832 RUCKER AVE 2016-01-01 MF Import

� Pioposed Modificalion lo the Residence oi Joel 8 Kathy Larsen February 12, 2004 Everett, Washington ORA Project Number: 04-065-Report 1 � � assumed that the high groundwater level is a foot above its current level, the bottom of the new slab-on-grade must be two feet above current groundwater elevation or at elevation 499 feet. If, as the homeowner demands, the bottom of the basement floor is placed at an elevation below the recommended elevation of 499 feet, the area will need to be permanently dewatered. And the homeowner must accept all the risk associated with buildi�g and maintaining a permanent dewatering system as well as the risk of damp or wet floors, mildew, and toxic mold. The homeowner must realize that some molds can render the home unsafe for human occupancy. To minimize the risk of groundwater contact with the basement floor, the basement floor should be placed on a system of supporting and filtering aggregates, synthetic filters, vapor retarders, and drains. The under-drain system, from bottom to top, should consist of the native Silty SAND soil; a three-inch this layer of imported, fine SAND, a layer of filter fabric similar to Mirafi� 180N; a six-inch layer of well-graded, free-draining, rounded to sub-rounded GRAVEL with four-inch diameter, Schedule 40, perforated pipes connected to a header system and tightlined to the off-site discharge point; a layer of 8 mil polyethylene sheeting; two- to three-inch thick layer of well-graded SAND. The groundwater must be permanently lowered to a level of at least six inches below the bottom of the free-draining gravel beneath the entire basement area. Issues associated with permanently lowering the water table are discussed later in this report. 6.3.2 Garage Slabs Garage slabs-on-grade sliould be supported on a minimum four-inch-thick, suitable, free-draining, sand or gravel base that follows gradation and compaction recommendations piovided in this report. A vapor retarder such as 6-mil polyethylene sheeting should be included beneath the slab to minimize transmission of moisture ttirough the concrete floor. A minimum, two-inch thick layer of clean sand may be piaced on top of the polyethylene sheeting to protect the sheeting and to enhance the curing of the concrete slabs. Otto Rosenau & Associates, Inc. Page 8 of 13