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HomeMy WebLinkAbout602353004 Geotech Assessment f(ZEoCo-LfL ~- ~L~S-3 OS-~ fa o7-7>S-2 ocs~ SHANNON &WlLSON.INC. May 20, 2005 RJECEf\/'ED AUS - 1 2006 JHffRSON COYNTY DCO Mr. Keith Helms 2400 Perkins Lane West Seattle, V'LA 98199 RE: GEOLOGIC SLOPE STABILITY EV ALVA TION, HELMS PROPERTY ON HIGHWAY 101, BRINNON, WASHINGTON Dear Mr. Helms: This letter summarizes our observations, conclusions, and recommendations regarding slope stability and development of the property referenced above for single-family residences. We understand that you propose to subdivide (short plat) the existing 20-acre property into four, 5-acre parcels. Jefferson County Geologic Hazard Area Maps indicated that the landslide hazard rating of the slopes on the property is moderate. Consequently, we have prepared this letter 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 presented in this letter are based on observations made during our visit to the site on April 22, 2005; available published geologic, topographic, and soil maps; and a site plan provided by Clark Land Office. SITE DESCRIPTION The site is located in Brinnon, on the northwest comer of the intersection of Highway 101 and the Dosewallips River Road (see Figure 1). As shown on Figure 2, the irregularly-shaped 20-acre property is approximately 850 to 1,220 feet long (north-south) by approximately 760 to 890 feet wide (east-west). The eastern portion of the property has historically been mined for sand and gravel. As a result, the topography across the site...consists of a flat lowland along Highway 101, a steep slope (old quarry face) about 100 to 115 feet high that rises up to the west at about 31 to 40 degrees, and a flat upland. The old quarry face slope transitions to a less steep, 31 degree slope to the south along the Dosewallips River Road. 21-1-20323-001 Mr. Keith Helms May 20, 2005 Page 2 The lowland portion of the site and the old quarry face support little vegetation; scotch broom, grasses, and scattered small trees (alder, fir, and madrona) are present in scattered areas across the slope. The upland portion of the site has been cleared in the past, and t~e existing vegetation includes scotch broom, grasses, blackberries with scattered madrona, fir, and cedar trees up to about 1 foot in diameter. An existing pole barn is located on the upland portion of the site (Figure 2); remnants of previous buildings, including concrete pads, are also present. The south-facing slope above the Dosewallips River Road is forested with alder, fir, hemlock, madrona, maple, and cedar up to 1 '12 feet in diameter. The trunks of a number of the trees on this slope are bowed down hill, which is indicative of shallow soil creep. Soil creep is the slow, gradual downslope movement of near-surface soils under the effects of gravity and water and occurs on most slopes to some degree. An existing one-lane gravel road traverses from the lowland portion of the site, up and across the south-facing slope, to the southwest comer and upland portion of the site (Figure 2). No springs, seeps, or hydrophilic vegetation (vegetation indicative of wet soil conditions or near-surface groundwater) were observed on the site or nearby portions of the properties adjacent to the site. We understand that property will be divided into four, 5-acre parcels. Three parcels will be located on the upland portion of the site; one will include the lowland portion of the site along Highway 101. The locations and dimensions of the proposed parcels are shown on Figure 2. GEOLOGIC CONDITIONS Published geologic maps of the area indicate that the site is underlain by Pleistocene-age (13,500 to 17,000 years old) Vashon Recessional Outwash delta or alluvial fan sand and gravel deposits. The presence of these soils was confirmed in exposures in the old quarry face. Specifically, approximately the lower 80 to 100 feet of the face consist of dense, stratified, slightly gravelly SAND to slightly sandy ORA VEL with cobbles and scattered boulders. The apparent dip of the bedding is to the east between about 17 and 22 degrees. The coarse, dipping, stratified nature of the sediment is consistent with a delta or alluvial fan deposit. It is likely that this delta or alluvial fan deposit was the result of deposition from relatively high- 2] .1- 20323.00 J - LI /wp/lkd 21-1-20323-001 Mr. Keith Helms May 20, 2005 Page 3 energy streams flowing out of the Dosewallips River drainage out of the Olympic Mountains to the west and into Pleistocene Lake Russell (a lake that covered much of the Puget Sound - Lowland when ice sheets of the Vashon Stade blocked the existing drainage to the ocean through the Strait of Juan de Fuca). Soils exp_osed in the upper 15 to 20 feet of the old quarry face appear to be similar in composition and density to the underlying delta deposits. However, these upper soils are less stratified, with crude lenses, bedding, and cross bedding, and only a slight dip towards the east. These upper soils are also likely Vashon Recessional Outwash but are the result of another somewhat different depositional environment (e.g., ice-contact deposit). Since cessation of excavation activities in the quarry, soils on the quarry face have loosened and raveled, creating deposits of loose sand and gravel along the toe of the slope. CONCLUSIONS AND RECOMMENDATIONS Slope Stability Geologic hazard maps indicate that the slopes on the site pose a moderate instability hazard. Based on our observations, it is our opinion that the most significant hazard related to slope instability is associated with shallow surface sloughing associated with the steep slope of the old quarry face. Based on our observations at the site and our experience with similar soils, it is our opinion that the potential for deep-seated instability is very low. It appears that excavation of the quarry face resulted in an over-steepened condition with regard to long-term stability. Over time, the soils in the quarry face have weathered and raveled and been deposited at the toe of the slope. Weathering and raveling of the quarry face also causes the crest of the slope to erode and recede to the west. For example, at the north end of the old quarry face slope, we observed a number of small trees that had apparently been located at the crest, but due to erosion of the old quarry face, had been undermined and toppled down the face of the slope. Similar slope movement anywhere along the slope should be expected to continue in the future. 21-]-20323-00] -L1/wp/lkd 21-1-20323-001 Mr. Keith Helms May 20, 2005 Page 4 With enough time, raveling and movement of weathered material on the old quarry face will result in a flatter, more stable slope. However, it is very difficult to estimate the rate at which the slope is flattening. Please note that there is some risk of future instability present on all hillsides, such as the slopes on this site, which the owner must be prepared to accept. Such instability could occur because of future water line breakslleaks, uncontrolled natural 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 development will 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 can be reduced by not oversteepening 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 can also be reduced by maintaining a slope as dryas possible (e.g., locating septic drainfields away from the slope, routing roof downspouts and yard drains away from the slope, and minimizing the amount of surface water that could flow down the face of the slope), and placing and maintaining a vegetative cover. The following provides additional recommendations to reduce the risk of soil movement affecting development of this site. 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 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 angle of repose of the slope material, the design life of the structures, and the risk the owner of lhe structure is willing to assume. As previously discussed, the regression rate for the slope is unknown as the risks a future property owner may be willing to accept. However, a reasonably conservative building setback for buildings on the upland portion of the site can be based on the angle of repose of the sand and gravel raveling from the old quarry face. Based on our measurements in the field and experience with similar 21-1-20323-00] -L1/wp/lkd 21-1-20323-001 Mr. Keith Helms - May 20, 2005 Page S soils, the angle of repose for the sand and gravel raveling from the old quarry face is about 30 to 33 degrees. We recommend that the buildingsetback be based on a slightly flatter slope 27 degrees (i.e., 2 Horizontal to 1 Vertical [2H:l V]) to provide an additional factor of safety. Using this criterion, the survey information provided by Clark Land Office (see Figure 2), and our observations at the site, we recommend a minimum building setback of 60 feet from the - crest of tb--e slope of the old quarry face. For the flatter, forested slope on the south side of the site, we recommend a minimum building setback of 30 feet. The recommended 60- and 30- foot setbacks (and transition zone between the two recommended building setbacks) are shown on Figure 2. For buildings at the base of the slope, we recommend a minimum building setback of 15 feet from the toe of the slope. Soils may accumulate within the recommended minimum IS-foot setback as soil weathers from the old quarry face. Consequently, it may be necessary to periodically remove the soils behind structures that accumulate within the IS-foot setback zone. Septic Drainfield Location A septic drainfield should be located as far as practical from the slopes. By placing the septic drainfield as far as practical from the bluff, the potential for water from the drainfield to find its way to soils on the slopes is reduced. We recommend that the minimum building setbacks also be used for septic drainfields. Drainage Reducing the amount of water entering and discharging onto a slope can reduce the risk of slope movement. Due to the relatively free-draining nature of the soils observed at the site, it is our opinion that extensive subdrainage measures are not required. However, drains should be constructed and maintained to collect water from impermeable surfaces that may be associated with the proposed development (e.g., roof, decks, patios, and driveways) and directed in a tightline to a suitable discharge point. There are a number of suitable discharge points at this site, including the existing road ditches along Highway 101 and the Dosewallips River Road, or infiltration trenches Qn each parcel. We recommend that the same minimum setback criteria from the crest of the slope for septic drainfields be used for infiltration trenches on the upland parcels. 21-] -20323-001-L1/wp/lkd 21-1-20323-001 Mr. Keith Helms May 20, 200S Page 6 For structures on the upland parcels that may have basements, we recommend that footing drains and gravel backfill be placed around the outside perimeter of structures and the uphill side of interior basement walls to reduce the potential for damp basement walls due to the possible future presence of water (e.g., after heavy rainstorms or snow melt). Footing subdrains should consist of slotted, 4-inch-diameter minimum, plastic pipe bedded in washed, %-inch gravel. Typical installation details for these drains are shown in Figure 3. 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 structures. These foundation drainage recommendations may also be appropriate for structures on the lowland parcel. However, if basements are planned for structures on this lower parcel, subsurface explorations should be performed to evaluate the depth to groundwater (due to its proximity to Hood Canal and relatively low ground surface elevation). Foundation drainage recommendations should be reviewed and modified as needed based on the subsurface conditions observed in the explorations. Based on our understanding of the limited, single-residence development of the 5-acre parcels, it is our opinion that the anticipated discharge of water collected from impermeable surfaces and footing drains as outlined above will not significantly affect the pre-development drainage conditions on the adjacent properties. Impermeable surface around buildings (e.g., paved drives) on the upland portion of the site should be minimized to reduce potential changes in the existing site drainage characteristics and impacts on adjacent sites. Erosion Hazard We note that according to published U.S. Department of Agriculture (USDA) soil maps, surficial soils on the site are classified as Grove series gravelly soils with slight to moderate erosion hazards. In our opinion, the erosion hazard of the soils exposed in the old quarry face is somewhat higher. 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 earthwork for the proposed development will not significantly affect soil erosion and associated hazards on the site. 21-1-20323.ool-L1 /wp/lkd 21- I -20323-001 Mr. Keith Helms Ma y 20, 200S Page 7 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 additional costs often result from silty or clayey subgrades or backfill, which when exposed to wet conditions and/or construction traffic, may become unstable and muddy and require removal and replacement with clean, compacted, structural fill. Based on the estimated silt (fines) content of the soils exposed in the old quarry face, most of the site soils are anticipated to have a sufficiently small fines content to preclude them from becoming muddy or unstable when subject to wet conditions. However, there may be some soils present (e.g., topsoil on the upland parcels) that could contain sufficient fines to potentially produce a muddy or unstable soil when wet. 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 %-inch fraction. Any fines should be nonplastic. It is anticipated that much of the site soils wi]) meet this criterion. ~ 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 silty sub grade soils are encountered and there is to be vehicular traffic over these exposed subgrade soils during construction, the size or type of equipment may have to be limited to prevent soil disturbance or these subgrade soils may need to be protected (e.g., covered with about 8 inches of compacted crushed rock or gravel). ~ No soil should be left exposed to moisture or 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 or gravel. 2] -]-20323-001-U/wp/lkd 2 I - 1-20323-001 Mr. Keith Helms May 20, 200S Page 8 ~ 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 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 and recommendations presented 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 use of Mr. Helms 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 visit 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. 21- 1-20323-00 1-L1/wp/lkd 21-1-20323-001 Mr. Keith Helms May 20, 200S Page 9 Shannon & Wilson has prepared the enclosed, "ImpOltant 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, SHANNON & WILSON, INC. William J. Perkins, L.E.G. Associate W JP:1W /wjp Enclosures: Figure 1 - Vicinity Map Figure 2 - Site Plan Figure 3 - Subdrainage and Backfilling Important Information About Your Geotechnical Report c: Ken Clark, Clark Land Office 21-j-20323-ool-1.I/wp/lkd 21-1-20323-001 J N ~ _80 - 'r~~y; . I . . ':-', I I. '. ". ,I:" " . . (.J <( \ If) L: 0 .s:::. 'S <( III 0 0 "ll <Xl :.;; 0 izj 0; Cl OJ ;;: ~ OJ u: C; " '" '" '" 0 "ll ~ C; " '" '" '" 0 S':l ~ ?5i ---, ..!!! u: ./ ./ o f------1 1/2 1----1 I Scale in Miles 1 I Helms Property Brinnon, Washington NOTE Map adapted from 1 :24,000 USGS topographic map of Brinnon, WA quadrangle, dated 1953, revised 1985. VICINITY MAP May 2005 21-1-20323-001 SHANNON & WILSON, INC. FIG. 1 Geotechnical and Environmental Consultants File: Ji\211\20323-001\21-1-20323-001 Fig 2.dwg Date: 05-18-2005 Author: SAC - - - --- ~------ ::;>lIl o c 3 8: -l5' DCC "OC/l o (1) (;;ot -Dl o (") "O^" CD a" ~ ~Cb ~ ~. ~ ~ S~ Ie:;);-t o <0 ....~ ~ [.0.... (be, 0'- & rf' fj P.l 0" ~ ~ F=> .:) -'I' ....~o~ ~ C/l 5" "0 (1) ::;>lIl D C .., -. :;) a: -l5' DCC "OC/l o (1) - - C/l0' -Dl o (") "O^" (1) "'en ::::00 ~.... ::.. CD> ~ ~z N gZ 0 ;;0 0 5. z 01 g'QO ~':e ~;= "C/l !irO blz ". Ul ~Z ~~ ." G') N N ..... I ..... I N o W N W I o o ..... OJ .., S'I ::l CD g 3" en ~lJ el a ~-g ~~ o ::l !'J ~8ab "O3~(") a (1) - ~ ~. ;; ~ o' 3 ;::o.;;l 2a.::r-o ~ (1).g - ~. 0 g- ct;;;'8: ~ 5" 5' o"OCC C (1) en a:~~ gs:[ n (1) ~ g[g;c en C ..... c:g.~ (1) :E (1) CD ~ - 0._ o z o -l m C/l .... o o , J en =i m "0 r )> Z g-~:!! _ _.co (1) - C o.::r..., (1) ....:cDl r;v~o. "'3Dl c.Den"O 6 ::(0 ~O'o. -'<- CD Q a :s. Dl 3 ~ ~ . o.r~ wDl::r I ::J _. .... a. 0' ~ -. 60~ CJ'l31Dl . @"O - 0- :"! C/l (") Dl CD 5' 'TI (1) ~ '" o o ~ u:: Pavement or 15" Impervious Soil On-Site Sandy GRA VEU gravelly SAND Backfill or Backfill Meeting Gradation Requirements for Structural Fill (See Note 2) Excavation Slope Contractor's Responsibility 6" Min. Cover of 3/4-inch Gravel (6" Min. on Sides of Pipe) Sloped to Drain Away from Structure Subdrain Pipe o <C en NOTES Washed 3/4-inch Gravel Damp Proofing Vapor Barrier Floor Slab Washed 3/4-inch Gravel Not to Scale 1. Imported structural fill should consist of well-graded granular soil with not more that 5% fines (by weight based on minus 3/4" portion) passing No. 200 sieve (by wet sieving) with no plastic fine. o .c '5 <C It) o o N o N ,;, o iri "iii o 2. 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 eartb pressures and possibly damage the wall. Cl 3: '0 o-i Cl u:: o o ~ N '" o <"! S! ~ o '" '" N '" o S! ~ ..., 3. 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: D1557-70, Method C). Otherwise compact to 90% minimum. SUBDRAIN PIPE 4" minimum diameter perforated or slotted pipe; tight joints; sloped to drain (6"/100' min. slope); provide c1ean-outs. Perforated pipe holes (3/16" to 318" 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. Helms Property Brinnon, Washington SUBDRAINAGE AND BACKFilLING - May 2005 21-1-20323-001 SHANNON & WILSON, INC. FIG 3 Geotechnical and Environmental Consultants . III SHANNON & WILSON, INC. Geotechnical and Environmental Consultants Attachment to and part of Report 21-1-20323-00 I Date: May 20. 2005 To: Mr. Keith Helms 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 ofthe 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 geotechnicallenvironmental 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 of2 1/2005 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 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 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 ANDIOR 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 andlor 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 Page 2 of2 112005