4704 HARBOR LN 2018-01-02 MF Import

be properly controlled so that the erosion of the hillside is minimized. There is little to no discussion of this issue in either report. The Nelson report eludes to gravel filled ditches and pipes, but nothing definitive is presented. • As shown in the photos, the creek already has much silt and dirty water in it from this slide. This will only get worst during the rainy season. • There must be a design to control all the Anderson's surface water from flowing down the hillside and if the water is collected in a pipe system, the disposal of that water needs to be designed. If there is not a ;.gal agreement to cross or use adjacent private property, then this practice must stop and a means to go to the public storm sewer developed. A design is required for approval. Recommendations As said above, Jacobs Associates recommends the following: • We be asked to review the structural / civil design of the retaining wall system when available. A more detailed design of the wall and the hillside is required before any construction should begin. We should also review the calculations. Nothing should be built until that review is completed. • Your attorney should investigate if a large wall like the one proposed can be built in a wetland buffer zone. There are less intrusive ways from both a construction standpoint and visual from the Boulevard Bridge to prevent further erosion or movement of the hillside (see photos). • The 'spring' that is now flowing and eroding the hillside needs to be addressed. t A design of how to control this flowing water so that it does not erode and cause additional instability needs to be submitted for review. The majority of this work is on Chase property but the soil material came from the Anderson's property. • Agreements for access and to convey water in pipes across your property should be obtained. If you entertain an agreement, then a detailed engineering, erosion control and restoration plan must accompany the request. • Like the geotechnical report recommends, we agree that all of Anderson's soil should he removed from your property. The geotechnical report appears to state that this should be done everywhere below the vertical wall, but the cross section drawing only shows it to be on the Anderson property. JA thinks it should be done everywhere and if the approach in the Anderson's geotechnical report is followed, then when completed the soil and hillside should stabilized to the bottom of the ravine. • We also recommend that if water is conveyed in a pipe to the creek below that proper water dissipaters need to be installed to prevent erosion at the bottom. The design presented in the Anderson's geotechnical report is suitable. Summary After reviewing both the geotechnical and the vegetation restoration reports: Jacobs Associates strongly recommends that you request more drawings and reports that discuss the final design and how the Chase properties will be stabilized and improved in detail. The two reports appear to ONLY be concerned with the Anderson property and how to 1109 1" Avenue, Suite 501, Seattle, Washington 98101 Phone: (206)588.8200 Fax: (206)588-8201 Page J q/i3