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Home My WebLink AboutBLD2021-00259-05- Stormwater or Approved Stormwater Washington Project Consultants, PLLC 212 S Rhododendron DR Port Townsend, WA 98368 Phone (360) 890-0752 The Refuge – Cabin #2 Page 1 of 2 STORMWATER MANAGEMENT REPORT - SUPPLEMENT Project: The Refuge – Addition of 4 BR Cabin (#2) MLA #14-0064 Location: 2275 Duckabush Road, Brinnon, WA Owner: The Refuge: Col. James A. Engren, Ret. Stormwater Supplement Report by: Marc A. Horton, PE Date: January 15, 2021 Attachments: Attachment 1: Location Map Attachment 2: Site Plan Attachment 3: Stormwater Calculation Worksheet Attachment 4: Flow Chart – Figure 2.4.1 Attachment 5: Construction Pollution Prevention Fact Sheet Attachment 6.: “Small” Project Certification Worksheet Attachment 7: Amended Drainage & Erosion Control Report (2017) Attachment 8: Water System and Storm Drainage Plan and Profile (2017) Attachment 9: Stormwater Pollution Prevention Plan (2017) Proposed Development: This report addresses stormwater management for addition of a 4 BR Cabin (Cabin #2) at the existing facilities at The Refuge (Olympic Mountain Retreat and Conference Center) off Duckabush Road near Brinnon, WA (Attachment 1). The latest improvements at this facility were completed under MLA #14- 0064 (application package April 2017). At that time, several facilities were approved for construction, including:  4 Small Cabins  A Cook Shed  Waterworks Building  Cabin #1 (2 BR) 1/15/2021 Apr 27 2021 Washington Project Consultants, PLLC 212 S Rhododendron DR Port Townsend, WA 98368 Phone (360) 890-0752 The Refuge – Cabin #2 Page 2 of 2 The owner would now like to add Cabin #2, a 4 BR Cabin of 1750 square feet (impervious coverage). All past improvements created 137,873 sf of impervious surface on the 17.8-acre site. The addition of the 1750 sf cabin will increase this coverage to 139,623 sf (about 18% of the site). The location of the proposed new cabin is shown on the site plan (Attachment 2) Regulatory Requirements: This Cabin was not included in the Amended Phase I approvals of 2017, and therefore, has been assessed as a new project under the County’s stormwater application requirements. A Stormwater Calculation Worksheet was developed (Attachment 3) showing less than 35% total coverage, and defining the project as “new development”. Figure 2.4.1 (Western Washington Stormwater Management Manual) for new development was used to show that this project is a “Small” project” under the County’s system (Attachment 4). Small projects need to meet Minimum Requirement #2 (Construction SWPPP) following the “Construction Pollution Prevention Fact Sheet” (Attachment 5), and complete the “Small” Project Certification Worksheet. (Attachment 6) Existing Conditions: The drainage, soils, and general information for the 17.8 acres under MLA #14-0064 is described in the attached 2017 Amended Phase 1 Drainage & Erosion Control Report (Attachment 7). The regulatory framework and specifics were provided and approved in 2017. For this project, the pertinent components of the stormwater management system include a collection system of catch basins and 12” pipe leading to a dispersion trench. The system has been functioning without issues since installation. Proposed Stormwater Management: This project will add less than 2000 sf to the Refuge facility and be less than a 1% increase in impervious surface at the facility. The design of collection / dispersion of stormwater for the area of Cabin #2 was oversized for the contribution of the existing two buildings (about 1750 sf) and adjacent parking and roads. The design anticipated several more cabins and will be sufficient for this increased drainage caused by Cabin #2. Apr 27 2021 D: \ _ J o b s \ _ Q E \ _ T h e R e f u g e \ _ D W G \ T h e R e f u g e ( 1 8 b ) . d w g , 0 1 w w b C V R , 1 1 / 6 / 2 0 1 7 2 : 0 2 : 4 8 P M Attachment 1 Apr 27 2021 A t t a c h m e n t 2 A p r 2 7 2 0 2 1 Apr 27 2021 Apr 27 2021 Apr 27 2021 Apr 27 2021 Apr 27 2021 Apr 27 2021 Apr 27 2021 AMENDED PHASE 1 THE REFUGE - MLA14-00064 DRAINAGE & EROSION CONTROL REPORT FOR THE PROPERTY LOCATED AT OLYMPIC MOUNTAIN RETREAT & CONFERENCE CENTER 2275 DUCKABUSH ROAD, BRINNON, WASHINGTON 98320 APNs. (PHASE 1 Underlined) 502-074-025, 502-083-017, 502-083-018, 502-083-019, & 502-083-020 Prepared for Col James A Edgren, USA, Ret 2275 Duckabush Road, PO Box 641 Brinnon, Washington 98320 Quadra Engineering, SP 1630 Walnut St Port Townsend, WA. 98368 (360) 379-9117 February 21, 2017 AMENDED April 17, 2017 Attachment 7 Apr 27 2021 INTRODUCTION Quadra Engineering was hired by, James Edgren, to provide services for the phased expansion of the existing Christian retreat and conference center at, 2275 Duckabush Road, WA. The expansion will result in the addition of: - Four single-room sleeping cabins without water/sewer services; - A cook-shed with a restroom and a shower room; - A waterworks building containing pumps and domestic & fire suppression reservoirs; - A multi-use building with various multi-use rooms, bathrooms, and commercial kitchen; - A Chapel with restrooms; - Four (4) residential cabins with full utility services; - Supporting on-site sewerage systems (OSS); - A supporting / private Group-A water system; - Gravel driveways / parking / circulation improvements. and drive; - Supporting stormwater management measures / systems. With preliminarily approved Binding Site Plan (BSP) and Conditional Use Permit (CUP), see MLAl4- 00064/ZON l4-00029/SUB l 4-00008, the project is proceeding to the first phase. This report pertains to PHASE 1 exclusively; the work includes construction of: PHASE I AREA SF ACRES BUILDINGS (4) CABINS 800 0.018 (1) COOK SHED 240 0.006 (1) WATERWORKS 864 0.020 (1) CABIN 888 0.020 REV NEW BUILDINGS 1904 0.046 REV SURFACING GRAVEL - MAINT 2100 0.048 CONCRETE HC PARKING 600 0.014 MAINTENANCE 2700 0.062 GRAVEL - NEW 3627 0.083 REV NEW PAVEMENT 0 0.000 WALKS & PATIOS 144 0.003 NEW IMPERVIOUS SURFACING 3771 0.087 REV LANDSCAPE (includes OSS Drainfield) 6000 0.138 UTILITIES ITEM NO. UNITS SEPTIC SS PIPE 570 LF REV TANKS 5 EACH REV DRAINFIELD 9971 SF REV WATER 3" WATER 180 LF REV 2" WATER 400 LF 1-1/2" WATER 160 LF 1" WATER 190 LF Apr 27 2021 II. DESCRIPTION OF PROPERTY The reader/reviewer is advised to refer to the image provided on the cover of this report, the Phase-1 plans, and/or the underlying Binding Site Plan (BSP). The property includes five (5) Rural Residential 5 (RR-5) parcels with a combined total area of 17.8-acres. It fronts and is accessed via Duckabush Rd; along its north boundary. It has a secondary access from Coyote Road, a private road that intersects Duckabush Road near the property’s north most point, then loops southwestward, then returns to property’s west-most boundary and continues thru a southern boundary. The property is bound on the: - North by the Duckabush Road, a public right-of -way, then by parcels zoned R-5 developed as single- family residences. - East by parcels zoned R-5, developed as single-family residences; - South by a parcel zoned R-5, designated forestland. - West by a portion of Coyote Road, a private roadway, then by R-5 zoned parcels, vacant and developed single-family residences. Critical Areas: - A Type-Ns stream traverses, bisecting north to south, the western portion of the property (west-most parcel). Approximately half way thru the parcel, a secondary creek/stream, flowing from the northwest, discharges to it. The Type-Ns stream discharges to a Type-F stream at a southern boundary. - A Type-F stream traverses the west-most southern corner of the property and continues southeast. The confluence of this and the Type Ns stream above is located along the southwest boundary. - The buffers for these streams are 50-ft for the Type-Ns and 150-ft for the Type-F. Existing improvements include: - The Lodge; - Cook shed with shower and restroom (permit pending); - Four 1-room cabins with pier block foundations and no water services (permits pending); - Waterworks building for fire & domestic use for the Lodge; - Caretakers residence; - Out-buildings including a groundskeeper garage, greenhouse, woodsheds, etc; - 2 wells, power, and on-site sewage systems (OSS); - Gravel driveways, parking areas, and park-like landscaping; - A drainage ditch, a portion of which has been rock lined as a landscaping feature; and - A drainage ditch that traverses the property, from the northeast corner to the middle of the southern boundary. The south half of this ditch has rock-lined sides. - Rock bordered pond. - A single-family residence on the southeast parcel that is leased by The Refuge. Soils: Per the USDA - NRCS’s online soil survey (http://websoilsurvey.nrcs.usda.gov/app/) is a Grove (GoC), a very gravelly loamy sand with the following characteristics: - A glacial outwash with a restrictive depth of more than 80 inches; - Somewhat excessively drained soil; - A high to very high capacity to transmit water through the limiting layer with a saturated hydraulic conductivity (Ksat) of 5.95 to 19.98-in/hr, respectively; - A water table depth of more than 80 inches. On-site septic / soil profile pits were generally consistent with this description with the additional qualification that the soil is highly variable throughout the property. Some locations have interbed lenses of silty loam in course sands; others include fine sandy loams, sandy clay loam, and gravelly sands; and others include yet another mix of soil types. Apr 27 2021 Drainage: The principle drainage patterns that exist on the property: - The majority of the southeastern quarter of the property sheet flows southward into forestland; with the remainder flowing westward to the drainage ditch. - The majority of the middle swash of the property (middle 2 parcels) drains via sheet and concentrated flows, south and eastward on slopes ranging approximately between 2 and 45%, to the drainage ditch and pond. o The ditch originates at the northeast corner of the property at an 18” culvert under Duckabush Road. From there it traverses southwest, first thru an existing ditch, and continues along/thru a portion of the ditch that has rock-lined sides, to a constructed pond located near the middle southern boundary the property. The pond is located in a large shallow depression that is mostly maintained in a park-like condition. o The depression/pond, when over-burdened by a storm event, the detained runoff drains thru a broad, shallow, grass-lined swale southward to an existing ditch on the southern boundary. - A swash of the property, located east of the Type-Ns stream and west of the middle drainage course noted above, drains east and southward (away from the stream) via sheet and small localized concentrated flows to the caretaker’s residence lawn and to the forestland southeast of it. - The majority of the west-most parcel drains, over slopes as high as 60% and as low as 2%, to a seasonal (Type Ns) stream that originates at a 24” culvert under Duckabush Road at the northwest corner of the property. From there it flows southward and discharges to a Type F stream at the southwest corner of the property. III. BASIS OF DESIGN: With 73% of the property’s forest being retained, Full Dispersion is appropriate. All new development will incorporate appropriate dispersion BMPs and/or infiltration BMPs where practical. Quantity: Flow control is not required unless less than 65% of the forest is retained and/or dispersion BMPs are not used. Under these conditions, Flow Control will be accomplished using: - Infiltration trenches - Bio-retention thru amending and placing the retained duff/topsoil on all “green” areas. - Increasing the capacity of the existing pond and metering the discharge per the Stormwater Management Manual for Western Washington (SWMMWW), 2012 edition. Quality: The project will mitigate impacts during construction and for the permanent facilities. A SWPPP will be developed and a Construction Stormwater Pollution Prevention Permit will be acquired. The SWPPP will specify LID methods/BMPs so that they may be incorporated into the permanent facilities. These include: - Compost berm silt barriers that can be left in-place or incorporated in to the landscaping. - Retention of forest duff/topsoil that will be amended with compost if necessary and placed over disturbed areas as part of finished grading operations. - Avoiding concentrating flows by directing/dispersing runoff into vegetated areas as quickly as practical. - Avoid conveying runoff across parking areas when practical. IV. METHODOLOGY Jefferson County requires the use of the Department of Ecology (DOE) February 2012 Stormwater Management Manual for Western Washington (SWMMWW). The proposed new impervious surface area is greater than 2,000-sf. and the proposed land disturbing activity is more than 5,000-sf and is classified a “Large Project”. As a result, Minimum Requirements #1 through #9 are required. Apr 27 2021 Phase 1 Design: With the exception of the waterworks building and its infrastructure - the work for this phase will be within the swash located between the Type-Ns stream and the middle drainage course noted above. Stormwater in this tributary area infiltrates during typical storm events. During more intense and anomalous storm events runoff sheet flows southward toward the caretaker’s residence and the forestland adjoining it. It then disperses and infiltrates. This pattern will be maintained to provide effective stormwater management. While the runoff from the new waterworks building is negligible, roof runoff will be conveyed to a drywell for infiltration. Disturbed areas not being covered by driveways or roof will be restored using stripped and retained forest topsoil and seeded to promote retention. Runoff exceeding the capacity of the soil will sheet flow into the adjoining forest. This drywell will be removed and the litter trap converted to an in-line catch basin of a larger stormdrain and management system. Soil profile pits in the proximity of the drywell provide: Pit # Depth (inches) Description Group Q-10 0-14 Brown-red sandy loam (top soil) A/B 14-40 Loamy fine sand w/ sandy clay loam B/C 40-66 Gravely sand A/B 66-74 Loamy fine sand w/ sandy (sticky)clay loam D >74 Gravely sand A/B F-3 0-72” Gravelly silt loam, gravelly sandy loam, gravelly medium sand, & gravel C-A Given the variability of the soil: - The drywell excavation will be inspected and approved by the engineer prior to placing filter fabric. - The minimum 180-cf of gravel is increased to 240-cf (8.9-cy). REV - The drywell will be placed so that its bottom is no lower than 44-inches below the existing grade. V. CONCLUSIONS Prior to breaking ground, the CESCL shall inspect and approve the installed the temporary erosion control measures. During construction temporary erosion control measures shall be inspected as required in the CSWGP 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 Olympic Mountain Retreat & Conference Center, for its proposed development of “The Refuge”. 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, Quadra Engineering 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 Apr 27 2021 generally accepted professional engineering principles and practice. This warranty is in lieu of all others, either expressed or implied. Quadra Engineering, SP Harold T. Andersen, P.E. Jay M. Ward Designer Apr 27 2021 APPENDICES A.) SITE SURFACING TABLE B.) SWMMWW Figure 2.4.1 – FLOW CHART FOR DETERMINING DEVELOPMENT REQUIREMENTS C.) SWMMWW 2.5.1 - MINIMUM REQUIREMENTS SITE CHECKLIST D.) CRITICAL AREA MAPS Apr 27 2021 APPENDIX A Apr 27 2021 AREA SF ACRES % exist BOUNDARY 774906 17.789 100% STREAMS (SEASONAL) 13733 0.315 1.8% EXISTING BUILDINGS 10424 0.239 GRAVEL 54415 1.249 PAVEMENT 170 0.004 WALKS/PATIOS 268 0.006 POND 1146 0.026 EXISTING IMPERVIOUS 66423 1.524 8.6% PREVIOUS 708483 16.265 91.4% INCLUDES PARKING: STANDARD STALLS 16 EACH HANDICAPPED STALL 1 EACH PHASE I AREA SF ACRES % exist BUILDINGS (4) CABINS 800 0.018 (1) COOK SHED 240 0.006 (1) WATERWORKS 864 0.020 NEW BUILDINGS 1904 0.044 0.2% SURFACING GRAVEL - MAINT 2100 0.048 CONC HC PARKING 600 0.014 MAINTENANCE 2700 0.062 GRAVEL - NEW 2980 0.068 NEW PAVEMENT 0 0.000 WALKS & PATIOS 144 0.003 NEW SURFACING 3124 0.071 0.4% UTILITIES SEPTIC / SEWER 5361 0.123 WATER 865 0.020 STORMWATER 209 0.005 UTILITIES 6435 0.148 0.8% LANDSCAPE SEE PS/SW2 6000 0.138 0.8% TOTAL 13787 0.317 1.8% Apr 27 2021 APPENDIX B Apr 27 2021 Apr 27 2021 APPENDIX C Apr 27 2021 APPENDIX D Apr 27 2021 DNR Streams Landslide Hazard Apr 27 2021 Critical Aquifer Recharge Area Apr 27 2021 Draft January 11, 2021 Marc Horton – Washington Project Consultants Page 1 of 1 document2 Attachment 8 – need copy Apr 27 2021 D: \ _ J o b s \ _ Q E \ _ T h e R e f u g e \ _ D W G \ T h e R e f u g e P 1 ( 5 d ) . d w g , S W P P P 1 , 2 / 2 2 / 2 0 1 7 9 : 2 5 : 3 3 P M Attachment 9 Apr 27 2021