McColl Fence Addition GEOTECHNICAL ASSESSMENT Prepared For: Stuart McColl 1038 Hooker Road Sequim, WA 98382 SEPTEMBER 2012 Prepared By: Trent T. Adams, EIT Justin C. Wilson, PE NTI ENGINEERING & LAND SURVEYING 717 South Peabody Street Port Angeles, WA 98362 Phone: (360) 452-8491 Fax: (360) 452-8498 Email: info@nti4u.com
September 21 th, 2012 Stuart McColl 1083 Hooker Road Sequim, WA 98382 Subject: Geotechnical Report for the property described as Tax Parcel Number 083022-500056, 15 Glen Lane located in Section 22, T30N, R8W, W.M., Clallam County, WA 98363. Dear Mr. McColl: 1.0 Purpose and Scope At your request, Trent Adams, EIT, with NTI Engineering & Land Surveying, conducted a geotechnical investigation of the above-mentioned property on September 3, 2012. The purpose of this investigation was to examine the site soils at the subject property and provide recommendations regarding development of the property in accordance with the Clallam County Code. It is our understanding that development plans for the property include the construction of a fence in the Southeast corner of the property. 2.0 Site Description The site is located on the south side of Glen Lane as it leaves Highway 101. The property is bounded by fencing to the west, north, and part of the eastern perimeter. The property slopes to the south with slopes ranging from approximately five (5) to seven (7) degrees extending to the top of a steep slope. The steep slope is approximately seventy (70) feet high with slopes ranging from approximately twenty-nine (29) to forty-five (45) degrees. The above-mentioned property is located within a designated erosion hazard area by Clallam County.
Page 2 3.0 Site Geology and Soils FIGURE 1 VICINITY MAP SHOWING PROJECT LOCATION The site soils are Wyecreek-Stormking-Pistol complex, 20 to 50 percent north slopes as mapped by the National Resources Conservation Service of the U.S. Department of Agriculture (http://websoilsurvey.nrcs.usda.gov/app/websoilsurvey.aspx). This soil unit is formed from colluvium and residuum parent materials, which are derived from basalt and till. 4.0 Geotechnical Exploration 4.1 Soil Observations Visual observation of the site soils in disturbed areas indicate that the surface soils appear to be the mapped Wyecreek extremely gravelly sandy loam. This unit is classified as GM, gravelly sandy loam. 4.2 Vegetation The surface of the soil to the west of the concrete patio foundation is moderately vegetated with ivy and small shrubs. The steep slope to the south of the concrete patio is also well vegetated with ivy, salal, and trees. These trees are quite large, showing long term development in the area. The trees on the steep slope to the south do not show evidence of instability from soil creep or sloughing from saturation.
Page 3 FIGURE 2 VEGETATION OF NATIVE SLOPES TO THE SOUTH 4.3 Hydrology and Drainage In the vicinity of the proposed development, no surface depressions or runoff channels were observed. Surface runoff is generally sheet flow, running south towards Lake Sutherlund. According to the NRCS of the USDA, the hydrologic group for the Wyecreek soil unit is C and the drainage class is Well drained. While the soil has a slow infiltration rate, the area is mapped as having a low frequency and duration of wet periods. The Wyecreek soil can become erosive on slopes greater than three (3) degrees when surface runoff is present. 5.0 Recommendations 5.1 Proposed Development The existing concrete patio foundation wall and preliminary fence location is shown in Figure 3. The fence posts were initially installed approximately one (1) foot away from the face of the concrete patio. The posts shown will be removed to accommodate an increased offset distance from the face of the concrete patio foundation wall.
Page 4 FIGURE 3 VIEW LOOKING EAST SHOWING THE EXISTING CONCRETE PATIO FOUNDATION WALL The proposed development includes construction of a fence with a height ranging from eight (8) feet to twelve (12) feet. The fence is located a distance of three and a half (3.5) feet from the face of a concrete patio foundation wall. Concrete footings for the fence range in depth from three (3) feet to five (5) with footing widths ranging from eighteen (18) to twenty-four (24) inches. The proposed fence location is now three and a half (3.5) feet away from the face of the wall 5.2 Soil Bearing Pressures Development of the proposed fence includes installation of concrete footings to provide lateral support against wind and dead loads. The depth of embedment for concrete footings varies per post, depending on localized loading conditions. Structural calculations provided by 4 Seasons Engineering show the proposed fence has been designed to resist the given loading conditions based on soil parameters provided in Table 1806.2 Presumptive Load-Bearing Values of Soils of Chapter 18 of the 2009 IBC. Soil parameters of the Wyecreek soil unit observed at the site are consistent with the estimated soil properties selected in the structural report. 5.3 Groundwater According to the NRCS of the USDA, the depth to the water table of the Wyecreek soil unit is greater than six (6) feet. Excavation for fence post footings shall be limited to a maximum of five (5) feet to prevent groundwater intrusion to the excavation. 5.4 Lateral Support
Page 5 Excavation near foundations reduces lateral support provided by soil backfill and potentially requires mitigation. The excavation volume per footing is less than 0.6 cubic yards with a minimum offset distance of eight (8) feet, center to center of each footing. The proposed excavation for fence post footings can be expected to have a low to insignificant impact on lateral support to the existing concrete patio foundation. Excavation for footings shall be limited to the dimensions shown in the structural report to prevent loss of lateral support to the concrete patio foundation during excavation. Footings installed in this manner will not cause sliding of native soils or loss of lateral strength support to the concrete patio foundation. Installation of concrete footings for the fence addition will provide additional long term lateral support to the concrete patio foundation due to the advantage of it s inherent high strength material properties opposed to the native soil. 5.5 Slope Stability The native slopes at the project site are stable based upon site observations and available records. Moderate vegetation exists on the native slopes providing protection from erosion. The bulkhead at the toe of the steep slopes at the site guards the shoreline from erosive wave action from Lake Sutherland. Disturbance to the native slopes shall be limited to that which is required to complete installation of the fence addition. Excavation work shall occur between June 1 st and October 31 st to prevent negative impacts from surface water and ground water on slope stability. Excavation shall not occur during any rainfall periods. 5.6 Conclusion It is in our opinion that development of the proposed fence addition as described in this report will not remove lateral support to the existing concrete patio foundation. Site soils can be expected to remain stable during development when carried out within the provisions of this report. The proposed fence addition shall be constructed in conformance with all requirements of the Clallam County Department of Community Development including, but not limited to, the 2009 International Building Code, and applicable clearing, grading, drainage, and erosion control requirements. 6.0 Limitations The observations and conclusions of this report apply only to the subject property and they are not transferable to nearby or adjoining property. This report is the sole property of Stuart McColl and may be used by others only with their permission.
APPENDIX
448260 448260 123 41' 38'' 123 41' 38'' 5325450 5325380 5325310 5325240 5325170 5325100 5325030 Page 1 of 3 48 4' 49'' 48 4' 34'' Soil Map Clallam County Area, Washington 48 4' 48'' 48 4' 33'' 5325030 5325100 5325170 5325240 5325310 5325380 5325450 123 42' 12'' 123 42' 12'' 447630 447630 ± 447700 Longfellow Rd 447700 429D7 447770 447770 447840 447840 Map Scale: 1:3,310 if printed on A size (8.5" x 11") sheet. 447910 447910 101 Meters 0 45 90 180 270 Feet 0 150 300 600 900 W 447980 447980 499P7 448050 Olympic National Forest Rd Glen Ln 448050 35 448120 448120 Sportsman Rd 448190 448190 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey
Page 2 of 3 Soil Map Clallam County Area, Washington MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Units Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Gully Short Steep Slope Other Political Features Cities Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Map Scale: 1:3,310 if printed on A size (8.5" 11") sheet. The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for accurate map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: UTM Zone 10N NAD83 This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Clallam County Area, Washington Survey Area Data: Version 8, Jul 2, 2012 Date(s) aerial images were photographed: 6/25/2006 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey
Soil Map Clallam County Area, Washington Map Unit Legend Clallam County Area, Washington (WA609) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 35 Louella gravelly loam, 30 to 65 percent slopes 429D7 Wyecreek-Stormking complex, 50 to 90 percent north slopes 10.5 17.4% 8.8 14.6% 499P7 Wyecreek-Stormking-Pistol complex, 20 to 50 percent north slopes 25.4 42.3% W Water 15.5 25.7% Totals for Area of Interest 60.2 100.0% Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 3 of 3
Map Unit Description: Wyecreek-Stormking-Pistol complex, 20 to 50 percent north slopes Clallam County Area, Washington Clallam County Area, Washington 499P7 Wyecreek-Stormking-Pistol complex, 20 to 50 percent north slopes Map Unit Setting Elevation: 1,740 to 2,600 feet Mean annual precipitation: 60 to 90 inches Mean annual air temperature: 43 to 45 degrees F Frost-free period: 150 to 170 days Map Unit Composition Wyecreek and similar soils: 40 percent Stormking and similar soils: 30 percent Pistol and similar soils: 20 percent Description of Wyecreek Setting Landform: Mountain slopes Parent material: Colluvium and residuum derived from basalt and till Properties and qualities Slope: 20 to 50 percent Depth to restrictive feature: 20 to 40 inches to lithic bedrock Drainage class: Well drained Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.57 to 1.98 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Very low (about 1.7 inches) Interpretive groups Land capability (nonirrigated): 7e Other vegetative classification: western hemlock/oregongrape/ swordfern, Olympic (CHS139) Typical profile 0 to 5 inches: Extremely gravelly sandy loam 5 to 20 inches: Extremely gravelly sandy loam 20 to 32 inches: Extremely cobbly sandy loam 32 to 36 inches: Unweathered bedrock Description of Stormking Setting Landform: Mountain slopes Parent material: Colluvium and residuum derived from basalt and till Properties and qualities Slope: 20 to 50 percent Depth to restrictive feature: 40 to 60 inches to lithic bedrock Drainage class: Well drained Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 1 of 3
Map Unit Description: Wyecreek-Stormking-Pistol complex, 20 to 50 percent north slopes Clallam County Area, Washington Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.57 to 1.98 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Very low (about 2.3 inches) Interpretive groups Land capability (nonirrigated): 7e Other vegetative classification: western hemlock/oregongrape/ swordfern, Olympic (CHS139) Typical profile 0 to 4 inches: Extremely gravelly sandy loam 4 to 16 inches: Extremely gravelly loam 16 to 30 inches: Extremely gravelly sandy loam 30 to 43 inches: Extremely gravelly sandy loam 43 to 47 inches: Unweathered bedrock Description of Pistol Setting Landform: Mountain slopes Parent material: Colluvium and residuum derived from basalt and till Properties and qualities Slope: 20 to 50 percent Depth to restrictive feature: 20 to 40 inches to densic material Drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr) Depth to water table: About 12 to 36 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Very low (about 2.9 inches) Interpretive groups Land capability (nonirrigated): 6e Other vegetative classification: western hemlock/oregongrape/ swordfern, Olympic (CHS139) Typical profile 0 to 7 inches: Very gravelly loam 7 to 19 inches: Very gravelly loam 19 to 29 inches: Very gravelly silt loam 29 to 60 inches: Very gravelly silt loam Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 2 of 3
Map Unit Description: Wyecreek-Stormking-Pistol complex, 20 to 50 percent north slopes Clallam County Area, Washington Minor Components Northpoint Percent of map unit: Data Source Information Soil Survey Area: Clallam County Area, Washington Survey Area Data: Version 8, Jul 2, 2012 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 3 of 3
Water Features Clallam County Area, Washington Water Features This table gives estimates of various soil water features. The estimates are used in land use planning that involves engineering considerations. Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The four hydrologic soil groups are: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Surface runoff refers to the loss of water from an area by flow over the land surface. Surface runoff classes are based on slope, climate, and vegetative cover. The concept indicates relative runoff for very specific conditions. It is assumed that the surface of the soil is bare and that the retention of surface water resulting from irregularities in the ground surface is minimal. The classes are negligible, very low, low, medium, high, and very high. The months in the table indicate the portion of the year in which a water table, ponding, and/or flooding is most likely to be a concern. Water table refers to a saturated zone in the soil. The water features table indicates, by month, depth to the top (upper limit) and base (lower limit) of the saturated zone in most years. Estimates of the upper and lower limits are based mainly on observations of the water table at selected sites and on evidence of a saturated zone, namely grayish colors or mottles (redoximorphic features) in the soil. A saturated zone that lasts for less than a month is not considered a water table. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 1 of 4
Water Features Clallam County Area, Washington Ponding is standing water in a closed depression. Unless a drainage system is installed, the water is removed only by percolation, transpiration, or evaporation. The table indicates surface water depth and the duration and frequency of ponding. Duration is expressed as very brief if less than 2 days, brief if 2 to 7 days, long if 7 to 30 days, and very long if more than 30 days. Frequency is expressed as none, rare, occasional, and frequent. None means that ponding is not probable; rare that it is unlikely but possible under unusual weather conditions (the chance of ponding is nearly 0 percent to 5 percent in any year); occasional that it occurs, on the average, once or less in 2 years (the chance of ponding is 5 to 50 percent in any year); and frequent that it occurs, on the average, more than once in 2 years (the chance of ponding is more than 50 percent in any year). Flooding is the temporary inundation of an area caused by overflowing streams, by runoff from adjacent slopes, or by tides. Water standing for short periods after rainfall or snowmelt is not considered flooding, and water standing in swamps and marshes is considered ponding rather than flooding. Duration and frequency are estimated. Duration is expressed as extremely brief if 0.1 hour to 4 hours, very brief if 4 hours to 2 days, brief if 2 to 7 days, long if 7 to 30 days, and very long if more than 30 days. Frequency is expressed as none, very rare, rare, occasional, frequent, and very frequent. None means that flooding is not probable; very rare that it is very unlikely but possible under extremely unusual weather conditions (the chance of flooding is less than 1 percent in any year); rare that it is unlikely but possible under unusual weather conditions (the chance of flooding is 1 to 5 percent in any year); occasional that it occurs infrequently under normal weather conditions (the chance of flooding is 5 to 50 percent in any year); frequent that it is likely to occur often under normal weather conditions (the chance of flooding is more than 50 percent in any year but is less than 50 percent in all months in any year); and very frequent that it is likely to occur very often under normal weather conditions (the chance of flooding is more than 50 percent in all months of any year). The information is based on evidence in the soil profile, namely thin strata of gravel, sand, silt, or clay deposited by floodwater; irregular decrease in organic matter content with increasing depth; and little or no horizon development. Also considered are local information about the extent and levels of flooding and the relation of each soil on the landscape to historic floods. Information on the extent of flooding based on soil data is less specific than that provided by detailed engineering surveys that delineate flood-prone areas at specific flood frequency levels. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 2 of 4
Louella B Jan-Dec None Wyecreek C Jan-Dec None Stormking B Jan-Dec None Wyecreek C Jan-Dec None Stormking B Jan-Dec None Pistol C/D January 1.0-3.0 1.7-3.3 None None C/D February 1.0-3.0 1.7-3.3 None None C/D March 1.0-3.0 1.7-3.3 None None C/D April 1.0-3.0 1.7-3.3 None None C/D November 1.0-3.0 1.7-3.3 None None C/D December 1.0-3.0 1.7-3.3 None None Water Jan-Dec None Page 3 of 4 Water Features Clallam County Area, Washington Report Water Features Water Features Clallam County Area, Washington Map unit symbol and soil name Hydrologic group Surface runoff Month Water table Ponding Flooding Upper limit Lower limit Surface depth Duration Frequency Duration Frequency Ft Ft Ft 35 Louella gravelly loam, 30 to 65 percent slopes 429D7 Wyecreek- Stormking complex, 50 to 90 percent north slopes 499P7 Wyecreek- Stormking-Pistol complex, 20 to 50 percent north slopes W Water Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey
Page 4 of 4 Water Features Clallam County Area, Washington Data Source Information Soil Survey Area: Clallam County Area, Washington Survey Area Data: Version 8, Jul 2, 2012 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey