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HomeMy WebLinkAboutBLD2006-00389 Stormwater Management Plan R 0 0 DRAINAGE, EROSION, AND SEDIMENT CONTROL PLAN FOR PARCEL 0976500009 , a , tom N R1 a Yr " }' .. ., �';. �"�., . n -4 1 '. - to ,JM t .f M� 'r fx a� .f„ .� j it T 11 - a 1 Ii*'R ( 3 M Pi J is i., :: ..:.: j ��� 'SI'01 VA. C` Prepared for: 11 O' Seahome L 23747 Cyr Services, Inc. - 0 4'C15TEO -0' ' oNAL"fAG\'' i 2- '� APPROVED STORMWATER PLA N EXPIRES 8-25-07 I ......_.,1 IOC t4 ak NORTHWESTERN TERRITORIES, INC. 717 S. Peabody St. Port Anc eles, W 98362, 360-452-8491 ttPFERSO COUNTY SIGNATUR bf RFE Cn. . 'ITV 13 1".dry. • • DRAINAGE,EROSION, AND SEDIMENT CONTROL PLAN Prepared For Seahome Services, Inc. December 2005 For the Property Described as Tax# 976500009 Section 4, Township 28 North, Range 1 East, W.M. Jefferson County, Washington r^ .. • Prepared by NORTHWESTERN TERRITORIES,INC. 717 S. Peabody Street 3vonggjA Port Angeles,Washington 98362 'hone 360-452-8491 Fax 360-452-8498 m q pITA`Ni __TZ Web Site www.nti4u.com E-mail info@nti4u.com afh Tv. cs.►-►,yid roe.wenn 4cf rows w • SEAHOME SERVICES, INC. PROJECT c al CO N 1) 1-1 ✓( ° 1LUDLO -__.,.. .. -c-vc7, QUILCEN --f (-, . ,_ ,/ .- *'r r lE . r c-- , ..._. , irce,,i, 111 0 , ... i.: r f • BRINNON y,.;: `� - PORT - LUDLOW VICINITY MAP , • „ r- 6, .,. „ -,•: f. --, /0 77 NORTHWESTERN TERRITORIES, INC. x: Ve_ Engineers — Land Surveyors — Geologists � Construction Inspection — Materials Testing _ `� L -'•y Nil 717 SOUTH PEABODY,PORT ANGELES,WASHINGTON 98362,(360)452-8491 • DRAINAGE, EROSION, AND SEDIMENT CONTROL PLAN for PARCEL 976500009 6 _ -s '0-5 - 41. .ri .[ ,t, i • ' 1:4,...., J:'1-'--' ' • --::117t7L--.--;°,-..7:..,...3„i'i'..-..FH1::1—::r.—kri 4,, . •,, _ A. • 'le-- .- ' - i -'- ; j SEAHOME F` T. SERVICES 1 kt,... '' ` PROJECT Seahome Services,Inc. Project Neighborhood Map i 1 . i r•• .+'ry F. v i 111 0 • DRAINAGE, EROSION, AND SEDIMENT CONTROL PLAN for PARCEL 976500009 E Z "�q UAI AI)WN .� + `. n 1E9C09lI _- -- p• Jero z4 , . y J` S976600009 ct p.` k .9)9.0. . a...... .«. ... • - c ,•rg Seahome Services, •Inc. Project Area Map t 1 1 _ .. shy I' j 1: i iv 0 • . HOOD CANAL Ifs NIGH..- .__._-..____- + O <i 'i3 r --C,; -z S\ .. 31'E .3 i I ce it co o ,. cif- / 7 \ 1 z a a`' U E U o ,. VI E-I o, w n ! n i § Uix �. — �"_ © .-r pA O ,_ 4. / F- (D a CC OD i4 Q� x - a Vi w Wa 4 I 4) . I n n w ri Wth O 1 N 1i • I 1-1 w ,o 0 1:\5 ca tr. h p Il 63 Y o m Q 3 ‘ IW G \ o • 0 yra • o .rI. a ....\....\ \ " so2 o d . v i 46 E PI-AT >cl- 9 aOf N . H j,,- s V • • I \ {. 1 A I J -1 I E Q ./i 3 NI. Q i i O• Q i_ 11 - 11 11 , w 111 11 A wJ 1 1 , a 0 0 /,' '1 w Q Q co0 awcZ 1 E m Nz Q0 1 D O U) 1 p �� 1111 it mQ, 1 ill- 3 Q + CZ Q �Q 1 il11 0 Ili li I V O 111 i ill, ' ii CO al4 11 E v 11 D O 11 , ezQ v • • 11f ' QIy . 7D y1 m 3E t 04S I —/+J, iir 0 1' 1 i vi . • EROSION AND SEDIMENT CONTROL PLAN PREPARED FOR: SEAHOME SERVICES, INC. INSTALL ADDITIONAL SILT FENCING JUST ABOVE THE LINE OF ORDINARY HIGH WATER ONLY IF WORK WILL EXPOSE SOILS ON THE SLOPE ABOVE. MEAN HIGH WATER MARK a. ._ f TOP OF BANK / TTOP OF BANK •`.J SILT FENCING EXTEND SILT FENCING 15 FEET a-� BEYOND LIMITS OF EXPOSED j h0 SOIL TOP OF BANK I ROUTE ALL RUNOFF FROM ROOF J DRAINS, CURTAIN DRAINS, INTER— CEPTION DITCHES AND THE LIKE I TO THE TIGHTLINE PIPE TO BE ROUTED DOWN THE STAIRS PER THE DRAINAGE REPORT. CABIN ❑ ❑ i 1 ' I 50 25 0 50 SCALE IN FEET i Q l I .t l I `` I DEC ,.=1' � WAS.tip � 4 - NORTHWESTERN TERRITORIES, INC. - - !' 23747 , 4w Engineers - Land Surveyors - Geologists O EGISTER t ®.0 Construction Inspection - Materials Testing ONAL El4C5 717 SOUTH PEABODY,PORT ANGELES,WASHINGTON 98362,(360)452-8491 EXPIRES 8-25-07 STANDARD TEMPORARY EROSION AND SEDIMENT CONTROL PLAN NOTES • All erosion and sediment control Best Management Practices shall be selected,constructed,and maintained in accordance with the Washington Department of Ecology Stormwater Management Manual for Western Washington(current edition). • The construction and maintenance of erosion and sediment control measures shall be the responsibility of the contractor. The contractor shall not deviate from the approved plans without prior approval from the Jefferson County Public Works Department.The contractor shall have a set of approved plans on the site whenever construction is in progress. • The erosion and sediment control measures depicted on this plan are minimum requirements to meet anticipated site conditions. As conditions dictate during construction,the contractor shall implement additional measures as necessary to ensure erosion and sediment control. • Construction vehicle access shall be limited to one route,whenever possible. Quarry spalls or crushed rock shall be applied to the access in order to prevent sediment from being transported onto roads.If this should occur,roads shall be cleaned thoroughly by shoveling or sweeping. • Clearing shall be phased so that only areas that are being worked are exposed.All exposed and unworked soils shall be stabilized by appropriate Best Management Practices.From October 1 through April 30,unworked soils shall not be left exposed for more than 2 days.From May 1 through September 30,unworked soils shall not be left exposed for more than 7 days. • All erosion and sediment control measures shall be maintained in a satisfactory condition until such time as land disturbing activities are completed and the potential for onsite erosion has passed. • The contractor shall request inspection of temporary erosion and sediment control measures by the Jefferson County Public Works Department[(360)385-9160]as soon as practicable after installation. viii • • DRAINAGE, EROSION, AND SEDIMENT CONTROL PLAN for PARCEL 976500009 ABSTRACT This project consists of the construction of a beach access stair system and related work on a one acre parcel at 7701 Oak Bay Road, Port Ludlow,Washington. This plan also provides for the construction of a tightline pipe to convey stormwater runoff from the existing improvements as well as a future home. The pre-development runoff is not calculated since the system will discharge directly to marine waters. The post-development runoff is estimated based on a standard 24 hour storm having mean recurrence intervals of 25 years. Post-development runoff is used to design the tightline stormwater pipe. Construction phase erosion and sediment control measures are proposed to prevent soil from leaving the site during construction of the improvements. A detail drawings for erosion control measures is included at the beginning of this report. The following BMPs shall be implemented in addition to any that may later be necessary due to changing or unforeseen site conditions. 1. Silt fencing shall be installed below the limits of any work which will expose soil to the elements for more than 24 hours. The location of the silt fencing is shown on the Erosion and Sediment Control Plan map included at the beginning of this report. 2. Additional silt fencing shall be installed just above the line of ordinary high water if any work will expose soils on the slope above the beach for more than 24 hours. 3. Existing runoff from roof drains, interception ditches, and tightline pipes shall be routed to the tightline pipe to be constructed down the beach access stair system per this plan. The stair assembly shall include a six inch diameter tightline pipe to transport stormwater runoff from the uplands to discharge immediately above the line of ordinary high water. The pipe shall be rigidly secured to the stair assembly. The discharge point shall be at ground level into a basin of quarry spalls for energy dissipation. 4. Runoff from future structures shall be routed to the same tightline pipe down the beach access stair system. 5. Silt fencing shall be installed across the lower limits of any future home construction and shall extend 25 feet beyond the limits of any exposed soil. ix • i DRAINAGE, EROSION, AND SEDIMENT CONTROL PLAN for PARCEL 976500009 Ft CONTENTS I. PROJECT OVERVIEW 1 A. Project Description 2 B. Existing Site Conditions 2 1. Topography 2 2. Vegetation 4 3. Drainage 6 C. Adjacent Areas 8 II. DESIGN CRITERIA 8 A. Soils 8 B. Rainfall 10 C. Hydrologic Model 11 D. Time of Concentration 12 1. Predevelopment Condition 12 2. Predevelopment Time of Concentration 15 3. Post-development Condition 15 4. Post-development Time of Concentration 17 III. RUNOFF 17 A. Pre-development Runoff 17 B. Post-development Runoff 17 C. Mitigation 18 IV. EROSION AND SEDIMENT CONTROL PLAN 18 A. Site Specific Construction Phase BMPs 19 x • • B. Stabilization and Sediment Trapping (Erosion and Sediment Control Requirement Number 1) 20 1. Stabilization of Exposed Soils 20 2. Sediment Trapping 23 C. Delineate Clearing and Easement Limits (Erosion and Sediment-Control Requirement Number 2) 25 D. Protection of Adjacent Properties (Erosion and Sediment Control Requirement Number 3) 25 E. Timing and Stabilization of Sediment Trapping Measures (Erosion and Sediment Control Requirement Number 4) 26 1. Timing of Installation of BMPs 26 2. Stabilization of slopes of structural BMPs 26 F. Cut and Fill Slopes (Erosion and Sediment Control Requirement Number 5) 26 G. Controlling Off-Site Erosion (Erosion and Sediment Control Requirement Number 6) 26 H. Stabilization of Temporary Channels and Outlets (Erosion and Sediment Control Requirement Number 7) 27 I. Underground Utility Construction (Erosion and Sediment Control Requirement Number 9) 27 J. Construction Access Routes (Erosion and Sediment Control Requirement Number 10) 28 K. Removal of Temporary BMPs (Erosion and Sediment Control Requirement Number 11) 28 L. Dewatering Construction Sites (Erosion and Sediment Control Requirement Number 12) 29 M. Control of Pollutants Other than Sediment (Erosion and Sediment Control Requirement Number 13) 29 1. Control of Toxic Substances 29 2. Petroleum Spills 30 N. Maintenance (Erosion and Sediment Control Requirement Number 14) 30 O. Financial Responsibility 31 xi • DRAINAGE, EROSION, AND SEDIMENT CONTROL PLAN for PARCEL 976500009 r vt "irQY Y wr • >f.... - - Photo 1 I. PROJECT OVERVIEW This project consists of the construction of a beach access stair system and related work ton a one acre parcel at 7701 Oak Bay Road, Port Ludlow, Washington. This plan also provides for the construction of a tightline pipe to convey stormwater runoff from the existing improvements as well as a future home. Photo 1 shows the building site and the view beyond to Hood Canal on the eastern end of the parcel. The existing layout of the site is shown on the area and site maps included at the beginning of this report. A geotechnical report for the site was prepared by this office and provides additional information about the site. • • A. Project Description This project consists of the construction of a beach access stair system. The drainage, sediment and erosion control features of the plan are directed toward the stair system but they also provide for the eventual construction of a home on the parcel. B. Existing Site Conditions The following summary of site conditions represents existing conditions. 1. Topography The site is somewhat long and narrow with the axis oriented east and west as shown on the Area and Site Maps included at the beginning of this report. The geotechnical report prepared by this office discusses the topography in more detail. The ground generally slopes to the east, toward the beach, but there is some slope to a small ravine located off the parcel to the north. volt 1 'Al icf• -y , f t 44rr::.,.., P4 - y$, s� ,..'''.-.Fe f r F i 4 F .y i .Flf� • - i f i- c ,'J L9 r :�4 '4 Ni "- , �, „ .. • P` f"s - 2 ,. O aft; = ' Photo 2 Photo 2 is a view of the small ravine to the north, taken from the top of the slope at the parcel's northern boundary. 2 _.. ' • • Photo 3 is an air photo of the area. The parcel is indicated by the white arrow. The small ravine is located to the north(right on photo)of the parcel. 4/10 r , ',,,,-,..lie-',..,,,,.. - • r ,,,;,, 'mas.. t- .:" t fi r „ - :.' emu: _ i,y I\ rs. Photo 3 Photo 4 is a view of the cabin from near the top of the marine slope. Note the rise on the left(south) side of the parcel. 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Vegetation The site is heavily vegetated with natural vegetation. The upper part is forested with very heavy brush and ground cover. Photo 6 shows typical vegetation on the upper part of the parcel. • '. `.• '.''L'..s',7 '''., ''.'‘': ' '..':'' '.• l'. ' ,i .."''^ I:47*i'401.•=—.,, _..._,...P,... .., *„. s zt.,,-..i,, g-5. _ 0- '•-,-k--:";7:,1;*-:#., ?...',. c--....---:%-.. ..--•,:',:etti ^-•P.,.* ",--.4^`'":-->" to •E';';*2,.'-14' -1 s''V.1"4..,./c. „,.^4,•46. _.:=1*(4. , , -' „-..,„z ..- -:<r.,t,41 t 9.. -4-)...,,--..-_•--ik.49,...Q.- -,- - -^'''''.' .'-- ',' , ,..„-,.' 1-..er ,.34'-ve- , • =.--_. , __.,,-4., lk--. - • • ,-, . --1,. ‘'----,----.. - ,-f1 Px, - -4,.---- .:?-•,t, "3-"A '''' *--• = - --` .'-'W' ' -=4-,- • - ,. .. -.ay.... --4. - ...=. '' , ',.. e.t-i4 -..--.S .:...?1 P 72 .` --,.• - .; - — .4,,... 4 .r.,.. ,, --,,-_-- --.--t- -_. s... ,_,.. -,....., -- r, „. -., -...., , '-/- 3' -..'t..- -_-".44. 7.....::-.V.";'.. ''''',. .5.„.,`. 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I.--. 0..1-4-`, "--.1 •=, _ ,'4;-.V.-7,,,--,....._-"-•=-; '' - -..'‘4,, - t .--...7),°'=);:i*---, _.;;,--; '-'•".‘. ' ;C____,- ' - ,..._^--- • '' ..'",,. •• " ., - '-'N..'"..4. 1,-..• „7-2,-.....-• —.7...VINV 4 ',-••-•'4, NS. ._ Photo 6 4 • • ri y'• °.a I y d `" �m .x;,`,'�i$ r.'' gar.. s- x ..^ ?. X'ib„- '�` y�sr `Sa Photo 7 Photo 7 shows vegetation in the vicinity of the existing cabin. Note the dense ground cover. Also obvious in these photos is the preponderance of,_ ntspla that grow well with copious amounts of water. This indicates an excess of surface water runoff with little infiltration on the upper (western) portion of the parcel. Photo 8 shows vegetation on the lower (eastern) part of the parcel. , 4•�J + to • • Photo 8 5 ! i • • . +� '� �.__ i t_ y4 a.. !' ,' .c� P 4 gyp..:1 ,� .--',• x�. `,, .1, cam' t.� ,g, a., •x - ✓a .T .f. t-fir'- I P'Y �•, r f yy 7 Y 51. k # '�^'f �a , fit' 4..k4„,.4t.1 (!/ 'tea'. i �Si � `• Y i e��t`h. Z. S0 i ‘ v.' ' —If*" I ,,:n. 4%.*::P/It - ,--• '_,'.i.,‘,,t.-4,v1,._ ,, _"...,,,,,_,-,Ift / 4,,ttx Photo 9 Photo 9 shows ground cover vegetation on the slope above the beach. The brush is very dense here making views of the actual ground surface difficult to obtain. 3. Drainage The building site presently drains in sheet flow to the north and east. As noted above, the ground on the upper (western) part of the parcel is not particularly r. permeable and produces much runoff. may Y 4 ,1 �_qq e.. , Y , ! il f ''/ 1 I 4z1114141111 •s,41111) 1191 - , f,-,:._, a j x !lt�+►.w �. � .,ram �'` - 4.144:- •••-*lit -,-6 ''''.. . - -1144Prir—' . *Mr',,.-..7 1:11. 1:k. lottip -y- `. y zr,f• 4. , ticto, Z , .eita. Photo 10 Some effort has been made to collect this runoff with piping as shown in Photo 10. The network of small pipes extends around the cabin and attempts to control the runoff from the upper part of the parcel. 6 • • • 4 Try A f r 't .'w:, �-' f ". .vr ' at '•1-frn 144, 4`. o <[ y s�y $ N I* �` y.%);` * '' Mee Nur\ :'N.' ..,...• ray ~- 'P �ti .k•. .1 —?/:. 4e, ). 00,,,, a.- t y..'.x.:_k '��.�is:.ff�'� - uk- +�( "'�ai�cy.,k, r,et � h .t � 4.014, Photo 11 Photo 11 shows a part of this system further downstream, to the south of the cabin. Drainage across the lower portion of the uplands is primarily by sheet flow across the lawn shown in Photo 12 with some runoff going onto adjacent properties to the north (in the background of the photo) and the rest over the slope to the west (right background of the photo). \ Alli , • Photo 12 7 • • . C. Adjacent Areas The site is surrounded by rural residential lands on the north and south sides. Oak Bay Road, a County road, lies a short distance to the west from the parcel. Hood canal forms the eastern side of the parcel. The Area Map included at the beginning of this report shows a good overview of the neighborhood. s,of � •. 4 t -,z 4, ,,,-., .-1,,41,,,,,i4 ,- . . er___. _ ,, ,.. 41'r t.,3 y �` • to 't SS�� e� i � ,.. .`4' `,tom - ' 1 -"':� ,. .' .e M ✓ k ti u ,1„.44.." fir �t m�� w � � { ' -_,— ,-,- • '-'t.-r.1,1 --': .:rt,'t.„ s j r --, ,11. 7-...,e, „or- , - -,, -,,,,,,, - -,,,:-. . ., ; ›-,,,,67,-,,,,,-,-,, 7j - .-=--'-,. ' y _ter\. Photo 13 Photo 13 shows beach front homes on the north side of the parcel. II. DESIGN CRITERIA The following criteria are specific to this project site and will not apply to other properties, even those that may be nearby. A. Soils The site may be found on map number 52 of the Soil Survey of Jefferson County Area, published by the U. S. Soil Conservation Service, a portion of_which:.is reproduced'here as Figure 1. 1 '. 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'-. we 2.,.:r •- 9. t X .7,r �'?' .X = z,y as� +,. n e iC ', Isi � , ) m yx *vr - :Wit, , ,.., - F f { f .,f` 7 `v ri « s}. � �`1`t,"x 'firw ''�() v q.: P t 7� p� w x ask- �.. r ::: -, } r .`i- , + s sk S '0c'i ,"`.;�,i 7 -, ' s �'a -' w cry 4'� t r+.r.;,. 7Yzlr,.: , "Ito, aa• t - „: .. 4 'r".-.,Y.i '1`,, `:., ><.n �k r s,t. a,s.°ty , W 5C ,( 'r Lri., 'R' r f N"� ., 6 r h.5 Y.. Figure 1 Figure 1 can be compared with the Area Maps at the beginning of this report for orientation. Map number 52 predicts that the soils on this site are type CfD, Cassolary sandy loam on slopes ranging between 15 and 30 percent. The Soil Survey of Jefferson County Area describes Cassolary sandy loam as being well drained soils on uplands formed of reworked glacial and marine sediments. The well drained descriptor appears to apply well to the soils on the lower part of the parcel, below the cabin. The gravel content of the soils exposed on the marine slope does not agree well with the Cassolary soil description. The soils above the cabin are not as well drained and may be closer related to the Swantown gravelly loam, (SuB)soils, shown to the immediate north on the soils map. Cassolary soils belong to hydrologic group C while Swantown soils are group D soilsi This report assumes that the soils above the cabin are Swantown and those below ,' Cassolary soils. s y 9 411 • Photo 14 shows an exposed section of soils to the north of the cabin. Note the random gravel content and the very sandy fines. - -3 a i . ALL WEANER WR NYG PAPER - - SHIRT POCKET Ak Weatner Notebook No.135 Photo 14 B. Rainfall The total amount of precipitation falling over a 24 hour period during a storm having a mean recurrence interval of 2 years, will be 1.5 inches. This information was taken from a 2 year, 24 hour Isopluvial Map published by the U.S. Soil Conservation Service, a portion of which is reproduced here as Figure 2. The project location is marked on the map. TON II { I 9N I t i 281 S HOME SERVICE•,IN►.- • PR•JEC• InFr_:N 26N I I 1OW 9W 8W 7W 6W 5W 414' .3W 21,V PJ 1 Figure 2 L „' �`;�th 10 • The isopluvial lines represent total precipitation in 24 hours, in tenths of inches. 2 year rainfall data is used in the calculation of times of concentration for the site. The total amount of precipitation falling over a 24 hour period during a storm having a mean recurrence interval of 25 years, will be 2.8 inches. This information was taken from a 25 year, 24 hour Isopluvial Map published by the U.S. Soil Conservation Service, a portion of which is reproduced here as Figure 3. The project location is marked on the map. 31N =oN j l F,tv f SEA IOME SERMCE ,I ! PR ECT SITES L / i I I 2EN iW Figure 3 The rainfall distribution is assumed to be a Type IA distribution per standard practice in the area. C. Hydrologic Model Because hydrologic and hydraulic calculations are only performed for the purpose of sizing the tightline pipe system, there is no need for a continuous hydrologic simulation. Only the peak flow is needed. This plan uses a hydrograph based method of calculating runoff which is described in Urban Hydrology for Small Watersheds, Technical Release No. 55, and the Western Washington Supplement to Technical Release No. 55, both published by the U. S. Soil Conservation Service. This same type of method is given in the King County Surface Water Design Manual, published by the King County Public Works Department, and the 1992 Stormwater Management Manual for the Puget Sound Basin (The Technical Manual)published by the Washington State Department of Ecology 11 • • This method yields runoff volumes that are significantly different from those determined using the rational method. This plan uses the suggested runoff curve numbers given in Table 2-2a of Technical Release No. 55. D. Time of Concentration The length of time that it takes a drop of rainfall to travel from the uppermost point of a basin to the point of discharge from the basin, or to the point where flows are to be calculated, is referred to as the time of concentration (Tc). This is the sum of the time it takes for runoff to flow across the various types of flow channels as it crosses the basin. For this project the time of concentration is little affected by development since the new home site is located near the bottom of the drainage basin (entire parcel). The following calculations are per Section III-1.4.2, pages III-1-13 through III-1-16, of the Washington State Department of Ecology's STORMWATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN,THE TECHNICAL MANUAL, (DOE). 1. Predevelopment Condition The time of concentration is first determined for the existing condition of the basin. a. Unconcentrated Flow Immediately after falling to the ground, rainwater initially travels as unconcentrated sheet flow for a period of time (Tt)calculated by: 0.80 0.42 (NsL) Tt = = 51.79 min 0.527 0.4 (P2) (SO) Where: Ns = 0.800 = Sheet flow Manning's n (DOE Table III-1.4) P2 = 1.5 = 2 yr, 24 hr rainfall (in) SO = 0.0500 = Slope of flow path (ft/ft) L = 150 = Length(L) of flow path (ft) 12 • • This is flow across the upper (western) portion of the parcel through ground cover as shown in Photo 15 } . ;•: .:J ! ? : V--,q ae.. W''•i V g" f to ?3^ ar 6 33G, f t".... r,.r4 ,...;to, '' 'It..., "----- r •...,,, Ahritire ,,,t: Photo 15 b. Shallow Concentrated Flow As sheet flows run together and become concentrated, they travel as shallow concentrated flow for a period of time (Tt) calculated by: L Tt = = 2.36 min 60 Ks SQRT(S0) Where: Ks = 5 =Velocity factor(Ks)(per DOE Table III-1.4) SO = 0.0800 = Slope of flow path(ft/ft) L = 200 = Length (L) of flow path (ft) This is flow through the brush alongside the road shown in Photo 16. 13 • • • • _ • ti • g ivy :-..� ••e .a-•. Photo 16 c. Open Channel (Intermittent) Flow Flows next travel through intermittent open channels for a period of time (Tt) calculated by: L Tt= - - - - - - - = 0.38min 60 Kc SQRT(SO) Where: Kc = 17 =Velocity factor(Kc) (DOE Table III-1.4) SO = 0.1500 = Slope of flow path (ft/ft) L = 150 = Length(L)of flow path (ft) This is flow down the grassy slopes below the cabin as shown in Photo 17. 14 • III �t a a 4 -,, , ''fit 4,` ` y }� G _ fi 4 ..i; "; ..-: .-�'�.5„'�` y (b c A F4 , , 1 � r K f 4. . � � -" �`. �„ � -rt� �y...Yr — aVlx cam .`. ' - .. *igi ; 4^-,:•;74:Nr,":,.4:- -,'-t- '..--4':',_-.,:r..!:t.4':'f, ' sue' li `4-�f — Y.' 11'.r. £ '." i � - 4�setii �.� ��� -rS arc „ � �.� �.. �i [3 . + `' # - , --`am"•;> r�i. _ ._ ., *.-. "''�' 3• ��-�?.`mv-..'.'. Photo 17 2. Predevelopment Time of Concentration As noted above, the time of concentration (Tc) is the sum of the time it takes for runoff to flow across the various types of flow channels as it crosses the basin. For the predevelopment condition: Tc= the sum of the various Tt's = 54.52 min This is rounded to 55 min for use in further calculations. 3. Post-development Condition The time of concentration is next determined for the proposed, post-developed condition of the basin. There is little change in time of concentration from the pre- developed to the post-developed condition since most changes in land use will occur in areas where flows are already relatively rapid, allowing little opportunity for the increased flow velocities that will reduce the time of concentration. 15 i • a. Unconcentrated Flow Immediately after falling to the ground, rainwater initially travels as unconcentrated sheet flow for a period of time(Tt)calculated by: 0.80 0.42 (NsL) Tt= = 51.79 min 0.527 0.4 (P2) (SO) Where: Ns = 0.800 = Sheet flow Manning's n (per DOE Table III1.4) Ps = 1.5 = 2 yr, 24 hr rainfall (in) SO = 0.0500 = Slope of flow path (ft/ft) L = 150 = Length (L) of flow path (ft) This is unchanged from the pre-development condition. b. Shallow Concentrated Flow As sheet flows run together and become concentrated, they travel as shallow concentrated flow for a period of time (Tt) calculated by: L Tt= = 1.31 min 60 Ks SQRT(S0) Where: Ks = 9 =Velocity factor(Ks)(per DOE Table III-1.4) SO = 0.0800 = Slope of flow path (ft/ft) L = 200 = Length(L) of flow path (ft) This is reduced from the pre-developed condition. c. Open Channel (Intermittent)Flow As shallow concentrated flows from several sources run together, they cut open channels that flow as intermittent streams. Flows travel through these intermittent open channels for a period of time (Tt)calculated by: 16 • • L Tt _ = 0.65min 60 Kc SQRT(S0) Where: Kc= 10 =Velocity factor(Kc) (per DOE Table III-1.4) SO = 0.1500 = Slope of flow path (ft/ft) L = 150 = Length(L)of flow path (ft) This will be increased from the pre-developed condition due to the replacement of the existing grass with natural vegetatioin. 4. Post-development Time of Concentration As noted above, the time of concentration (Tc) is the sum of the time it takes for runoff to flow across the various types of flow channels as it crosses the basin. For the post-development condition: Tc = the sum of the various Tt's = 53.74 min This is rounded to 54 min for use in further calculations. III. RUNOFF While not necessary for the purposes of this report, pre-development runoff was calculated for the site. These values are reported but calculations are not included. Full calculations for post-development flow at the 25 year level are included in Appendix I. A. Pre-development Runoff A catalog of assumed pre-development conditions and calculations of the pre- development, weighted runoff curve numbers is included in Appendix I. These are the conditions that were assumed to prevail before development of the site. Under these conditions, the site has a weighted runoff curve number of 86.9. Complete calculations of the pre-development runoff are contained in Appendix I. The pre-development runoff is calculated to be 0.83 cfs for the 25-year storm. B. Post-development Runoff A catalog of assumed post-development conditions and calculations of the post- development, weighted runoff curve numbers is also included in Appendix I. These are the conditions that will prevail after development of the site. Under these conditions, the site will have a weighted runoff curve number of 86.6. 17 • • Complete calculations of the post-development runoff are contained in Appendix I. The post-development runoff is calculated to be 0.95 cfs for the 25-year storms, a slight increase from the predevelopment rate. C. Mitigation Construction phase erosion and sediment control measures are proposed to prevent soil from leaving the site during construction of the improvements. A detail drawing for erosion control measures is included at the beginning of this report. To mitigate increased levels of runoff from the future full development of this parcel, and to provide a higher level of protection against erosion of the marine slope, existing runoff from roof drains, interception ditches, and tightline pipes shall be routed to the tightline pipe to be constructed down the beach access stair system per this plan. Runoff from future structures shall also be routed to the same tightline pipe down the beach access stair system. Design (sizing) calculations, including flood routing calculations, are included in Appendix I. The stair assembly shall include a six inch diameter tightline pipe to transport stormwater runoff from the uplands to discharge immediately above the line of ordinary high water. The pipe shall be rigidly secured to the stair assembly. The discharge point shall be at ground level into a basin of quarry spalls for energy dissipation. To mitigate potential erosion and sediment impacts, the requirements of the erosion and sediment control plan shall be followed. Site specific mitigation measures are listed near the beginning of the erosion and sediment control plan. General guidelines and recommendations are in following sections. IV. EROSION AND SEDIMENT CONTROL PLAN This portion of the plan was prepared with the goal of preventing damage to adjoining or downstream properties due to erosion and sediment deposition and preventing the degradation of the quality of the receiving waters during the construction phase of this project. To ensure that the provisions of this Erosion and Sediment Control Plan are followed during construction, the complete text of this Erosion and Sediment Control Plan should be included in the construction plans for this project. Where formal construction plans will not be prepared for all or portions of the work, a copy of this document should be made available to the contractor and appropriate subcontractors. Subcontractors that will not be receiving copies should be made aware of the plan's existence and advised where copies can be obtained. Water quality controls, commonly referred to as Best Management Practices, or BMPs acre necessary to prevent three distinct types of impacts. The first:cons ts.of,damage dcine f as � m: 18 • • the result of soils being taken up by running water. This type of damage typically consists of rifling, rutting and loss of topsoil. The next type of damage is the degradation of water quality that occurs as the water transports the smaller soil particles. The last type of damage occurs when the running water reduces its velocity and drops the suspended soils. The Erosion and Sediment Control features (BMPs) of this plan are designed to address all three types of damage with the emphasis on preventing the initial soil uptake. Successful prevention of soil uptake will also prevent damage caused by degradation of water quality and by soil deposition. While the measures described below for preventing soil uptake should theoretically prevent any removal of soil, common sense advises that additional measures will be necessary and indeed, the DOE Manual requires additional measures. These additional measures will allow deposition of transported soils under controlled conditions before flows leave the project site or enter the receiving waters. The site specific types of BMPs and their locations are described immediately below in sub- section A. Specific details of the BMPs and the standards required by the DOE manual follow as sub-sections B - O. A. Site Specific Construction Phase BMPs The following BMPs shall be implemented in addition to any that may later be necessary due to changing or unforeseen site conditions. 1. Silt fencing shall be installed below the limits of any work which will expose soil to the elements for more than 24 hours. The location of the silt fencing is shown on the Erosion and Sediment Control Plan map included at the beginning of this report. 2. Additional silt fencing shall be installed just above the line of ordinary high water if any work will expose soils on the slope above the beach for more than 24 hours. 3. Existing runoff from roof drains, interception ditches, and tightline pipes shall be routed to the tightline pipe to be constructed down the beach access stair system per this plan. The stair assembly shall include a six inch diameter tightline pipe to transport stormwater runoff from the uplands to discharge immediately above the line of ordinary high water. The pipe shall be rigidly secured to the stair assembly. The discharge point shall be at ground level into a basin of quarry spalls for energy dissipation. 4. Runoff from future structures shall be routed to the same tightline pipe down the beach access stair system. 5. Silt fencing shall be installed across the lower limits of any future home construction and shall extend 25 feet beyond the limits of any exposed soil. 19 • • It is expected that minor adjustments, especially the installation of additional BMPs where an unexpected need arises, will be necessary during the construction phase of this project. For this reason, discussions of various BMPs that are not specifically required are included below. These BMPs should be considered as being held in ready reserve against the possibility that they will be needed. The following subsections discuss the various BMPs that may be incorporated in this plan. Reasons for their use, limitations and benefits associated with specific BMPs, and additional information are provided. B. Stabilization and Sediment Trapping (Erosion and Sediment Control Requirement Number 1) These requirements are to be considered general in nature and provide a framework for deciding when and where various BMPs should be utilized. They are intended to provide guidance in quickly selecting BMPs for use in unexpected situations. They apply to both soils that are not yet at final grade and to those that are at final grade, including soil stockpiles. 1. Stabilization of Exposed Soils The stabilization of exposed soils is the single most important element of this plan. If exposed soils are protected such that soil particles are not picked up by running water, erosion will not occur. Protection of exposed soil consists of four main areas of effort. a. Minimize Disturbance of Vegetation Existing vegetation on the site comprises the best overall protection against erosion. To protect this resource and to keep the risk of erosion at a minimum, clearing and grading activities outside of the areas necessary to construct the improvements shall be kept to an absolute minimum. Patches of existing vegetation that are within the clearing/grading limits and may be left intact without hindering the project, shall be left alone whenever possible. Care shall be taken that existing vegetation is left intact wherever possible around the perimeter of the project and particularly along the lower side of the project. Vegetation in drainage corridors and immediately below soil disturbing activities is the most valuable and as such is to be provided with the most protection. b. Minimize the Length of Time the Soil is Unprotected Where grading is necessary for construction activities, the grading should be delayed as long as reasonably possible to minimize the length of time that the soil is exposed to the elements. Where exposure of bare soil is necessary to accomplish certain portions of the • work, such portions of the work should be completed promptly in order to reduce the chance of an erosive rainfall event catching the soil unprotected. 20 • 1111 c. Ensure Prompt Revegetation of Disturbed Areas Every effort shall be made to ensure a healthy stand of protective vegetation is established as soon as possible. Reseeding of areas which are to be planted with grass shall be accomplished within 14 days if grading operations are completed within a planting season. If grading operations are completed outside of a planting season, reseeding shall occur within 7 days following the beginning of the next planting season. If substantial portions of the project are ready for reseeding at the beginning of or during a planting season, such portions may be promptly reseeded without waiting for completion of work on other portions of the project. Planting seasons are considered to be between March 1 and May 15 and between August 15 and October 1 where irrigation is impractical. Where irrigation is practical, the planting season is considered to be between March 1 and October 1. i j ? i 21 • • The following seed mix has been tested and found to be adequate for use for erosion control and for slope stabilization in Western Washington: Seed Type Percent by Weight Chewing Fescue 40 Colonial Bentgrass, Var. Astoria 10 Perennial Rye 40 White Clover 10 100 Other mixes, selected with regard for the soils, uses of the site, method of application, and expected weather may be used if desired. The recommendations of the seed supplier should be sought and strongly considered in selecting a mix. If the season or construction scheduling will not allow prompt revegetation of an area where construction activities have been completed, the area should be covered with plastic sheeting, straw, mulch or other covering chosen to match the situation and with due regard for the length of time that the area is expected to remain uncovered. d. Protective Coverings Protective coverings are highly recommended for application to exposed soils that are not being actively worked for an extended period of time. An extended period of time is considered to be 2 days between October 1 and April 30 or 7 days between May 1 and September 30. Protective coverings include plastic sheeting, straw, mulch, commercial sod and other coverings. The particular type of protective covering used should be chosen based on the steepness of the slope of the area to be covered, the size or the area to be covered, the time of year, the length of time the covering will remain, proximity to wetlands or other sensitive areas, the amount of existing vegetation between the exposed soil and the downhill project boundary, cost, and the visual impact of the covering. The best covering is existing vegetation, which should be disturbed as little as possible. Commercial sod is the next best covering but its use is often precluded by cost. Clear plastic sheeting is suitable for steep slopes but is difficult to apply PP Y and maintain in moderate to high winds. Black plastic sheeting is not appropriate during growing seasons except for short periods of time. Loose straw, either straight from bales or shredded, makes an adequate ground covering on gentle to moderately steep slopes (no steeper than 2 horizontal to 1 vertical) if it is wet to the point of limpness. Straw is generally effective where the distance from the top to the toe of the slope is no more than 100 feet. 22 • • Early application of gravel bases, pavements, and special landscaping items such as washed rock over plastic sheeting is considered to be a suitable protective covering where otherwise required. 2. Sediment Trapping Stormwater runoff from areas of exposed soil shall not be permitted to leave the project site without first having passed through an appropriate sediment trapping system or device. The type of sediment trap should be chosen based on the potential for erosion from exposed soils, the expected velocity and depth of flows, the proximity to downstream sensitive areas, and the length of time that the upstream soils will remain exposed to the elements. a. Sheet Flow Through Grassy or Heavily Vegetated Areas Runoff from exposed slopes that are less than 150 feet from top to bottom (measured along the slope) can be adequately treated by routing flows through bands of dense grass or other heavy vegetation. The vegetated band should be a minimum of one fifth as wide as the width of the exposed slope, but no narrower than 10 feet. For example, a band of exposed soil 75 feet wide should have a minimum of 15 feet of dense grass for sediment trapping. The vegetated band width above is for a slope no steeper than 10 percent. Where the slope of the vegetated area is between 10 and 20 percent, add 50 percent to the minimum width. Where the slope is greater than 20 percent, the minimum width should be doubled. For this type of sediment trapping system to be effective, flows must cross the vegetated area in sheet flows. If flows are expected to arrive at the vegetated band in concentrated flows, creation of a small artificial delta may be necessary to force a sheet flow. b. Grassy Swales Grassy swales are used to treat runoff from larger areas than sheet flows across bands of vegetation. Although grassy swales are usually thought of as permanent features, they can often be utilized during the construction phase. Unfortunately, there is usually insufficient time before the main construction effort to reshape landforms to provide the necessary slopes, widths, etc., and grow vegetation in the swale. Either an area must be found that is already vegetated and that meets the minimum requirements for a grassy swale or commercial sod must be placed along the sides and bottoms of the swale immediately after the swale is constructed. The following standard requirements for grassy swales were taken from the Draft Stormwater Guidelines published by the Washington;State Department of Fisheries in 1990 and are recommended for use here due to their simplicity. 23 • • More specific design criteria are more appropriate for use on large or complex sites. i. Soils Gravelly and coarse sandy soils should be avoided in order to maximize water contact with vegetation and the soil surface. ii. Design Criteria The grassy swale should be designed based on a two-year, 24-hour peak flow and the following: (A) Velocity Velocities should be less than 1.50 feet per second. (B) Depth of Flow The flow depth should be less than 4 inches. (C) Slope The longitudinal slope should average two to four percent. Rock or log check dams or terraces should be installed as necessary to achieve slopes of less than four percent. iii. Dimensions Grassy swales should be located to obtain maximum length. If less than 200 feet long, the width should be increased by an amount proportional to the reduction below 200 feet in order to obtain the same area of vegetation contact. iv. Side Slopes Side slopes should be no steeper than three horizontal to one vertical. c. Interceptor Swales Interceptor swales are shallow trenches constructed with a single pass of a large dozer equipped with one to three ripper teeth. The preferred configuration of ripper teeth for construction of interceptor swales is two teeth positioned on the outside of the ripper assembly. This type of swale construction will tear through existing sod without removing it. Leaving the sod in place will protect against erosion of the swale bottom on steeper slopes. Swales thus constructed are intended to intercept sheet flows and infiltrate them into the soil. When flows are greater than can be infiltrated, the swales will provide a path for runoff of excess flows. Such excess flows will run along the swale until they are either infiltrated or they enter interceptor ditches. Interceptor swales are especially effective adjacent to property lines.which-run more or less straight up and down a slope and where only sheet flows are to be • 24 intercepted. In order to be effective, the surface of the ground must not be regraded during the life of the swale. Grading or blading of the surface of these swales will defeat their purpose. Construction of interceptor swales causes only minimal disruption of the ground contours. For this reason the swales need not be removed or otherwise treated at the end of their usefulness. d. Other Sediment Trapping Devices and Systems Many other effective sediment trapping systems and devices are listed in Table II-2.1 of the 1992 DOE Manual. Complete details and descriptions of them are included elsewhere in the DOE Manual. They should be used where appropriate and as described in the Manual. C. Delineate Clearing and Easement Limits (Erosion and Sediment Control Requirement Number 2) Appropriate clearing limits, property lines, easement lines, and similar boundaries shall be determined prior to starting construction. Clearing, grubbing, grading and similar operations shall not begin until the appropriate limits are staked in the field. Once these stakes are set, care shall be taken that the stakes are not disturbed. D. Protection of Adjacent Properties (Erosion and Sediment Control Requirement Number 3) As required by the DOE Manual, no flows from exposed or disturbed soils are to leave the project site without first having been treated with some type of sediment trapping/filtering system or device. The proposed arrangement of these devices and systems is described above. The individual items are discussed in more detail in the section on Sediment Trapping above. The protective measures shown on the site plan are designed to prevent sediment deposition on adjacent properties. To the extent that the various items are constructed as designed and other work on the site progresses as envisioned, sediment should not be deposited on neighboring properties. Last minute changes in other items of work on this project, responses to previously unknown site conditions, or unexpected weather may require that revisions to the sediment trapping provisions of this plan be made rapidly. To this end, the previous section on Sediment Trapping contains design criteria, comments, information about BMPs, and similar information that is intended to be used in rapidly responding to changing needs and changing site conditions. As soon as a previously unexpected threat to adjacent properties becomes apparent, sufficient measures shall be taken to either eliminate the source of the threat or to provide an adequate level of defense against the threat. The measures taken shall provide a level of defense against sediment deposition on adjacent properties at least as secure as those provided by the remainder of this plan. 25 • 1111 E. Timing and Stabilization of Sediment Trapping Measures (Erosion and Sediment Control Requirement Number 4) It is essential that the various sediment trapping systems and devices be constructed prior to exposing the upslope soils to the elements. Both the timing of construction of the measures and the stabilization of the slopes of the structural BMPs are mandatory parts of this plan. 1. Timing of Installation of BMPs In keeping with the goal of providing positive sediment trapping or removal for all runoff from exposed soils before the runoff leaves the project site, no soil shall be exposed, or grading operations performed, until all of the required BMPs in the drainage path below the area to be exposed have been completed. Clearing, grubbing, and grading operations necessary for the construction of the BMPs are excepted from this requirement. 2. Stabilization of slopes of structural BMPs It is critical that the slopes of ditches, berms, ponds, and similar structural items be stabilized. These slopes will not only shed as much silt as any other exposed slope, but their erosion could cause the failure of the structural BMP. This could easily result in the failure of the BMP to perform its task of forcing sediment deposition to occur in a controlled location. This would leave open the potential for erosive transport of soil from a much larger area than that originally exposed on the slope of the BMP. F. Cut and Fill Slopes(Erosion and Sediment Control Requirement Number 5) Newly created slopes shall be covered or otherwise protected as provided for elsewhere in this plan. The faces of newly created fill slopes shall be well compacted. Since it is often impossible for typical compaction equipment to adequately compact the outer one to three feet of a fill, it will be necessary for compaction equipment to be operated up and down the face of the slope after the fill is completed. Operating tracked equipment in this manner will provide a certain amount of slope roughness which is desirable in slowing the velocity of running water and in retaining seed and fertilizer. After cut or fill slopes are covered, they should be monitored to ensure that the covering is functioning as intended and that rills are not forming under or through the covering. G. Controlling Off-Site Erosion (Erosion and Sediment Control Requirement Number 6) The BMPs specified by this plan are intended to prevent damage to downstream and/or adjoining properties. To the extent that construction of this project is performed as intended and all elements of this plan are implemented, there should be no off-site erosion. It is possible that extensive covering of slopes and similar practices could increase the volume of peak floods, especially if a storm event greater than a two year event were to occur before the site were completely revegetated,and the stormwater infiltration/detention systems completed. 26 • • The possibility of this occurring increases significantly if construction is delayed and exposed slopes must be covered through a winter rainy season instead of having been successfully revegetated. While this is not expected to occur, is possible that the vagaries of the construction trade will cause this to happen. If this does occur, downstream drainage channels shall be inspected before the end of the Fall planting season and an inventory made of areas where increased flows would reasonably be expected to cause erosion. Such areas shall then be protected in a manner consistent with the goals and guidelines included within this plan. Those BMPs noted above as being held in "ready reserve"on this project may be brought up to active status by their use in such off-site situations. H. Stabilization of Temporary Channels and Outlets(Erosion and Sediment Control Requirement Number 7) Channels, slopes, embankments, trenches, and similar areas of disturbed soil which are required for the implementation of this erosion control plan shall be subject to the same erosion control requirements as other portions of the project. In addition to the general protective requirements, specific armoring methods are included in the appropriate details. I. Underground Utility Construction (Erosion and Sediment Control Requirement Number 9) Underground utility construction shall proceed subject to the following criteria. A major source of potentially contaminated flows is from pumping or otherwise dewatering trenches. For this reason, flows discharged from pumping or other method of trench dewatering shall be closely monitored and, except where there is no visible turbidity, treated as described below in the Section titled "Dewatering Construction Sites." Where feasible, no more than 500 feet of trench shall be opened at one time. Where consistent with safety and space considerations, stockpiles of excavated soils shall be placed on the uphill side of the trench. Any such stockpiles shall be protected from erosion as provided for in this plan. Trenches shall be backfilled and revegetated as soon as reasonably possible following placement of utilities. Wherever trenches run more or less straight up and down a slope, either the backfill shall be mounded over the trench or waterbars or similar BMPs shall be utilized as necessary to prevent the backfilled trench from becoming a water course. Simply covering the exposed soil may not prevent the trench from conveying waters. Where the upstream end of a pipe is subject to inundation, it shall be temporarily capped or plugged at the end of each day's work to prevent soil from being washed into the pipe. 27 • • The underground utility locate service, 1-800-424-5555, shall be called a minimum of 48 hours (2 working days) prior to beginning any excavation and arrangements made to have all buried utilities marked. J. Construction Access Routes (Erosion and Sediment Control Requirement Number 10) It is expected that minor amounts of soil will be tracked onto paved roads, especially when unexpected circumstances such as rains and delays occur. To prevent this from becoming a nuisance or source of sedimentation, the roads shall be cleaned thoroughly at the end of each day if there is evidence of any significant accumulation of soil. Sediment shall be removed from roads by shoveling or sweeping and be transported to a controlled sediment disposal area. Washing of the street shall be allowed only after sediment is removed in this manner. Wherever construction, delivery, and similar vehicles enter paved roads from this project, the following provisions shall be followed to minimize the transport of soil onto the paved road. During periods of dry weather (where the soil is too dry to adhere to the tires of construction vehicles) construction vehicles may access paved streets directly from the project site with monitoring and occasional sweeping of the paved street as necessary to prevent accumulations of soil. During periods of wet weather (where soil readily adheres to the tires of vehicles) the vehicles may access graveled roads directly from the project site as necessary, but shall not access paved roads without first having been routed over areas where existing grass or other vegetation remains or routed down a minimum of 150 feet of graveled road. Access routes over grass or other vegetation shall be changed occasionally to ensure that wheel ruts are not allowed to develop and that the vegetation is not unduly worn down. K. Removal of Temporary BMPs (Erosion and Sediment Control Requirement Number 11) Temporary Erosion Control Facilities shall be promptly (within 60 days) removed, once their presence is no longer required. During their removal, any entrapped sediment shall be disposed of in suitable locations on the project site where they will not be subject to erosion. Disturbed areas left after the removal of sediments shall be promptly stabilized. As an alternate to the removal of entrapped sediments, they may be stabilized in place by the application of suitable BMPs such as sodding,mulching, seeding, etc. In no case shall sediments be left in a channel or where they would be washed into receiving waters by the next storm. The role of the Erosion Control Facilities is to prevent sediments from entering waters, not to merely delay it until after construction is completed. 28 • 411 L. Dewatering Construction Sites (Erosion and Sediment Control Requirement Number 12) Discharges from pumps used in dewatering trenches or other portions of a construction site shall be dispersed by one of the following methods: Directing flows onto existing heavily vegetated areas. If this is done, the flows shall be directed against objects such as old tires or stumps, capable of disrupting concentrated flows. Directing flows onto a pad constructed of clean, pit run gravel or washed drain rock or pea gravel. The pad shall be a minimum of 15 feet square and flows shall be directed into a circle of 6 - 8 inch diameter stones to assist in dispersing flows into sheet flows. Directing flows directly into a grassy swale or other sediment trapping BMP, constructed per this plan. In no case shall flows discharged from a pump be allowed to remain as a concentrated flow. Every effort shall be made to break the flows into sheet flows. In all cases, flows from dewatering shall be routed through a sediment trapping BMP before being released off of the site. M. Control of Pollutants Other than Sediment (Erosion and Sediment Control Requirement Number 13) All potential pollutants other than sediments that may occur on the site during the construction process shall be handled and disposed of in a manner that does not cause contamination of stormwater. 1. Control of Toxic Substances No toxic or noxious substances shall be used, stored or disposed of on or off the project site in conjunction with the project except in full compliance with all applicable federal, state and local laws and regulations and the recommendations of the supplier of the substance. The product label or instructions for use and the Material Safety Data Sheets (MSDS)for such products shall be kept on the site until the product has been used up or removed from the site and properly disposed of. While not commonly thought of as a hazardous material, common fertilizer can be very damaging if allowed to enter receiving waters. Fertilizers shall only be used in accordance with the recommendations of the supplier and any concentrations such as dribbles or leaks shall be cleaned up. In the event of a spill or other unusual event involving toxic or hazardous materials, work in the vicinity shall be immediately stopped and the following agencies notified: 29 • • Washington State Department of Ecology, (206) 459-6000 during normal business hours or(206) 753-2353 after hours. If the incident presents a threat to life, health, or property, the Fire and Police Departments shall be notified by dialing 911. 2. Petroleum Spills The following requirements are included to ensure compliance with Part 40 of CFR 112 in cases where SPCC Plans are required. They shall be followed on all projects. Storage of fuel for construction vehicles and fueling of construction vehicles shall be performed in accordance with the following requirements: a. Driver Training All employees assigned to operate fuel trucks will be properly trained in appropriate regulations and safety procedures. Training shall include proper inspection and use of tanks, hatches, valves, pumps, hoses and fuel delivery equipment. b. Fueling of Vehicles Fuel nozzles shall be locked when not attended and hoses shall be rewound or otherwise properly stored when not in use. Unattended fueling which relies on the proper operation of automatic shutoff nozzles shall not be permitted. c. Parking of Fuel Tankers Parking areas for fuel trucks shall be selected such that spills will not leave the area. Fuel trucks shall not be parked closer than 25 feet to a conveyance BMP such as a grassy swale or interceptor swale. When fuel trucks must be taken to other portions of the project to fuel equipment, they must be continuously attended or returned to the staging/storage area. Fuel trucks shall be locked with the wheels chocked when unattended and not in use. d. Containment of Spills Spills shall be immediately diked and every effort made to stop spillage. Each fuel truck shall carry a long handled shovel for use in containing spills. In the event of a spill, the U. S. Environmental Protection Agency, Seattle, Washington (206) 442-1263, shall be notified as soon as possible. If the magnitude of the spill is such that it presents an immediate threat to life, health, or property, it shall II be promptly reported by dialing 911. N. Maintenance (Erosion and Sediment Control Requirement Number 14) This section constitutes the Operation and Maintenance Manual for the erosion and sediment control BMPs used during the construction phase of this project. 30 • • Most of the various BMPs required to maintain water quality during the construction phase of this project are of a temporary nature. They are neither intended nor expected to remain in service for months at a time. The typical BMP often has a life expectancy of only 6 - 12 weeks unless time and effort are expended to bring it back to its original condition. Foul weather, rough use, overloading and similar conditions will reduce the life of these items. It is critical that all of the erosion and sediment control BMPs be maintained in their intended condition until they have served their purpose and are ready to be removed. The project foreman shall inspect the various parts of the system at least once daily during rainy weather. In addition, the foreman shall perform additional inspections during or immediately after significant rainfall. Any damaged or non-functioning components of the system shall be repaired before noon of the next day. In addition to verifying that the various BMPs are functioning as intended, the foreman shall check for formation of rills, deposits of silt and similar indications that the system is not functioning properly. If it is found that the system is not performing its role in preventing erosion and sedimentation, additional BMPs shall be provided as necessary. Specific maintenance instructions for the various erosion and sediment control BMPs are contained in the DOE Manual. O. Financial Responsibility Construction, operation, maintenance, replacement, and final removal of the erosion and sedimentation control BMPs is an integral part of the construction of this project. When referenced as such by the construction contract or similar documents, this plan forms a part of the construction plans for this project. In such cases the erosion and sedimentation control work is covered under applicable financial instruments such as the contractor's and developer's bonds to the same extent as all other items of work shown in the construction plans. 31 • Appendix I Drainage Calculations ! 11 • File: SEAH01.WB2 Date: December 10, 2005 PROJECT: Seahome Services, Inc. drainage BASIN DATA Predevelopment Undetained Detained Total Area: 1.0000 (Ac) + 0.0000 (Ac) = 1.0000 (Ac) Cn: 86.9 100.0 Tc: 55 (min) 55 (min) Postdevelopment Basin Data Undetained Detained Total Area: 0.9082 (Ac) + 0.0918 (Ac) = 1.0000 (Ac) Cn: 86.6 98.0 Tc: 54 (min) 54 (min) RAINFALL Peak 24 hr rainfall depth Basin Rainfall (Qr) 2 yr storm: 1.50 (in) 0.4901 (cfs) 25 yr storm: 1.80 (in) 0.5881 (cfs) 100 yr storm: 3.30 (in) 1.0781 (cfs) PREDEVELOPMENT RUNOFF Peak Pre-Devt Runoff (Qpre) 2 yr storm: 0.0519 (cfs) 25 yr storm: 0.0827 (cfs) 100 yr storm: 0.2712 (cfs) POSTDEVELOPMENT RUNOFF Peak Runoff From Peak Runoff From Undeveloped Port'n Developed Port'n (Undetained) (Detained) (Qposl) (Qpos2) 2 yr storm: 0.0455 (cfs) 0.0175 (cfs) 25 yr storm: 0.0732 (cfs) 0.0215 (cfs) 100 yr storm: 0.2441 (cfs) 0.0415 (cfs) Peak Runoff From Entire Basin (Qpos) 2 yr storm: 0.0629 (cfs) 25 yr storm: 0.0947 (cfs) 100 yr storm: 0.2855 (cfs) • PROJECT: Seahome Services, Inc. drainage RUNOFF CURVE NUMBER CALCULATIONS Total Parcel Size (acres) : PRE-DEVELOPMENT Pervious lundetained► I Impervious (detained) Runoff I Runoff Area Curve No. I Area Curve No. Land Use (acres) (Cn) (A x en) I Land Use (acres) (Cn) (A x en) Young Second Growth Timber and brush 0.65040 86.00 55.93 I Young Second Growth Timber and brush 0.00000 86.00 Gravel driveway 0.12000 91.00 10.92 I Gravel driveway 0.00000 91.00 Roofs 0.02300 98.00 2.25 I Roofs 0.00000 98.00 Lawn/landscaping 0.20660 86.00 17.77 I Lawn/landscaping 0.00000 86.00 Revegetated areas, natural 0.00000 85.00 I Revegetated areas, natural 0.00000 85.00 Subtotal Pervious Area = 1.00000 Remainder Area = 0.00000 98.00 Total Impervious Area = 0.00000 100.00 Total Pervious Area = 1.00000 86.88 I -• 0.00 Total Impervious Area = 0.00000 1.000 100.00 Total Area = 1.00000 86.88 I Weighted Average Runoff Curve Number of Pervious Portion (rounded) 86.9 I Weighted Average Runoff Curve Number of Impervious Portion (rounded) 100.0 Predevelopment Weighted Average Runoff Curve Number of Entire Parcel (rounded) 86.9 POST-DEVELOPMENT Pervious (undetained) ) Impervious (detained) Runoff I Runoff Area Curve No. I Area Curve No. Land Use (acres) (Cn) (A x Cn) I Land Use (acres) (Cn) IA x Cn) Young Second Growth Timber and brush 0.43820 86.00 37.69 I Young Second Growth Timber and brush 0.00000 86.00 Gravel driveway 0.14000 91.00 12.74 I Gravel driveway 0.00000 91.00 Roofs 0.00000 98.00 I Roofs 0.09180 98.00 9.00 Lawn/landscaping 0.15000 86.00 12.90 I Lawn/landscaping 0.00000 86.00 Revegetated areas, natural 0.18000 85.00 15.30 I Revegetated areas, natural 0.00000 85.00 Subtotal Pervious•Area = 0.90820 - Remainder Area = -0.00000 98.00 -0.00 I Total Impervious Area = 0.09180 9.00 Total Pervious Area = 0.90820 78.63 ( 0.09 Total Impervious Area = 0.09180 0.908 I 98.00 Total Area = 1.00000 86.57 I Weighted Ave. Runoff Curve Number of Pervious Portion (rounded) = 86.6 I Weighted Ave. Runoff Curve Number_of-Impervious`Portion (rounded) = 98.0 Postdevelopment Weighted Average Runoff Curve Number of Entire Parcel (rounded) 87.6 I • III PROJECT: Seahome Services, Inc. drainage 25 yr storm (B) Total Basin Area = 43560 sq ft = 1.0000 Ac Storm Duration = 24 hr Peak Rainfall Intensity = 0.588 cfs Total Rainfall Volume = 6534 cu ft Total, 24 hr rainfall = 1.80 in Rainfall Data Standard SCS Type lA 24 hr hyetograph (adj 'd) Total Cumulative from King Co Drn Manual Basin Precip Precip Rainfall Depth Depth Time % Cumulative Time P Pr Prc (min) Precip % Precip (hrs) (cfs) (in) (in) 0 0.00 0.00 0.00 0.0000 0.0000 0.0000 10 0.40 0.40 0.17 0.0436 0.0072 0.0072 20 0.40 0.80 0.33 0.0436 0.0072 0.0144 30 0.40 1.20 0.50 0.0436 0.0072 0.0216 40 0.40 1.60 0.67 0.0436 0.0072 0.0288 50 0.40 2.00 0.83 0.0436 0.0072 0.0360 60 0.40 2.40 1.00 0.0436 0.0072 0.0432 70 0.40 2.80 1.17 0.0436 0.0072 0.0504 80 0.40 3.20 1 .33 0.0436 0.0072 0.0576 90 0.40 3.60 1.50 0.0436 0.0072 0.0648 100 0.40 4 .00 1.67 0.0436 0.0072 0.0720 110 0.50 4 .50 1.83 0.0545 0.0090 0.0810 120 0.50 5.00 2.00 0.0545 0.0090 0.0900 130 0.50 5.50 2.17 0.0545 0.0090 0.0990 140 0.50 6.00 2.33 0.0545 0.0090 0.1080 150 0.50 6.50 2.50 0.0545 0.0090 0.1170 160 0.50 7.00 2.67 0.0545 0.0090 0.1260 170 0.60 7.60 2.83 0.0653 0.0108 0.1368 180 0.60 8.20 3.00 0.0653 0.0108 0.1476 190 0.60 8.80 3.17 0.0653 0.0108 0.1584 200 0.60 9.40 3.33 0.0653 0.0108 0.1692 210 0.60 10.00 3.50 0.0653 0.0108 0.1800 220 0.60 10.60 3.67 0.0653 0.0108 0.1908 230 0.70 11.30 3.83 0.0762 0.0126 0.2034 240 0.70 12.00 4.00 0.0762 0.0126 0.2160 250 0.70 12.70 4 .17 0.0762 0.0126 0.2286 260 0.70 13.40 4.33 0.0762 0.0126 0.2412 270 0.70 14 .10 4 .50 0.0762 0.0126 0.2538 280 0.70 14 .80 4.67 0.0762 0.0126 0.2664 290 0.82 15.62 4.83 0.0893 0.0148 0.2E2 300 0.82 16.44 5.00 0.0893 0.0148 0.2955, 310 0.82 17.26 5.17 0.0893 0.0148 0.3107' r... 320 0.82 18.08 5.33 0.0893 0.0148 0.3254` 330 0.82 18.90 5.50 0.0893 0.0148 0.3402 340 0.82 19.72 5.67 0.0893 0.0148 0.3550 350 0.95 20.67 5.83 0.1035 0.0171 0.3721 360 0.95 21.62 6.00 0.1035 0.0171 0.3892 370 0.95 22.57 6.17 0.1035 0.0171 0.4063 380 0.95 23.52 6.33 0.1035 0.0171 0.4234 • • PROJECT: Seahome Services, Inc. drainage 25 yr storm (B) Total Basin Area = 43560 sq ft = 1 .0000 Ac Storm Duration = 24 hr Peak Rainfall Intensity = 0.588 cfs Total Rainfall Volume = 6534 cu ft Total, 24 hr rainfall = 1.80 in Rainfall Data Standard SCS Type 1A 24 hr hyetograph (adj'd) Total Cumulative from King Co Drn Manual Basin Precip Precip Rainfall Depth Depth Time % Cumulative Time P Pr Prc (min) Precip % Precip (hrs) (cfs) (in) (in) 390 0.95 24.47 6.50 0.1035 0.0171 0.4405 400 0.95 25.42 6.67 0. 1035 0.0171 0.4576 410 1.33 26.75 6.83 0.1448 0.0239 0.4815 420 1.33 28.08 7.00 0.1448 0.0239 0.5054 430 1.33 29.41 7.17 0.1448 0.0239 0.5294 440 1.80 31.21 7.33 0.1960 0.0324 0.5618 450 1.80 33.01 7.50 0.1960 0.0324 0.5942 460 3.40 36.41 7.67 0.3703 0.0612 0.6554 470 5.40 41.81 7.83 0.5881 0.0972 0.7526 480 2.70 44 .51 8.00 0.2940 0.0486 0.8012 490 1.80 46.31 8.17 0.1960 0.0324 0.8336 500 1.34 47.65 8.33 0.1459 0.0241 0.8577 510 1.34 48.99 8.50 0.1459 0.0241 0.8818 520 1.34 50.33 8.67 0.1459 0.0241 0.9059 530 0.88 51.21 8.83 0.0958 0.0158 0.9218 540 0.88 52.09 9.00 0.0958 0.0158 0.9376 550 0.88 52.97 9.17 0.0958 0.0158 0.9535 560 0.88 53.85 9.33 0.0958 0.0158 0.9693 570 0.88 54.73 9.50 0.0958 0.0158 0.9851 580 0.88 55.61 9.67 0.0958 0.0158 1.0010 590 0.88 56.49 9.83 0.0958 0.0158 1.0168 600 0.88 57.37 10.00 0.0958 0.0158 1.0327 610 0.88 58.25 10.17 0.0958 0.0158 1.0485 620 0.88 59.13 10.33 0.0958 0.0158 1.0643 630 0.88 60.01 10.50 0.0958 0.0158 1.Q802"-_ , - 640 0.88 60.89 10.67 0.0958 0.0158 1.0960 F,: 650 0.72 61.61 10.83 0.0784 0.0130 1.10907' 660 0.72 62.33 11.00 0.0784 0.0130 1.1219 670 0.72 63.05 11.17 0.0784 0.0130 1.1349 :; 680 0.72 63.77 11.33 0.0784 0.0130 1.1479 690 0.72 64.49 11.50 0.0784 0.0130 1.1608 700 0.72 65.21 11.67 0.0784 0.0130 1.1738 710 0.72 65.93 11.83 0.0784 0.0130 1.1867 720 0.72 66.65 12.00 0.0784 0.0130 1.1997 730 0.72 67.37 12.17 0.0784 0.0130 1.2127 740 0.72 68.09 12.33 0.0784 0.0130 1.2256 750 0.72 68.81 12.50 0.0784 0.0130 1.2386 760 0.72 69.53 12.67 0.0784 0.0130 1.2515 770 0.57 70.10 12.83 0.0621 0.0103 1.2618 III 411 PROJECT: Seahome Services, Inc. drainage 25 yr storm (B) Total Basin Area = 43560 sq ft = 1.0000 Ac Storm Duration = 24 hr Peak Rainfall Intensity = 0.588 cfs Total Rainfall Volume = 6534 cu ft Total, 24 hr rainfall = 1.80 in Rainfall Data Standard SCS Type lA 24 hr hyetograph (adj 'd) Total Cumulative from King Co Drn Manual Basin Precip Precip Rainfall Depth Depth Time % Cumulative Time P Pr Prc (min) Precip % Precip (hrs) (cfs) (in) (in) 780 0.57 70.67 13.00 0.0621 0.0103 1.2721 790 0.57 71.24 13.17 0.0621 0.0103 1.2823 800 0.57 71.81 13.33 0.0621 0.0103 1.2926 810 0.57 72.38 13.50 0.0621 0.0103 1.3028 820 0.57 72.95 13.67 0.0621 0.0103 1.3131 830 0.57 73.52 13.83 0.0621 0.0103 1.3234 840 0.57 74 .09 14 .00 0.0621 0.0103 1.3336 850 0.57 74 .66 14 .17 0.0621 0.0103 1.3439 860 0.57 75.23 14 .33 0.0621 0.0103 1.3541 870 0.57 75.80 14 .50 0.0621 0.0103 1.3644 880 0.57 76.37 14 .67 0.0621 0.0103 1.3747 890 0.50 76.87 14 .83 0.0545 0.0090 1.3837 900 0.50 77.37 15.00 0.0545 0.0090 1.3927 910 0.50 77.87 15.17 0.0545 0.0090 1.4017 920 0.50 78.37 15.33 0.0545 0.0090 1.4107 930 0.50 78.87 15.50 0.0545 0.0090 1.4197 940 0.50 79.37 15.67 0.0545 0.0090 1.4287 950 0.50 79.87 15.83 0.0545 0.0090 1.4377 960 0.50 80.37 16.00 0.0545 0.0090 1.4467 970 0.50 80.87 16.17 0.0545 0.0090 1.4557 980 0.50 81.37 16.33 0.0545 0.0090 1.4647 990 0.50 81.87 16.50 0.0545 0.0090 1.4737 1000 0.50 82.37 16.67 0.0545 0.0090 1.4827 1010 0.43 82.80 16.83 0.0468 0.0077 1.4904 1020 0.40 83.20 17.00 0.0436 0.0072 1.4976 1030 0.40 83.60 17.17 0.0436 0.0072 1.5048 1040 0.40 84 .00 17.33 0.0436 0.0072 1.5120 1050 0.40 84 .40 17.50 0.0436 0.0072 1.5192-- -.. _ 1060 0.40 84.80 17.67 0.0436 0.0072 1.5264 , 1070 0.40 85.20 17.83 0.0436 0.0072 1.5336 1080 0.40 85.60 18.00 0.0436 0.0072 1.5408 1090 0.40 86.00 18.17 0.0436 0.0072 1.5480 1100 0.40 86.40 18.33 0.0436 0.0072 1.5552 1110 0.40 86.80 18.50 0.0436 0.0072 1.5624 1120 0.40 87.20 18.67 0.0436 0.0072 1.5696 1130 0.40 87.60 18.83 0.0436 0.0072 1.5768 1140 0.40 88.00 19.00 0.0436 0.0072 1.5840 1150 0.40 88.40 19.17 0.0436 0.0072 1.5912 1160 0.40 88.80 19.33 0.0436 0.0072 1.5984 • III . PROJECT: Seahome Services, Inc. drainage 25 yr storm (B) Total Basin Area = 43560 sq ft = 1.0000 Ac Storm Duration = 24 hr Peak Rainfall Intensity = 0.588 cfs Total Rainfall Volume = 6534 cu ft Total, 24 hr rainfall = 1.80 in Rainfall Data Standard SCS Type lA 24 hr hyetograph (adj'd) Total Cumulative. from King Co Drn Manual Basin Precip Precip Rainfall Depth Depth Time % Cumulative Time P Pr Prc (min) Precip % Precip (hrs) (cfs) (in) (in) 1170 0.40 89.20 19.50 0.0436 0.0072 1.6056 1180 0.40 89.60 19.67 0.0436 0.0072 1.6128 1190 0.40 90.00 19.83 0.0436 0.0072 1.6200 1200 0.40 90.40 20.00 0.0436 0.0072 1.6272 1210 0.40 90.80 20.17 0.0436 0.0072 1.6344 1220 0.40 91.20 20.33 0.0436 0.0072 1.6416 1230 0.40 91.60 20.50 0.0436 0.0072 1.6488 1240 0.40 92.00 20.67 0.0436 0.0072 1.6560 1250 0.40 92.40 20.83 0.0436 0.0072 1.6632 1260 0.40 92.80 21.00 0.0436 0.0072 1.6704 1270 0.40 93.20 21.17 0.0436 0.0072 1.6776 1280 0.40 93.60 21.33 0.0436 0.0072 1.6848 1290 0.40 94.00 21.50 0.0436 0.0072 1.6920 1300 0.40 94.40 21.67 0.0436 0.0072 1.6992 1310 0.40 94 .80 21.83 0.0436 0.0072 1.7064 1320 0.40 95.20 22.00 0.0436 0.0072 1.7136 1330 0.40 95.60 22.17 0.0436 0.0072 1.7208 1340 0.40 96.00 22.33 0.0436 0.0072 1.7280 1350 0.40 96.40 22.50 0.0436 0.0072 1.7352 1360 0.40 96.80 22.67 0.0436 0.0072 1.7424 1370 0.40 97.20 22.83 0.0436 0.0072 1.7496 1380 0.40 97.60 23.00 0.0436 0.0072 1.7568 1390 0.40 98.00 23.17 0.0436 0.0072 1.7640 1400 0.40 98.40 23.33 0.0436 0.0072 1.7712 1410 0.40 98.80 23.50 0.0436 0.0072 1.7784 1420 0.40 99.20 23.67 0.0436 0.0072 1.7856 1430 0.40 99.60 23.83 0.0436 0.0072 1.7928 1440 0.40 100.00 24 .00 0.0436 0.0072 1.800- "" " 1450 0.00 100.00 24 .17 0.0000 0.0000 1.8000 ,� 1460 0.00 100.00 24.33 0.0000 0.0000 1.8000 1470 0.00 100.00 24 .50 0.0000 0.0000 1.8000 1480 0.00 100.00 24.67 0.0000 0.0000 1.8000' 1490 0.00 100.00 24 .83 0.0000 0.0000 1.8000 1500 0.00 100.00 25.00 0.0000 0.0000 1.8000 100.00 1.8000 • 410 Date: 12-10-10E PIPE HEAD LOSS Pipe diameter (inches) : 6 D = 0.50 ft Flow (one only) GPM: Q = 0.10 cfs CFS: 0.1 Q = 44 .88 gpm Length of pipe (feet) : 800 L = B00 ft Friction factor Hazen-Williams (C) : 150 (50-200) H1 = 0.15 ft = 0.06 Mannings (n) : 0.0082 ( .005-.05) H1 = 0.10 ft = 0.04 Darcy-Weisbach (f) : 0.014 ( .01-1) H1 = 0.09 ft = 0.04 R\, 11 :SEC 2 2 2005 1