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HomeMy WebLinkAbout978900021 Geotech Assessmentl^_ SEATTLE PORTLAND SHANNON ~WII...SON, INC. FAIRBArlKS GEOTECHNICAL AND ENVIRONhAENTAL CONSULTANTS AIJCHORAGE DEN'JER ~~ j{ ~[ ~~~ SAINT LOUIS ~~ 111E \\\Y{ June 18, 2004 Jim and Mary Ann Bettner 2135 Buck Lane Road JEE~ERSON COUNT DC Colville, WA 99114 RE: GEOLOGIC SLOPE STABILITY EVALUATION, OLYMPUS BOULEVARD PROPERTY (PARCEL N0.978900021), PORT LUDLOW, WASHINGTON Dear Mr. and Mrs. Bettner: This letter report summarizes our observations, conclusions, and recommendations regarding slope stability and development of the property referenced above for asingle-family residence. Jefferson County has indicated that this property is located in a Landslide Hazard Area and that a geotechnical report would be required to assess the stability of the site. Consequently, 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. These conclusions and recommendations are based on observations made during our site visits on May 18, June 11, and June 16, 2004; available published geologic, topographic, and soil maps; and an undated conceptual site development sketch provided by you. SITE DESCRIPTION The site is located between Olympus Boulevard and Admiralty Inlet, south of Mats Mats Bay (see Figure 1). The property is approximately 250 feet long (east-west) by approximately 50 feet wide (north-south). The topography across the site rises from sea level at Admiralty Inlet, to about 60 feet to the west. From east to west, the topography includes the following. - A sand and gravel beach with scattered boulders and driftwood. - Anear-vertical waterfront bluff (approximately 35 to 40 feet high} that slopes up to the west at about 75 to 80 degrees. - A relatively flat upland that slopes up to the west at about 5 to 10 degrees. 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 21-1-20122-001 Jim and Mary Ann Bettner June 18, 2004 Page 2 St-CANNON F~WILSON, INC. The bluff supports little vegetation. Where present, vegetation on the bluff includes scattered areas of grasses and small alder and fir trees typically less than 4 inches in diameter. At the crest of the bluff, an approximately 2-foot-diameter madrona and a 1-foot-diameter alder tree are growing over and down the face of the bluff. Approximately 2-foot-diameter fir trees in similar growth positions along the crest of the bluff were observed on nearby properties. Vegetation on the upland portion of the site typically consists of fir trees up to about 2% feet in diameter and a few cedar trees. Undergrowth in the upland portion of the site includes sword fern, salal, ivy, grasses, and small deciduous trees. In general, the salal and madrona are indicative of relatively well-drained conditions in the near-surface soils. No springs, seeps or hydrophilic vegetation (vegetation indicative of wet soil conditions or near surface groundwater) were observed on the site or on the bluff portions of the properties adjacent to the site. We understand that the proposed development includes, atwo-bedroom residence located approximately 65 feet from the crest of the bluff. The conceptual site development sketch shows that the septic tanks for the residence would be located approximately 50 feet from the crest of the bluff. The septic drainfield and sand filter would be located toward the west end of the property, at least 140 feet west of the crest of the bluff. GEOLOGIC CONDITIONS Published geologic maps of the area indicate that the site is underlain byPleistocene-age (13,500 to 17,000 years old} Vashon Lodgement Till. Lodgement till is typically an unsorted mixture of clay, silt, sand, and gravel with occasional cobbles and boulders that is deposited directly beneath an advancing glacier. Vashon Lodgement Till was deposited directly beneath the Vashon Stade ice sheet that advanced from Canada across the Puget Sound region approximately 17,000 years ago. The ice sheet that overrode the till and the underlying soils is estimated to have been on the order of 3,000 to 4,000 feet thick in this area. Consequently, the till and the underlying soils have been compacted to a very dense or hard state because of the weight of the overriding ice. 21-1-20122-001-RpdWP/jnd 21-1-20122-001 Jim and Mary Ann Bettner June 18, 2004 Page 3 SHANNON ~WiLSON, INC. Subsurface explorations were not performed at this site for this evaluation. However, the soils observed in the bluff on this and adjacent sites confirm the presence of Vashon Lodgement Till. Specifically, soils exposed in the bluff face consist of very dense, gray, unsorted, silty, gravelly sand with scattered boulders and cobbles. Sub-vertical joints or fractures in the till exposed in the bluff were observed at about 5- to 40-foot spacings. Cuttings from septic test holes excavated by others on the upland portion of the site and float in the 5-foot-high road cut at the west end of the property appear to be gray, silty, gravelly sand similar in composition to the till observed in the bluff. Based on these observations, it is likely that till underlies most of the site. Since the retreat of the glacier, typically the upper few feet of the very dense soils have loosened and weathered, and topsoil has developed at the ground surface. Weathered till was observed in the upper 2 to 3 feet of the bluff face where the soil at these depths appears brown and contains some roots. CONCLUSIONS AND RECOIVIMENDATIONS Slope Stability Geologic hazard maps indicate that the bluff is unstable and show the location of recent landslides. Slope movements appear to be associated with the oversteepend condition and spalling of the bluff face. The bluff is the result of ongoing wave erosion at the beach levee. The very dense till that forms the bluff appears to erode and span from the near-vertical faces caused by wave erosion. Evidence of recent spalling was observed on the bluff south of the site where it appeared that an approximately 10- to 12-foot-wide by about 2-foot-thick piece of till spalled away from the bluff along a joint and landed on the beach. In addition, while the very dense glacially overridden till maybe stable at relatively steep slopes (e.g., 45 degrees or more), the relatively loose weathered soils and topsoil that forms from the till is not as competent and is susceptible to movement, resulting in localized movements in the weathered soils at the crest of the bluff. Based on the joint spacing and the size of the recent span to the south, it appears that spalling causes the bluff to regress in about 1- to 5-foot increments. Evidence ofdeep-seated ' ` slope movements that would extend farther across the upland portion of the site was not observed. a~ -~ -aoiz2-ooi-x~vwn~na 21-1-20122-001 Jim and Mary Ann Bettner June 18, 2004 Page 4 ~~~~ ~vv~~~~~. i~~. With enough time, spalling and movement of weathered material and topsoil toward the base of the bluff would result in a flatter, more stable slope. However, wave erosion at the toe of the bluff does not allow these soils to accumulate at the toe and maintains the bluff in an over- steepened condition. The rate at which the bluff is receding because of erosion and spalling is unknown. However, the growth positions of the trees observed at the crest of the bluff indicate that the rate is slow enough for these trees to adjust their growth positions to accommodate the regression. Based on this observation, it is likely that the average rate the bluff is receding is on the order of a few inches or less per year. While the average yearly regression rate may be a few inches, in some years no noticeable regression may occur, while in other years spalling may result in several inches or a few feet of regression. Please note that there is some risk of future instability present on all hillsides, which the owner must be prepared to accept. Such instability 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 could cause sliding. The following provides further discussion of risk reduction measures that could be effective at this site. Provided the risk reduction measures discussed in this letter are implemented, it is our opinion that the proposed development would not adversely impact the stability of adjacent properties. Measures to Reduce the Risk Posed by Slope Movement In general, the risk of soil movement on a slope could be reduced by not over-steepening a slope (e.g., do not excavate the toe of the slope) and not increasing the weight on a slope (e.g., do not place yard debris or fill on or at the crest of the slope). The risk of soil movement on a slope could also be reduced by maintaining a slope as dry as possible (e.g., locate septic drain fields away from the slope, route roof downspouts and yard drains away from the slope, and minimize the amount of surface water that could flow down the face of the slope), and maintaining a vegetative cover (in the case of the bluff maintaining a vegetative cover at the crest). The following provides additional recommendations to reduce the risk of soil movement affecting development of this site. 21-1-20122-001-Rpt/WP/jnd 21-1-20122-001 Jim and Mary Ann Bettner June 18, 2004 Page 5 Building Setback S~iA~df~®~ ~1NI~~~~l, ~3~~. The measures discussed above could 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 a 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. As previously discussed, the precise regression rate for the bluff is unknown, but it appears to be on the order of a few inches or less per year. Based on these observations, inferences, and our experience, we recommend a minimum building setback of 40 feet from the crest of the bluff. Greater risk reduction could be achieved with greater building setbacks. The conceptual site development sketch indicates that the residence would be located 65 feet from the crest of the bluff, which exceeds the recommended minimum 40-foot setback. Septic Drain Field Location The septic drain field should be located as far as practical from the bluff so that the potential for water from the drain field to find its way to the crest of the bluff is reduced. We recommend that a minimum 40-foot setback from the crest of the bluff be used. The conceptual site development sketch indicates that the drain field and sand filter would be located over 140 feet from the crest of the bluff, which exceeds the recommended minimum 40-foot setback. Drainage - In general, reducing the amount of water entering and discharging onto a slope could reduce the risk of slope movement. Drains should be constructed and maintained to collect water .__, from impermeable surfaces that could be associated with the proposed development (e.g., roof, decks, patios, and driveways) and directed in a tightline to a suitable discharge point. In our opinion, the existing road ditch at the west end of the property would provide a suitable discharge point. A catch basin and pump would be required to collect the water and pump it up to the west end of the property to the road ditch. We also recommend that a backup gravity-feed tightline be placed from the catch basin to the toe of the bluff. The purpose of the gravity-feed tightline would be to provide a temporary discharge for stormwater to the toe of the bluff in the event of a power outage or some other event where the pump system is disabled. The discharge 2 1-1-201 22-00 1-RpUWP/jnd 21-1-20122-001 Jim and Mary Ann Bettner June 18, 2004 Page 6 point for the backup gravity-feed tightline should be constructed to allow dispersion of the water and dissipation of energy to reduce the potential for erosion. Placing cobbles and boulders on the beach directly beneath the pipe to forma 3- to 5-foot-diameter mat would be one method to provide water dispersion and energy dissipation. In addition to surface drainage, we recommend that footing drains be installed around the perimeter of the residence and on the upslope side of interior footings 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 2. Figure 2 also includes subdrainage and foundation wall backfill recommendations. On-site soils would likely 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 water collected from impermeable surfaces and footing drains as outlined above would not significantly affect the predevelopment drainage conditions on the adjacent properties. Impermeable surfaces around the proposed building (e.g., paved drives) should be -- minimized to reduce potential changes in the existing site drainage characteristics and impacts on adjacent sites. Erosion Hazard According to published U.S. Department of Agriculture (USDA) soil maps, surficial soils on the upper slope are classified as Swantown gravelly loam on 0 to 8 percent slopes. The USDA maps indicate that these soils have none to slight erosion hazard. To reduce the potential for soil erosion and associated hazards during construction at the site, 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 2 1-1-201 22-00 1-Rpi/WP/jnd 21-1-20122-001 Jim and Mary Ann Bettner June 18, 2004 Page 7 earthwork for the proposed development would not significantly affect soil erosion and associated hazards on the site. Wet Weather Earthwork In western Washington, wet weather generally begins about mid-October and continues through about mid-May, although rainy periods may occur at any time of the year. Therefore, it would be advantageous to schedule earthwork during the normally dry weather months of mid- May through mid-October. Earthwork performed during the wet winter months will generally prove more costly. 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 `J by dry weight passes the No. 200 mesh sieve, based on wet-sieving the minus 3/4-inch fraction. Any fines should benon-plastic. , - The ground surface in and surrounding the construction area should be sloped and sealed with asmooth-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 size or type of equipment may have to be limited to prevent soil disturbance, or the subgrade may need to be protected (e.g., covered with an adequate thickness of compacted crushed rock). - No soil should be left exposed to moisture or be uncompacted. A smooth-drum vibratory roller, or equivalent, should be used to seal the surface. Soils that become too wet for compaction should be removed and replaced with clean crushed rock. - Excavation and placement of structural fill during wet weather should be observed on - a full-time basis by a geotechnical engineer (or representative) experienced in wet weather earthwork, to determine that all unsuitable materials are removed and suitable compaction is achieved. Covering work areas, soil stockpiles, or slopes with plastic, sloping, ditching, installing sumps, dewatering, and other measures should be employed, as necessary during construction, to permit 21-1-20122-001-RpdWP/jnd 21-1-20122-001 Jim and Mary Ann Bettner June 18, 2004 Page 8 SAN®N ~~NI~~~~, ~~G. proper completion of the work. Straw bales and/or geotextile silt fences should be aptly located to control soil movement and erosion. LIMITATIONS The conclusions in this letter are based on site conditions visually observed during our reconnaissance at and around the site 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 exclusive use of Mr. and Mrs. Bettner in the evaluation of the stability of this site. With respect to possible future construction, it should be made available for information on 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. 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 and others in understanding the use and limitations of our report. zi-~ -zoiaz-oo~ -xpvwPi~na 21-1-20122-001 Jim and Mary Ann Bettner ~~~~~ ~I~~~i~a. li~l~. June 18, 2004 Page 9 We appreciate the opportunity to provide geologic services to you, and we are available to answer any questions regarding our observations, conclusions or recommendations contained in ~f this letter. Sincerely, SHANNON & WILSON, INC. ~~ ' ~~ ~~~ . - En nearing Grog ~ '~~ 200i ~ O~ t9 ~ $ ~d `'~ used ~oo~ f William Jose h Pt~r~E11S `, William J. Perkins, L.E.G. Senior Principal Engineering Geologist WJP/wJp Enclosures: Figure 1 -Vicinity Map Figure 2 - Subdrainage & Backfilling Important Information About Your Geotechnical Report C: Mr. David Martin -Miller Bay Water .~(_ i~.. v e-~~~F 1 ~~ (` 21-1-20122-001-RpdWP/jnd 21-1-20122-001 - I~ = r~~I ~ Ju VVashin ton ~ o , ~I, Basalt Point .9p,, Port g 1 - ~' ° ~~; ~ 'll Ludlow ` ~\~ / ~ !~~~ ` ~ ~ 1. Ij$I! 1 ~ PROJECT -~ I. a << _:'~ , -~ ~~f ~ • r` _ [-5 LOCATION '~ ~ i fvLa~~R? Is~ `,,: ~ - (" IVICLtS ~ x~rryll ~ i ~~ oa~28 lI'TCLtS - -_ ,r )/ - _ _ '~,-7~ BCL ~~ ~~'~1 -~ ~I~._~ \~~ ~~\`_ 1t Ligh[a ~ 111 ~ 1 ~\ It :'I I A~ * ~. it ~ ~ . •~` \\ !~ ~~'~ Colvos Rocks ~i J\I 1 ~ ~ ~ n ~ p I I 1 j 1t;'' \ Oro ~ u~~I oCiF;ht ~. + I / \` I ~ I ; i I J `I \ \I\'., i ~ '.n~, ~Snakc Rack I L. ~' ' 1 ~ PROJECT I _ . i~ , ` '\~ I LOCATION i. ~~~ ~r ' CI~ort •Lu I2Zw ~P U~. I~ ,,~ - _ ` ~ In In! ~ ' i I '382 .III 't 111 I ( t i 1 1t } I . r,~ll {•, I IIII I ' ~ 1 'I 1 ~~ ®I ~~ \ ~~ Swansonyille ~=~ 1 ~ J ' ~ I - _ ~ _ r ~. -_.- - _,. __v -._., - '__-_ I\ 1 ~ I .I ; ~ 8 ~~~ ~ ~ I ~ ,~,~, u , F> ' I 'I ~~ I ~~ , ~I ~• I ~' III gout j !, u ~ ~ ~ 1 ~' 1 rl j ~ l' ~ - ~ ~~~ / P ,n . l~U u' _ ~ , ~~ ~ ~.I /l ,. ,_ , T - ~--_-- _/-. ~'o _ fPoi•t~Lud w ; G?a v - r.' I I ~t~r tank h X~~ ~ - ~~ /1 ~`. ~ _ 1 ~ ~ .Ill /~ /" '1_ _ ~~PrM~i5: ~ I 'I i i / J / I ~/ _. /I ~.rv ~~ _ _ ~ ., , _ ,.;~ ~I ~-- 9 - S ~ ~~~~- - ~' ,, ~ '~~ „~. U `o 0 N r O 0 0 112 1 Scale in Miles NOTE Map adapted from 1:24,000 USGS topographic map of Port Ludlow, WA quandrangle, dated 1953, photorevised 1973. L Wall 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 2" to 4" Washed ~ 4" Min Pea Gravel Not to Scale MATERIALS Drainage Sand & Gravel with the Following Specifications: o o ° ° Pea Gravel ° ° ° o a 1 g~~ ° o ° Damp Proofing Min. ° ao ° ° ° Weep Holes ~~ (See Note 1) Vapor Barrier o°` o Floor Slab ° o o ° v Ov o'm p'v - ° 'o o ° °° o ° o o ~ °18" Min. a a • a ° ~ o ° 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) U a i; L a' 0 N ~o 0 m 0 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 1. 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. 2. 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. 3. 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. 4. 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 % of Modified Proctor maximum dry density (ASTM: D1557-70, Method C). Otherwise compact to 92 minimum. Sloped to Drain Away from Structure ~- Drainage Sand & ~ Gravel or Washed SHANNON & WILSON, INC. Attachment to and part of Report 21-1-20122-001 - Geotechnical and Environmental Consultants Date: June 17, 2004 To: Jim and Mary Ann Bettner 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 geotechnicaUenvirorunental report is based on a subsurface exploration plan designed to consider a unique set ofproject-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 maybe affected as a result of natural processes or human activity. Because a geotechnicaUenvironmental 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 geotechnicaUenvironmental 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 maybe 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. I /2004 A REPORT'S CONCLUSIONS ARE PRELIMINARY. The conclusions contained in your consultant's report are preliminary because they mustbe 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 recommendations if another party is retained to observe construction. THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION. Costly problems can occur when other design professionals develop their plans based on misinterpretation of a geotechnicaUenvironmental 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 oftheir plans and specifications relative to these issues. BORING LOGSAND/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 fmal boring logs and data are customarily included in geotechnicallenvironmentalreports. 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. `J 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 geotechnicaUenvironmental 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 1 /2002