Preliminary Stormwater Management

Report

SW Bible Church

Owner: SW Bible Church Prepared for: William Wilson Architects

Prepared by: James Desmond

Project Engineer: Ryan Milkowski

July 2017 | KPFF Project #10101700054

KPFF’S COMMITMENT TO SUSTAINABILITY

As a member of the US Green Building Council,

a sustaining member of Oregon Natural Step,

and a member of the Sustainable Products

Purchasers Coalition, KPFF is committed to the

practice of sustainable design and the use of

sustainable materials in our work.

When hardcopy reports are provided by KPFF,

they are prepared using recycled and recyclable

materials, reflecting KPFF’s commitment to

using sustainable practices and methods in all

of our products.

1

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Table of Contents Project Overview ................................................................................................................................................ 2

Purpose of this Report .................................................................................................................................... 2

Project Description ......................................................................................................................................... 2

Existing Conditions ............................................................................................................................................. 2

Proposed Conditions .......................................................................................................................................... 3

Hydrologic Analysis ............................................................................................................................................ 3

City of Beaverton/Clean Water Services Jurisdiction ......................................................................................... 3

Drainage Basins .............................................................................................................................................. 3

Detention ........................................................................................................................................................ 4

Conveyance .................................................................................................................................................... 4

Water Quality ................................................................................................................................................. 4

Operations and Maintenance......................................................................................................................... 5

Tables

Table 1: Drainage Area Comparison................................................................................................................... 3

Table 2: Pre and Post Development Flows......................................................................................................... 4

Table 3: Vegetated Facility Summary ................................................................................................................. 4

Appendices

Appendix 1a: Geotechnical Exhibit

Appendix 1b: Soil Survey Report

Appendix 2: Basin Maps

Appendix 3: Basin Hydrographs

Appendix 4: Water Quality Calculations

Appendix 5: Conveyance Calculations (Not included in this submittal)

Appendix 6: Operations & Maintenance Manual (Not included in this submittal)

* NOTE: Items with asterisk will be included in final storm report

2

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Project Overview

Purpose of this Report

This report describes the stormwater management design strategies for the proposed development. The basis for this report is the City of Beaverton 2007 Engineering Design Manual (EDM) and the requirements outlined therein. The purpose of the proposed stormwater management facilities is to protect existing public stormwater infrastructure and to improve the overall health of the watershed.

Project Description

The project consists of a new 3-story addition to the existing Southwest Bible Church building, located at the intersection of SW Murray Blvd and SW Weir Rd in Beaverton, Oregon (see Figure 1 – Vicinity Map). The project site is bounded by SW Sapphire Ln to the north, SW Murray Blvd to the east, SW Weir Rd to the south, and Shadow Creek Park to the west. The new addition will also require civil site work to modify associated asphalt paved surface parking lot, and utilities. There is no required work in the public right of way.

Existing Conditions The topography of the project site and adjacent public frontages generally slope down from north to south and east to west. The elevations range from 250 feet to just 235 feet, with the low points at the south of the site. Along the southern property line, there is a slope leading down to the roadway. The grade difference between the existing finished floor elevation and the parking lot is approximately 1-7 feet, with the larger grade difference being located on the western edge of the sanctuary. The existing finished floor elevation of the sanctuary is approximately 253.88 feet, while the grades in the proposed building footprint have a low spot of 243.20 feet. Current site drainage consists of two storm drains with outfalls into a wooded area west of the sanctuary. The one discharging from the north is from an existing leach field. The other discharging storm pipe is a roof drain from the existing church sanctuary. Runoff from these outfalls that isn’t absorbed by surrounding vegetation flows to a catch basin, which is routed to detention tanks located on the south side of the site, then out into the public storm drainage system (City of Beaverton/CWS jurisdiction). From rumor, it flows through a water quality swale and a storm filter vault before flowing offsite. A geotechnical exhibit is provided in Appendix 1a. This summarizes 3 boring results and a CPT location. Soils on site are poor, ranging from medium to very stiff silts/clays. A soil survey report was also conducted to determine the existing soil type and curve number. This can be found in Appendix 1b

3

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Proposed Conditions In the proposed conditions, the wooded area will be taken over by a new addition, which will serve as a new preschool facility. This facility will have a Finished Floor Elevation (FFE) of 242.88, approximately 1 foot lower than the existing grade. The new addition will consist of 3 stories over a 12,250 SF footprint. Per Tualatin Valley Fire, a 26-foot wide fire lane will be required to the south of the new addition. This will mean the elimination of approximately 36 parking spaces in order to regrade the fire lane to meet the FFE of 242.88. Proposed walkways will be graded in order to tie back in to existing walkways/conditions. Per the City of Beaverton pre-application conference notes, no new frontage improvements shall be required. The proposed grading will require the rerouting of existing storm lines to allow for the construction of the new addition. The parking lot will be sloped from the southern building face down to a proposed vegetated storm water facility. The facility will have outfalls from new impervious roof area that flows into the planter. Due to poor soils, vegetated treatment and underground detention facilities will be required for storm water management.

Hydrologic Analysis The stormwater design for this site was calculated utilizing the Autodesk Storm and Sanitary Analysis 2017 (SSA) modeling software. The SCS-TR-55 (NRCS) method (with a Type 1A storm distribution) was used for all drainage calculations to determine the stormwater runoff values for both pre and post development flows. Soil type D has been assumed when selecting the CN values for pervious areas in the pre and post developed conditions. The curve number values used are 98 for impervious areas and 86 for Type D soils: woods/grass combination landscaping. The minimum time of concentration is 5 minutes. Calculations have been provided in Appendix 3.

City of Beaverton/Clean Water Services Jurisdiction

Drainage Basins

The newly proposed preschool addition will be its own basin, routed to a surface treatment planter for water quality, and then routed into a detention chamber underground. The chamber will be sized to handle new impervious areas.

Table 1: Drainage Area Comparison

4

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Detention

Due to the unknown extent of existing public storm systems downstream, and the presence of onsite detention facilities, the project is designed to handle on-site detention before discharge to the public system. The change from pervious to impervious area means the peak post-development flows to the Beaverton storm system must not exceed peak pre-development flows (see Table 2 below). The detention facility has been sized to accommodate new impervious area only. See Appendix 3 for basin hydrographs.

Table 2: Pre and Post Development Flows

Conveyance

The design narrative and calculations for the conveyance system will be included in the final project storm report.

Water Quality

Per Clean Water Services Chapter 4, Section 4.05.5, we are required to treat new impervious area, as well as three times the modified impervious area. The areas will be treated by two planters. One will treat the new impervious area from the new roof runoff, and another adjacent planter will treat 3 times the modified impervious area. Table 3 below shows a summary of the areas and facilities treating them.

Table 3: Vegetated Facility Summary

Part of the modified impervious area will include existing roof area, picked up by a roof drain being rerouted to SP-A. The planters have been sized according to the LIDA method. Refer to Appendix D for Calculations and LIDA forms.

5

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Operations and Maintenance

The Operations and Maintenance (O&M) Plans for this project will be included in the final project storm report.

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing.

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Appendix 1a

Geotechnical Exhibit

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing.

B-3

B-2CPT

ATTEMPTED HAND AUGER AT TOP OF SLOPE0 TO 1 FT - SOFT SILT WITH GRAVEL 1 TO 2 FT - DENSE SILTY GRAVEL WITH SAND (REJECT ROCK)HAND AUGER REFUSAL AT 2 FEET

B-1

APPROXIMATEBUILDING LOCATION

0 TO 9.5 FT - MEDIUM STIFF TO STIFF CLAY9.5 TO 23 FT - MEDIUM STIFF SILT23 TO 42.5 FT - STIFF TO VERY STIFF CLAY42.5 TO 50 FT - VERY STIFF SILT

4" AC24" AGGREGATE BASE2.3 TO 7.5 FT - MEDIUM STIFF TO STIFF SILT7.5 TO 9.5 FT - MEDIUM STIFF CLAY9.5 TO 23 FT - MEDIUM STIFF SILT23 TO 25 FT - MEDIUM STIFF CLAY

0 TO 10 FT - MEDIUM STIFF SILT

ATTEMPTED INFILTRATION AT 5'. NEGLIGABLEINFILTRATION OBSERVED. NO, MEASURABLEDROP IN WATER LEVEL DURING DURATION OFTEST

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Appendix 1b

Soil Survey Report

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing.

Hydrologic Soil Group—Washington County, Oregon(SW Bible Church - Proposed Addition)

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

7/21/2017Page 1 of 4

5032

730

5032

740

5032

750

5032

760

5032

770

5032

780

5032

790

5032

800

5032

810

5032

820

5032

830

5032

840

5032

850

5032

860

5032

870

5032

730

5032

740

5032

750

5032

760

5032

770

5032

780

5032

790

5032

800

5032

810

5032

820

5032

830

5032

840

5032

850

5032

860

5032

870

513390 513400 513410 513420 513430 513440 513450 513460 513470 513480 513490 513500

513390 513400 513410 513420 513430 513440 513450 513460 513470 513480 513490 513500

45° 26' 57'' N12

2° 4

9' 4

3'' W

45° 26' 57'' N

122°

49'

38'

' W

45° 26' 52'' N

122°

49'

43'

' W

45° 26' 52'' N

122°

49'

38'

' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS840 35 70 140 210

Feet0 10 20 40 60

MetersMap Scale: 1:733 if printed on A portrait (8.5" x 11") sheet.

Soil Map may not be valid at this scale.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI)Area of Interest (AOI)

SoilsSoil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating LinesA

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating PointsA

A/D

B

B/D

C

C/D

D

Not rated or not available

Water FeaturesStreams and Canals

TransportationRails

Interstate Highways

US Routes

Major Roads

Local Roads

BackgroundAerial Photography

The soil surveys that comprise your AOI were mapped at1:20,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can causemisunderstanding of the detail of mapping and accuracy of soilline placement. The maps do not show the small areas ofcontrasting soils that could have been shown at a more detailedscale.

Please rely on the bar scale on each map sheet for mapmeasurements.

Source of Map: Natural Resources Conservation ServiceWeb Soil Survey URL:Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercatorprojection, which preserves direction and shape but distortsdistance and area. A projection that preserves area, such as theAlbers equal-area conic projection, should be used if moreaccurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data asof the version date(s) listed below.

Soil Survey Area: Washington County, OregonSurvey Area Data: Version 14, Sep 16, 2016

Soil map units are labeled (as space allows) for map scales1:50,000 or larger.

Date(s) aerial images were photographed: Aug 3, 2014—Aug23, 2014

The orthophoto or other base map on which the soil lines werecompiled and digitized probably differs from the backgroundimagery displayed on these maps. As a result, some minorshifting of map unit boundaries may be evident.

Hydrologic Soil Group—Washington County, Oregon(SW Bible Church - Proposed Addition)

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

7/21/2017Page 2 of 4

Hydrologic Soil Group

Hydrologic Soil Group— Summary by Map Unit — Washington County, Oregon (OR067)

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

1 Aloha silt loam C/D 2.2 96.5%

45B Woodburn silt loam, 3 to7 percent slopes

C 0.1 3.5%

Totals for Area of Interest 2.3 100.0%

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils areassigned to one of four groups according to the rate of water infiltration when thesoils are not protected by vegetation, are thoroughly wet, and receiveprecipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) andthree dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) whenthoroughly wet. These consist mainly of deep, well drained to excessivelydrained sands or gravelly sands. These soils have a high rate of watertransmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. Theseconsist chiefly of moderately deep or deep, moderately well drained or welldrained soils that have moderately fine texture to moderately coarse texture.These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consistchiefly of soils having a layer that impedes the downward movement of water orsoils of moderately fine texture or fine texture. These soils have a slow rate ofwater transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) whenthoroughly wet. These consist chiefly of clays that have a high shrink-swellpotential, soils that have a high water table, soils that have a claypan or claylayer at or near the surface, and soils that are shallow over nearly imperviousmaterial. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter isfor drained areas and the second is for undrained areas. Only the soils that intheir natural condition are in group D are assigned to dual classes.

Rating Options

Aggregation Method: Dominant Condition

Hydrologic Soil Group—Washington County, Oregon SW Bible Church - ProposedAddition

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

7/21/2017Page 3 of 4

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—Washington County, Oregon SW Bible Church - ProposedAddition

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

7/21/2017Page 4 of 4

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Appendix 2

Basin Maps

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing.

EXISTING CONDITIONS

SOUTHWEST BIBLE CHURCHSCALE 1 INCH = 40 FEET

EXH-A

PROPOSEDCONDITIONS

SOUTHWEST BIBLE CHURCHSCALE 1 INCH = 40 FEET

EXH-B

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Appendix 3

Basin Hydrographs

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing.

Calculation Spreadsheet:

Peak Storm Drainage Runoff Flows

Appendix C

Job Name: SW Bible Church

City of Beaverton #:-

KPFF Job #: 1700054

Design Engineer: JD

Check Engineer: RM

Updated 8/4/2017 Page 1

Calculation Spreadsheet:

Peak Storm Drainage Runoff Flows

Appendix C

Job Name: SW Bible Church

City of Beaverton #:-

KPFF Job #: 1700054

Design Engineer: JD

Check Engineer: RM

a

Updated 8/4/2017 Page 2

Calculation Spreadsheet:

Peak Storm Drainage Runoff Flows

Appendix C

Job Name: SW Bible Church

City of Beaverton #:-

KPFF Job #: 1700054

Design Engineer: JD

Check Engineer: RM

a

Updated 8/4/2017 Page 3

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing.

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Appendix 4

Water Quality Calculations

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing

E E E E

E E

E

E

E

E

E

EXISTING CONDITIONSWITH PROPOSED SITE

OVERLAY

SOUTHWEST BIBLE CHURCH

EXHIBIT ASCALE 1 INCH = 60 FEET

BASIN A

BASIN B

TREATMENT REQUIRED:

3* (MODIFIED IMPERVIOUS AREA - PERMANENT REMOVAL)3* (7346 - 2744) = 13,806 SF

NEW IMP. AREA: 13,683 SF

WQ TREATMENT AREA: 27,489 SF

PLANTER REQ'D TO BE UPSIZED, INCREASINGPERMANENT REMOVAL AREA

TREATMENT REQUIRED:

3* (MODIFIED IMPERVIOUS AREA - PERMANENT REMOVAL)3* (7051 - 3078) = 11,919 SF

NEW IMP. AREA: 13,683 SF

WQ TREATMENT AREA: 25,062 SF

LEGEND

BASIN C13683 SF

3078 SF

7051 SF

BASIN C

BASIN A

MODIFIED IMPERVIOUSAREA

PERMANENT REMOVAL

NEW IMPERVIOUS AREA

BASIN NAME TYPE OF SURFACEAREA

BASIN B

Low Impact Development Approaches Handbook 19

Clean Water Services LIDA Sizing Form

Total ImperviousArea treated (sq.ft.)

(*Must equal total from Step 2 or additional LIDA facilities or Water Quality Facilities must be added.)

Project Title:

Project Location:

Contact Name/Title/Company:

Phone/e-mail:

STEP 1: Determine Impervious Area Requiring Treatment Total Site Area (acres):

Total Existing Impervious Area (sq.ft.):

Proposed New Impervious Area (sq.ft.):

Impervious Area Requiring Treatment (sq.ft.) (Refer to Design & Construction Standards Chapter 4 for instructions to calculate this area, which will be less than or equal to the new plus existing site impervious area.)

STEP 2: Deduct Impervious Area LIDA Credits Porous Pavement (sq. ft.):

Green Roof (sq. ft.):

Other Credits as approved (sq. ft.):

Total Credits (sq. ft.):

Remaining Impervious area (sq. ft.) (Total from Step 1 – Total Credits):

STEP 3: Size LIDA Facilities for Remaining Impervious Area

IA: Impervious area treated

(sq.ft.)

SF, Sizing Factor

LIDA facility size (sq.ft.) (IA x SF)

Infiltration Planters/Rain Garden 0.06

Flow-through Planter 0.06LIDA Swale 0.06Vegetated Filter Strip 0.06

Total Impervious Area treated (sq.ft.) must equal total from Step 2 or additional LIDA facilities or Water Quality Facilities must be added.

Low Impact Development Approaches Handbook 19

Clean Water Services LIDA Sizing Form

Total ImperviousArea treated (sq.ft.)

(*Must equal total from Step 2 or additional LIDA facilities or Water Quality Facilities must be added.)

Project Title:

Project Location:

Contact Name/Title/Company:

Phone/e-mail:

STEP 1: Determine Impervious Area Requiring Treatment Total Site Area (acres):

Total Existing Impervious Area (sq.ft.):

Proposed New Impervious Area (sq.ft.):

Impervious Area Requiring Treatment (sq.ft.) (Refer to Design & Construction Standards Chapter 4 for instructions to calculate this area, which will be less than or equal to the new plus existing site impervious area.)

STEP 2: Deduct Impervious Area LIDA Credits Porous Pavement (sq. ft.):

Green Roof (sq. ft.):

Other Credits as approved (sq. ft.):

Total Credits (sq. ft.):

Remaining Impervious area (sq. ft.) (Total from Step 1 – Total Credits):

STEP 3: Size LIDA Facilities for Remaining Impervious Area

IA: Impervious area treated

(sq.ft.)

SF, Sizing Factor

LIDA facility size (sq.ft.) (IA x SF)

Infiltration Planters/Rain Garden 0.06

Flow-through Planter 0.06LIDA Swale 0.06Vegetated Filter Strip 0.06

Total Impervious Area treated (sq.ft.) must equal total from Step 2 or additional LIDA facilities or Water Quality Facilities must be added.

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Appendix 5

Conveyance Calculations (Not included in this submittal)

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

Appendix 6

Operations & Maintenance Manual (Not included in this submittal)

SW Bible Church | KPFF Consulting Engineers FINAL STORMWATER MANAGEMENT REPORT

This page deliberately left blank to facilitate double-sided printing

111 SW 5th Avenue, Suite 2500, Portland, OR 97204

503-227-3251 | www.kpff.com