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HomeMy WebLinkAboutRevised SWARR Arborist Report 8-9-17SWARR Storage Tank Coating Investigation Arborist Report and Tree Replanting Plans PSE SWARR Storage Tank Site 2100 Benson Drive South Submitted to: Dave Jenness and Elaine Babby, PSE Prepared by: Otak, Inc. 11241 Willows Road NE, Suite 200 Redmond, WA 98052 Otak Project No. 31983.i June 15, 2017 Updated August 9, 2017 i otak K:\project\31900\31983I\ProjectDocs\Reports\SWARR Arborist Report.docx Table of Contents SWARR Storage Tank Coating Investigation Arborist Report Page Section 1—Introduction .......................................................................................... 1 Section 2—Discussion ............................................................................................. 2 Section 3—Recommendations ............................................................................... 3 Appendices Appendix A— Tree Map Appendix B— Tree Table Appendix C— Images Figures Figure 1— Site Aerial Figure 2— Tree Removals Figure 3— Tree Replanting Plan Figure 4— Tree Replanting Plan Alternative Figure 5— City of Renton Tree Protection Fence Detail Section 1—Introduction 1 otak This arborist assessment and report was prepared to inform the PSE tank coating investigation team and the City of Renton of select existing tree conditions. A site visit was conducted on April 18, 2017 and a second site visit was conducted on August 7, 2017 to locate the trees using a handheld GIS supplemented with tape measurements in the field. The site is 727,887 square feet in size and located in the City of Renton jurisdiction on a lot zoned R-8. The tank coating investigation requires visual inspection of underground propane tanks in eight specific locations. The trees noted in this report and tree table are growing at or near the northeast location of one of the inspection excavation sites. Fifteen trees are located within the excavation limits required for the visual inspection of the propane tanks at the northeast corner of the site. These fifteen trees are numbered 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 and 17. The excavation is likely to extend deeper than 4’ below the ground surface in order to visually inspect the full cross section of the underground propane tanks. To comply with OSHA standards the excavation will need to provide a 1:1 slope to ground surface 4’ above the floor of excavation in order to protect personnel who are in the trench from potential trench failure. This expands the necessary soil excavation limits and the potential tree impacts. Seven trees are near the excavation limits but are unlikely to be detrimentally impacted by the excavation and inspection activities. These seven trees are trees 1, 2, 18, 19, 20, ROW 1 and ROW 2. Tree protection measures, discussed further in section 3, should be used to ensure retention of these trees. The trees are identified on the tree map in Appendix A by their tree numbers which correspond to the tree numbers of the tree table in Appendix B. The trees in the field are not tagged. The tree table also includes the diameter at breast height (DBH), common name, botanical name, health rating, condition rating, and comments about each tree. The health and condition ratings use a range of excellent, good, fair, and poor. These ratings are based on observations of each tree including the size; indications of relative vigor for species and location; canopy health including density, symmetry, and leaf or bud conditions; injury; abnormal insect activity; root damage and/or restrictions; trunk health; indications of parasitic and saprobic fungi; and dead and/or hanging limbs. Section 2—Discussion 2 otak The work proposed will require removal of significant trees and potentially reduce the visual buffer for two neighbors at 732 South 19th Street and 1812 Burnett Avenue South. These neighbors are at a much higher elevation than the facility and look over the Benson Drive South right-of-way and down at the subject site. The elevation difference between the on- site planting locations and the neighbors provides a challenge to meeting the intent of the code for providing a visual buffer. If new trees are planted on the subject property they are not likely to provide the visual buffer for ten to twenty years because the only available location on PSE’s property would place them in a low area at the base of the road embankment, see image 1. One solution is to plant some of the visual buffer plantings on the subject property and part of the visual buffer plantings on the east side of the Benson Drive South right-of-way. Alternatively, all of the mitigation trees can be placed on the subject property but the elevation changes between the neighbors and the newly planted trees would not achieve the visual buffer for many years after they are planted. View from west side of Benson Drive South, in line with view of subject site from 1812 Burnett Avenue South; the dotted red line indicates trees proposed to be removed for site investigative work Section 3—Recommendations 3 otak Otak recommends that fifteen trees be removed prior to excavation for visual inspection of the underground tanks. These trees recommended for removal are numbered 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 and 17. The excavation required will compromise the majority of these trees root zone and are likely to destabilize these fifteen trees. The existing visual buffer will be removed, impacting the neighbors at 732 South 19th Street and 1812 Burnett Avenue South. The best location for newly planted trees to provide visual buffer to the neighbors is on the Benson Drive South road embankment to the east of the travel lanes, within the public right-of-way. This is the best solution because it provides a visual buffer planting that will perform more quickly due to the elevation difference between the neighboring property and the subject property. Locating the visual buffer planting in the right-of-way will also diminish the vigor and expanse of Himalayan blackberry, a noxious weed. The alternative is to provide replacement visual buffer tree plantings entirely on the subject property. Otak also recommends tree protection measures for trees 1, 2, 18, 19, 20, ROW 1 and ROW 2 along with other trees on-site. Trees 1, 2 and 18 should have temporary construction fencing installed and maintained for the duration of work; the temporary construction fencing should be located at the outside drip line edge nearest the work to prevent excavation equipment and excavated soil from being placed on their root zone. Tree protection measures for tree 19 would include installing temporary construction fencing eight feet south of tree 19 and extending at least thirty feet, centered on the trunk of tree 19. Tree protection measures for tree 20 would include installing temporary construction fencing eight feet north of tree 20 and extending at least twenty feet, centered on the trunk of tree 20. Lastly, the arborist mulch generated from the removal and chipping of trees 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 and 17 should be spread within the drip line of the remaining trees but outside of the lawn area. Arborist mulch should be placed between three and six inches deep and feathered within a few inches of the trunk to avoid contact with the tree trunk. Prepared by: Tom Early, PLA Landscape Architect, State of Washington, #1199 Certified Arborist with Tree Risk Assessment Qualification, PN-5622A Appendix A - Tree Maptree # 20 tree # 19 tree # 1 tree # 2 tree # ROW 1 tree # ROW 2 tree # 5 tree # 4 tree # 3 tree # 8 tree # 7 tree # 6 tree # 10 tree # 9 tree # 11 tree # 16 tree # 15 tree # 14 tree # 18 tree # 17 tree # 13 tree # 12 NORTH NOT TO SCALE TREES LABELED IN GREEN WITH YELLOW LEADERS ARE RETAINED AND TREES LABELED IN RED ARE PROPOSED FOR REMOVAL PSE SWARR Tree Table 1 of 1 Tree #DBH Common Name Botanical Name Health Condition Comments 1 19.8 Douglas fir Pseudotsuga menziesii Excellent Good Intact leader, great form, good color, healthy twig elongation, small amount of deadwood, young and vigorous with canopy space to continue to full mature height 2 24.5 Douglas fir Pseudotsuga menziesii Excellent Good Intact leader, great form, good color, healthy twig elongation, small amount of deadwood, young and vigorous with canopy space to continue to full mature height 3 12.1 Douglas fir Pseudotsuga menziesii Fair Fair Located on slope in which ex avation deeper than 4' is likely to disrupt root plat because of OSHA layback requirements for trenching; fair health and condition rating due to suppression from neighboring trees 4 17 Douglas fir Pseudotsuga menziesii Good Good Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 33- 50% of potential canopy width, do not isolate due to concerns over windfirmness 5 17.3 Black Pine Pinus nigra Good Good Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 50% of potential canopy width 6 11.9 Douglas fir Pseudotsuga menziesii Fair Fair Located on slope in which ex avation deeper than 4' is likely to disrupt root plat because of OSHA layback requirements for trenching; fair health and condition rating due to suppression from neighboring trees 7 15.6 Douglas fir Pseudotsuga menziesii Good Good Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 33- 50% of potential canopy width, do not isolate due to concerns over windfirmness 8 14.4 Douglas fir Pseudotsuga menziesii Good Good Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 33- 50% of potential canopy width, do not isolate due to concerns over windfirmness 9 9.9 Douglas fir Pseudotsuga menziesii Fair Fair Fair health and condition rating due to suppression from neighboring trees, crowded by nearby trees which is impacting approximately 33-50% of potential canopy width, do not isolate due to concerns over windfirmness 10 19.9 Douglas fir Pseudotsuga menziesii Good Good Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 33- 50% of potential canopy width, do not isolate due to concerns over windfirmness 11 10.7 Black Pine Pinus nigra Fair Fair Located on slope in which ex avation deeper than 4' is likely to disrupt root plat because of OSHA layback requirements for trenching; fair health and condition rating due to suppression from neighboring trees 12 19.5 Douglas fir Pseudotsuga menziesii Good Good Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 33- 50% of potential canopy width, do not isolate due to concerns over windfirmness 13 10.4 Black Pine Pinus nigra Fair Fair Fair health and condition rating due to suppression from neighboring trees, crowded by nearby trees which is impacting approximately 50% of potential canopy width, do not isolate due to concerns over windfirmness 14 11.5 Black Pine Pinus nigra Fair Fair Located on slope in which ex avation deeper than 4' is likely to disrupt root plat because of OSHA layback requirements for trenching; fair health and condition rating due to suppression from neighboring trees 15 14.9 Douglas fir Pseudotsuga menziesii Fair Fair Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 33- 50% of potential canopy width, do not isolate due to concerns over windfirmness 16 12.3 Douglas fir Pseudotsuga menziesii Fair Fair Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 33- 50% of potential canopy width, do not isolate due to concerns over windfirmness 17 18.2 Black Pine Pinus nigra Good Good Intact leader, good color and healthy twig elongation, somewhat crowded by nearby trees which is impacting approximately 50% of potential canopy width 18 19.5 Douglas fir Pseudotsuga menziesii Good Good Intact leader, good color and healthy twig elongation 19 19.8 Bitter Cherry Prunus emarginata Good Fair Three main stems with a union at 3' above ground surface (AGS) and at 8' AGS, ivy up 40'+ in two stems 20 29 Deodar cedar Cedrus deodara Good Fair Lost top at ~35' with four regenerating stems extending approximately 15 to 20 feet above main stem, all regenerating stems are well attached and one is dominant , natural crown asymmetry to southwest due to light competition from trees to north and east ROW 1 ~14 Big Leaf Maple Acer macrophyllum Good Fair Located on road embankment due west of tree #11, acute angle at main stem union ~25' AGS ROW 2 ~14 Big Leaf Maple Acer macrophyllum Good Fair Located on road embankment due west of tree #9, acute angle at main stem union ~20' AGSAppendix B - Tree Table Appendix C—Images Image 1: subject trees with tree 1 indicated on right and tree 18 indicated on left; note the houses in the background and their elevation above the site. View is looking east along northern fence-line of site. Image 2: looking north with tree 14 indicated on left, tree 16 in middle and tree 17 on right; note swale to left of tree 14 descends approximately ten to fifteen feet and meets Benson Drive South road embankment Appendix C—Images Image 3: tree ROW 1 indicated on left and tree ROW 2 on right; image taken from bottom of swale looking northwest, note elevation gain and inability to see neighbor’s houses Image 4: tree 19 indicated on left with an abundance of ivy and tree 20 on right, these trees are to be retained; view is looking east towards northeast corner of site Figure 1 Figure 1 – Site Aerial: Google snapshot with visual buffer between the site and western neighbor’s indicated with white arrows and proposed tree removals approximated in white dotted line; callouts indicate site image location and directions 1 2 3 4 TREE PROTECTION FENCE DETAIL. DRIPLINE METHOD Figure 5 - City of Renton Tree Protection Fence Detail