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HomeMy WebLinkAboutConstruction Stormwater Pollution Prevention Plan - BLD Engineering / Geo-tech Reports - 12/21/2017 Thy if fl^45 MUST BE QN THE JOB SITE MR INSPEOriON Construction Stormwater Pollution Prevention Plan for Shearer Logging & Single Family Residential Property 401 NE Timberline Drive Parcel No. 12320-34-00030 Mason County, Washington December 21, 2017 Project#17195 RECEIVED JAN 0 8 2018 615 W. Alder Street TO BE KEPT IN THE PARCEL FILE Prepared For: Tom Shearer PO Box 1959 Belfair, Washington 98528 �� CLYDt s AS TIT Prepared By: IP Envirotech Engineering, PLLC PO Box 984 43045 q� Belfair, Washington 98528 �� �FCIsTER��G��� Phone: 360-275-9374 �810NALE� Envirotech Engineering,PLLC(Envirotech)has completed this construction stormwater pollution prevention plan (SWPPP) in conjunction with the stormwater management plan for a residential property located at 401 NE Timberline Drive, identified as parcel number 12320-34-00030 in Mason County,Washington. The following sections in this SWPPP includes Project Description, Existing Site Conditions, Adjacent Areas, Critical Areas, Soils, Erosion Problem Areas, Construction Phasing/ Schedule, Engineering Calculations, and the twelve (12) required SWPPP elements per the 2005 Department of Ecology Stormwater Management Manual. Project Description Information pertaining to the Project was provided by the property owner, and observations from a field visit by Envirotech. The proposed development is expected to consist of a new single family residence,driveway and other ancillary features typical of this type of development. The size of the property is 13.78 acres. It is anticipated that the residential structures will cover approximately 6200 square feet (sf), and the driveways will encompass an additional 7050 sf in size.The total proposed impervious surface area is 13,250 sf. The total land area that has already been disturbed due to logging is approximately 3.00 acres. It is anticipated that additional land disturbance will not result from the proposed development. Cut and fill quantities were approximated to be 200 cubic yards (cy) and 200 cy, respectively. See the accompanying stormwater management plans for an illustration of current and proposed site features. Existing Site Conditions The Project is currently vacant land with few improvements such as a road. Clearing and light grading is apparent. This includes past logging and stumping. The property is surrounded by rural residential development. Timberline Drive extends along the north side of the property, and the Union River and other water features on the south portion of the property.Vegetation on and near the property consists primarily of 2"d growth firs, alders, and other trees and shrubbery common to this area of the Pacific Northwest. Descending slopes exceeding 15% are located on and beyond the property. Average slope grades are up to approximately 23%with a vertical relief of approximately 15 feet. Some steeper slopes were observed, but negligible vertical height and influence on the project. Ascending grades are generally located to the northwest of the planned development. This slope is relatively minor within 300 feet of the Project,with no apparent slope grades of at least 15%. The upland area of the property is situated on a gentle hillside. Landforms are primarily of glacial origin with centuries of weathering overburden.Most of the property consists of alluvium. The majority of the stormwater runoff originating upslope from the anticipated development is Envirotech Engineering Shearer Single Family Residence Ph.360-275-9374 Page 1 of 8 401 NE Timberline Drive,Belfair Fax:360-2754789 Parcel 12320-34-00030 December 21,2017 expected to be minimal to moderate. Significant scour, erosion and sediment transport was not apparent near the planned development. The Union River, stream and wetland on the property have drainage issues,and is distant from the proposed project. There are no apparent water bodies or wetlands located upslope from the planned development that would significantly influence the Project. It appears that development will be at least 25 feet above the ordinary high water mark of the Union River. Adjacent Areas Adjacent areas include vacant land,waterways, and rural residential development. A rock quarry is also nearby. Site disturbance is not expected to disturb adjacent areas if all provisions in the stormwater management plan are followed.However,the aforementioned areas have the potential to be affected by the site disturbance. Downstream drainage appears to follow the Union River in a southerly direction for at least 2 miles.This project is within the Hood Canal watershed. Critical Areas Critical areas on this property include moderately hazard slopes, wetland stream and the Union P Pert3' Y P > river.A critical aquifer is not known to exist beneath the property. This project is not anticipated to disturb any critical area, and special requirements are limited to environmental buffers from the surface water and wetland. Soils Information on infiltration rates and soil conditions pertaining to the Project was accomplished by Envirotech. For complete details, see the Geological Assessment prepared for the Shearer Logging and Single Family Residential Property,dated December 21,2017. Selected information pertaining to the drainage aspect of the project is provided below. The following subsurface conditions are estimated descriptions of the Project subgrade utilizing information from the depth of penetration at all testing, sampling, observed and investigated locations. Soils for this project were described utilizing the Unified Soil Classification System (USCS). Using the USCS in conjunction with estimated relative densities and other anticipated engineering properties of the soil, susceptibility for potential landslides, erosion and seismic hazards may be assessed. The Project is primarily composed of undisturbed, native soils, without indications of substantial fill. However, some fill could be present. Competent bearing soils were encountered at 18 inches below the existing ground surface in locations where the ground was probed. For engineering purposes,these native soils consist of distinguishable layers,as presented below. Soils within the upper 6 feet of natural ground were observed to be primarily moist, brown silty Envirotech Engineering Shearer Single Family Residence Ph.360-275-9374 Page 2 of 8 401 NE Timberline Drive,Belfair Fax:360-2754789 Parcel 12320-34-00030 December 21,2017 sand with gravel (SM). Soils below the upper SM layer could be a conglomerate of sand, silt and clay. This is based on nearby well reports,site geology,and/or knowledge of the general area. According to the USDA Textural Classification System, the site soils are primarily classified as sandy loam. Some pockets of gravelly soils was also observed. Soil structure may be described as granular. According to the "Soil Survey of Mason County," by the United States Department of Agriculture, Soil Conservation Service (SCS), the site soils are described as Everett gravelly loamy sand, with 5% - 15% slopes, Belfast silt loam, with 0 — 3% slopes, and Indianola loamy sand,with 5%to 15%slopes. From the water well report(s) and knowledge of the general area, permanent groundwater is at least 50 feet directly below the property at the building pad location. Surface seepage or perched groundwater at shallow depths was not observed on-site,nor indicated on the well reports. The soil samples obtained at the Project site during the field investigation were preserved and transported for possible laboratory testing. Visual classification of soils was performed in the field at all observed soil profiles. Visual classifications were performed in accordance with the American Standards for Testing and Materials(ASTM D2488). The general results from the visual classification are presented above in the Subsurface Conditions Section. Specifically, soils within the upper 4 feet in one testing location consisted of approximately 12% gravel, 55% sand-sized soils, and 33% fines with no plasticity indicating a very low content of clay within the fine fraction. Minor variations observed during the visual classification of particle size content(i.e. gravel, sand, fines), or isolated pockets within the soil stratification were insignificant in relation to the overall engineering properties of the soil. Based on the fines content, erodibility of the site soils is considered to be moderate. However, soils on disturbed slopes are more apt to erode than disturbed soils on flat ground. Based on the fines content and fraction of clay within the fines content, settleability of the site soils is expected to be moderate to fast. Permeability is expected to be high for this site due significance of moderate density,poorly graded granular soils. According to the 2005 Stormwater Management Manual for Western Washington prepared by the Washington State Department of Ecology Water Quality Program, infiltration rates are determined per the USDA Textural Classification of the soils, and an appropriate factor of safety. Based on the soils consisting predominantly of sandy loam, and utilizing a factor of safety of 2, site infiltration for stormwater facilities should be 0.33 inches/hour. Water quality for this project is achieved by the soil subgrade beneath the sub-base water storage area. The Cation-Exchange Capacity (CEC) of the soils, based on soil texture and testing as provided above,the CEC ranges from a minimum of 15 to 40 meq/100g. Based on the abundance of organic matter in the top soil,the CEC values may be much higher. Envirotech Engineering Shearer Single Family Residence Ph.360-275-9374 Page 3 of 8 401 NE Timberline Drive,Belfair Fax:360-2754789 Parcel 12320-34-00030 December 21,2017 Erosion Problem Areas There are no identified or mapped erosion hazard areas for this property where development is expected to occur. Construction Phasing Construction phasing for this project may occur, such as developing the second house sometime after the initial development is complete. The following includes the recommended construction sequence and procedure for project development: 1. Delineate clearing and easement limits. 2. Construct all required temporary erosion control features. 3. Clear vegetation required for site development. 4. Perform initial earthwork and rough grading for constructing the roadway, driveways, building pads, stormwater management facilities, etc. If necessary, exposed soils in stock piles must be protected with plastic covering or County approved method. 5. Complete final grading of the subgrade, and materials placement per the plans and specifications. This includes dredging sediments from temporary sediment facilities, if necessary. 6. Maintain all temporary erosion and sediment control facilities, as needed, in order to provide the required protection of downstream water quality. Additional temporary erosion control shall be rendered throughout the duration of the project, if necessary. 7. Provide permanent erosion control in order to stabilize the project. 8. Remove temporary erosion sedimentation control facilities after construction is complete, and the site is sufficiently stabilized. Construction Schedule Some clearing and grading, including past logging has already occurred. Construction of the single family residence is expected to commence in March 2018. Successive phases are not anticipated. Wet season erosion control will most likely be required for this project. However, wet season construction constraints are not necessary for critical areas. Engineering Calculations Standard sediment ponds and traps were not utilized for this project. However, sedimentation due to construction runoff is anticipated to be retained on site. Significant diversions and waterways were not utilized for this project. The drainage report consists of calculations for 100yr-24hr and 6mo-24hr storm events. Runoff was shown to be contained on-site due to a 100yr-24hr event. Consequently, stormwater accumulated from a 2yr-24hr temporary erosion storm event will be easily accommodated. Envirotech Engineering Shearer Single Family Residence Ph.360-275-9374 Page 4 of 8 401 NE Timberline Drive,Belfair Fax:360-275-4789 Parcel12320-34-00030 December 21,2017 Operation and Maintenance An operation and maintenance schedule for construction activities are provided below within the Specific Construction SWPPP Items. An operation and maintenance schedule for all proposed permanent stormwater facilities shall be required under a separate cover. If required by the Agency,an operation and maintenance Declaration of Covenant shall be implemented to cover all privately owned and maintained stormwater facilities. Specific Construction SWPPP Items The following 12 items are addressed herein per the 2005 Department of Ecology Stormwater Manual. 1.0 Mark Clearing Limits Clearing limits shall be delineated on-site by the owner/ contractor. Activities are not permitted beyond the designated clearing limits without prior approval and/or permits. Additional clearing is not anticipated due to previous logging. 2.0 Establish Construction Access Construction access shall be limited to a single entrance to access the project during construction. A stabilized construction access adjacent to Timberline Drive shall be built per the erosion control plans. 3.0 Control Flow Rates Properties and waterways located downstream from the construction site is protected from erosion by adhering to the stormwater management manual by containing all construction runoff on-site due to the 2yr 24hr storm event. Due to this, a downstream analysis is not necessary for this project during construction.Temporary retention/detention stormwater facilities, if any, shall be functional prior to the construction of site improvements. Additional or different stormwater flow control may be necessary if current designed facilities are not functioning as intended. If permanent infiltration ponds are used for flow control during construction, these facilities should be protected from siltation during the construction phase. 4.0 Install Sediment Controls Sediment controls deemed adequate for this project are naturally vegetated terrain, and silt fencing. See the stormwater management plan for locations and details. 5.0 Stabilize Soils Soil stabilization is necessary for this project.Temporary seeding and permanent soil stabilization requirements are provided in the stormwater management plans. This also includes stabilizing all exposed and unworked soils from runoff and wind erosion. Envirotech Engineering Shearer Single Family Residence Ph.360-275-9374 Page 5 of 8 401 NE Timberline Drive,Belfair Fax:360-2754789 Parcel 12320-34-00030 December 21,2017 6.0 Protect Slopes Both natural and fill slopes shall be protected per the stormwater management plans. This includes stabilizing with vegetation,and maintaining natural vegetation. 7.0 Protect Drain Inlets There are no existing drain inlets that will be influenced by this project.Proposed inlets should be protected with fabric or other standard control until the project is stabilized. 8.0 Stabilize Channels and Outlets All designed channels and outlets, if any, shall be stabilized with vegetation, riprap, or other appropriate means. See the stormwater management plans for locations and details. A roadside swale may be warranted in order to divert water away from the development. 9.0 Control Pollutants Pollution generated from construction must be controlled at all times. Control of pollutants other than sediments includes the following: 1. All pollutants other than sediments, including waste materials and demolition debris,that occur on-site shall be handled and disposed of in a manner that does not cause contamination of stormwater. Woody debris may be chopped and spread on site. 2. Cover, containment and protection from vandalism shall be provided for all chemicals, liquid products,petroleum products,and non-inert wastes present on the project site. 3. Maintenance and repair of heavy equipment and vehicles involving oil changes,hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge or spillage of pollutants to the ground or into stormwater runoff must be conducted using spill prevention measures, such as drip pans. Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Emergency repairs may be performed on-site using temporary plastic placed beneath and,if raining,over the vehicle. 4. Wheel wash or tire bath wastewater shall be discharged to a separate on-site treatment system or to the sanitary sewer, if available. 5. Application of agricultural chemicals including fertilizers and pesticides shall be conducted in a manner, and at application rates that will not result in loss of chemical to stormwater runoff. Manufacturers' recommendations for application rates and procedures shall be followed. 6. BMP's shall be used to prevent or treat contamination of stormwater runoff by pH modifying sources. These sources include, but are not limited to, bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters,waste streams generated from concrete grinding and sawing, exposed aggregate processes, and concrete pumping and mixer washout waters. Stormwater discharges shall not cause or contribute to a violation of the water quality standard for pH in the receiving waters. 7. Construction sites with significant concrete work shall adjust the pH of stormwater if necessary to prevent violations of water quality standards. 8. --- ------ -- ---- - - -- _ -_--------------- ------------ - - Envirotech Engineering Shearer Single Family Residence Ph.360-275-9374 Page 6 of 8 401 NE Timberline Drive,Belfair Fax:360-275-4789 Parcel 12320-34-00030 December 21,2017 10.0 Control Dewatering Although dewatering will not be likely for this project, special provisions are required to be followed when dewatering. The outlet for dewatering shall be located in a position as to prevent sediments and pollution from leaving the site.This may be accomplished by pumping water into a sedimentation pond,or other standard control. 11.0 Maintain BMP's All temporary BMP's must be inspected and maintained accordingly.This includes the following: Stabilized Construction Entrance The stabilized construction entrance shall be inspected at reasonable increments. Increased usage of the construction entrance warrants more frequent inspections. Additional rock shall be added periodically to maintain proper function of the pad. Silt Fence All silt fencing shall be inspected immediately after each rainfall and at least daily during prolonged rainfall.Any required repairs shall be made immediately. Straw Loose straw is subject to blowing, and should be inspected each day. Keep straw moist or tied down in order to deter blowing.Add new straw if necessary. Hay bales shall be bound with wire or appropriate measure. Check for raveling after each major rainfall event.Bales may need to be stakes to prevent movement. Permanent Vegetation Permanent vegetation shall initially be inspected regularly to insure establishment and healthy growth. Once established, vegetation may need to be periodically fertilized for continuous growth.Vegetation shall be re-established in areas, if necessary. While active construction is in process,all temporary erosion and sediment control facilities shall be inspected and immediately maintained if necessary per the requirements provided above. In the event that construction activities are discontinued for at least 4 consecutive days, the owner shall be responsible for the inspection, and immediate maintenance if necessary, of all temporary erosion and sediment control facilities immediately after storm events, and at least once every 7 days. In addition to the aforementioned inspection and maintenance schedule, the owner shall install additional erosion and sediment control facilities if proposed erosion and sediment control measures prove to be inadequate. Envirotech Engineering Shearer Single Family Residence Ph.360-275-9374 Page 7 of 8 401 NE Timberline Drive,Belfair Fax:360-275-4789 Parcel 12320-34-00030 December 21,2017 Preserving Natural Vegetation Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been removed or damaged. if the flagging or fencing has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. If tree roots have been exposed or injured, "prune" cleanly with an appropriate pruning saw or lopers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees (fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier. Dust Control Respray area as necessary to keep dust to a minimum. Concrete Handling Containers shall be checked for holes in the liner daily during concrete pours and repaired the same day. Maintenance Responsibility Inspection, maintenance, and financial liability of all temporary/ permanent erosion and sedimentation control facilities shall ultimately be the responsibility of the owner or owner's representative who is utilizing the facilities. Currently, the following proponent is in charge of this responsibility: Tom Shearer PO Box 1959 Belfair, Washington 98528 12.0 Manage the Project The designated manager for this project is: Tom Shearer PO Box 1959 Belfair, Washington 98528 Envirotech Engineering Shearer Single Family Residence Ph. 360-275-9374 Page 8 of 8 401 NE Timberline Drive,Belfair Fax: 360-275-4789 Parcel 12320-34-00030 December 21,2017