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' Addendum to Storm Drainage Report <br /> ' Purpose of Addendum This Addendum is prepared to provide drainage calculations and <br /> remediation proposals to correct the failure of a rockery underdrain and <br /> subsequent failure of the porous pavement recently installed in the <br /> ' Seaway Lot 2A Exotic Tool Welding site. Seaway Lot 2A is a 6.22 acre <br /> parcel, of which 1.2 acres was constructed as a commercial site in the <br /> Seaway Center development. The site now consists of one building <br /> and associated parking. It has been decided to remove the porous <br /> pavement and replace it with standard impervious pavement, a storm <br /> drain conveyance system and infiltration trench system to provide the <br /> required flow control, and a StormFilter structure to provide water <br /> ' quality treatment. <br /> See attached Exhibits EX-1 and EX-2 for the following discussions.The <br /> following outlines the chronology,steps and proposed corrective tasks. <br /> Calculations for the new proposed facilities are attached. <br /> ' Project Review The site slopes from high side on the east to the low side on the west. <br /> Porous pavement was proposed and constructed on about a third (or <br /> more) of the paved area. The pavement alternates between porous and <br /> ' impervious. There is porous pavement on the west and east sides,of the <br /> building. The interior drive was constructed with an inverted crown, <br /> with water collecting at centerline of drive. There is a low point in the <br /> pavement on west side of building/site. <br /> As-built survey of constructed pavement was performed. The site was <br /> constructed approximately 0.54' higher due to construction surveyor <br /> using top of monument box rather than actual monument in the box. <br /> This did not show any added effects on the drainage characteristics of <br /> the constructed condition. GeoEngineers letter received addressing <br /> infiltration in fill January 18, 2008,prior to approval of WHP plans by <br /> City of Everett.The outfall pipe to the rockery wall on the west side of <br /> the building failed and plugging of wall drain apparently occurred. <br /> Pavement/rockery failure occurred October 2008 on the west side of <br /> building. The rockery and pavement was replaced November 2008, the <br /> wall drain was reconnected. New pavement failures since November <br /> ' 2008 have occurred and will continue to occur without this proposed <br /> remediation. Saturation/hydro-static imbalance/subsurface piping <br /> occurring under the pavement are believed to be the causes of the <br /> ' subsurface settlement. The west portion of porous pavement <br /> /infiltration was constructed in fill. Settlement has occurred causing <br /> pavement failure and building slab separation and cracking. <br /> WHPacific received the contractor's as-built mark-ups August 19, <br /> 2009. Water and sanitary services constructed slightly different than <br /> design plan. This engineer found no significant issues with field <br /> Seaway Center Lot 2A—Storm Drainage Addendum P:fExotic Tool Welding1035123fDesignlReports135123,storm ADDEiVDUM.doc <br /> WHPacific,Inc. December 2,2009/Page 1 <br />