FOUNDRY_Revised Sampling Plan_Supplmtal Sub-Slab Vapor Sampling 5.12.14-OCR

GEQSCIENCE
GROUP
May 12, 2014
Fotmdry Uptown, LLC and
Foundry Partners, LLC
7804 Fairview Road, Plvffi 327
Charlotte, North Carolina 28226
Attention: Mr. Chris Warren
Reference: Revised Sampling Plan -Supplemental Sub-Slab Vapor Sampling
The Foundry-601 South Cedar Street Building
Charlotte, North Carolina
Geoscience Project No. CH13.0014.EV
Consulting Engineers
It is our understanding that the North Carolina Brownfields Program (NCBP) has requested
that additional sub-slab vapor samples be collected at the subject site. The purpose of this
proposed sub-slab vapor sampling event is to further assess the potential for vapor intrusion
into the existing buildings at 601 , 619, and 623 South Cedar Street.
INTRODUCTION
The project site is located along the southeastern side of South Cedar Street, immediately east
of its intersection with West Hill Street in Charlotte, North Carolina. The site is comprised of
Mecklenburg County Parcel ID Nos. 07318103, 07318107, 07318109, 07318201, and
07318205. Three (3) commercial buildings currently occupy the property. The existing
buildings have physical addresses of 601, 619, and 623 South Cedar Street, respectively.
Background: On March 21, 2013, Geoscience installed temporary sub-slab vapor
monitoring points (SSV-1 through SSV-3) on the property. The approximate locations of the
points are indicated on the attached Figure No. CH13.0014.EV-A. Geoscience attempted to
install a fourth monitoring point in the northwestern portion of the 601 South Cedar Street
building. However, the tenant space that we were provided access to in that portion of the
building had a wood framed floor elevated above the concrete slab that was in contact with
the ground surface. The wood framed floor prevented direct access to the concrete slab. As
a result, no sub-slab sample was collected from beneath that portion of the 601 South Cedar
Street building during that sampling event. However, Geoscience returned to the site and
installed a temporary sub-slab vapor monitoring point (SSV-6) in a vacant tenant space
located in the northwestern portion of the 601 South Cedar Street building in March 27 2014.
Analysis of these initial sub-slab sampling events revealed the presence of several VOCs in
the soil gas beneath the buildings. However, none of the compounds detected exceed the
current (January 2014) acceptable soil gas concentration screening levels for residential or
industrial/ commercial properties.
500 Clanton Road
Suite K
Charlotte. North Carolina
28217
Telephone
704.525.2003
Facsimile
704.525.2051
Foundry Uptown, LLC and
Foundry Partners, LLC
Geoscience Project No. CH13.0014.EV
May 12, 2014
Page2
PROPOSED SAMPLING PLAN
Sampling Locations: Ten (10) additional sampling locations are proposed on the subject
site. The approximate locations of the proposed samples (PV-1 through PV-10) are indicated
on Fig. No. CH13.0014.EV-A, attached. As shown, one (1) additional sample will be
collected at 623 South Cedar Street, five (5) additional samples will be collected at 619
South Cedar Street and four (4) additional samples will be collected at 601 South Cedar
Street.
Temporary sub-slab monitoring points will be established at the selected locations. These
temporary monitoring points will be created by grouting~ inch diameter Teflon tubing into a
hole drilled through the building floor slab. The soil gas samples will be collected
approximately one inch or less below the bottom of the concrete slabs that comprise the
lower level floors of the buildings. The newly installed sub-slab vapor monitoring points
will be allowed to equilibrate for approximately 24 hours before samples are collected.
It is our understanding that the two (2) portions of the 601 South Cedar Street building share
a common floor slab. We further understand that this floor slab extends under the breezeway
that separates the building sections. Therefore, proposed monitoring point PV-9 is
anticipated to be close to the center of the floor slab. Should the floor slab not extend
between the building portions, a temporary soil gas monitoring well at least 5 feet deep will
be set at the proposed location of PV-9.
Sampling Strategy: Various types of information will be obtained and recorded for this
sampling effort. The "DWM Indoor Air Building Survey and Sampling Form" will be used
to record data regarding building type, building contents, occupant information, sampling
information, and prevailing weather conditions during the sampling event.
The sample canisters, monitoring points and associated tubing will be enclosed within plastic
shrouds. Throughout the sample collection process, an approximately 25% helium
atmosphere will be maintained within the shroud. Prior to sample collection, three (3)
volumes of the sampling train will be purged from the monitoring point at a rate not to
exceed I 00 ml/min. Following the purge, a helium detector will be used to monitor the
concentration of helium in gases being drawn through the sampling train. Helium
concentrations measured in the sampling train that are less than 10% of the shroud
concentration will be considered acceptable.
Each sub-slab gas sample will be collected using a I-Liter Summa canister fitted with a flow
orifice pre-calibrated to collect a sample over a 10 minute period (100 ml/min.). Once the
sampling period has been completed, the canister will be boxed and shipped to the laboratory
for analysis. The collected samples will be analyzed for VOCs by EPA Method T0-15. In
addition, each sample will be analyzed for helium content.