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HomeMy WebLinkAboutSWP272190 TECHNICAL INFORMATION REPORT ' PROJECT: STRATFORD PLACE 92-48 zl �J 0 PREPARED FOR: CAMWEST DEVELOPMENT P.O. BOX 308 KIRKLAND WA 98083 ";ITY OF REWON RECEIVED DEC 1 11992 PREPARED BY: WSTOMER SERVICE JOHN R. NEWELL PACIFIC ENGINEERING DESIGN, INC. 130 ANDOVER PARK EAST, SUITE 300 ' SEATTLE, WA 98188 (206) 431-7970 Ne ' 1270' ��i�S1�1;1S7'ERF'��' (2a�►9Z NA1 F EXPIRES: 9/5/ l December 9, 1992 ' TABLE OF CONTENTS ' I. Project Overview . . . . . . . . . . . . . . 1-3 II. Preliminary Conditions Summary . . . . . . . 1-13 ' III. Off-Site Analysis . . . . . . . . . . . . . . 1-6 IV. Retention/Detention Analysis and Design . . . 1-38 ' V. Conveyance Systems Analysis and Design . . . 1-11 ' VI. Special Reports and Studies . . . . . . . . . 1-19 VII. Basin and Community planning Areas . . . . . . ' VIII. Other Permits . . . . . . . . . . . . . . . . . IX. Erosion/Sedimentation Control Design . . . . 1-8 ' X. Bond Quantities Worksheets . . . . . . . . . . . XI. Retention/Detention Facility Summary Sheet ' and Sketch . . . . . . . . . . . . . . . . . . . XII. Maintenance and Operations Manual . . . . . . . . I. PROJECT OVERVIEW PROJECT OVERVIEW: ' The proposed project is for the subdivision of 3 . 06 acres of land into 14 single family lots. The present site contains three wood frame houses, associated roadways/driveways, lawns and sheds. The northerly one half of the site has tree cover consisting of a mixture of deciduous ' and conifer trees. The developed site will contain one cul-de-sac roadway and 14 lots. The ' easterly tier of lots (1 through 6) will require some grading during the home construction phase to provide access and adequate building/lawn areas. The site lies within the Cedar River Drainage Basin and drains from east to west across the site. There are off-site flows whichh enter the site along the easterly boundary which will be conveyed to NE 16th Street ' using back yard drainage swales and/or interceptor drains. A small portion consisting of curb gutter and concrete sidewalk adjacent to NE 16th Street will by-pass the detention system and flow to the west. ' This amount of by-pass is insignificant since the total area amounts to approximately 0. 04 acres. It should be noted no additional asphalt pavement will be added to NE 16th Street for full road improvements because the present pavement width is presently 181 . ' Since the site consists of Indianola soils which exhibit very good percolation rates an infiltration tank will be used for storm detention. ' The tanks will be located on lots 12 , 13 , and 14 within the front yard setback. The plat lies within Zone 2 of the Aquifer Protection Ordinance; therefore storm water will require biofiltration prior to being discharge by means of percolation. The biofiltration facility is located within the rear yards of lots 12 , 13 and 14 and supplies and equivalent area for biofiltration instead of the required 200 foot length. ' Since all site runoff except for the minor amount within NE 16th Street will be infiltrated back into the ground as ground water recharge this plat development runoff will be less in the developed state than exists presently. The detention system was design for the 100 year/24 hour event with a factor of safety of 4 . 8 : 1 based on the actual percolation tests. ' King County Building and Land Development Division Page 1 of 2 TECHNICAL INFORMATION REPORT (TIR) WORKSHEET ' ProjectOwner CAMWEST DEVELOPMENT, INC. Project Name STRATFORD PLACE Address 924 BELLEVUE WAY NE Location ' Phone (206) 637-9747 Township Project Engineer JOHN R. NEWELL Range PACIFIC ENGINEERING DESIGN INC. Company SectionProject Size 133290 S.F. AC 3.06 ' Address Phone 206) 431-7970 Upstream Drainage Basin Size AC 3.6 PART 3 - OF . .I I w 11- [M Subdivision DOF/G HPA Shoreline Management Short Subdivision 0 COE 404 Rockery ' 0 Grading DOE Dam Safety Structural Vaults 0 Commercial FEMA Floodplain Other Other 0 COE Wetlands HPA :PARTS SITE AND . - Community RENTON HIGHLANDS ' Drainage Basin CEDAR RIVER PART 6 SITE CHARACTERISTICS'7 ' River Floodplain Stream 0 Wetlands 0 Critical Stream Reach 0 Seeps/Springs ' Depressions/Swales High Groundwater Table Lake Groundwater Recharge 0 Steep Slopes Other ' 0 Lakeside/Erosion Hazard ' Soil Type Slopes Erosion Potential Erosive Velocities -• INDIANOLA �� �o — SI►aL�-,}- SYS(—'� 0 Additional Sheets Attatched ' ,2 . 1/90 Page 2 of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET ,. REFERENCE LIMITATION/SITE CONSTRAINT 1 Ch.4-Downstream Analysis N/A 0 ■ a i o a 0 Additional Sheets Attatched PART, MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION FOLLOWING CONSTRUCTION I ® Sedimentation Facilities ] Stabilize Exposed Surface ® Stabilized Construction Entrance ® Remove and Restore Temporary ESC Facilities n Perimeter Runoff Control EZ Clean and Remove All Silt and Debris ' ® Clearing and Grading Restrictions ® Ensure Operation of Permanent Facilities ® Cover Practices E::] Flag Limits of NGPES XCX Construction Sequence 0 Other Other ® Grass Lined Channel 0 Tank ® Infiltration Method of Analysis Pipe System 0 Vault Depression SBUH Open Channel Energy Dissapator 0 Flow Dispersal Compensation/Mitigation ! Dry Pond Wetland Waiver of Eliminated Site Storage 0 Wet Pond 0 Stream Regional Detention Brief Description of System Operation INFILTRATION TANK TO DISCHARGE RUNOFF VIA PERCOLATION Facility Related Site Limitations 0 Additional Sheets Attatched ' Reference Facility Limitation N/A &'1q'i6l El(j'J�V 1 f7j OMNI K J Drainage Easement Cast in Place Vault Other Access Easement ® Retaining Wall 0 Native Growth Protection Easement ' Rockery>4'High Tract Structural on Steep Slope Other SIGNATUREPROFESSIONAL - I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attatchments. To the best of my knowledge the information provided here is accurate. sry,w&a.r. r 1, 1/90 II . PRELIMINARY CONDITIONS SUMMARY 1 1 1 January 7, 1992 ' OFFICE OF THE HEARING EXAMINER CITY OF RENTON REPORT AND RECOMMENDATION ' APPLICANT: CAMWEST DEVELOPMENT, INC. File No.: ECF;PP;V-099-91 LOCATION: 2400 NE 16th Street SUMMARY OF REQUEST: Stratford Place, a 14 lot subdivision consisting of 13 new single-family houses and one existing single-family house. A Variance is requested from Section 9-12-8.G.14 of the Subdivision Ordinance to decrease the plat access road off- set from 200 feet to 130 feet. ' SUMMARY OF ACTION: Planning Division Recommendation: Approval with Conditions ' PLANNING DIVISION REPORT: The Planning Division Report was received by the Examiner on January 21, 1992. ' PUBLIC HEARING: After reviewing the Planning Division Report, examining available information on file with the application, and field checking the property and surrounding area, the Examiner conducted a public hearing on the subject as follows: MINUTES The hearing was opened on January 28, 1992, at 9:05 a.m. in the Council Chambers of the Renton Municipal Building. Parties wishing to testify were affirmed by the Examiner. ' The following exhibits were entered into the record: Exhibit #1 - Yellow File containing application, proof of posting ' and publication and other documentation pertinent to this request. Exhibit #2 - Tree Cutting and Land Clearing Plan ' Exhibit #3 - Neighborhood Vicinity Map ' Exhibit #4 - Preliminary Plat Map Exhibit #5 - King County Stormwater Design Manual (4 sheets) ' Exhibit #6 - Map Showing Offset Exhibit #7 - October 3, 1991 Letter from Mr. Blake to Mr. ' Forsander CamWest Development, ECF;PP;V-099-91 ' January 7, 1992 Page 2 ' The hearing opened with a presentation of the staff report by PAUL FORSANDER, Senior Planner, Development Planning Division, who stated that the property was zoned R-1, single family residential, ' annexed in 1960; existing public services such as water, sewer, storm drainage, and fire protection were available to the site, as well as parks and schools; transit routes were about one block east on Edmonds Avenue. The proposed project was an allowed use under the Comprehensive Plan and was in compliance with existing zoning and subdivision regulations. The project received a Determination of Non-significance by the Environmental Review Committee. There were three existing houses on the site, one of which would be retained and moved, while the other two were to be demolished. The offset variance was being requested to avoid placing the street in the back yard of the existing homes ' on the west side of the Camas cul-de-sac. The property in the southwest corner was not available to be part of this proposal. Since NE 16th Avenue was not fully improved, the applicant would need to provide curbs, gutters, sidewalks, and additional street lighting along NE 16th. All of the lots except for lot number one satisfy area dimensional requirements. The Subdivision Code requires corner lots to be wider and deeper than interior lots, btfi it didn't appear to Mr. Forsander as though that lot would be deficient in any way and staff was not recommending that the proposed lot size be revised. In answer to the Examiner's question, Mr. Forsander agreed that wider and deeper corner lots were required by code. Mr. Forsander stated that the subdivision would generate approximately 140 average weekday vehicle ' trips per day resulting in no significant traffic impact. The site slopes about 15%, east to west and is generally rolling from north to south. A tree retention plan would be required to maintain the character of the site and surrounding area. There are subdivisions with similar cul-de-sacs in the area, such as the Camas Subdivision to the west. Mr. Forsander.advised that the Parks and Recreation Department would like the applicant to review the Recreation Comprehensive Plan since there was no recreation proposed on site, and would work with ' the applicant to develop some sort of mitigation program. About eight school-age children would be generated by this project which would make no significant impact on the schools. The applicant had proposed to place the stormwater detention facilities within the right-of-way, and had requested a ' variance from the stormwater code, but this is departmental policy, not a code requirement. Staff has proposed working with the applicant to accomplish a different approach, which could include location of stormwater retention in a separate tract, or a drainage easement across the front or back yards of the lots, or in the right-of-way and that then could be vacated to make a private street. Staff would not ' recommend approval of city maintenance of a private drainage facility within the right-of-way. The Examiner asked if the preliminary plat was premature since at this point he should be provided with a storm drainage plan that he could approve. Mr. Forsander answered that there had been a storm ' drainage analysis but staff was recommending that this facility not be in the right-of-way and believed that bio filtration swales could be located in the front yards.of the properties on the west side of the cul-de- sac. The site is not within the sewer moratorium area. ' Mr. Forsander reviewed the four criteria for granting a variance and stated that staff believed there was a hardship created by the existing pattern of subdivisions, short plats, and streets surrounding the property. The issue of public welfare relates to traffic safety, and the issue, although not defined as ' such in the code, is that 200 feet is required to minimize turning movement conflicts between streets. In the case of the existing Dayton Court south of NE 16th, Mr. Forsander felt that there would not be conflicting turning movements between the two cul-de-sacs. What the Traffic Department was ' concerned about was people turning out to the left, and people turning left out of the cul-de-sac across the street. The recommendation was for four inch double centerline traffic buttons and additional street lighting, so that when people turned out, they would get an audible warning and vibrations to the steering wheel if they strayed over the center line. With proposed improvements, staff did not believe ' the street would be unsafe. In terms of granting special privilege, Mr. Forsander said there were 1 � G3 CamWest Development, :nc. ECF;PP;V-099-91 ' January 7, 1992 Page 3 ' several instances of similar offsets throughout the city. Staff recommendation was approval, subject to conditions as summarized: that the applicant provide a tree preservation plan to minimize cutting of ' trees; that the applicant evaluate the feasibility of connecting the existing 6" water line near the northeast corner .of the property with the existing 16" water main located on NE 16th street, forming a loop and, if feasible, then would recommend that this connection be required; that the applicant extend ' the existing 8" sewer line to the east property line; that the applicant modify the proposal and submit revised plans to locate the storm drainage facilities in a separate tract or storm drainage easement prior to issuance of any site improvement or construction permits for the street; that the applicant be responsible for traffic and street improvements such as curbs, gutters, sidewalks, street lighting ' improvements along NE 16th;'that the applicant meet with representatives of the Parks and Recreation Department to discuss the impact of the project on recreational facilities, and make a voluntary contribution to the Parks fund. As for the subdivision street improvements, the applicant shows a ' planting circle at the end of the cul-de-sac which would not be allowed by the Fire Department, as that area would be needed for fire equipment turnaround. Regarding storm' drainage,£Mr° Forsander noted that the applicant could request approval to construct the storm drainage facilitie's-within the right-of-way and then vacate the street. As long as the street was constructed to city standards and the applicant agreed to maintain it, that probably would satisfy the department. He didn't believe the City Council would agree to city maintenance of the storm ' drainage system. The Examiner stated that he was concerned about the corner lot issue. Mr. Forsander replied that this lot was platted the same as all the other lots, although technically required to be platted wider, and when asked how that provision could be ignored, he answered that it couldn't be ' ignored, and would have to be modified unless a variance was requested. ERIC CAMPBELL, P.O. Box 308, Kirkland, WA 98033, testified for the applicant, stating that lot widths were.60 feet for the interior and 70 feet for the corner lot, as required by code, and he felt that t the lots sizes for the proposed project did meet the code. The Examiner advised that there were two different standards; one was the Zoning Code, which the applicant had cited, the other was the Subdivision Ordinance,which required that corner lots be platted wider than interior lots, the main ' reasons being that a corner lot had two front yards, and to keep the block front looking similar. Mr. Campbell replied that the corner lot could be made one foot wider to meet the code. Regarding tree retention, he said that they would need to be able to clear lots one, two and three where existing houses ' must be demolished, and lots seven and eight to which a house would be moved. A predominate amount of trees were located right in the middle on lots 12 and 13, and although the applicant was taking great pains to save trees, he requested that part of the staff recommendation be altered to allow for necessary tree cutting. The Examiner. stated that was a provision of the code that he was not ' involved with, but obviously, accommodation for reasonable setbacks and building envelopes could be made. Beyond that, he would abide by staff recommendation. Mr. Campbell addressed the question of storm drainage and the reason why the applicant was proposing it to be located in the right-of-way, stating that he believed Renton had adopted the King County Surface Water Design Manual (KCSWDM), and he felt that there was a conflict with unwritten policies of the city of Renton. Mr. Campbell quoted from the KCSWDM, stating that it specified that stormwater retention could be constructed in the right-of-way. The Examiner said he didn't believe all of the provisions of the ' KCSWDM had been adopted, to which Mr. Campbell replied that he believed the water pollution aspects and the retention capacity of the core requirements had been adopted and that stormwater retention was allowed in the right-of-way. He declared that the Homeowner's Association would be ' willing to maintain it, and he felt it made more sense to have those facilities in the right-of-way if and when Renton did decide to maintain it. The Examiner stated that matter was up to the City Council, which a number of years ago had a strict policy against maintaining private stormwater retention systems. Mr. Campbell further stated that there was no problem with contributing $2,100 to the recreation and.parks fund. CamWest Development, �. c. ECF;PP;V-099-91 January 7, 1992 Page 4 GARY NORRIS, William E. Popp Associates, First Interstate Centers Suite 314, 225 108th AVE NE, Bellevue, WA 98004, spoke to the offset left turn issue, stating that code specified 200 feet to minimize the conflict in left-turning traffic, although that was an issue, he believed people had a tendency to observe left-turning traffic and to be aware. More to the point, he felt, was the confusion created by left-turn maneuvers that cross one another and he believed that was the motivation for the 200-foot ' offset. In his opinion, with the alignment of the driveways in this case, this maneuver does not occur, therefore, that area of conflict between those two entering left-turn maneuvers would be eliminated. He believed that to be the critical issue. The Examiner asked whether that was more critical than those ' leaving the plat making a left turn across 16th. Mr. Norris agreed that it could be, but there would be vehicles maneuvering in both lanes that would view one another as they were sitting in their plat access roads. The Examiner asked about the topography and whether there was good sight distance, to which ' Mr. Norris replied that there was good sight distance, sloping to the west. THOMAS BLAKE, 1624 Camas AVE NE, Renton, 98056, stated that he had very strong concerns about the 35% variance for street offset being requested. He said the staff report didn't refer to the ' owner of record, which he had found to be Mr. and Mrs. Dance. `He felt that it was significant that the applicant was not the owner of record, because one of the criteria for variance was hardship, and here was a developer with a contingent earnest money asking for a variance and pleading hardship ' because the property next door was not for sale. If that property were part of the proposal, the variance that would be asked for would be about 7%. He felt that there was not enough room between Dayton and Camas to allow construction of a new street. Regarding neighborhood characteristics, Mr. Blake said that the property was originally platted as five acre tracts, and the surrounding area ' currently was a mixture of differing uses, such as mini-farms, and would-not be developable as row- to-row houses. The staff report noted that there were other streets in the area that didn't comply with the 200-foot offset, but the engineering report conflicted with that, saying there were no other streets ' in the vicinity that had less than the 200-foot offset. He felt that the important question was not whether there were streets that were closer together, but rather, were there streets closer together because a variance had been granted. ' Mr. Blake stated that he had owned his property on Camas since 1968, and he was concerned that a precedent would be set if a variance of 35% was allowed, and he felt that he had not heard anything said that would substantiate that there had actually been such significant variances allowed. The other ' matter of his concern was the forecast that there would only be eight children on the block of 14 houses. He said they had 28 kids living on Camas Avenue with basically the same number of houses. He asked for clarification on the term, traffic buttons. The Examiner stated that placing the buttons gave an audible signal that made drivers a little more aware of what was happening. Mr. Blake noted that adding.an extra street would decrease the safety factor in the area, stating his real concern was for pedestrians, as this street was the main walking access to two nearby schools. He felt that adding street lights might help at night but requested the timed type rather than automatic type as they often didn't work correctly. He noted that the hardship that was being claimed was because of the way the property had been platted; someone chose to sell a piece off, and then came back pleading hardship because of it. He felt that perhaps the southwest corner lot could be purchased to avoid this variance. ' The Examiner stated he was looking at reasonable use of the site and that this project, as it stood, was what was being considered at this time and he would not be considering the southwest corner. Mr. Blake said that traffic safety was the issue he wished to speak to and he didn't see that road bumps ' would help at all. As far as the special privilege provision, he asked whether other streets had been given a 35% variance. He.advised that he had found a staff comment in the report which mirrored his concerns about the possibility of resulting traffic accidents. CamWest Development, Inc. ECF;PP;V-099-91 January 7, 1992 Page 5 Mr. Forsander stated that comments were frequently received from other departments which were out of that department's range of expertise. CLINT MORGA.N, Development Services, stated that he had reviewed the project and would prefer to see a 200-foot offset but had also considered the extenuating circumstances that existed in development of this property. He noted that traffic volumes were very low as both ends were dead ends, and the road usage was limited. He felt the 130-foot offset called for appropriate mitigation such as street lighting and traffic buttons as reinforcement of the center line. Mr. Forsander commented that the owners of record, Michael and Mary K. Vance, were unintentionally left off the staff report. Mr. Blake said that one problem with cul-de-sacs is there may be 143 daily trips by people that live there, but others turn in, find out it's a cul-de-sac and go back out, increasing traffic about double. The Examiner called for further testimony regarding this project. There was no one else wishing to Ispeak, and no further comments from staff. The hearing closed at 10:02 a.m. FINDINGS, CONCLUSIONS & DECISION: Having reviewed the record in this matter, the Examiner now makes and enters the following: FINDINGS: 1. The applicant, CamWest Development, Inc, filed requests for approval of a 14-lot Preliminary I Plat and a variance to permit the creation of a road intersection less than the required 200 feet from another intersection. I 2. The yellow file containing the staff report, the State Environmental Policy Act (SEPA) documentation and other pertinent materials was entered into the record as Exhibit #1. 3. The Environmental Review Committee (ERC), the City's responsible official, issued a Declaration of Non-Significance (DNS) for the subject proposal. 4. The subject proposal was reviewed by all departments with an interest in the matter. 5. The. subject site is located at 2400 NE 16th Street. The site is on the north side of NE 16th Street. The site is located about midway between Edmonds Avenue NE on the east and Blaine Avenue NE on the west. Dayton Court NE, which forms a "T" intersection with 16th from the south, generally aligns with the east property line of the subject site. 6. The subject site is a 3.08 acre "L" shaped site. The parcel is approximately 252.47 feet wide (east-west) and approximately 589.90 feet deep (north-south). The parcel has approximately 151.16 feet of frontage along NE 16th Street. A separate legal parcel approximately 150 feet deep by approximately 101 feet wide is located in the southwest crook of the "L." 7. Three existing homes are located on the subject site. Two homes are located near the southeast corner of the site. One of these two homes is located approximately 100 feet north of NE 16th and the other is located approximately 200 feet north of NE 16th. These two homes would be removed if the development is approved. The third home is located near the northeast corner 1 ' CamWest Development, �..C. P ' ECF;PP;V-099-91 January 7, 1992 Page 6 ' of the site, approximately 450 feet north of NE 16th Street. This home would remain but would probably be moved since, as now proposed, it would straddle a lot line. S. The parcel slopes gently upward from the southwest to the northeast approximately 20 feet, from an elevation of 300 feet to an elevation of 320 feet. 9. The applicant proposes developing Dayton Avenue NE to serve the plat. This roadway would be a 50 foot wide cul-de-sac approximately 445 feet long. The applicant proposed a landscaped island in the center of the turnaround but the Fire Department recommended its removal. Dayton would not be a through street and would form a "T" intersection with NE 16th at the south boundary of the proposed plat. Existing lots with homes south of 16th would not permit any extension south of 16th. ' 10. The 14 lots would run from the soa�theast corner of the plat around to the north and west and back down the west side of Camas. ' 11. Proposed Lots 1 through 6 are all 7,200 square feet in area or just over that size. Proposed Lot 7 is approximately 8,000 square feet. Proposed Lots 8 and 9 are both slightly larger than 9,000 square feet, while the remaining 5 lots, Proposed Lots 10 through 14 are all just over the 7,200 ' square feet required by the R-1 zoning. 12. Proposed Lots 1 through 5 and 12 through 14 are generally rectangular. The remaining lots which abut the cul-de-sac are wedge shaped. The frontage along the curved end of the cul-de-- sac creates the irregularity in these five lots. The rectangular lots are generally 70 to 72 feet wide by 101 feet deep. ' 13. Proposed Lot 1, which is a corner lot, was not platted wider than its complementary interior lots (Section 9-12-8(X)(6)(d)). The applicant indicated that lot lines could be shifted to provide the code-mandated width. 14. The distance between the proposed Dayton and Camas, which is west of the site, is approximately 195 feet. ' 15. The segment of Dayton Court NE which is south of 16th Street would be offset approximately 130 feet from the segment the applicant proposes constructing to the serve the plat. The applicant has requested the variance to permit this 130-foot offset since the code requires a ' minimum offset of 200 feet. (Section 9-12-8(G)(14)) 15. An existing tier of homes is located along the west boundary of the proposed plat. These homes ' are located along the east side of Camas Avenue. 16. East of the site are homes located in mixed fashion along Edmonds Avenue NE, with some homes along the Edmonds frontage and a couple of homes located interior to the frontage where ' access is provided by easements or private roadways. 17. While many of the existing lots in the neighborhood are large lots which resulted from earlier ' platting patterns, the lots and homes located west of the site, along Camas and Blaine, approach the 7,200 square-foot lot size permitted in the R-1 zone. 18. The applicant proposes utilizing the public right-of-way for storm drainage requirements rather ' than providing easements or detention on developable portions of the site. A system on the CamWest Development, inc. ECF;PP;V-099-91 January 7, 1992 Page 7 public right-of-way would require maintenance by the city as opposed to a private system. Such detention requires specific approval of the City Council (Section 4-22-13(E)). If the ' council disapproves of off-site detention, the applicant can provide it on-site, according to the Public Works staff. Staff has recommended that the system comply with ordinary requirements, be located on private property, and be maintained by the property owners. 19. The map element of the Comprehensive Plan designates the area in which the subject site is located as suitable for the development of single-family uses, but does not mandate such development without consideration of other policies of the Plan. 20. The subject site was annexed to the city with the adoption of Ordinance 1822, adopted in March, 1960. The single-family zoning that the site retains, R-1, was attached at that time. 21. As indicated above, the area is developed primarily with single-family homes. The lot sizes vary from those that just meet the code's minimum requirements of 7,200 square feet to large ' lots over an acre in size. The superblock the subject site is located on has lots which represent both extremes. West of the site are lots that reflect the minimum lot size, while the lots in the center of the block, including the subject site, exceed an acre in size and the lots on the east end of the block are about a half acre in size. ' 22. The trend in this area of the city and in the Kennydale area is to replat many of the larger lots. The smaller lots are being short platted as two to four-lot short plats and larger acreage is being ' full platted into more than four lots. 23. NE 16th Street is not improved to full city standards. Staff has recommended that the applicant widen the frontage and provide the required off-site improvements including curbs, gutters and sidewalks adjacent to the site. In order to provide a safer right-of-way in this location, staff also recommended that the applicant install center-line traffic buttons to delineate the roadway and install street lights in the vicinity of the subject site. ' 24. The site is served by the Renton School District with Hillcrest, McKnight, and Hazen schools located within one and one quarter miles of the site. The 14 homes, actually 13 new homes, ' would be expected to add approximately 8 students to the school system. 25. The population of the area is expected to increase by about 30 people. ' 26. Staff reports that the additional traffic, approximately 110 trips per day, can. be handled on the existing street system. Staff supported the variance, indicating that the interplay of the two segments of Dayton, the existing leg south of 16th and the proposed leg north of 16th should ' not interfere with each other since the left turn maneuvers will not overlap as they might if the roadway segments were reversed (with the north leg east of the south leg). Staff believes that appropriate street lighting and lane designations should minimize any impact on NE 16th in this vicinity. Staff reports that sight distance provides for safe maneuvering. ' 27. The site is served by Gene Coulon Park and the McKnight play field. Staff recommended that the applicant provide $150.00 per lot to offset the impact of this development on the city's park ' system. The applicant has agreed to contribute $2,100.00 ($150.00 x 14) to the parks' system. 28. The site is served by city water and sewer service. The site is not located in the city's sewer ' moratorium area. CamWest Development, ECF;PP;V-099-91 January 7, 1992 Page 8 ' 29. There was objection to the issuance of the variance for the 130-foot street offset proposed by the applicant. ' CONCLUSIONS. Preliminary Plat 1. The proposed Preliminary Plat appears to serve the public use and interest. While the division of the site into additional lots will involve some tradeoffs including additional population density, additional traffic, loss of greenspace and rural atmosphere, it also provides additional housing choices in an area with existing and adequate public services, it is compatible with the area's zoning and is compatible with the Comprehensive PIan. ' 2. The plat provides fourteen lots that all meet or exceed the minimum standards for single-family development in the R-1 zone. Most of the lots.are regularly shaped, rectangular parcels that can accommodate the usual single-family home. Those lots which are not rectangular follow the ' fashion of lots perched around the bulb of a cul-de-sac road - they are wedge shaped and, like the rectangular lots, provide a sufficient envelope for a building. 3. The development will actually have the impact of only eleven additional homes since three homes already exist on the subject site. Therefore, the impacts are less than an entirely new 14-home subdivision. In any event, staff has indicated that the area schools, roads and utility infrastructure can accommodate the proposed development's students, traffic and population. ' 4. The development is compatible with both the zoning and Comprehensive Plan which calls for this area to be developed with single-family homes. It also accommodates these homes in a developing urban area where there are sufficient services, avoiding the sprawl out into the less- accommodating rural areas east of the city. 5. The applicant has also agreed to make provision for the recreational needs of the new residents by contributing to the-city's park fund, thereby meeting both state and city mandates to provide for parks and recreation. ' 6. The applicant will have to accommodate the additional width for Proposed Lot 1 since no request for a variance from the corner lot width provision was in evidence. 7. The applicant is entitled to approach the City Council on the issue of accommodating the ' development's storm water runoff on the public right-of-way If that option fails, the applicant will have to provide retention/detention on the site. .This office recommends, as did staff, that the storm drainage requirements be met on private property and not on the public right-of-way. ' It is inappropriate to pass on the costs of maintaining the system to the general public when the subject development is creating the need. ' Variance 8. Variances may be granted when the property generally satisfies all the conditions described, in part, below: a. The applicant suffers undue hardship caused by special circumstances such as: the size, shape, topography, or location where code enforcement would deprive the owner of rights and privileges enjoyed by others similarly situated; ' CY CamWest Development, Inc. ' ECF;PP;V-099-91 January 7, 1992 Page 9 b. The granting of the variance would not materially harm either the public welfare or ' other property in the vicinity; C. The approval will not constitute a special privilege inconsistent with the limitations on ' other property in the vicinity; and d. The variance is the minimum variance necessary to allow reasonable development of the subject site. The applicant's property appears ripe for the variance requested. ' 9. The applicant's property is sandwiched between two roadways that make it impossible to carve out any access road on the subject site which would provide the required 200 feet of offset from an adjacent roadway. To the east of the site is Dayton Court. That roadway is approximately 135 feet from the western boundary of the subject site. That is the maximum distance that can be provided by the offset since the western limit of the subject site is 135 feet from the existing Dayton Court. On the west, the applicant would have to contend with the proximity of Camas, which is approximately 195 feet from the western boundary of the subject site. There is no way to serve interior portions of the subject site without intruding on the normally required 200-foot offset on one side or the other. Therefore, the location of the subject site creates a hardship that cannot be avoided if the lot is to be developed further. 10. While further development of the parcel is not guaranteed, the current zoning does permit parcel sizes substantially smaller than would result if the applicant were not permitted additional development rights. The three acre parcel now supports three' homes, whereas the current R-1 zoning permits approximately six (6) homes on an acre. The neighborhood reflects older platting and new platting patterns with the newer patterns favoring lots that approach the minimum lot size of 7,200 square feet. The applicant is entitled', if reasonable, to develop to ' those standards. 11. While there was a neighbor in opposition to the applicant's request, traffic engineering testified ' that the proposed offset would not result in an unsafe situation, particularly if appropriate street lighting is installed and the roadway is appropriately delineated. Staff testified that left-turn maneuvers should not interfere with one another and that sight distance- was sufficient to permit safe turning into and out of the respective side. streets. ' 12. In addition, the potential traffic will be spread out over the course of a day and staff did not believe that this additional load would create any undue problems on area roads. While the ' neighbor suggested that a private road could permit additional but less intense development, this would not eliminate the proposed intersection but merely create a private driveway in the same location. This alternative is no more acceptable than that proposed. While the traffic count might be reduced somewhat, the offset would still be less than optimal. Since staff indicated ' that the traffic conditions would not be unsafe, there is no reason to consider this alternative. In addition, it would result in the applicant being deprived of the development opportunities that exist for neighboring property. 13. The approval will not constitute a grant of special privilege to the applicant. It will extend to the applicant the ability to divide the subject site in a manner equivalent to the division found in the neighborhood. The applicant seeks to create a subdivision with lots meeting or exceeding ' code requirements and similar in size and shape to the parcels found both east and west of the 1 G c2 l CamWest Development, inc. ECF;PP;V-099-91 ' January 7, 1992. Page 10 site where older, larger lots are being replatted to more modest-sized parcels. While staff did not provide any clear citation to a similar grant of a variance' for roadway offset, that does not .' negate the relief the applicant seeks. The circumstances in this case justify variance relief since similarly sized lots have been carved out of older, larger parcels and staff has indicated that approval would not jeopardize the public health, safety, or welfare. The approval merely ' permits the applicant to make reasonable use of the property, where reasonable use is lots meeting or exceeding the standards found in both the Zoning and Subdivision Codes. 14. The variance requested appears to be the minimum variance which will afford the applicant reasonable use of the subject site. The number of lots created in this case does not determine the minimum variance necessary, since the roadway offset from the proposed road and the existing road is the constraining factor in this case. There is no way that the offset can be ' increased, given the existing dimensions and location of the subject property. The subject property, as it exists at the current time, is the basis for,any review. A variance is granted or denied based upon the circumstances of the subject site at the time the variance is requested. is. In conclusion, the request for a variance is appropriate under the circumstances that now exist, since it will not result in granting the applicant excess development potential and does not result in unsafe traffic conditions. ' RECOMMENDATION The City Council should approve the 14-lot Preliminary Plat subject to the following conditions: ' 1. The applicant comply with the conditions imposed by the ERC. ' 2. The applicant install an appropriate on-site storm.water retention/detention system subject to the approval of the Department of Public Works. ' 3. The applicant provide $2,100.00 to the park fund for recreational projects. 4. The applicant install the required onsite and offsite improvements along both the proposed roadway and the site's frontage on NE 16th including, but not limited to, ' curbs, gutters, sidewalks and street lighting. The applicant provide other street improvements on NE 16th Street such as curbs, ' gutters and sidewalks, and street lighting and lane delineation between the subject plat and the streets both east and west of the plat that are located less than the normally required offset as determined by the Public Works Department. 6. The applicant, if feasible, shall create a looped water system subject to the approval of the Department of Public Works. ' 7. The applicant shall comply with the city's tree retention requirements. 8. The corner lot, Proposed Lot 1, shall be platted wider than interior lots. CamWest Development, inc. ' ECF;PP;V-099-91 January 7, 1992 Page 11 DECISION ' The Variance for less than the required 200-foot offset between adjacent streets is approved subject to the conditions for plat approval. ' ORDERED THIS 7th day of February, 1992. Lot- FRED J. K FMAN ' HEARING EXAMINER TRANSMITTED THIS 7th day of February, 1992, to the parties of record: Paul Forsander, Senior Planner Michael & Mary K. Vance ' 2400 NE 16th Renton, WA 98056 Eric Campbell P.O. Box 308 Kirkland, WA 98033 ' Gary Norris William E. Popp Associates First Interstate Center, Suite 314 225 108th AVE NE Bellevue, WA 98004 Thomas Blake ' 1624 Camas AVE NE Renton, WA 98056 ' Chester Samples 1824 Camas AVE NE Renton, WA 98056 Evelyn Voth 1616 Camas AVE NE Renton, WA 98056 ' Karen Prell 2411 164th AVE SE ' Kent, WA 98042 Cheryl Bachmeier 1632 Camas AVE NE ' Renton, WA 98056 Cam-West Development, ...c. ECF;PP;V-099-91 January 7, 1992 Page 12 TRANSMITTED THIS 7th day of February, 1992, to the following: , ' Mayor Earl Clymer Councilman Richard M. Stredicke Don Erickson, Zoning Administrator Lynn A. Guttmann, Administrator Members, Renton Planning Commission Jim Hanson, Development Services Manager ' Gary Gotti, Fire Marshal Ronald Nelson, Building Director Lawrence J. Warren, City Attorney Jay Covington, Mayor's Executive Assistant Transportation Systems Division Valley Daily News Utilities System Division ' Pursuant to Title IV, Chapter 8; Section 15 of the City's Code, request for reconsideration must be filed ' in writing on or before 5:00 P.M. February 2I, 1992. Any aggrieved person feeling that the decision of the Examiner is ambiguous or based on erroneous procedure, errors of law or fact, error in judgment, or the discovery of new evidence which could not be reasonably available at the prior hearing may make a written request fora review by the Examiner within fourteen (14) days from the date of the Examiner's decision. This request shall set forth the specific ambiguities or errors discovered by such appellant, and the Examiner may, after review of the record, take further action as he deems proper. ' An appeal to the City Council is governed by Title IV, Chapter 8, Section 16, which requires that such appeal be filed with the City Clerk, accompanying a filing fee of $75.00 and meeting other specified requirements. Copies of this ordinance are available for inspection or purchase in the Finance Department, first floor of City Hall. ' The Appearance of Fairness Doctrine provides that no ex parte (private one-on-one) communications may occur concerning pending land use decisions. This means that parties to a land use decision may ' not communicate in private with any decision-maker concerning the proposal. Decision-makers in the land use process include both the Hearing Examiner and members of the City Council. All communications concerning the proposal must be made in public. This public communication ' permits all interested parties to know the contents of the communication and would allow them to openly rebut the evidence. Any violation of this doctrine would result in the invalidation of the request by the Court. ' The Doctrine applies not only to the initial public hearing but to all Requests for Reconsideration as , well as Appeals to the City Council. TH. . ' i) t,,543 , 9` 1 60 NJ too JO 102.54, , 6•]9 /,1 `, 1J 5..,z 6p i ,JLSJ W41 b". 1 _ _ _ _ ] I-17 ------ 190 + 190 19 ------------- (u o+e 1 - o la3 z I©3 3 e 1 ;t laze ,� bo •. 4 + leis ' --- ----_ ------ ---- 3� �� �> 1 --- i - u ^" 0 5 t IB16 �Z� 77J 180 Z 1810 , 75. ------ ----- I t 1908 44 3 9s.,° I r 2115 + 2 251.721 ' Ill 17 Il /) - b A 1 405 III (n � 1 � � �. Il / On" u a-------------- 25 I i ----------- 1 1632 .162a 26 v 17 V 4 JoI ZJ?_7 _ 16 24 257.J �f 16 "•x 1615 ° ! :� -----T- ;is7_5z_�-- Q Q 15� ptr� I IS t �� � � _.1 �• � it � �2 CC) Et 1 9 '. 60 Uo-A, I�g/S I 70 16.20�N+ ,e ii 8),I 71. 16TH ST. /OZJ -s I 7S 96 1 so I 96 Io9J 11105 , c3 I «n n, o,�R ��•• c�n - LEE l.l_I tt- -I � is I I �• � ,11 0 1 � o Q•• -I`�r r �...+..nw.. - « r o J I i•'----� � I 16 'I I 'i z W 117.7- -� I° 101 I r---- i I I - Q 2szi cr o Is z i It—1 00 '�=' � , s r 213 4 U — —— — ' Q I 17 r Id 4 �.• �r If l 5 0 W 13l)� 1. ' �16. 09 id ' ,a� l 6 '^ \ a 12- - - ui 24 6 I"T"J I -- Rio ' �'- ;� 2 3(i 14 s In r Q \`•l ! --���----111- i0 � r- --,',j'; -- oo-- 13 wnl I , �jgr�o Q r / g 1� 9 an ^� °NJ. 14TH ST. � b 3a °o , , , Z. $ 3 (I) jII131 6Ll,2) Jtl , m 1 N.E. f3TH_ PL. 13 ° ~ $ a ° 131i 1316 R -Lij l�tO #7 1. G J ,1.21 " 1 •� $ I! 13 1 $ 6.i5 �63.Oj� 1 � � I -- •:sz.3 I of 1" 12 Mrs- ------------ •00' /i6 24'-.�st,: .• /!sue''?" I •f._- h W O o\ \ c s? _��0 N , W + \/ °'N �• hi 4.�� 46.F 60 40 20 40 00 FEET l4 - o Ne9'ST 38"E I G FY Q . 6 O .cs•"o 3. ® PRE L IM11VA Y FL A 7r MAP NB9.3T'3B"E ''' • DETAIL. 74 •,, i I .,� PLAT NAME NTS = STRATFORD PLACE .� ♦s � ��_' — C Ct # OWNER DEVELOPER= CAM WEST .t ,\ �y REAL ESTATE DEVELOPMENT.808 3aS h 3� �•• t I 5� !J. ���"'jjj 0 RO. BOX 308,K/RKLANO,WA. A9QRi SURVEYOR : TRt•COUNTY LAND SURVEY/NC COMPANY I %y09 'J�3 /029 MARKET ST., K/RKLANO, WA R8033 AREA -- 133,538 S.F. ••• 3.06AC. �1 poV2 H 10 5 I g.e O y zs'' NO. OF LOTS : 14 W W 13 i ( �204 set ZONING: R-l 7200 NL L/Ne PROPOSED USE= Single Family Residential PERCENTAGE OF AREA IN STREET= 20 7E.?GT5•E-4C o _�� L/N2,TyTP/G4L 4LL 2 Z � io 20• _ Lors o I of/T V NG. TV- W : o / 5•F I o p0 5 �M a �—sirE � I -�23� � o. 'o I I s f l v VE.•-. L � r.'rE' o uI of ti ` LEGAL DESCRIPTION AW aCGL .4+ P4RCC'L .4 OF Ss/O.OT.OL.4 r NO. 004'77,,4CCO.aO/NG --"�``'''• / TO THE SHOOT PLOT .QeCOQOEO 4/.140P;1 ,r[iyG COUNTj� -- - ;; - QEC000/NG /✓O. 707 050534.' I r/rt/c r� /N TH� C/Tf= OF OENTON, COUNTY OF!C/NG,STATE V/C/N/ry M4.4 was</iNGrON. Z: 7 HE WEST 125 F�BT OF T/,'E NOItTN aOO,--- U OF T04CT 2/4 Or i//LLMdNS LGKE -WvSN/NGTON GvllOBn/ . I / I •r �;- ' OF EOEN 5/On/GOA PE.Q ,aECOdO.EO S /N OF PG4T3,PaGE 12 .¢ECO.Q05 OF .IG//vo COUNTY; ' �,, C' TOGETNEII W/TH vN edSEMENS""FOQ/NG.¢ESS,G'G.OESS OY.el1 Il .� 4C,405.5 4N0 U,00N THE WEST /S FEET OF PaQCELS .4 ,dA ,e OF SHORT PLAT NO. 04q 3 7 LL/N.O E.Q KING COUNTEY QECOR•0/NG NO. 717055ETD/V= COUNTYOFK/NG, ST N GTNr" C/Ty OF - I - - ..- �,. �I2G•-l9 •.li;'_2B2�3Z' ' N.E. /6TH Sr TOB NO .9/023 , AUGUST 2,/99/ � ,�. . oEe SITE ANnLvs.s ' III . OFF-SITE ANALYSIS OFF-SITE ANALYSIS: ' Attached with this section is a report by Collins & Associates entitled "Stratford Place Level Downstream Analysis" which was presented with the preliminary plat application and discusses off-site drainage considerations and the downstream system. ' Since this plat will be served by an infiltration tank using ground water recharge less runoff will occur in the developed condition than now occurs in the partially developed state. There is no apparent evidence of flooding, overtopping and/or erosion associated with the downstream conveyance system within 1/4 mile of the proposed ' development . Since runoff downstream of the site will be less in developed state than in the pre-developed one the net effect of adding this 14 lot plat will result in less flow in the downstream conveyance system than presently exists . Therefore the intent of Core Requirement ' #2 at page 1 . 2 , 2-1 has been satisfied. There are two sources of off-site drainage which are tributary to this ' project . These are the roadway improvements adjacent to N. E. 16th Street frontage which will bypass the infiltration structure and the off-site sheet flows flowing into the site along the east property line. ' N.E. 16TH Street BYPASS A hydro graph was developed for this 0 . 041 acre portion which will ' bypass the new infiltration system. This is Basin 9 and hydrograph 9 and shows a peak flow of 0 . 035 cfs and a total volume of 394 c . f . for the 100 year event . The maximum allowed runoff from this site would be 0 . 16 cfs based on 3 . 06 acres (undeveloped) for the 100 year/24 hour event . The maximum rate after development will be 0 . 04 cfs ( -) from the undetained frontage improvements along N. E. 16th Street . This 0 . 04 cfs is less than 0 . 16 cfs runoff allowed by code. In fact , the 0 . 04 cfs ' runoff will be the maximum generated by this development since all other runoff will be recharged into the ground after biofiltration using a tank infiltration system. ' OFF-SITE ALONG EAST PROPERTY LINE The area east of the property which drains as sheet flow across the east ' property line consists of a single family residential area lying between Edmonds Avenue N.E. and the property. This basin is approximately 3 . 90 acres and contains 8 dwelling units . This runoff will be conveyed by a ' new swale and was determined to be 0 . 87 and 1 . 13 cfs for the 25 year and 100 year events respectively. /�o N u I I w o mil � XI i I j I`— :� ,. _: ,I ,^ _.__ • 8 ° ��-• rI Ion , �- JGV�T, 1 a ao 10 �► a 8 {(,1.u3'� r 7/ I �� k io CJ O � / k C3 S3 3 9K ^ x I 1 l r- 1 L�c oo Ell 13: a / ,, • x I 11 x I I o ,1 99Z It irt,�' I I I Ii I I II ,r NX 681. N 2 I x — II II � .�90•b60`989�1 �,..% l !w4 � �.� Lla II � / w , cot y, ri Ix" ' 10 19 92 John Newell Inc. page 1 / / P g STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT ' INFILTRATION DESIGN BASIN SUMMARY BASIN ID: B11 NAME: EAST OFFSITE 25 YR EVENT ' SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 90 Acres BASEFLOWS: 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 3 . 40 inches AREA. . : 2 . 91 Acres ' TIME INTERVAL. . . . : 10. 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . . 24 . 16 min IMPERVIOUS AREA ABSTRACTION COEFF: 0. 20 AREA. . : 0. 99 Acres CN. . . . : 98 . 00 TcReach - Sheet L: 270. 00 ns: 0. 1500 p2yr: 2 . 00 s: 0. 0740 TcReach - Channel L: 570. 00 kc: 17 . 00 s: 0. 0050 PEAK RATE: 0. 87 cfs VOL: 0. 47 Ac-ft TIME: 480 min ' BASIN ID: B12 NAME: EAST OFFSITE WITH 100 YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 90 Acres BASEFLOWS: 0 . 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 3 . 90 inches AREA. . : 2 . 91 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . : 24 . 16 min IMPERVIOUS AREA ' ABSTRACTION COEFF: 0. 20 AREA. . : 0. 99 Acres CN. . . . . 98 . 00 TcReach - Sheet L: 270. 00 ns: 0. 1500 p2yr: 2 . 00 s: 0 . 0740 TcReach - Channel L: 570. 00 kc: 17 . 00 s: 0. 0050 PEAK RATE: 1. 13 cfs VOL: 0. 58 Ac-ft TIME: 480 min 10/19/92 John Newell, Inc. page 2 ' STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT INFILTRATION DESIGN --------------------------------------------------------------------- --------------------------------------------------------------------- ' HYDROGRAPH SUMMARY ' PEAK TIME VOLUME HYD RUNOFF OF OF Contrib NUM RATE PEAK HYDRO Area cfs min. cf-AcFt Acres --------------------------------------------- --------------------------------------------- ' 1 0. 029 480 1193 cf 3 . 06 2 0. 073 1440 3917 cf 3 . 06 3 0. 108 760 6064 cf 3 . 06 ' 4 0. 156 760 8573 cf 3 . 06 5 0. 527 480 10304 cf 3 . 06 6 0. 840 480 17183 cf 3 . 06 7 1. 060 480 21347 cf 3 . 06 8 0.747 480 1928 cf 0. 00 9 0. 035 470 394 cf 0. 04 10 0. 550 460 23765 cf 3 . 06 11 0. 871 480 20294 cf 12 1. 134 480 25238 cf 3 . 90 1 1 ' aZ1U l 5T(ZATFOE D PC AC F 17 ' 545T OFF-51 TE DLZ Al NAC29 IFIPE2 pious (0,255) C 3,4a) = 0, 99 Ac, CrJ qS Olo T(d) 5C_oPE (5NEE-T FGow) (346- 3W Z70 = -7,4°lo SNALLOU/ SV�A�E f DFVE60PEP) ` U, E CN/JN.NEC- L _ 57 o , 5= 0,50 ' SASt /D = // f l Z S ve 24 Hz ) ' 13A51M l0 = IZ dU c���Z¢N2 14uD2o 10 = 12 3 3, ' (O0u¢ OISZ @ Q= I,13CFS �02 R©a �. � (tov��) ' / HE, NZ,5 MAN-MADE CHANNELS VARIABLES LIST: ' Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS �ARIABLE TO BE SOLVED (Y,Q, B,M,S OR N) ? Y Q (CFS) ? . 87 RESULTS (FT) ? 0 (FT/FT) ? 3 Y= 0.47 FT S (FT/FT) ? . 005 A= 0. 67 SF (FT-1/6) ? . 030 P= 2 . 99 FT V= 1. 30 FPS F= 0. 47 SUB-CRITICAL FLOW <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- C;FF S(f + S`f T�_ IOJ C to MAN-MADE CHANNELS ARIABLES LIST: Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS LIABLE TO BE SOLVED (Y,Q,B,M,S OR N) ? Y I (CFS) ? 1. 13 RESULTS B (FT) ? 0 (FT/FT) ? 3 Y= 0. 52 FT (FT/FT) ? . 005 A= 0. 82 SF N (FT^1/6) ? . 030 P= 3 . 31 FT V= 1. 38 FPS F= 0.48 SUB-CRITICAL FLOW lShift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- IV. RETENTION/DETENTION ANALYSIS AND DESIGN 1 �TeA7Fo2o P��c� c1z lc07 O.€TE"77omI DEsr Al ' SITE- A2EA -- 3.C&A1= 150/L5- 1Nc ( (NDIAN06,4) 6 P-6J IP A NouSEs t (Z(,CZZ) _ 4163 S.F- 0,O9S57 Ac ' D127" ROAD (!ZO)(14) (70)(1o) 1-G50)(10) - 56,5T0 S,F = 0, 13¢g9'Ac ' LAwNs Frc zzo) 5o 5,F. ' 34 !so s,F, UODEVE-OPED = 2,0¢s4-6 Ac. CURVE NO f-l0(l,SE5 CN= T6 AEE4 = ©,loA c ' 1-4WNvs Chl- Gg A2FA s O,78 Ac Q12r,LOAD C,Al = 7Z AREA = O, 13 A c. WOODS- ZHO CN E75 A-12FA = Z,OSA-c ' 7oTAL AG, Cry-I PD S/7�= CUR V IF l\l P��Vlous - 57, l7 A = Z 96 A c ' �M PE;2VIOU 1, q3,C) o, /o A c ' ,QFVC-&OPED (COND/Z2a,,S NO of uNlrs 14 A = (0,,443)(3,Oco)- 1,4ZAc CN- 76 Olu PE2 viou,s = 53,7°/6 l44-c. c a - 68 EXIS711!6 T2n TIMEs— LgwN ( Ltif--5T 1=z-ow) L- /.�o' 5= 6,iS,7/0 WC PO5 SNEET ;ccOW) — /00 , S= /0`/d ' WOODS ( SHOT FLOW) L= 7 0/ S= 2,86010 WOO D5 ( 5HAU.0W) L= 28' 5 = 7, lo°lo KI C)ODS ( 6 HA U-0 w) L= !Za' 5= 3./'Z°/6 ' 5TI214TFOIED PCAcE 921cO7 _DEFFVOO" ,DFSICW ©�VELO/ � CO�/D/7/y�/5 T2AVF T/�'lES 4 A W ti/ C - 140 ' S= (3 Zp - 318.7)/ !4o w 0,9°1d ' SHAuvW - 200' S= 11,9J�2�� 3,4`i6 PIPE L - �1S S= 5�8%a ' -v C�EV,ELt�(�E13 Tf�UEC. 7/t-�F Z311S ,SEA 6AsiN15 ' QAIqTA o 9-� P_ Z,a Ity2/z4K ' Cd NPU7EIZ C. eA-11\1 ll-�TPA -eASl ti/ LESt6HIlRaq ' S / EXIST/AIC, YVj ? iz - Z4 H2 A5 2 W/ lv V/Z - 24 H2 Ih./1 /0©\/2 — Z4HR 1 861 /0 VE - 24H4 87 KI/ tZsy/Z-24HC ' 136 �� �� W/ /oO ye-24- HE 1 l LI �3 2� 38 ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' TABLE 3.5.2C "n" AND "k" VALUES USED IN TIME CALCULATIONS FOR HYDROGRAPHS ' 'n;Shoot Flow Equation Manning s Values(For the initial 300 ft of travel) n,' Smooth surfaces(concrete,asphalt,gravel,or bare hard packed soli) 0.011 ' Fallow fields or loose"surface(no residue) 0.05 Cultivated soil with residue cover(s <- 0.20 ft/ft) 0.06 Cultivated soli with residue cover(S>0.20 ft/ft) 0.17 ' Short prairie grass and lawns 0,15 Dense grasses 0.24 Bermuda grass 0.41 Range(natural) 0.13 Woods or forest with light underbrush 0•40 Woods or forest with dense underbrush 0.80. 'Manning values for sheet How only,from Overton and Meadows 1976(See TR-55,1986) 'k'Values Used in Travel Tlmo/Time of Concentration Calculations Shallow Concentrated Flow (After the Initial 300 ft.of sheet flow,R - 0.1) k, 1. Forest with heavy ground litter and meadows(n-0.10) 3 2. Brushy ground with some trees(n - 0.060) 5 3. Fallow or minimum tillage cultivation(n -0.040) 8 4. High grass(n - 0.035) 9 5. Short grass,pasture and lawns(n-0.030) 11 6. Nearly bare ground(n-0.025) 13 7. Paved and gravel areas(n-0.012) 27 Chamwl Flow(Intermittent)(At the beginning of visible channels:R-0.2) k, ' 1. Forested swale with heavy ground litter(n - 0.10) 5 2. Forestod drainage course/ravine with defined channel bed(n-0.050) 10 3. Rock-linod watorway(n-0.035) 15 4. Grassed waterway(n-0.030) 17 5. Earth-lined waterway(n-0.025) 20 6. CMP pipe(n-0.024) 21 7. Concrete pipe(0.012) 42 - 8. Other waterways and pipes 0.508/n Channel Flow(Continuous stream,R -0.4) k, 9. Meandering stream with some pods(n -0.040) 20 10. Rock-lined stream(n-0.035) 23 11. Grass-fined stream(n-0.030) 27 12. Other streams,man-made channels and pipe 0.807/n" **See Chapter 5.Table 5.3.6C for addftkxW Manningy'n'values for open channels 3.5.2-7 1/90 1 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 1 FIGURE 3.5.2A HYDROLOGIC SOIL GROUP OF THE SOILS IN KING COUNTY HYDROLOGIC HYDROLOGIC ' SOIL GROUP GROUP* SOIL GROUP GROUP* Alderwood C Orcas Peat D Arents, Alderwood Material C Oridia D Arents, Everett Material B Ovall C Beausite C Pilchuck C Bellingham D Puget D Briscot D Puyallup B Buckley D Ragnar B 1 Coastal Beaches Variable Renton D Earlmont Silt Loam D Riverwash Variable Edgewick C Salal C Everett A Sammamish D Indianola A 41---- Seattle D Kitsap C Shacar D Klaus C Si Silt C Mixed Alluvial Land Variable Snohomish D ' Neilton A Sultan C Newberg B Tukwila D Nooksack C Urban Variable Normal Sandy Loam D Woodinville D HYDROLOGIC SOIL GROUP CLASSIFICATIONS A. (Low runoff potential). Soils having high infiltration rates, even when thoroughly wetted, and consisting chiefly of deep, well-to-excessively drained sands or gravels. These soils have a high rate of water transmission. ' B. (Moderately low.runoff potential). Soils having moderate infiltration rates when thoroughly wetted, and consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. 1 C. (Moderately high runoff potential). Soils having slow Infiltration rates when thoroughly wetted, and consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately fine to fine textures. These soils have a slow rate of water transmission. ' D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a hardpan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission. * From SCS, TR-55, Second Edition, June 19W, Exhibit A-1. Revisions made from SCS, Soil Interpretation ' Record, Form #5, September 1988. 1 3.5.2-2 I/90 1 ( KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TABLE 3.5.211 SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982) ' Runoff curve numbers for selected agricultural, suburban and urban land use for Type 1A rainfall distribution, 24-hour storm duration. CU E NUMBERS BY HYDROLOGIC SOIL GROUP LAND USE DESCRIPTION A B C D Cultivated land(1): winter condition 86 91 94 95 Mountain open areas: low growing brush and grasslands 74 82 89- 92 ' Meadow or pasture: 65 78 85, 89 Wood or forest land: undisturbed 42 64 76'- 81 Wood or forest land: young second growth or brush (�D 72 81 - 86 ' Orchard: with cover crop 81 88 92 94 Open spaces, lawns, parks, golf courses, cemeteries, landscaping. ' good condition: grass cover on 75% or more of the area 8p 86, - 90 fair condition: grass cover on 50% to 75% of the area 77 85 90 92 Gravel roads and parking lots 76 85 89., 91 ' Dirt roads and parking lots C2' 82 87 89 Impervious surfaces, pavement, roofs, etc. 98 98 98 98 ' Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 100 Single Family Residential (2) ' Dwelling Unit/Gross Acre % Impervious (3) 1.0 DU/GA 15 Separate curve number 1.5 DU/GA 20 shall be selected 2.0 DU/GA 25 for pervious and 2.5 DU/GA 30 impervious portion 3.0 DU/GA 34, of the site or basin 3.5 DU/GA 38 4.0 DU/GA 42 4.5 DU/GA 46 4 5.0 DU/GA 48 5.5 DU/GA 50 6. DU/GA 52 6.5 DU/GA 54 NOTE 45113 -DU/ NC. 1 7.0 DU/GA 56 3% tMpEev t�uS Planned unit developments, % impervious ' condominiums, apartments, must be computed commercial business and industrial areas. ' (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering Handbook, Section 4, Hydrology, Chapter 9, August 1972. (2) Assumes roof and driveway runoff is directed into street/storm system. (3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers. 3.5.2-3 INO I� oil rary RAN pun , I I MWAMM ` ( � • �� I* ���� �� � ��� `' �' 1.:=ram► MWER r-all --� Neiw•li► _ .! — �► gib,-� ' •ate FWA ME ro ML f-Rpm pie IMPmilli ►�v �� i MLO amp AIWMLK 1 IMI� . v ` /I//as E w� Via. o I�� Sl Nq NOW, mu I1/ � - �FfK-mma--,z , w- Ells !k ■� �W6Olt ✓ I ' gal .� -. ���POW.fir' do r �i � ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 4.4.5 TANKS Section 1.2.3 contains the definition of detention tanks and the limitations on their use. ' Design Criteria For Tanks Capacity/Discharge: Volume/outflow analysis shall be in accordance with the performance requirements in Chapter 1 and the hydrograph methods in Chapter 3. Restrictor/orifice structure design shall be per ' Section 4.4.7. - The minimum pipe size allowed for a detention tank is 36" dia. Materials: Pipe material, joints, and protective treatment for tanks shall be in accordance with WSDOT/APWA Standard Specifications Section 9.05, and AASHTO designations as noted below: - Galvanized, corrugated iron or steel pipe and pipe arch, Treatment 1 through 6 ' - Aluminized Type 2 corrugated steel pipe and pipe arch (meets AASHTO designations M274 and M36) - Galvanized steel spiral rib pipe, Treatment 1 through 6 - Aluminum spiral rib pipe ' - Corrugated aluminum pipe and pipe arch Galvanized structural plate pipe and pipe arch, Treatment 1 through 6 - Reinforced concrete pipe - Corrugated high density polyethylene pipe (CPEP) - Smooth interior . ' - Concrete vaults (see Section 4.4.6). Structural Stability: All tanks shall meet structural requirements for overburden support and traffic loading if appropriate. HS-20 live loads must be accommodated for tanks lying under roadways or parking areas. Metal tank end plates must be designed for structural stability at maximum hydrostatic loading conditions. Flat end plates generally require thicker gage material than the pipe and/or require reinforcing ribs. Tanks shall be placed on stable, well consolidated native material with a suitable bedding. Tanks shall not be ' allowed in fill slopes, unless analyzed in a geotechnical report for stability and construction practices. Buoyancy: In moderately pervious soils where seasonal groundwater may induce flotation, buoyancy tendencies must be balanced by ballasting with either backfill or concrete backfill, providing concrete ' anchors, by increasing the total weight, or by providing subsurface drains to permanently lower the groundwater table. Calculations mu;st be submitted which demonstrate stability. Minimum Access Requirements: The maximum depth to vauIbinvert shall be 20 feet. Spacing between ' access openings for tanks shall not exceed 100 feet. 36-i chiminimum diameter CMP riser-type manholes of the same gage as the tank material per Figure 4.4.5A and B may be used for access along the length of the tank and at the upstream terminus of the tank if the tank is designed with a common inlet/outlet so that it is a backup system rather than a flow through system. Note, Figure 4.4.5E is not allowed for use in roadways, driveways, parking stalls, or anywhere it would be subjected to vehicular loads. All tank access ---Y openings must be readily accessible by maintenance vehicles. ' Access Roads: Access roads are required to all detention tank control structures and risers. The access roads shall meet the requirements for access roads described in Section 4.4.4. Locking Lids: All tank access openings shall have round, solid, locking lids using 1/2" diameter alien head ' screw locks (see KCRS Dwg. No. 49). Control Structures: Outflow control structures are described in Section 4.4.7. ' Note, control and access manholes shall have additional ladder rungs to allow ready access to all tank access pipes when catch is filled with water. Details ' Standard tank details are shown in Figures 4.4.5A and B. Control structure details are shown in Section 4.4.7. 4.4.5-1 1/90 fd,f ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL i ' 4.5.2 MAXIMUM INFILTRATION RATE TESTS The following maximum infiltration rate tests are required in order to provide a conservative estimate of the ' potential outflow rates for: existing areas providing infiltration, such as closed depressions/wetlands; and, for proposed infiltration facilities. In general, the maximum infiltration rates determined through these tests => should not be significantly faster than those shown in Table 4.5.1A for the given soil texture class. If they are significantly faster, the testing procedure, the soil texture classification (Figure 4.5.1 B) or the specific ' site conditions should be reassessed. Surface Maximum Infiltration Test ' The surface maximum infiltration test is used to estimate the average surface maximum infiltration rate (IJ of the surface soils in a closed depression, retention pond, detention pond, infiltration pond, or in a proposed ponding area that will be constructed by berming (as opposed to excavating). The test is ' designed to simulate the physical process that will occur during design storm event conditions, therefore, a saturation period is required to approximate the soil moisture conditions that would occur during a major storm event. A pipe is employed to allow only the vertical maximum infiltration to be measured so that it may be used to compute the rate of infiltration over the area of infiltration. ' Testing Procedure (1) Without removing loose top soil and surface debris, a 4-foot-long, 6-inch-inner-diameter section of ' pipe is driven into the soil a depth of 6 inches. (2) The pipe is filled and kept to a minimum depth of at least one foot of water above the ground surface, at the bottom inside the pipe, for a period of not less than 4 hours (the saturation period). (3) Following the saturation period, the pipe is filled to the top and the time required for the water to fall every inch, down to 6 inches below the top of the pipe, is recorded. ' (4) The rates for all one-inch times are then averaged to estimate the maximum infiltration rate (I.). This process Is repeated three times, and the average three tests used to compute the maximum infiltration rate (Im) for the test using the following equation: ' Im = E(Im),,z,3/3); inches/min Sub-Surface Maximum Infiltration Test ' The sub-surface maximum infiltration test is used to estimate the maximum sub-surface vertical infiltration rate at a particular level in the soil horizon that corresponds with the lowest finished grade elevation of a ' proposed infiltration tank or pond. The test is designed to simulate the physical process that will occur during design storm event conditions, therefore, a saturation period is required to approximate the soil moisture conditions that would occur during a major storm event. A pipe is employed to allow only the vertical infiltration rate to be measured so that the computed maximum infiltration may be used to compute ' the rate of seepage over the area of interest for varying head. Testing Procedure ' (1) A hole is dug to the finished grade elevation of a proposed infiltration tank or pond and of sufficient diameter to allow a 6-inch-inner-diameter section of pipe to be placed in the hole and driven into the soil at test elevation a depth of 6 inches. (2) The pipe is filled and kept to a minimum depth of one foot of water above the test elevation, at the bottom inside of the pipe, for a period of not less than 4 hours (the saturation period). (3) Following the saturation period, the pipe is filled to the top and the time required for the water to fall ' every inch, down to 6 inches below the top of the pipe, is recorded. 4.5.2-1 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL I� (4) The rates for all one-inch times are then averaged to estimate the maximum infiltration rate (I.). This ' process is repeated three times, and the average of the three tests used to compute the maximum infiltration rate (Im) for the test using the equation shown above for surface Infiltration tests. Methods of Analysis Use of Im in Hydrologic Analysis: Once Im for a given soil surface elevation has been computed it may be used to develop a stage/discharge curve for use in the "level pool routing" method described in Section ' 3.5.4, in Chapter 3. At a given stage the discharge can be computed using the area of the surface through which infiltration will occur using the following equation: Q, = Im A,/720; (720 converts inches per minute to feet per second), ' where: Q, = the outflow due to infiltration, in ft3/sec. Al = the area of the infiltration surface, in ft2. ' The area (A,) available at each stage is determined by planimeter or noted from the areas of contours used in developing the storage available at each stage. Note: for design of proposed infiltration tanks or ponds ' a factor of safety of 2.0 must be applied to the potential infiltration discharge by dividing by 2.0 (0,/2.0) for each stage on the stage/discharge curve. i t ' 4.5.2-2 1/90 f 7� 1 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 4.5.3 INFILTRATION TANKS ' Infiltration tanks consist of underground pipe that has been perforated to allow detained surface water to be infiltrated. (Note: Special Requirement #5: Special Water Quality Controls, Section 1.3.4 and Special Requirement #6: Coalescing Plate Oil/Water Separators, Section 1.3.6 in Chapter 1, must be met if proposed to Infiltrate runoff from paved areas.) Limitations ' o Not allowed on slopes greater than 25% (4:1). o Infiltration surface elevation (bottom of trench) must be in native soil (excavated at least one foot in ' depth). Design Criteria ' o A soils report must be prepared which demonstrates compliance with the requirements in Sections 1.2.3 and 1.3.12, in Chapter 1. ' o A minimum of one soils log, extending a minimum of 3 feet in depth below the bottom of the proposed tank, that describes the S.C.S. series of the soil, the textural class of the soil horizon through the depth of the log, and notes any evidence of high groundwater level, such as mottling, shall be obtained for each proposed tank. ' o Bottom of infiltration tank trench shall be at least one foot above the seasonal high groundwater level. o A minimum of three sub-surface infiltration tests shall be performed for each proposed tank as described in Section 4.5.2. o Tanks may be located under pavement provided that a catch basin with a grate cover is placed at ' the end of the tank such that; if the tank infiltration capacity is exceeded, the overflow would occur out of the catch basin at an elevation of at least one foot below that of any overlying pavement, and in a location which can accommodate the overflow and meet the requirements of Section 1.2.1, in ' Chapter 1. o The spacing and construction of structures, materials allowed, accessibility for maintenance, easements and hydraulic design methods shall be the same as those described for detention tanks ' in Section 4.4.5. o Minimum spacing between parallel tanks shall be equal to 1.5 times the depth from the bottom of the lowest tank and the ground surface. o All tanks shall be a minimum of 20 feet from any structure, property line, NGPE, and 100 feet from any septic tank/drain field. o All tanks shall be a minimum of 50 feet from any steep slope. A geotechnical report must address the potential impact of the tank infiltration on the steep slope. ' o Filter fabric shall be placed over the top of the tank drain rock prior to backfilling. Method of Analysis ' The size of the tank shall be determined by using the hydrograph methods described in Chapter 3 and the stage/discharge curve developed from the maximum infiltration rate as described in Section 4.5.2. The storage volume in the tank is used to detain runoff prior to infiltration with the perforations providing the outflow mechanism. The perforations (holes) in the tank must be one inch in diameter and located in the ' 4.5.3-1 1/90 Imo( KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL bottom half of the tank starting at an elevation of 6 inches above the invert of the tank. The number and spacing of the perforations should be sufficient to allow complete utilization of the available infiltration capacity of the soils with a safety factor of 2.0 without jeopardizing the structural integrity of the tank. The area (A,) used for determining the potential infiltration from the tank shall be computed by multiplying the ' width of the tank times 2, and then times the length of the tank. 4.5.4 INFILTRATION PONDS Infiltration ponds are constructed by either excavation or constructing a berm. If the later method is used the surface top soil must be removed from the proposed ponding area. They function by storing detained runoff while infiltration occurs. Limitations o Not allowed on slopes greater than 25% (4:1). ' o Infiltration surface elevation (bottom of trench) must be in native soil (excavated at least one foot in depth). ' Design Criteria o See Figure 4.5.4A for sample detail. ' o A soils report must be prepared which demonstrates compliance with the requirements in Sections 1.2.3 and 1.3.12 in Chapter 1. o Bottom of the proposed pond must be at least one-foot above the seasonal high groundwater level. io A minimum of one soils log, extending a minimum of 3 feet in depth below the bottom of the proposed pond, that describes the S.C.S. series of the soil, the textural class of the soil horizon through the depth of the log, and notes any evidence of high groundwater level, such as mottling, shall be obtained for each 10,000 square feet (plan view area) of proposed pond infiltration surface area. o A minimum of three sub-surface infiltration tests shall be performed for each proposed pond as described in Section 4.5.2. o An overflow route must be identified in the event the pond infiltration capacity is exceeded and designed to meet the requirements of Section 1.2.1, in Chapter 1. o The construction of structures, materials allowed, accessibility for maintenance, easements, and hydraulic design methods shall be the same as those described for detention ponds in Section 4.4.4. ' o All ponds (at the maximum potential water surface elevation) shall be a minimum of 20 feet from any structure, property line, NGPE, and 100 feet from any septic pond/drain field. ' o All ponds shall be a minimum of 50 feet from any steep slope. A geotechnical report must address the potential.impact of the pond infiltration on the steep slope (see Section 1.3.11, in Chapter 1). Method of Analysis The size of the pond shall be determined by using the hydrograph methods described in Chapter 3 and the stage/discharge curve (incorporating the 2.0 factor of safety) developed from the maximum infiltration rate as described in Section 4.5.2. The storage volume in the pond is used to detain runoff prior to infiltration. The potential infiltration area (A,) used for sizing the pond shall be computed by measuring the surface area (plan view area) below the maximum design water surface. ' 4.5.4-I 1/90 l ! 1 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL i �— 4.6 WATER QUALITY FACILITY DESIGN ' See the overview of Surface Water Policies in the Reference section, for a discussion of the mechanisms of pollutant removal and water quality benefits of wet ponds and swales. ' Exemption: Runoff from roofs will not require water quality treatment for proposed projects required to provide any of the water quality facilities in this Section provided the roof runoff will of flow through the water quality facility, and the BALD Division determines granting this exemption will not produce significant ' adverse impacts to downstream water quality. Note, this exemption does not exempt projects from providing peak rate runoff control for runoff from roofs, however, it may allow significant reduction in the required size of the water quality facilities contained in this Section. Liner to Prevent Groundwater Contamination Significant concern exists regarding the potential contamination of groundwater resources (both potable ' and aquatic) from inadequately treated surface water runoff that may be immediately infiltrated at water quality control facilities serving impervious areas of intensive use (such as for proposed arterial roadways, and multi-family residential, commercial, manufacturing and industrial projects). These water quality facilities include wetponds, water quality swales and biofiltration facilities located over rapidly draining soils. ' In order to address this concern, these water quality facilities, proposed to be located in soils with a minimum infiltration rate (see Section 4.5.1), or permeability, of more than 9 inches per hour (0.15 inches per minute), must have a "lining" system to prohibit infiltration under the water quality facility. Of course, ' infiltration facilities provided for peak rate runoff control would be located downstream of these and any other water quality control facilities. Design Criteria o The liner material must be either a commercial heavy plastic pond liner (minimum 40 mil) or a bentonite clay (minimum 12" thick). o A layer of (track) compacted top soil (minimum 18" thick shall be placed over the liner prior to seeding with the appropriate seed mixture (see Section 5.5.4, in Chapter 5). 4.6.1 WATER QUALITY SWALES Water Quality Swales ' Water Quality Swale shall be designed to meet the requirements of Special Requirement #5: Special Water Quality Controls, Section 1.3.5, in Chapter 1. Design Criteria ' o See Figure 4.6.1A for detail. ' o The materials allowed, vegetation required, accessibility for maintenance, easements, and hydraulic design methods shall be the same as those described for open channels in Section 4.3.7. Method of Analysis ' The width of the Swale bottom shall be determined by using the hydrograph methods described in Chapter 3 to compute the required design flow. j-1'min.freeboard 3(min) FIGURE 4.6.1A WATER QUALITY SWALE d=0.25' Design Water Surface ' 2 yr,24 hr design storm Width as required flow(Developed Conditions) 4.6.1-1 1/90 ��� 7 3 ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ,l 1 1.2.3 CORE REQUIREMENT #3: RUNOFF CONTROL Proposed must projects provide runoff control through a combination of peak rate runoff control facilities and on-site biofiltration measures as described below. Peak Rate Runoff Control Proposed projects must provide peak rate runoff control to limit the developed conditions peak rates of runoff from specific design storm events not to exceed the pre-development peak rates for the proposed project site "existing conditions" as described below. Three basic methods for peak rate runoff control are possible: detention, retention, and infiltration. Detention is the collection and temporary storage of surface water (typically over several hours) with the outflow rate restricted--usually to the pre-developed outflow rate. Retention is the collecting and holding of surface and stormwater with effectively no surface outflow (outflow occurs by evapotranspiration). Infiltration is the soaking of surface water into the ground (typically for several hours or days). ' Infiltration not only reduces or eliminates surface runoff, but also helps to maintain the hydrologic balance of the surface water system. Infiltration can limit erosion and recharge groundwaters that supply water to wetlands, streams, and wells. Preserving infiltration after development is by far the most ' effective mechanism in preventing adverse impacts to the surface water system. Because of these benefits, King County encourages the use of infiltration systems for runoff control where the appropriate soil conditions exist. 1 Proposed project peak rate runoff control must be located on-site. An exemption from on-site peak rate runoff control may be granted for the special conditions specified at the end of this core requirement section. 1 Biofiltration Proposed project runoff resulting from more than five thousand square feet of impervious surface, and subject to vehicular use or storage of chemicals, shall be treated prior to discharge from the project site by on-site biofiltration measures as described in Section 4.6.3 in Chapter 4. The biofiltration design flow rate shall be the peak rate of runoff for the 2-year 24-hour duration design storm event. Note, biofiltration facilities installed following peak rate runoff control facilities may be sized to treat the allowable release rate (pre-developed) for the 2-year 24-hour duration design storm event for the peak rate runoff control facility. Biofiltration facilities installed prior to peak rate runoff control facilities shall be sized based on the developed conditions. Proposed Project Site "Existing Conditions" ' In performing the analysis for the design of runoff control, it is essential to first determine the proposed project site "existing conditions" from which the pre-development runoff rates can be computed for specific design storms. Existing conditions are not always synonymous with those of the natural, totally undeveloped site. In some instances substantial modifications (such as diversions, piping, clearing, and grading) have already increased and altered surface water runoff leaving the site, but no permit, nor accompanying engineering plan, was ever approved. In other instances, an approved drainage system exists and the existing system must be analyzed for its performance. There are two definitions for proposed project site "existing conditions" depending on the site. ' Sites with Existing Approved Drainage Systems: The proposed project site "existing conditions" are defined as those that occur with the existing drainage facilities constructed per approved permits and engineering plans. The current performance of existing drainage and detention facilities shall be ' determined by using the analysis methods described in Section 3.5 in Chapter 3. Sites with No Existing Approved Drainage Systems: The "existing conditions" are defined as those that existed prior to May 1979, which is the date of publication of "Requirements and Guidelines for Storm ' Drainage Control in King County" by the King County Public Works Department's Hydraulics Division, the 1.2.3-1 1/90 2, KING COUNTY, WASHINGTON, SURFACE WATER DESIGN .M,A,NU'AL Usually retention facilities will not be a cost effective means for providing peak rate runoff control, but ' rather are employed to control the increased volume of runoff from a proposed projects as is required by Special Requirement #7: Closed Depressions in Section 1.3.7 of this Chapter. The pre- and post-development peak runoff rates for the 100-year, 7-day duration'design storm events are evaluated, along with the standard peak rate runoff control performance curve, when retention facilities are employed in order to control increased volume of runoff from proposed projects. In these cases, retention facilities shall be analyzed and sized using the methods described in Section 3.6 in Chapter 3, and designed using the design standards contained in Section 4.4 in Chapter 4. Note, in some cases, retention facilities will have significant infiltration capability and, in these cases, must also meet the design standards contained in Section 4.5 in Chapter 4. ' > Infiltration Facilities Infiltration facilities, as with detention systems, must be sized to meet the required peak rate runoff ' control performance curve. More restrictive runoff control curves may be required under conditions specified in the "Special Requirements" Section 1.3 of this chapter. Note, the factors of safety for infiltration systems are incorporated within the methods of analysis and design standards described in Section 4.5 in Chapter 4. For the design requirements and standards for infiltration facilities see Section 4.5 in Chapter 4. There are many practical limitations on infiltration facilities, due to the very slow permeability rates of some soils and the need to prevent contamination of groundwater resources. Because of these practical ' limitations, King County allows infiltration facilities only in the following Soil Conservation Service series soils: Arents ("An" only), Everett, Indianola, Klaus, Neilton, Pilchuck, Puyallup and Ragnar. A soils report is required for all proposed infiltration facilities to verify the mapped soils series or to classify,the series of the soil (if previously unmapped). Soils logs are prepared to provide the data for the report and to investigate and confirm that the seasonal high:groundwater is at least 1 foot below the:bottom of a proposed infiltration system. Where doubt exists as to the depth of seasonal high groundwater an investigation must be conducted during the winter months prior to permit approval. ' Infiltration facilities may not be operated until all proposed project improvements which produce surface runoff are complete, especially revegetation and landscaping. In the case of projects with individual lots remaining undeveloped, these lots must contain and infiltrate their runoff through individual sediment traps (see Section 5.4.4.1 in Chapter 5) acting as infiltration ponds as until permanent improvements and landscaping are established. Infiltration facilities must be designed based on infiltration testing and a soils report prepared by a professional civil engineer with expertise in soil engineering. An emergency overflow path must be identified for infiltration facilities and noted on the engineering —.` plan. This overflow path must be analyzed to meet the requirements of Core Requirements #1 (see Section 1.2.1) and #2 (see Section 1.2.2) for the 100-year, 24-hour duration design storm, except Downspout Infiltration Systems (see Section 4.5.1 in Chapter 4). Infiltration facilities may be especially useful in the following circumstances, provided the proper soil conditions are present and all requirements can be met. (1) The proposed project discharges to a closed depression. ' (2) The proposed project discharges to a severely undersized conveyance system that restricts the runoff volume that can be accommodated. ' (3) The proposed project is in a Critical Drainage Area requiring runoff volume control. ' 1.2.3-4 1/90 � l KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 1.3.12 SPECIAL REQUIREMENT #12: SOILS ANALYSIS AND REPORT ' Threghold Requirement IF the soils underlying a proposed THEN a soils analysis and report shall ' project have not been mapped, or if the be prepared and stamped by a existing soils maps are in error or not of professional civil engineer with expertise sufficient resolution to allow the proper in soils to verify and/or map the engineering analysis of the proposed underlying soils by addressing the site to be performed. . . minimum as described below. Minimum Analysis and Report The soils analysis and report shall, at a minimum, characterize and classify the underlying soils based on the SCS Classification system and soil texture method, identify any impacted areas containing expressions of groundwater interflow, and describe any special characteristics of the underlying soils ' that should be addressed by the proposed project. These special characteristics shall include, but not be limited to; load bearing capacity; suitability for use as general site fill, roadway and pond embankment materials; erodibility during construction; and, the ability to support vegetation for ' stabilization. ' 1.3.12-1 1/90 i� �� ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 1.3.5 SPECIAL REQUIREMENT #5: SPECIAL WATER QUALITY CONTROLS Threshold Req_ulrement IF a proposed project will construct THEN a wetpond meeting the standards more than 1 acre of impervious surface described below shall be employed to that will be suEect to vehicular�sQ or treat a project's runoff prior to storage of chemicals and: discharge from the site. A wetvault or DOES �-107 water quality swale, as described below, APPL TO (a) proposes direct discharge of may be used when a wetpond is not y runoff to a regional facility, feasible. ST2 AfI F-01ZP receiving water, lake, wetland, or ' P( cE closed depression without on-site peak rate runoff control; OR (b) the runoff from the project will ' discharge into a Type 1 or 2 stream, or Type 1 wetland, within one mile from the project site... ' Wetponds or Wetvault Wetponds and Wetvaults contain a permanent pool of water depending on the frequency and quantity of ' inflow, and (for Wetponds) the rate of permeability of the underlying soil. The Wetponds and Wetvaults fill with the initial onset of frequent storms such that the major portion of the volume of runoff is treated. The principal mechanism of treatment is settlement due to establishment of calm conditions. In Wetponds treatment is enhanced by the mechanisms of biofiltration and biologic activity. ' The size of the Wetpond or Wetvaults shall be determined as follows: (1) The design water surface area in the Wetpond or Wetvault shall be a minimum of one percent of the impervious surface area in the drainage sub-basin contributing to the facility. (2) The design volume of the Wetpond or Wetvault shall be a minimum of the total volume of ' runoff (see Chapter 3: Hydrologic Analysis) from the tributary sub-basin proposed developed conditions using a water quality design storm event having a total precipitation (Pt-wq), where Pt-wq is one-third of the two-year, 24-hour total precipitation (P2/3, Pz is obtained from Figure 3.5.1 C). This water quality design storm event approximates the runoff from the mean annual ' storm event. Water Quality Swale ' Water Quality Swales treat runoff by acting as filters for the runoff from frequent storms. The principal mechanism of treatment is slowing of particles to which pollutants are attached allowing them to settle out. This treatment is enhanced by the "taking-up" of the dissolved fraction of pollutants by the vegetation. i 1.3.5-1 1/90 ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL The Water Quality Swale shall be designed based on the following criteria: ' (1) The Water Quality Swale width and profile must be designed to convey the peak runoff for the 2-year, 24-hour design storm event for the tributary sub-basin proposed developed conditions at a maximum design-6ep of-0.25 0o an maximum design velocity of 1.5 foo�er second, ' esigne usin a an nn1 gs n value o 33 avmg minimum o 3:1 si eT s o s, an�3c— providing minimum nimum o of—ne foot of fre`be o—""7arc above the design water surface. (2) Above the peak runoff for the 2-year, 24-hour duration design storm event for the proposed ' ��� developed conditions, runoff must bypass the Water Quality Swale in a separate conveyance to the point of discharge. A mechanism must be provided at the bypass point to take the water quality swale 'off-line". (3) The design length of the Water Quality Swale shall be 200 feet for each 5 acres of impervious surface subject to vehicular use or storage of chemicals in the tributary drainage sub-basin. Hydraulic analysis and design standards for Wetponds and Wetvaults, and Water Quality Swales can be found in Section 4.6 of Chapter 4: Hydraulic Analysis and Design. ' 1.3.5-2 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' 1.3.6 SPECIAL REQUIREMENT #6: COALESCING PLATE OIL WATER SEPARATORS ' Threshold Requirement IF a proposed project will construct THEN a coalescing plate or equivalent, more than 5 acres of impervious surface oil/water separator (as described ' ( that will be subject to: below) shall be employed to treat the project's runoff prior to treatment by a (a) petroleum storage or transfer; OR wetpond, wetvault, or water quality (b) high vehicular use (more than swale, and/or discharge from the ' 2,500 vehicle trips per day); OR project site. (c) heavy equipment use, storage or maintenance... ' Coalescing plate oil/water separators consist of a bundle of plates made of fiberglass or polypropylene Installed in a concrete vault. The plates are closely spaced (not less than 3/4-inch apart) and are inclined at an angle of from 450 to 60' from horizontal. These plates improve the hydraulic conditions ' that promote removal of oil and fine suspended sediments and assist in concentrating the pollutants for removal. Because of this enhanced removal efficiency, they require frequent inspection and maintenance to operate as designed. ' The coalescing plate oil/water separator shall be designed based on the following criteria: (1) The design flow rate for determining the quantity of runoff to be treated, and the required plate ' area, shall be the peak rate of runoff (QWq) from the tributary drainage sub-basin proposed developed conditions. QWq is determined using a water quality design storm event (computed using the methods described in Chapter 3: Hydrologic Analysis) having a total precipitation (P,_Wq), where P,_ is one-third of the 2-year, 24-hour total precipitation (P2/3, P2 is obtained ' from Figure 3.5.1 C). This water quality design storm event approximates the runoff from the mean annual storm event. (2) Peak runoff in excess of QWq must bypass the coalescing plate oil/water separator vault. A ' mechanism must be provided at the bypass point to take the separator "off-line". (3) Coalescing plate oil/water separators shall treat runoff prior to discharge to special water quality control and/or peak rate runoff control facilities. Hydraulic analysis and design standards for coalescing plate oil/water separators are described in Section 4.6.4 in Chapter 4. i` ' 1.3.6-1 1/90 ' 10 7 92 John Newell, Inc. age 1 / / P STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT ' INFILTRATION DESIGN BASIN SUMMARY BASIN ID: B1 NAME: EXISTING SITE W/ 2YR. ' SBUH METHODOLOGY . TOTAL AREA. . . . . . . • 3 . 06 Acres BASEFLOWS: 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2 . 00 inches AREA. . : 2 . 96 Acres ' TIME INTERVAL. . . . : 10. 00 min CN. . . . : 59 . 17 TIME OF CONC. . . . . : 44 . 32 min IMPERVIOUS AREA ABSTRACTION COEFF: 0. 20 AREA. . : 0. 10 Acres ' CN. . . . : 98 . 00 TcReach - Sheet L: 130. 00 ns: 0. 1500 p2yr: 2 . 00 s: 0. 0615 TcReach - Sheet L: 100. 00 ns: 0. 4000 p2yr: 2 . 00 s: 0. 1000 TcReach - Sheet L: 70. 00 ns: 0. 4000 p2yr: 2 . 00 s: 0. 0286 ' TcReach - Shallow L: 28 . 00 ks: 5. 00 s: 0. 0710 TcReach - Shallow L: 120. 00 ks: 5. 00 s: 0. 0317 PEAK RATE: 0. 03 cfs VOL: 0. 03 Ac-ft TIME: 480 min ' BASIN ID: B2 NAME: EXISTING SITE W/ 10 YR. SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0. 00 cfs ' RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2 . 90 inches AREA. . : 2 . 96 Acres TIME INTERVAL. . . . : 10. 00 min CN. . . . : 59 . 17 TIME OF CONC. . . . . : 44 . 32 min IMPERVIOUS AREA ' ABSTRACTION COEFF: 0 .20 AREA. . : 0 . 10 Acres CN. . . . . 98 . 00 TcReach - Sheet L: 130. 00 ns: 0. 1500 p2yr: 2 . 00 s: 0 . 0615 ' TcReach - Sheet L: 100. 00 ns: 0. 4000 p2yr: 2 . 00 s: 0 . 1000 TcReach - Sheet L: 70. 00 ns: 0 . 4000 p2yr: 2 . 00 s: 0. 0286 TcReach - Shallow L: 28 . 00 ks: 5. 00 s: 0. 0710 . TcReach - Shallow L: 120. 00 ks: 5. 00 s: 0. 0317 ' PEAK RATE: 0. 07 cfs VOL: 0. 09 Ac-ft TIME: 1440 min BASIN ID: B3 NAME: EXISTING SITE W/ 25 YR. SBUH METHODOLOGY ' TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 3 . 40 inches AREA. . : 2 . 96 Acres ' TIME INTERVAL. . . . : 10. 00 min CN. . . . : 59 . 17 TIME OF CONC. . . . . : 44 . 32 min IMPERVIOUS AREA ABSTRACTION COEFF: 0. 20 AREA. . . 0. 10 Acres CN. . . . . 98 . 00 ' TcReach - Sheet L: 130. 00 ns: 0. 1500 p2yr: 2 . 00 s: 0. 0615 TcReach - Sheet L: 100. 00 ns: 0 . 4000 p2yr: 2 . 00 s: 0. 1000 TcReach - Sheet L: 70. 00 ns: 0. 4000 p2yr: 2 . 00 s: 0. 0286 ' TcReach - Shallow L: 28 . 00 ks:5. 00 s: 0. 0710 TcReach - Shallow L: 120. 00 ks:5. 00 s: 0. 0317 PEAK RATE: 0 . 11 cfs VOL: 0. 14 Ac-ft TIME: 760 min ' 10/ 7/92 John Newell, Inc. page 2 STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT INFILTRATION DESIGN BASIN SUMMARY=====_______________________ ' BASIN ID: B4 NAME: EXISTING SITE W/ 100 YR. SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0 . 00 cfs ' RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 3 . 90 inches AREA. . : 2 . 96 Acres TIME INTERVAL. . . . : 10. 00 min CN. . . . : 59 . 17 ' TIME OF CONC. . . . . : 44 . 32 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 0. 10 Acres CN. . . . . 98 . 00 ' TcReach - Sheet L: 130. 00 ns: 0. 1500 p2yr: 2 . 00 s: 0. 0615 TcReach - Sheet L: 100. 00 ns: 0. 4000 p2yr: 2 . 00 s: 0. 1000 TcReach - Sheet L: 70. 00 ns: 0.4000 p2yr: 2 . 00 s: 0. 0286 TcReach - Shallow L: 28 . 00 ks: 5. 00 s: 0. 0710 TcReach - Shallow L: 120. 00 ks: 5. 00 s: 0. 0317 PEAK RATE: 0. 16 cfs VOL: 0. 20 Ac-ft TIME: 760 min BASIN ID: B5 NAME: DEVELOPED SITE W/ 2 YR. ' SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA ' PRECIPITATION. . . . : 2 . 00 inches AREA. . : 1. 64 Acres TIME INTERVAL. . . . : 10. 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . . 3 . 13 min IMPERVIOUS AREA ABSTRACTION COEFF: 0. 20 AREA. . : 1. 42 Acres CN. . . . : 98 . 00 PEAK RATE: 0. 78 cfs VOL: 0. 24 Ac-ft TIME: 470 min CA ') mo 141 ° N S ° 3Za, � �/7s/• ° .08. ! 1 3 :S 032,05"W //9.2/' o N PIPE) In ° ° ° /0• CD ° /11.87• 1 X, 7. 71_ N W ' 10/ 9/92 John Newell, Inc. page 1 STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT ' INFILTRATION DESIGN BASIN SUMMARY ' BASIN ID: B5 NAME: DEVELOPED SITE W 2 YR. SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2 . 00 inches AREA. . : 1. 64 Acres ' TIME INTERVAL. . . . : 10. 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . . 23 . 15 min IMPERVIOUS AREA ABSTRACTION COEFF: 0. 20 AREA. . : 1. 42 Acres - CN. . . . : 98 . 00 TcReach - Sheet L: 140. 00 ns: 0. 1500 p2yr: 2 . 00 s: 0. 0090 TcReach Shallow L: 200. 00 ks: 27 . 00 s: 0. 0340 TcReach - Channel L: 95. 00 kc:42 . 00 s: 0. 0580 PEAK RATE: 0. 53 cfs VOL: 0. 24 Ac-ft TIME: 480 min ' BASIN ID: B6 NAME: DEVELOPED SITE W/ 10 YR. SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0. 00 cfs ' RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2 . 90 inches AREA. . : 1. 64 Acres TIME INTERVAL. . . . : 10. 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . : 23 . 15 min IMPERVIOUS AREA ' ABSTRACTION COEFF: 0. 20 AREA. . : 1. 42 Acres CN. . . . . 98 . 00 PEAK RATE: 0. 84 cfs VOL: 0. 39 Ac-ft TIME: 480 min BASIN ID: B7 NAME: DEVELOPED SITE W/ 25 YR. SBUH METHODOLOGY ' TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 3 . 40 inches AREA. . : 1. 64 Acres ' TIME INTERVAL. . . . : 10. 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . : 23 . 15 min IMPERVIOUS AREA ABSTRACTION COEFF: 0. 20 AREA. . : 1. 42 Acres CN. . . . . 98 . 00 ' PEAK RATE: 1. 06 cfs VOL: 0.49 Ac-ft TIME: 480 min 10/ 9/92 John Newell, Inc. page 2 STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT INFILTRATION DESIGN --------------------------------------------------------------------- --------------------------------------------------------------------- BASIN SUMMARY BASIN ID: B8 NAME: DEVELOPED SITE W/ 100 YR. SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 06 Acres BASEFLOWS: 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 3 .90 inches AREA. . : 1. 64 Acres TIME INTERVAL. . . . : 10. 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . : 23 . 15 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1. 42 Acres CN. . . . : 98 . 00 PEAK RATE: 1. 30 cfs VOL: 0. 59 Ac-ft TIME: 480 min 1� 1 1 1 1 L/ r 10 19 92 John Newell, Inc. page 1 / / P 5 STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT INFILTRATION DESIGN BASIN SUMMARY BASIN ID: B9 NAME: OFFSITE NE 16TH ST W/ 100 YR. SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0. 04 Acres t(- BASEFLOWS : 0. 00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 3 .90 inches AREA. . : 0. 02 Acres TIME INTERVAL. . . . : 10. 00 min CN. . . . : 68 . 00 TIME OF CONC. . . . . : 0. 29 min IMPERVIOUS AREA ABSTRACTION COEFF: 0. 20 AREA. . : 0. 02 Acres CN. . . . : 98 . 00 TcReach - Shallow L: 151. 00 ks:27. 00 s: 0. 1000 PEAK RATE: 0. 03 cfs VOL: 0. 01 Ac-ft TIME: 470 min 1 1 1 �'2tot� 10/19/92 John Newell, Inc. page 1 ' STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT INFILTRATION DESIGN --------------------- HYDROGRAPH SUMMARY PEAK TIME VOLUME HYD RUNOFF OF OF Contrib ' NUM RATE PEAK HYDRO Area cfs min. cf-AcFt Acres L 1 0. 029 480 1193 cf 3_. 06''Ly(L�24�}Q 'F�-K, COODI?0t7 5_ 2 0. 073 1440 3917 cf 3 . 061OLAV qA H2. EX CprtpITEOtAS 3 0. 108 760 6064 cf 3 . 06, s ( 24 "7 &X- COh41D!"-(-,(aNS 4 0. 156 760 8573 cf _3 . 06i0o\,jQ/Z4t lZ EX, CoMDl7loN5 5 0. 527 480 10304 cf _3_. 06 _ �c,�{Z /Z4 H2 Dev\ CL-A DM(Dt-LS - - 6 0. 840 480 17183 cf 3 . 06 41��� ) 7 H2 D�U CC)NOI itUt�LS 7 1. 060 480 21347 cf 3_. 06 .LS VIV j��Q C)Ev, CC)t-kDiTIONS_.. ' 8 1. 297 480 25693 cf _3 . 06_ (()D \�Q )Z4N1? UEU, C0t41D OiAS 9 0. 035 470 394 cf _ 0. 04 .tn0_y12(24He_ _IAA ktDg4 ST, .DFV,__. f OrFSrrF-"- tJo T To ' INF�LT,ZA,Ztor4 97 A R F-,A = C]Co A r OFF SvTT AVZE-4 ADJAGFt,�'j To c-1E ICTEi ST = (��o)�&�-� - 1�3oos,� = 0,04-1 A c ' NOZ� l�' o� PPvrIT (�72OH Q) To MO02 - i � nv� r_x�sTs , NF w b�V�LuP'�1EN`T"v�l�LCor�S�S-( r� � CUtLB/G(A"[TF-tZ SIDFU.7�(� ' PA,U 'T = �z+s�C11.0) OSO S,F, 0,0Z4A-c- CN- 95 LAW N = Cs) C t5o)= -1Sc-) S,F, = o, 0 17 Ac- 2 ( � �,ZIOIq 0 ' IEGEND 100�-I. Hyd No. 8_ F?(C(---SS A�-TFZ WEI.LTRATOO Hyd No. 10 _ t LC2AS10__ cc, 03 0 0 M w u c 00 0 0 1 ' 3 6 9 12 15 18 h 24 27 Time in Hours Hyd No. : 8 Rate: 0. 75 cfs Time: 8 . 00 hr Vol 0. 04 Ac-ft Int: 10. 00 min ' Hyd No. : 10 Rate: 0. 55 cfs Time: 7. 67 hr Vol 0. 55 Ac-ft Int: 10. 00 min IZ/k-(E = 0 333 IN I I AIP 4' � ) L- 14-q A2 � t�.PLTCZAZ OG 4 - �2) CD(A) 14-R) ' q'I = O,SS cr-5 DIUE2T O,Ss cis FROM HL�Dkzo ':' b Tv H�JDZ# 10 PEZC, .(Z1�TT 2F=PoR-7) = 1 ' (0" Z,CoS c s ' R. s. _ TEST wi-: (ZATC— TAB(-r-- 4, s, _- Z,(DS /n,ss = 4, s . I OMCLUStoN TQY 4' � P&R—I:O2NT1=D 7AI-ItL CI S ©"/O L= 14 9 ' \Ivt-c l- PE-9c_, ? 7r-- = MINA lit-A, — t '1131�itt�1 Coo�)'Twl O tScH-a.tz.c F 0 I SS C F s ' SZoQPGI- (Z1=d D lno AIL f Z4 HZ- = 1-1 4-2 C,F, ' 1-1 38 10 9 92 John Newell Inc. page 1 / / P g STRATFORD PLACE PLAT FOR CAMWEST DEVELOPMENT ' INFILTRATION DESIGN �t STAGE STORAGE TABLE UNDERGROUND PIPE ID No. S3 Description: 4 FT. DIA PIPE Diameter: 4 . 00 ft. Length: 149 . 00 ft. Slope. . . . 0. 0000 ft/ft STAGE <----STORAGE----> STAGE <----STORAGE ---> STAGE <----STORAGE----> STAGE <----STORAGE----> -(ft)----cf---_- Ac-Ft-_--_(ft)----cf-----Ac-Ft-_---(ft)----cf----- Ac-Ft-_--_(ft)----cf----- Ac-Ft-__- [Li 295.00 0.0000 0.0000 296.10 418.50 0.0096 297.20 1055 0.0242 298.30 1652 0.0379 295.10 12.470 0.0003 296.20 472.41 0.0108 297.30 1114 0.0256 298.40 1696 0.0389 295.20 35.001 0.0008 296.30 527.69 0.0121 297.40 1173 0.0269 298.50 1737 0.0399 U vJ 295.30 63.803 0.0015 296.40 584.04 0.0134 297.50 1231 0.0283 298.60 1775 0.0407 295.40 97.448 0.0022 296.50 641.33 0.0147 297.60 1288 0.0296 298.70 1809 0.0415 ' V 295.50 135.09 0.0031 296.60 699.42 0.0161 297.70 1345 0.0309 298.80 1837 0.0422 295.60 176.11 0.0040 296.70 758.12 0.0174 297.80 1400 0.0321 298.90 1860 0.0427 IU 295.70 220.07 0.0051 296.80 817.28 0.0188 297.90 1454 0.0334 i 299.00 1872 0.0430 295.80 266.59 0.0061 296.90 876.82 0.0201 298.00 1506 0.0346 0 295.90 315.34 0.0072 297.00 936.19 0.0215 298.10 1557 0.0357 J 1 296.00 366.04 0.0084 297.10 995.57 0.0229 298.20 1606 0.0369 17 ' UC)L (ZEQ'D ( DT--f1D) 13 C;�" CC)EA-D) TOTAL C,F lb (`\?D/ 7('.J 41-', 1- co 1 1 � �03� ' S72A7Fo1�0 )Ct4CE [CIO FIC.T2AT/O oE-S Ir,ti/ f5CAa,E OF "P4c5 LIIVITATIO,�" Wf sHACL WSE Tf-�,F OU I L I/ALFA/T A254 IVETN0 D TO 5/ZE T PF-- ! 16 FIC.T A 6V4 SW�1LFe THE 8/OF/LrOAi'1Ob1 CUILL 55 LUC11175D 57Wq CUNC VIA -5 ON LOTS 1,31/¢. P-115 A2EA I/ ICL 5E FFN6ff9,56) A ��12AC 0�51GN.97.�0>°� (4'9 DFvIGN FCOIU DbP%'H /5 2E,45DA146F Vl = U.-7c Al2�A ,rWIZAIISHED IN IORO OSZFO 810 FI C A7f0N �StNALE a4 f (1015 (GS� l(O ,o) /0 50 S,F PE-Ob ' O K.. CPECIL. 10o y2 FL.ov.) ClIPACITY e 5= O,SO%o y = DEPTff = 6,13 ' 8 /0,, C 5077oM VJIDT) 0, 8q `/s 1 5 - 3I MAN-MADE CHANNELS VARIABLES LIST: ' Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS VARIABLE TO BE SOLVED (Y,Q,B,M,S OR N) ? B C Y (FT) ? .33 RESULTS Q (CFS) ? .53 _________________ (� (� (�L 11I� ✓�C�J E'LO PE M (FT/FT) ? 3 B= 5.25 FT S (FT/FT) ? .02 A= 2.06 SF — 7 N (FT^1/6) ? .35 P= 7.34 FT _ �I V= 0.26 FPS F= 0.09 SUB-CRITICAL FLOW O 3� <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu VARIABLES LIST: MAN-MADE CHANNELS Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS VARIABLE TO BE SOLVED (Y,Q,B,M,S OR N) ? Y Q (CFS) ? 1.3 RESULTS B (FT) ? 10.5 M (FT/FT) ? 3 Y= 0.13 FT S (FT/FT) ? .005 A= 1.46 SF N (FT^1/6) ? .03 P= 11.34 FT ' V= 0.89 FPS F= 0.44 SUB-CRITICAL FLOW ' <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- MAN-MADE CHANNELS ' VARIABLES LIST: Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS ' VARIABLE TO BE SOLVED (Y,Q,B,M,S OR N) ? Y ' Q (CFS) ? .27 -----RESULTS B (FT) ? 10.5 M (FT/FT) ? 3 Y= 0.03 FT ' S (FT/FT) ? .058 A= 0.27 SF N (FT^1/6) ? .030, P= 10.66 FT V= 1.01 FPS ' F= 1.12 SUPER-CRITICAL FLOW 1 ' <Shift> <Prt Sc> print- <Return> repeat--- ----<Space Bar> back to menu ---------------------- ------------- ----------------------- �w MAN-MADE CHANNELS VARIABLES LIST: Y - FLOW DEPTH B CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE 1 Q - FLOWRATE M CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS VARIABLE TO BE SOLVED (Y,Q,B,M,S OR N) ? Y Q (CFS) ? 1.3 RESULTS B (FT) ? 6.5 ' M (FT/FT) ? 3 Y= 0.18 FT S (FT/FT) ? .005 A= 1.24 SF N (FT^1/6) ? .03 P= '7.62 FT V= 1.05 FPS F= 0.46 SUB-CRITICAL FLOW ' ,Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- 70.98' CJ� 9 5'-54" P_._(Perforatedl 57.5'-54"O CAP. a =0% AP.C 2.,,56 32.5'L t. 5' /f90 32.5'L t. S.D. M.H. 02 54 TYPE It S.D. M.H. */ ti 54"0 TYPE 11 o � $' RIM 3/0* RIM 309.Of �! Inv (36'�/295.00 00 b o (1�i1298.85ZZ o ,? O' vIAIAGE E,6,l I'T 10'DRAINA6E ES "T o �" o °p /4 U o 8� h 6 RE/AFORCL-D 50 D. . yP OS 30p. 0 00 S=2. 0' -;CO;IT=1 3 r S=0.50/. 30 '� 7/./5' 72.0 ' 1'e 30\ 0 y, ° 9/0-SWALE SEE DETAIL 20 DRAINA GE E 5 M T ......................._.............................................................................................................. NE KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 4.6.3 BIOFILTRATION FACILITIES _. Core Requirement #3, in Section 1.2.3, in Chapter 3, specifies when biofiltration facilities must be provided to treat proposed project runoff. Note, biofiltration facilities may be installed prior to, or following, peak rate runoff control facilities. ' Facilities designed to improve the quality of storm and surface water runoff through the application of biofiltration have been shown by a number of studies to be effective in removing a significant amount of the total suspended solids, fine sediments, some non-soluable heavy metals, and some nutrients from the runoff. Locally, a study currently on-going by Professor Richard Horner of the University of Washington's ' Civil Engineering Department, sponsored by the Washington State Department of Ecology, the Municipality of Metropolitan Seattle (METRO), King County, and the cities of Bellevue, Mountlake Terrace and Redmond, has produced significant results and developed guidelines for sizing biofiltration swales and filter ' strips. In addition, work performed by Dr. Gary Minton, Resource Planning Associates, for the City of Seattle "Water Quality: Best Management Practices" Manual has demonstrated the practical application of the results of both theoretical and empirical research to the design of biofiltration facilities. ' There are two types of biofiltration facilities described in this Section. They are biofiltration swales and filter strips. A biofiltration swale is essentially a vegetation lined channel with the runoff treated by flowing at a shallow depth and relatively slow velocity through the vegetation. The biofiltration swale is best suited to treat runoff that has been collected and concentrated such as at the outfall to a peak rate runoff control ' facility. Filter strips are areas covered by vegetation over which runoff sheet flows at a very shallow depth and in a dispersed manor. Filter strips are well suited to treating runoff from impervious areas such as parking lots where frequent gaps in the extruded asphalt curbing provide dispersed inflow points to the ' filter strip. Design Criteria ' General o Biofiltration swales and filter strips shall be designed consistent with the requirements for conveyance system analysis and route design criteria in Section 4.3.2 and the design criteria for ' open channels in Section 4.3.7, unless superseded by the following design criteria. o Biofiltration swales shall have a maximum bottom width of 50 feet. ' o Biofiltration swales shall have one foot high (and one foot keyed below the swale invert) check dams placed every 50 feet along their length starting 20 feet downstream from the inflow point. The check dams shall have 2:1 side slopes and be constructed of rip rap per table 4.3.6A (100 % passing an 8" ' sieve). o Curbing for impervious areas tributary to filter strips shall be designed with a one-foot gap for every 5 feet of curbing. o The transverse slope of impervious areas tributary to filter strips shall be level, and the cross slope shall not exceed 10 percent. ' Geometries o Biofiltration swales shall be trapezoidal or rectangular in shape, based on the side slope and stabilization criteria contained in Section 4.3.7. o The length of biofiltration swales should be at least 200 feet, wherever feasible. The length may be reduced to a minimum of 50 feet provided the surface area of the design water surface at the ' biofiltration design flow is equal to that computed based on a 200 foot length (see Method of Analysis below). o The 200 feet of biofiltration swale length may be achieved by dividing the swale into segments ' (minimum 50 feet in length) with interconnecting pipes to transfer runoff between segments. This is particularly useful on slopes which exceed 6 percent where the segments can traverse the slope and thus "step" the biofiltration Swale down the slope. ' 4.6.3-1 1/90 (�� ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL o Filter strips are limited to treating runoff from 140 square feet of tributary impervious surface per unit ' lineal foot length of filter strip. o Filter strips shall be a minimum of 15 feet in width and a maximum of 30 feet in width (both ' measured in the plan view). Slope o Biofiltration swales may have slopes up to 6 percent. o Where the slope of a biofiltration swale will be less than 0.5 percent, or the seasonal mean ground water level will be at or above the swale bottom, emergent wetland vegetation must be planted. o Filter strips shall have a minimum slope of 2 percent and a maximum slope of 15 percent. ' o The transverse slope of filter strips (at the point where the filter strip meets the impervious surface) shall be level. o Runoff from a filter strip shall be intercepted a the bottom of the strip by a swale sized to convey the ' peak rate of runoff for the maximum design storm event away from the bottom of the strip. Vegetation ' Biofiltration swales and filter strips shall be vegetated based on the physical conditions using either an urban (lawn and other areas to be frequently mowed), rural (for use in areas to be left un-mowed and more natural in appearance), or wetlands (swales only) seed mixture (per Section 5.4.4 in Chapter 5). ' Methods of Analysis Use Manning's Equation Method for Preliminary Sizing of Open Channels, as described in Section 4.3.7, to ' determine the cross-sectional geometry of a biofiltration swale using the following parameters. Biofiltration Design Flow Rate ' o Biofiltration swales shall be sized using a biofiltration design flow rate as specified in Core Requirement #3, in Section 1.2.3 of Chapter 1, using the hydrograph methods described in Chapter 3. ' o Filter strips shall be sized by providing 0.23 square feet of strip per one foot length of tributary unit area of impervious surface. 11 2 Manning's Roughness "n" o Use a Manning's "n" of 0.35 when sizing a biofiltration swale for biofiltration function. Use an appropriate Manning's "n" from Table 4.3.76 (such as 0.027 for lawns) when evaluating the swale for ' conveyance capacity and maximum velocity for stability. Slope— V' o Regardless of the actual proposed biofiltration swale slope, use a slope of 2 percent when sizing the swale for biofiltration function. Use actual proposed slope when evaluating the swale for conveyance capacity and stability. ' Velocity o The velocity of runoff through the biofiltration swale or filter strip at the biofiltration flow rate shall not exceed 1.5�feet per second. / ( l ' 4.6.3-2 1/90 ` -7 �� KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL o The velocity of runoff through the biofiltration swale or filter strip for the maximum conveyance capacity design flow rate (see Core Requirement #4, Section 1.2.4, in Chapter 1) shall not exceed 5 feet per second. ' Design Flow Depth o Biofiltration swales shall be designed using a design flow depth at the biofiltration design flow rate by ' assuming a winter design height of vegetation as shown in Table 4.6.3A. TABLE 4.6.3A DESIGN FLOW DEPTH BY TYPE OF VEGETATION ' Type of Vegetation Winter Design Height Design Flow Depth ' Urban (lawns) 3 Inches 1 inch Rural (natural areas) 6 inches 4 inches Wetlands (wet areas) 10 inches 8 inches ' Design Process Biofiltration Swales 1. Compute the biofiltration design flow rate. 2. Determine the preliminary route and actual slope. 3. Compute the bottom width of the Swale based on the proposed vegetation type and side slopes (3 . ' to 1 preferred). d 2% 4. Check the velocity at the biofiltration design flow rate (Ignore the check dams and use the actual swale slope). If in excess of 1.5 feet per second, re-design the swale by decreasing the actual swale ' slope, stepping down the slope by dividing the swale into segments, or increasing the width. 5. If the swale length must be less than 200 feet In length, compute the surface area of the design water surface at the biofiltration design flow rate and widen the shortened swale to provide an equivalent surface area. ' 6. Use the conveyance capacity maximum design flow rates and establish the required swale depth to provide adequate freeboard. 7. Check the maximum velocity in the swale at the maximum design flow rate (Ignore the check dams when computing the maximum velocity.) If greater than 5 feet per second re-design the swale by ' decreasing the actual swale slope, stepping down the slope by dividing the swale into segments, or increasing the width. ' Filter Strips 1. Compute the required width of the filter strip by calculating the length of of tributary unit area of impervious surface per one foot length of strip and multiplying times 0.23 feet. ' 2. Determine the preliminary design of the filter strip. 3. Size the Swale at the toe of the filter strip to convey the maximum design flow rates from the area tributary to the filter strip. 4.6.4 COALESCING PLATE OIL/WATER SEPARATORS Coalescing plate oil/water separators are used to effectively remove oil and grease from surface water. They operate by using differential gravity separation of particles that have a different density than water. ' Particles of higher density than water (such as sediments) will settle down to the bottom, while particles with a lower density than water (such as oils) will rise to the top. Once separated from the water column the particles of interest can be removed. The most effective separator designs employ a series of parallel ' inclined plates that shorten the distance particles have to settle and provide for self-cleaning of the plates ' 4.6.4-I 1/90 �f 71 1 V. CONVEYANCE SYSTEMS ANALYSIS AND DESIGN 1 C0IFVE`k1Al,,(-,E CALCS. ON-t)tTE /, NO, OF Lo T� - /4 2. ACrzc-,-cam = 3,06 1>(414c- /-4/3-06- 4, 53 1Du,/hC- ' U55 0,5/ 61,5E RA71COAL. ME7-H00 45 f-IODIFI D :�,y /9 q0 MANUA-L. ' USE /00y2 6TOV-1 To CHC-06 (ONVELIAflCE USE T(c) MIN .= Co,5 /cal!N, brz = 0,673 4, CALC C FOE P-OAD P1 w qo) f 31 S(,ZS))l 7-5 = 1 _ 5, CiLC G ML 107 W/o 2/CU 7 ZOO S,F - 0,I-7 A-c ' 1-bUSE 0 DoivEtvA y = 30-00 SF, = 0,01 Ac. I-AVW 5 f LDS 'l�f G - a tv Ac -7 0,52- A-- / 2, ZCZ x 40z 3 0/q s F 0, 083 Ac ' A-Z 16,744 INN- X 46L- 26,-q0. 6� 615 A -3 Z, SCE INz- K 40z 4000, 0. t)q2 -4 /l, 4-yb 1M7- x 407- = 18 393. 0, 4ZZ -5 4,037 !07 x 40z (o 4 Sq, O, /48 ' A 6 M,Z4/ rN z )� 401- Zgz&E,, 0, &7z A - !7 /, !S& (/,(7 y 407- /4 G4q, 0, lE(o A-9 !8, q76 rr L X 46Z = 30 3�1, D, 6,ci7 13353G 3.�65 ( 2�0I)( Tc,) ,G3 � � II MAN-MADE CHANNELS VARIABLES LIST: Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS VARIABLE TO BE SOLVED (Y,Q,B,M,S OR N) ? Y Q (CFS) ? 3 . 81 Mo V, (I lt-kTN LE RESULTS B (FT) ? 10. 5 F20N M (FT/FT) ? 3 Y= 0. 25 FT S (FT/FT) ? . 005 A= 2 . 85 SF N (FT-1/6) ? . 030 P= 12 . 10 FT V= 1. 34 FPS ' F= 0. 48 SUB-CRITICAL FLOW <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- 1 L�SC ,lS IN :l�J'�UJ(��E �-0 D 2MIt-1C LC CONVEYANCE SYSTEM ANALYSIS AND SIZING TABLE USING THE RATIONAL METHOD z Location Area C C•A Sum To i IR QR Pipe Typ. Slope OF V V L T� A ' Sub Basin Number ac C A (min. R (c.f.s. in. n ft.ft. (pipe (pipe (at (ft.) (min. w From To ( ) ) ) ( ) ( ) full full Q ) ) Ca Sig 2; !� J�D lZ ), O(% 0 ob `!,�✓ ? ' C� R Z3 U,I(o O ' z - ,7 ►'� ���1' U��I �.?S C�,�14, ' z r-c i3 G,(�i5 :-�,' 1,28 t � -�, ��r �.3} I��' 7 ,g�'7 ooJo �� �r��b 440o_ ��� �,40 r � 1 a O Fit ' t tV z a O n �t� j f�:; �ll I-, rJ•�'iv �l 4-lC J),1`{- :o(� � :�(� 1 _'f.l �? �i/� _ )v �, ,.J O (-V ,W J G a �/�;I o3 0o n �•���'�7 a � a d z d z _ � z Project: 5�C(Z f�TO(Zr, PLL� R IUo PR 3 ,q Calcs by: . N C-Uu E LL- Job No: Ozo 4� ' - --- a dOLU&IN @&MAAWIN0W E(�TIQd&-F1 CI0WLMPiRM A R x A x I'll(for vulcus Yil"s of n) Ater, Hydric. RI/I 1 % VaLrIous Ysluss of n Lj- sq. Radius, 4 .012 .013 .014 A15. .016 .017 .018 .019 021 .023 .024 .027 .030 .031 .032 13 3 r 1 04", 3.84 3.47 3.17 3.04 2.70 2.43 2.35 2.28 20 .1 Itl 2 6.0 el 5.61 5."1 4.86 4.56 4.29 4.05 2.21 li 8 1 .35 167 i .303 i 106 13.0; 12.08 10 11.22 .47 9.82 9.24 8.73 8.27 7.48 6.83 6.55. 5.82 5.24 5.07 4.91 4.76 .55 208 151 I�ii 23.74 21.91 20.34 18.99 17.80 16.75 15.82 14.99 13.56 12.38 - 1.87 0.55 9.49 9.19 8.90 8.63 . 2 .'SO .357 .312 38 35.63 1 33.08 30..98 28.95 27.24 25.73 24.38 22.06 20.14 19.30 17.15 15.44 14.94 14.47 14.064 1. .'2.! 412. .461 SG6 j 69.9? j 64.6 55.98 I 52.49 9.40 46 L5 44.20 39.99 36.51 34." 31.10 27.99 27.09 26.24 25.45 5.03 6.90 2 0 i 6 2 1.? 3-5 520 .919 97.54 1 9 1.%S S'5.35 1 150.33 75.86 71.87 50.58 45.52 44.05 42.67 41.38 Z 1 j 2.41 j .43/ 516 1.385 3 71'6 158.4 147.1 1 137.3 1118.7 2i.2 114.4 1084 09 5.83 76.29 6866 66.45 64.37 62.42 ,4 3.14 .5 QC 1 .630 1.979 245.1 22G.2 210. 19 183.8 173.0 163�4 15-4.,8 40,0 2.5 108-9 98.03 1 94.87 91.90 89.12 .1 41 .625 i .731 3,588 4,44.3 410.2 90.9 355.5 333.3 313.7 2962 280.6 I 254.0 231.8 222.2 197.5 177.7 172.0 1 G6.6 161.6 6 17 )7 .750 j .825 j 5.832 I 722.6 667.0 i 619.3 I 578.1 541.9 510.1 481.7 455.4 412.9 377.0 361:3. 1 321.1 289.0 279.7 271.0 262.7 42 9.621 .875 j 915 I S.803 1089 i006 934.2 871.9 817.4 769.4 726.6 688.4 622.8 568.7. 545.0 484.4 436.0 421.9 408.7 396.3 45 12 6 1.0.0 1.00 12,57 1 3556 ;436 1 333 1244 1167 1098 1037 982.2 - 869.2 811.9 778.1 1 1 1 691.6 622.4 602.4 5.83.5 565.9 5.9 1.125 1 1 065 946-8 1 852.1 OF 17.21 2130 1966 826 1704 1597 1503 1420 1345 1 1217 1 ill 1 $24.7 74 .9 774.7 6,- 19.6. 1.25 .16 22.78 2621 26,04 2418 2257 2116 1991 1880 178 612 472 1410 1253 1128 1092 105-8 1025 236 29.37 3637 3��58 3118 2910 2728 1 2567 2425 2297 L2 078 .1 898 1818 1616 1455 1408 1364 1322 6 23.8 1 315 N) 72 28.3 j --5o 1.310 37U4 4568 123 3932 36-1 3441 13238 13058 2897 2621 2393 2294 12039 1835 1776 1720 1668 78 33.2 1.625 i 1382 45.86 5679 l 5242 4,868 4543 4-53 j 4009 j 3786 3587 I 3245 1963 21139 2124 2271 21911 2129 2065 3 84 38.5 1.75 1 I.452 55.88 6920 6388 5932 5536 5190 4885 461 4370 3954 3610 3460 4.2 1 875 1.521 1 3075 27&8 2678 21595 2516 67.20 33i8 7678 1 7130 6654 6238 5871 1 5545 5253 4753 4340 4159 3697 3327 3220 3119 3024 5 i 50.3 2.00 1.117 79.77 9880 9120 I 8469 7904 7470 .6971 6587 6240 56-46 5155 4940 14391 3952 3824 3705 3593 102 i 56,7 2.125 64 7 10721 9291 8710 6198 93 39 12614 9955 7743 7335 6636 6059 5807 5162 4645 4495 4355 4223 108 i63.6 2.25 1.717 109 2 113526 12486 11594 10821 10145 9548 9017 8543 7729 7057 6763 6011 5410 5236 5072 4918 1-14 70.9 i 2.375 1.780 j 126.2 15624 14422 13392 12499 11718 11029 10416 9668 8928 8152 7812 6944 6249 6049 5859 56-81 120 78.5 2.50 1.642 144.7 1716537 915 155 14332 13436 126-45 11943 11314 10237 9347 8957 7962 7166 6934 6718 6514 15- i 126 F.6 6 2.625 1 1.902 j i 64.7 20404 i 15834 17419 16323 1 53C-3 j14403 13602 12887 11659 10645 10202 9068 8161 7898 7651 7419 0 2.?-0 1 9r 3-DS9 213-22 1 19799 18479 i 11324 i 63 05 j 15399 114589 13I99 12051 11549 10266 I 9239 8941 8662 83919 ; E iC3 9 L;t, 2 1 2:!-.j 2 C-7 01-7 2 4 GO 2 2 2 D 1 20805 19504 '18357 17337 16425 14860 13568 13003 11558 10402 10067 9752 9456 i44 113A 3.03 1 2.080 235.2 29132 26891 249)0 2 3 3 C--5 21849 2()563 IN21 646 15199 14566 22947 1652. 11276 10924 10-593 11111fk 1125 1 2� 12992 12573 12 160 II 11811 2.137 2'1,2.2 3248:1 29983 1-25965 21361 22928 21654 20515 18561 1 6947 16241 14436 5 5 13 2.7 12'0 1 2j!.l 361063 33289 30 2 22777 2 060 7 8615 18031 16028 14425 13960 13523 13114 ' 2.194 11 2E;8�0 2 ILM 7 25456 2404 1 I V 143.1 j 3.375 21250 322.0 39682 36514 33 4 1 h 4 j 31905 29911 28152 26588 25188 22789 20808 19941 7725 15952 15438 14995 14502 I GS i 153.9 I 3.50 2 354.7 43943 40 63 37665 35154 32957 131018 29295 27753 25110 22927 21971 19530 17577 17010 16478 15979 )74 1165.1 1625 2 38S.6 48254 44542 41360 38603 36190 34061 32169 30476 27573 25176 24127 21446 19301 18679 18095 175-46 _18;•j 176.7 3.750 2.414 426.6 52319 48756 45274 42255 39614 37284 35213 33359 30182 27558 26409 23475 21127 206446 19607 19207 Note:To obtain ticw,Q,Multiply values given in table by slope,SI/I. - w ELEMENTS OF CIRCULAR SECTIONS 09 oor a 0.8 / cr 07 P c _ _ QOQ-C O� 0.6 Q�0 3 0.5 oil u_ o 1 \-p 0.4 O\5G P 0.3, Q�pQO Y`yp�PJ OG\�� 07 Q �OPOP fL�\OAP . ' 0.2 P OQO P� 0.1 i 0.0 0.4 0.2 0.3 0.4 0.5 0.6 0.7 0.e 0.9 1.0 1.1 LY PROPORTIONAL AREA, DISCHARGE, VELOCITY, HYDRAULIC RADIUS Chart 6 30 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL o Table 4.3.2A list the required widths and building setback lines for drainage easements. Conveyance facilities must be placed in the center of the easement. TABLE 4.3.2A EASEMENT WIDTHS AND BUILDING SETBACK LINES For Pipes: BSBL Inside Diameter (ID) Easement Width (From Easement) ID < 18" 10 feet 5 feet ' 18" < ID < 36" 12 feet 5 feet 36" < ID < 60" 15 feet 7.5 feet 60" < ID ID plus 10 feet 10 feet ' For Channels: BSBL Top Width of Channel Easement Width (From Easement) ' W < 10 feet W plus 10 feet on one side 5 feet 10 feet < W < 30 feet W plus 15 feet on one side 7.5 feet 30 feet < W W plus 15 feet on both sides 10 feet 4.3.3 RATIONAL METHOD During the preparation of this manual, the need was acknowledged to continue to allow a simple method ' for analyzing and sizing conveyance elements for small drainage subbasins. Due to it's familiarity by the civil engineering profession, and long history of use in King County, t e ecision was made to continue to allow the use of the Rational Method with some specific limitations. ' Limitations o Only for use in predicting a conservative peak flow rate to be used in determining the required ' capacity for conveyance elements. o Drainage subbasin area (A) cannot exceed 25 acres for a single calculation. ' o The time of concentration (T,) must be computed using the method described below and cannot exceed 100 minutes. It is made equal tove minutes when computed to be less than five minutes. Equation G-';-I`Akt-ALk-TeS ' The following is the traditional Rational Method equation: QR = CIRA where: QR = peak flow, (cfs) for a storm of peak rainfall intensity "IR' of a given return frequency (R) ' C = estimated runoff coefficient (ratio of rainfall that become runoff) ' IR = peak rainfall intensity (inches/hour) for a given return frequency (R) A = drainage subbasin area (acres) 4.3.3-1 1/g0 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL "C" Values The allowable runoff coefficients to be used in this method are shown in Table.4.3.3A by type of land cover. These values were selected following a review of the values previously acceptable for use in the I Rational Method in King County and as described in several engineering handbooks. The values for single family residential areas were computed as composite values (as illustrated below) based on the estimated percentage of coverage by roads, roofs, yards and unimproved areas for each density. For drainage basins containing several land cover types, the following formula may be used to compute a composite runoff coefficient "Cc". Cc _ ((C, x A,) + (C2xA2)+... + (C„xA„))/A, ' where: A; = total area (acres) A,2„ areas of land cover types (acres) C,2,n = runoff coefficients for each area land cover type TABLE 4.3.3A RUNOFF COEFFICIENTS - "C" VALUES FOR THE RATIONAL METHOD* GENERAL LAND COVERS ' LAND COVER _ C LAND COVER C Dense forest 0.10 Playgrounds 0.30 ' Light forest 0.15 Gravel areas 0.80 Pasture 0.20 Pavement and roofs 0.90 Lawns 0.25 Open water (pond, 1.00 lakes, wetlands) SINGLE FAMILY RESIDENTIAL AREAS (Density is in dwelling units per gross acreage (DU/GA)) LAND COVER LAND COVER DENSITY C DENSITY C 0.20 DU/GA (1 unit per 5 ac.) 0.17 3.00 DU/GA 0.42 0.40 DU/GA (1 unit per 2.5 ac.) 0.20 3.50 DU/GA 0.45 0.80 DU/GA (1 unit per 1.25 ac.) 0.27 4.00 DU/GA 0.48 1.00 DU/GA 0.30 4.50 DU/GA 0.51 ' 1.50 DU/GA 0.33 5.00 DU/GA 0.54 2.00 DU/GA 0.36 5.50 DU/GA 0.57 2.50 DU/GA 0.39 6.00 DU/GA 0.60 For land covers not listed above, an area-weighted "C x At" sum should be computed based on the following equation: C x A, _ (C,xA,) + (C2xA2) + ...+(C„xA„), where A, _ (A, + A2 + ...+A„), the total drainage basin area. (For use only in determining peak design flow for analyzing and sizing pipes, culverts or channels) 4.3.3-2 C� r l': - 1/90 ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL "IR' Peak Rainfall Intensity The peak rainfall intensity (IR) for the specified return frequency (R) design storm is determined using a unit peak rainfall intensity factor (iR) for a given return frequency (R) design storm using the following equation: IR _ (PR)N) where: PR = is the total precipitation at the project site for the 24-hour duration design storm event for the given return frequency (from the Isopluvial Maps in Figures 3.5.1 C through 3.5.1 H) iR = (a,)(T.)"bR' ; the unit peak rainfall intensity factor Where Te = time of concentration (minutes), calculated using the method described below only ( ,, minimum value is 6.3 minutes) („ aR and bR are coefficients (from Table 4.3.3B) used to adjust the equation for the design storm return frequency (R) This "i," equation was developed by SWM Division staff from equations originally developed by Ron Mayo, ' P.E.. It is based on the original Renton/Seattle Intensity/Duration/Frequency (I.D.F.) curves. Rather than requiring a family of curves for various locations in King County this equation adjusts proportionally the Renton/Seattle I.D.F. curve data by using the 24-hour duration total precipitation isopluvial maps. This adjustment is based on the assumption that the localized geo-climatic conditions that control the total volume of precipitation at a specific location also control the peak intensities proportionally. Figure 4.3.3A has been included to demonstrate that this unit peak rainfall intensity (iR) will generate a ' curve with the same characteristics as the historic 25 year I.D.F. curve. Note, T, must not be less than 6.3 minutes or greater than 100 minutes. On the historic I.D.F. curves the lower limit was set at 5 minutes, 6.3 minutes was selected based on the mathematical limits of the equation coefficients. ' TABLE 4.3.3E COEFFICIENTS FOR THE RATIONAL METHOD "iR" -EQUATION DESIGN STORM RETURN FREQUENCY (YEARS) aR bR 2 Year 1.58 -_--- 0.58 5 Year 2.33 0.63 ' 10 Year 2.44 0.64 25 Year 2.66 0.65 50 Year 2.75 0.65 =� 100 Year 2.61� 0.63 4.3.3-3 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL FIGURE 4.3.3A RATIONAL METHOD UNIT PEAK RAINFALL INTENSITY(25 YEAR STORM) "its" 0 ai 0 rn co m us r� Lo LL-s r n LLs � �U LL3 p c-4 ' LLi 0 ' 6.3 Minutes MinimumIlk- LL, 0 r> r� O� DO f l^ lCS d- tl' N O O O O O t> O O r-D C> ' i25 (inches/hour) For basins with T longer than 100 minutes use the Hydrograph Analysis Method to obtain QR ' (See Section 3.5) ' 4.3.3-4 1/90 Q � � i ' KING COUNTY WASHINGTON SURFACE WATER DESIGN MANUAL T. Time of Concentration (Rational Method Only) The time of concentration is defined as the time it takes runoff to travel overland (from the onset of precipitation) from the most hydraulically distant location in the drainage basin to the point of discharge. Note that when the C,, of a drainage basin exceeds 0.60, it may be important to compute the T. and peak rate of flow from the impervious area separately. The computed peak rate of flow for the impervious ' surface alone may exceed that for the entire drainage basin using the total drainage basin T, The higher of the two peak flow rates shall then be used to size the conveyance element. The T', is computed by summation of the travel times(s) (T,) of overland flow across separate flow path segments defined by the six categories of land cover from the chart published in 1975 by the Soil Conservation Service shown in Table 4.3.3C. The equation for time of concentration is: Tc. = T, + T2 +...+ T where: ' T,2 n = consecutive flow path segments of different land cover category or having significant difference in flow path slope TABLE 4.3.3C kR VALUES FOR T, USING THE RATIONAL METHOD ' Land Cover Category kR Forest with heavy ground litter and meadow 2.5 Fallow or minimum tillage cultivation 4.7 Short grass pasture and lawns 7.0 Nearly bare ground 10.1 Grassed waterway 15.0 ' Paved area (sheet flow) and shallow gutter flow 20.0 Travel time for each segment is computed using the following equation: ' Tt = L/60V (minutes) (Note, the T, through an open water body (such as a pond) shall be assumed to be zero with this method.) where: ' L = the distance of flow across a given segment (feet) V = average velocity across the land cover (feet/second) ' Average velocity (V) is computed using the following equation (or read from Figure 4.3.36): V = kR fso ' where: kR = time of concentration velocity factor (feet/second) (see Table 4.3.3C) ' so = slope of flow path (feet/feet) 4.3.3-5 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL FIGURE 4.3.313 AVERAGE VELOCITIES FOR ESTIMATING TRAVEL TIME FOR OVERLAND FLOW* 'For use with the Rational Method only; From Soil Conservation Service,Tech.Release No.55,January 1975 O O O O 0000 N (0 u7 It M N O to 11r M N 00 0 0 0 O O O O O O QO O O O 00000 O O 0 0 O o0 N ( i N ... .... ...... ............................................ ....... ............. 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N SV �q •� �hJ a J`h!�' � :... ................................................... .:.. .. ........................:............:....... ...... :.:.....;.. ....:.. ....... �i�Vi ... .... ..............i............i ... ..:................ .............. ..I...:. ....:..... :........................:.............:...........................:.;.:.. �a� U? o s 0 d ...... ................................................................. .€. . .;... ....... ............i................... ...... p�4 o s ....... ... ch i M Asa c�'s I � N N O O O O O O O O cn co r-- (o to •Q• (o N +— to O 0 0 0 0 O O O O O 00 O O O O C:)0000 O O O O O 0 (11/11)adols asmoojalem 4.3.3-6 1/'90 ' VI . SPECIAL REPORTS AND STUDIES COLLINS & ASSOCIATES ' CONSULTING CIVIL ENGINEERS AND PLANNERS Phone (206) 885-0102 ' STRATFORD PLACE LEVEL DOWNSTR'TAM ANALYSIS Cam West Development Inc. !` Job Number 1170 L K yq !� OF wy�' 1 ° 1 A L.ENG i Prepared July 12, 1991 1 1 prepared by: Michael K. Haley P.E. 1 1 1 8195 — 166th Ave. NE — Suite 101, Redmond, WA 98052 P.O. Box 2332, Redmond, WA 98073 overview The proposed project is located on a 3.06 acre site approximately 300 feet West of Edmonds Avenue N.E. and just North of N.E. 16th ' Street in the City of Renton (refer to sketch #1). To the North, East and West of the site are single family dwellings. Currently the ' site is developed for residential use by three single family homes. The site will be subdivided into 14 single family lots served by the addition of a 32 foot wide street extending North from N.E. 16th Street approximately 430 feet. and terminating in a cul-de-sac (refer to sketch #2) . The existing dwellings will either by removed from the site or relocated within a new lot on site. Storm water runoff ' will be collected from all impervious surfaces and routed by a drain system to a pipe detention system at the Southeast corner of the site. Discharge from the detention system will flow into the existing storm drain located in N.E. 16th Street right of way The site generally slopes from the Northwest to the Southeast at ' approximately 9%. The undeveloped portions of the site are covered by second growth woods and forest. The underlying soil is composed of Indianola loamy fine sand (refer to sketch #3) . See Map 28 A txl_ . Sb. _ unTM�-''_i —C, D--,: E 3 5 ��> N 7ITN SI Ei �? l_ f TN Si33��'('•.,, '°+` I : 34 tg 35 36 A. 1j�Nl JIAO ! uIITNK G� I•.NArLI.' 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Y try,'- _ BEM '� �"•.; i` .rill Planc y •I:;' i EvCri.• a Ur !�; 1'¢ v f R£NTON 1.9 MI. 12'3O' (Joins sheet 1 1) RdC / , Off Site Drainage Condition The off site drainage area to the site is limited by the adjacent developments to be approximately 3.6 acres in size. The drainage area extends to the east approximately 300 feet to Edmonds Ave. NE ' and drains across the entire east property line ( refer to sketch #4 The description of this the off site drainage area is conservative in that it ignores the channelization effects of urbanization. For instance, the drainage divide formed by Edmonds Ave. NE may be further influenced by curb and gutter which actually direct flow to ' the South rather than onto the site. However, for the purpose of this analysis the off site flow conditions are conservatively ' simplified. �._J I � ►;—x-- � I I � -j+-I-. i�tifiE. 2(5T s' F - r� 2 I x zoo Soo I 7 ) 317 �� � r. 1,866,094.03N -� , ►I fin i i ►2' -- x 1 � z II ��� I `►! n y ii ( I ► �+ �K N '189 0 x ' ,,.,,_! t1 it t 11 I► I ► t1 285 I 14n I _ � ► I O 1 I T ES �W I k I of �t IN I f�� Q �I . • x I R ti IWI I I , �-iN•�. `y"�S� - I I I x BR I n I ► I 2154 k tl G {—'x-6—x— n It b X II x Ik 53 I I II 'A Lea X1 241 b t ` 234 .______.x_ _x a ;` 3 x x r �292_ N 18 S,510.48 x x � .._x R G ZJoo 2� on uj 7 Downstream �em— off and on site flows are directed to the Southwest across the si down a slop of e of 9% . Runoff is channeli2ed by the road section o.. Street below the site. Approximately 15 feet Southwest of NE 16th ed to the the site runoff is collected by a catch basin and convey a 12 inch concrete pipe. At the end of the 12 west 100 feet by g es into an 18 inch concrete pipe which inch pipe the runoff dischar o s the flow to the south through a series f 18 inch pipe conve Y segments with slopes greater than 2.0% (reference Renton as built segmer roximately data) . The 18 inch pipe system continues south for app 1600 feet at which point it joins the pipe system set in the right of ' way of State route 900. The pipe system in state route 900 is also 18 inc h concrete and conveys flow to the west ultimately discharging ' into Lake Washington. (refer to sketch No.5) . 1 7 W 7J3- ' 7 C3! 71" 7 7Jh7 Ih[ ire F �W,t !h 7Jh 2 1F 7S4< 71J,�) �t 7 7 -t 7M-t 7n-3 1C L1 1cTN IT < Z 7X1 1 7X7-U 7 7X7-t In X7 w ,d. 7n-c 7X7-1 7` t-+ 7A*-t 7 x u 7,OFt Y 7N►-7 / 7_ T.L" HC 1tTN - ' t tux-x WX- icce-t � Ip0-Il tuu-t� WT-1 V-f� it„� ��Z�1E — // tom!t! \ Problem Analysis ' A field investigation of the down stream system, on July 10, 1991, revealed no evidence of an existing drainage problem. With respect to the proposed site, drainage problems will be minimized with the ' addition of the detention system by limiting the site peak discharge to predeveloped levels for the 2 and 10 year storms. This overall effect will retard impacts on the downstream system. No evidence of insufficient system capacity was observed during the field ` investigation. Further analysis of the downstream system will be conducted at final design and any specific problems identified will be ' addressed at that time. 1 r� � fR R Z A - AG R A '`�J J 11335 NE 122nd Way (Rittenhouse-Zeman&,Associates,Inc.) Suite 100 Engineering&Environmental Services Kirkland,WA 98034-6918 (206)820-4669 FAX(206)821-3914 27 February 1992 W-8143 Cam West Development, Inc. P.O. Box 308 Kirkland, WA 98083 iAttention: Mr. Eric Campbell Subject: Subsurface Water Infiltration Testing Proposed Stratford Place Development ' Renton, Washington ' Dear Eric: As requested, this letter report provides the results of our recent subsurface exploration and infiltration testing for the above referenced project. The scope of our work was limited to building lot number 14 of the proposed development,with the purpose of addressing the minimum geotechnical requirements set forth ' in the King County Surface Water Design Manual Section 4.5.3 for a vertical infiltration test report. The project site is located north of Northeast 1 Gth Street between Camas Avenue Northeast and Edmonds Avenue Northeast in Renton,Washington. The subject property,the proposed new road and residential lots, and the approximate locations of our test pits/infiltration tests are noted on the Site and Exploration Plan, ' Figure 1, enclosed with this report. ' The following engineering considerations and recommendations are based on our field exploration conducted for this project on 25 February 1992. The scope of our services consisted of the field exploration tprogram, visual interpretation of site surface and subsurface conditions, field infiltration testing as outlined above, and preparation of this report. This report has been prepared in accordance with generally accepted ' geotechnical engineering practices for the exclusive use of Cam West Development and their agents for specific application to this project. The scope of work for this evaluation was performed in accordance with ' our telephone conversation on 17 February 1992, at which time we were verbally authorized Eric Campbell to proceed: L� AGRA / ' Earth&Environmental Group Cam West Development W-8143 27 February 1992 Page 2 SITE AND PROJECT DESCRIPTION The project site is located north of Northwest 16th Street between Camas Avenue Northeast and Edmonds Avenue Northwest in Renton, Washington. The parcel measures approximately 240 feet in an east-west orientation and 600 feet from north to south. The parcel currently contains a gravel access road and three single family residences. Undeveloped portions of the property are vegetated by a mixed assemblage of evergreen trees, with moderately dense blackberry bushes in the more open areas. The proposed construction would consist of adding a new paved cul-de-sac entering the site from Northeast 16th Street to the south. Fourteen residential home lots would be developed along the new cul-de-sac with one lot likely dedicated to surface water management. Subsurface Exploration Our subsurface exploration program for this project consisted of advancing three backhoe test pits, TP-1 ' through TP-3, at the approximate locations shown on the Site and Exploration Plan, Figure 1, attached with this report. Test pit logs with interpretive descriptions of conditions encountered are presented at the end ' of this report. Test pits were excavated by a rubber-tired backhoe operated by a local excavating company under subcontract to our firm. In-situ strength and quality attributes of materials encountered in the test pits were estimated by our observer based on experience with similar soils and on the difficulty incurred during ' excavation. Disturbed, but representative samples of the soils encountered in the test pits were retrieved, classified in the field, and transported in sealed plastic containers to our laboratory for further evaluation. The depths shown on the test pit logs are approximate, and where the soil contacts were undulating or gradational, represent typical values. ' Subsurface conditions disclosed in our test pits generally consisted of about 6 inches of topsoil and humus ' overlying a loose to medium dense, orange-brown sand to a depth of 3.5 to 5 feet. Below this surficial sand, test pits TP-1 and TP-3 encountered medium stiff, wet, tan to gray mottled silts to depths of 5.5 and 8.8 feet respectively. In each of the three test pits, the lowest stratigraphic unit encountered was a medium dense, ' moist to wet sand with a trace of silt. This lower sand unit was never fully penetrated by our test pits, which were taken to total depths of 11 to 12 feet. No groundwater seepage was encountered in any of our test ' pits. Changes in groundwater conditions should however be anticipated in response to seasonal changes in precipitation, changes in on and offsite land usage, and other factors. Mottling of silty soils noted in the ' test pit logs is interpreted to indicate that a "perched" groundwater condition develops above these soils where they impede the vertical infiltration of near surface water. No such perched groundwater was ' observed at the time of exploration. Detailed interpretive logs of each test pit are appended to this report. �^ AGRA Earth&Environmental Group Cam West Development W-8143 27 February 1992 Page 3 Soil Classification The Soil Conservation Service Soil Survey maps for the project area, published in 1973, indicate that the site is underlain by Indianola loamy fine sand. In our experience, such broad-ranging classification systems are ' useful for preliminary analyses, however, site-specific exploration and testing, as reported in other sections of this report, are most useful for design purposes. Infiltration Testing Infiltration testing was performed in general accordance with Section 4.5.3 of the King County Surface Water Design Manual, at the approximate locations shown on the Site and Exploration Plan, Figure 1. The general procedure for the testing involves driving a 4-foot long,6-inch diameter pipe embeded a distance of 6 inches into the soil horizon to be tested. The pipe is filled and water is kept at a minimum depth of 1 foot inside the pipe for a saturation period of at least 4 hours. After the saturated period, the pipe is filled with water ' and the time recorded for each 1-inch of water drop for the first 6 inches is recorded. This process is repeated 3 times and the 1-inch drop times averaged to estimate the infiltration rate. Three infiltration tests were performed for this project; one in each of the three test pits. Each infiltration test was run at a depth of approximately 6 feet below the ground surface at the test location. In test pits TP-1 and TP-2, the lower sand was the soil unit exposed at the testing depth. In test pit TP-3, the silt unit was the soil exposed at the test elevation. Calculated infiltration rates were as follows: TP-1 1.5 ' inches/minute, TP-2 1.6 inches/minute, TP-3 had a very low infiltration rate, dropping only 2 inches during the 4 hour saturation period and testing interval of 1 hour. This variability in infiltration rates is not surprising considering the soil type at each of the test locations. It should be noted that a medium sand unit similar to that at test elevations in TP-1 and TP-2 occurs below the silt soil tested in TP-3. It is our opinion that an infiltration test performed at the location of test pit TP-3 at a depth of 9 feet or more in the lower sand unit, would likely give an infiltration rate similar to those measured in test pit TP-1 and TP-2. Site Preparation Prior to site grading, any site surface runoff and groundwater seepage should be collected and routed away to a proper drainage to facilitate earthwork and foundation construction. Once surface runoff and groundwater seepage are controlled, site structures and associated buried utilities below the proposed construction area should be removed, relocated, or abandoned in-place in accordance with applicable State and local regulations. If necessary, localized excavations made below final grade for the removal of utilities in the building area should be backfilled with structural fill as outlined in the following section of this report. �^ AG RA ' Earth&Environmental Group ' Cam West Development W-3143 27 February 1992 Page 4 All building, pavement and sidewalk areas, and areas to receive "structural fill" should be cleared of all ' vegetation, topsoil, uncontrolled fill, and debris. Based on our explorations, we estimate a stripping effort will typically encounter on the order of one foot of topsoil and roots, with up to approximately 2 feet of ' man-placed fill locally, though the depths of organic soils or fill may be deeper around tree root balls or existing site structures, respectively. ' We recommend that foundation, floor subgrade, pavement areas, and areas to receive structural fill be prerolled and compacted with a roller or other suitable heavy equipment to a firm and non-yielding condition in order to achieve a minimum compaction level of at least 90 percent of the modified Proctor maximum dry density as determined by the ASTMO 1557 test procedure. The upper 1 foot of subgrade soil in pavement areas should be compacted to at least 95 percent of its modified Proctor maximum dry density. Due to the silty nature of the bulk of the site soils, prerolling and compaction can only be done when the ' soils are at or very near the optimum moisture content. The optimum moisture content is that which allows the greatest soil density under a given compactive effort. Prerolling and compaction of wet, silty soils may ' reduce those soils to mud, and require extensive removal of the disturbed soils with attendant increased cost. The need for prerolling may best be assessed in the field. Any soft, wet, or significantly organic areas disclosed by prerolling, should be excavated as necessary to reveal firm, non-organic soils and backfilled with structural fill as described subsequently. The near-surface site soils are often silty and consequently are highly moisture-sensitive. Such silty soils are highly prone to disturbance when subjected to traffic in wet site conditions. To reduce site disturbance, ' the contractor should minimize traffic above prepared subgrade areas and direct surface and groundwater away from the work areas. In very wet conditions, the use of a working surface of quarry spalls or sand and gravel may be required to protect the subgrade, especially from vehicular traffic. Ideally, earthwork should be performed during the drier summer months to keep site disturbance to a minimum. Structural Fill All fill placed in the building, sidewalk and parking areas, as well as backfilled utility trenches should be placed in accordance with the recommendations presented herein for structural fill. Prior to structural fill placement, the surfaces to receive structural fill should be prepared as previously described in the Site Preparation section of this report. All structural fill should be free of organic material, debris, and other deleterious materials. The maximum individual particle size of soils used for structural fill applications should ' be less than 6 inches in diameter. �^ AG RA ' Earth&Environmental Group/� Cam West Development W-8143 27 February 1992 Page 5 Structural fill should be placed in lifts no greater than 8 inches in loose thickness and each lift should be ' uniformly compacted to at least 90 percent of the modified Proctor maximum dry density. In paved areas, we recommend the upper 1 foot of fill soils be compacted to at least 95 percent of the modified Proctor ' maximum dry density. We recommend that a representative of RZA be present during grading and fill placement so that a representative number of density tests may be conducted as the structural fill placement occurs. In this way, the adequacy of earthwork may be evaluated as it proceeds. The suitability of soils for structural fill use depends primarily on the particle size distribution and moisture content of the soil when it is placed. As the amount"fines" (that soil fraction passing the U.S. No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate ' compaction becomes more difficult or impossible to achieve. Generally, soils containing more than about 5 percent fines by weight, based on the soil fraction passing the U.S. No. 4 sieve, cannot be compacted to a firm, and non-yielding condition when the moisture content is more than a few percent above optimum. The optimum moisture content is that which yields the greatest soil density under a given compactive effort. The near-surface site soils could possibly be used for structural fill provided that they are suitably free of organic material and cleared of debris, and that their moisture content is carefully maintained within about two percent of optimum. Placement of the soils would more readily be accomplished during the drier summer months when the soils could be moisture conditioned by spreading and/or windrowing. In the event that inclement weather or wet site conditions prevents the use of on-site soil or non-select ' material for structural fill, we recommend that a"clean,"free-draining gravelly sand be used. Such material should generally contain less than 5 percent by weight passing the No. 200 Sieve, based on that soil fraction ' passing the U.S. No. 4 Sieve and not contain discrete particles greater than 6 inches in diameter. It should be noted that the placement of structural fill is in many cases weather-dependent. Delays due to inclement weather are common, even when using select granular fill. We recommend that site grading and subsurface ' utility work be scheduled for the drier months, if at all possible. In wet weather conditions, reuse of the silty site soils may not be practical for utility trench backfill, as control of the moisture content to allow ' compaction by aeration and drying is commonly not feasible. C=Y AG RA Earth&Environmental Group ' Cam West Development W-8143 27 February 1992 Page 6 r Embankment Fill Permanent fill embankments placed on slopes steeper than 5H:1V (horizontal:vertical) should be keyed and benched into firm stable soils underlying the site. The key slot should be at least 8 feet wide and 3 feet deep, however, it may need to be larger, depending upon embankment size and slope configuration. The hillside benches cut into the native soil should be at least 4 feet in width. The face of the embankment should be compacted to the same 90 percent relative density as the body of the fill. This may be accomplished by overbuilding the embankment and cutting back to the compacted core. Alternatively, the surface of the slope may be compacted as it is built, or upon completion of the embankment fill placement. In any case, no uncompacted fills should remain on site except in landscape berms or other non-structural applications. 1 Foundation Considerations We recommend that new residences for this project be provided with foundations designed in accordance with minimum sizing and bearing pressure guidelines as set forth in the Uniform Building Code Tables 29-a and 29-b. We recommend that all structures be supplied with a continuous footing drain, separate from the roof drainage system, consisting of a 4-inch diameter perforated pipe set at foundation grade and backfilled on all sides with 6 inches of pea gravel or washed round rock. This pipe should be graded to drain by gravity to a suitable tightline discharge. ' CLOSURE The conclusions and recommendations presented in this report are based on our knowledge of the ' proposed development and upon our exploration and engineering studies. The goal of our work was to address the minimum requirements set forth in the King County Surface Water Design Manual Section 4.5.3 r for geotechnical investigations for infiltration tanks. Our exploration work was limited to Lot number 14 of the proposed development, and we cannot comment conclusively on soil conditions outside of the explored lot. Since this project was in the planning phase at the time of this writing, we recommend that RZA AGRA ' be allowed to review completed development plans and specifications in order to verify that our recommendations were adequately interpreted and implemented. r r 1 '=Y AGRA ' Earth&Environmental Group jrrl �C� ' Cam West Development W-8143 27 February 1992 Page 7 We appreciate the opportunity to provide you with this information. If you have any questions regarding this report or require further information, please do not hesitate to call. Respectfully submitted, RZA AGRA, Inc. Bruce W. Guenzler 1 ' Senior Staff GeologistT✓f.1 ° x Kurt D. Merriman, ' Senior Geotechnical Engio PIIAi, Enclosures: Logs TP-1 through T -3 Site and Exploration Plan, Figure 1 ' cc: Mr. John Newell =Y A G R A ' Earth&Environmental Group 17�1 q, TEST PIT LOGS ' Depth feet Soil Classification W-8143 Test Pit TP-1 0.0 - 0.5 Dark brown topsoil and sod 0.5 - 3.5 Loose to medium dense, damp to moist, orange-brown, medium SAND, trace silt 3.5 - 5.5 Medium dense, wet, mottled, tan, fine sandy SILT 5.5 - 11.0 Medium dense, moist to damp, gray medium SAND, trace silt, trace gravel No Seepage or caving Test Pit TP-2 ' 0.0 - 0.5 Dark brown topsoil and roots 0.5 - 5.0 Loose to medium dense, moist, orange-brown, medium SAND, trace silt 5.0 - 11.0 Medium dense, moist, gray, medium SAND, trace silt No Seepage or caving Test Pit TP-3 0.0 - 0.5 Dark brown organic topsoil SUS ' 0.5 - 5.0 Medium dense, moist, orange-brown, medium SAND, trace silt Zc(6, 5.0 - 8.8 Medium stiff, wet, mottled tan to gray, fine sandy SILT 8.8 - 12.0 Medium dense, moist to wet, gray medium SAND, trace silt, trace gravel No Seepage or caving 1 5 I 4 I 3 I 2 1 I ACCESS DRIVE H w w cc TP-3 3 , s ui 12 13 14 Z 'TP-1 TPA■-2 ® G LEGEND TP-3 L9 INDICATES TEST PIT/INFILTRATION TEST NUMBER AND APPROXIMATE LOCATION DRAWING BASED ON PLAN BY TRI COUNTY, DATED JUN 1991. PROPOSED N RZA-AGRA W.O. STRAFFORD PLACE DEVELOPMENT ENGINEERING E ENVIRONMENTAL SERVICES DESIGN RENTON, WASHINGTON 0 40 80 11335 N.E. 122nd Way DRAWN sulto too SITE & EXPLORATION PLAN SCALE IN FEET Klrkland, Washington DATE 88034-6918 SCALE FIGURE 1 VII . BASIN AND COMMUNITY PLANNING AREAS 1 E4 H w a a w x E-+ O H H H rr r rr rr rr r rr r r� rr sr �r rr r r �r r �r r IX. EROSION/SEDIMENTATION CONTROL DESIGN _57tZATFO2U Pt ACE gzlo zo �E2oYON/5-FO/YIENTA7/0r (-ON 2UL DECI?U,SE OF SIZE- OF THE SITE) �50IL,5 C»`I ,`>/TE Cr 1 l fi` , 3to E C4r ' TEE 51 TE 4 Lo(fA-T D/J OF THE' F1OR .TP_A7i l-1 It-ACICit E1YT�51V W, _ OF CH�e t,)V , j I NT E&EP;rOc' 5WALE.5, CAl7 .14 �,511.d PVV T,EGTiON � A C01,45 IZUC7101-1 47-1,1 TIZANL.E WILL 561FF1C,5 l0 ' CO147/ZOL AND 5fi�-DIMEN-tf 7'10�_/) 0OWF-Vf-rZ1 PE-P- CODE- PFOUIOE:"C-NTS FOu1­ID (A//7H/,, l Co2E ,Ef-'T 3 AT PAGE 1,2,3 `4 INFIM'ZA 101-1 FA-CIURZ/ -5 /?A-t/ ll1o7 SE OPE/74-TE UNTIL. &::L PIZOPOSED R17O /1_=G7 114P170v& 1r_NTL ICI ILN P2OD"6S 5U2FA-CE ; WOFA:7 A2F_ Coi-IPL.I"TED. THj�-2E Fo[ZE EACH 15UILO 6 0T MUS-r NAVE IT.5 OVII-t 710t./ CdNTIZOL ,sySTEM b THEZEMZE L� stGl-I A 5,FD1",5N-T TRAP 7D Acc091007C 7NE LAIwEsT Lo75, TH5SE T/ZAPs VVILL OEE pAr-! TI1� ' ►-t+ vE t N75 D 51��/ ; k4O wr_-y,�2 EAc.N L off' II I L Nuv Coats t' Q(T 7HG FA-CILIT) C(\17'/ . Tf-1 E 7-IM'IE outi-011,40, ' L Ac6 5-" Z-o 7 (PeE-L, Pt,47) OA71) g300 .5, P, CO)CIPLIT ST012A6F__ VoL "E ' A(5FZ9 L5 - CV-PP_ Zz = Z�2 o ' . L = q0 5= I Z°/6 ! AV6 - - LOTS f 7"N261 7 L= do° 5= 6% 4V6 - - tO7,5 8 T/-/241 /Z a usE 90 ' NI AX,) :P8C IN r z°�� V t � LOT � A SLOPE Arc EA = qZ 40 5F (11\4A-X) D,Z/ q 'L S W L=to S7t/Z%d (Z2z)(Z,p)z,z�o, (3 ez)(o,2/) o°?�, Tot45 ' V(56()) = (01-16)1,05 = I5,Z C,F, VA lZ sip C+ s cT Ki ' A ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' - e. Grid Pavers -modular concrete units with interspersed void areas which can be used to armor the streambank while maintaining porosity and allowing the establishment of vegetation. 5.4.3.6 VEGETATIVE STREAMBANK STABILIZATION Purpose To protect streambanks from erosion through the use of vegetation. Conditions Where Practice Applies Creek, stream and river banks downstream from, or within, a construction site which may be adversely ' affected by excess runoff resulting from construction activities. Design Criteria/Specifications ' o Design must be prepared based on criteria and input/review from a qualified fisheries biologist. See Chapter 4, Section 4.3.7, Open Channels, Bioengineered Channels and Bank Stabilization. 5.4.4 SEDIMENT RETENTION A sediment trap of sediment pond must be used as the-primary-structural control measure to treat silt- laden runoff from exposed areas, wherever feasible. Permanent peak rate runoff control facilities (except infiltration systems) may also be used for sediment retention. They must be thoroughly cleaned prior to construction approval. ' ram✓ In those cases where site constraints will not allow small areas to be served by a sediment trap or sediment pond, one or more of the other measures described in this section shall be employed. Sediment traps are used r drainage areas up to 3 acres and sediment ponus used for drainage areas 7 up o fi0 acres. hese limitations on rainag ae areas will require that several or more sediment retention ' measures will be required for any project with drainages areas of more than 10 acres. Figure 5.4.4A Illustrates the use of these ESC structural practices. 5.4.4.1 SEDIMENT TRAP ' Purpose ' To collect and store sediment from site cleared and/or graded during construction. It is intended for use on drainage areas with no unusual drainage features, and for projects with anticipated short build-out time (approximately 6 months or less). It is a temporary measure with a desi n life less than_1 year. It is to be maintained until the site area is permanently protected against erosion by vegetation an runoff ' from impervious surfaces is directed to permanent drainage facilities. Conditions Where Practice Applies Where the tributary drainage area,,,Ls 3 acrey or less. _ Design Criteria/Specifications ' The sediment trap may be formed completely by excavation or by construction of a compacted embankment. It shall have a 1.5 foot deeQ Su___m_r? for sediment storage. The outlet shall be a weir spillwa se with the lower 2 feet acting as a filter for sedimenLand the upper foot as the ' ove gw soil way_daptf _ A filter fabric fence must be.provided to filter the runoff from the trap prior to discharge from the sita o See Figure 5.4.4E for detail. ' 5.4.4.1-1 1/90 2� � KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL o The temporary sediment trap volume is the volume of sediment storage computed (not to _. exceed 1.5' in depth) Ijus the volume resulting from providing a 2' deep settlement zone above ' the sediment storage, while not exceeding trap side slopes of 3:1. o Computing the sediment storage volume -The sediment storage volume required is the volume required to contain the annual sediment yield to the trap and can be estimated by using the ' Universal Soil Loss Equation (USLE) developed by the United States Department of Agriculture. ASED = R*K*LS*CV*PR ' Where ABED = annual sediment yield in tons per acre R' = rainfall erosion index; use R`=2.22(P2)22; where P2 is the ' 2 year/24 hour precipitation in Inches (See 2 year - 24 hour Isopluvial Map in Figure 3.5.1 C) K = soil erodibility factor, from Table 5.4.4A or as determined ' by field and laboratory testing by a geologist, soil scientist, or geotechnical engineer. LS = length-slope factor; from Table 5.4.4E (note, lengths measured are horizontal distance from a plan view) CV = cover factor, use 1.0 which represents no ground cover during the construction process. ' PR = erosion control practice factor; use 1.3 which represents compacted and smooth slopes. ' Note, the USLE rainfall erosion index equation for the SCS Type 1 A storm region is R=10.2 (P2)2.2, where P2 is the total precipitation for the 2 year, 6 hour duration design storm. Since the total precipitation for the 2 year, 6 hour duration design storm is equal to exactly one-half of the ' total precipitation for the 2 year, 24 hour duration design storm, the equation can be rearranged as shown. o Annual sediment yield calculation, step-by-step procedure: ' a. Compute the R value by obtaining the P2 value from the 2-year/24-hour Isopluvial Map in Figure 3.5.1 C. ' b. Divide the site into areas of homogeneous SCS. soil type and of uniform slope and length. C. Note the K value from the SCS soils chart (Table 5.4.4A) for each soil type. d. Determine the LS value for each uniform area (See Table 5.4.413). e. Compute the annual sediment yield (Asad) in tons per acre for each homogeneous/uniform area by multiplying R times the K and LS values for each area. f. Multiply the annual sediment yield (Ased) for each area by the acreage to be exposed ' (only that area to be cleared) of each area. Sum the results to compute the total annual sediment load (in tons) to the trap (L.J. o The sediment storage volume (Vsed) is then determined by dividing the total annual sediment load in tons (Lsed) by an average density for the sediment deposited (/1,v9). Use/,jv9= 0.05 ton per cubic foot. Vsed = Lsed/loavg ' 5.4.4.1-2 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' o To complete the design of the temporary sediment trap: ' a. The "Pond Geometry Equations" section in the "Reference" portion at the back of the Manual may also be useful in designing the sediment trap. b. A 3:1 aspect ratio between the trap length and width of the trap is desirable. Length is ' defined as the average distance from the inlet to the outlet of the trap. This ratio is included in the computations for Figure 5AAC for the surface area at the interface between the settling zone and sediment storage volume. ' C. Determine the bottom and top surface area of the sediment storage volume to be provided (see Figure 5.4.4C) while not exceeding 1.5' in depth and 3:1 side slope from the bottom of the trap. Note the trap bottom should be level. ' d. Determine the total trap dimensions by adding an additional 2' of depth above the surface of the sediment storage volume, while not exceeding 3:1 side slopes, for the required settling volume. (see Figure 5.4.4C) ' TABLE 5.4.4A HYDROLOGIC SOIL GROUP OF THE SOILS IN KING COUNTY ' SOIL SOIL EROD- EROD- HYDROLOGIC IBILITY HYDROLOGIC IBILITY SOIL GROUP GROUP' FACTOR,-K- SOIL GROUP GROUP* FACTOR,'K' t Alderwood C 0.15 Orcas Peat D 0.00 Arents, Alderwood C 0.15 Oridia D 0.49 Arents, Everett B 0.17 Ovall C 0.17 Beausite C 0.15 Pilchuck C 0.10 Bellingham D 0.32 Puget D 0.28 Briscot D 0.32 Puyallup B 0.28 Buckley D 0.32 Ragnar B 0.32 Coastal Beaches Variable 0.05 Renton D 0.43 ' Earlmont Silt Loam D 0.37 Riverwash Variable Edgewick C 0.32 Salal C 0.37 Everett A 0.17 Sammamish D 0.37 Indianola 0.15 Seattle D 0.00 Kitsap C 0.32 Shacar D 0.00 ' Klaus C 0.17 SI Silt C 0.37 Mixed Alluvial Land Variable 0.10 Snohomish D 0.32 Neilton A 0.10 Sultan C 0.37 Newberg B 0.32 Tukwila D 0.00 Nooksack C 0.37 Urban Variable - ' Norm. Sandy Loam D 0.24 Woodinville D 0.37 HYDROLOGIC SOIL GROUP CLASSIFICATIONS A. (Low runoff potential). Soils having high Infiltration rates, even when thoroughly wetted, and consisting chiefly of deep,well-to-excessively drained sands or gravels. These soils have a high rate of water transmission. B. (Moderately low runoff potential). Soils having moderate infiltration rates when thoroughly wetted, and consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. C. (Moderately high runoff potential). Soils having slow Infiltration rates when thoroughly wetted, and consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately fine to fine textures. These soils have a slow rate of water transmission. ' D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a hardpan or clay layer at or near the surface,and shallow soils over nearly Impervious material. These soils M1 have a very slow rate of water transmission. ' From SCS,TR-55, Second Edition,June 1936, Exhibit A-1. Revisions made from SCS, Soils Interpretation Record, Form #5, September 1988. 5.4.4.1-3 1/90 - � x b r � z Slope IS values for following slope lengths 1,ft(m) IS values for following slope lengths 1,ft(m) _... A Slope gradient 10 20 30 40 50 60 70 80 90 100 150 200 250 300 350 400 450 500 600 700 800 900 1000 CAJ C7 ratio S. "; (3.0) (6.1) (9.1) (12.2) (15.2) (18.3) (21.3) (24.4) (27.4) (30.5) (46) (fit) (76) (91) (107) (122) (137) (152) (183) (213) (244) (274) (305) r 0.5 0.06 0.07 0.07 0.08 0.08 0.09 0.09 0.09 0.09 0.10 0.10 0.11 0.11 0.12 0.12 0.13 0.13 0.13 0.14 0.14 0.14 0.15 0.15 I(NI:1 1 0.08 0.09 0.10 0.10 0.11 0.11 0.12 0.12 0.12 0.12 0.1.1 0.1.1 0.15 0.1G 0.16 0.16 0.17 0.17 0.18 0.18 0.19 0.19 0.20 z L 0.10 0.12 0.1.1 0.15 0.16 0.17 0.18 0.19 0.19 6.2'0 0.23 0.25 0.26 0.28 0.29 0.30 0.32 0.33 0.34 0.36 0.37 0.39 0.40 :1 0.1.1 (1.18 0.20 0.22 0.23 0.25 0.26 0.27 0.28 0.29 0.32 0.35 0.38 0.40 0.42 0.41 0.45 0.4G 0.49 0.51 0.54 0.55 0.57 G' �. 4 0.16 0.21 0.25 0.28 0.30 0.33 0.35 0.37 0.38 0.40 0.47 0.53 0.58 0.62 0.6G 0.70 0.73 0.76. 0.82 0.87 0.92 0.96 1.00 CI] 311:1 5 0.17 0.24 0.29 0.34 0.38 0.41 0.45 OAS 0.51 0.53 0.66 0.76 0.85 0.93 1.00 1.07 1.13 1.20 1.31 1.42 1.51 1.G0 1.6 9 6 0.21 0.30 0.37 0.43 0.48 0.52 0.56 0.60 0.64 0.67 0.82 0.95 1.06 1.16, 1.26 1.34 1.43 1.60 1.65 1.78 1.90 2.02 2.13 7 0.26 0.37 0.45 0.52 0.58 0.61 0.69 0.74 0.78 0.82 1.01 1.17 1.30 1.43 1.54 1.65 1.75 1.8.1 2.02 2.18 2.33 2.47 2.61 U' 12'4:1 8 0.31 0.44 0.54 0.63 0.70 0.77 0.83 0.89 0.9.1 0.99 1.21 1.40 1.57 1.72 1.85 1.98 2.10 2.22 2.43 2.62 2.80 2.97 3.13 9 0.37 0.52 0.64 0.74 0.V 0.91 0.98 1.05 1.11 1.17 1.44 1.66 1.85 2.03 2.19 2.35 2.49 2.62 2.87 3.10 3.32 3.52 3.71 10:1 10 0.43 0.61 0.75 0.87 0.97 1.06 1.15 1.22 1.30 1.37 1.68 1.94 2.16 2.37 2.56 2.74 2.90 3.06 3.35 3.62 3.87 4.11 4.33 11 0.50 0.71 0.86 1.00 1.12 1.22 1.32 1.41 1.50 1.58 1.93 2,23 2.50 2.74 2.95 3.1s 3.35 3.53 3.87 4.18 4.47 4.74 4.99 8:1 12.5 0.61 0.86 1.05 1.22 1.36 1.49 1.61 1.72 1.82 1.92 2.35 2.72 3.04 3.33 3.59 3.84 4.08 4.30 4.71 5.08 5.43 5.76 6.08 � 15 0.81 1.14 1.40 1.62 1.81 1.98 2.14 2.29 2.43 2.56 3.13 3.62 4.05- 4.43 4.79 5.12 5.43 5.72 6.27 6.77 7.24 7.68 8.09 0 6:1 16.7 0.96 1.36 1.67 1.92 2.15 2.36 2.54 2.72 2.88 3.04 3.72 4.30 4.81 5.27 5.69 6.08 6.45 6.80 7.45 8.04 8.G0 9.12 9.62 z N 5:1 20 1.29 1.82 2.23 2.58 2.88 3.16 3.41 3.65 3.87 4.08 5.00 5.77 6.45 7.06 7.63 8.16 8.65 9.12 9.99 10.79 11.54 12.24 12.90 v) p 4'f.:1 22 1.51 2.13 2.61 3.02 3.37 3.69 3.99 4.27 4.53 4.77 5.84 6.75 7.54 8.26 8.92 9.54 10.12 10.67 11.68 12.62 13.49 14.31 15.08 C; 1� 4:1 25 1.86 2.63 3.23 3.73 4.16 4.56 4.93 5.27 5.59 5.89 7.21 8.33 9.31 10.20 11.02 11.78 12.49 13.17 14.43 15.58 16.66 17.67 18.63 30 2.51 3.56 4.36 5.03 5.62 6.16 6.65 7.11 7.54 7.95 9.74 11.25 12.57 13.77 14.88 15.91 16.87 17.78 19.48 21.04 22.49 23.86 25.15 TJ 3:1 33.3 2.98 4.22 5.17 5.96 6.67 7.30 7.89 8.43 8.95 9.43 11.55 13.34 14.91 16.33 17.64 18.86 20.00 21.09 23.10 24.95 26.67 28.29 29.82 � 35 3.23 4.57 5.60 6.46 7.23 7.92 8.55 9.14 9.70 10.22 12.52 1.1.46 16.16 17.70 19.12 20.44 21.68 22.86 2.5.04 27.04 28.91 30.67 32.32 (7 2%:1 40 4.00 5.66 6.93 8.00 8.95 9.80 10.59 11.32 12.00 12.65 15.50 17.89 20.01 21.91 23.67 25.30 26.84 28.29 30.99 33.48 35.79 37.96 40.01 (77 45 4.81 6.80 8.33 9.61 10.75 11.77 12.72 13.60 14.42 15.20 18.62 21.50 24.03 26.33 28.44 30.40 32.24 33.99 37.23 40.22 42.99 45.60 48.07 2:1 50 5.64 7.97 9.76 11.27 12.60 13.81 14.91 15.9.1 16.91 17.82 21.83 25.21 28.18 30.87 33.34 35.65 37.81 39.85 43.66 47.16 50.41 53.47 56.36 5.5 6.48 9.16 11.22 12.96 14.48 15.87 17.14 18.32 19.43 20.48 25.09 28.97 32.39 35.48 38.32 40.97 43.45 45.80 50.18 54.20 57.94 61.45 64.78 � lY:1 57 6.82 9.64 11.80 13.63 15.24 16.69 18.03 19.28 20.45 21.55 26.40 30.48 34.08 37.33 40.32 43.10 45.72 48.19 52.79 57.02 60.96 64.66 68.15 �-3 60 7.32 10.35 12.68 14.64 16.37 17.93 19.37 20.71 21.96 23.15 28.35 32.74 36.60 40.10 43.31 46.30 49.11 51.77 56.71 61.25 65.48 69.45 73.21 19:1 66.7 8.44 11.93 14.61 16.88 18.87 20.67 22.32 23.87 25.31 26.68 32.68 37.74 42.19 46.22 49.92 53.37 56.60 59.66 65.36 70.60 75.47 80.05 84.38 70 8.98 12.70 15.55 17.96 20.08 21.99 23.75 25.39 26.93 28.39 34.77 40.15 44.89 49.17 53.11 56.78 60.23 63.48 69.54 75.12 80.30 85.17 89.78 d 75 9.78 13.83 16.94 19.56 21.87 23.95 25.87 27.66 29.34 30.92 37.87 43.73 48.89 53.56 57.85 61.85 65.60 69.15 75.75 81.82 87.46 92.77 97.79 I X:I 80 10.55 14.93 18.28 21.11 2:1.60 25.85 27.93 29.85 31.66 33.38 40.88 47.20 52.77 57.81 62.44 66.75 70.80 74.63 81.76 88.31 94.41 100.13 105.55 85 11.30 15.98 19.58 22.61 25.27 27.69 29.90 31.97 33.91 35.74 43.78 50.55 56.51 61.91 66.87 71.48 75.82 79.92 87.55 94.57 101.09 107.23 113.03 `~ 90 12.02 17.00 20.82 24.04 26.88 29.4-1 31.80 34.00 36.06 38.01 46.55 53.76 60.10 65.84 71.11 76.02 80.63 84.99 93.11 100.57 107.51 114.03 120.20 C) 9.5 12.71 17.97 22.01 25.41 28.41 31.12 3:3.62 35.94 38.12 40.18 49.21 56.82 63.53 69.59 75.17 80.36 85.23 89.84 98.42 106.30 113.64 120.54 127.06 z 1:1 100 13.36 18.89 23.14 26.72 29.87 32.72 35.34 37.78 40.08 42.24 51.74 59.74 66.79 73.17 79.03 84.49 89.61 94.46 103.48 111.77 119.48 126.73 133.59 'Calculated from s 4.56 X s 65.41 X r / ` IS + +0.065�1 IT IS s topographic factor Z' at + 10.0m s + 10,000 `72.5t / 1-slope length,ft(m X 0.3049) s-slope steepness, r-. m-exponent dependent upon slope steepness (0.2 for slopes G 1^o,0.3 for slopes I to 3%, r 0.4 for slopes 3.5 to 4.5%,and 0.5 for slopes>5 ) KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL FIGURE SAAA ESC STRUCTURAL PRACTICES cc 3 o O YI I d � U c ro. C ' ' Sediment Trap O Drainage Area < 3 Ac. i Filter Fence �4fe 1 Sediment Pond l Baffle Drainage Area Sediment Trap b'or < 10 Ac. Drainage Area < 3 Ac. a or Swale Riser ' \ X x x �' Filter Fabric Fence, Rock Protection rainage Area <1 Ac. y Outf all Ur NGPE 5.4.4.1-5 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' FIGURE SAAC SEDIMENT TRAP SIZE AND DIMENSIONS Vsed - sediment storage volume (cu. ft.); Ab — bottom area (sq. ft.); Aset- area of sediment storage volume (sq. ft.) bw - bottom width (ft.); bl - bottom length (ft.); tw - top width (3.5 feet total depth); tl - top length (ft.) Vsed Ab Aset At bw bl tw tl Vsed Ab Aset At bw bl tw tl 230 0 459 1323 0 421 211 63 11114 6480 8379 11163 40 16261 183 370 45 540 1452 1 45 22 66 11568 6765 8700 11532 41 165 62 186 484 96 627 1587 2 48 23 69 12032 7056 9027 11907 42 168 63 189 602 153 720 1728 3 51 24 72 12505 7353 9360 12288 43 171 64 192 ' 728 216 819 1875 4 54 25 75 12986 7656 9699 12675 44 174 65 195 861 285 924 2028 5 57 26 78 13477 7965 10044 5 13068 4 177 66 198 1003 360 1035 2187 6 60 27 81 13976 8280 10395 13467 46 180 67 201 1153 441 1152 2352 7 63 28 84 14485 8601 10752 13872 47 183 68 204 ' 1312 528 1275 2523 8 66 29 87 15002 8928 11115 14283 48 186 69 207 1479 621 1404 2700 91 69 30 90 15529 9261 11484 14700 49 189 70 210 1656 720 1539 2883 10 72 31 93 16064 9600 11859 15123 50 192 71 213 1841 825 1680 3072 11 75 32 96 16609 9945 12240 15552 51 195 72 216 ' 2035 936 1827 3267 12 78 33 99 171631 10296 12627 15987 521 1981 73 219 2238 1053 1980 3468 13 81 34 102 17725 10653 130201 16428 53 2011 74 222 2451 1176 2139 3675 14 841 35 105 18297 11016 134191 16875 54 2041 751 225 2671 1305 2304 3888 15 87 36 108 18877 11385 138241 17328 55 2071 76 228 ' 2901 1440 2475 4107 16 90 37 111 19467 11760 14235 17787 56 2101 77 231 3140 1581 2652 4332 17 93 38 114 20065 12141 14652 18252 57 213 78 234 3388 1728 2835 4563 10 96 39 117 20673 12528 15075 18723 58 21679 237 3645 1881 3024 4800 19 99 40 1201 21289 12921 15504 19200 59 219 80 240 ' 3911 2040 32191 5043 20 102 41 123 219151 13320 15939 19683 60 222 81 243 4186 2205 3420 5292 21 105 42 126 225491 13725 16380 20172 61 225 82 246 4469 2376 3627 5547 22 108 43 129 23193 14136 168271 20667 62 228 83 249 4762 2553 3840 5808 23 111 44 132 23845 14553 17280 21168 63 231 84 252 5064 2736 4059 6075 24 1141 45 135 24507 14976 17739 21675 64 234 85 255 5374 2925 4284 6348 25 117 46 138 25178 15405 18204 22188 65 2371 86 258 5694 3120 4515 6627 26 120 47 141 25857 15840 18675 22707 66 240 871 261 6023 3321 47521 6912 27 123 48 144 26546 16281 19152 23232 67 243 88 264 6360 3528 4995 7203 28 126 49 1471 1 272431 16728 19635 23763 68 246 89 267 ' 6707 3741 5244 7500 29 129 50 150 27950 17181 201241 24300 69 249 90 270 70631 3960 5499 7603 30 132 51 153 28665 17640 20619 24843 70 252 91 273 7427 4185 5760 81121 31 1351 52 156 29390 18105 21120 25392 71 255 92 276 7801 4416 6027 8427 32 138 53 159 30123 18576 21627 25947 721 258 93 279 ' 8184 4653 6300 8748 33 1411 54 162 30866 19053 22140 26508 73 261 94 282 8575 4896 6579 9075 34 144 55 165 31617 19536 22659 27075 74 264 95 285 8976 5145 6864 9408 35 147 56 168 1 323781 20025 23184 27648 75 2671 96 288 9385 5400 7155 9747 36 150 57 171 33147 20520 237151 28227M100 291 9804 5661 7452 10092 37 153 58 174 33926 21021 24252 28812 294 10232 5928 7755 10443 38 156 59 177 34713 21528 24795 29403 297 10668 6201 8064 10800 39 159 60 180 35510 22041 25344 30000 300 ' 5.4.4.2 SEDIMENT POND Purpose ' To collect and store sediment from sites cleared and/or graded during construction prior to establishment of permanent vegetation and/or construction of permanent drainage facilities. It Is usually a temporary measure with a design life less than 1 year; however, it may be a more permanent facility,. especially if required to provide runoff quality control until the site area is permanently stabilized. Conditions Where Practice Applies ' Where the tributary drainage area is 10 acres or less. ' 5.4.4.2-1 1/90 � 1 � S717_A7.. W PACE 1 S.ED lMC--N T TOA,F Fo e G oT 1 1 1 i ' 1 1 1 ! ! X. BOND QUANTITIES WORKSHEETS ! To Ba ! ' XI . RETENTION/DETENTION FACILITY SUMMARY SHEET AND SKETCH T SUPPur7 1 PI RP 1, 1 r r XII . MAINTENANCE AND OPERATIONS MANUAL i 1 1 1 ' 1 1 1 i r 1 1 1 1 1 i 1 ' TYPICAL PROPERTIES AND CHARACTERISTICS ' SUPAC' Nonwoven geotextiles are manufactured in the USA with 100% manmade fibers which are mechanically interlocked by needlepunching and heat NONWOVEN GEOTEXTILES bonding.This proprietary process produces three dimensional fabrics which ' are highly permeable and extremely tough. Supac N is made from polypropylene, a petrochemical based polymer that is essentially chemically and biologically inert. Supac will not decompose in soil due to bacterial or fungal action. In normal use it is unaffected by acids, alkalis, oils and most chemical solvents. If increased resistance to sunlight is required, UV stabilized Supac is available. PROPERTY TEST PROCEDURE 4NP SNP 8NP 10NP 12NP 16NP 5NP(UV) 8NP UV 12NP Weight,oz./sq.yd. ASTM D-1910 4.1 5.3 8.0 10.0 12.0 16.0 5.3 8.0 12.0 Thickness,mils ASTM D-1777 40 55 90 100 120 160 55 80 120 Tensile Strength,lbs. ASTM D-1682' 115 165 330 435 540 750 165 345 495 Elongation,% ASTM D-1682 65 65 65 80 80 90 65 65 65 Puncture Strength,lbs. ASTM D-751" 75 95 140 170 210 255 90 135 200 Mullen Burst Strength,psi ASTM D-3786 260 345 450 550 660 800 300 450 700 Coefficient of Permeability, cm/sec. Constant Head 0.10 0.10 0.22 0.30 0.40 0.30 0.50 0.25 0.50 ' Permittivity,sec. ' Coefficient of Permeability Thickness 0.98 0.72 0.96 1.18 1.31 0.74 3.58 1.23 1.64 Washed EOS Corps of Engineers CW-02215 70-100 70-100 60.100 60-70 80-100 80-120 50-70 70-100 70-100 ' Abrasion Resistance, lbs. ASTM D-1175"' Taber Test(1000 cycles, 1 kg.) 35 65 150 200 235 370 55 135 200 NOTE: Typical is the average value for the warp and fill directions for the typical fabric weight. '2" x 3"jaw faces were used for testing all fabrics except 4NP and 5NP. "Tension testing machine with ring clamp;steel ball replaced with a 5/16"diameter solid steel cylinder with hemispherical tip centered within the ring clamp. "'The values tested are for the soft or beard side of the fabric. A x Flow Rate Constant Head Method 85 gal/ftl/min. ' Falling Head Method 270 gal/1112/min. (20 cm to 10 cm) ' Transmissivity (lateral permeability) 3 2 psi confining pressure 4.0 x 10-1 cm/sec. Color of Supac 4NP and 5NP is natural (white) BMW �. I (100X) 5NP "r Needlepunched Nonwoven / Polypropylene Geotextile Flow Rate Constant Head Method 125 gal/ftl/min. Falling Head Method 360 gal/(t2/min. (20 cm to 10 cm) ' Transmissivity 2 psi confining pressure 1.3 x 10-1 cm/sec. i Color of Supac 8NP-16NP is natural (white) or gray. 8NP r 4 ION 1 al Nonwoven Gcaotexthes. IHILLIPS SUPAArc FD GE Phillips Fibers Corporation has the capability of manufacturing a wide range of nonwoven needlepunched polypropylene geotextiles. Currently produced are fabrics from four (4) to sixteen (16) ounces per square yard. 1 Typical Properties of SUPAC® N Nonwoven Ceotextiles ' 4NP 5NP 5NP SNP 10NP 12NP 16NP 5NP(UV) SNP(UV) 12NP(UV) PROPERTY TEST PROCEDURE (LOW Silt EOS) Fence Weight,oz./sq.yd. ASTM D-1910 4.1 5.3 5.3 8.0 10.0 12.0 16.0 5.3 8.0 12.0 Thickness,mils ASTM D-1777 40 55 60 90 100 120 160 55 80 120 ' Tensile Strength,lbs. ASTM D-t682' 115 165 210 330 435 540 765 165 345 495 Elongation,% ASTM D-1682 65 65 70 65 80 80 90 65 65 65 Puncture Strength,lbs. ASTM D-751 Modified 75 95 85 140 170 210 255 90 135 200 ' Mullen Burst Strength,psi ASTM D 751 260 345 275 450 550 660 800 300 450 700 Coefficient of Permeability, Constant Head 0.10 0.10 0.20 0.22 0.30 0.40 0.30 0.50 0.25 0.50 cm/sec. -1 Coefficient of Permeability Permittivity,sec. Thickness 0.98 0.72 1.31 0.96 1.18 1.31 0.74 3.58 1.23 1.64 ' Washed EOS Corps of Engineers CW02215 60.120 60-140 45-70 45-100 60-70 80.100 80-120 45-70 60-100 60-100 ASTM D-1175 Abrasion Resistance,lbs. Tabor Test(1000 cycles,1 kg.) 140 200 210 325 100 tD0 NOTE:Typical is the average value for the warp and fill directions for the typical fabric weight. '2"x 3"jaw faces were used for testing all fabrics except 4NP and 5NP. Consult your sales engineer/representative or distributor if a minimum value is required or if clarification is needed relative to a SUPAC physical property or test method. Suggested SUPAC`°N Uses FUNCTION 4NP SNP SNP 8NP 10NP 12NP 16NP 5NP(UV) 8NP(UV) 12NP(UV) (LOW EOS) Drainage r r r r Separation r r r ' Reinforcement r r r r Embankment Stabilization r r r r Sedimentation Control Railroad Trackbed Stabilization r r r r ' Protective Liner For Impermeable Membranes r r r r USES: *Trench Drains *Edge Drains *Roof Gardens *Reinforced Soil Walls*Protective Liner for Impermeable Membranes *Silt Fences *Stabilization of: Access Roads, Embankments, Railroad Track Beds, Log Sorting Yards, Dams and Drilling Sites Standard Roll Dimensions 4NP 5NP 5NP SNP 10NP 12NP 16NP 5NP(UV) 8NP(UV) 12NP(UV) (LOW Silt EOS) Fence ' Width,ft.+ 15 15 15 15 15 15 15 3 15 15 Length,ft. 300 300 300 150 150 150 100 300 150 150 Typical Gross Weight,lbs. J 150 1 185 1 185 150 175 210 185 37 150 1 205 ' Square Yards 500 1 500 1 500 1 250 250 250 167 100 1 250 1 250 +Roll widths less than 15'available upon request. I V s DURA-FLEX VLDPE SPECIFICATIONS 1 Typical Properties Typical Value* ' 20 mil 30 mil 40 mil 60 mil Property Test Method (0.5mm) (0.75mm) (1.0mm) (1.5mm) ' Thickness, mils, minimum ASTM D 1593 18 27 36 54 Density (g/cc), maximum ASTM D 1505 0.935 0.935 0.935 0.935 ' Melt Index (g/10 min., maximum) ASTM D 1238 0.6 0.6 0.6 0.6 Carbon Black content(%) ASTM D 1603 2 -3 2 -3 2 -3 2 -3 Carbon Black Dispersion ASTM D 3015 A-1,A-2,B-1 A-1,A-2,B-1 A-1,A-2,B-1 A-1,A-2,B-1 Tensile Properties ASTM D 638 1. Ultimate Tensile Strength Type IV specimen 75 110 140 210 (pounds/inch width) at 20 inches/minute ' 2. Ultimate Elongation (%) 1000 1000 1000 1000 3. Modulus of Elasticity 15,000 15,000 15,000 15,000 (secant modulus; pounds/square inch) Tear Strength (lbs.) ASTM D 1004 Die C 9 14 17 28 Puncture Resistance (lbs.) **FTMS 101 C 2065 30 45 55 80 Low Temperature Brittleness ASTM D 746 <-94° F <-94° F <-94° F <-94° F Dimensional Stability ASTM D 1204 ± 3 ± 3 ± 3 ± 3 (% change max.) 212' F, 15 min. Resistance to Soil Burial ASTM D 3083 (% change'max. in orig. value) type IV specimen A. Ultimate Tensile Strength at 20 inches/minute 10 10 10 10 B. Ultimate Elongation 10 10 10 10 Environmental Stress Crack ASTM D 1693 >2000 >2000 >2000 >2000 (hours) Condition C (modified NSF 54) Field Seam Properties ' 1. Shear Strength ASTM D 3083 20 32 35 72 (pounds/inch), min. (modified NSF 54) (or 12"elong.) (or 12"elong.) (or 12"elong.) (or 12"elong.) 2. Peel Strength ASTM D 413 20 32 35 72 ' (pounds/inch), min. (modified NSF 54) FTBt FTB FTB FTB Roll Dimensions 1. Width (feet): 22.5 22.5 22.5 22.5 2. Length (feet): 1000 .800 600 400 �u 3. Area (square feet): 22,500 18,000 13,500 9000 4. Weight(pounds, approx.): 2250 2700 2700 2700 All values,except when specified as minimum or maximum,represent average lot property values. '`• '•Federal Test Method Standards. t Film Tear Bond(FTB)is defined as failure of one of the sheets by tearing,instead of separating from the other sheet at the weld interface area(sheet fails before weld). '7 19 • POLY-FLEX HDPE SPECIFICATIONS Typical Properties m Typical Value* - A , v.,...., ' 20 mil 30 mil 40 mil 60 mil 80 mil 100 mil Property Test Method (0.5mm) (0.75mm) (1.0mm) (1.5mm) (2.Omm) (2.5mm) ' Thickness, mils, minimum ASTM D 1593 18 27 36 54 72 90 Density (g/cc), minimum ASTM D 1505 0.94 0.94 0.94 0.94 0.94 0.94 Melt Index (g/10 min., maximum) ASTM D 1238 0.4 0.4 0.4 0.4 0.4 0.4 ' Carbon Black content(%) ASTM D 1603 2-3 2-3 2-3 2-3 2-3 2 -3 Carbon Black Dispersion ASTM D 3015 A-2 A-2 A-2 A-2 A-2 A-2 Tensile Properties ASTM D 638 ' 1. Tensile Strength at Yield Type IV specimen 50 75 100 150 200 250 (pounds/inch width) at 2 inches/minute 2. Tensile Strength at Break 85 125 165 250 330 400 (pounds/inch width) ' 3. Elongation at Yield (%) 13 13 13 13 13 13 4. Elongation at Break(%) 750 750 750 750 750 750 5. Modulus of Elasticity 90,000 90,000 90,000 90,000 90,000 90,000 ' (1%secant; pounds/square inch) Tear Strength(lbs.) ASTM D 1004 Die C 15 23 31 47 63 79 Puncture Resistance(lbs.) ••FTMS 101 C 2031 100 140 180 260 340 420 ••FTMS 101 C 2065 40 53 65 90 120 155 ' Hydrostatic Resistance ASTM D 751 165 245 330 495 660 800 (lbs./square inch) Low Temperature Brittleness ASTM D 746 <-94°F <-94°F <-94°F <-94'F <-94°F <-94°F Dim ensional'Stability ASTM D 1204 ± 1 ± 1 ± 1 ± 1 ± 1 ± 1 (%change max.) 212°F, 15 min. Volatile Loss (%) ASTM D 1203 0.4 0.4 0.4 0.4 0.4 0.4 Resistance to Soil Burial ASTM D 3083 (%change max. in orig. value) type IV specimen A. Tensile Strength at Yield & Break at 2 inches/minute 10 10 10 10 10 10 ' B. Elongation at Yield b1 Break 10 10 10 10 10 10 Ozone Resistance ASTM D 1149 no no no no no no 7 days, 100 pphm cracks cracks cracks cracks cracks cracks 104°F, bent loop ' Environmental Stress Crack ASTM D 1693 >2000 >2000 >2000 >2000 >2000 >2000 (hours) Condition C (modified NSF 54) Water Absorption (% change ASTM D 570 0.1 0.1 0.1 0.1 0.1 0.1 max in original weight) Coefficient of Linear Thermal ASTM D 696 1.2 1.2 1.2 1.2 1.2 1.2 Expansion (cm/cm °c)x 10' Moisture Vapor Transmission ASTM E 96 0.040 0.030 0.025 0:020 0.018 0.017 Rate(g/100 in' day) 100'F, 100% relative humidity ' Roll Dimensions 1. Width (feet): 22.5 22.5 22.5 22.5 22.5 22.5 2. Length (feet): 1000 800 600 400 300 250 3. Area (square feet): 22,500 18,000 13,500 9000 6750 5625 ' 4. Weight(pounds. approx) 2250 2700 2700 2700 2700 2800 All values,except when specified as minimum or maximum,represent average lot property values. '•Federal Test Method Standards. 1 21 I , W �Y Polyethylene Geomembranes 1 I T 114 Y h r? •1 �, M..i , ,d, ' M'�?4fY 1 II �IJI,S a4!1 lyk I pgo-i '1�) 1 I n I II I ,..t� I f�..::•<', ('IMM'•`I,1 7i,�i"•'T Y,t 'P Pr_ Poly-Flex Geo ova. bre nes•®• ' s - • Offer a cost-effective method for lining envi- ronmental control and water conservation facilities. ���.• �..,,n y� „ ---�� ��= � .�.�' ,�, _ • Prevent leachate and waste liquid components from leaking from impoundments and subse- t 4 = quently entering and contaminating ground water. Utilize specially compounded polymers that provide the best protection to the site. A Chevron Corporation Brine Storage Pond,Fannett,Texas 4X combination of good chemical resistance, high tensile strength, high environmental „10111 stress crack resistance, low permeability, and I. Ji , ( �, � � .A �•, f„= �, �tr���lf� ��� �r � M� ��,� ,fir high puncture resistance makes Poly-Flex product Geomembranes the most suitable for �g civil engineering applications. ! sr • Are manufactured using materials which resist IN the degrading effects of exposure to sunlight and leachates. '" au /ter+ V 1 - ,�.m ( .� qf... t a•r , ¢� M, + t Southwest Public Service Project,Muleshoe,Texas/Engineer:SPS ®�11901,2Z7- L w,•�"`a y: M. _ ,.;,�.+.r � S✓' ,f'k�MX .� a�.{1?� �dt �:ewr �Y a i1 .. •"`^`�7'�'' �#+-•",r.-�-,qua. �'�et�i��� "'''['" ����,. 1�-.. �. �� ' it`i !��Z, N4'� A. t / „^."� utl)w>+'A•"" ' � 49"fr J 'V1.; 4 �Y"fd RI �)#'�•;Fr��r 'Lx� ."r-.�„ tx..nt "'"'ir� ,,,J • �'- Witty. �;:;. 8.. �`d ' iaa.� csk N, u C ' North Umberland Gold Mine,Round Mountain,Nevada Hot Shoe Welder with Digital Temperature Control V M , fLEX« Polyethylene Geomembpanes m k �J� �xir /W u � '•���'�{ �Gn'p4 y`p,y� "+ The table below indicates that Poly-Flex HDPE geomembranes are resistant to most acids, alkalies and hydrocarbons. In addition, Poly-Flex does not contain plasticizers, which tend to leach out and cause membrane failure. y z 3 l S„1C,. t �Gr.;.$ du,� ,:- �11�mffl R " yyyyJ ,� s' 7L �� � "�' r tff �s � � P L POLY-FLEX CSPE PVC S ACIDS BASEST HEAVY METALS ALIPHATIC HYDROCARBONS O O AROMATIC HYDROCARBONS O O CRUDE PETROLEUM O O ; ALCOHOLS .` SALTS ULTRAVIOLET LIGHT O = good O = poor p : r s PROPERTY TEST METHOD TEST RESULTS (TYPICAL VALUES) �r 20 mil 30 mil 40 mil 60 mil 80 mil 100 mil .: Density ASTM D 1505 0.94 0.94 0.94 0.94 0.94 0.94 (9/cm') Tensile Strength at Yield ASTM D 638 50 75 100 150 200 250 (pounds/inch width) t , Y � Break at Strength e ens Til Sh Bk ASTM D 638 85 125 165 250 330 400 *r x. t ; (pounds/inch width) Elongation at Break ASTM D 638 750 750 750 750 750 750 (percent) Secant Modulus ASTM D 638 90,000 90,000 90,000 90,000 90,000 90,000 (pounds/inch') >r ' u Tear Resistance ASTM D 1004 15 23 31 47 63 79 1 } , (pounds force) '. Puncture Resistance FTMS 101 C 2031 100 140 180 260 340 420 (pounds force) M Environmental Stress Crack ASTM D 1693 >2000 >2000 >2000 >2000 >2000 >2000 (hours to failure) ilk k a W, .. " r 4.k.,.. ,. :... ,tt f3 7 �. w =�67`"-x—r _. �,r'S'rc,*f't ". � ',a`•"'V'wT'^''...T ^tsk`ii-'' ; �`... 'k.;ii&�c'�N ��4G�+�S��� �}•sr +.at�,"��a,?I° w "��F�MS;vF fi�y��S � �,�,t( t'��.�;,°4H�af� � �'���R��,'� Hadd Steve � ,.,K'N" :n r" ..3C�"� .i;;r: � 'r it ��"� Y 1 ry r , p•A r "°� Sales Representative w. Cr�J. PolyethyleneGeomembranesf or a Pollution yt„r 2000 West Marshall Drive Grand Prairie, Texas 75051 800-527.3322 214.647-4374 1a r r�t�fi Ext. 308 Fax 214.988.833 '�1 �` +, ,g a h"'P'�tvYk .r+.�.• � ,+ �•?r,� �q a.,>�"4 �+" ?r �,�,q" "�"� � •s 'k'y aRP ?h& q : 4.„. has .rk *!�' `�'•`�' ,,i. �9'a�r'.. ma( ° vy `W ds. r .�P ` '',�,'/r '�'�'•``• -v�y `s. fi r �+w>�s '�' �����F,�`§�"z,�,d++,. `� �?„+�taR »L.,.� +�.�@''�t" N+,� '� 4y�koy� �i�,i�la�a �;�"+�°� @'.�;' ah's �''..' 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