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Home My WebLink AboutBLD2009-00314 Geotechnical Report ~~ • 41 7 j NTI ENGINEERING & SURVEYING \ 717 SOUTH PEABODY STREET,PORT ANGELES,WA 98362 Engineers■Land Surveyors II Geologists Construction Inspection■Materials Testing i S E P 1 7 2009 ;y N 7' (360)452-8491 1-800-654-5545 FAX 452-8498 E-Mail:info@nti4u.cbm www.m14u.com ;i 1/ DRAINAGE & EROSION CONTROL REPORT FOR THE PROPERTY LOCATED ON FLASH ROAD, QUILCENE, JEFFERSON COUNTY, WASHINGTON PARCEL NO. 701293001 LOCATED IN GOVERNMENT LOTS 3 & 4 SECTION 28, TOWNSHIP 27 NORTH, RANGE 1 WEST, W.M. Prepared for Fred & Lorraine Pleines M. W ,e',F OF WA y 4,F 040-01 r .fo 41i30 O , ''4. j!;��,S�,sT,E� „, APPROVED S ONAL. G STORMWATER PLAN Prepared-by DEC 1 4 2009 4 Kate Waddell, P.E. JEFF Rso c u Y DEPT.OF M NI Y : • P. T NTI Engineering & Land Surveyin SIGNATURE: 717 South Peabody Port Angeles,WA 98362 360-452-8491 www.nti4u.com August 6, 2009 othERSO jti filly CCU • • INTRODUCTION NTl Engineering and Land Surveying was hired by Fred and Lorraine Pleines to develop a drainage and erosion control plan and report for their proposed residential home site on Flash Road in Quilcene. Situate in Jefferson County, Government Lots 2 and 3, Section 28, Township 27 North, Range 1 West. As part of this analysis, a stormwater collection and on-site infiltration system has been designed and a temporary and permanent erosion and sediment control plan has been prepared for the construction of a private single-family residence and driveway. II. DESCRIPTION OF SITE The home site is a 5.10 ± acre parcel on Flash Road. The lot is bordered on the north, west and south by residential lots. The site will be accessed from Lindsay Hill Road located to the west via Flash Road, which is private. This road bisects the property from north to south and is located along the west margin of a level terrace. Slopes adjacent to this terrace are steep, up towards the west and down towards the east to the shoreline of Dabob Bay, a marine water body. The lot is undeveloped and heavily covered with native vegetation on the steep slopes. The terrace has been substantially cleared at some time in the past. The underlying soils are mapped as Beausite (BdE), which are classified in SCS soils group "B". III. METHODOLOGY Jefferson County requires the use of the Department of Ecology (DOE) February 2005 Stormwater Management Manual for Western Washington. Based on the manual, new development with a proposed impervious area greater than 2,000 square feet but less than 5,000 square feet and a conversion of native vegetation to lawn of less than 3/ of an acre determines minimum requirements 1 through 5 shall be applied to this property. These minimum requirements are and will be met as follows: Minimum Requirement #1 Preparation of Stormwater Site Plan • A complete site plan has been included in the appendix of this report. Minimum Requirement #2 Construction Stormwater Pollution Prevention (SWPP) • The SWPPP includes twelve elements. Each element will be addressed separately as follows: Element #1 Mark Clearing Limits o The central terrace on property, which includes the building site, was cleared in the past as evidenced on the enclosed aerial photo. No additional clearing is proposed. Element#2 Establish Construction Access o The construction access to the site will be the same as the final driveway access. 6t 1 7 2009 • i o The existing driveway is graveled. No additional rock base is required Element#3 Control Flow Rates o A minimum of a 50' vegetative buffer will be maintained down slope of all construction activities. The roof runoff will be infiltrated on site per Chapter 3, Volume III, Sections 3.1.1 & 2. The driveway runoff will be un- concentrated and dispersed with a minimum flow path of 50 ft up-slope of the top of bank. No streams will be impacted from the runoff. Element #4 Install Sediment Controls o To minimize erosion during construction, a straw wattle will be installed, see plan for location and details. o The natural vegetation buffer will remain down slope of all development. Element #5 Stabilize Soils o To minimize the soil erosion forces of raindrop impact, flowing water and wind erosion during construction, the contractor will follow the exposed and unworked soil schedule set by DOE for all soils on site. From October 1 through April 30, no soils shall remain exposed and unworked for more than 2 days, and from May 1 to September 30, no soils shall remain exposed and unworked for more than 7 days. o All exposed soils caused by construction activities shall be stabilized and hydroseeded or sodded upon completion of the project. Element #6 Protect Slopes o No work is planned for the steep slope below the building site. Native vegetation will be protected and added to as necessary to maintain a covered slope. o There will be no discharge of concentrated runoff towards the steep slope during or after construction. Element #7 Protect Drain Inlets o There are no inlets existing or planned down-slope of the building site. Element#8 Stabilize Channels and Outlets o No channels or outlets existing within or down-slope of the building site. Stormwater during construction will sheet flow across the site through the temporary BMPs. o The home site terrace is relatively flat which will decrease the velocity of stormwater runoff during and after construction. Element #9 Control Pollutants o All chemicals, liquid products, petroleum products and non-inert wastes present on site shall be covered, contained and protected from vandalism and handled in a manner to minimize contamination of stornyatpr7 2009 2 • • o To minimize pollutants generated by heavy equipment and vehicles, all maintenance and repairs shall be conducted using spill prevention measures such as drip pans. Element#10 Control De-watering o The underlying soils are classified in SCS group "B". As this class of soils is permeable, the need for dewatering should be minimal. It is recommended however, that construction take place during the dry season. If de-watering is necessary it shall be done in compliance with the 2005 DOE manual. Element#11 Maintain BMPs (best management practices) o It is the contractor's responsibility to maintain the temporary erosion and sediment control measures and to install the permanent erosion and sediment control measures set forth in this report and plan. o After construction is complete, maintenance of permanent erosion and sediment control measures are the owner's responsibility. o All temporary erosion and sediment control measures shall be removed within 30 days after final site stabilization is achieved or as needed if longer. Element#12 Manage The Project o Management of this project can best be conducted in accordance with DOE if the guidelines set forth in this report and plan are followed to ensure that the long term goals of environmental protection and site stability are achieved. Minimum Requirement #3 Source Control of Pollution • As stated in Element#9, to minimize pollutants generated by heavy equipment and vehicles, all maintenance and repairs shall be conducted using spill prevention measures such as drip pans. • Source control of pollutants during construction can be maintained on this job by implementing the temporary erosion and sediment control measures set forth. • Long-term source control of pollution is the responsibility of the property owner and includes all categories of household and yard chemicals and pollutants. Minimum Requirement #4 Preservation of Natural Drainage Systems and Outfalls • The natural drainage route on the site is infiltration and sheet flow or excess to the east and south and north. • The vegetated portion of the site will continue to sheet flow as it did prior to development. Minimum Requirement#5 On-site Stormwater Management • The roof downspouts will be directed to an infiltration system designed to provide dispersion of excess flow on the surface. This facility will be located a minimum of 50 feet from steep slopes and at least 10 feet from property lines. • The runoff from the driveway will be un-concentrated and dispersed for a S E P 1 7 2009 3 • • minimum distance of 50 feet up-slope of the top of bank. • Routine observation and maintenance by the owner is highly recommended and necessary to maintain a functioning drainage system on site. A functioning drainage system should infiltrate and if necessary disperse the runoff without causing erosion on site or downstream. IV. 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 straw wattle 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. Due to the size of the site, the minimal slope of the land in the area of the building site and the permeable nature of the underlying soils, the single-family residence roof runoff will be infiltrated on site and the driveway runoff will be dispersed. V. LIMITATIONS This report has been prepared for the exclusive use of Fred and Lorraine Pleines 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. 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 & SURVEYING 1 7 2009 Kate Waddell, P.E. Design Engineer 4 • • G:\Gen\Kate\Drainage DOE 2009\Pleines\drainage report.doc APPENDIX 1.) WWHM REPORT 2.) GEOTECHNICAL REVIEW WITH SITE PHOTOS 3.) SEPTIC AS-BUILT 4.) CRITICAL AREA MAPS (JEFFERSON CO.) 5