2026.01.16_100% CD Stormwater Report (1).pdf

PROPERTY OF THE UNITED STATES GOVERNMENT. This is controlled unclassified information. Do not remove the CUI marking. Properly destroy or return document when no longer needed.

Project: Alburg Springs, LPOE

Location: Alburg Springs, Vermont

Description: 100% CD Stormwater Report

Date: 01/16/2026

1 Stormwater Report 100% CD

1.1 Introduction

The Alburg Springs Land Port of Entry (LPOE) project is a federal development project with a footprint that exceeds 5,000 square feet which makes it subject to Section 438 of the Energy Independence and Security Act (EISA) enacted by Congress in 2007. The intent of this stormwater report is to summarize applicable federal, state, and local regulations, calculate the 95th percentile storm event and required runoff volume for retention, and explain the existing stormwater system and the proposed stormwater management strategy for meeting EISA 438 Option 1.

1.2 Federal, State, and Local Regulations

In compliance with EISA Section 438, the 95th percentile storm was calculated using 30 plus years of historical data from a nearby weather station. Precipitation, snow fall, snow depth, and temperature data were obtained from a weather station at Burlington International Airport (BTV) from January 1st, 1980 to December 31st, 2024 for a total of 35 years.

As instructed in EISA 438, rain events that were 0.1” or less were removed from the data. Snow melt was approximated by adding up snow fall and snow depth from the previous day with snow fall of the current day and subtracting out snow depth of the current day. If the maximum temperature of the day was greater than 32 degrees Fahrenheit, the difference was counted as snow melt. To get the snow melt into an approximate liquid amount, a snow to water ratio of 10:1 was used. Snow melt events with less than 0.1" of water equivalent were removed from the data.

Using the above method, the 95th percentile storm was calculated using the remaining rain events and snow melt water equivalent events and was found to be 1.12”. This was the value used for the design storm to retain.

The State of Vermont has stormwater requirements regulated by the 2017 Vermont Stormwater Management Manual (VSMM). This includes standards regarding water quality, groundwater recharge, channel protection (1-year), overbank flood protection (10-year), and extreme flood protection (100-year).

This project is exempt from state regulations due to the existing impervious area being less than 1 acre and new development or redevelopment being less than 0.5 acre.

The Town of Alburgh and Village of Alburgh do not have their own stormwater regulations.

See Appendix A - 95th Percentile Storm Event Data.

1.3 95th Percentile Storm Runoff Volume

The required runoff volume to retain was calculated using HydroCAD (SCS TR-20 method). The disturbed area of 0.40 acres was modeled using the design storm of 1.12” (95th percentile storm) as calculated in Section 1.2 of this report. The disturbed area for this project includes 0.13 acres of disturbed impervious area, 0.22 acres of disturbed pervious area, and 0.05 acres of site balanced undisturbed impervious area to offset 0.05 acres of disturbed impervious area that is unable to be captured due to site topography. Based on the modeling results, the stormwater system must be sized to retain 0.014 acre-feet which is equal to 610 cubic feet.

See Appendix B – Stormwater Plans for the disturbed area breakdown and Appendix C – Post- Development HydroCAD Report for the calculated runoff volume.

1.4 Existing Stormwater System

The existing site has a small, closed drainage collection system consisting of stormwater piping and a singular catch basin. Stormwater runoff from the field to the west of the site sheet flows down to the border crossing, commingling with the stormwater runoff from the existing garage, parking area, and western side of Alburg Springs Road and collects into an existing catch basin. This existing catch basin has two inlets, one pipe from the south collecting field and roadside stormwater runoff and two pipes from the north. One of these northern pipes is a sump drain and the other collects stormwater runoff from the southern portion of the existing building’s roof. The existing building has a second roof drain on the northern side which discharges into an existing northern drainage ditch prior to reaching Lake Champlain. The outlet from the existing catch basin goes under Alburg Springs Road and discharges into an existing southern drainage ditch prior to reaching Lake Champlain.

1.5 Proposed Stormwater System

A new shallow channel will be installed behind the building to collect stormwater runoff from the existing field to the west, rooftop of the existing building, proposed addition and the northern portion of the existing garage. The channel will drain to a system of drainage inlets and 15” HDPE pipes draining to a subsurface detention system that has an approximate footprint of 32’ by 14’. Prior to detention, a hydrodynamic separator will be provided to provide pretreatment and reduce sediment in the subsurface detention system.

The system includes precast concrete modular 2’-0” tall (I.D.) chambers placed on a system with a PVC liner (SingleTrap). The system can be accessed and maintained via two inlets at the northern and southern ends of the system. Following detention, the system will discharge to the existing catch basin, south of the facility. The catch basin is to be replaced and reconnected to the existing drainage pipes. A similar cut-off swale is proposed along the western side of the proposed parking area to capture stormwater runoff from the field to the west, concrete pads, concrete sidewalk, and the southern portion of the existing garage. This stormwater runoff will be conveyed along the proposed retaining wall through a grass-lined swale and into the catch basin along Alburg Springs Road. There are three proposed roof drains, one on the southern side of the building and two on the northern side of the building. On the southern side of the building, the roof drain daylights directly into the inlet grate. On the northern side of the building, the roof drain on the northwest corner will turn horizontal underground and connect into the new inlet. The roof drain in the center of the northern side of the building will turn horizontal underground and connect into the new storm pipe. All stormwater runoff from the building roof will be pretreated by the hydrodynamic separator and captured in the proposed subsurface detention system.

To enhance the project site’s resilience and stormwater runoff control, thus meeting the requirements of EISA 438 Option 1 to the maximum extent technically feasible, the project is proposing to install a precast concrete subsurface detention system with an outlet control structure to detain the 95th percentile storm runoff from the disturbed area of the site. Due to proximity to ledge, an infiltration practice with minimum 3’ vertical separation to ledge was not feasible. The geotechnical report containing test pit logs can be found in the appendices. It is a state requirement to provide 3’ vertical separation from ledge for infiltration practices and recommended to provide stormwater treatment prior to discharging to groundwater.

Rainwater harvesting was considered but due to the limited amount of water usage within the existing building, it wouldn’t have a meaningful impact.

As calculated in Section 1.3, 0.014 acre-feet or 610 cubic feet of runoff volume is required to be detained for the 95th percentile storm. The subsurface detention system provides 0.019 acre-feet or 828 cubic feet of storage, effectively detaining the 95th percentile storm through a 5” thick internal concrete weir and 1” orifice within the weir wall designed to slowly release the storm volume to the maximum extent practicable. Per state stormwater regulations, extended detention is only required down to the 1” minimum orifice size due to clogging concerns.

The 100-yr flood elevation for Lake Champlain is 102 ft above sea level. Under ASCE 24, the design flood elevation for a non-critical action facility is set at 2 ft (minimum). Given the basement level of the building is set at approximately 116 ft, all the equipment and the building will be outside of this range. As detailed in the geotechnical report, groundwater wasn’t detected in the test pits performed and the proposed subsurface detention system sits 16.6 ft above the 100-year flood elevation of Lake Champlain. Based on this information, buoyancy of the proposed subsurface detention system is not anticipated to be a concern for this project.

See Appendix B – Stormwater Plans and Appendix D – Foundation Engineering Report.

1.6 Conclusion

The stormwater design for the Alburg LPOE project meets the requirements outlined in EISA Section 438 Option 1 to the maximum extent technically feasible by detaining the 95th percentile storm event.

Best regards, STANTEC CONSULTING SERVICES INC.

Riley Galus PE

Civil Engineer Phone: (802) 497-6327 riley.galus@stantec.com

Appendices:

Appendix A - 95th Percentile Storm Event Data Appendix B – Stormwater Plans dated 01-16-2026 Appendix C - Post-Development HydroCAD Report dated 01-16-2026 Appendix D – Foundation Engineering Report dated 12-13-2024

Appendix A - 95th Percentile Storm Event Data

0.2

0.4

0.6

0.8

1.2

1.4

1.6

1.8

2.2

2.4

2.6

2.8

3.2

3.4

3.6

3.8

P re c ip it a ti o n in c h e s

Year

Burlington International Airport Weather Station Precipitation Events Greater than 0.1

Inches from 1/1/1980 to 12/31/2024

0.5

1.5

2.5

3.5

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

S to rm E v e n t

D e p th in c h e s

Percentile

Percentiles for Storm Events Greater Than 0.1 Inches

95% Storm Event = 1.12"

Appendix B – Stormwater Plans dated 01-16-2026

R D

R D

R D

R D

R D

R D

SD SD SD SD

SD

124.5

UD

U D

U D

U D

123.5

123.5

124.5

125.5

SD

126 S

SD

SD

SD

SD

126.5

123 124

SD SD SD

127.5

128.5

129.5

129.5128.5

121.5

W W

W

W

W

UD UD

U D

124.5

123.5

124.5

127.5

8.5

G

AS

130.5131

129.5

6.5

5.5

U G

C U

G C

UG

C

UG

C

UGE

UGE

UGE

UGE

UG

E

UG

E

UGE

U G

E

UGE

UG

E

UG

E

UG

E

UG

E

UG

E

UGE UGE UGE UGE

U G

E

UGE UGE

E

U G

E

UGE

U

G E

U G

E

E

E

E

E E

E E

UGE

UGEE

E

UGC

U G

E

C

UGE UGE

UGE

E

UGE UGE

UGC UGC

U G

E

5.5

4.5

123.5

122121.5

122.5

122.5

UP

NEW PRECAST CONCRETE CATCH BASIN (CB-9)

CONNECT EXISTING PIPES, ABANDON 6" PVC

AND 6" STEEL PIPE

NEW PRECAST CONCRETE

HYDRODYNAMIC SEPARATOR (CB-3)

NEW 15" HDPE PIPE

NEW PRECAST CONCRETE

CATCH BASIN (CB-2)

NEW 15" HDPE PIPE

6" PVC UNDERDRAIN

NEW PRECAST CONCRETE

CATCH BASIN (CB-4)

FOUR (4) 2'-0" TYPE IV

STORMTRAP SUBSURFACE

STORMWATER DETENTION UNITS

SEE SHEET C-503 FOR DETAILS

NEW OUTLET CONTROL

STRUCTURE (CB-8)

SEE SHEET C-503 FOR DETAILS

1.5' WIDE GRASSED

DRAINAGE SWALE SEE

DETAIL ON SHEET C-501

ACCESS OPENING WITH CAST IRON

MANHOLE COVER LABELED "DRAIN" (CB-7)

NEW 15" HDPE PIPE

ACCESS OPENING WITH CAST IRON

MANHOLE COVER LABELED "DRAIN" (CB-6)

NEW 15" HDPE PIPE

NEW 15" HDPE PIPE

NEW 15" HDPE PIPE

NEW 15" HDPE PIPE

NEW PRECAST CONCRETE

CATCH BASIN (CB-5)

GRADING LIMITS

(TYP.)

NEW PRECAST CONCRETE

CATCH BASIN (CB-1)

NEW 2" PVC SUMP

DRAIN CONNECTED TO

CB-5, SEE P-100

PROPOSED CLEANOUT

PROPOSED CLEANOUT

PROPOSED CLEANOUT

6" PVC ROOF DRAIN

NEW 6" PVC

ROOF DRAIN

PROPOSED CLEANOUT

CONNECT ROOF DRAIN TO

PROPOSED DRAINAGE PIPE,

SEE DETAIL 9 ON SHEET C-502

NEW ROOF DRAIN, SEE

SHEET A-210, TO DRAIN

INTO CB-5 GRATE

FF = 124.67'

EXISTING

CANOPY

FF = 125.99'

ALBURGH SPRINGS RD.

SHEET NOTES

LEGEND

N

C-004

STORMWATER DEVELOPMENT PLAN

Mark Date Description

GENERAL NOTES

CHECKED BY

DRAWN BY

FLOOR NUMBER

DRAWING TITLE

SHEET

NUMBER

SUBMISSION DATE

SUBMISSION STAGE

GSA PM

GSA PROJECT NO.

PROJECT

DESCRIPTION

PROJECT TITLE

BULDING NAME

CITY/ST./ZIP

ADDRESS

BUILDING NUMBER

PRIME CONTR. NO.

PRIME ORDER NO.

CONST. CONTR.

A/E

SUB A/E

CONST. CONTR. NO.

SHEET SIZE:

DATE DRAWN:

36 X 48

95% CONTRACT PLANS

11/07/25

11/07/25GM

CG

SH

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T I

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IFI

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SHEET OF SHEETS

PROPERTY OF THE UNITED STATES GOVERNMENT This is controlled unclassified information. Do not remove the CUI marking. Properly destroy or return documents when no longer needed.

CIVIL

PR

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O F T

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T T his is co nt ro lle d u nc las sif ied in fo rm ati on

. D o n ot re mo ve th e C

UI

m ar kin g.

P ro pe rly de str oy or re tu rn do cu me nt s w he n n o l on ge r n ee de d.

75 Kneeland Street Boston, MA 02111

617.542.6650 silverschwartz

GSA

193 Tilley Drive Suite 101 South Burlington VT 05403-4440

GSA Alburgh Springs LPOE

GSA

Alburgh Springs LPOE

303 Alburgh Springs Rd, Alburgh Springs, VT 05440

PROGRESS PRINT NOT

FOR CONSTRUCTION

100% SUBMITTAL

01/16/26

1. CONTRACTOR SHALL CONTACT DIG SAFE AT 1-888-DIG-SAFE PRIOR TO COMMENCING

WORK. CONTRACTOR SHALL VERIFY LOCATION OF ALL OVERHEAD AND UNDERGROUND

UTILITY LINES AND TAKE NECESSARY PRECAUTIONS IN STRICT ACCORDANCE WITH

OSHA STANDARDS DURING CONSTRUCTION.

2. SEE C-201 FOR STORM SEWER DETAILS.

DISTURBED IMPERVIOUS AREA (0.13 AC)

DISTURBED PERVIOUS AREA (0.20 AC)

UNDISTURBED IMPERVIOUS AREA (0.11 AC)

SITE BALANCED DISTURBED IMPERVIOUS AREA (0.05 AC)

SITE BALANCED UNDISTURBED IMPERVIOUS AREA (0.05 AC)

100% CONTRACT PLANS

01/16/26

01/16/26

(0.05 AC)

(0.05 AC)

(0.12 AC)

(0.13 AC)

(0.22 AC)

(0.05 AC)

(0.05 AC)

R

R D

R D

R D

R D

R D

R D

R D

R D

R D

R D

R D

SD SD SD SD SD SD SD SD SD

SD

SD

RD

124.5

UD

UD

U D

U D

U D

U D

U D

U D

SD

123.5

123.5

124.5

125.5

SD

SD

SD

S

S

S

SD

SD

SD

SD

SD

SD

SD

SD

126.5

SD SD SD SD SD SD

127.5

128.5

129.5

129.5 128.5

121.5

W W

W W

W W

W

W

W

W

W

UD UD UD UD

U D

U D

124.5

123.5

124.5

127.5

8.5

G

AS

G

AS

130.5

129.5

6.5

5.5

U G

C U

G C

U G

C U

G C

UG

C

UG

C

UG

C

UG

C

UGC

UGE

UGE UGE UGE

UGE

UGE

UGE UGE

UG

E

UG

E

UG

E

UG

E

UGE

UGE

UGE

UGE

U G

E U

G E

U G

E

UGE

UGE

UG

E

UG

E

UG

E

UG

E

UG

E

UG

E

UG

E

UG

E

UG

E

UGE

UGE UGE UGE UGE UGE UGE UGE UGE

U G

E U

G E

UGE UGE UGE UGE

E

U G

E U

G E

U G

E U

G E

UGE

UGE UGE UGE

U G

E U

G E

U G

E U

G E

U G

E

E

E

E

E E

E

EUGE

UGE

UGE

UGE

UGE

UGE

E

E

UGC UGC UGC

U G

E U

G E

UGE UGE UGE UGE

UGE

UGE

U G

E

E

UGE UGE UGE UGE

UGC UGC UGC UGC

U G

E U

G E

U G

E

5.5

4.5

123.5

121.5

122.5

122.5

FF = 124.67'

EXISTING

CANOPY

FF = 125.99'

126.88

TOW = 125.5

TOW = 124.5

TOW = 126.5

TOW = 126.5

PROPOSED PRECAST CONCRETE CATCH

BASIN (CB-9)

CONNECT EXISTING PIPES, ABANDON 6"

PVC AND 6" STEEL PIPE

PROPOSED PRECAST CONCRETE

HYDRODYNAMIC SEPARATOR (CB-3)

SEE DETAIL 2, SHEET C-503

PROPOSED 15"

HDPE PIPE PROPOSED PRECAST

CONCRETE CATCH BASIN

(CB-2)

PROPOSED 15"

HDPE PIPE

PROPOSED 6" PVC

UNDERDRAIN

PROPOSED PRECAST CONCRETE

CATCH BASIN (CB-4)

FOUR (4) 2'-0" TYPE IV

STORMTRAP SUBSURFACE

STORMWATER DETENTION UNITS

SEE DETAIL 3, SHEET C-503

PROPOSED OUTLET CONTROL

STRUCTURE (CB-8)

SEE DETAIL 1, SHEET C-503

TOW = 129.0 TOW = 130.0

TOW = 130.0

TOW = 129.0

TOW = 128.0

TOW = 128.0

ALBURGH SPRINGS RD.

PROPOSED 1.5' WIDE

GRASSED DRAINAGE SWALE

SEE DETAIL 14, SHEET C-502

PROPOSED

ABAAS ACCESS,

MAX. 2% SLOPE

PROPOSED CIP RETAINING WALL

TOW = 124.5'

HT = ~2'

SEE DETAIL 15, SHEET C-501

PROPOSED CAST IN

PLACE CONCRETE

RETAINING WALL

TOW = 124.5'

HT = ~2'

SEE DETAIL 15,

SHEET C-501

PROPOSED ACCESS OPENING WITH CAST IRON

MANHOLE COVER LABELED "DRAIN" (CB-7)

PROPOSED 15"

HDPE PIPE

PROPOSED ACCESS OPENING WITH CAST

IRON MANHOLE COVER LABELED "DRAIN"

(CB-6)

PROPOSED 15"

HDPE PIPE

PROPOSED 15"

HDPE PIPE

124.8 124.6

124.4

124.2

TOW = 131.0

125.99 125.49 124.99

125.99

125.49 124.99 124.49

124.67

124.17 123.67

123.17

124.50

124.50

PROPOSED 15" HDPE PIPE

PROPOSED 15"

HDPE PIPE

PROPOSED PRECAST

CONCRETE CATCH BASIN (CB-5)

GRADING LIMITS

(TYP.)

PROPOSED PRECAST

CONCRETE CATCH BASIN

(CB-1)

PROPOSED 2" PVC

SUMP DRAIN

CONNECTED TO CB-5

(SEE P-100)

UP

PROPOSED CLEANOUT

PROPOSED CLEANOUT

PROPOSED CLEANOUT

PROPOSED 6" PVC

ROOF DRAIN

PROPOSED

6" PVC ROOF

DRAIN

PROPOSED CLEANOUT

PROPOSED CIP RETAINING WALL

TOW = 126.5'

HT = ~3'

SEE DETAIL 14, SHEET C-501

PROPOSED PRECAST CONCRETE

BLOCK RETAINING WALL

TOW = 131.0

HT = ~6'

SEE DETAIL 4, SHEET C-501

CONNECT ROOF DRAIN TO

PROPOSED DRAINAGE PIPE,

SEE DETAIL 9, SHEET C-502

PROPOSED ROOF DRAIN

TO DRAIN INTO CB-5

GRATE (SEE SHEET A-210)

125.97

126.36

126.74 127.00 126.96

126.86

126.43

126.78

126.90

SHEET NOTES

LEGEND

N

C-104

DRAINAGE AND GRADING PLAN

Mark Date Description

GENERAL NOTES

CHECKED BY

DRAWN BY

FLOOR NUMBER

DRAWING TITLE

SHEET

NUMBER

SUBMISSION DATE

SUBMISSION STAGE

GSA PM

GSA PROJECT NO.

PROJECT

DESCRIPTION

PROJECT TITLE

BULDING NAME

CITY/ST./ZIP

ADDRESS

BUILDING NUMBER

PRIME CONTR. NO.

PRIME ORDER NO.

CONST. CONTR.

A/E

SUB A/E

CONST. CONTR. NO.

SHEET SIZE:

DATE DRAWN:

36 X 48

100% CONTRACT PLANS

1/16/2026

1/16/2026GM

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SHEET OF SHEETS

PROPERTY OF THE UNITED STATES GOVERNMENT This is controlled unclassified information. Do not remove the CUI marking. Properly destroy or return documents when no longer needed.

CIVIL

PR

OP

ER

TY

O F T

HE

U

NI

TE

D

ST

AT

ES

G

OV

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NM

EN

T T his is co nt ro lle d u nc las sif ied in fo rm ati on

. D o n ot re mo ve th e C

UI

m ar kin g.

P ro pe rly de str oy or re tu rn do cu me nt s w he n n o l on ge r n ee de d.

75 Kneeland Street Boston, MA 02111

617.542.6650 silverschwartz

GSA

193 Tilley Drive Suite 101 South Burlington VT 05403-4440

GSA Alburgh Springs LPOE

GSA

Alburgh Springs LPOE

303 Alburgh Springs Rd, Alburgh Springs, VT 05440

PROGRESS PRINT NOT

FOR CONSTRUCTION

100% SUBMITTAL

1/16/2026

1. CONTRACTOR SHALL CONTACT DIG SAFE AT 1-888-DIG-SAFE PRIOR TO COMMENCING

WORK. CONTRACTOR SHALL VERIFY LOCATION OF ALL OVERHEAD AND UNDERGROUND

UTILITY LINES AND TAKE NECESSARY PRECAUTIONS IN STRICT ACCORDANCE WITH

OSHA STANDARDS DURING CONSTRUCTION.

2. SEE C-201 FOR STORM SEWER DETAILS.

SD SD SD SD SD SD SD SD SD

SD

SD

RD

UD

UD

U D

U D

U D

U D

U D

U D

SD

123.5

123.5

124.5

125.5

SD

SD

SD

S

S

S

SD

SD

SD

SD

SD

SD

SD

SD

126.5

SD SD SD SD SD SD

127.5

128.5

UD UD UD UD

U D

U D

124.5

123.5

122.5

124.5

127.5

6.5

U G

C U

G C

U G

C U

G C

UG

C

UG

C

UGE

UGE UGE UGE

UGE

UGE

UGE

UGE

U G

E U

G E

U G

E

UGE

UGE

UG

E

UG

E

UG

E

UG

E

UG

E

UG

E

U G

E U

G E

UGE UGE UGE UGE

E

U G

E U

G E

U G

E U

G E

UGE

U G

E U

G E

U G

E

E

E

E

E

EUGE

UGE

UGE

UGE

UGE

UGE

E

E

UGC UGC UGC

U G

E U

G E

UGE UGE UGE UGE

UGE

UGE

U G

E

E

UGE UGE UGE UGE

U G

E U

G E

U G

E

5.5

4.5

123.5

121.5

122.5

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG

UG UG UG

UG

UG

UG

UG

UG

UG

OH

OH

OH

OH

OH

OH

OH

OH

O H

O H

O H

O H

O H

O H

R D

R D

R D

R D

R D

R D

R D

R D

R D

R D

FF = 124.67'

EXISTING CANOPY

FF = 125.99'

PROPOSED PRECAST CONCRETE CATCH BASIN (CB-9)

RIM = 121.50

PROPOSED 15" HDPE INVin (NE) = 118.45 PROPOSED 6" PVC INVin (N) = 119.50

EX. 12" RCP INVin (S) = 118.57 EX. 18" CMP INVout (E) = 118.40

CONNECT EXISTING PIPES, ABANDON 6" PVC AND 6"

STEEL PIPE

PROPOSED PRECAST CONCRETE

HYDRODYNAMIC SEPARATOR (CB-3)

RIM = 122.8

15" HDPE INVin (W) = 118.9 15" HDPE INVin (N) = 118.8

15" HDPE INVout (S) = 118.7

SEE DETAIL 2, SHEET C-503

PROPOSED 15" HDPE

SLOPE = 0.005 FT/FT

LENGTH = 65'

PROPOSED PRECAST

CONCRETE CATCH BASIN (CB-2)

RIM = 122.5

15" HDPE INVin (W) = 119.2 15" HDPE INVout (S) = 119.1

PROPOSED 15" HDPE

SLOPE = 0.026 FT/FT

LENGTH = 58'

6" PVC UNDERDRAIN

SLOPE = 0.046 FT/FT

LENGTH = 56'

PROPOSED PRECAST CONCRETE

CATCH BASIN (CB-4)

RIM = 125.8

15" HDPE INVout (N) = 120.6

PROPOSED FOUR (4) 2'-0" TYPE IV

STORMTRAP SUBSURFACE

STORMWATER DETENTION UNITS

SEE DETAIL 3, SHEET C-503

PROPOSED OUTLET CONTROL STRUCTURE (CB-8)

RIM = 122.2

5" CONCRETE INTERNAL WEIR INV = 120.6

1" ORIFICE WITHIN WEIR WALL INV = 118.55

18" HDPE INVin (N) = 118.55 18" HDPE INVout (S) = 118.55

SEE DETAIL 1, SHEET C-503

PROPOSED ACCESS OPENING WITH CAST IRON

MANHOLE COVER LABELED "DRAIN" (CB-7)

RIM = 122.4 (MATCH PROPOSED GRADE)

15" HDPE INVout (S) = 118.6

SEE DETAIL 4, SHEET C-503

PROPOSED 15" HDPE

SLOPE = 0.008 FT/FT

LENGTH = 12'

PROPOSED ACCESS OPENING WITH CAST IRON

MANHOLE COVER LABELED "DRAIN" (CB-6)

RIM = 122.7 (MATCH PROPOSED GRADE)

15" HDPE INVin (N) = 118.6

SEE DETAIL 4, SHEET C-503

PROPOSED 15" HDPE

SLOPE = 0.013 FT/FT

LENGTH = 4'

PROPOSED 5" HDPE

SLOPE = 0.008 FT/FT

LENGTH = 12'

PROPOSED 15" HDPE

SLOPE = 0.005 FT/FT

LENGTH = 24'

PROPOSED 15" HDPE

SLOPE = 0.031 FT/FT

LENGTH = 42'

PROPOSED PRECAST CONCRETE

CATCH BASIN (CB-5)

RIM = 124.8

2" PVC INVin (SUMP DRAIN) = 119.8

15" HDPE INVin (S) = 119.3 15" HDPE INVout (E) = 119.0

PROPOSED PRECAST CONCRETE

CATCH BASIN (CB-1)

RIM = 124.0

6" PVC INVin (RD) (S) = 120.8 15" HDPE INVout (E) = 120.7

UP

PROPOSED ROOF

DRAIN TO DRAIN INTO

CB-5 GRATE (SEE

SHEET A-210)

PROPOSED 2" PVC

SUMP DRAIN

CONNECTED TO

CB-5 (SEE P-100)

PROPOSED CLEANOUT

PROPOSED 6" PVC

ROOF DRAIN

CONNECT ROOF DRAIN TO

PROPOSED DRAINAGE PIPE,

SEE DETAIL 9, SHEET C-502

PROPOSED CLEANOUT

PROPOSED 6" PVC

ROOF DRAIN

BU

ILD

IN

G

PR

OP

OS

ED

P

RE

CA

ST

C

ON

CR

ET

E

CA

TC

H

BA

SI

N (C

B- 1)

RI

M

4.0 8"

P

VC

IN

Vi n (

RD

S)

0.8

" H

DP

E

IN

Vo ut

(E

0.7

PR

OP

OS

ED

P

RE

CA

ST

C

ON

CR

ET

E

CA

TC

H

BA

SI

N (C

B- 2)

RI

M

2.5

" H

DP

E

IN

Vi n (

W

9.2

" H

DP

E

IN

Vo ut (S

9.1

PR

OP

OS

ED

P

RE

CA

ST

C

ON

CR

ET

E

HY

DR

OD

YN

AM

IC

S

EP

AR

AT

OR

(C B-

3)

RI

M

2.8

" H

DP

E

IN

Vi n ( W

8.9

" H

DP

E

IN

Vi n (

N)

8.8

" H

DP

E

IN

Vo ut (S

8.7

PROPOSED 15" HDPE

SLOPE = 0.026 FT/FT

LENGTH = 58'

PROPOSED 15" HDPE

SLOPE = 0.005 FT/FT

LENGTH = 65'

PROPOSED 15" HDPE

SLOPE = 0.008 FT/FT

LENGTH = 12'

EXISTING GRADE

PROPOSED GRADE

PROPOSED

ELECTRICAL

CONDUIT

PROPOSED

ELECTRICAL CONDUIT

PROPOSED ELECTRICAL

CONDUIT

PROPOSED

ELECTRICAL

CONDUIT

DRAINAGE PROFILE

STA. 0+00 TO STA 2+00

VERTICAL EXAGGERATION: 1:1

24" MINIMUM PIPE

COVER (TYP.)

12" MINIMUM VERTICAL

SEPARATION TO CONDUIT

(TYP.)

PR

OP

OS

ED

O

UT

LE

T

CO

NT

RO

L S

TR

UC

TU

RE

(C B-

8)

RI

M

2.2

5" C

ON

CR

ET

E

IN

TE

RN

AL

W

EI

R

IN

V

0.6

1" O

RI

FI

CE

W

IT

HI

N W

EI

R

W

AL

L I

NV

8.5

" H

DP

E

IN

Vi n ( N)

8.5

" H

DP

E

IN

Vo ut (S

8.5

SE

E

DE

TA

IL

1, SH

EE

T C-

PR

OP

OS

ED

P

RE

CA

ST

C

ON

CR

ET

E

CA

TC

H

BA

SI

N (C

B- 9)

RI

M

1.5

" H

DP

E

IN

Vi n (

NE

8.4

6" P

VC

IN

Vi n (

N)

9.5

EX

. 1 2"

R

CP

IN

Vi n ( S)

8.5

EX

. 1

8" C

MP

IN

Vo ut

(E

8.4

CO

NN

EC

T

EX

IS

TI

NG

P

IP

ES

, A

BA

ND

ON

6" P

VC

A

ND

6"

ST

EE

L P

IP

E

PROPOSED 15" HDPE

SLOPE = 0.013 FT/FT

LENGTH = 4'

PROPOSED 15" HDPE

SLOPE = 0.008 FT/FT

LENGTH = 12'

PROPOSED GRADE

PR

OP

OS

ED

P

RE

CA

ST

C

ON

CR

ET

E

CA

TC

H

BA

SI

N (C

B- 5)

RI

M

4.8 2"

P

VC

IN

Vi n (

SU

MP

D

RA

IN

9.8

" H

DP

E

IN

Vi n (

S)

9.3

" H

DP

E

IN

Vo ut (E

9.0

PR

OP

OS

ED

P

RE

CA

ST

C

ON

CR

ET

E

CA

TC

H

BA

SI

N (C

B- 4)

RI

M

5.8

" H

DP

E

IN

Vo ut

(N

0.6

PROPOSED 15" HDPE

SLOPE = 0.026 FT/FT

LENGTH = 42' PROPOSED 15" HDPE

SLOPE = 0.027 FT/FT

LENGTH = 26'

PR

OP

OS

ED

P

RE

CA

ST

C

ON

CR

ET

E

HY

DR

OD

YN

AM

IC

S

EP

AR

AT

OR

(C B-

3)

RI

M

2.8

" H

DP

E

IN

Vi n ( W

8.9

" H

DP

E

IN

Vi n (

N)

8.8

" H

DP

E

IN

Vo ut (S

8.7

SE

E

DE

TA

IL

2, SH

EE

T

C-

PROPOSED GRADE

EXISTING GRADE

PROPOSED

ELECTRICAL CONDUIT

PROPOSED

ELECTRICAL CONDUIT

DRAINAGE PROFILE

STA. 10+00 TO STA 10+68

VERTICAL EXAGGERATION: 1:1

24" MINIMUM PIPE

COVER (TYP.)

12" MINIMUM VERTICAL

SEPARATION TO CONDUIT

(TYP.)

12" MINIMUM VERTICAL

SEPARATION TO CONDUIT

(TYP.)

24" MINIMUM PIPE

COVER (TYP.)

SHEET NOTES

LEGEND

N

C-201

DRAINAGE PLAN AND PROFILE

Mark Date Description

GENERAL NOTES

CHECKED BY

DRAWN BY

FLOOR NUMBER

DRAWING TITLE

SHEET

NUMBER

SUBMISSION DATE

SUBMISSION STAGE

GSA PM

GSA PROJECT NO.

PROJECT

DESCRIPTION

PROJECT TITLE

BULDING NAME

CITY/ST./ZIP

ADDRESS

BUILDING NUMBER

PRIME CONTR. NO.

PRIME ORDER NO.

CONST. CONTR.

A/E

SUB A/E

CONST. CONTR. NO.

SHEET SIZE:

DATE DRAWN:

36 X 48

100% CONTRACT PLANS

1/16/2026

1/16/2026GM

CG

SH

EE

T I

DE

NT

IFI

CA

TIO

N

DISCIPLINE

PR

OJ

EC

T I

DE

NT

IFI

CA

TIO

N

BU

ILD

IN

G

BIM FILE NAME

CO

NT

RA

CT

OR

S

RE

VI

SI

ON

B

LO

CK

GR

AP

HI

C

SC

AL

E

KE

Y

PL

AN

ST

AM

P

OR

S

EA

L

DE

SI

GN

ER

ID

EN

TIF

IC

AT

IO

N

OW

NE

R

ID

EN

TIF

IC

AT

IO

N

SHEET OF SHEETS

PROPERTY OF THE UNITED STATES GOVERNMENT This is controlled unclassified information. Do not remove the CUI marking. Properly destroy or return documents when no longer needed.

CIVIL

PR

OP

ER

TY

O F T

HE

U

NI

TE

D

ST

AT

ES

G

OV

ER

NM

EN

T T his is co nt ro lle d u nc las sif ied in fo rm ati on

. D o n ot re mo ve th e C

UI

m ar kin g.

P ro pe rly de str oy or re tu rn do cu me nt s w he n n o l on ge r n ee de d.

75 Kneeland Street Boston, MA 02111

617.542.6650 silverschwartz

GSA

193 Tilley Drive Suite 101 South Burlington VT 05403-4440

GSA Alburgh Springs LPOE

GSA

Alburgh Springs LPOE

303 Alburgh Springs Rd, Alburgh Springs, VT 05440

PROGRESS PRINT NOT

FOR CONSTRUCTION

100% SUBMITTAL

1/16/2026

DRAINAGE PLAN

M

AT

C H

L

IN

E A

M

AT

C H

L

IN

E A

1. CONTRACTOR SHALL CONTACT DIG SAFE AT 1-888-DIG-SAFE PRIOR TO COMMENCING

WORK. CONTRACTOR SHALL VERIFY LOCATION OF ALL OVERHEAD AND UNDERGROUND

UTILITY LINES AND TAKE NECESSARY PRECAUTIONS IN STRICT ACCORDANCE WITH

OSHA STANDARDS DURING CONSTRUCTION.

Appendix C – Post-Development HydroCAD Report dated 01-16-2026

9S

Post-Development

Disturbed Area

9R

Existing Ditch

8P

StormTrap 2.0

9P

CB

CB-8

Routing Diagram for Alburg Post-Development Conditions Prepared by Stantec Consulting Ltd.

HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Subcat Reach Pond Link

Alburg Post-Development Conditions Prepared by Stantec Consulting Ltd.

Page 2HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Rainfall Events Listing (selected events)

Event# Event

Name

Storm Type Curve Mode Duration

(hours)

B/B Depth

(inches)

AMC

1 95% Type II 24-hr Default 24.00 1 1.12 2

Page 3HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Area Listing (selected nodes)

Area

(acres)

CN Description

(subcatchment-numbers)

0.130 98 Disturbed Impervious Area (9S)

0.220 74 Disturbed Pervious Area (9S)

0.050 98 Site Balanced Disturbed Impervious Area (9S)

0.400 85 TOTAL AREA

Page 4HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Soil Listing (selected nodes)

Area

(acres)

Soil

Group

Subcatchment

Numbers

0.000 HSG A

0.000 HSG B

0.000 HSG C

0.000 HSG D

0.400 Other 9S

0.400 TOTAL AREA

Page 5HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Ground Covers (selected nodes)

HSG-A

(acres)

HSG-B

(acres)

HSG-C

(acres)

HSG-D

(acres)

Other

(acres)

Total

(acres)

Ground

Cover

Subcatchment

Numbers

0.000 0.000 0.000 0.000 0.130 0.130 Disturbed Impervious Area

0.000 0.000 0.000 0.000 0.220 0.220 Disturbed Pervious Area

0.000 0.000 0.000 0.000 0.050 0.050 Site Balanced Disturbed Impervious

Area

0.000 0.000 0.000 0.000 0.400 0.400 TOTAL AREA

Page 6HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Pipe Listing (selected nodes)

Line# Node

Number

In-Invert

(feet)

Out-Invert

(feet)

Length

(feet)

Slope

(ft/ft) n Diam/Width

(inches)

Height

(inches)

Inside-Fill

(inches)

1 8P 118.55 118.45 12.0 0.0083 0.013 15.0 0.0 0.0

2 9P 118.40 117.00 70.0 0.0200 0.025 18.0 0.0 0.0

Type II 24-hr 95% Rainfall=1.12"Alburg Post-Development Conditions

Page 7HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Time span=0.00-48.00 hrs, dt=0.01 hrs, 4801 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q

Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method

Runoff Area=0.400 ac 45.00% Impervious Runoff Depth=0.43"Subcatchment 9S: Post-Development Flow Length=121' Slope=0.0500 '/' Tc=2.2 min CN=WQ Runoff=0.30 cfs 0.014 af

Inflow=0.02 cfs 0.014 afReach 9R: Existing Ditch Outflow=0.02 cfs 0.014 af

Peak Elev=119.26' Storage=0.006 af Inflow=0.30 cfs 0.014 afPond 8P: StormTrap 2.0 Outflow=0.02 cfs 0.014 af

Peak Elev=118.48' Inflow=0.02 cfs 0.014 afPond 9P: CB-8 18.0" Round Culvert n=0.025 L=70.0' S=0.0200 '/' Outflow=0.02 cfs 0.014 af

Total Runoff Area = 0.400 ac Runoff Volume = 0.014 af Average Runoff Depth = 0.43" 55.00% Pervious = 0.220 ac 45.00% Impervious = 0.180 ac

Page 8HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Summary for Subcatchment 9S: Post-Development Disturbed Area

Runoff = 0.30 cfs @ 11.93 hrs, Volume= 0.014 af, Depth= 0.43"

Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.01 hrs Type II 24-hr 95% Rainfall=1.12"

Area (ac) CN Description

* 0.130 98 Disturbed Impervious Area

* 0.220 74 Disturbed Pervious Area

* 0.050 98 Site Balanced Disturbed Impervious Area

0.400 Weighted Average

0.220 55.00% Pervious Area

0.180 45.00% Impervious Area

Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs)

2.2 121 0.0500 0.91 Lag/CN Method, Subcatchment 9S: Post-Development Disturbed Area

Runoff

Hydrograph

Time (hours) 484644424038363432302826242220181614121086420

F lo w

(c fs

0.32

0.3

0.28

0.26

0.24

0.22

0.2

0.18

0.16

0.14

0.12

0.1

0.08

0.06

0.04

0.02

Type II 24-hr

95% Rainfall=1.12"

Runoff Area=0.400 ac

Runoff Volume=0.014 af

Runoff Depth=0.43"

Flow Length=121'

Slope=0.0500 '/'

Tc=2.2 min

CN=WQ

0.30 cfs

Page 9HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Summary for Reach 9R: Existing Ditch

[40] Hint: Not Described (Outflow=Inflow)

Inflow Area = 0.400 ac, 45.00% Impervious, Inflow Depth = 0.43" for 95% event Inflow = 0.02 cfs @ 12.47 hrs, Volume= 0.014 af Outflow = 0.02 cfs @ 12.47 hrs, Volume= 0.014 af, Atten= 0%, Lag= 0.0 min

Routing by Stor-Ind+Trans method, Time Span= 0.00-48.00 hrs, dt= 0.01 hrs

Reach 9R: Existing Ditch

Inflow Outflow

Hydrograph

Time (hours) 484644424038363432302826242220181614121086420

F lo w

(c fs

0.024

0.023

0.022

0.021

0.02

0.019

0.018

0.017

0.016

0.015

0.014

0.013

0.012

0.011

0.01

0.009

0.008

0.007

0.006

0.005

0.004

0.003

0.002

0.001

Inflow Area=0.400 ac

0.02 cfs

Page 10HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Summary for Pond 8P: StormTrap 2.0

[44] Hint: Outlet device #2 is below defined storage

Inflow Area = 0.400 ac, 45.00% Impervious, Inflow Depth = 0.43" for 95% event Inflow = 0.30 cfs @ 11.93 hrs, Volume= 0.014 af Outflow = 0.02 cfs @ 12.47 hrs, Volume= 0.014 af, Atten= 93%, Lag= 32.5 min Primary = 0.02 cfs @ 12.47 hrs, Volume= 0.014 af

Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.01 hrs Peak Elev= 119.26' @ 12.47 hrs Surf.Area= 0.010 ac Storage= 0.006 af

Plug-Flow detention time= 137.6 min calculated for 0.014 af (100% of inflow) Center-of-Mass det. time= 137.6 min ( 928.2 - 790.6 )

Volume Invert Avail.Storage Storage Description

#1 118.60' 0.019 af 159.8" W x 24.0" H Box StormTrap 2.0 L= 31.7'

Device Routing Invert Outlet Devices

#1 Device 3 120.10' 48.0" W x 6.0" H Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads

#2 Device 3 118.55' 1.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #3 Primary 118.55' 15.0" Round Culvert L= 12.0' Ke= 0.500

Inlet / Outlet Invert= 118.55' / 118.45' S= 0.0083 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 1.23 sf

Primary OutFlow Max=0.02 cfs @ 12.47 hrs HW=119.26' (Free Discharge) 3=Culvert (Passes 0.02 cfs of 1.55 cfs potential flow)

1=Orifice/Grate ( Controls 0.00 cfs) 2=Orifice/Grate (Orifice Controls 0.02 cfs @ 3.93 fps)

Page 11HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Pond 8P: StormTrap 2.0

Inflow Primary

Hydrograph

Time (hours) 484644424038363432302826242220181614121086420

F lo w

(c fs

0.32

0.3

0.28

0.26

0.24

0.22

0.2

0.18

0.16

0.14

0.12

0.1

0.08

0.06

0.04

0.02

Inflow Area=0.400 ac

Peak Elev=119.26'

Storage=0.006 af

0.30 cfs

Page 12HydroCAD® 10.10-4a s/n 01592 © 2020 HydroCAD Software Solutions LLC

Summary for Pond 9P: CB-8

[57] Hint: Peaked at 118.48' (Flood elevation advised) [79] Warning: Submerged Pond 8P Primary device # 3 OUTLET by 0.03'

Inflow Area = 0.400 ac, 45.00% Impervious, Inflow Depth = 0.43" for 95% event Inflow = 0.02 cfs @ 12.47 hrs, Volume= 0.014 af Outflow = 0.02 cfs @ 12.47 hrs, Volume= 0.014 af, Atten= 0%, Lag= 0.0 min Primary = 0.02 cfs @ 12.47 hrs, Volume= 0.014 af

Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.01 hrs Peak Elev= 118.48' @ 12.47 hrs

Device Routing Invert Outlet Devices

#1 Primary 118.40' 18.0" Round Culvert L= 70.0' Ke= 0.500 Inlet / Outlet Invert= 118.40' / 117.00' S= 0.0200 '/' Cc= 0.900 n= 0.025 Corrugated metal, Flow Area= 1.77 sf

Primary OutFlow Max=0.02 cfs @ 12.47 hrs HW=118.48' (Free Discharge) 1=Culvert (Barrel Controls 0.02 cfs @ 0.95 fps)

Pond 9P: CB-8

Inflow Primary

Hydrograph

Time (hours) 484644424038363432302826242220181614121086420

F lo w

(c fs

0.024

0.023

0.022

0.021

0.02

0.019

0.018

0.017

0.016

0.015

0.014

0.013

0.012

0.011

0.01

0.009

0.008

0.007

0.006

0.005

0.004

0.003

0.002

0.001

Inflow Area=0.400 ac

Peak Elev=118.48'

18.0"

Round Culvert n=0.025

L=70.0'

S=0.0200 '/'

Appendix D – Foundation Engineering Report dated 12-

12-2024

FOUNDATION ENGINEERING REPORT

ALBURG SPRINGS LAND

PORT OF ENTRY

ALBURG SPRINGS, VERMONT

DECEMBER 13, 2024

Prepared For:

Schwartz Silver

75 Kneeland Street

Boston, MA 02111

PROJECT NO. 7945.2.00

42 3rd Avenue

Burlington, MA 01803 www.mcphailgeo.com

(617) 868-1420

December 13, 2024

GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERS

42 3rd Avenue

Burlington, MA 01803

(617) 868-1420

Schwartz Silver

75 Kneeland Street

Boston, MA 02111

Attention: Kerri Frick, AIA

Reference: Addition to the Alburg Springs Land Port of Entry; Alburg Springs, Vermont

Foundation Engineering Report – Executive Summary

Enclosed is our Foundation Engineering Report for the above-referenced project. The following is an executive summary of the report. Our services were conducted in accordance with our proposal for geotechnical engineering services dated October 16, 2024, and the subsequent authorization of Schwartz Silver.

It is understood that the proposed development includes the construction of two (2) approximately 500-square-foot (plan area) additions: one abutting the south side of the customs building and the other abutting the west side of the customs building. Both additions are understood to contain a basement level with a lowest level slab at Elevation

+117.

It is recommended that foundations for support of new additions consist of conventional spread footings. Footings should bear directly on the natural glacial till deposit or bedrock and be proportioned utilizing an allowable net bearing pressure of two (2) tons per square foot. The lowest level slabs area recommended to consist of conventional soil-supported slabs-on-grade. Underslab and perimeter foundation drainage are recommended.

Other detailed geotechnical engineering recommendations and criteria for foundation design are documented in the report, as well as foundation construction considerations such as rock removal and building pad preparation, construction dewatering, and on-site reuse of excavated soil. Furthermore, construction observation considerations are also presented herein.

We look forward to continued participation with the design team during the remainder of the project. Should you have any questions concerning the recommendations presented herein, please do not hesitate to call us.

Sincerely, McPHAIL ASSOCIATES, LLC

Dylan W. Locke Jonathan W. Patch, P.E.

VT PE# 018.0098849 Expires July 31, 2026 \\McPhail-fs4\McPhail\Working Documents\Reports\7945_AlburgSpringsLPOE_FER_121324.docx

SGAF/dwl/jwp/tjf

CONTENTS:

1.0 - INTRODUCTION

1.1 - GENERAL

1.2 – PURPOSE AND SCOPE

1.3 – AVAILABLE INFORMATION

1.4 – ELEVATION DATUM

2.0 – SITE AND PROJECT DESCRIPTION

2.1 – EXISTING SITE CONDITIONS

2.2 – PROPOSED DEVELOPMENT

3.0 – SUBSURFACE EXPLORATIONS

4.0 – SUBSURFACE CONDITIONS

4.1 – SOIL AND BEDROCK CONDITIONS

4.2 – GROUNDWATER CONDITIONS

4.3 – EXISTING FOUNDATION CONDITIONS

4.4 – IN SITU INFILTRATION TESTING

5.0 – GEOTECHNICAL RECOMMENDATIONS

5.1 – FOUNDATION DESIGN RECOMMENDATIONS

5.2 – RECOMMENDATIONS FOR BUILDING PAD PREPARATION

5.3 – LOWEST LEVEL SLAB RECOMMENDATIONS

5.4 – GROUNDWATER CONSIDERATIONS

5.5 – RESISTANCE TO LATERAL FORCES

5.6 – RADON MITIGATION SYSTEM

5.7 – SEISMIC DESIGN CONSIDERATIONS

6.0 – FOUNDATION CONSTRUCTION CONSIDERATIONS

6.1 – GENERAL RECOMMENDATIONS

6.2 – BEDROCK REMOVAL AND BUILDING PAD PREPARATION

6.3 – GROUNDWATER CONTROL

6.4 – PROOF COMPACTION OF SUBGRADES FOR HARDSCAPE

6.5 – VIBRATION MONITORING

6.6 – REUSE OF ON-SITE SOILS

7.0 – FUTURE WORK

7.1 – DESIGN ASSISTANCE

7.2 – BIDDING PHASE CONSULTATION

7.3 – CONSTRUCTION OBSERVATION

8.0 – LIMITATIONS

FIGURES:

FIGURE 1: PROJECT LOCATION PLAN

FIGURE 2: SUBSURFACE EXPLORATION PLAN

FIGURE 3: GRAIN SIZE DISTRIBUTION – FILL

FIGURE 4: LIMITS OF GRAVEL BORROW

FIGURE 5: FOUNDATION DRAINAGE DETAIL

FIGURE 6: LATERAL EARTH PRESSURES FOR DESIGN OF BELOW-GRADE WALLS

APPENDICES:

APPENDIX A: EXPLORATION AND LABORATORY TESTING PROCEDURES

APPENDIX B: TEST PIT LOGS AND PHOTOGRAPHS

FOUNDATION ENGINEERING REPORT ALBURG SPRINGS LAND PORT OF ENTRY

DECEMBER 13, 2024 PAGE 1

1.0 - INTRODUCTION

1.1 - GENERAL

This report presents the results of our subsurface exploration program and foundation design study for the proposed addition to the US Border Crossing at Alburg Springs located in Alburg Springs, Vermont. Refer to the Project Location Plan, Figure 1, for the general site locus.

The subsurface exploration program was conducted, and the foundation engineering services were performed in accordance with our proposal for geotechnical engineering services dated October 16, 2024, and the subsequent authorization of Schwartz Silver.

These services are subject to the limitations contained herein.

1.2 – PURPOSE AND SCOPE

The purpose of the subsurface exploration program and foundation engineering study was to document the subsurface soil, bedrock and groundwater conditions at the site to provide geotechnical engineering recommendations for economical foundation design for the proposed additions.

Foundation design includes foundation support of the proposed building additions and their lowest level slabs, treatment of the lowest level slabs in consideration of groundwater, lateral earth pressures on foundation walls, and seismic design considerations in accordance with the provisions of the Vermont Fire and Building Safety Code, 2015 Edition (Code), which corresponds to the 2015 Edition of the International Building Code (IBC). Foundation construction considerations relating to geotechnical aspects of the proposed construction are also presented herein.

1.3 – AVAILABLE INFORMATION

Information available to McPhail Associates, LLC (McPhail) included the following:

• A 20-scale plan entitled “Existing Conditions” prepared by Trudell Consulting

Engineers dated August 9, 2024.

• A set of architectural drawings for the proposed addition entitled “GSA Alburg

Springs LPOE – Option C, 303 Alburg Springs Rd, Alburg Springs, VT 05440” prepared by Schwartz Silver dated October 10, 2024.

• A geothermal feasibility study entitled “Preferred Alternative Feasibility Report

(Submission 4)” prepared by Alares Engineering dated March of 2023.

DECEMBER 13, 2024 PAGE 2

1.4 – ELEVATION DATUM

Elevations cited herein are in feet and are referenced to the North American Vertical Datum

1988 (NAVD88).

2.0 – SITE AND PROJECT DESCRIPTION

2.1 – EXISTING SITE CONDITIONS

The existing US Border Crossing at Alburg Springs consists of a single customs building occupying an approximately 800-square-foot plan area, and a detached garage/storage building occupying an approximately 400-square-foot plan area. It is understood that the customs main building has a basement with a lowest level slab at Elevation +117, is two stories in height, and has an attached sallyport that fronts onto Alburg Springs Road to the east for vehicular customs check-in. The buildings are surrounded by wooded areas and are in close proximity to the Canada-United States border to the north.

Grades at the site generally slope up from west to east with grades Alburg Springs Road varying from approximately Elevation +122 to Elevation +124 up to Elevation +137 to

Elevation +141 at the western side of the site.

2.2 – PROPOSED DEVELOPMENT

It is understood that the proposed development includes the construction of two (2) approximately 500-square-foot (plan area) additions: one abutting the south side of the customs building and the other abutting the west side of the customs building. Both additions are understood to contain a basement level with a lowest level slab at Elevation

+117. We understand that the basement slabs associated with both additions would match the existing basement slab. The project will also require the installation of new utilities and a leach field.

It is understood that the customs building and additions would be heated/cooled via a ground source heat pump (geothermal energy). Reportedly, one geothermal test well has been installed, and the building will require two (2) more geothermal wells to satisfy the energy load requirements of the project.

3.0 – SUBSURFACE EXPLORATIONS

The approximate location of the subsurface explorations is indicated on the enclosed

Subsurface Exploration Plan, Figure 2. The following subsurface explorations were completed under contract to McPhail:

• Three (3) test pits (TP-1, TP-2, and TP3) completed on November 15, 2024, by CSS, LLC under contract to McPhail.

Exploration procedures and soil classification methods are contained in Appendix A.

DECEMBER 13, 2024 PAGE 3

The test pits were excavated to depths ranging from approximately 1.8 to 7.8 feet below the existing ground surface and terminated within the glacial till deposit, or on bedrock.

Test pit logs and photographs are contained in Appendix B.

4.0 – SUBSURFACE CONDITIONS

4.1 – SOIL AND BEDROCK CONDITIONS

A detailed description of the subsurface conditions encountered in the explorations is documented on the test pit logs contained in Appendix B as described above. Based on the explorations performed at the site by McPhail, the following is a description of the generalized subsurface conditions across the site encountered from ground surface downward.

Generalized Subsurface

Strata

Approximate Thickness

(Feet)

Top of Soil Strata

(Elevation)

Topsoil 0.8 Ground Surface

(El. +125 to El. +126)

Fill

(TP-2 only)

El. +125.2

(Where encountered)

Glacial Till

1 in TP-2 where fully penetrated to greater than

3.2 in TP-3

El. +124.2 to El. +125.2

(Where encountered)

Bedrock - El. +118.2 to El. +124.2

(Where encountered)

Topsoil: The existing ground surface at the test pits was generally observed to consist of an approximately 0.8-foot-thick layer of topsoil. In general, the topsoil was observed to consist of a loose to compact, dark brown, silty sand with organic fibers and roots.

Fill Material: In test pit TP-2, a fill layer was observed underlying the topsoil. The fill layer was generally observed to consist of very dense, dark brown silty gravel, some sand, with some shale fragments (cobbles) throughout. The fill is believed to consist of reworked natural glacial till. A grain size distribution of a sample of the fill material is presented in the enclosed Figure 3.

Glacial Till: In test pits TP-1 and TP-3, a glacial till deposit was observed underlying the topsoil. The glacial till was generally observed to consist of dense to very dense, dark brown silty gravel, some sand, with some shale fragments (cobbles) throughout. The elevation of the surface of the glacial till deposit at test pits TP-1 and TP-3 is indicated on Figure 2.

Bedrock: The fill material and glacial till deposit were underlain by bedrock in test pits TP-1 and TP-2. The top of the bedrock corresponds to the Stony Point Shale geologic group which

DECEMBER 13, 2024 PAGE 4

consists of a black calcareous shale with thin interlayers of gray limestone. The elevation of the surface of the bedrock at test pits TP-1 and TP-2 is indicated on Figure 2.

4.2 – GROUNDWATER CONDITIONS

Groundwater was not encountered in the completed test pits. It is anticipated that future groundwater levels across the site may vary from those reported herein due to factors such as normal seasonal changes and alterations of existing drainage patterns or become perched on the surface of the relatively impervious glacial till or bedrock surfaces particularly during or following periods of heavy precipitation.

4.3 – EXISTING FOUNDATION CONDITIONS

The 2-story structure contains one level of below-grade space with a lowest level slab located at approximately Elevation +117.0. It is anticipated that the existing building is supported on spread footing foundations that bear directly on the bedrock. The bottom of the existing foundation was not exposed in test pit TP-2 due to refusal on bedrock at a depth of 7.8 feet which corresponds to Elevation +118.2. No indications of damp proofing or waterproofing were observed along the exposed exterior face of the foundation wall in test pit TP-2. Furthermore, a foundation drain pipe was not observed.

4.4 – IN SITU INFILTRATION TESTING

In situ infiltration tests were performed within test pits TP-1, TP-2, and TP-3 utilizing a constant head Pask Permeameter. The tests were performed within the fill material and the glacial till deposit generally 0.8 to 4 feet below ground surface. The infiltration tests were performed in general accordance with ASTM D5126 and the Pask Permeameter manufacturer directions. The results of the tests in test pits TP-1 and TP-2 were nondeterminate due to the large percentage of shale cobbles at the tested elevation.

The result of the in situ infiltration test in TP-3 is presented in the table below. It should be noted that the existing site soils are heterogeneous in composition and variable in density;

thus, it is anticipated that the coefficient of permeability will be highly variable and the results of our permeability testing may not be representative of all site soils.

Test Location Field Saturated

Hydraulic

Conductivity, Kfs

(inch/hour) Exploration

Depth below GS

(ft)

Elevation

TP-3 0.8 +124.2 4.94

DECEMBER 13, 2024 PAGE 5

5.0 – GEOTECHNICAL RECOMMENDATIONS

5.1 – FOUNDATION DESIGN RECOMMENDATIONS

Based on the scope of the proposed construction and the subsurface conditions encountered at the site, it is recommended that the proposed additions to the existing building be founded on conventional spread footing foundations.

The following parameters are recommended for the design of the foundations:

• Footings should bear directly on a 6-inch minimum to 12-inch maximum thickness of

3/4-inch crushed stone placed directly over the undisturbed, glacial till deposit or intact sound bedrock.

o In the event that the surface of the natural glacial till deposit or intact sound bedrock is below the design bottom of footing elevation, gravel borrow should be placed and compacted over the surface of the glacial till deposit or intact sound bedrock following the removal of existing topsoil, fill, disturbed glacial till, or disturbed bedrock fragments. Refer to Section 5.2 – Recommendations for Building Pad Preparation below for additional information.

• For continuity of design for the varying materials supporting the footings, footings should be designed utilizing an allowable net bearing pressure of two (2) tons per square foot.

• The minimum footing width for continuous footings (including haunched or thickened slabs supporting structural load) and isolated footings should be 24 inches and 30 inches, respectively.

• Frost Protection:

o Perimeter foundations and interior foundations bearing on soil below unheated areas should be provided with a minimum of 5-foot thickness of soil cover as frost protection.

o Foundations bearing on bedrock should be provided with a minimum 2-foot thickness of soil cover as frost protection.

o Interior foundations below heated areas should be located such that the top of foundation concrete is a minimum of six (6) inches below the underside of the lowest level slabs.

• Proposed footings to be located directly adjacent to existing foundations should bear at the same elevation as the existing foundations.

• Where foundations are to be supported on the intact sound bedrock surface, loose and displaced rock resulting from rock excavation methods should be removed, including disturbed bedrock below the design bottom of footing level that results from rock excavation.

DECEMBER 13, 2024 PAGE 6

o The intact sound bedrock should be leveled such that the surface slopes at no more than a rate of 12 horizontal to 1 vertical.

o A minimum 6-inch thickness of ¾-inch crushed stone should be placed between the bottom of footing and the sound bedrock surface.

• Foundations should be designed in accordance with the Code.

5.2 – RECOMMENDATIONS FOR BUILDING PAD PREPARATION

As stated above, existing topsoil, and/or fill material must be removed from below the proposed addition footprints. Based on the test pits performed in the vicinity of the proposed building footprint, the surface of the glacial till is anticipated to range from approximately Elevation +124.2 to Elevation +125.2 and the surface of the bedrock is anticipated to range from approximately Elevation +118.2 to Elevation +124.2. Anticipating that the design bottom of footing elevation for the below-grade space of the building will generally be at about Elevation +116, it is anticipated that footings will bear on bedrock.

Furthermore, up to about 8 feet of bedrock removal is anticipated to be required.

Should the surface of the natural undisturbed glacial till or sound bedrock be below the design bottom of footing or slab, the following parameters are recommended for the use of gravel borrow to raise the subgrade for support of proposed footings and slabs:

• Gravel Borrow o Refer to the attached Figure 4 for the required lateral and vertical limits of gravel borrow for support of spread footings which are as follows:

▪ The plan limits of the placement of gravel borrow should extend laterally beyond the edges of the footings for a horizontal distance equal to the depth measured from the design bottom of footing elevation to the surface of the natural, inorganic glacial till deposit or bedrock, plus two (2) feet.

• Example: where the surface of the natural soil is four (4) feet below the design bottom of footing elevation, compacted gravel borrow will be required to extend laterally outward from the edge of the footing for a horizontal distance of six (6) feet.

o Gravel borrow should derive from an off-site source and consist of a well-graded sand and gravel with less than 8 percent by weight passing the No.

200 sieve.

o Gravel borrow should be placed in lifts having a compacted thickness of 6 inches and be compacted to a minimum of 95 percent of its modified Proctor maximum dry density.

Gravel borrow needs to be placed in-the-dry on an undisturbed bearing surface.

DECEMBER 13, 2024 PAGE 7

5.3 – LOWEST LEVEL SLAB RECOMMENDATIONS

The lowest level slabs are recommended to consist of conventional soil-supported slabs-on-grade. The slabs should be underlain by a polyethylene vapor barrier spread across the surface of a 12-inch thickness of compacted 3/4-inch crushed stone placed over a layer of filter fabric that is spread across the undisturbed glacial till or bedrock subgrade or over gravel borrow that is placed and compacted over the undisturbed glacial till or bedrock subgrade.

5.4 – GROUNDWATER CONSIDERATIONS

In consideration of the lowest level slab being below the proposed exterior finished grades, it is recommended that perimeter and underslab foundation drainage be provided. The perimeter and underslab drains are intended to minimize groundwater intrusion into the below grade space due to conditions when groundwater may become temporarily elevated due to precipitation events, surface water run-off, and/or seasonal groundwater changes.

The underslab and perimeter drainage systems are not intended to lower the existing groundwater level. Furthermore, unless a perimeter drainage system is also constructed around the existing building footprint outside the addition footprint, then the perimeter drainage system may not be effective in minimizing groundwater intrusion into the existing basement should it be occurring.

A conceptual foundation drainage detail is attached as Figure 5. The following is recommended for the design of the perimeter and…