Laserfiche WebLink
} e � <br /> AS UA E , <br /> Consultants in Geotechnical Engineering, Geology <br /> and <br /> Environmental Earth Sciences <br /> April 18,2008 <br /> Project No.T-5922-1 <br /> Mr. Steve Pesce <br /> PacLand <br /> 11235 SE 6th Street, Suite 220 <br /> Bellevue,Washington 98004 <br /> Subject: Stormwater Detention.Pond Liner <br /> Seaway Center Lot 3C <br /> 23rd Drive West and 60th Street NW <br /> Everett,Washington <br /> References: 1. Preliminary Geotechnical Report, Seaway Center Lot 3C,Project No.T-5922-1, prepared by <br /> Terra Associates,Inc., dated October 22,2007 <br /> 2. Subsurface Exploration, Geologic Hazards and Preliminary Geotechnical Engineering Report, <br /> Seaway Center,Lot 3,Project No.G95103A,prepared by Associated Earth Sciences,Inc., <br /> dated January 14, 1998 <br /> 3. Letter—Storm Water Detention Pond Considerations, Seaway Center,Lot 3,Project No. <br /> G95103A,prepared by Associated Earth Sciences,Inc.,dated January 9, 1998 <br /> Dear Mr.Pesce: <br /> As requested, we reviewed the referenced geotechnical documents to address options for lining the proposed <br /> offsite stormwater detention pond located in the northeastern portion of Seaway Center Lot 3, about 600 feet <br /> north of Lot 3C. A plan sheet by PacLand titled Offsite Stormwater Pond, dated January 17, 2008 indicates the <br /> pond will be setback approximately 65 feet from the crest of western sideslope of the Narbeck Creek ravine. The <br /> pond will be constructed with two cells having bottom elevations of Elev. 413 and Elev. 415. These elevations <br /> are about 3 to 7 feet below existing surface grades. <br /> In our opinion, the pond liner may consist of compacted soil or a flexible membrane. Both liner systems should <br /> extend up the interior pond slopes to an elevation at least 12 inches above the maximum stored water elevation. <br /> Based on our conversation with you,we understand that grading associated with planned construction on Lot 3C <br /> will require a significant volume of excavation export. The soils observed in the upper 5 to 6 feet of our site <br /> explorations at Lot 3C are glacial till consisting predominantly of silty sand with varying amounts of gravel. In <br /> our opinion, the soil liner can be constructed using the on-site till soils provided they contain at least 20 percent <br /> fines(material passing the#200 sieve). Laboratory testing of soils observed in our site explorations indicate that <br /> much of the on-site till soils meet this gradation requirement. Review of the referenced Associated Earth <br /> Sciences, Inc. (AESI) documents indicates that glacial till may also be encountered in the planned pond <br /> excavation. <br /> 12525 Willows Road, Suite 101, Kirkland, Washington 98034 <br /> Phone (425) 821-7777 0 Fax (425) 821-4334 ` � <br />