 1 sandy and more till-like with depth, moist. Stiff 10 15 FILL: Brown silt,very moist. Medium Stiff 6 Sampled coal and wood pieces. 20 Loose Z 10 25 Bedrock: SANDSTONE, gray. Hard = 50/4" Boring terminated at 28 feet. Note: Poor recovery. BORING LOG TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-6 Boring No. B-2 Logged by: ABK Date: 12/15/97 Approximate Elev. Consistency/ a (N) Moisture Soil Description Relative Depth E Blows/ Content Density (ft.) U) ft. N Organic Silt Topsoil,trace to little clay, Soft moist to very moist. Gray, gray-brown and rust-mottled Very clayey SILT, some dark orange staining, Stiff Moist. 23 Orangish-brown SILTY SAND with 5 GRAVEL,fine to medium, few bedrock Medium clasts,very cobbly with difficult drilling Dense around 6 feet,wet at 8 feet. Z 33 Orange-brown and rusty CLAYEY SILT, 10 scattered pieces of coal, moist, 1/4 inch lamination of dark brown organics at 9 Hard feet. 50/6" Gray CLAYEY SAND to SILTY SAND, 15 fine, moist.Water perched at about Very 12 feet. Dense Gray 50 , partially laminated with organics, (Bedrock). Seam of coal 20 encountered at 19 feet. Hard /4" Continue with Rock Coring Log on next page... BORING LOG TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-7 Rock Coring Log B-2 Project Feature: Elevation Driller/Equipment: Geoboring Start Date Sampler/Method: Cable Tool Finish Date Coordinates: Hole Diameter Rock Mass PL Elev. Depth Box Run%Rec./Graphic Classification and Rating or Remarks (feet) # #. RQD Log Physical Condition RMRJ Q UCS' End of au er and SPT sampling. Bedrock, no coring. 25 1 100/55 BEDROCK: Sandstone, gray,fine-grained, soft to medium hard,fractures with average apparent dip of 15 to 35 degrees, some are coal-filled or organic-filled. 30 2 100/60 Coal from 32 to 33 feet. 1 35 3 100/80 Coal from 35 to 37 feet. Interbedded coal and sandy clay from 39 to 40 4 40/40 49 feet. (Note: no recovery in run#5) 2 Circulation loss from 39 to 49 feet. 45 5 Oro NA 50 'Rock Strength Tests (in psi): Logged by: ABK PL= Poiat Load Test UCS = Unc(p6ned Compressive Strength LLUU ROCK CORING LOG TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-8 Rock Coring Log B-2 Project Feature: Elevation Driller/Equipment: Geoboring Start Date Sampler/Method: Cable Tool Finish Date Coordinates: Hole Diameter Rock Mass PL Elev. Depth Box Run%Rec./Graphic Classification and Rating I or Remarks (feet) # # RQD Log Physical Condition RMRJ Q UCS` 50 6 90/80 3 Interbedded coal and sandy clay from 53 to 55 feet. 55 7 100/80 4 60 Boring terminated at 58.9 feet. 65 70 75 'Rock Strength Tests (in psi): Logged by: ABK PL= Poiat Load Test UCS = UncgoAned Compressive Strength Lu ROCK CORING LOG TERRA NORTH 405 UPPER AND LOWER SITES RENTON, WASHINGTON ASSOCIATES Geotechnical Consultants Proj. No. T-3453 Date DEC. 1997 Figure A-9 Boring No. B-3 Logged by: ABK Date: 12/15/97 Approximate Elev. Consistency/ a (N) Moisture Soil Description Relative Depth E Blows/ Content Density (ft ) ft. (/o) Organic Brown Silt Topsoil Soft Gray and gray-brown mottled SILT, hairline fractures and scattered 15 organics, moist. 5 Very Stiff to Hard Scattered seams of rocks and clasts, silty sand, rusty spots, pocket of coal. 28 10 Scattered coal seams and dark brown organics soil. 48 Bluish-gray SILTY SAND, fine to Dense medium,wet. 15 Boring terminated at 16 feet. Refusal on large boulder. Redrilled 5 feet away and met with refusal at 8 feet. BORING LOG &0A TERRA NORTH 405 UPPER AND LOWER SITES ASSOCIATES RENTON, WASHINGTON Geotechnical Consultants Proj. 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APPENDIX B GOLDER ASSOCIATES,INC.REPORTS 6 � Golder Associates Inc. 4104-148th Avenue,N.E. = GO���r Redmond,WA 98052 V V Telephone(425)883-0777 c Ass® S Fax(425)882-5498 August 22,1997 Our ref: 973-1212 Terra Associates,Inc. 12525 Willows Road,Suite 101 Kirkland,WA 98034 ATTENTION: Ted Schepper RE: PRELIMINARY ABANDONED MINE ASSESSMENT Dear Ted: Please find attached a copy of the preliminary report written by SubTerra.Please note that SubTerra are waiting for test pit photographs to complement this report. The major concerns are: 1) Lack of topographic control for location of topographic features and test pits etc. These data are needed to better assess the relationship between the geology and topographic features. 2) TT#1 found evidence for a mine opening. Due to its elevation,this feature would imply a deeper coal seam than that viewed in TT#5 where a shallow un- worked coal seam,situated about 10 feet below the surface was found. This seam appears to have an apparent dip of approximately 100 to the north or northeast rather than 350 indicated on the geological map. 3) Features hidden beneath the blackberries.Two sinkholes were observed near the north west edge of the Parcel 3. The smaller hole (TT#4) was about 5 feet in diameter,2 foot deep with vertical sides,i.e.,fairly fresh. A rusty,steel, 1 inch pipe was observed in the northern face of the hole. The second sinkhole was much older and longer (--20 feet by--10 feet) with gently sloping sides. Removal of the bush this weekend by Opus may reveal other features of importance. The work has answered some questions but raised a few more.To would advise the following actions; • Observe the site after the bush has been removed. • Have a surveyor complete a map of the site complete with the locations of the most recent test pits. OFFICES IN AUSTRALIA,CANADA,GERMANY,HUNGARY,ITALY,SWEDEN,UNITED KINGDOM,UNITED STATES August 22,1997 2 973-1212 • Investigate by drilling whether there is a deeper coal seam than the one we followed in TT#3. These issues can be discussed in the meeting that you are planning for next week Please advise me of its timing in due course. On a budgetary note,the test pitting took three hours longer than estimated due to the number of features revealed beneath the blackberries and the difference in the dip of the coal seam to the geological record. These costs amount to an increase of approximately$700 which you were able to verbally approve during yesterday's telephone conversation. This amount added to the approved budget to date bring the total to$7,525. The budget must be about 95% complete at the time of writing. I look forward to your reply after you have had a chance to review the preliminary report. Sincerely, ' GO ER IATES INC. Ian B' op Se * r Geophysicist I /psry 08M bl.doc Golder Associates Mining Engineering Civil and Mining Rock Mechanics Mine Subsidence SubTerra Inc. Solid Waste Disposal Tunnel Engineering Concrete/Shotcrete Technology Construction Bid Documents 21 August, 1997 Dr. Ian Bishop Associate Golder Associates, Inc. 4104 148th Avenue NE Redmond, WA 98052 Re: Visual Site Reconnaissance and Preliminary Abandoned Mine Assessment Proposed Oaksdale Business Park in Renton, Washington Dear Dr. Bishop: At your request we have completed a visual site reconnaissance and preliminary, or Phase 1, abandoned mine assessment of the above subject site. The scope of work contained in our August 11, 1997 proposal included: 1. Examination of abandoned mine plans available from the Washington State Department of Natural Resources (DNR). We understand that you already have the pertinent maps, however, we will review our fiche to determine whether there are additional relevant records. 2. Digitizing the most recent plans for incorporation in an AUTOCAD drawing of the site. 3. Retrieval and examination of the historical aerial photographs of the site. 4. A preliminary site reconnaissance to observe current conditions. 5. Evaluation of supplemental data and information (e.g., historical production records) in our possession to determine the potential for the presence of additional workings beyond those shown on the mine plans. 6. Planning a preliminary site investigation program designed to confirm or refute the presence of additional workings. 7. Preliminary evaluation of potential impacts of the abandoned mines on the developable site area. This scope was subsequently extended to include a limited site exploration program utilizing a trackhoe to dig up to eighteen (18)feet deep exploratory trenches. This program was intended to confirm the presence of a coal seam dipping at 35 degrees and striking east-west across the site for input to planning a more extensive, geophysical exploration program. 8003 118th Avenue N.E., Kirkland, WA 98033 (206) 827-8003 FAX (206) 889-8150 ',SubTerra, Inc. Golder Associates 8/21/97 Monster Road Geophysical Investigation Phase I Approach As part of our assessment, we reviewed a preliminary geotechnical study by Terra Associates, Inc., dated February 15, 1997, in which the presence of abandoned mine workings was noted. In addition to the data from the Terra report, a regional geologic map, archival mine records, historical aerial photographs dating from 1936, and a detailed 1990 topographic map of the western portion of the site, prepared by BRH, Inc., were used in completing our preliminary assessment and the preliminary plan of the site shown in Drawing 1. Preliminary investigations indicate that the underground workings located on the subject site were probably part of the Black River mine, which had recorded production during the 1890's, but no further information or mine maps are available. Another abandoned mine, the Diamond Mine is located to the east of Monster road at the approximate location shown on Drawing 1. This mine was worked from 1927 until 1931 and produced approximately 6,000 tons of coal according to mine records maintained by the Division of Natural Resources. Additional un-recorded production occurred after 1890, as evidenced by the present condition of the on-site workings and the visibility of on-going excavation in the 1936 aerial photograph. The location and trend of caved workings or surface cuts and spoils piles that were visible on the aerial photographs, were also identified during the visual site reconnaissance. The approximate location of this area is shown on Drawing 1. Because no mine maps or production records were available, the extent of the workings and undermined areas can only be inferred. Additional information has been gleaned from a limited subsurface exploration program during which approximately 500 linear feet of exploration trench was dug ranging from 4 to 18 feet in depth. A summary of the results of the Phase I study and limited site exploration is presented in the following paragraphs. Results of the Preliminary Site Reconnaissance A brief description of the site was provided in the February 1997 report by Terra Associates, and will not be duplicated here. The focus of our site reconnaissance was along the western edge of the approximate 150 foot tall bedrock hill that rises above the Green River/Duwamish floodplain and forms the core of the subject parcel. The west side of the subject bedrock hill is characterized by steep forested slopes with an approximate forty-foot tall near vertical cut adjacent to Burlington Northern railroad tracks at the southwest portion of the bedrock hill. An overgrown road grade ran in a north-south direction along the west side of the bedrock hill from the railroad tracks to a point about 500 feet north of the tracks. At the northern end of the road an extensive area of modified land was encountered. This area of modified land was visible in the 1936 air photo as an extensive west-north-west trending excavation at this location. This site was also displayed as a coal prospect in a 1948 regional geologic map of the area., The modified land consisted of an east -west trending topographic depression into the hill slope that measured about 150 feet east west by about 80 feet north-south. 2 - SubTerra, Inc. Golder Associates 8/21/97 Monster Road Geophysical Investigation The depression contained local spoils that contained good quality coal. The slopes along the depression contained loose soil with coal fragments. Evidence of ongoing-raveling and soil creep along these slopes was seen in the form of bowed and tilted trees. What appeared to be the main spoils pile from these workings extended to the west and downslope of the depression a distance of about 120 feet down the floor of the regional floodplain. This apparent spoils pile was covered with heavy brush and was not assessed >, during the field reconnaissance. A continuation of the overgrown road grade extended in a southeasterly direction towards the top of the hill and a broad north sloping area that was clear of trees but covered with thick blackberries: Five test pits had been completed in this area during the February 1997 ; Terra and Associates study, but no evidence of the test pits could be found. We were particularly interested in locating test pit TP-1, which encountered coal to the east of the ' excavated area. Our Initial Understanding of the Geology and Coal Seams Our initial understanding of the geology of the site was based upon our visual reconnaissance, data from the Terra and Associates test pits, and review of available geologic literature. In general, the geology of the site appeared to consist of a thin veneer of flat lying glacial sediments that were deposited atop relatively steeply dipping Eocene age (about 50 million years ago) volcanic and sedimentary units that are part of the Puget Group. At the subject site, the Puget Group rocks are represented by the volcanic related Tukwila formation and sandstone and siltstone of the Renton Formation. The Renton Formation is the host of a number of coal seams, one of which underlies the subject site, as discussed below. The glacial sediments on the property were deposited about 15,000 years ago during the Vashon Stade of the Frazer glaciation. During this period a continental ice sheet, up to about 3,000 feet thick in the Renton area, occupied much of the area known as the Puget Lowland. At the project site, a dense, unsorted mixture of sand silt and gravel was deposited at the sole of the advancing glacial ice sheet and these sediments are referred to as lodgement till. The till was consolidated to a dense state by the weight of the ice and typically is characterized by relatively high strength and relatively low permeabilities. Based on the visual reconnaissance and test pit data, the till is estimated to be less than about 10-15 feet thick across the site. Across the northern and western portion of the site the till is apparently absent, as the sandstone was encountered at the surface in these areas. The Tukwila formation is exposed in the railroad cut along the southwest portion of the parcel, and has previously been mapped by others elsewhere in the south half of the site. This formation is characterized by andesitic lava flows and breccia, with conglomerates and arkosic sandstones, that were deposited in a high-energy depositional environment. The Renton formation conformably overlies the Tukwila formation and is characterized by sediments deposited in a meandering stream type environment at the edge of the continent. Interbedded sand and silt and clay were deposited as channel and overbank 3 SubTerra, Inc. Golder Associates 8/21/97 Monster Road Geophysical Investigation (flood) deposits, as the ancient stream channels migrated back and forth across a broad floodplain. The coal seams represent persistent swampy areas along the floodplain, that gradually subsided and allowed accumulating organic matter to be buried and eventually preserved as coal. Based on previous geologic mapping, the coal encountered at the site has been correlated with the Black River Bagley coal seam. Following deposition, both the Tukwila and Renton formations were folded and faulted during the uplift of the Cascade Range. The folding and faulting caused many of the originally flat-lying coal seams to slope (dip) steeply and to locally crop out at the surface. In the area where the surface excavation was encountered, the Black River-Bagley coal seam reportedly trends approximately west-north-west and dips 35 degrees down to the north. The surface expression of the coal seam was therefore interpreted to form a line across the south central portion of Parcel 3 based on available geologic data. Results of the Trenching Program A one day trenching program was carried out to further investigate the site and to provide data for input to the geophysical investigation program. In the absence of survey control and topographic data for Parcel 3, the trenches could only be very approximately located. These very approximate locations are provided on Drawing 1. Highlights of the results of the trenching program are presented below. Test Trench No. 1 was located in an east-west trending depression thought to be a collapsed mine access. Coal and wood fragments were first encountered at a depth of about eight (8) feet. Numerous cut timbers were extracted between 8 and 14 feet and the collapsed outline of a mine entry could be observed on either side of the trench. The approximate alignment of the opening was similar to the line of the syncline axis shown on Drawing 1. A second test pit that was dug to a depth of 14 to 16 feet approximately 20 feet east of TT#1 encountered spoils to a depth of about 14 ft but no evidence of the mine workings. Test Trench No. 2 was located east of TT#1 and was dug approximately 70 feet from the south to the north on a bench immediately below the apparent highwall left by the workings shown in the 1936 aerial photograph. No solid coal seams were encountered, however, coal mine spoils existed to depths of at least 17 feet. An intermittent seepage occurred at the base of the trench at a location approximately east-south-east of the opening observed in TT#1, however, no evidence of collapsed workings was encountered. Native materials were observed in the slopes at the north and south ends of the trench. Test Trench No. 3 was located approximately 100 feet east of TT#2 and was dug from the property line at the Metro fence north approximately 260 feet. This trench encountered what appeared to be Tukwila formation at a depth of about 4 feet for the first 50 feet then graded into the softer sandstone of the Renton Formation. Subsequent inspection indicated that the first 50 feet of trench contained large boulders which were underlain by Renton formation sandstone. Trace coal was encountered at a depth of 14 ft approximately 80 feet from the fence and a continuous 3-4 foot thick coal seam was encountered between 10 and 14 feet deep between 150 and 230 feet from the fence. 4 SubTerra, Inc. Golder Associates 8/21/97 Monster Road Geophysical Investigation Test Trench No. 4 was located just north of the end of TT#3 in a six foot wide sinkhole. No evidence of coal was found in the trench which was deepened to 18 feet. Weak , soft, caving soils were encountered from the top to the bottom of the trench. Test Trench No. 5 was excavated at right angles to TT#3 about 180 feet from the fence to determine the eastwards extent of the coal seam. The coal seam was observed to thin out and disappear in about 15 feet. Test Trench No. 6 was located approximately 200 feet east of TT#3 and was dug from the property line at the Metro fence north approximately 100 feet. No evidence of coal or carboniferous materials was observed in sections of the trench that were dug to depths of 14 feet. Trenching in this area was curtailed so that sufficient time was available for backfilling of all excavated trenches and exploration of the long depression along the property line between Parcels 3 and 4-B. Test Trench No. 7 was located in a north-south depression located approximately along the north-south boundary between Parcel 3 and Parcel 4-B. This depression is approximately twelve feet wide and appears to be a cut that was probably made to explore for coal. Coal with an apparent thickness of about 6 feet was found about 1 foot below the ground surface in the face of the north facing headwall. As the trench was extended towards the north, the apparent dip of the top of the coal was observed to change from about 300 south to about 100 north. Part of the coal seam had been removed in the base of the trench. Test Trench No. 8 was extended south from the start of TT#7 a distance of about twenty feet. The coal seam disappeared just beyond the crest of the slope grading immediately into yellow sand. Interpretation of the Data Without the benefit of production records or mine maps it is difficult to quantify the extent and location of undermined areas. However, we would normally not anticipate that the undermined areas would be large, as a large mine would have more difficulty avoiding a State of Washington law circa 1900, that required all coal mine operators to file an annual mine plan with the state. The extent of the excavation encountered during the field reconnaissance, and the visibility of this excavation in the 1936 photo suggest that some undocumented work took place after the Black River mine was reportedly abandoned in the 1890's. The following interpretations are considered to be very preliminary. Inferred data and information, including geologic contacts, dip, and dip and strike directions are very approximate and based strictly on non-quantitative field observations. 1. Test Trench No. 1 probably encountered the remnants of the 207 ft long Black River mine slope. There is inconclusive evidence that the encountered slope was mined in an easterly direction, however, it was mined at a depth below the coal seam encountered in Test Trench Nos. 3, 7 and 8. There is therefore some potential for a second, lower seam to exist at the site. 5 SubTerra, Inc. Golder Associates 8/21/97 Monster Road Geophysical Investigation 2. A thin, 3 to 4 foot thick coal seam occurs at shallow depth beneath part of the western 100 feet of Parcel 1)�This seam strikes about east-south-east and dips towards the north at between 10'and 200. It is unlikely that this seam would have been mined using underground methods due to its relatively shallow depth. 3. No coal was discovered in areas east of Test Trench No.3. However, trenching was not extended across the marked wetland area due to time constraints and uncertainty regarding disturbance of the marked area. It is unlikely that extensive coal workings underlie this part of the site, however, a relatively inexpensive drilling program would confirm the presence or absence of mineable coal seams at depths beyond those reachable by trenching. 4. The north-south trending depression located approximately on the property line between Parcels 3 and 4-B is believed to be an exploratory dozer cut and may well be the "prospect" mapped and referred to in Warren at al,(1945). 5. Very soft, caving soils underlying developed sinkholes were encountered to depths of 18 feet in the northwest part of Parcel 3. There is no evidence that these sinkholes are associated with coal mining, however, the encountered conditions may pose constraints on site development. It is recommended that Terra Associates conduct additional site investigation in this area. 6. It is likely that the ground west and immediately south of the depression, including the area referred to as the "strip-pit from the 1936 air photo", has been disturbed by mining. This report was prepared for the exclusive use of Golder Associates, Inc., their Client Terra, Associates, and Terra Associates client Opus Northwest, LLC and is considered to be a preliminary investigation of the potential impacts of abandoned mines on the Monster Road Property. We trust that the report is sufficient for your present purpose. Please feel free to call us if you have any questions regarding the enclosed materials. We may be reached at (425) 827-8003. Best Regards Chris D. Breeds President References: Warren, Norburath, Grivetti, and Brown, 1945. The Coal Fields of King County. Provides location of the Diamond Mine and Black River prospects. George Watkin Evans, 1912. Bulletin No. 3, The Coal Fields of King County. Chapter 5 contains a description of the Black River mine. "In the north half of Section 24, T23N, R4E at Black River Junction, a mine was opened in the latter part of the eighties. A small slope was sunk for a distance of 207 feet on Pe bed which dips to the north at 25 degrees. At the r 6 SubTerra, Inc. Golder Associates 8/21/97 Monster Road Geophysical Investigation foot of the slope, the bed flattened considerably, evidently approaching the syncline that lies between this point and the beds that outcrop north of the Columbia and Puget Sound railroad in Section 13. No great amount of work was done here, but the writer is informed that what coal was mined was of good quality. The mine was closed in 1892, and has remained closed since that data." Terra Associates, 1997. Preliminary Geotecnical Study Oaksdale Business Park Renton, Washington. Prepared for OPUS Northwest LLC by Terra Associates, February 15, 1997. Provides a description of the site and location of test pits and observed mine hazards. Schasse, H., Koler, M.L., Eberle, N.A., and Christie, R.A., 1994. The Washington State Coal Mine Map Collection, OFR 94-7, June 1994. Provides mine map locations and mine production information. 7 Golder Associates Inc. 4104-148th Avenue,N.E. __� = Golder Redmond,WA 98052 Telephone(425)883-0777 Associates Fox(425)882-5498 November 26, 1997 Our ref: 973-1212 Terra Associates, Inc. 12525 Willows Road, Suite 101 Kirkland, WA 98034 ATTENTION: Ted Schepper RE: AERIAL PHOTOGRAPH INTERPRETATION,MONSTER ROAD Dear Ted: Following our telephone conversation of Tuesday, November 18, 1997, we understand that your client, OPUS Northwest LLC does not wish to proceed with the complete scope of works for the Phase II abandoned mine assessment at this time. These works were detailed in a change order, dated November 3, 1997(GAI 1997). In particular, OPUS does not wish to commit to drilling a borehole to investigate the potential existence of a second coal seam on the site. Accordingly, this letter report details the tasks completed to date and presents the analysis of the aerial photographs. 1. SUMMARY OF WORK TO DATE The scope of works completed to date include: Phase I 1. Examination of abandoned mine plans available from the Washington State Department of Natural Resources (DNR). 2. Digitization of the most recent plans for incorporation in an AutoCAD drawing of the site. 3. Retrieval and examination of the historical aerial photographs of the site. 4. A preliminary site reconnaissance to observe current conditions. 5. Evaluation of supplemental data and information (e.g. historical production records). 6. Planning a preliminary site investigation program designed to confirm or refute the presence of additional workings. 7. Preliminary evaluation of potential impacts of the abandoned mines on the developable site area. 8. Limited site exploration utilizing a track-hoe to dig eighteen (18) feet deep exploratory trenches. The program was intended to confirm the presence of a coal seam dipping at approximately 35 degrees to the north and striking east-west across OFFICES IN AUSTRALIA,CANADA,GERMANY,HUNGARY,ITALY,SWEDEN,UNITED KINGDOM,UNITED STATES November 26, 1997 2 973-1212 the site for input to the planning of a more extensive exploration program utilizing geophysical or intrusive methods. The Phase I exploration noted in (8) above, revealed a thin 3-4 ft. thick coal seam beneath part of the western 100 feet of Parcel A(a.k.a. Parcel 3) (TT3) and soft caving soils in the northwest part of Parcel A(TT4). The located seam strikes east-southeast and dips between 10 and 20 degrees to the north. An exploration trench dug approximately 200 feet east of the located coal seam did not encounter coal. A second trench (TTl) dug in a hollow on the hillside on the northern edge of Parcel B (a.k.a. Parcel 4B) found evidence for a second coal seam located approximately 40 feet below the seam described above. The preliminary abandoned mine assessment reports should be read in conjunction with this document(Golder Associates, 1997, Sub Terra 1997). 2. PHASE II 2.1. Original scope The original objectives outlined in the change order for Phase H were to delineate areas suitable for 7onstruction, areas that should only be used for parking, and areas that should not be developed,based solely on abandoned mine issues. This was to be accomplished by: 1. Adding features (buildings, earth movement and waste piles) from aerial photographs to the AutoCAD Drawings of the site to better understand the history of the site. 2. Drilling one or two boreholes to investigate whether a second, deeper and workable coal seam is located within the site boundaries. 3. Completion of annotated photographic plates of the test trenches for incorporation in a final report. 4. Preparation of a final report and recommendations for proposed building locations. Items 2 and 4 have not been authorized by the client at the time of writing. 2.2. Annotated photographs of the test trenches Annotated photographs of the test trenches dug by Sub Terra, Inc. are included with this report. The information obtained from these trenches was detailed in the preliminary abandoned mine assessment report presented to you in August. Note that the locations of the test trenches presented in that report were based on measurement from fence lines, and pre-date the detailed topographic survey completed in late October. The updated locations of the test trenches can be seen on the attached plates. The trenches were excavated to confirm the presence and state of a coal seam dipping at 35 degrees to the north. They were not dug or logged for the purpose of soil characterization. Golder Associates November 26, 1997 3 973-1212 2.3. Survey Control Following the submission of the preliminary report, all the blackberries were cleared from Parcel A. This allowed a walk-over surface inspection of Parcel A and the placement of test trench marker flags for the planned topographic survey. During this walkover, the only extra features of interest noted were: 1. A wall footing denoted by a single line of red bricks 120 ft. west of TT4. 2. A gravel track running west from Monster Road, approximately 100 ft. south of northern-most boundary of Parcel A. 3. Concrete foundation slabs adjacent to Monster Road. Bush, Roed &Hutchins, Inc(BRH, 1997) supplied AutoCAD maps detailing the survey control established at the site, the detailed topography and the locations of most of the trenches completed as part of(8) above. The survey markers for test trenches TTl,TT2 and TT8, the northern end of TT6, and the southern end of TT3, were not picked up by the surveyor. The locations of these have been estimated from field measurements and are shown on the plates. The locations of the two sinkholes and a wall foundation are also shown. Note that a small iron pipe was located on the edge of TT4. TT4 investigated the most recent sinkhole. The preliminary report described evidence for the existence of a mine portal in TTL This test trench was dug in an east-west orientated, topographic, depression that cuts into the hillside. Assuming that this was a portal to a coal seam, the elevation of the feature (64 ft.) indicates a deeper coal seam approximately 40 feet below the coal seam viewed in TT3. Without a boring, we can make no comment as to the quality of any coal in this seam or whether it would have been economic to mine. 3. AERIAL INTERPRETATION WORK 3.1. Introduction To better understand the development history of the site, the aerial photographs of the site for the years 1936, 1970 and 1995 were scanned into a computer. These date were then merged with the AutoCAD survey map supplied by BRH. The best-fit results are shown in the following plates: Plate 1. 1936 aerial photograph overlain by site plan Plate 2. 1970 aerial photograph overlain by site plan Plate 3. 1995 aerial photograph overlain by site plan By best fit, we mean that the relative position of the aerial photograph to the survey data has been obtained by stretching the scanned photographic images to optimize their fit relative to the 1997 topographic data set. This process entailed making some assumptions about the positions of Monster Road, the rail track and other features. Golder Associates November 26, 1997 4 973-1212 However, the final fit appears to effectively match the survey data, so any errors in matching the photographs should be of the order of several feet. 3.2. The Diamond Mine This mine was located east of Monster Road. A digitized copy of the mine map supplied by the DNR was overlain on to the 1936 aerial photograph (Plate 1, features labeled-m-). Note that this photograph was taken four years after the last recorded workings in the Diamond mine (DNR 1997). A house and an entrance way, (labeled bunker in the mine plan), were matched to corresponding features on the 1936 photograph. Fitting the mine map to the photograph using these features as reference points produced the result shown in Plate 1. It is interesting to note that the mine portal,digitized from the mine map, correlates well with the end of a linear feature, of similar orientation, located in the photograph. This feature is interpreted as the approach cut running down to the mine portal. This same incised feature is still evident on the 1970 photograph. 3.3. Features in Plot A and B 3.3.1. 1936 photograph. This is the earliest aerial photograph of the site. It shows cultivated field above and below the steep slope separating Parcel A from Parcel B. Within Parcel A, the photograph reveals two major vehicle tracks running east-west from Monster Road and one minor east-west vehicle track to the south. The northern pair of tracks run to a collection of buildings, the largest of which is located 15 ft. north of the sinkholes identified in Phase I. Plate 1 indicates that TT3 runs along the eastern edge of a marked change in the reflectivity of the surface materials. To the east, the surface appears uniform with well defined boundaries,indicating a cultivated field or pasture. West of this line, and east of the edge of the hillside, the surface is dark and patchy indicating a mixture of uncultivated (vegetation) and disturbed ground. The two sinkholes are located in this area. All the areas of disturbed ground are therefore located west of this trench. The incised gully is not visible in this photograph (TT7) although clear on the 1970 photograph (Plate 2). This indicates that the gully interpreted as a prospect trench in the preliminary report was dug after the 1936 photograph was taken. One hundred feet east of TT3 there is a pronounced cut in the hillside, shown by a shadow. A few feet east of this topographic feature, which still exists today, are two parallel features which indicate that the crop, shown by the east west closely spaced lines, is growing more poorly in this part of the field. These features are interpreted as the influence of the foundations from a large pre-1936 building. Foundations can cause this effect by reducing the soil cover, altering the local drainage and creating soils with Golder Associates November 26, 1997 5 973-1212 lower moisture and nutrient content. The brick foundation structure at the north end of this feature (noted during the walkover survey)may be related to part of this structure. The hillside that separates Parcel A and B shows lobes of material interpreted as end- tipped mine spoil spreading down the side of the slope. Most of the surface of these lobes shows significant vegetation which would indicate some years of latency since the bulk of the spoil was deposited. However, there appear to be several areas of disturbed ground (poorly vegetated) which would indicate more recent mining activity. 3.3.2. 1970 photograph. The Diamond Mine buildings are not evident on the photographs. Some of the topographic features such as the feature interpreted as the approach cut are still evident. The bunker road has been widened and extended towards what is now the Metro works. This road appears to pass over the mine portal. All the buildings in Parcel A have been removed and the farming has passed to pasture. Cattle tracks (shown in white) run across the field and down into the old mine workings. The central east-west track is still in use. The photograph indicates that the building that must have occupied the concrete foundation slabs located adjacent to Monster Road must have been built after 1936 but removed before 1970. As noted in 3.3.1, the gully(T77) is clearly visible in this photograph. The land north of Parcel A and B has been re-graded, with the construction of a railway spur and buildings. 3.3.3. 1995 photograph. The Diamond mine site has been completely re-graded and no trace remains of the older mining related features. The top of the hill, south of Parcel A, is now fenced (METRO). Vegetation (blackberries) have encroached across much of the site as the land has fallen into disuse and away from farming. There has been further development of the commercial buildings to the north of both parcels. The hillside on the south western side of Parcel B has been cut back and re-graded. 4. DISCUSSION The aerial photographs cover most of the changes in land use between 1936 and the present day. The history of this use appears to be fairly complete although the building Golder Associates November 26, 1997 6 973-1212 adjacent to Monster Road (Parcel A) was not photographed while erect. From some of the surrounding artifacts present in the field,it is likely that it was a small farm. The incised gully in to which TT7 was placed is not evident on the 1936 photograph, which would indicate that it post dates the photograph. All the remainder of the mining related features (spoil piles, strip mining, tracks etc.) present in the 1936 photograph are situated west of TT3. East of TT3, and west of Monster Road, the ground appears to have been used only for farming. The study has relocated the survey plans for the Diamond Mine with some degree of confidence. None of the recorded workings underlie the site. This letter should be read in conjunction with the preliminary report produced in August (GAI, 1997). At this stage, a full Phase II abandoned mine assessment has not been completed because of the potential for a deeper coal seam beneath Parcel A. We trust that the report is sufficient for your present purpose. Please feel free to call us if you have any questions regarding the enclosed materials. We may be reached at (425) 883-0777. Sincerely, GOLDER ASSOCI-AES INC. Ian Bish h.D. Senior ophysicist David P. Findley Associate IB/DPF/ta 11 Z6 ib l.doc Golder Associates November 26, 1997 7 973-1212 References BRH, 1997. Topographic survey for Opus Northwest: Oakesdale Ave SW&Monster Rd, Renton, King County, Washington. Bush,Roed &Hutchings,Inc., 21st October 1997. DNR, 1997. Letter dated February loth, 1997 from Timothy Walsh (Washington State Department of Natural Resources) to Terra Associates, detailing; 1. Production figures for the mine as reported to the Sate Mine Inspector: year tonnage 1927 120 1928 698 1929 1,434 1930 3,839 1931 195 2. Copy of the mine map for the Diamond mine, scale ---1:30, no date. GAI, 1997. Preliminary abandoned mine assessment, letter dated August 22, 1997 with report from SubTerra. Golder Associates Inc., 973-1212. SubTerra 1997. Visual site reconnaissance and preliminary abandoned mine assessment, proposed Oaksdale Business Park in Renton, Washington. 21 August 1997. Golder associates � w S. r 74•. 1, : 34 J .4Y L 2i'e Ji 4} J rs N rT" ." V }3I 4 'k r } � _ '" rk� '�' x +fir `� �T t•. �� 4'y„}'a•+,��, n�f�;v �`� 41, of f� e ;. "� i�33�y,,• �" � �, ,fix,��. a r r ' ' • •� •• • • • • 0 SubTerra, Inc. Golder Associates, Inc. 11/26/97 Monster Road Geophysical Investigation 1�a n'a5 r �g t« � kirz ,r f x ^3 a: v� Photo A Looking south, coal was encountered at a depth of 10 Photo B Close up of coal and weathered bedrock, looking to 14 feet beneath weathered sandstone and siltstone. South. Plate 3 Test Trench #3 - Coal Seam in the Weathered Renton Formation Project No. 97-26 SubTerra, Inc. Golder Associates, Inc. 11/26/97 Monster Road Geophysical Investigation s.: h,. •�' r"`�ic. " yam ' .1's»�;��,+I...- -AKJ. mdf Photo A Existing sinkhole prior to excavation TT#4. �{' p. i� �^�.`r"'d►'t� "?'so-.. � �: QW e� ^'r ,.r t L. Rn, W Photo B Iron pipe in fill soil of TT#4. Soft fill soil extended to below the 18-foot reach of the trackhoe. Plate 4 Test Trench No. 4 - Existing Sinkhole with Soft Caving Soils. Project No. 97-26 SubTerra, Inc. Golder Associates, Inc. 11/26/97 ` Monster Road Geophysical Investigation y"r,""+♦P` K3!° n>�.r{ p•' � .. c'S'vy�.R'A a"�R+c'�R'�y ' j^�; 1 4 ! ',ad •^a'],` +L )u 'Dt�eyx SFr t •:r�i�. � t„ I a� ,� �` �;� �x.►s•e1*+���-�a+���'�t � . �' r ,��t.�>� Y a f lk g' 4 , F 5 f " rn Photo A Looking SE at junction of TT#5 and TT#3. Weathered Photo B TT#5 Looking East. Coal seam pinches out about clay rich sandstone and siltstone atop coal seam. 15 feet East of TT#3. Plate 5 Test Trench No. 5 - Coal Seam Beneath Weathered Renton Formation. Project No. 97-26 • r sy ".A.Fi ;"�" S � A /x�i '�R*H 'ia}S f�fs�Y'i.�':�.~�! °gyp�dY• �, tZ ;��. ''�+yrs;Ma.+.•'k it &} a,�4 �x � z Ex RVA � k ,STLYxfwi"" h � s`l xc :.a rvgw ,..hIM. N ay W M SubTerra, Inc. Golder Associates, Inc. 11/26/97 Monster Road Geophysical Investigation RIF R . w S pt' Photo A Looking North along old exploration trench, prior to digging TT#7. f: Y -N y , Photo B Looking NW along West side of TT#7 showing zone where coal was extracted and excavation was subsequencly filled. Plate 7 Test Trench No. 7 - Old Exploratoin Trench with Coal Extracted. Project No. 97-26 SubTerra, Inc. Golder Associates, Inc. 11/26/97 Monster Road Geophysical Investigation 71 df Photo A TT#7- Photo looking South. Coal was encountered within about one foot of the surface. N. 511 Tx ='WO r . r a"�'�t� ` tii +ems ✓ ..:k f ar, � '�5�4 ➢4ioAYrit x y:R try` �,,,�. in t:+ �y¢ r '-�E M1 1 Photo B TT#7 - Looking South. Coal terminates abruptly against a fine sand. Plate 8 Test Trench No. 8 - Shallow Coal Seam Pinches Out to the South in Old Strip Pit Area. Project No. 97-26