09003_Florence Mill_Soil Vapor Memo_2018.12.10

AECOM
1600 Perimeter Park Drive, Suite 400
Morrisville, NC 27560
Phone: [phone]
Fax: [phone]
Memorandum

This memorandum summarizes the installation of the vapor barrier system for the Snack Bar / Rest
room building at the subject site. The site is registered with the North Carolina Brownfield program
under Contract Number 09003-05-81. Specifications included in the Environmental Management Plan
(EMP) [AECOM, August 2017] specified that high density polyethylene (HDPE) sheeting of 40 mil
thickness be installed as a vapor barrier to prevent Vapor Intrusion from the traces of organic
compounds that remain in the soil and groundwater of the site from prior site occupants. Due to the
relatively high frequency of stub-out plumbing connections within the target building, the construction
company elected to utilize a Geo-Seal® system manufactured by Land-Science Technologies. The
core of the Geo-Seal® system is a spray-on composite material that serves as the primary sealant.
The core is sprayed onto an HDPE liner placed over the gravel base for the building. After smoke
testing to confirm an adequate seal, a final bond sheet is laid over the composite core in preparation
for the installation of the concrete slab. The following summarizes the observations of the installation in
December 2017, and subsequent activities.

Documentation
AECOM arrived at the project site the morning of December 13, 2017. Contaminant Control Inc. (CCI)
was performing the Geo-Seal® system installation. At that time the gravel base had been installed,
and each of the stub-up pipes had been fitted with a blue sleeve that ran below the gravel surface.
CCI was in the process of placing the green HDPE liner over the gravel base, and fitting the stub-up
pipes with black sleeves which were secured to the HDPE and to each pipe with a blue duct tape. The
seams of the HDPE liner were sealed with glue and blue tape.
While the original design called for a single slotted pipe to be installed as a vent within the gravel, CCI
had instead placed a Geo-Seal® Vapor-Vent™ system along the top of the gravel with two vent
stacks. The stacks were placed to vent vapors from underneath the building to atmosphere. Thus,
there would be two vent pipes within the footprint of the building rather than the single vent originally
sketched on the eastern end of the building. This change had been previously discussed and deemed
an improvement on the overall design.
Date: Thursday, November 29, 2018
To: Tracy Wahl (NC Brownfields – Asheville Regional Office)
CC: John Condray and Jimmy Clay (Town of Forest City)
From: Conan Fitzgerald (AECOM)
Subject: Florence Mill Brownfield Project: Vapor Barrier System documentation

Page 2

In the afternoon CCI began to spray the composite Geo-Seal® Core over the HDPE, with a target
minimum thickness of 40 mil. The core was placed over the HDPE in all areas, as well as over the
taped joints for the stub-up pipes.
Evaluation
For the purposes of testing the building footprint was divided into east and western areas, separated
by a concrete block divider installed as part of the building foundation. Small sections of the liner
system were cut out for measuring, to compare against to the 40 ml (0.040 inch) objective. All
sections passed, with the East section ranging from 0.0785 to 0.1290 in, and the western side ranging
from 0.1190 to 0.1330 in.
After the cut sections were patched, CCI proceeded to conduct smoke testing. A slice of the center of
each section was cut, and then smoke was applied to the underside of the liner. In each area 2-3
stub-ups required additional core spray. Once this was complete, smoke was visible from the vent
indicating that the system was properly directing surface vapors to the vent system. A thick patch was
installed over each smoke insertion point, and the seal was considered complete. The following day
the white protective Geo-Seal® bond was placed as the final step in preparation for concrete.
Subsequently, once the building was installed, the vents were piped to the attic portion of the building
and vented through the roof.
Summary
The GeoSeal™ system as installed by CCI was consistent with the specifications in the 2017 EMP,
and should be more than adequate to minimize vapor intrusion in the subject building.
Attachments
Attachment A Photo Documentation
Attachment B As-Built Drawings

References
AECOM, “Environmental Management Plan – Florence Mill in Forest City, NC”, August 16, 2017.

Attachment A
Photo Documentation

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
1
Date:
12/13/17

Direction Photo
Taken:
Northwest

Description:

Site Overview. CCI
installing Green Plastic
Base

Photo No.
2
Date:
12/13/17

Direction Photo
Taken:
West

Description:

East Side Green Plastic
Base installation
complete

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
3
Date:
12/13/17
Direction Photo
Taken:
Northwest

Description:
Focus on Stub-up
Seals

Photo No.
4
Date:
12/13/17
Direction Photo
Taken:
East

Description:

Vent Pipe Connection

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
5
Date:
12/13/17
Direction Photo
Taken:
North

Description:

Begin spraying
GeoSeal on east side

Photo No.
6
Date:
12/13/17
Direction Photo
Taken:
North

Description:

Spraying GeoSeal on
west section

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
7
Date:
12/13/17
Direction Photo
Taken:
Northeast

Description:

Geoseal Layer
installation complete on
East Side. Prepping
final forms for concrete
in the background

Photo No.
8
Date:
12/13/17
Direction Photo
Taken:
East

Description:

Geoseal Close Up
Southern Wall Edge

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
9
Date:
12/13/17
Direction Photo
Taken:
North

Description:

Geoseal Layer
installation complete on
West Side

Photo No.
10
Date:
12/13/17
Direction Photo
Taken:
North

Description:

Smoke Test in progress
on Western Section

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
11
Date:
12/13/17
Direction Photo
Taken:
Northeast

Description:

Begin Installing White
Protective Sheet

Photo No.
12
Date:
12/13/17
Direction Photo
Taken:
East

Description:

Ready for Concrete

Page 7 of 10

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
12
Date:
8/22/18

Direction Photo Taken:
Facing North

Description:

Vapor Barrier vent system in Snack Bar
roof.

Page 8 of 10

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
12
Date:
8/22/18

Direction Photo Taken:
Facing North

Description:
Vapor Barrier vent system in Snack Bar
roof.

Page 9 of 10

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
12
Date:
8/22/18

Direction Photo Taken:
Facing South

Description:
Vapor Barrier Riser enters attic
(typical).

Page 10 of 10

PHOTOGRAPHIC LOG
Client Name:
Forest City
Site Location:
Florence Mill
Project No.
60547658
Photo No.
12
Date:
8/22/18

Direction Photo Taken:
Facing South

Description:
Vapor Barrier Vent exits building on
north side (typical for 2).

Attachment B
As-Built Drawings