954 NORTH PARK DR 2023-10-31 - Laserfiche WebLink

GeoTest Services, Inc. Proposed Swimming Pool — 954 North Park Drive, Everett, WA September 6, 2019 Project No. 19-0361 • Proper drainage controls have a significant effect on erosion. All surface water and any collected drainage water upslope should be directed around the proposed development. All collected stormwater should be directed to an appropriate collection system. • All areas disturbed by construction practices should be vegetated or otherwise protected to limit the potential for erosion as soon as practical during and after construction. Areas requiring immediate protection from the effects of erosion should be covered with either plastic, mulch or erosion control netting/blankets. Areas requiring permanent stabilization should be seeded with an approved grass seed mixture, hydroseeded with an approved seed -mulch -fertilizer mixture or landscaped with a suitable planting design. In addition to the preceding recommendations, typical erosion control measures during construction will be required. These measures can included a rocked construction entrance or downslope silt fencing, depending on the regulations of the City of Everett and/or the governing jurisdiction. No other mitigations are required to address erosion hazards on the property. Mitigation of Geologic Hazards Because water is substantially less dense than soil, construction of a below -ground swimming pool would be considered an overall reduction in surcharge provided that the associated earthwork is minimal (i.e. fill is not added at the crest of the slope). GTS did not observe any noticeable signs of deep-seated instability during our visits to the site and during our review of published geological information or aerial imagery. Evidence of near -surface instability was noted on the existing bluff to the north of the subject property, but not on the existing slopes that are directly east and west of the proposed pool location. Provided that excavated soil from pool construction is exported from the site, rather than redistributed in the vicinity of the pool, it is GTS's opinion that the construction of the proposed pool will neither increase nor decrease the stability of the existing slopes. That said, GTS recommends that the proposed pool be set back at least 15 feet from the steep slopes to the east and west of the pool footprint. Surface water runoff and subsurface saturation can destabilize a slope. It is imperative that the design and construction of the pool consider the possibility of leaks and the potential need for homeowners to seasonally drain the pool water. No pool drainage system should be daylighted on or near the hazardous slopes. The use of a thick pool liner, pool water meter to monitor flow rates, or other appropriate measure should be employed to confirm that possible leaks in the pool walls or bottom can be safely managed. In addition, GTS recommends that a curtain drain be installed between the proposed pool and the top of adjacent steep slopes, in order to intercept any water that could leak through the pool and potentially reach the top of the slopes. The design of the pool itself is beyond the scope of our investigation. However, GTS is available for consultation with the design team for possible questions regarding pool design or drainage considerations. 13