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Home My WebLink AboutTalbot Hill Arborist Report Addendum (2)PSE Talbot Hill Substation Arborist Report Addendum K:\project\31900\31983H\ProjectDocs\Reports\Talbot Hill Arborist Report Addendum.doc 11241 willows road ne suite 200 redmond, wa 98052 phone (425) 822-4446 Assignment The arborist report addendum is a response to a City comments. The first City comment was a request to provide individual justification regarding the selective removal of trees to the southwest corner of the substation, to the west of the entrance to the substation. The second City comment is in regards to a planting plan for the plantings described in the arborist report, supplemental visual buffer plantings. Selective Tree Removals The selective removal was for trees #100, 101, 102, 103, 104, 105, 108, 109, 113, 115 and 116. The City concern is that the trees may be trimmed instead of removed. Potential targets of these trees include the electrical equipment within the substation, the perimeter security fence of the substation, distribution power lines, distribution power pole, transformers, and transmission tower. These targets are within the target zone of these trees proposed for removal. See image A. Specifically, the tree part of concern with these seven Douglas fir trees is having their limbs or tops broken and dislodged during a high wind event and those part(s) striking the electrical equipment within the substation or one of the other targets. Trees #100, 101, 103, 104, 105 and 115 are between 95 and 110 feet tall. The trunks of these trees are located approximately 105 to 120 feet from the electrical equipment within the substation, see figures A and B. These trees heights are equal to or within 1.5 times the distance to the electrical equipment. Additionally, these Douglas fir trees are healthy and are highly likely to continue gaining height so the risk will increase if the proposed risk mitigation is not acted on now. The risk can be mitigated through converting the removed trees to wildlife snags instead of complete removal. There is a nice wildlife snag to the west of tree 107, see image C. Wildlife snag heights should be approximately equal to the distance to the nearest target, likely the perimeter security substation. Topping or “wind sail” pruning are not appropriate risk mitigation options because they will increase the long-term and short-term risk, respectively, in these trees. Trees #100, 101, 103, 104, 105, 108 and 115 are still recommended to be removed due to their risk To: Kerry Kriner, PSE From: Tom Early, Otak, Inc. Date: February 28, 2017 Project No.: 31983.h Kerry Kriner, PSE Page 2 Talbot Hill Arborist Report Addendum March 2, 2017 K:\project\31900\31983H\ProjectDocs\Reports\Talbot Hill Arborist Report Addendum.doc to the substation electrical equipment, perimeter fence, distribution power lines, distribution power pole, transformers, and/or transmission tower. Trees #102, 109, 113 and 116 are recommended to be retained and monitored, a change from the original recommendation of removal. This change is due to the likelihood of failure and impact being somewhat likely at this time. Please see the tree table below which summarizes the original recommendation, the revised recommendation and the rationale for the revised recommendation; the highlighted rows are the recommendations which have changed. Supplemental Visual Buffer Plantings The visual buffer plantings include Vine Maple, Western Serviceberry, Beaked Hazelnut, California Wax Myrtle, Silk Tassel and Strawberry trees planted at 6 feet triangular on-center spacing. The vine maple and western serviceberry are proposed to be 6 feet tall and the other plants are to be 5 gallon container at the time of installation. This visual buffer planting is 50% evergreen species to maximize the screening provided by the planting while also providing some variation to improve ecological services as well as aesthetics. The planting plan and details are part of the plan submittal, titled “Visual Barrier Planting Plan – Talbott Hill Substation” and are attached to this addendum. Please let me know if other questions or concerns come up. Tom Early, Otak, Inc. Certified Arborist PN-5622A, Tree Risk Assessment Qualified Landscape Architect, Washington State # 1199 Figure A: distance of tree #103 to nearest electrical element within substation Kerry Kriner, PSE Page 3 Talbot Hill Arborist Report Addendum March 2, 2017 K:\project\31900\31983H\ProjectDocs\Reports\Talbot Hill Arborist Report Addendum.doc Figure B: distance of tree #115 to nearest electrical element within substation Figure C: google aerial showing substation area of selective tree removal on left, area of tree removal for storm water facility on right and direction of tree numbering Kerry Kriner, PSE Page 4 Talbot Hill Arborist Report Addendum March 2, 2017 K:\project\31900\31983H\ProjectDocs\Reports\Talbot Hill Arborist Report Addendum.doc Image A: panoramic image showing selective tree removals to west of entrance driveway indicated with white arrows, specifically trees #100, 101, 103, 104, 105, 108 and 115; image also shows substation fence on far right and distribution power pole, lines and transformers; view is looking west from southern boundary of substation Image B: proposed selective tree removals to reduce risk for substation, view from southeast corner of playfield looking to the north Kerry Kriner, PSE Page 5 Talbot Hill Arborist Report Addendum March 2, 2017 K:\project\31900\31983H\ProjectDocs\Reports\Talbot Hill Arborist Report Addendum.doc Image C: existing wildlife snag to the west of tree #107 Kerry Kriner, PSE Page 6 Talbot Hill Arborist Report Addendum March 2, 2017 K:\project\31900\31983H\ProjectDocs\Reports\Talbot Hill Arborist Report Addendum.doc Tree Table Tree # Original Recommended Action Revised Recommended Action Rationale for Revised Recommendation 100 Remove Convert to wildlife snag High risk due to likely failure and impact with significant or severe consequences to energized electrical equipment 101 Remove Convert to wildlife snag High risk due to likely failure and impact with significant or severe consequences to energized electrical equipment 102 Remove Retain Changed due to low or moderate risk at this time 103 Remove Convert to wildlife snag High risk due to likely failure and impact with significant or severe consequences to energized electrical equipment 104 Remove Convert to wildlife snag High risk due to likely failure and impact with significant or severe consequences to energized electrical equipment 105 Remove Convert to wildlife snag High risk due to likely failure and impact with significant or severe consequences to energized electrical equipment 106 Retain Retain No change in recommendation 107 Retain Retain No change in recommendation 108 Remove Convert to wildlife snag High risk due to likely failure and impact with significant or severe consequences to energized electrical equipment 109 Remove Retain Changed due to low or moderate risk at this time 110 Retain Retain No change in recommendation 111 Retain Retain No change in recommendation 112 Retain Retain No change in recommendation 113 Remove Retain Changed due to low or moderate risk at this time 114 Retain Retain No change in recommendation 115 Remove Convert to wildlife snag High risk due to likely failure and impact with significant or severe consequences to energized electrical equipment 116 Remove Retain Changed due to low or moderate risk at this time