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HomeMy WebLinkAbout965000026 Geotech AssessmentSHANNON &WILSON, INC · GEOTECHNICAL AND .':.NVIROi',,Itt;IENTAL C~%SULTANTS SEATTLE R:CHLAND PORTLAHD FAIRBANKS ANCHORAGE October 6, 2003 Dr. Raymond P. Miller, P.E. 3235 10th Avenue West Seattle, WA 98119 RE: GEOLOGIC SLOPE STABILITy EVALUATION, MILLER PROPERTY LOT 168 ON KALA POINT DRIVE, KALA POINT, WASHINGTON Dear Dr. Miller: This letter summarizes our observations, conclusions, and recommendations regarding slope stability and development of your property (Parcel No. 965000026) referenced above for a single-family residence. Jefferson County Geologic Hazard Area Maps indicate that the landslide hazard rating of slopes adjacent to the site range from slight to high. As the proposed building location is within a landslide hazard area buffer, we have prepared this report in accordance with the Unified Development Code for Jefferson County to evaluate the potential for slope movement and provide recommendations for development of the site with respect to slope stability. Our conclusions and recommendations are based on observations made during our visit to the site on September 4, 2003, available published geologic, topographic, and soil maps, and an undated site plan provide by Dr. Miller. Preliminary observations and conclusions were provided to Dr. Miller orally upon completion of the site visits. SITE DESCRIPTION The site is located north of Kala Point, near Port Townsend Bay, as shown on Figure 1. Figure 2 shows that the property is between 362 feet and 378 feet long (northeast-southwest). The property is approximately 160 feet wide (northwest-southeast) along the northeast side of the property and narrows'to approximately 74 feet wide along Kala POint Drive along the southwest edge of the property. The approximate location of the proposed residence is also shown on Figure 2. 400 NORTH 34TH STREET' SUITE 100 P.O. BOX 300303 SEATTLE, WASHINGTON 98103 206.632.8020 FAX 206.695.6777 TDD: 1.800.833.6388 21-1-09964-001 Dr. Raymond P. Miller October 6, 2003 Page 2 ~dC~i SHANNON 6WILSON, INC. The topography in the general vicinity of the site includes a steep waterfront slope, a moderately sloping bowl-like depression above the waterfront slope, and a relatively flat upland. The steep waterfront slope is approximately 80 to 100 feet high, is located about 30 to 45 feet northeast of the northeast property line, and slopes up to the west at about 27 to 33 degrees. Near the east comer of the property, a relatively flat upland is located above the steep waterfront slope. However, to the north, a bowl-like depression lies between the steep waterfront slope and the upland. The maximum height of the bowl-like feature is approximately 50feet with side slopes on the order of 20 to 24 degrees. The south end of the bowel is located on the property and extends several hundred feet to the north °n to other properties. Vegetation across the site and the adjacent waterfront slope includes fir, cedar, and madrona trees up to about 2 ½ feet in diameter with lesser numbers of alder and maple trees. Undergrowth includes sword fern, salal, salmon berry and grasses. Within the bowl, most of the trees have been cut, but the stumps and remaining trees appeared to be mostly fir and cedar up to about 2 ½ feet in diameter. Some of the trunks of the trees in the bowl and on the waterfront slope are bowed down hill, which is indicative of shallow soil creep. Soil creep is the slow gradual down slope movement of near surface soils under the effects of gravity and water and occurs on most slopes to some degree. The presence of madrona and salal are indicative of well- drained surficial soils beneath the site. GEOLOGIC CONDITIONS Published geologic maps of the area indicate that the upland portion of the site is underlain by Pleistocene-age (13,500 to 17,000 years old) Vashon Lodgement Till, which is underlain on the slope by Pleistocene-age Vashon Advance Outwash. Vashon Advance Outwash typically consists of sand with lesser amounts of silt and gravel. The advance outwash was depgsited on the pre-existing land surface, in front of the continental Vashon Stade ice sheet that advanced from Canada across the Puget Sound region approximately 17,000 years ago. Lodgement till is typically an unsorted mixture of clay, silt, sand, and gravel with occasional cobbles and boulders that was deposited directly beneath the ice sheet as the glacier advanced over the area. The Vashon Lodgement Till was deposited directly beneath the Vashon Stade ice sheet that covered this area approximately 13,500 to 17,000 years before present. The ice sheet that overrode the till and the underlying soils (including the advance outwash) is estimated to be on the order of 2 ~-l-0o~o,00]-u/wraa 21-1-09964-001 Dr. Raymond P. Miller October 6, 2003 Page 3 SHANNON &WILSON, INC. 3,000 to 4,000 feet thick in this area. Consequently the till and the underlying advance outwash have been compacted to a very dense or hard state. Since the retreat of the glaciers, the upper few feet of the very dense/hard soils have loosened and weathered, and topsoil and/or colluvium have developed at the ground surface. Colluvium is weathered material that has reached its present location due to the forces of water and gravity and is typically found on and at the base of slopes. Subsurface explorations were not performed at this site for this evaluation. However, soils observed in the septic drain field test pits near the east end of the property confirm the presence of Vashon Lodgement Till beneath the upland portion of the site. Specifically, weathered till, consisting of dense, gray, slightly silty, gravelly SAND with scattered cobbles was observed in the test pits between depths of approximately ½ and 1½ feet below the ground surface. Below a depth of about 1V2 feet, the till appeared to be very dense and relatively unweathered. During our site visit, we looked for springs, seeps, and other evidence of near-surface groundwater. Evidence of springs, seeps or other evidence of near-surface water was not observed on the upland portion of the site, the bowl to the north, or the steep waterfront slope. We noted that during our site visit, we were able to walk across most of the upland portions of the site and the bowl on the adjacent property to the north. The steep waterfront slope was inaccessible. Consequently, observations of groundwater conditions on the slope are based on observations made while standing at the top of the slope. CONCLUSIONS AND RECOMMENDATIONS Slope Stability Geologic hazard maps indicate that recent slope movements have occurred along the steep waterfront slope, but do not identify the type of slope movement. Based on our experience in the Puget Sound region, instabilities on waterfront slopes can generally be categorized as either shallow or deep-seated slides. Shallow slides typically involve movement of the upper topsoil, colluvium or weathered soil on or near a slope and are usually the result of an oversteepened condition (often caused by wave erosion at the toe of the slope) and saturation of the sufficial soils. When deep-seated slides involve the underlying very dense and/or hard soils, it is often the 21-1-09964-1301-L 1/wp/lkd 21 - 1-09964-001 Dr. Raymond P. Miller October 6, 2003 Page 4 '5 SHANNON &WILSON, INC. result of perched groundwater or thin sandy seams with relatively high groundwater pressures and gradients within the.geologic unit. There is some evidence of relatively shallow slope movements on scattered areas of the steep waterfront slope. However, based on the size of the trees generally on the waterfront slope, these shallow slope movements would appear to be relatively infrequent (e.g., several tens of years between recurrence of shallow slides at the same location); and given the distance between the proposed residence and the steep waterfront slope (i.e., 135 feet or more), it is our opinion that shallow slides on the steep waterfront slope present a relatively low risk to the proposed residence. With regard to deep-seated slope instability, the large bowl-like depression on the north comer of the property and extending farther to the north may be the scarp of a prehistoric deep-seated landslide, now removed and no longer active. The presence of relatively 'large trees (and stumps) within and immediately down-slope of the bowl and the relatively smooth ground surface within the bowl suggest that this may be a relatively old slide scarp on which no significant movement has occurred at least within the last few hundred years. As such, the potential for deep-seated soil movement on the slope of the subject property can be considered, relatively low, in our opinion. It is likely that the topographic and/or groundwater conditions that may have caused the deep-seated slope movement are no lOnger present. The most significant risk posed to the proposed structure may be from movement of shallow topsoil and/or colluvium that have formed within the bowl over the years. However, based on the relatively gentle slopes within the bowl, it is our opinion that the risk posed by shallow soil movements within the head scarp is low. While in our opinion the risk posed by potential shallow or deep-seated slope instability is relatively low, please note that there is some risk of future instability (shallow or deep-seated) present on all hillsides, which the owner must be prepared to accept. Such ihstability could occur because of future water line breaks/leaks, uncontrolled drainage, unwise development in adjacent areas, or other actions or events on a slope that may cause sliding. The following provides further discussion of risk reduction measures that may be effective at this site. Provided that the risk reduction measures discussed in this letter are implemented, it is our opinion that the proposed develo'>ment will not adversely impact the stability of adjacent properties. 2 l- 1-09964-00 I-LI/wp/lkd 21-1-09964-001 Dr. Raymond P. Miller October 6, 2003 ~ ~,.,- ~ ~: Page 5 SHANNON ~WiLSON, INC. Measures to Reduce the Risk Posed by Slope Movement In general, the risk of soil movement on a slope can be reduced by not oversteepening a slope (e.g., do not excavate the toe of a slope or place side cast fill at the top) and not increasing the weight on a slope (e.g., do not place yard debris or fill on or at the crest of a slope). The risk of soil movement on a slope can also be reduced by maintaining a slope as dry as possible (e.g., locate septic drain fields away from slopes, route roof downspouts and yard drains away from slopes, and minimize the amount of surface water that could flow down slope faces), and maintaining a vegetative cover on slopes. The following provides additional recommendations to reduce the risk of soil moVement. Building Setback The measures discussed above may reduce the risk of soil movement on a slope. One of the most cost-effective measures to reduce the potential impact of slope movement is to provide an adequate building setback so that if soil movement on the slope does occur, the hazard to the structure is minimal. An appropriate setback is a function of the rate or risk of slope movement (regression rate), the design life of the structure, and the risk the owner of the structure is willing to assume. In general, the slopes of the bowl-like feature in the vicinity of the proposed residence are significantly flatter than the angle of repose of the underlying till or advance wash and are near the angle of repose of the topsoil and colluvium weathering from the underling very dense or hard soils. In our opinion, a minimum horizontal distance between the outside edge of the proposed residence footing and the edge of the break in slope (at the same elevations) of 15 feet would be adequate for this site. In order to achieve this minimum recommended horizontal distance for the proposed building location, the building foundations nearest the bowl (northeasterly comer) will need to extend to a depth of about 7 feet below the present ground surface. This can be accomplished by stepping down the foundation wall and footings in this area. This minimum horizontal building foundation setback is illustrated on Figure 3. We note that at this elevation, it is anticipated that the foundation subgrades should consist of very dense or hard glacially overridden soils, which should provide adequate bearing for spread footing foundations to 21-1-09964-00 l-L1/wp/lkd 21 - 1-09964-001 Dr. RaymOnd P. Miller October 6, 2003 Page 6 SHANNON 6WILSON, INC; support the residence. At this location, the residence would thus be setback approximately 135 to 145 feet from the northeast-facing steep waterfront slope. Drainage In general, reducing the amount of water entering and discharging onto the slope can reduce the risk of slope movement. Drains should be constructed and maintained to collect water from impermeable surfaces on the property (e.g., roof, decks, patios, and driveways) and directed in a tightline to a sUitable discharge point. Upon reviewing the site conditions and various options for discharge (including upland discharge) it is our opinion that the road ditch along Kala Point Drive (see Figure 2) or an infiltration trench at the southwest portion of the property would provide a suitable discharge point without significantly impacting the stability of the slopes on the site or increasing the surface water discharge or sedimentation to adjacent properties beyond pre-development conditions. A sump and pump may be required to convey the water collected in the vicinity of the building to the discharge point. In addition to surface drainage, we recommend that footing drains be installed around the perimeter of the building to improve soil drainage in the immediate vicinity of the structure. Footing subdrains should consist of slotted, 4-inch diameter minimum, plastic pipe bedded in washed, 3/8-inch pea gravel. Typical installation details for these drains are shown in Figure 4. Figure 4 also includes subdrainage and foundation wall backfill recommendations. On-site soils would not be suitable for use as drainage sand and gravel. Note that the perimeter subdrain invert should be located at least 18 inches below the lowest adjacent grade. Roof or other drains should not be connected to the footing subdrains. The discharge from footing drains should be routed by means of a tightline to a suitable discharge point as previously discussed. All outside grades should slope away from the residence. Based on our understanding of the limited, single-residence development of this property, it is our opinion that the anticipated discharge of roof and footing drains as outlined above will not significantly affect the pre-development drainage conditions on the adjacent properties. Impermeable surface around the residence (e.g., paved drives) should be minimized to reduce potential changes in the existing site drainage characteristics and impacts on adjacent sites. 21-1-09964-001-LI/wp/lkd 21-1-09964-001 Dr. Raymond P. Miller October 6, 2003 Page 7 SHANNON ~WILSON, INC. Erosion Hazard We note that according to published USDA soil maps, surficial soils on the site are classified as Whidbey gravelly sandy loam on 0 to 15 percent slopes. The USDA maps indicate that these soils are slightly to moderately erodable. To reduce the potential for soil erosion and associated hazards, the following wet weather earthwork recommendations are presented. Provided that these wet weather earthwork recommendations and prudent construction practices are used, it is anticipated that the future earthwork for the proposed development will not significantly affect soil erosion and associated hazards on the site. Wet Weather Earthwork The on-site silty soils are susceptible to changes in moisture content, and could become muddy and unsuitable if wet and/or subjected to construction traffic. The following recommendations are applicable if earthwork is to be accomplished in wet weather or in wet conditions: Fill material should consist of clean, granular soil, of which not more than 5 percent by dry weight passes the No. 200 mesh sieve, based on wet-sieving the minus 3A-inch fraction. Any fines should be non-plastic. The ground surface in and surrounding the construction area should be sloped and sealed with a smooth-drum roller to promote runoff of precipitation away from work areas and to prevent ponding of water. Earthwork should be accomplished in small sections to reduce exposure to wet conditions. If there is to be vehicular traffic over the exposed subgrade during construction, the subgrade should'be protected with a compacted layer (generally 8 inches or more) of clean crushed rock. The size or type of equipment may have to be limited to prevent soil disturbance. Where loosened soil may be exposed to moisture or uncompacted, a smooth drum vibratory roller, or equivalent, should be used to seal the surface where practicable. Soils that become too wet for compaction should be removed and replaced with clean crushed rock. 21-1-09964-001-L1/wp/lkd 21-1-09964-001 OCT t 6 Dr. Raymond P. Miller i ' ~- October 6, 2003 ! ~ Page 8 . '. -~ . . . SHANNON &WILSON, INC. Covering work areas, soil stockpiles, or slopes with plastic, sloping, ditching, installing sumps, dewatering, and other measures should be employed, as necessary, to permit proper completion of the work. Straw bales and/or geotextile silt fences should be aptly located to control soil movement and erosion. Construction Observation With respect to implementing the risk reduction measures outlined in this letter, we recommend that a geotechnical engineer/engineering geologist or their representative observe geotechnically related construction, including drainage installation and building footing locations once they are excavated. The building footing locations should be observed to determine if foundation depths provide the minimum horizontal setback outlined in this letter and to provide recommendations for additional excavation as needed. These observations may appropriately be accomplished by Dr. Raymond P. Miller, P.E., the OWner, who is a licensed professional geotechnical engineer. - ¢ LIMITATIONS The conclusions in this letter are based on site conditions visually observed during our site reconnaissance and inferred from published geologic, Soils, topographic, and hazard maps and assume that observed conditions are representative of the subsurface conditions throughout the site; i.e., the subsurface conditions are not significantly different from those inferred from the site reconnaissance or indicated on geologic maps. If, during subsequent site activities (e.g., construction), subsurface conditions different from those inferred in this letter are observed or appear to be present, we should be advised at once so that we can review those conditions and reconsider our conclusions where necessary. Within the limitations of scope, schedule, and budget, the conclusions presented in this letter were prepared in accordance with generally accepted geologic engineering principles and Practices in this area at the time this letter was prepared. We make no other warranty, either express or implied. This letter was prepared for the use of Dr. Miller in the evaluation of the stability of this site. With respect to possible future construction, it should be made available for information on 21-1-09964-00 I-LI/wp/lkd 21-1-09964-001 Dr. Raymond P. Miller October 6, 2003 Page 9 SHANNON ~WiLSON. INC. factual data only and not as a warranty of subsurface conditions, such as those interpreted from the site visits and discussion-of geologic conditions included in this letter. Please note that the scope of our services did not include any environmental assessments or evaluation regarding the presence or absence of wetlands or hazardous or toxic material in the soil, surface water, groundwater, or air on, or below, or around this site. We are able to provide these services and would be pleased to discuss these with you if the need arises. Shannon & Wilson has prepared the attached, "Important Information About Your Geotechnical Report," to assist you in understanding the use and limitations of our report. We appreciate the opportunity to provide geologic services to you, and are available to answer any questions regarding our observations, conclusions or recommendations contained in this letter. Sincerely, S~ INC. / William J. Perkins, L.E.G. Senior Principal Engineering Geologist WJP:JW/wjp Enclosures: Figure 1 - Vicinity Map Figure 2 - Site Plan Figure 3 - Building Setback Figure 4 - Subdrainage and Backfilling Important Information About Your Geotechnical Report 21-1-09964-001-Ll/wp/tkd 21-1-09964-001 Project Location Washington II 'Piles 24! Airport ~..._.~-~t20 '~ · · 0 1/2 1 Scale in Miles NOTE Map adapted from 1:24,000 USGS topographic map of Port Townsend South, WA quadrangle, dated 1953, revised 1981. POi~T TOWNSEND BAY PROJECT LOCATION ..%* . .:'~ala Point ~..Piles o o Miller Property Kala Point, Washington VICINITY MAP October 2003 21-1-09964-001 I SHANNON &WILSON, INC. I C-eotechnical and Environmental Consultants I FIG. 1 File: I:~Dmfting~211\09964-001~l-1-09964-001 fig 2.dwg Date: 10-02-2003 Author:. CNT Kala Point Drive L = 73.98 R = 320.00 '"-.,. ................. - ..... iii.'"'"""~.'" .j ; "' ...................... ~ ......... ' .............. ~ ...... ' ~.~"""'""..-/' i .... /////' /' .- ....'"~ ..~/ //// /.// I\ ......................................... .~Z? --. ./. //w .... ./..' . ...... ~ Y" / ×./ ,....' ./. ./" ....- ....-' . .... . ! - /. ,. ,, ,/ /, .., ...~ .. .... _,, ......... ~ . ./ ×-/ :.. / ~. t~ .................. / ./ -.- / /f ~ " , / /' /' .." ..-'" . .... ~- ~..~ I w× × ~ /' ×~ ×× I , I..' .× ×' /' ," ./ /× .~ .~ ./ /" ~ ..... . .... I ': ....... -./ ../ / ×' ," /' /' /' .,' ,." ." - .... I · ./// /' ,../ /" ,./ I " " . ~ . I,./.// ...-/ ,/' .../ .,.-"''"/ I ',./'×' ' ~ L ~. 160.00 / .~ S41 ° 38' 31"E / ~ " Approx. Top of Steep Waterfront Slope /- \/~ . . \/- ·.---~?.. . . Depth Vades BI uilding Foundation . ;, '[ ,,; ~~/.~ti/7~ _ 15' (Min.) Horizontal distance between edge of foundation and existing ground surface within the bowl at the same elevation as the bottom of the building foundation Not to Scale Miller Property Kala Point, Washington BUILDING SETBACK October 2003 21-1-09964-001 SHANNON & WILSON, INC. Geotechnical and Environmental Consultants FIG. 3 Pavement or 10" to 15" Impervious Soil Backfill Meeting Gradation Requirements for Structural Fill (See Note 2) Excavation Slope Contractor's Responsibility 6" Min. Cover of Pea Gravel (6" Min. on Sides of Pipe) Subdrain Pipe Sloped to Drain Away from Structure 18" Min. Wall .:.- .~ ;! OCT t 6 :='~¥¥~ !~: ~and&~ .... .-~: .... !': ~".i.!,--..:.-~..,-~::.-'~ : Pea Grovel Damp Proofing Weep Holes (See Note 1) Vapor Barrier Floor Slab o o18" to 4" Washed 4" Min Pea Gravel Not to Scale MATERIALS Drainage Sand & Gravel with the Following Specifications: % Passing Sieve Size by Weight 1-1/2" 100 3/4" 90 to 100 1/4" 75 to 100 No. 8 65 to 92 No. 30 . 20 to 65 No. 50 5 to 20 No. 100 0 to 2 (by wet sieving) (non-plastic) SUBDRAIN PIPE 4" minimum diameter perforated or slotted pipe; tight joints; sloped to drain (6"/100' min. slope); provide clean-outs. Perforated pipe holes (3/16" to 1/4" dia.) to be in lower half of the pipe with lower quarter segment unperforated for water flow. Slotted pipe to have 1/8" maximum width slots. . NOTES Drainage gravel beneath floor slab should be hydraulically connected to subdrain pipe on the down-slope side of the structure only. Use of 2" dia. weep holes as shown is one applicable method. Imported structural fill should consist of-well-graded granular soil with not more than 5% fines (by weight based on minus 3/4" portion) passing No. 200 sieve (by wet sieving) with no plastic fines. Backfill within 18" of wall should be compacted with hand-operated equipment. Heavy equipment should not be used for backfill, as such equipment operated near the wall could increase lateral earth pressures and possibly damage the wall. All backfill should be placed in layers not exceeding 4" loose thickness and densely compacted. Beneath paved or sidewalk areas, compact to at least 95% Modified Proctor maximum dry density (ASTM: D1557, Method C). Otherwise compact to 92% minimum. Miller Property Kala Point, Washington SUBDRAINAGE AND BACKFILLING October 2003 21-1-09964-001 SHANNON & WILSON, INC. Geotechnical and Environmental Consultants FIG. 4 SH I SO IN.C,,: :~ Oeotechnical and Environmental COnsUltants Attachment to and part of Report 21-1-09964-001 Date: October 6, 2003 To: Dr. Raymond P. Miller, P.E. Seattle, Washington IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL REPORT CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS. Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may not be adequate for a construction contractor or even another civil engineer. Unless indicated otherwise, your consultant prepared your report expressly for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended purpose without first conferring with the consultant. No party should apply this report for any purpose other than that originally contemplated without first conferring with the consultant. THE CONSULTANT'S REPORT IS BASED ON PROJECT-SPECIFIC FACTORS. A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of project-specific factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as access roads, parking lots, and underground utilities; and the additional risk created by scope-of-service limitations imposed by the client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report may affect the recommendations. Unless your consultant indicates otherwise, your report should not be used: (1) when the nature of the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a refrigerated warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation, or configuration of the proposed project is altered; (3) when the location or orientation of the proposed project is modified; (4) when there is a change of ownership; or (5) for application to an adjacent site. Consultants cannot accept responsibility for problems that may occur if they are not consulted after factors which were considered in the development of the report have changed. SUBSURFACE CONDITIONS CAN CHANGE. Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a report whose adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for example, groundwater conditions commonly vary seasonally. Construction operations at or adjacent to the site and natural events such as floods; earthquakes, or groundwater fluctuations may also affect subsurface conditions and, thus, the continuing adequacy of a geotechnical/environmental report. The consultant should be kept apprised of any such events, and should be consulted to determine if additional tests are necessary. MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS. Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data were extrapolated by your consultant, who then applied judgment to render an opinion about overall subsurface conditions. The actual interface between materials may be far more gradual or abrupt than your report indicates. Actual conditions in areas not sampled may differ from those predicted in your report. While nothing can be done to prevent such situations, you and your consultant can work together to help reduce their impacts. Retaining your consultant to observe subsurface construction operations can be particularly beneficial in this respect. Page 1 of 2 1/2003 A REPORT'S CONCLUSIONS ARE PRELIMINARY. The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can be discerned only during earthwork; therefore, you should retain your consultant to observe actual conditions and to provide conclusions. Only the consultant who prepared the report is fully familiar with the background information needed to determine whether or not the report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by applicable recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of the report's recommendationsif another party is retained to observe constmcti0n. THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION. Costly problems can occur when other design professionals develop their plans based on misinterpretation ofa geotechnical/environmental report. To help avoid these problems, the consultant should be retained to work with other project design professionals to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and to review the adequacy of their plans and specifications relative to these issues. BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT. Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results, and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in geotechnical/environmental reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or other design drawings, because.drafters may commit errors or omissions in the transfer process. To reduce the likelihood of boring log or monitoring well misinterpretation, contractors should be given ready access to the complete geotechnical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared for you, you should advise contractors of the report's limitations, assuming that a contractor was not one of the specific persons for whom the report was prepared, and that developing construction cost estimates was not one of the specific purposes for which it was prepared. While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with your consultant and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy of subsurface information always insulates them from attendant liability. Providing the best available information to contractors helps prevent costly construction problems and the adversarial attitudes that aggravate them to a disproportionate scale. READ RESPONSIBILITY CLAUSES CLOSELY. Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design disciplines. This situation has resulted in wholly unwarranted claims being lodged against consultants. To help prevent this problem, consultants have developed a number of clauses for use in their contracts, reports and other documents. These responsibility clauses are not exculpatory clauses designed to transfer the consultant's liabilities to other parties; rather, they are definitive clauses that identify where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities and take appropriate action. Some of these definitive clauses are likely to appear in your report, and you are encouraged to read them closely. Your · consultant will be pleased to give full and frank answers to your questions. The preceding paragraphs are based on information provided by the . ASFE/Association of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland z - -z -.? Page 2 of 2 1/2003