1020 NORTH PARK DR 2022-02-23 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No.961916 Mason Residence Addition and Deck August 24,2016 Everett,Washington Page 8 125 All grading operations and drainage improvements planned as part of this development should be planned and completed in a matter that enhances the stability of the slope, not reduces it. Excavation spoils associated with foundation subgrade excavations or temporary access for equipment should not be stockpiled near the slope, or be allowed to encroach on the slope. Also, runoff generated within the site should be collected and routed into a permanent discharge system away from the slopes. The slopes should be monitored on an ongoing basis, especially during the wet season, for any signs of instability, and corrective actions promptly taken should any signs of instability be observed. Lawn clipping and any other household trash or debris should never be placed on sloping ground. The soils encountered on this site are considered moisture-sensitive and may disturb easily when wet. To lessen the potential impacts of construction on the steep slope and to reduce cost overruns and delays,we recommend that construction take place during the drier summer months if possible. If construction takes place during the rainy months, additional expenses and delays should be expected. These extra expenses could include additional erosion control and temporary drainage measures to protect the slope, placement of a blanket of rock spalls to protect exposed subgrades, and the need for importing all-weather materials for structural fill. Under no circumstances, should water be allowed to flow over, or concentrate on the slope, both during construction and after construction has been completed. We recommend that stormwater runoff from the roof drains, paved areas, and yard drains be collected and tightlined to a suitable discharge point. The slope should be protected from erosion. We recommend that all disturbed areas be replanted with vegetation to re-establish vegetation as soon as possible. No fill or structures of any sort should be placed near the top of this slope without a specific evaluation. Stormwater runoff should not be allowed to concentrate or flow over the slope. Specific recommendations for erosion control are presented in the Erosion Control and Slope Protection Measures subsection of this report. Erosion Control and Slope Protection Measures The erosion hazard for the on-site soils are interpreted to be slight to moderate, 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 slopes. Stockpiles should be covered with plastic sheeting during wet weather and stockpiled material should be kept at least 35 feet away from the top of any slope. Disturbed NELSON GEOTECHNICAL ASSOCIATES, INC.