5900 36TH AVE W Geotech Report 2025-07-29

Mr. Richard Burrell February 9,2006 i.. The locations and extent of toe drains will be best determined in the field at the time of construction; however, they should be constructed so they will not receive water discharged by the dispersion pipes. This likely can be accomplished by covering the toe drain with at least two feet of relatively impermeable structural fill. Fill material derived from the on-site glacial till soils will generally be suitable for accomplishing this. We recommend that the sub-fill drains consist of a mat of four- to six-inch diameter quarry spalls constructed I along the axis of the drainage corridor. The mat should have a minimum thickness and width of at least 1.5 feet and 10 feet, respectively; however, final drain dimensions should be based on field conditions observed at the time of construction. We recommend covering the rock mat with a geotextile fabric, such as Mirafi 140N or I equivalent, to provide a separation layer between the rock and the overlying fill. The sub-fill drains should daylight several feet beyond the toe of the structural fill. As an alternative, the sub-fill drainage mat could be stubbed against the gabion barrier at the toe of the fill embankment,provided the lower approximately five feet of Ithe embankment fill between the Reno mattress and the sub-fill drain is constructed using four- to six-inch diameter quarry spalls. IWestern Outfall Location I As discussed, the western outfall is proposed to discharge to a swale located adjacent the Boeing railroad spur through a single, 25-foot long perforated pipe. The information provided to us shows the dispersion pipe constructed at grade and enveloped in a minimum of 24 inches of 6- to 12-inch diameter rip-rap (quarry spalls). IBased on our field observations, it is our opinion that the planned western outfall location is suitable for discharging site stormwater using the dispersion system shown on Sheet D-1.6 of the project plans. However,we I recommend placing a geotextile separation layer, such as Mirafi 140N or equivalent, between the soil subgrade and the rip-rap. We trust the information presented is sufficient for your current needs. If you have any questions or require I additional information,please call. I Sincerely yours, TERRA ASSOCIATES,INC. I <4Aitk- John C. S. Project:►, . a. ,s3 ,r, V 3 I �AI/ ,G _ , ,, .., _,:„..„,� , ,,,,.- 00 I Theode f . Sch•,' t;�''Y '' ?i- '.- Pr1nCi °` c Encl: I Project No.T-5738 IPage No.3