Loading...
Geotech.pdf1 Group May 13, 2014 Northwest, Inc. Ms. Chris Schuetz 8124 Talbot Road Edmonds, Washington 98026 Geotechnical Engineers, Geologists & Environmental Scientists G-3659 Subject: Geotechnical Evaluation of Impact of Recent Tree Cutting, 8001 Talbot Road, Edmonds, Washington Dear Ms. Schuetz: GEO Group Northwest, Inc. has completed a geotechnical evaluation of the above -subject property (the project site). This report has been prepared in accordance with our services agreement with you dated May 9, 2014. PROJECT DESCRIPTION We understand that tree cutting and pruning activities recently were performed on a portion of the property at 8001 Talbot Road in Edmonds, Washington. This area is located on a steep slope along a ravine that runs along the length of the property. This area is located on the eastern portion of the property, near Talbot Road, as illustrated in the enclosed location map. We understand that the City of Edmonds has requested a geotechnical assessment of the impacts from the recent tree cutting on the slope and of the cutting debris that was left on the slope and in the stream bed. GEOLOGIC OVERVIEW Published geologic mapping of the site vicinity reports that surface soils at the site consist of Quaternary -age glacial till deposits of the Fraser Glaciation, apparently underlain with older non - 13240 NE 20th Street, Suite 10 Bellevue, Washington 98005 Phone 425/649-8757 Fax 425/649-8758 May 13, 2014 G-3659 Ms. Chris Schuetz Page 2 glacial deposits of the Whidbey Formation. The glacial till soils typically consist of dense, non- layered mixtures of sand, gravel, and silt, with occasional cobbles. The glacial till deposits typically are relatively impermeable to groundwater. The Whidbey deposits typically consist of compact, layered, medium- to coarse-grained sand that is commonly oxidized and may contain peat layers. SITE RECONNAISSANCE On May 9, 2014, Mr. Keith Johnson, a project geologist from GEO Group Northwest, Inc., visited the site and performed a reconnaissance of the area where the recent tree cutting had occurred. We observed that three trees appeared to have been recently cut on the site, and several other trees were pruned. Stumps from the three cut trees remain in place; the cut tree trunks and branches were observed to be lying mostly on the slope of the ravine. We observed no areas of soil disturbance or clearing in the area. We also observed no evidence of bulk sloughing of soils or erosional rutting of the ravine slopes. The asphalt driveway along the north side of the ravine is in good condition and does not exhibit obvious settlement or distress. The stream at the bottom of the ravine was observed to be flowing without significant obstruction, such as from sloughed soils or vegetation debris. We observed that several apparently older, rotted and moss -covered tree trunks were strewn on the ravine slopes and across the bottom of the ravine. The area also has an overgrowth of nettles, blackberry vines, and young alder. Soils observed on the ravine slopes consisted of moderately well -graded, pebbly sand. We also observed that the ground surface is populated with burrow holes which typically are a few to several inches in diameter and appear to be from rodents, possibly mountain beavers. We found that the surface soils typically were loose to medium dense to a depth of at least 3 feet based on probing them with a 0.5" -diameter steel probing rod. We observed water flowing along the bottom of the ravine, but no seepage on the adjacent slopes. Soils at the base of the ravine exhibited a surface of gravel and cobbles, and efforts to probe through these materials were unsuccessful. The gravel and cobbles may be a surface that has developed as the sand in the soils has been eroded by the stream flow. 1 Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington. U.S. Geological Survey Miscellaneous Field Studies Map MF -1541, 1983. GEO Group Northwest, Inc. May 13, 2014 Ms. Chris Schuetz G-3659 Page 3 Based on the conditions that we observed, it is our opinion that the soils present on the ravine slopes in this area consist of advance glacial outwash deposits of the Fraser Glaciation. The outwash deposits are not noted as present at this location in the cited geologic map but are reportedly found elsewhere nearby, and stratigraphically situated below the glacial till deposits and above the Whidbey deposits. The composition of the observed soils and their loose condition near the ground surface are typical of advance outwash deposits. CONCLUSIONS AND RECOMWNDATIONS In our opinion, the soil conditions in the area of recent tree cutting do not appear to have been adversely affected by the recent tree cutting. Retention of the stumps from the cut trees and the lack of observed disturbance to the surface soils should prevent an increase in erosion potential of the slopes in the area. The smaller cut branches left on the slope, however, does have the potential to kill off the vegetation on which it rests. We recommend, for this reason, that the majority of this material be removed manually so that the existing vegetation is allowed to thrive. From a slope stability perspective, the three large trunks that remain do not require removal, in our opinion, because they occupy limited areal coverage and do not pose a hazard to structures or the public. LIMITATIONS This report has been prepared for the specific application to this site and proposed project, and for the exclusive use of Ms. Chris Schuetz and her authorized representatives or agents. Any use of this report by other parties is solely at that party's own risk. We recommend that this report be included in its entirety in the project contract documents for reference during construction. Our findings and recommendations stated herein are based on field observations, our experience and judgment. The recommendations are our professional opinion derived in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in this area and within the budget constraint. No warranty is expressed or implied. In the event that soil conditions not anticipated in this report are encountered during site development, GEO Group Northwest, Inc. should be notified and the above recommendations should be re-evaluated. GEO Group Northwest, Inc. May 13, 2014 Ms. Chris Schuetz CLOSING G-3659 Page 4 If you have any questions regarding this report, or if we may be of further service, please do not hesitate to contact us. Sincerely, GEO GROUP NOR Project Geologist William Chang, PE Principal Engineer Enclosure: Location Map (from Schuetz Tree Evaluation, by Arbor Options Consulting Arborists) GEO Group Northwest, Inc. Arbor Options Consulting Arborists Scheutz Tree Evaluation May 2, 2014 Appendix A — Tree Location Map SEE ackryw MAP q001 rl Izi , edit W& 2 - STREAM STREAM CHANNEL LARGE WQOpY DEBRIS PLAN r SCALE w-- ro E