1209 MADRONA AVE 2016-10-05 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No. 870113 Packer Property March 11,2013 Retaining Walls and Steep Slope Evaluation Page 10 Everett,Washington Additional expenses could include the need for placing additional erosion control and temporary drainage measures to protect the slopes, the need for placing a blanket of rock spalls on exposed subgrades and construction traffic areas, and the need for importing all-weather material for structural fill. Under no circumstances, should water be allowed to flow over, or concentrate on the site slopes, both during construction and after construction has been completed. We recommend that stormwater runoff from the roof drains, yard drains, and other hard surfaces be collected and tightlined to a suitable discharge point at the bottom of the slope as is currently the case. These systems should be implemented and maintained on a regular basis. The slopes should be protected from erosion. We recommend that all disturbed areas be replanted with vegetation to re-establish vegetation cover as soon as possible. Erosion Control and Slope Protection Measures The erosion hazard for the on-site soils is listed as high, but the actual hazard will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices(BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site or flowing over the steep slope. Stockpiles should be covered with plastic sheeting during wet weather and stockpiled material should be placed no closer than 30 feet from the top of the slope. Disturbed areas should be planted as soon as practical, and the vegetation should be maintained until it is established. The erosion potential for areas not stripped of vegetation should be low. Protection of the steep slope area should be performed as required by the City of Everett. Specifically,we recommend that after the recommended improvements are completed, the slope not be disturbed or modified through placement of any fill or removal of the vegetation. No additional material of any kind should be placed on the slope or be allowed to reach the slope, such as excavation spoils, lawn clippings, and other yard waste, trash, or soil stockpiles. Trees should not be cut down or removed from the slope unless a mitigation plan is developed, such as the replacement of vegetation for erosion protection. Vegetation should not be removed from the slopes. Replacement of vegetation should be performed in accordance with City of Everett code. Any future improvements within the backyard area should be the subject of a specific geotechnical evaluation. Under no circumstances should water be allowed to concentrate on the steep slope. NELSON GEOTECHNICAL ASSOCIATES, INC.