1415 BROADWAY CM HEATING 2023-09-25

k Geotechnical Engineering Evaluation NGA File No. 1213420 CM Heating Additions January 8,2021 Everett,Washington Page 11 Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out and routed into a permanent storm drain. We recommend the use of footing drains around the structures. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch- diameter, rigid, slotted or perforated, PVC pipe surrounded by free-draining material wrapped in a filter fabric. We recommend that the free-draining material consist of an 18-inch-wide zone of clean (less than three-percent fines), granular material placed along the back of walls. Pea gravel is an acceptable drain material. The free-draining material should extend up the wall to one foot below the finished surface. The top foot of backfill should consist of impermeable soil placed over plastic sheeting or building paper to minimize surface water or fines migration into the footing drain. Footing drains should discharge into tightlines leading to an appropriate collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. Stormwater Infiltration: Due to the dense, silty nature of the site soils, it is our opinion that the infiltration capacity of the native onsite soils is limited. In our opinion, low impact design infiltration systems could be considered for the site, including, but not limited to rain gardens and pervious pavements, however this should be determined by the project civil engineer during the final design process. An overflow component directed to an approved point of discharge should be incorporated into any low impact design systems. Alternatively, stormwater generated on the site could be detained and ultimately discharged into an existing stormwater system, likely in the neighboring roadway. CONSTRUCTION MONITORING We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations,to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications.We should be contacted a minimum of one week prior to construction activities and could attend pre-construction meetings if requested. NELSON GEOTECHNICAL ASSOCIATES, INC. � IA 2\