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Home My WebLink AboutBLD2013-00135 Drainage I I DRAINAGE & EROSION CONTROL REPORT IFOR THE PROPERTY LOCATED AT 6602 CAPE GEORGE RD I JEFFERSON COUNTY, WASHINGTON PARCEL NO. 001301030 IPrepared for Heinith Family Trust I 2937 NE 47TH Avenue Portland, OR 97213 • 't �'+•, „ 7 Mitt' • r 1 ' iiir iy. iv - . . I ' * 6' 41 '15 ' ir ' . 41 'Aii 4 . Ilk '.1".. - 4‘.v . - • ' •+�� , 1 7 yr' ♦ � 4 •: w II gJ t 4III"4—t 1•,. tAles,:'''rc t-ti--t t,tN,t,..r'' y ' - ��:M : f,i 1 T i 4 Ii •1 er 1 .,k. *.* I b.'* • r.,•:. 4 % •d' frAllilit g. ,.. . i., _ ,..... ,, , !. r -i:,. s. f AilikYv ' —-4 I I NTI Engineering & Land Surveying 717 South Peabody Port Angeles, WA 98362 I 360-452-8491 www.nti4u.com I November 2012 I I INTRODUCTION NTI Engineering and Land Surveying was hired by Robert and Fran Heinith to develop a I drainage and erosion control plan and report for their proposed residential home site at 6602 Cape George Rd. Situated in Jefferson County, Northeast 1/4 , Section 30, Township 30 North, Range 1 West. As part of this analysis, an on-site stormwater I infiltration system has been designed and a temporary erosion and sediment control plan has been prepared for the construction of a private single-family residence, shop/garage, bathhouse and driveway/parking areas. III. DESCRIPTION OF SITE I The home site is located on of a single-family lot fronting and accessed via an existing gravel drive from Cape George Road. It is bound on the: - North by Lane de Chantal, a 60-ft wide private easement containing a private road, I - South by a developed single-family parcel, - East by Cape George Road, a 60-ft wide public right-of-way containing a public road, and - West by an undeveloped single-family parcel. IThe site slopes moderately to the southwest at approximately 15%. The site has minor PP Y improvements including water, power, septic drainfield and a gravel driveway. The site is Ipartially cleared of trees and understory vegetation the rest of the site and parcel are covered with maturing trees and light to moderately dense understory growth. The USDA Natural Resources Conservation Service Soil WEB site notes the parcel has 3 soil types Iwith the following general characteristics. - CfD — Cassolary sandy loam, is well drained and has a capacity to transmit water at a rate between 0.20 and 0.57 in/hr; excavated cuts are prone to failure. The Itypical soil profile is: 0 to 3 inches: Sandy loam I 3 to 23 inches: Sandy loam 23 to 49 inches: Stratified fine sandy loam to silty clay loam 49 to 60 inches: Sand I - HuD—Hoypus gravelly loamy sand, which is somewhat excessively drained and has a capacity to transmit water at its most limiting horizon at a rate between 5.95 I and 19.98 in/hr; excavated cuts are prone to failure. The typical soil profile is: 0 to 2 inches: Gravelly loam 2 to 8 inches: Gravelly loam I 8 to 36 inches: Very gravelly loam 36 to 60 inches: Very gravelly loam I - TuD—Tukey gravelly loam, is moderately well drained and has a capacity to transmit water at its most limiting horizon at a rate between 0.00 and 0.06 in/hr; excavated cuts are prone to failure. The typical soil profile is: I 0 to 2 inches: Gravelly loam 2 to 8 inches: Gravelly loam 8 to 36 inches: Very gravelly loam I 36 to 60 inches: Very gravelly loam I IIII. SITE INVESTIGATION: Based on undocumented, anecdotal comments of gravelly sand being found at depths of I 5-ft plus a soil profile hole was dug at the location of the proposed drywell September 27, 2012 to determine if the underlying soil was suitable for the infiltration of stormwater having the following characteristics: I _ Negligible total suspended solids (TSS) by limiting the tributary area to roofs. Negligible organic loading by routing the roof runoff through a catch basin configured (Organic Litter Trap) to capture leaf litter and other organic matter to Ireduce the likelihood of biomass development. Soil Profile: I - 3" forest litter - 4" fine sandy loam traces of gravel; high organic content - 12" fine sandy loam; irregular mottling assumed to be vegetative artifacts; very I - course roots 18" gravelly sandy loam, trace cobbles; irregular vertical mottling assumed to be vegetative artifacts; medium roots I - 12" lightly cemented stratified fine sandy loam, trace of cobbles — silty clay, trace of cobbles; 8" vertical mottling penetration; medium to fine roots - 18" Very gravelly cobbly sand IWater table was not encountered. IV. METHODOLOGY I Jefferson County requires the use of the Department of Ecology (DOE) February 2005 Stormwater Management Manual for Western Washington (SWMMWW). The proposed new impervious surface area is greater than 2,000-sf. and the proposed land disturbing I activity is more than 7,000-sf and is classified a "Large Project". As a result, Minimum Requirements #1 through #10 are required. IDesign Considerations: Based on profile pit the soil is reasonably described as a Cassolary-Hoypus complex. I While the USDA-NRCS provides a range of the saturated hydraulic conductivity for these two soils between 0.2-in/hr to 20-in/hr; Table 5.10 of the Urban Runoff Quality Management manual (WEF/ASCE, 1998) indicates typical infiltration rates for these soils Ibetween 1-in/hr to 8-in/hr. Given the variability of the soils in the profile a conservative 2-in/hr is applied in the calculations. A correction factor of 0.5 is applied due to the characteristics of the runoff Iwhich will increase the longevity of the system, allow easy inspection and accessibility for maintenance. I I I Table 5.10 Typical infiltration rates of various soil groups. I Saturated Soil conservation infiltration rate service group 'Typical soil type mm h in. hr A Sand 2(X) ti.0 A Loamy sand SO 2.0 I B Sands loam 25 1.0 B LoamI2.7 0.5' C Silt loam 6.3' 0.25' I D Sandy clay loam 3.8 0.15 Clay loam and silty clay loam <2,3 <0.09 D ('lay < 1.3 <0.05 Minimum acceptable infiltration rate is 7.6 mmh 10.3 in..hr1. Sites with soils aith lesser rates should not be used. ITable 5.10 - Urban Runoff Quality Management manual (WEF/ASCE, 1998): I Pile Evil Y'er Neq __i_. L f �1 u = 21 Ito cs.SCEN OS SIxExCxN 9� x,.- P n,.H m .mnn nx�n -._I�_�._�...�______-� xm p., 9MYt C°7 N f�.MxO+SUxi Gx-tl hrM d[rJ S NAIM. 6 d fluxel 1 OYYw) fladx.l Allp w• „ Pon"To t vs».n i�s�er�n.»1vrnrew n�sard 1 fu:,z;,•Ve v.rt, I^ i I l v�n ean�. nblo v • e cA.e e l nrvrvI aWc,.coAmv ry _� e{FecillNnv r�`eavn lxl `u h - ..h I )rh vans FI fqq-YFrar 1 U Nvu.,A, "Tx ,ON d!f fiYx1' 11 F,:Y.n iil I �i�� mecum, „y n,�nns ®�® FH AN xrx-.w -o .., n cl�..Y. r� AR Lis wti l o I n a;l ` B'�III�IA rib AA.k�ue,AAA J raw”...eMr ,q q �—y w SMiY M:w+RA I a 7eMwr irrEv W. R" of�t�.. x-.;.n= -- 1In sei,-4.aR11__-_J., ae w.r u..s a B0l"4.[I.+IJ> I Y o. L ,0,�Ix Y - 1.5l r: 1.5 ...xl „'... ^'"w a - ^x0]x r l p In Ylrol -r- q�Nw Omn•x�r(101 ULImr C-^':±�Pi. IO WRIx moo I J "' I _ Onni-0Numba Outpr) KA frA4t)N e w.a LII ..Fl�nx•rr[[r �1 e 1 �r .a+rod 0 -k J 1 Y I rs r C r-..... _J IFo I •mcF.vw I Q 011 SM1 GMlnn l +a�+ ,. ) sYiYnw I I Iasnoiz 104P t WWHM-3 screen shoot with 95+% roof runoff infiltration: ' Minimum Requirements Site Checklist: Stormwater Management Manual for Western Washington (SMMWW) - Section numbers refer directly to the SMMWW Section 2.5 of Volume I - Sheets numbers refer directly to the engineered plans. ' 2.5.1 Minimum Requirement#1: Preparation of Stormwater Site Plans This is a "Large Project". The sheet, "Stormwater Control Plan", sheet 3 of 5, addresses improvement elements to be constructed for permanent stormwater management of this site. It was developed to be integral to this check list. ' 2.5.2 Minimum Requirement#2: Construction Stormwater Pollution Prevention(SWPP)1: Mark Clearing Limits ( ) ' - Shown in Note 5.1 of Notes on Sheet 5 of 5 Element 2: Establish Construction Access - Shown in Note 5.3 of Notes on Sheet 5 of 5 Element 3: Control Flow Rates - Worksite is well isolated by vegetated grasses and weeds, forest with light understory growth and duff which adequately retain runoff. ' Element 4: Install Sediment Controls - Shown in Note 5.3 of Notes on Sheet 5 of 5 Element 5: Stabilize Soils - Shown in Notes 7 and 8 of Notes on Sheet 5 of 5 ' Element 6: Protect Slopes - 30-ft Slope Buffer shown on all Plan sheets;Buffer flagging is specified in Note 5.1 of Notes on Sheet 5 of 5. Element 7: Protect Drain Inlets - Shown on "Erosion Control Plan"- Sheet 4 of 5 Element 8: Stabilize Channels and Outlets ' - Not applicable Element 9: Control Pollutants - Shown in Notes 10 & 11 of Notes on Sheet 5 of 5 Element 10: Control De-Watering - Not anticipated on this site Element 11: Maintain BMPs ' - Shown in Note 9 of Notes on Sheet 5 of 5 Element 12: Manage The Project - Addressed in Notes of Notes on Sheet 5 of 5 ' 2.5.3 Minimum Requirement#3: Source Control of Pollution Roof runoff is conveyed via closed conduit to drywell- avoiding potential contamination that could result from flowing over driveway or parking areas ' 2.5.4 Minimum Requirement#4: Preservation of Natural Drainage Systems and Outfalls The site and drainage designs are consistent with maintaining the existing drainage patterns to ' an extent feasible. 2.5.5 Minimum Requirement#5: On-site Stormwater Management ' On-site management is accomplished using dispersion of gravel drive and parking area. Utilizing a dry, 95% of roof runoff is infiltrated; the balance is allowed to flow to forest. 2.5.6 Minimum Requirement#6: Runoff Treatment Runoff from the gravel drive and parking area is bio-retained in forest and other vegetated filters. 2.5.7 Minimum Requirement#7: Flow Control All runoff is retained on-site ' 2.5.8 Minimum Requirement#8: Wetlands Protection Not applicable ' 2.5.9 Minimum Requirement#9: BasinNVatershed Planning Given width of vegetated buffer around the worksite and the designed retention of runoff, no negative impacts to the watershed are expected. 2.5.10 Minimum Requirement#10: Operation and Maintenance An Operation and Maintenance Manual is included with this report. 1 1 1 I V. CONCLUSIONS Prior to breaking ground the temporary erosion control measures set forth in this report and plan shall be installed on site to minimize erosion and control sediment discharge during construction activities. These measures include a compost berm and standard soil stabilization BMP's. During construction temporary erosion control measures should be inspected regularly and repaired as necessary. Once the site is developed and stabilized, these BMPs can be removed. VI. LIMITATIONS This report has been prepared for the exclusive use of the Heinith Family Trust for their proposed construction of a private home. The recommendations in the report apply only to the property that was examined and they are not applicable to other locations. I The investigation and recommendations contained in this report are based upon site conditions as they existed at the time of our site inspections. During construction, if subsurface or other conditions are discovered that are significantly different from those ' described in the report, NTI should be advised at once so that we can review the conditions and reconsider our recommendations, where necessary. Unanticipated soil conditions are commonly encountered on construction sites, especially when the topography has been altered years ago. Such unexpected conditions frequently require that additional expenditures be made to attain a properly constructed project. We recommend that a contingency be established in the project budget and schedule to cover unexpected conditions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted professional engineering principles and practice. This warranty is in lieu of all others, either expressed or implied. NTI ENGINEERING & SURVEYI NG ' 911N J KsoF i s, , z 0' o � z (81 cs 4$910 Q` Us/G�STERE° ANAL EI , 7r Ja . d Justin Wilson, P.E. Project Manager Principal APPENDICES A.) STORMWATER SITE PLAN SUBMITTAL TEMPLATE B.) STORMWATER CALCULATION WORKSHEET C.) FIGURE 1 : NEW DEVELOPMENT FLOWCHART D.) CRITICAL AREA MAPS(JEFFERSON CO. MAP SERVER) E.) CALCULATIONS:WESTERN WASHINGTON HYDROLOGY MODEL-3 F.) OPERATIONS AND MAINTENANCE SHEETS G.) NO STREAM LETTER FROM DEPT OF NATURAL RESOURCES . I 1 I I I I 1 I I I I I I I I I I I I