ESBD_545166_1785800787830_TXDOT Files July 2026.pdf

8310-1 N Capital of Texas Hwy, Suite 250, Austin, Texas 78731 | tel: 512 346-110

July 20, 2026

Subject: TxDOT Driveway Application Materials & Coordination - BRA EWCRWS

201 Co Rd 496, Taylor, TX 76574

Dear Prospective Contractor:

Find enclosed the following documents for the TxDOT driveway permit application for the Brazos River Authority East Williamson County Raw Water System (EWCRWS) Treatment Plant Expansion Project.

Form 1058 – Permit to Construction Access Driveway Facilities

Variance Letter - Driveway Spacing and TIA Waiver

Environmental Checklist

Driveway Exhibit – TXDOT DW EXB

Culvert Exhibit – TXDOT CUL EXB

Culvert Exhibit – TXDOT OUT EXB

Drainage Report with Appendix C – Culvert Report

These materials are provided to support your application for a TxDOT driveway permit. It is the contractor’s responsibility to secure this permit. The enclosed documents can be emailed to Shane Brown (Tommy.Brown@txdot.gov) at the Georgetown/Williamson County Office as one application package.

Additional work proposed within the TxDOT right-of-way is shown the Pond Outfall Exhibit (reference TXDOT OUT EXB.pdf). The attachments also include an extensive Drainage Report for the EWC WTP that supports site drainage models, stormwater system design, and otherwise supports adequacy of the existing TxDOT discharge swale along FM 1331. The Work proposed within the TxDOT right-of-way must be coordinated with TxDOT prior to construction.

Sincerely, Glenn Barin, PE, PMP, CCM, DBIA Vice President CDM Smith Inc.

Texas Registration F-3043 mailto:Tommy.Brown@txdot.gov

BARINGD

Text Box

SAMPLE ONLY

8310-1 N Capital of Texas Hwy, Suite 250, Austin, Texas 78731 | tel: 512 346-110

Shane Brown Texas Dept. of Transportation Georgetown/Williamson County Area Office Austin, Texas 78626753

Subject: Variance Letter – Driveway Spacing and TIA Waiver Brazos River Authority – East Williamson County Water Treatment Plant 201 Co Rd 496, Taylor, TX 76574

Dear Mr. Brown, The proposed relocated driveway for the Brazos River Authority’s East Williamson County Water Treatment Plant is intended for continued access, with driveway use at four vehicles per hour (VPH) or less, is not intended to increase traffic along FM 1331. The site has an existing driveway and gate to access the existing infrastructure, and the proposed driveway will relocate the driveway for improved entry-exit to both existing and proposed facilities on site.

Additionally, the required driveway spacing, based on the 65-mph posted speed limit on FM 1331, is 425 feet as per Access Management Manual, Table 2-2: Other State Highways Connection Spacing Criteria (p2-13). The nearest driveway (for a residence) to the proposed relocated driveway is approximately 320 feet. The proposed driveway location is preferred due to it being a current access point to the site.

The proposed driveway and onsite road are intended to be formalized for continued access.

Therefore, we request a waiver from the Traffic Impact Analysis for the proposed driveway access, and we request a variance from the minimum requirement of 425 feet.

Feel free to contact me at 512-636-0526 or baringd@cdmsmith.com if you have any questions regarding this request.

Sincerely, Glenn Barin, PE, PMP, CCM, DBIA Vice President CDM Smith Inc.

Texas Registration F-3043 cc: Aaron Vaughan, Brazos River Authority 7/20/2026 mailto:baringd@cdmsmith.com

ENVIRONMENTAL ISSUES CHECKLIST FOR DONATION AGREEMENTS & DRIVEWAYS

This checklist provides a first level evaluation of potential environmental issues associated with driveways and Donation Agreement (DA) project activities occurring within TxDOT right-of-way (ROW). All responses must be completed with reference to the databases provided, or, in the absence of a database, with the best knowledge of the preparer.

Project Details Project Name: ___________________________________________________________

CSJ: _______________________________ Roadway: ____________________________

Project Limits: from________________________ to_____________________________

County: _______________ GPS Coordinates (DD): ______________________________

Project Description (state if project in DA or driveway, and describe project activities):

Environmental Issues

2. Is the proposed action within a historic district, or adjacent to a historic property or district? See Texas Historic Sites Atlas and attach the figure(s) of the results to support your answer.

If new ROW or easements are required or donated, further coordination is needed.

*4.

1. Will new ROW or easements be required or donated for the project? If so, note the acreage: _________________

*3. Are there known or potential hazardous material encroachments into the project area, including visual evidence of soil and groundwater contamination, dump sites, tanks, or other sources of contamination?

If new ROW or easements are required or donated, please complete and attach a Hazardous Materials Initial Site Assessment (ISA).

Yes No

Are cemeteries present within or adjacent to the project? See Texas Historic Sites Atlas.If so, will any contruction activities or extension of the pavement be within 15 feet of the existing ROW boundary? YES NO

Will the project cross or otherwise have the potential to affect possible jurisdictional waters of the U.S. (including wetlands)? See Definition of "Waters of the United States" and National Wetlands Inventory Wetlands Mapper and attach the figure(s) of the results to support your answer.

*5.

For driveway projects, only the questions marked with a "*" require answers.

http://atlas.thc.state.tx.us/Map http://ftp.dot.state.tx.us/pub/txdot-info/env/toolkit/510-02-ds.docx https://www.fws.gov/wetlands/data/mapper.html https://www.fws.gov/wetlands/data/mapper.html http://atlas.thc.state.tx.us/Map http://atlas.thc.state.tx.us/Map

*7. Will there be associated trimming or removal of trees or other woody vegetation that could affect migratory birds or their nests, including ground-nesting birds?

*9. Is the project located within designated critical habitat for federally-listed threatened or endangered species? See USFWS Critical Habitat Mapper and attach the figure(s) of the results to support your answer.

*10.

*11. Would the project include excavation greater than 3 feet in depth within Karst Zones 1, 2, or 3? See Travis and Williamson Counties Karst Zones and attach the figure(s) of the results to support your answer.

If the project includes excavation deeper than 3 feet in a Karst Zone, please enter the maximum depth of excavation:_____________________

Is there suitable habitat for federally and state listed threatened or endangered species within the project area? Please provide the appropriate documentation (i.e. maps, photos, impacted species table, etc.) to support your answer.

8.

ENVIRONMENTAL ISSUES CHECKLIST FOR DONATION AGREEMENTS

Yes No

6.

Is the project within the boundary of the Lost Pines Habitat Conservation Plan Area (LPHCP)?

Has a participation certificate issued by the LPHCP conservation plan been obtained? YES NO; If so, please attach to this checklist.

Is the project located within any Salamander Critical Habitat? See Travis and Williamson Counties Karst Zones and Salamander Critical Habitat Map

*12.

Is the proposed project within the designated Edwards Aquifer Recharge or Contributing Zones? See TCEQ Edwards Aquifer Map Viewer and attach the figure(s) of the results to support your answer.

The project must have TCEQ approval before construction may begin. It is the responsibility of the applicant to provide TSS load removal for all new impervious cover in TxDOT ROW. TSS load removal should be provided off TxDOT ROW by the applicant's onsite BMPs. Please attach the draft WPAP or CZP as applicable, and select one of the following:

The Donation Agreement project activities are included in the overall WPAP or CZP; or, A separate WPAP or CZP application will be made to authorize the activities within the ROW.

Is there evidence of ground-nesting birds in the project area? YES NO https://fws.maps.arcgis.com/home/webmap/viewer.html?webmap=9d8de5e265ad4fe09893cf75b8dbfb77 http://www.co.bastrop.tx.us/upload/page/0094/docs/LPHCP_Plan_Area_Map.pdf https://www.arcgis.com/home/webmap/viewer.html?webmap=953ab0462a0c4f2f870c3524e5f12b8e&extent=-99.175,29.9405,-96.302,31.1516 http://www.co.bastrop.tx.us/upload/page/0094/docs/LPHCP_Plan_Area_Map.pdf https://www.tceq.texas.gov/gis/edwards-viewer.html https://www.arcgis.com/home/webmap/viewer.html?webmap=953ab0462a0c4f2f870c3524e5f12b8e&extent=-99.175,29.9405,-96.302,31.1516 https://www.arcgis.com/home/webmap/viewer.html?webmap=953ab0462a0c4f2f870c3524e5f12b8e&extent=-99.175,29.9405,-96.302,31.1516

PLEASE NOTE: The project area will need to be included in the development’s Storm Water Pollution Prevention Plan.

The project sponsor must provide a signed copy of this checklist, a location map, project layout sheet, and project plans, along with the required supporting documentation to support any questions answered “Yes” to their TxDOT Area Office contact to be sent to the TxDOT Austin District Environmental Section.

An environmental specialist will then be assigned to discuss further assessment requirements. Upon the conclusion of the environmental review of your Donation Agreement project, you will receive an Environmental Clearance Memo via email that will include all necessary environmental commitments for the project. Such commitments may include, but are not limited to the following:

migratory birds, protected species, Construction General Permit (CGP) TXR150000, vegetation, water quality BMPs, and hazardous materials.

By signing this document, the project donor certifies that the responses noted above are true and represent appropriate due diligence with regard to potential environmental issues associated with this project.

Project Donor

Company

Telephone/Email

ENVIRONMENTAL ISSUES CHECKLIST FOR DONATION AGREEMENTS

To be completed by TxDOT Austin District Environmental Section (if necessary):

ENV ID # __________________________ Environmental Specialist ___________________________

Notes

Review Complete ___________________

Email

Date

Per TXDOT policy, a migratory bird commitment and SW3P are required for all Donation Agreement projects. A CGP TXR150000 is only required for Donation Agreement projects with soil disturbance of one (1) acre or more. Details of these commitments, as well as any other commitments previous listed, will be provided in the Environmental Clearance Memo.

BARINGD

NOT APPLICABLE

Critical Habitat for Threatened & Endangered Species [USFWS]

Sources: Esri, TomTom, Garmin, FAO, NOAA, USGS, © OpenStreetMap contributors, and the GIS User Community

10/14/2025 0 0.15 0.30.07 mi

0 0.25 0.50.13 km

1:12,120

BARINGD

EWC WTP

$%&'()*&+,*-(..(&/)0+*102+3(4)*5&%)3*60+4)*&+,*7&.&/&+,4%*1%(3(8&.*9&:(3&3

?@ABCDEFGCDHEAIGIJIDHKL

A@LMINKENLCBOEPIFO

?@ABCDEFGCDHEAIGIJIDHKL

A@FA@LMINKENLCBOEPIFO

QRGGSTCGGKEUGIBKI@

AIGIJIDHKLEA@LMINKENLCBO

PIFO

QRGGSTCGGKEUGIBKI@

AIGIJIDHKLEA@FA@LMENLCBO

PIFO

VLITCAEWEXCGGCIJARDEYILAB

ZI@DIE[K\CRDA

VLITCAEWEXCGGCIJARD

]R@DBCKAEYILABÊRDKA

àabc

A5 A4

A3

B5 B4

B3

C

C

C

D

D

D

E5 E4

E3

J J

UP

BRAZOS RIVER AUTHORITY

EWCRWS TREATMENT PLANT EXPANSION

DESIGN SERVICES - PHASE 1D PROJECT

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

DW-EXBTXDOT DRIVEWAY EXHIBIT

N

XR

EF

s:

[C

D M

S_

, C

ST

W

P0

, 3 -0

TO

PO

, V

ST

W P1

, C

ST

W

P0

, C

YP

W P0

, M

W Z0

G

C -2

D C iv il

Ex po rt, M

W Z0

C

H

2D C

IV

IL

E

XP

O R

T, M

W Z0

BT

-2 D

C iv il Ex po rt, M W

Z0

C W

2D

C

IV

IL

E

XP

O

R T, M W

Z0

FL

2D C iv il

Ex po rt, C

ST

W

P1

, C

ST

W P3

, M

W Z0

C

T, M

W P0

U

W , G en er at or

, E

SW

P1

, S W

Z0

C 6A

, S W

Z0

FC

, S

W Z0

FM

, S W

Z0

C 6C

, S W

Z0

C 6D

, S W

Z0

C 6B

, A W

Z0

AB

_C

2D , A

W Z0

AB

_C 2D

, A W

Z0

AB

_C

2D , E xi st in g

Ba ck w as h To w er c on ne ct io n, R _M

W Z0

PS

, M W

Z0

R W

2D

C

IV

IL

E

XP

O

R T, E W

Z0

ST

, M

W Z0

PS

2D

C iv il Ex po rt, M W

Z0

PC

2D C iv il

Ex po rt, M

W Z0

M

C

2D C iv il

Ex po rt, S

W Z0

C

2D _S

H

AR

ED

D , S

W Z0

LA

_S H

AR

ED

D

, S W

Z0

LA

_S

H

AR

ED

D , S

W Z0

LA

_S H

AR

ED

D

, S W

Z0

LA

_S

H

AR

ED

D , S

W Z0

LA

_S H

AR

ED

D

, S W

Z0

LA

_S

H

AR

ED

D , M

W Z0

PS

2D

C iv il Ex po rt-

Fo r S ite P la n, M

SP

S

- E

LE

C

TR

IC

AL

D , T

SP

S

- E

LE

C

TR

IC

AL

D

, M W

Z0 0R

3A -2

D C iv il

Ex po rt, M

W Z0

0R 4A

-2 D

C iv il Ex po rt, M W

Z0 0C

4B -2

D C iv il

Ex po rt, M

W Z0

0C 5B

-2 D

C iv il Ex po rt, M W

Z0 0C

2D -2

D C iv il

Ex po rt, M

W Z0

0C 3B

-2 D

C iv il Ex po rt, S W

Z0

M B_

SH

AR

ED

D , A

W Z0

M

B_ C

2D , S

W Z0

EB

_S H

AR

ED

D

, S W

Z0

EB

_S

H

AR

ED

D , C

ST

W

P0

, P h

1D B

R A

EW

C

W

TP

-F ed er at ed M od el

3D

V ie w , R

_M W

Z0

G P-

2D C iv il

Ex po rt, R

_M W

Z0

G P-

2D C iv il

Ex po rt, R

_M W

Z0

G P-

2D C iv il

Ex po rt]

Im ag es

La st s av ed b y:

C

O

YL

EZ

T im e:

/1

6/

1:

:1

AM

C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -D

W -E

XB

.d w g

PLAN

PLAN

PROFILE

N

ISSUED FOR DRIVEWAY PERMIT

A5 A4

A3 A2

A1

B5 B4

B3 B2

B1

C

C

C

C

C

D

D

D

D

D

E5 E4

E3 E2

E1

J J

UP

BRAZOS RIVER AUTHORITY

EWCRWS TREATMENT PLANT EXPANSION

DESIGN SERVICES - PHASE 1D PROJECT

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

CUL-EXB-1TXDOT CULVERT EXHIBIT PLAN & PROFILE

La st s av ed b y:

C

O

YL

EZ

T im e:

/1

6/

0:

:3

AM

C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -C

U L-

EX

B.

dw g

PLAN PLAN

PROFILE

N N

La st s av ed b y:

C

O

YL

EZ

T im e:

/1

6/

:1 5:

A

M C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -C

U L-

EX

B.

dw g

BRAZOS RIVER AUTHORITY

EWCRWS TREATMENT PLANT EXPANSION

DESIGN SERVICES - PHASE 1D PROJECT

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

CUL-EXB-2TXDOT CULVERT EXHIBIT SECTION & DETAIL

SECTION 1

SECTION 2

s av ed b y:

C

O

YL

EZ

T im e:

/1

5/

:0 9:

A

M C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -C

U L-

EX

B.

dw g

BRAZOS RIVER AUTHORITY

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

CUL-EXB-3TXDOT CULVERT DETAILS I

s av ed b y:

C

O

YL

EZ

T im e:

/1

5/

:0 9:

A

M C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -C

U L-

EX

B.

dw g

BRAZOS RIVER AUTHORITY

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

CUL-EXB-4TXDOT CULVERT DETAILS II

s av ed b y:

C

O

YL

EZ

T im e:

/1

5/

:0 9:

A

M C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -C

U L-

EX

B.

dw g

BRAZOS RIVER AUTHORITY

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

CUL-EXB-5TXDOT CULVERT DETAILS III

s av ed b y:

C

O

YL

EZ

T im e:

/1

5/

:0 9:

A

M C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -C

U L-

EX

B.

dw g

BRAZOS RIVER AUTHORITY

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

CUL-EXB-6TXDOT CULVERT DETAILS IV

H

(Typ) 1"

Longitudinal reinforcing

AS1

H

AS4

S

1"

M

(Typ)

FILL HEIGHT 2 FT AND GREATER

CORNER OPTION "B"CORNER OPTION "A"

4" Min

2"

AS5

S

1" Max

AS7

(Typ) 1"

AS4

noted otherwise) 1" (Typ unless

AS2

AS8

AS3

AS1

FILL HEIGHT LESS THAN 2 FT

CORNER OPTION "B"CORNER OPTION "A"

6" Min 2" Max (Typ)

1" 1"

2" Min (Typ)

A A

TS

TS

TB

TT

TS TS

A A

TS

TT

TB

TS

TS

4d Min radius (Typ)

TS

for TS ≤ 5" for TS ≥ 6"

SECTION A-A

1 12" Max for TS ≤ 5"

4" Min for TS ≥ 6"

36 0.20

MATERIAL NOTES:

GENERAL NOTES:

(Showing top and bottom slab joint reinforcement.)

Outer cage circumferential reinforcement at groove end.

Provide 0.03 sq. in./ft. minimum longitudinal reinforcement at each face in slabs and walls. This minimum requirement may be met by the transverse wires when wire mesh reinforcement is used.

Provide Class H concrete (f`c = 5,000 psi).

Designs shown conform to ASTM C1577. Refer to ASTM C1577 for information or details not shown.

See Box Culverts Precast Miscellaneous Details (SCP-MD) standard sheet for details and notes not shown.

In lieu of furnishing the designs shown on this sheet, the contractor may furnish an alternate design that is equal to or exceeds the box design for the design fill height in the table. Submit shop plans for alternate designs in accordance with Item "Precast Concrete Structural Members (Fabrication)."

AS2 (top) AS3 (bottom)

AS2 (top) AS3 (bottom)

Longitudinal reinforcement

AS2 (top) AS3 (bottom) AS4 (side)

Minimum length is equal to spacing of longitudinal reinforcing plus 2" (Typ)

2" Max radius (Typ)

4d Min radius (Typ)

Length is equal to spacing of longitudinal reinforcing plus 2". (10" Min) (Typ)

2" Max radius (Typ)

For box length = 8'-0"

AS1 thru AS4, AS7 and AS8 are minimum required areas of reinforcement per linear foot of box length. AS5 is minimum required area of reinforcement per linear foot of box width.

BOX DATA

SECTION DIMENSIONS

Fill M Lift

S H TT TB TS Height (Min)

AS1 AS2 AS3 AS4 AS5 AS7 AS8

Weight

(ft.) (ft.) (in.) (in.) (in.) (ft.) (in.) (tons)

5 2 8 7 6 < 2 - 0.19 0.27 0.18 0.14 0.19 0.19 0.17 6.0

5 2 6 6 6 2 < 3 0.22 0.20 0.16 0.14 - - - 5.1

5 2 6 6 6 3 - 5 0.16 0.14 0.14 0.14 - - - 5.1

5 2 6 6 6 10 0.15 0.14 0.14 0.14 - - - 5.1

5 2 6 6 6 15 0.18 0.18 0.14 - - - 5.1

5 2 6 6 6 20 0.26 0.23 0.24 0.14 - - - 5.1

5 2 6 6 6 25 0.33 0.29 0.29 0.14 - - - 5.1

5 2 6 6 6 30 0.39 0.34 0.35 0.14 - - - 5.1

5 3 8 7 6 < 2 - 0.19 0.31 0.21 0.14 0.19 0.19 0.17 6.6

5 3 6 6 6 2 < 3 45 0.18 0.24 0.19 0.14 - - - 5.7

5 3 6 6 6 3 - 5 36 0.14 0.17 0.16 0.14 - - - 5.7

5 3 6 6 6 10 36 0.14 0.16 0.17 0.14 - - - 5.7

5 3 6 6 6 15 35 0.16 0.21 0.22 0.14 - - - 5.7

5 3 6 6 6 20 35 0.21 0.27 0.28 0.14 - - - 5.7

5 3 6 6 6 25 35 0.26 0.34 0.34 0.14 - - - 5.7

5 3 6 6 6 30 35 0.31 0.41 0.41 0.14 - - - 5.7

5 4 8 7 6 < 2 - 0.19 0.33 0.24 0.14 0.19 0.19 0.17 7.2

5 4 6 6 6 2 < 3 45 0.16 0.27 0.22 0.14 - - - 6.3

5 4 6 6 6 3 - 5 45 0.14 0.19 0.18 0.14 - - - 6.3

5 4 6 6 6 10 36 0.14 0.18 0.18 0.14 - - - 6.3

5 4 6 6 6 15 35 0.14 0.23 0.24 0.14 - - - 6.3

5 4 6 6 6 20 35 0.17 0.30 0.31 0.14 - - - 6.3

5 4 6 6 6 25 35 0.21 0.37 0.38 0.14 - - - 6.3

5 4 6 6 6 30 35 0.25 0.44 0.45 0.14 - - - 6.3

5 5 8 7 6 < 2 - 0.19 0.35 0.26 0.14 0.19 0.19 0.17 7.8

5 5 6 6 6 2 < 3 45 0.14 0.29 0.24 0.14 - - - 6.9

5 5 6 6 6 3 - 5 45 0.14 0.21 0.20 0.14 - - - 6.9

5 5 6 6 6 10 45 0.14 0.19 0.20 0.14 - - - 6.9

5 5 6 6 6 15 36 0.14 0.24 0.25 0.14 - - - 6.9

5 5 6 6 6 20 35 0.15 0.31 0.32 0.14 - - - 6.9

5 5 6 6 6 25 35 0.18 0.38 0.39 0.14 - - - 6.9

5 5 6 6 6 30 35 0.21 0.46 0.47 0.14 - - - 6.9

REINFORCING (sq. in. / ft.)

A5 A4

A3 A2

A1

B5 B4

B3 B2

B1

C

C

C

C

C

D

D

D

D

D

E5 E4

E3 E2

E1

J J

UP

BRAZOS RIVER AUTHORITY

EWCRWS TREATMENT PLANT EXPANSION

DESIGN SERVICES - PHASE 1D PROJECT

TBPELS Firm Registration No. F-3043

8310-1 N. Capital of Texas Highway, Suite 250 Austin, TX 78731 Tel: (512) 346-1100 RFP NO. 26-1392

OUT-EXBTXDOT POND OUTFALL EXHIBIT

XR

EF

s:

[C

D M

S_

, C

ST

W

P0

, 3 -0

TO

PO

, V

ST

W P1

, C

ST

W

P0

, C

YP

W P0

, M

W Z0

G

C -2

D C iv il

Ex po rt, M

W Z0

C

H

2D C

IV

IL

E

XP

O R

T, M

W Z0

BT

-2 D

C iv il Ex po rt, M W

Z0

C W

2D

C

IV

IL

E

XP

O

R T, M W

Z0

FL

2D C iv il

Ex po rt, C

ST

W

P1

, C

ST

W P3

, M

W Z0

C

T, M

W P0

U

W , G en er at or

, E

SW

P1

, S W

Z0

C 6A

, S W

Z0

FC

, S

W Z0

FM

, S W

Z0

C 6C

, S W

Z0

C 6D

, S W

Z0

C 6B

, A W

Z0

AB

_C

2D , A

W Z0

AB

_C 2D

, A W

Z0

AB

_C

2D , E xi st in g

Ba ck w as h To w er c on ne ct io n, R _M

W Z0

PS

, M W

Z0

R W

2D

C

IV

IL

E

XP

O

R T, E W

Z0

ST

, M

W Z0

PS

2D

C iv il Ex po rt, M W

Z0

PC

2D C iv il

Ex po rt, M

W Z0

M

C

2D C iv il

Ex po rt, S

W Z0

C

2D _S

H

AR

ED

D , S

W Z0

LA

_S H

AR

ED

D

, S W

Z0

LA

_S

H

AR

ED

D , S

W Z0

LA

_S H

AR

ED

D

, S W

Z0

LA

_S

H

AR

ED

D , S

W Z0

LA

_S H

AR

ED

D

, S W

Z0

LA

_S

H

AR

ED

D , M

W Z0

PS

2D

C iv il Ex po rt-

Fo r S ite P la n, M

SP

S

- E

LE

C

TR

IC

AL

D , T

SP

S

- E

LE

C

TR

IC

AL

D

, M W

Z0 0R

3A -2

D C iv il

Ex po rt, M

W Z0

0R 4A

-2 D

C iv il Ex po rt, M W

Z0 0C

4B -2

D C iv il

Ex po rt, M

W Z0

0C 5B

-2 D

C iv il Ex po rt, M W

Z0 0C

2D -2

D C iv il

Ex po rt, M

W Z0

0C 3B

-2 D

C iv il Ex po rt, S W

Z0

M B_

SH

AR

ED

D , A

W Z0

M

B_ C

2D , S

W Z0

EB

_S H

AR

ED

D

, S W

Z0

EB

_S

H

AR

ED

D , C

G -2

0, C

X- 5, P h

1D B

R A

EW

C

W

TP

-F ed er at ed M od el

3D

V ie w , R

_M W

Z0

G P-

2D C iv il

Ex po rt, R

_M W

Z0

G P-

2D C iv il

Ex po rt, R

_M W

Z0

G P-

2D C iv il

Ex po rt]

Im ag es

La st s av ed b y:

C

O

YL

EZ

T im e:

/1

4/

0:

:3

AM

C

:\U se rs \c oy le z\ D

C \A

C C

D oc s\ C

D M

S m ith In c\ Ph

D

B R

A

EW

C W

TP

E xp an si on

D es ig n\

Pr oj ec t F ile s\

C iv il\

C

AD

D

\C -O

U T-

EX

B.

dw g

PLAN

PLAN PROFILE

N

N

DETAIL A DETAIL B

INSERT CLIENT NAME OR LOGO HERE

REPORT

JUNE 2026

Drainage Report

Prepared for:

Brazos River Authority

East Williamson County Water Treatment Plant Expansion

Contents

1.0 Project Description

2.0 Hydrology

2.1 Modeling Methodology

2.2 Analysis Points

2.3 Hydrologic Soil Groups

2.4 Impervious Cover

2.5 Basins

2.6 Curve Numbers

2.7 Flow Paths

2.8 Precipitation

2.9 Hydrologic Modeling Results

3.0 Hydraulics

3.1 Modeling Methodology

3.2 Storage Areas

3.3 Hydraulic Modeling Results

3.3.1 Stormwater Piping System

3.3.2 Area Inlet Analysis

3.3.3 Analysis Points

4.0 Appendices

A.1.1 Existing Conditions

A.1.2 Phase 1B

A.1.3 Phase 1D

A.1.4 Ultimate Buildout

A.2.1 Existing Conditions

A.2.2 Phase 1B

A.2.3 Phase 1D

A.2.4 Ultimate Buildout

A.3.1 Phase 1B

A.3.1 Phase 1D

B.1.1 Existing Conditions

B.1.2 Phase 1B

B.1.3 Phase 1D

B.1.4 Ultimate Buildout

1.0 Project Description

A comprehensive drainage plan was developed for Phase 1B, Phase 1D, and the Ultimate Phase of the

Brazos River Authority – East Williamson County Regional Water System (EWCRWS) Expansion Project.

To verify that the proposed improvements would not increase peak flows beyond existing conditions, a detailed drainage analysis and PCSWMM model were prepared for each phase.

To manage runoff and mitigate both on-site and off-site ponding, stormwater infrastructure was designed for Phases 1B and 1D. These improvements include a conveyance system and two dedicated storage areas, designed to capture and convey the 100-year, 24-hr design storm event without ponding.

Additionally, the 500-year, 24-hr design storm was evaluated at critical locations to ensure protection of adjacent infrastructure and reduce flood risk.

This study evaluates the hydrologic and hydraulic performance of the site and its contributing watershed, encompassing a total drainage area of 142.7 acres, including 85.6 acres within the property limits. The analysis supports phased development planning and ensures compliance with drainage standards. See Figure 1.1. for the property location and full drainage study limits included in the calculations.

Figure 1.1 Drainage Study Limits

The analysis incorporates detailed site data, including proposed grading plans, sub-basin delineations, storm pipe layouts, and stage-storage curves. The drainage study was done in accordance with the

Williamson County Subdivision Regulations which requires the City of Austin Drainage Criteria Manual to be used for drainage calculations and design.

2.0 Hydrology

2.1 Modeling Methodology

A PCSWMM model was developed for existing conditions and each design phase to compute peak runoff within the drainage study limits. Methodology includes watershed delineation and sub-basin information and geometry, the hyetograph distribution, the calculated time of concentration, and the

Soil Conservation Service (SCS) Curve Number (CN) method for losses. Sub-basin information and geometry includes area, slope, percent impervious, width, and infiltration parameters. A 24-hour rainfall distribution was developed in HEC-HMS using the Williamson County rainfall intensity-duration-frequency. The runoff rate of each sub-basin was computed using these parameters for each timestep over a 30-hour model run. The methodology for each model parameter is outlined in following sections.

Hydrologic model results were used to size the proposed infrastructure.

2.2 Analysis Points

The main objective of the drainage plan is to ensure that post construction conditions do not result in an increase in peak flows from existing conditions. To confirm this, nine analysis point were chosen at various locations on the site. These points were chosen based on the locations of proposed site improvements and locations where flow runs offsite. Figure 2.1. presents the locations of the analysis points.

Figure 2.1 Analysis Points

The analysis points allow a comparison of existing condition peak flows to proposed conditions peak flows in locations where the drainage conditions are being changed or where flow is exiting the site. The following is a summary of the analysis points. Drainage areas referenced can be found in Appendix B.

▬ AP 1

In existing conditions, overland flow from existing drainage area (NW1) leaves the project property and discharges into the U.S. Army Corps of Engineers property containing Lake

Granger. In Phase 1B, this location is designed as a storage area with a weir overflow structure.

Phase 1B infrastructure directs flow from additional drainage areas (A1, A2, A3, A4, A5, A6, A7, A8, NW1) to this storage area. Phase 1D includes additional infrastructure to direct flow to this location, with additional drainage areas (A9, A10, A11, A12). This point analyses the flow leaving the site at each phase and is modeled as an outfall location.

▬ AP 2

In existing conditions overland flow from drainage area (NW2) leaves the project property through an existing offsite 42” RCP culvert across a private road on the northeast side of the site. No additional overland flow is contributed to this point in proposed conditions. This point is modeled as an outfall location.

▬ AP 3

In existing conditions overland flow from drainage area (B1) is directed through two existing on-site 18” RCP culverts flowing to the south end of the site. Runoff is routed through drainage areas (B3 and SR4) where it leaves the property.

▬ AP 4

In existing conditions overland flow from drainage areas (A1 and A2) is directed through an existing 18- inch RCP culvert which ultimately flows into the southern roadside ditch along FM

1331 and offsite. In Phase 1B, this culvert is removed and flow from contributing basins is direct though proposed storm infrastructure to the proposed storage area in the northwest corner of the site.

▬ AP 5

In existing conditions overland flow from drainage basins (W1 and W2) is directed through an existing 27-inch ellipticals RCP culvert which ultimately flows into the southern roadside ditch along FM 1331 and offsite. In Phase 1D, a new driveway will be proposed at this location along with a new culvert.

▬ AP 6

In existing conditions, overland flow from drainage basins (A1, A2, A3, W1, W2, B1, B2, B3) is directed to this location where ponding occurs. In proposed design phases flow is directed away from this location and a storage area is designed to control ponding away from essential infrastructure. In existing conditions this analysis point represents the flow at the location of ponding, and in proposed conditions this point represents the outflow of the designed storage area.

▬ AP 7

In existing conditions, a roadside swale along FM 1331 directs both on-site and off-site flow to a

36-inch culvert across the road, including drainage basins (A1, A2, A3, W1, W2, B1, B2, B3). This point represents the flow crossing FM 1331 and leaving the site and is modeled as an outfall location.

▬ AP 8

In existing conditions, a 30-inch culvert on the southeast corner of the site directs flow from AP

6 under Road 496 offsite. This point represents the flow crossing Road 496 and leaving the site

▬ AP 9

In existing conditions, a roadside swale along FM 1331 directs both on-site and off-site flow to a

36-inch culvert across the road, including drainage basins (A1, A2, A3, W1, W2, B1, B2, B3). In proposed conditions, a large amount of flow is directed away from the roadside ditch, while some overland flow from basins (B7 and B8) is directed into the swale. This point represents the flow in the roadside ditch.

2.3 Hydrologic Soil Groups

The “Drainage Study Limits” polygon was used to extract soil data for the site from the NRCS Web soil survey site. The project area hydrologic soil group (HSG) extents are shown below in Figure 2.2, with most HSG being Type D with a small area of Type C in the northeast corner of the property.

Figure 2.2 Hydrologic Soil Groups

2.4 Impervious Cover

The impervious cover was determined for existing and proposed conditions. The existing site conditions were determined from survey for on-site areas. Existing lagoons and the raw water reservoir were not included in the drainage area or impervious area calculation as they will not net runoff. The proposed impervious cover was calculated based on the design layout as of August 2025. Proposed impervious areas include the addition of roads and pipe chases and other building facilities, including electrical buildings, pump stations, and the chemical facility. The impervious layer for the Ultimate Buildout was started from the 1D proposed impervious area and additional elements were added based on the proposed site plan submitted in the PER. This will continue to be developed in future design phases and is subject to change. The locations of the impervious surfaces and types can be seen in Appendix B-1 for each phase. Based on the total contributing drainage area, the impervious cover percentage for each

Phase is available in Table 2.1. A decrease in contributing drainage area is seen in each phase as additional lagoons, clearwells, and open filters are proposed that will capture precipitation and not produce runoff.

Table 2.1 Impervious Area Calculation

Phase Total Contributing Area

(Acres) Impervious Area (Acres) Impervious %

Existing 142.7 10.3 7.2%

Phase 1B 142.7 11.3 7.9%

Phase 1D 138.5 16.9 12.3%

Full Buildout 135.5 20.3 15.2%

2.5 Basins

By using a combination of the proposed grading of the site, survey of existing conditions, and LiDAR topography for off-property locations, basins were delineated across the site to each main outfall location. The basins were further delineated into sub-basins to calculate the peak runoff and volume of each area, inflow to proposed inlets, peak water surface elevations at any location of ponding, and the changes between each design phase. The sub-basins delineated for existing conditions, and each subsequent design phase, 1B and 1D, and Ultimate Buildout are available in Appendix B-1.

2.6 Curve Numbers

The HSG, sub-basins, and impervious shapefiles were used to create an overlay layer, which defined the runoff conditions for each area, and a curve number was calculated for each sub-basin. Pervious areas, both existing and proposed conditions, were characterized as “Bush – brush-weed-grass mixture with brush the major element” or “Straight Row Crops”, and all impervious areas were described as “paved parking lots, roofs, driveways”, or “gravel” per TR-55 table 2-2b and 2-2a. This classification was chosen based on National Land Cover Database (NLCD). The area of each land type per basin was calculated in

GIS and multiplied by the CN for the corresponding soil type. The summation of the Land Type X CN for the entire basin was then divided by the area of the basin to give a calculated CN for each basin.

Appendix A-1 contains the calculated CN numbers for each basin in each design phase.

2.7 Flow Paths

The longest flow path for each sub-basin were traced for existing conditions and each subsequent design phase. The flow paths were used as an input to the SWMM model, using both the length and slope to calculate runoff. Slopes were estimated based on the proposed grading, site survey, and LiDAR topography. Using the flow paths, slopes, and land type, a time of concentration was calculated for each basin using the velocity method outlined in the USDA’s Technical Release 55 “Urban Hydrology for Small

Watersheds” (1986) partitioned in sheet flow, shallow concentrated flow, and channel flow regimes.

Although the Williamson County Drainage Criteria specifies a minimum time of concentration of 10 minutes, a more conservative value of 5 minutes was used in accordance with the City of Austin

Drainage Criteria Manual. Time of concentration calculations for each design phase are in Appendix A-2.

2.8 Precipitation

The rainfall intensity-duration-frequency (IDFs) from Williamson County, shown in Table 2.2, were used to create the hyetograph distribution for the 5-, 10-, 25-, 50-, 100-, 200-, and 500-year, 24-hour storms evaluated. Cumulative point precipitation depths of 5.15, 6.3, 8.04, 9.53, 11.2, 16.1 inches were used for the 5-, 10-, 25-, 50-, 100-, 200-, and 500-year distribution storms, respectively. These depths were input into HEC-HMS to create the 24-hr rainfall distribution. These hyetographs were input as a time-series in the PCSWMM model and are presented in Figure 2.3.

Table 2.2 Williamson County Depth-Duration-Frequency Values

Figure 2.3 HEC-HMS 24-Hour Frequency Storms

2.9 Hydrologic Modeling Results

Peak Runoff was calculated for each sub-basin with the SCS Dimensionless Unit Hydrograph (UH)

Method in PCSWMM using input parameters as described in previous sections. Results are summarized in Tables 2.3 – 2.6 and are available in Appendix B.

0:00 4:48 9:36 14:24 19:12 0:00 4:48

C u m u la ti v e

P re ci p it a ti o n in

Time (hr:mm)

5-yr, 24-hr 10-yr, 24-hr 25-yr, 24-hr 50-yr, 24-hr

100-yr, 24-hr 200-yr, 24-hr 500-yr, 24-hr

Table 2.3 Existing Peak Runoff

Basin 25-yr, 24-hr 100-yr, 24-hr 500-yr, 24-hr

A1 40.0 57.2 79.2

A2 54.0 75.0 101.7

A3 40.3 57.1 78.7

B1 19.7 26.9 35.9

B2 22.9 31.0 41.5

B3 41.8 59.1 81.2

E1 94.4 135.0 189.0

NW1 83.0 120.6 169.8

NW2 65.9 95.2 133.6

SR1 6.6 9.3 12.6

SR2 1.9 2.7 3.7

SR3 2.1 3.0 4.2

SR4 6.1 8.8 12.4

SR5 8.0 11.2 15.3

W1 117.5 169.5 238.1

W2 48.5 68.5 94.6

W3 31.7 45.1 62.2

Table 2.4 Phase 1B Peak Runoff

A1 29.2 42.5 59.6

A2 19.6 26.8 35.8

A3 2.7 3.6 4.6

A4 19.5 27.3 37.2

A5 8.8 11.6 15.1

A6 14.8 20.2 27.0

A7 20.4 29.3 40.8

A8 29.4 41.2 56.3

B1 6.9 9.6 12.9

B2 10.3 13.9 18.5

B3 5.1 6.8 9.1

B4 29.6 40.0 53.3

B5 45.5 64.1 87.7

B6 41.8 59.0 81.0

E1 94.4 135.0 189.0

NW1 83.0 120.6 169.9

NW2 65.7 95.0 133.5

SR1 6.6 9.3 12.6

SR2 1.9 2.7 3.7

SR3 2.1 3.0 4.2

SR4 6.1 8.8 12.4

SR5 8.0 11.2 15.3

W1 117.5 169.5 238.1

W2 24.5 34.8 48.4

W3 4.6 6.3 8.5

Table 2.5 Phase 1D Peak Runoff

A1 36.6 52.7 73.7

A10 14.5 19.5 25.7

A11 14.9 19.8 25.9

A12 4.6 6.2 8.2

A13 19.5 25.7 33.7

A14 2.0 2.7 3.7

A2 9.6 13.0 17.4

A3 0.9 1.2 1.6

A4 6.7 8.8 11.4

A6 2.7 3.8 5.2

A7 14.5 19.7 26.2

A8 5.5 7.6 10.3

A9 8.2 10.8 14.1

B1 5.2 7.2 9.7

B10 15.8 21.4 28.5

B11 9.5 13.0 17.6

B2 10.0 13.5 17.9

B3 5.0 6.8 9.1

B4 29.8 40.2 53.5

B5 11.5 15.8 21.3

B6 17.0 23.3 31.4

B7 12.6 16.4 21.4

B8 19.5 27.9 38.6

B9 5.9 7.9 10.4

E1 74.7 106.7 151.0

NW1 56.9 82.5 117.4

NW2 44.1 63.8 91.1

SR1 6.9 9.7 13.2

SR2 1.4 2.0 2.7

SR3 1.7 2.5 3.4

SR4 5.6 8.1 11.3

SR5 6.0 8.3 11.4

W1 114.7 165.4 232.3

W2 28.2 37.8 50.0

W3 3.4 4.6 6.1

Table 2.6 Ultimate Peak Runoff

A1 19.1 26.8 36.8

A10 15.5 20.3 26.3

A11 15.2 20.0 26.1

A12 5.1 6.6 8.5

A13 16.8 22.3 29.3

A14 3.7 4.9 6.5

A2 9.8 13.2 17.5

A3 0.9 1.2 1.6

A4 6.7 8.8 11.4

A6 5.7 7.5 9.8

A7 14.2 19.4 25.9

A8 5.5 7.6 10.3

A9 8.2 10.8 14.1

B1 5.2 7.2 9.7

B10 9.7 13.1 17.5

B11 9.4 13.0 17.5

B12 11.0 15.6 21.3

B13 3.0 3.9 5.0

B2 10.0 13.6 18.0

B3 5.0 6.8 9.1

B4 29.9 40.2 53.5

B5 11.5 15.8 21.3

B6 20.2 26.9 35.5

B7 13.0 17.0 22.3

B8 16.8 22.0 28.6

B9 9.4 12.7 17.0

E1 74.7 106.7 151.0

NW1 54.4 78.8 112.2

NW2 43.5 62.9 89.9

SR1 6.9 9.7 13.2

SR2 1.4 2.0 2.7

SR3 1.7 2.5 3.4

SR4 5.6 8.1 11.3

SR5 6.0 8.3 11.4

W1 114.7 165.4 232.3

W2 25.4 33.5 43.6

3.0 Hydraulics

3.1 Modeling Methodology

The PCSWMM model was used for the hydraulic analysis to confirm storm system sizing, evaluate designed storage areas, and analyze flow leaving the site. Runoff calculated in Section 2.0 was routed from each sub-basin to the hydraulic network. The models were run for 30-hours with the dynamic wave routing approach using a 0.1 minute time-step to ensure the peak runoff has been routed through the area and achieve numerical stability.

3.2 Storage Areas

Two storage areas were incorporated into the drainage modeling for Phases 1B and 1D. In Phases 1B, an existing pond was engineered as the outlet to the conveyance system, where flow is managed via an outlet structure and weir. In Phase 1D, a new storage area was proposed in the Southeast corner of the site, where flow can be slowly released via a 15” RCP outlet structure. Stage-storage curves were used to represent both proposed storage areas within the PCSWMM model. These stage-storage tables were developed based on the proposed grading plans for each respective design phase. These curves were input as depth-area curves in PCSWMM. The corresponding stage-storage curves used in the analysis are provided in Appendix A-3.

3.3 Hydraulic Modeling Results

3.3.1 Stormwater Piping System

The stormwater piping proposed in Phases 1B and 1D was sized for the 100-YR storm. The results in

Phase 1D for all storm piping are in Tables 3.1 and 3.2.

Table 3.1 Phase 1D Proposed Piping

Start End Diameter

(IN)

Slope (%) Q100 (CFS) V100 (FPS) D100 (FT)

Storm Drain A

STA 0 + 30 STA 0 + 42 24 0.5 71.0 10.1 Full

STA 0 + 42 STA 4 + 07 18 0.7 20.3 6.8 Full

STA 4 + 07 STA 5 + 30 18 0.5 9.7 5.8 Full

STA 5 + 30 STA 5 + 85 18 0.5 8.7 11.1 Full

Storm Drain Lat A3

STA 4 + 07 STA 1 + 04 18 0.5 13.0 7.5 0.63

Storm Drain Lat A4

STA 5 + 23 SA 0 + 23 18 0.5 1.2 0.7 Full

Storm Drain Lat A1

STA 0 + 42 STA 0 + 72 30 1.6 52.4 11.7 0.344

Storm Drain Lat A2

STA 0 + 42 STA 0 + 51 18 0.5 3.8 3.9 0.37

Storm Drain B

STA 0 + 30 STA 1 + 25 24 1.8 7.2 4.0 Full

STA 1 + 25 STA 3 + 19 24 1.1 7.6 4.3 Full

Storm Drain D

STA 0 + 30 STA 0+ 78 24 1.8 18.6 5.9 Full

STA 0 + 78 STA 2 + 59 24 4.4 19.4 12.0 0.37

Pond Outfall

STA 0 + 15 STA 0 + 83 15 2.4 9.8 8.0 Full

Table 3.2 Phase 1B Proposed Piping

Start End Diameter (IN) Slope (%) Q100

(CFS)

V100

(FPS)

D100 (FT)

Storm Drain 1

STA 1 + 00 STA 16 + 04 60 0.3 140.3 7.0 Full

STA 16 + 04 STA 19 + 81 48 0.3 80.7 6.6 Full

STA 19 + 81 STA 21 + 30 48 0.3 45.9 3.7 Full

STA 21 + 30 STA 22 + 67 42 0.3 41.0 4.4 Full

Storm Drain Lat C3

STA 1 + 00 STA 1 +34 18 1.0 25.7 14.5 Full

Storm Drain Lat C4

STA 1 + 00 STA 1 + 56 24 0.5 19.3 6.2 Full

Storm Drain Lat F1

STA 1 + 00 STA 1+39 18 0.5 19.6 11.1 Full

Storm Drain Lat F2

STA 1 + 00 STA 1 + 34 36 0.3 6.1 3.8 Full

Storm Drain SD-E

1 + 00 1+ 45 42 0.3 29.5 3.4 Full

Start End Diameter (IN) Slope (%) Q100

(CFS)

V100

(FPS)

D100 (FT)

1+ 45 1 + 72 42 0.3 17.5 4.5 Full

5 + 46 6 + 07 42 0.3 12.8 7.4 Full

Pond Outfall

STA 1 + 00 STA 2 + 13 15 0.2 16.2 13.2 Full

3.3.2 Area Inlet Analysis

The Area Inlets were designed to convey the 100-YR Storm using the PCSWM modeling results. The inlets were checked for locations of ponding due to backwater and that peak flows from the drainage basins have the capacity to pass through inlet openings without creating ponding. Calculations were completed for each inlet. Using the 100 -YR Peak Flow to each inlet, the inlets were sized to convey that capacity. The 100-YR and 500-YR WSE at each inlet were also analyzed to ensure ponding is mitigated and to be below finished floor elevation of adjacent essential infrastructure. This analysis is seen in

Tables 3.3 and 3.4.

Table 3.3 1D Inlets

Area

Inlet

100-

YR

WSE

500-

YR

WSE

Top of

Inlet Grading

Nearby infrastructure

Evaluated Elevation of

Nearby Infrastructure

(FT)

Clearance from 100-yr WSE to

Evaluated Elevation

(FT)

Clearance from 500-yr WSE to

Evaluated Elevation

(FT)

Clearance from 500-yr WSE to

Evaluated Elevation

(IN)

A6 575.3 575.4 577 Inlet Grading 577 1.7 1.6 19.0

A5 576.1 576.1 577 Inlet Grading 577.25 1.2 1.2 14.0

A4 575.4 575.8 576 Electrical

Building - FFE

577.25 1.8 1.5 18.0

A1 574.1 575.1 576 Edge of Road 576.3 2.2 1.2 14.0

A2 575.2 575.2 576 Edge of Road 577.1 1.9 1.9 22.4

B1 574.3 574.4 575 Inlet Grading 576 1.7 1.6 19.4

D1 574.6 575.1 575 Filter building 576.66 2.1 1.6 18.6

Table 3.4 1B Inlets

Area Inlet

100-

YR

WSE

500-

YR

WSE

Top of Inlet

Grading

Nearby infrastructure

Evaluated Elevation of

Nearby Infrastructure

(FT)

Clearance from 100-yr WSE to Evaluated Elevation

(FT)

Clearance from 500-yr WSE to Evaluated Elevation

(FT)

Clearance from 500-yr WSE to Evaluated Elevation

(IN)

1 576.7 576.7 577 Edge of Road 578 1.3 1.3 15.4

2 574.6 575.8 577 Edge of Road 578 3.4 2.2 26.7

3 574.6 574.7 576

Generator and

Fuel Storage -

FFE

576.5 1.9 1.8 21.7

4 572.2 572.3 575 Edge of Road 576.24 4.0 4.0 47.6

5 573.4 573.4 575 Pump station -

FFE

575.85 2.5 2.4 29.2

3.3.3 Discharge Analysis

As described in Section 2.2, nine analysis points were used to evaluate the change in peak flows discharging offsite from existing to proposed conditions. Tables 3.5 and 3.6 below compare peak flows from existing to Phase 1D and Ultimate conditions, respectively. All analysis points show a decrease in peak flow from existing conditions except for AP1.

As discussed previously, AP1 is located where flow discharges the northeast corner of the site into the

U.S. Army Corps of Engineers property containing Lake Granger. Lake Granger is a regional reservoir along the San Gabriel River that has a contributing drainage area of approximately 709 square miles. The change in drainage area contributing to Lake Granger from the site from existing to proposed conditions is 21.7 acres, resulting in a 0.005% increase in the contributing drainage area of Lake Granger. This constitutes an insignificant increase and therefore the analysis point was not evaluated on the basis of peak flow, but on flow velocity and erosion mitigation at the discharge point. Pond outlet structures, energy dissipators, and riprap aprons were designed to ensure discharging flows did not exceed erosive velocities. Tables 3.7 and 3.8 compare the inflow and outflow pond volumes at AP 1 in each design phase. Table 3.9 presents the full site percent change in peak flow from existing to prosed conditions.

Table 3.5 Comparison of Proposed to Existing Flows at Analysis Points – 100 Year, 25 Hour Storm

Analysis Point Location Existing (CFS) 1D (CFS) Ultimate

(CFS)

Δ

AP 1

Northwest Storage Outlet

Pond to Lake Granger, Discharge point for proposed stormwater conveyance system

44.3 184.7 160.68 140.4

AP 2

Northeast Existing Off-site 42"

Culvert

94.6 63.8 62.92 -30.9

AP3 Existing 18" On-site culvert 25.9 17.4 17.37 -8.5

AP 4 Existing On-site 18" culvert 113.2 23.3 26.91 -90.0

AP 5

Existing On-site culvert, Proposed 5' X 2' RBC under driveway to FM 1331

226.5 171.7 172.94 -54.8

AP 6

Proposed Southeast Storage

Pond Outflow

426.8 27.4 23.23 -399.4

AP 7

Existing 30" culvert under

Road 496 Outflow East

286.7 131.3 134.83 -155.5

AP 8

Existing 36" culvert under FM

1331 Outflow South

74.4 53.2 53.07 -21.3

AP 9

Roadside ditch along FM

1331, Outflow east to existing

36" Culvert

355.7 196.3 199.82 -159.4

Table 3.6 Comparison of Proposed to Existing Flows at Analysis Points – 500 Year, 25 Hour Storm

Analysis Point Location Existing (CFS) 1D (CFS) Ultimate

(CFS)

Δ

AP 1

Northwest Storage Outlet

Pond to Lake Granger, Discharge point for proposed stormwater conveyance system

118.5 273.0 247.4 128.9

AP 2

Northeast Existing Off-site 42"

Culvert

130.6 91.0 89.8 -40.7

AP3 Existing 18" On-site culvert 35.6 23.9 23.9 -11.6

AP 4 Existing On-site 18" culvert 249.0 31.4 35.4 -213.7

AP 5

Existing On-site culvert, Proposed 5' X 2' RBC under driveway to FM 1331

309.4 242.1 243.3 -66.1

AP 6

Proposed Southeast Storage

Pond Outflow

598.3 78.8 68.8 -529.4

AP 7

Existing 30" culvert under

Road 496 Outflow East

372.4 268.1 272.1 -100.3

AP 8

Existing 36" culvert under FM

1331 Outflow South

79.5 57.4 57.2 -22.3

AP 9

Roadside ditch along FM

1331, Outflow east to existing

36" Culvert

497.6 276.8 280.7 -216.9

Table 3.7 AP 1 Pond Volume

Phase 100-YR 25-YR 10-YR 5-YR 2-YR

Existing

Inflow 501,400 314,500 218,300 156,800 96,200

Outflow 311,400 118,100 1,769 0 0

Phase 1B

Inflow 1,328,920 852,100 604,000 417,300 268,600

Outflow 1,240,300 793,800 549,800 402,900 256,400

Phase 1D

Inflow 1,281,700 842,900 618,000 431,100 286,000

Outflow 1,221,600 794,500 561,620 418,900 275,200

Ultimate

Inflow 1,169,260 804,700 563,100 409,500 277,500

Outflow 1,118,300 735,700 526,080 398,000 267,000

Table 3.8 AP 1 Pond Peak Flow

Existing

Inflow 120.1 82.4 46.9 34.8 22.8

Outflow 44.3 8.7 0.2 0.0 0.0

Phase 1B

Inflow 299.5 202.4 140.2 108.4 75.2

Low Flow 14.4 14.0 13.4 12.2 9.8

Wier 186.8 92.0 17.8 0.0 0.0

Total Outflow 201.2 106.0 31.2 12.2 9.8

Phase 1D

Inflow 271.5 172.7 116.1 91.1 67.0

Low Flow 16.0 15.4 14.8 13.6 11.0

Wier 168.7 73.3 15.4 0.0 0.0

Total Outflow 184.7 88.7 30.2 13.6 11.0

Ultimate

Inflow 247.3 151.0 110.3 88.0 66.5

Low Flow 15.9 15.3 14.7 13.3 10.9

Wier 144.1 57.8 6.9 0.0 0.0

Total Outflow 160.0 73.1 21.6 13.3 10.9

Table 3.9 Full Site Percent Change in Peak Flow

1B 156.9 97.3 30.95 12.19 9.79

1D 140.4 80.0 30.0 13.6 11.0

Ultimate 115.7 64.4 21.4 13.3 10.9

Appendix A - Calculations

A.1 Curve Numbers

A.1.1 Existing Conditions

Name Gravel (ac) Impervious (ac) Pervious (ac)

Total (ac) Sum of Area x CN Final CN Type D Type C Type D Type C Type D

A1 0.0 0.0 0.4 0.0 6.7 7.1 532.0 74.5

A2 0.0 0.0 1.4 0.0 7.3 8.7 671.9 77.1

A3 0.1 0.0 0.5 0.0 6.4 7.0 528.5 75.1

B1 0.0 0.0 0.7 0.0 2.1 2.7 214.7 79.3

B2 0.0 0.0 1.5 0.0 3.4 4.9 391.4 80.5

B3 0.0 0.0 0.7 0.0 6.3 7.0 527.8 75.3

E1 0.4 0.0 2.3 0.0 21.6 24.3 1811.8 74.5

NW1 0.0 0.0 0.0 17.8 0.0 17.8 1301.8 73.1

NW2 0.0 0.2 0.5 14.7 0.0 15.1 1109.1 73.6

SR1 0.0 0.0 0.2 0.0 1.1 1.3 98.6 76.6

SR2 0.0 0.0 0.0 0.0 0.2 0.3 20.7 76.6

SR3 0.0 0.0 0.0 0.0 0.4 0.4 31.5 74.1

SR4 0.0 0.0 0.0 0.0 2.1 1.1 78.6 73.5

SR5 0.0 0.0 0.3 0.0 2.2 1.3 99.1 76.4

W1 0.2 0.0 0.7 0.0 27.2 28.1 2073.6 73.7

W2 1.0 0.0 0.3 0.0 9.6 10.9 821.2 75.3

W3 0.3 0.0 0.1 0.0 4.3 4.7 351.0 74.6

Total 2.3 0.2 9.6 32.5 101.0 142.8 10663.2 74.7

A.1.2 Phase 1B

Name Gravel (ac) Impervious (ac) Pervious (ac)

Total (ac) Sum of Area x CN Calculated CN D C D C D

A1 0.0 0.0 0.0 0.0 5.6 5.6 412.3 73.0

A2 0.0 0.0 0.6 0.0 1.7 2.3 179.7 79.3

A3 0.0 0.0 0.1 0.0 0.2 0.3 26.1 85.1

A4 0.0 0.0 0.4 0.0 2.7 3.1 237.3 76.4

A5 0.0 0.0 0.6 0.0 0.7 1.3 111.1 85.5

A6 0.1 0.0 0.6 0.0 2.0 2.6 210.8 79.6

A7 0.1 0.0 0.0 0.0 3.1 3.2 238.2 73.8

A8 0.8 0.0 0.0 0.0 4.5 5.3 400.3 75.7

B1 0.0 0.0 0.2 0.0 0.7 0.8 63.1 77.9

B2 0.0 0.0 0.4 0.0 0.9 1.2 99.6 80.9

B3 0.0 0.0 0.2 0.0 0.5 0.7 56.5 80.3

B4 0.0 0.0 1.7 0.0 3.7 5.4 435.3 80.6

B5 0.0 0.0 0.8 0.0 6.8 7.5 570.0 75.6

B6 0.1 0.0 0.7 0.0 6.6 7.3 553.9 75.4

E1 0.1 0.0 4.3 0.0 68.2 24.3 1813.9 74.5

NW1 0.1 0.0 0.0 17.8 35.5 17.8 1302.2 73.1

NW2 0.1 0.2 0.5 14.7 29.5 15.1 1108.3 73.5

SR1 0.0 0.0 0.2 0.0 1.1 1.3 98.7 76.6

SR2 0.0 0.0 0.0 0.0 0.2 0.3 21.0 76.6

SR3 0.0 0.0 0.0 0.0 0.4 0.4 31.6 74.1

SR4 0.0 0.0 0.0 0.0 2.1 1.1 78.6 73.5

SR5 0.0 0.0 0.4 0.0 2.2 1.3 99.2 76.4

W1 0.2 0.0 0.7 0.0 27.2 28.1 2073.6 73.7

W2 0.4 0.0 0.1 0.0 5.1 5.6 419.7 74.8

W3 0.1 0.0 0.1 0.0 0.5 0.6 48.1 77.9

Total 2.1 0.2 12.5 32.5 211.6 142.7 10689.2 74.9

A.1.3 Phase 1D

Gravel (ac) Impervious (ac) Pervious (ac)

Total (ac) Sum of Area x CN Final CN Type D Type C Type D Type C Type D

A1 0.0 0.0 0.0 0.0 5.2 5.2 379.3 73.0

A10 0.0 0.5 0.1 0.0 1.0 1.6 124.4 79.8

A11 0.0 0.4 0.3 0.0 0.9 1.6 133.1 82.3

A12 0.0 0.2 0.0 0.0 0.5 0.7 57.0 78.6

A13 0.0 1.2 0.4 0.0 1.6 3.1 259.0 82.6

A2 0.0 0.3 0.0 0.0 1.2 1.5 115.4 77.1

A3 0.0 0.0 0.0 0.0 0.1 0.1 7.6 79.2

A4 0.0 0.4 0.0 0.0 0.3 0.7 55.8 86.7

A6 0.0 0.2 0.0 0.0 0.6 0.8 59.8 77.1

A7 0.0 0.4 0.1 0.0 1.2 1.7 131.6 78.9

A8 0.0 0.1 0.0 0.0 0.7 0.8 64.0 76.2

A9 0.0 0.6 0.0 0.0 0.6 1.3 106.8 82.2

B1 0.0 0.1 0.0 0.0 0.7 0.8 62.1 76.7

B10 0.0 0.2 0.3 0.0 1.3 1.8 142.0 78.9

B11 0.0 0.3 0.0 0.0 1.3 1.6 123.5 77.2

B2 0.0 0.2 0.2 0.0 0.9 1.2 97.9 79.4

B3 0.0 0.1 0.1 0.0 0.5 0.7 55.7 79.0

B4 0.0 1.6 0.1 0.0 3.7 5.4 426.3 79.0

B5 0.0 0.3 0.1 0.0 1.5 1.9 147.1 76.9

B6 0.0 0.2 0.3 0.0 2.5 3.0 230.6 76.7

B7 0.0 0.2 0.2 0.0 1.9 2.3 173.0 78.2

B8 0.0 0.0 0.1 0.0 3.3 3.4 248.6 73.1

B9 0.0 0.2 0.0 0.0 0.7 0.9 74.1 82.4

E1 0.0 1.4 0.1 0.0 22.7 24.3 1804.8 74.2

NW1 0.0 0.7 0.0 1.5 15.7 17.8 1301.8 73.0

NW2 0.0 0.1 0.2 0.2 14.6 15.1 1106.3 73.4

SR1 0.0 0.2 0.0 0.0 1.1 1.3 97.3 75.7

SR2 0.0 0.0 0.0 0.0 0.2 0.3 20.9 77.3

SR3 0.0 0.0 0.0 0.0 0.4 0.4 31.7 74.5

SR4 0.0 0.0 0.0 0.0 1.0 1.1 78.6 73.5

SR5 0.0 0.2 0.0 0.0 1.1 1.3 98.0 75.6

W1 0.0 0.9 0.0 0.0 27.2 28.1 2069.0 73.6

W2 0.0 0.9 0.5 0.0 2.2 3.5 283.0 80.8

W3 0.0 0.2 0.0 0.0 0.4 0.6 47.4 79.1

Total 0.0 12.9 3.1 1.6 120.8 138.5 10406.0 75.1

A.1.4 Ultimate Buildout

Gravel (ac) Impervious (ac) Pervious (ac)

Total (ac) Sum of Area x CN Final CN Type D Type C Type D Type C Type D

A1 0.0 0.0 0.0 0.0 5.2 5.2 379.3 73.0

A10 0.0 0.5 0.1 0.0 1.0 1.6 124.4 79.8

A11 0.0 0.4 0.3 0.0 0.9 1.6 133.1 82.3

A12 0.0 0.2 0.0 0.0 0.5 0.7 57.0 78.6

A13 0.0 1.2 0.4 0.0 1.6 3.1 259.0 82.6

A2 0.0 0.3 0.0 0.0 1.2 1.5 115.4 77.1

A3 0.0 0.0 0.0 0.0 0.1 0.1 7.6 79.2

A4 0.0 0.4 0.0 0.0 0.3 0.7 55.8 82.9

A5 0.0 0.3 0.0 0.0 2.3 2.6 192.3 75.1

A6 0.0 0.2 0.0 0.0 0.6 0.8 59.8 77.1

A7 0.0 0.4 0.1 0.0 1.2 1.7 131.6 78.9

A8 0.0 0.1 0.0 0.0 0.7 0.8 64.0 76.2

A9 0.0 0.6 0.0 0.0 0.6 1.3 106.8 82.2

B1 0.0 0.1 0.0 0.0 0.7 0.8 62.1 76.7

B10 0.0 0.2 0.3 0.0 1.3 1.8 142.0 78.9

B11 0.0 0.3 0.0 0.0 1.3 1.6 123.5 77.2

B2 0.0 0.2 0.2 0.0 0.9 1.2 97.9 79.4

B3 0.0 0.1 0.1 0.0 0.5 0.7 55.7 79.0

B4 0.0 1.6 0.1 0.0 3.7 5.4 426.3 79.0

B5 0.0 0.3 0.1 0.0 1.5 1.9 147.1 76.9

B6 0.0 0.2 0.3 0.0 2.5 3.0 230.6 76.7

B7 0.0 0.2 0.2 0.0 1.9 2.3 173.0 78.2

B8 0.0 0.0 0.1 0.0 3.3 3.4 248.6 73.1

B9 0.0 0.2 0.0 0.0 0.7 0.9 74.1 82.4

E1 0.0 1.4 0.1 0.0 22.7 24.3 1804.8 74.2

NW1 0.0 0.7 0.0 1.5 15.7 17.8 1301.8 73.0

NW2 0.0 0.1 0.2 0.2 14.6 15.1 1106.3 73.4

SR1 0.0 0.2 0.0 0.0 1.1 1.3 97.3 75.7

SR2 0.0 0.0 0.0 0.0 0.2 0.3 20.9 77.3

SR3 0.0 0.0 0.0 0.0 0.4 0.4 31.7 74.5

SR4 0.0 0.0 0.0 0.0 1.0 1.1 78.6 73.5

SR5 0.0 0.2 0.0 0.0 1.1 1.3 98.0 75.6

W1 0.0 0.9 0.0 0.0 27.2 28.1 2069.0 73.6

W2 0.0 0.9 0.5 0.0 2.2 3.5 283.0 80.8

W3 0.0 0.2 0.0 0.0 0.4 0.6 47.4 79.1

Total 0.0 12.9 3.1 1.6 120.8 138.5 10406.0 75.1

A.2 Time of Concentration

A.2.1 Existing Conditions

NOAA 14

P2 (2-yr,24-hr) 3.31 Minimum Tc: 10 min *Input minimum Tc as specified by jurisdiction's drainage criteria

Optional Max Tc Check: 120 min *Input max Tc as a design check

AREA Drainage AreaImpervious AreaFlow Length

# (acre) (acre) (ft)

Paved/

Unpaved n L (ft) Slope (%) Δ Elev (ft) Tc (min)

Paved/

Unpaved

L (ft) Slope (%) Δ Elev (ft) V (fps) Tc (min)

Paved/

Unpaved n L (ft) Slope (%)

Side Slope

(x:1)

Bottom

Width (ft)

Top Width

(ft)

Channel

Depth (ft)

Channel

Cross section Area

"A" (SF)

Wet

Parameter

"P"

(ft) V (fps) Tc (min)

TOTAL Tc

(min)

A1 7.14 0.42 791.33 P 0.011 50 0.01% 0.0 5.30 U 436 0.37% 1.6 0.98 7.39 U 0.03 306 0.60% 4 30 62.0 4.00 184.0 62.98 7.9 0.65 13.33

A2 8.72 1.42 998.56 U 0.15 50 0.55% 0.3 9.30 U 106 2.19% 2.3 2.39 0.74 U 0.03 842 0.38% 4 10 42.0 4.00 104.0 42.98 5.5 2.55 12.59

A3 7.03 0.64 904.02 U 0.15 50 1.03% 0.5…