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Home My WebLink About03139 - Technical Information Report - Drainage �� SUPPLEMENTAL STORM DRAINAGE ANALYSIS S�✓�2� -_3�3,9 Proposed Kenworth Truck Facility Parking Lot improvement Renton, Washington Prepared for: Kenworth Trucking Company P.O. Box 9001 Renton, WA 98055 December 5, 2003 Our Job No. 11153 ��,NAL F �e - Z CIVIL ENGWEERING, LAND PLANNING, SURVEYING, ENVIRONMENTAL SERVICES - 15215 7ZND AVENUE SOUTH KENT,WA 98032 (425) 251-6222 (425) 251-8782 FAx °.t i BRANCN OFFICES ♦ OLYMPIA,WA • WALNUT CREEK, CA �'°<, ��.y� www.barghausen.com , E ~G ENG1N 3�3 y Ea�isting Storm System Summary Proposed Kenworth Truck Facility Parking Lot Improvement Project Description: This project proposes to construct approximately 1.5 acres of new asphalt pavement on the south end of the existing Kenworth Truck Facility. This site is located south of North 8th Street and just north of North 6th Street between Garden Avenue North and Houser Way in Renton, Washington. Please refer to the enclosed vicinity map for a more specific project location. This summary provides information about the existing storm drainage system on site and the reason why additional detention and water quality facilities are not needed. Existing Conditions: The existing 1.5-acre area is cunently a gravel parking lot, which serves as a roadway for trucks and for storage of production materials and cargo trailers. Slopes in the project are relatively flat, with existing drainage routed to the existing pavement and trench drain north and west of the project site. This trench drain conveys runoff west and north around the site perimeter and then to the storm facility. The runoff from the trench drain is routed through an existing oiUwater separator prior to discharging into an existing biofiltration swale. The bioswale discharges into an existing two-cell detention pond with a gravel filter. The detention system then discharges through a control structure into the existing storm drainage system in the North 8th Street (see the enclosed drawings illustrating the conveyance and storm system). Analysis: In the 1992 construction drawings of the Kenworth Truck Facility by SSOE, Inc., the project area is specified as a future division office. The existing ground is sloped to the west, so that area would drain to the trench drain. The drainage basin from the 1992 report was recreated using the construction drawings and the limits of construction. The calculations in the Storm Drainage Report for the Kenworth Truck Facility that accompanied the construction drawings were done with a project site of approximately 37.4 acres. This includes the proposed 1.5-acre project site. The recreated basin boundary matched the 37.4-acre basin. This exhibit is enclosed as a reference. In some preliminary calculations for the site (Andersen, Bjornstad, Kane, Jacobs, Inc, dated May 26, 1989), the post-developed site had almost 90 percent impervious area (89.6 percent) for the detention pond calculations. The construction drawings show less than 90 percent impervious area even if the detention pond area and the proposed 1.5-acre parking are included as impervious areas. From the construction drawings and the existing calculations, it can be assumed that the proposed parking area was included in the detention calculations as impervious surface (see the enclosed drawings). Conclusion: Since the project site was included in the construction drawings and storm calculations as proposed impervious surface, the water quality facility and detention pond was sized to accommodate runoff from this area and no new facilities need to be constructed. 11153.005.doc I � � � � � � Z � V � � _ _ _.. ep " �� KENWORTH'S OVERALL SITE PLAN ` � �� N.BTH Si. �k ��i � � �.—'—'—'_'� i�i 0 � ii , �� I � , . t .0 ,, . � �• �% . � i �. %, � � � .,�.,a ' � %' �� 0 t � I j i `� �'��''''.,, ! � z � � � � I R&D � soo.000 ��. —Y '`• '',.,, � � TANK B PUM �' �/ �a.��..,. Q ��.�,� � r �. � ��''ii i � \� � z �� . C�(� . .w� a �� ,z � � $�� ao � �� ' � �� • � a� � . . � � z ? ,� � -- '':'r"'� � � � a � � � ,.,� Y`�a f � � p � � � 9 "'" o '- E � � � ' � � � � � � � I� � ;�� o D � ,, � � * � � � 1 � � � � MAIN � a GAS ; �� SHU OFF , � +uawvY ; � ( I � � �� >,.o.,... � � �� . � - � � � � z Q�� Y �;pp � Z � � Y Q ��±.. � � � urnn ,�n.u..,uwae (1 _ � a Q Q2►�av,. � }� 0 �� }� VWwnLLCn�i[NIK � < ••+� � •flC 15C/.IXCxI l4G - _ � � W!r"� b�Y�w•'r. �s.��, rao��er s�T� �t �� ..�.�F � � '�� rp.,, �� { a - �N,�.�. � �I� � .. VACATED N.8TH 3TREET � � � Z � � � � C/1 Z � � a w � � z � � A