STORM TACOMA 02. Potential permitting requirements STANDARD DETAILS FOR RAIN GARDEN CONSTRUCTION. How to use this document

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1 R R G R P 02 STORM TACOMA 02 STANDARD DETAILS FOR RAIN GARDEN CONSTRUCTION Updated October 23, 2013 How to use this document Your rain garden will need to be designed and constructed in accordance with the specific constraints of your site and in compliance with any applicable codes and regula ons as they pertain to your rain garden. This document, in collabora on with the Rain Garden Handbook for Western Washington (Washington State University, 2013), is intended to walk the owner and/or contractor through the design process of the rain garden. Read through this document and fill out the applicable informa on to demonstrate the construc on methods and requirements that apply to your rain garden. Please note that this will be included as Exhibit B in the Homeowner Rebate Agreement. Required information to be submitted: Acknowledgement of poten al permi ng requirements (p.1) Rain garden sizing informa on (p.2) Site Plan and Rain Garden Facility Plan drawings (p. 3 4) sample plans located on pages Selected rain garden inflow conveyance op on Piped inflow conveyance (p.6) Vegetated swale inflow conveyance (p.7) Rock lined swale inflow conveyance (p.7) Selected rain garden overflow conveyance op on Piped overflow conveyance (p.8 9) Vegetated swale overflow conveyance (p.10) Rock lined swale overflow conveyance (p.10) Potential permitting requirements In general, there are several permi ng requirements that may apply to your rain garden construc on based on the size and loca on of your rain garden. Check the following boxes to demonstrate that you are aware of, and are in compliance with, these requirements. Addi onal informa on on permits can be obtained through the Permit Intake Center at (253) Permits, if required, can be obtained through the City of Tacoma Permit Intake Center located at: 747 Market Street Tacoma, WA Grade and Fill Does the rain garden propose to excavate and/or fill more than fi y cubic yards of soil? Yes No If you checked the yes box, please note that an addi onal grade and fill permit may be required for your project. Storm Connec on Does the rain garden propose a direct connec on to the stormwater system, i.e. the overflow connects through a pipe to the right of way? Yes No If you checked the yes box, please note that an addi onal stormwater connec on permit or sidewalk drain permit may be required for your project. City of Tacoma Environmental Services Department 326 East D Street Tacoma, WA (253)

2 2 Size your rain garden The proposed rain garden is to be sized in accordance with the Rain Garden Handbook for Western Washington available online at: acoma.org/raingarden. Based on the contribu ng area (impervious surfaces from which stormwater runoff is directed to your rain garden) and the infiltra on test results (obtained from Pierce Conserva on District), use the sec on tled Determine the Size of Your Rain Garden, star ng on page 18 of the Rain Garden Handbook for Western Washington to size your rain garden. Provide the following information for the proposed rain garden: Contribu ng area (square feet) Infiltra on rate (inches per hour) Ponding depth (inches) Performance level per Rain Garden Handbook (circle) Good Be er Best Sizing Factor (percentage) Total Top Surface of Ponding Area (square feet) Please note that if you size your rain garden to the Be er or Best performance standard you will be eligible for 100% of the rain garden rebate at $2.00 per square foot of contribu ng area that is directed to the rain garden (up to $2,000 maximum). If you design your facility to the Good performance standard you will be eligible for a prorated rebate at $1.68 per square foot of runoff that is directed to the rain garden (up to $1,680 maximum). Draw your site plan Use the space provided on the grid paper on page 3 to draw a site plan of your property to include the proposed size and loca on of the rain garden. The recommended scale of the grid paper is one square equals 4 feet by 4 feet (1 inch equals 16 feet). A sample site plan is provided on page 12. Please clearly label and draw to scale all of the following items on the Site Plan: Structures (including buildings, retaining walls, driveways, pa os, garages, etc.). Property boundaries. Note, if the parcel is too large to show the en rety on the site map at the proposed scale, only show those areas that include the rain garden and impervious surfaces which will direct runoff to the rain garden. Exis ng contour lines from the best available source, spot eleva ons or indica ons of direc on and steepness of slopes, with the source clearly iden fied. Exis ng contour informa on may be obtained from the City s GovMe website at: acoma.org/map. Exis ng (known) u li es (water service line, gas service line, underground power lines, etc.). Loca on of side sewer connec on from the house to sewer main, or if applicable indicate the loca on of all exis ng sep c components including connec on from house to sep c tank, sep c tanks, pump tanks, pre treatment units, primary drainfields and reserve drainfields. Loca on and dimensions of rain garden and all impervious surfaces. Note which impervious surfaces will direct their stormwater to the rain garden, as well as how the stormwater will be conveyed (i.e. sheet flow, piped, conveyance swale etc.). Legend (if symbols are used that are not labeled in the plan) and north arrow. Draw your rain garden facility plan Use the space provided on the grid paper on page 4 to draw a more detailed plan of your rain garden. The recommended scale of the grid paper is one square equals 1 foot by 1 foot (1 inch equals 4 feet). A sample rain garden facility plan is provided on page 13. Please clearly label and draw to scale all of the following items on the Rain Garden Facility Plan: Top Surface of Ponding Area footprint Freeboard (Overflow Containment) footprint Bo om area footprint Loca on and type of all stormwater conveyance to and from the rain garden (inflows and overflows) Plant loca ons, types (species names), spacing and sizes (size at purchase). Refer to page 11 for more informa on on plant selec on.

3 3 SITE PLAN Scale

4 4 RAIN GARDEN FACILITY PLAN Scale

5 5 Rain Garden Section The following details provide the required dimensions and depths for the construc on of the rain garden. Please note any devia ons from these standards on these details. The City will need to review and approve. Legend: Notes: 1. Rain garden to be sized using the 2013 Rain Garden Handbook for Western Washington, available at cityo acoma.org/raingarden. 2. Freeboard (overflow containment) shall be 2 minimum for contribu ng areas under 1,000 square feet, or 6 for contribu ng areas 1,000 square feet or greater. 3. Do not compact the rain garden soil mix. 3.1 Do not operate heavy equipment within the rain garden 3.2 Do not place or amend rain garden soil when the ground is frozen or when the soil is excessively wet. 4. Con nue mulch for a minimum of 2 0 past the top of bank eleva on or install landscape edging if rain garden is adjacent to turf. 5. Maintain rain garden soil mix depth to edge of ponding area, then taper to meet exis ng grade. Maximum slope of rain garden soil is 2:1.

6 6 Rain Garden Inflow: Piped Conveyance Check the box if the proposed rain garden will have a piped inflow conveyance. If piped inflow conveyance is used, the following construc on details apply. Note, the following page (page 7) contains the details for the other op on for inflow conveyance (conveyance swale). The rain garden will use piped inflow conveyance Legend: Notes: 1. Gravel or stream bed cobble splash pad minimum depth of 6 inches. Rock splash pad shall be a minimum of 1 foot wide and extend beyond the pipe outlet by a minimum of 1 foot inch diameter pipe shall be: 2.1 PVC, SDR 35, ASTM D3034; 3.2 CPEP, Single Wall Fully Corrugated AASHTO Standard M 252; or, 3.3 Duc le Iron, Class 50 or 52.

7 7 Rain Garden Inflow: Conveyance Swale Check the box if the proposed rain garden will have a conveyance swale for inflow conveyance. If a conveyance swale is used, you must select either a vegetated conveyance swale or a rock lined conveyance swale. The following construc on details apply. The rain garden will use an inflow conveyance swale (select op on below) Vegetated Conveyance Rock Lined Conveyance Legend: Notes: 1. Do not place plants that will restrict or concentrate the flow of water in the bo om of the swale. 2. Impervious liners instead of geotex le fabric are recommended if you have observed flooding issues in your basement or near your building founda on.

8 8 Rain Garden Overflow: Piped Conveyance Check the box if the proposed rain garden will have a piped overflow conveyance. If piped overflow conveyance is used, the following construc on details on this page and the following page (page 9) apply. Note, this page contains the details for the piped overflow conveyance op ons inside the rain garden. The following page contains the details for where the piped overflow conveyance discharges into the right of way through the curb. If the piped overflow conveyance op on is not selected (p. 9 10), overflow conveyance via a conveyance swale (p.10) must be selected. The rain garden will use piped overflow conveyance (select op on below) Beehive grate on piped overflow Open ended piped overflow Notes: 1. Beehive grate must be made of UV stabilized material inch diameter pipe shall be: 2.1 PVC, SDR 35, ASTM D3034; 3.2 CPEP, Single Wall Fully Corrugated AASHTO Standard M 252; or, 3.3 Duc le Iron, Class 50 or Piped overflow connec ons to the storm system, including discharging through the curb as shown on page 9, require a sidewalk drain permit. A separate inspec on by the City of Tacoma s Site Development Inspectors will be required. Contact Tacoma s Permit Intake Center at (253) for informa on.

9 9 Rain Garden Overflow: Piped Conveyance If piped overflow conveyance is used, the following construc on details on this page and the previous page (page 8) apply. Note, this page contains the details for where the piped overflow conveyance discharges into the right of way through the curb. The previous page contains the details for the piped overflow conveyance op ons inside the rain garden. If the piped overflow conveyance op on is not selected (p. 9 10), overflow conveyance via a conveyance swale (p.10) must be selected. Notes: 1. Beehive grate must be made of UV stabilized material inch diameter pipe shall be: 2.1 PVC, SDR 35, ASTM D3034; 3.2 CPEP, Single Wall Fully Corrugated AASHTO Standard M 252; or, 3.3 Duc le Iron, Class 50 or Piped overflow connec ons to the storm system, including discharging through the curb as shown on this sheet, require a sidewalk drain permit. A separate inspec on by the City of Tacoma s Site Development Inspectors will be required. Contact Tacoma s Permit Intake Center at (253) for informa on.

10 10 Rain Garden Overflow: Conveyance Swale Check the box if the proposed rain garden will have a conveyance swale for overflow conveyance. If a conveyance swale is used, you must select either a vegetated conveyance swale or a rock lined conveyance swale. The following construc on details apply. The rain garden will use an overflow conveyance swale (select op on below) Vegetated Conveyance Rock Lined Conveyance Notes: 1. Refer to page 7 for details of the vegetated or rock lined conveyance swale. 2. Minimum slope = 0.5%. If greater than 4% slope, consider erosion control op ons such as a rock check dam. 3. Dispersion trench consists of a minimum 6 inch wide by 6 inch deep by 24 inch long drain rock layer lined with geotex le fabric on the sides and bo om for separa on. 4. If the rain garden overflow conveyance swale discharges more than 10 feet away from the right of way, the dispersion trench is not required.

11 11 Planting your rain garden Rain gardens have three plan ng zones. Zone 1 is the bo om area of the rain garden, which is frequently wet during the rainy season. Zone 2 includes the side slopes, which occasionally may become wet when the rain garden ponds. Zone 3 includes the area around the perimeter of the rain garden, star ng above the top surface of ponding eleva on, where plants will grow in drier soil. More informa on on plan ng zones and appropriate plants to use for each zone can be obtained through the Rain Garden Handbook for Western Washington, available at acoma.org/raingarden. In general, the following guidelines should be met when proposing plants for rain garden design: At least 50% (by quan ty) should be evergreen plants. Leaf surfaces break up and slow down the velocity of flowing water (including rainfall). The rain garden needs to provide velocity reduc on the most during the rainy season when storm events are most intense and deciduous/ herbaceous plants are leafless. Do not leave large areas of soil unplanted or uncovered. Exposed soil can be a source for erosion during large storm events. Plant types can be overlapped (tree canopy can overlap shrubs and groundcovers) to reduce the area of exposed soil. Provide a variety of plant types with various roo ng structures. It is important to use a variety of plant types with various roo ng structures to encourage good soil health and porosity over the life of the rain garden. Typical plant types used in rain garden construc on include: Emergents. Rushes, grasses and sedges have shallow and fibrous roots that stay close to the soil surface. Large areas solely planted with only shallow rooted plants can some mes cause thick mats of roots to form which does not allow water to penetrate easily. Woody shrubs and trees. Woody shrubs and trees have a mixture of shallow fibrous roots and deeper structural roots that can penetrate deeper into the soil and increase soil porosity over me. Groundcovers. Groundcovers tend to form dense masses of vegeta on low to the ground surface. Low, dense vegeta on can be very effec ve at consolida ng the soil in areas otherwise prone to erosion such as the side slopes of the rain garden (plan ng zone 2). Herbaceous perennials. Herbaceous perennials do not have woody plant parts, and the above ground growth typically dies back in the winter.

12 02 S D R G C 12 EXAMPLE L D : The informa on presented in this packet is not a subs tute for codes and regula ons. The applicant is

13 02 S D R G C 13 EXAMPLE L D : The informa on presented in this packet is not a subs tute for codes and regula ons. The applicant is