21007_Hoke Street_VIWP_20180427

Aptus Management, PLLC
Environmental Management Solutions

Aptus Management, PLLC
109 Amber Court
Carrboro, NC 27510

April 27, 2018

Ms. Sarah Hardison Young VIA EMAIL: [e-mail]
Brownfields Project Manager
NC Division of Waste Management
217 W Jones St.
Raleigh, NC 27603-6100
SUBJECT: REVISED VAPOR INTRUSION INDOOR AIR TESTING WORK PLAN
PASSAGE HOME SITE – RALEIGH, NORTH CAROLINA BROWNFIELDS PROJECT NUMBER: 21007-17-092

Dear Ms. Young:

Based on your February 21, 2018 comments to the sub-slab vapor intrusion (VI)
assessment report submitted on January 13, 2018, Aptus Management, LLC (Aptus) has
prepared this work plan for conducting indoor air (VI) testing at the Passage Home, Inc.
site located at 500 Hoke Street in Raleigh, Wake County, North Carolina. A site location
map is provided in Drawing 1. A site map is also provided in Drawing 2 for the Passage
Home site, which includes parcels from 500 Hoke Street (with the existing building), 506
Hoke Street, and 1412 Garner Road.

Please note that this work plan addresses indoor air testing within the existing building
only. This work plan has been revised per NC Brownfields Program (NCBP) final review
comments received on April 10, 2018. A separate submittal is being prepared to address
assessment regarding the proposed greenhouse and urban agriculture structures at the
Passage Home site.
PRIOR SOIL GAS RESULTS
The findings from the October 11, 2017 sub-slab soil gas sampling of the existing building
indicated minimal detections of various volatile organic compounds (VOCs) at each of the
sampling locations except one analyte, tetrachloroethylene (PCE). PCE at the southwest
building quadrant sample location (SS-3) was the only analyte detected at a concentration
greater than the NC residential soil gas screening level (NCRSGSL). The soil gas
concentration was 590 ug/m3, versus the NCRSGSL of 280 ug/m3 (a 2.1-fold
exceedance). However, a risk assessment performed using the October 2017 NCDEQ’s
Risk Calculator showed the cumulative risk from vapor intrusion was acceptable.
Moreover, the detected PCE concentration was less than 17% of the nonresidential
NCSGSL of 3,500 ug/m3.

While the building is presumed to have good VI attenuation due to measured floor slab
thickness (6.5- to 8-inches) and the use of a commercial-grade heating, ventilating, and air
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conditioning (HVAC) system that will increase air exchange rates, indoor air testing was
recommended for confirmation purposes. This was due to the future use of the site as a
community center with intermittent presence of children inside the building.

Consequently, the objective of this sampling effort is to evaluate indoor air within the
building to confirm that PCE is below acceptable guideline levels and protective of future
site occupants.
SITE-SPECIFIC CHEMICALS OF CONCERN (COCs)
Based on the soil gas sampling testing, the only contaminant of concern at the site is PCE.
During review of the laboratory results from the October sampling, it was noted that 1,1,2-
trichloroethane (1,1,2-TCA) had a laboratory reporting limit (RL) that was greater than the
NCRSGSL. Discussions with the lab in this regard concluded that 1,1,2-TCA was not
detected in the samples and that concentrations were reported to the minimum detection
limit (MDL) of the method, given the presence of other analyte concentrations and matrix
interferences in the samples. Levels of 1,1,2-TCA from the soil gas testing were reported
in the range of 2.3 to 3.5 ug/m3. These concentrations, which were below the RLs, ranged
between 3.4 to 5.5 ug/m3. The NCRSGSL for 1,1,2-TCA is 1.4 ug/m3. While 1,1,2-TCA
was not detected in any of the samples, the MDLs ranged from 178% to 250% of the
NCRSGSL.

The current NC residential indoor air screening level (NCRIASL) for 1,1,2-TCA is 0.042
ug/m3. This is considerably lower than the soil gas screening level noted above.
Discussions with various laboratories indicate that, after final calculations, the lowest
possible lab detection limit for 1,1,2-TCA is 0.071 ug/m3 up to 0.11ug/m3. Since these
laboratory MDLs/RLs cannot reach the indoor air screening level for 1,1,2-TCA even under
ideal conditions, and each of the other detected chlorinated analytes (besides PCE) were
an order of magnitude below the NCRSGSLs, it is the opinion of Aptus that 1,1,2-TCA
should not be considered a site-specific COC.

Therefore, since guidance recommends that indoor air sample analyses be limited to the
chemicals of concern to eliminate background sources, this work plan will request analysis of only those analytes detected during the prior soil gas sampling for the indoor air sampling at the site, and omit analysis of 1,1,2-TCA. This is suggested
based on NCBP comments and because, according to air analysis laboratories, such low
screening levels (i.e., 1,1,2-TCA) appears to be beyond the scope of the current
methodologies available, as well as the current analytical instrumentation available. A list
of site-specific analytes, which includes PCE and daughter products, is shown below:

Acetone
2-Butanone (MEK)
Carbon Tetrachloride
Chloroform
Cyclohexane
cis-1,2-dichloroethene
trans-1,2-dichloroethene
Ethyl Acetate
Ethylbenzene
Heptane
Hexane
2-Hexanone (MBK)
Isopropanol
Naphthalene
Propene
Tetrachloroethylene
Tetrahydrofuran
Toluene
1,1,1-Trichloroethane
Trichloroethylene (TCE)
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
Vinyl Chloride
Xylenes

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SAMPLING WORK PLAN
Following receipt of initial comments from the NCBP, Aptus contacted the building
architect to obtain plans showing current and proposed building layouts. These were used
to select sampling locations for indoor air testing in relation to the prior sub-slab sampling,
as well as present future partitioning of the building floorplan located at 500 Hoke Street
(the Site).

According to Mr. Steve Vebber, Operations Management Consultant for Passage Home,
Inc., the estimated ages of building occupants upon completion of construction are as
follows:

• 90% of the people in the finished building will be 18 years of age or older, and
• The remaining 10% may be children that accompany the adult building occupants.

With this occupant breakdown, Aptus will collect the indoor air samples at a breathing
zone height of five (5) feet above floor level.

Aptus proposes to collect the samples at five locations inside the existing building, of
which one location will include a duplicate. One outdoor ambient air sample will also be
collected simultaneously upwind of the building at breathing zone height for background
comparison purposes. For comparison purposes, the existing layout drawing from the
architect was superimposed with the sample locations from the October soil gas sampling
event (see Drawing 3). The proposed indoor air sampling locations shown in Drawing 4
include an underlay of the architect’s proposed building layout following completion of
construction. Presently, the interior of the building (Drawing 3) is quite open with minimal
wall partitions. Thus, the locations proposed for this round of sampling should provide
sufficient characterization of the indoor air within the entire building. The actual locations
will be determined in the field based on visual observations, locations of walls, doors,
flooring conditions, etc. and/or as directed by the NCBP based on their review of this work
plan.

The work will be conducted in accordance with current Brownfield’s Program VI screening
levels and guidance1. (Note that the guidance document and the VI screening levels have
been updated since the prior testing was conducted. The screening levels for the COCs,
however, remained unchanged.) Additionally, per NCBP comments, since the prior
October sampling was conducted during warm weather conditions (average ambient
temperature 71.5 °F), we propose to conduct the indoor air sampling under similar
conditions (i.e., when temperatures are expected to remain above 60 °F throughout the
test period). This suggestion was provided in the NCBP comments so that additional
concurrent soil gas sampling will not be required. The Indoor Air Building Survey and
Sampling Form (Appendix C) will be completed and provided with the final report. The
testing lab will be contacted prior to sampling to ensure that the reporting limits will be
below residential Vapor Intrusion Screening Levels (Feb. 2018 version). Per EPA method

1 “Vapor Intrusion Guidance”, NCDENR, Division of Waste Management, Brownfields Program, March
2018, Version 2.
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TO-15, the analysis will include a lab control sample (LCS) and a lab blank sample for
QA/QC purposes.

Lastly, the report will include photos showing (1) each room (floors to ceiling) in which
sampling is conducted and (2) representative photos showing the sampling arrays.
Sample Collection

• Aptus will collect indoor air samples from five (5) locations within the building
footprint, per Drawing 4. The sample locations will be identified as A- 1 through A-5.
Location A-1 will involve a duplicate canister sample collected using an inline tee.
• An outdoor ambient air sample (A-6) will be obtained at simultaneously with the
indoor samples for background comparison purposes, in accordance with NCBP
guidance, for a total of five (7) air samples/analyses.
• The samples will be collected using 6-L Summa canisters equipped with 24-hour
flow regulators at each location. Tripods will be employed such that each canister
inlet port will be at a height of five feet (e.g., breathing zone height).
• Cannister vacuum readings will be collected prior to shipment, before and after
sampling, and the vacuum readings reported by the laboratory will be recorded and
provided to the Brownfields Program. If the initial vacuum prior to sampling is in
excess of 10% lower than the vacuum documented by the laboratory upon
shipment, the canister will not be used. A residual vacuum of up to -5 inches
mercury (Hg) must exist in the canister upon completion of the sampling event.
• Upon completion of the sampling, laboratory analysis request forms will be
prepared and the samples will be shipped under proper chain of custody for
laboratory analysis using EPA Compendium Method TO-15 “Determination of
Volatile Organic Compounds (VOCs) in Air Collected in Specially-Prepared
Canisters and Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS)”.
REPORTING

Upon receipt of the laboratory results, the concentrations will be compared to the
residential indoor air screening levels (NCRIASLs). A written report will be prepared
summarizing our field activities, observations, laboratory results, conclusions and
recommendations. The summa canister and flow controller log from the lab will be
provided as well with the final report. The findings and conclusions will be used to develop
the recommendations regarding the risk of vapor intrusion at the site.

Revised Vapor Intrusion Indoor Air Testing Work Plan April 27, 2018
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CLOSING

We hope that the presented work plan approach will meet with your approval. If you
should have questions regarding this submittal or associated documentation, please feel
free to contact us at [phone] at your convenience.

Sincerely, APTUS MANAGEMENT, PLLC

John Gallagher, PE Robert D. Hill, PE
Engineer of Record Principal Consulting Engineer

Attachments

cc: R. Hill – RDHEC

Aptus Management, PLLC

DRAWINGS