2223 TAYLOR DR 2020-06-30 - Laserfiche WebLink

GeoTest Services,Inc. October 24,2014 Jacobson Deck and Garage Improvements,Everett,WA Job No. 14-0554 Stormwater Drainage Improvements Our on-site observations indicated the presence of below-grade drains that extend from the existing residence and discharge out onto the slope. GTS understands that there are a total of 3 pipes that discharge on the slope. GTS recommends that existing drain pipes be improved to include"tightline" connections that extend down to below the toe of the slope. The construction of a tightline system should include a 4-inch diameter solid PVC pipe that directs collected stormwater down the slope. It is assumed that the tightline will be run above ground and rest on the slope. GTS recommends that the tightline pipe be anchored with a typical collar style pipe anchor at a maximum spacing of 30 feet. At the base of the slope, the rigid conveyance pipe should be fitted with an appropriately sized diffuser tee in order to mitigate concentrated flow discharge that would otherwise cause excessive erosion at the discharge location. The conveyance system and diffuser tee should be ultraviolet resistant (assumes above-ground placement) and of sufficient strength to resist water hammer effects due to the length of the pipe and steepness of the slope. We recommend that the diffuser tee be adequately anchored and located below the base of the slope. GTS also recommends that the diffuser tee be underlain by a separation fabric such Mirafi 140N or an approved performance equivalent and then covered with quarry spall or similar erosion control features in accordance with applicable City of Everett Code and Best Management Practices. The stormwater collection and discharge systems should be considered routine maintenance items and should be regularly checked for proper working order. Typically, collection systems should be checked at least twice a year and after any major storm event. "Cut-Off" Drains It is our opinion that a series of optional drainage improvements can be made around..the property that would pick up near-surface sources of stormwater runoff. GTS recommends that cut-off drains be placed at strategic locations to either the north of the house and in close proximity to established drive paths, or to the south of the house, running across the length of the property and parallel to the top-of-slope condition. Drains should extend at least 3 feet below existing site grades and consist of a minimum 4-inch diameter perforated PVC pipe, surrounded by a minimum of 6 inches of filtering media on each side (minimum 12 inch wide trench), with the discharge sloped to carry water to a suitable collection system. The filtering media may consist of an open-graded drain rock wrapped by a nonwoven geotextile fabric (such as Mirafi 140N or equivalent) or a graded sand and gravel filter. Backfill around the drain should contain less than 3 percent by weight passing the U.S. Standard No. 200 sieve (based on a wet sieve analysis of that portion passing the U.S. Standard No. 4 sieve). All drains should be constructed with cleanouts to allow for the periodic maintenance and inspection of the drain. . Cut-off drains should be tightlined to discharge down below the slope as referenced in the "Stormwater Drainage Improvements" section of this report. Figure 1, attached to this report, is a conceptual detail showing the primary elements of the drain system. Page 4 of,