WS-6619_30141_CA_O_20221206_RESPONSE

100 East Ruffin Street, Mebane, North Carolina 27302
Telephone [phone] ·Facsimile [phone]
www.terraquestpc.com

December 6, 2022

Ashley Dinkins via email: [e-mail]
Guilford County Environmental Health Supervisor
400 West Market Street, Suite 300
Greensboro, NC 27401

Re: Response to Monitoring Report review (September 26,2022 sampling event)
Brightwood Inn Property
6501 Burlington Rd., Whitsett, NC
NCDWM-UST Incident No. 30141

Dear Ms. Dinkins:

Terraquest Environmental Consultants, P.C. is responding to concerns regarding the previously submitted
Monitoring Report with supporting modeling for the UST release incident at the Brightwood Inn Property
in Whitsett, Guilford County, NC. The site vicinity and groundwater analytical results/site layout are
shown in Figures 2 and 5, respectively (attached). The three concerns brought forward included: 1 - lab
data accuracy with MDLs higher than 2L Standards, 2- the GCL violation of benzo[b]fluoranthene in
monitoring well MW1R, and 3 – the water supply well located at 6496 Burlington Road. Those concerns
are addressed as follows:

1. Concern over elevated MDLs and some exceeding respective 2L Standards. Groundwater
analytical results are attached as Table 2. There exist some regulatory compliance limits that are
improbable to meet using the published EPA methods for SW-846. The 2L Standard for
Benzo(b)fluoranthene in Brightwood laboratory reports 400-226481-1 and 400-226859-1 of 0.05
ug/L is an example of one of these limits. This level is 100x lower than the MDL listed in Table 1
of EPA method 625.1 for benzo(b)fluoranthene. Benzo(b)fluoranthene has a listed MDL of 4.8
ug/L ( https://www.epa.gov/sites/default/files/2017-08/documents/method_625-1_2016.pdf ).
The lab has been able to attain lower detection levels through improvements in the analytical
technology. Furthermore, the MDL is statistically calculated and will vary based upon dilution
factor. The current detection limit for Eurofins Pensacola’s standard 625.1 method is
approximately 30x lower than this listed MDL at 0.151 ug/L. Achieving an MDL that is lower than
the 2L Standard is not technologically possible. The data is accurate and in accordance with the
EPA methodology.

Note that in March 2022, ECS Southeast, LLP sampled the monitoring well network at the site and
the MDL for Benzo(b)fluoranthene in monitoring well MW1R was 8.3 ug/l (Pace Analytical). If
Terraquest had used Pace Analytical for this sampling event there would not be a question
regarding the data as there would be no detection. The point is that the MDLs are variable.
A. Dinkins
Brightwood Inn Property (Incident 30141)
Page 2 of 3

2. Concern over the GCL violation for Benzo(b)fluoranthene. As previously indicated, the GCL
“violation” would not be an issue if Pace Analytical had been used for the laboratory analyses.
However, since it was detected at an estimated concentration, Terraquest will address why it
should not be considered in the evaluation of closing this site.

The computer model used to simulate contaminate fate and transport is protective of sensitive
receptors; thus, the reported GCL violation can be dismissed for several reasons. First, the model
shows that NO contamination will travel beyond 210 feet from the source area and no sensitive
receptor is within that range. Second, the concentration of the compound is so small (1.24 ug/l)
that a compound-specific model running contaminant fate for just that amount of
benzo(b)fluoranthene would show that the compound has such little mass that it would not travel
beyond its current location. Computer modeling involves many inputs but relies heavily on
contaminant mass and seepage velocity. The mass of Benzo(b)fluoranthene is too miniscule to
migrate beyond its current location; let alone make it to the nearest receptor.

It should also be noted that the subject contamination is expected to be chiefly composed of
benzene, toluene, ethylbenzene, xylenes, naphthalene, and other such petroleum compounds.
“Benzo[b]fluoranthene is a colorless, aromatic hydrocarbon consisting of five fused rings and
formed by the incomplete burning of organic matter. Benzo(b)fluoranthene is primarily found in
gasoline exhaust, tobacco and cigarette smoke, coal tar, soot, amino acids and fatty acid pyrolysis
products.” (Source: https://pubchem.ncbi.nlm.nih.gov/compound/Benzo_b_fluoranthene) It is
not a petroleum compound and the byproduct of gasoline exhaust is not expected to impact the
dissolved-phase quality of groundwater seven feet below ground level.

3. Following the NCDWM-UST’s response, Terraquest visited the property at 6496 Burlington Road
and spoke with the property owner to confirm the presence of a water supply well. In addition
to the 6496 Burlington Road property, Terraquest personnel visited properties along Boone Valley
Road to confirm water usage. The Site Vicinity Map has been amended and is attached. The
closest receptors are the onsite water supply wells (#10) which are approximately 235 feet from
the plume. These wells are not in use as the property is connected to the municipal water system
and they are schedule for abandonment. The closest active water supply well is located at 6496
Burlington Road (#11) and is approximately 345 feet from the plume. The contaminant model
has shown that no contaminants will make it beyond 210 feet which is a conservative estimate
using conservative inputs.

This property is currently under contract for redevelopment. The concerns presented by Guilford County
Environmental Health have been addressed. Terraquest would like to reiterate again that the risk ranking
of the site should be reduced to Low Risk and efforts made to move the site toward closure. In summary,
specific reasons include:

• Very low levels of petroleum impact which contaminant modeling shows will not reach the
nearest active receptor. The size and mass of the contaminant plume are very small.

• Groundwater flow has historically been to the north and more recently west – northwest. The
nearest active receptor is located approximately 345 feet to the south.

A. Dinkins
Brightwood Inn Property (Incident 30141)
Page 3 of 3

• Laboratory data has been verified to be accurate. Benzo(b)fluoranthene is not a petroleum
compound and has an estimated concentration in groundwater. Again, contaminant modeling
shows the contamination will not impact receptors and this particular compound has insufficient
mass to migrate beyond its current location.

• The onsite water supply wells which are not in use will be abandoned.

If Guilford County Environmental Health and the NCDWM – UST don’t believe the site can be downgraded
due to the presence of Benzo(b)fluoranthene, then the site is not likely to be developed or additional work
performed. The responsible party is approximately 94 years old and has no interest in performing any
environmental work. The recent sampling and modeling were paid for by an interested developer that
will not spend additional funds beyond what is necessary to abandon the wells and close the site. If you
have any questions or concerns, please contact us. Thank you for your help on this project.

Sincerely,

Terraquest Environmental Consultants, P.C.
Michael J. Brown, P.G.
President

Attachments
Figure 2 - Site Vicinity Map
Figure 5 - Groundwater Analytical Results (9/26/22)
Table 2 - Summary of Groundwater Results

Cc: James Brown – NCDWM – UST WsRO Supervisor

ENVIRONMENTAL CONSULTANTS, P.C.
Table 2
Date: 10/27/2022
6200B6200B6200B6200B6200B6200B6200B6200B6200B6256200B6256200B6200B6200B6200B/6256200B6256256200B6200B625625625MADEP VPHMADEP VPHMADEP EPHMADEP EPH300Well ID
Date
Collected
MW1R 9/26/22 59.9 4.48 339 31.8 < 0.220 0.808 28.2 20.5 1.97 0.756 < 0.190 < 0.533 < 24.0 85.7 4.83 199/118 216 48 62.1 4.86 2.47 1.24 0.725 34.9 2,360 597 < 153 3,080 < 0.0630
MW2 9/26/22 < 0.130 < 0.410 < 0.500 < 1.60 < 0.220 < 0.200 < 0.760 < 0.700 < 0.630 0.191 < 0.190 0.432 < 24.0 < 0.530 < 0.710 < 3.00/< 0.171 < 0.690 < 0.151 < 0.131 < 0.820 < 0.560 < 0.151 < 0.161 < 5.02 < 26.0 < 167 < 156 < 329 2.04
MW3 9/26/22 < 0.130 < 0.410 < 0.500 < 1.60 < 0.220 < 0.200 < 0.760 < 0.700 < 0.630 < 0.194 < 0.190 0.85 54.1 < 0.530 < 0.710 < 3.00/< 0.174 < 0.690 < 0.153 < 0.133 < 0.820 < 0.560 < 0.153 < 0.164 11.1 < 26.0 169.2 < 152 17+<314 1.46
MW4 9/26/22 < 0.130 < 0.410 < 0.500 < 1.60 < 0.220 < 0.200 < 0.760 < 0.700 < 0.630 < 0.187 < 0.190 < 0.237 < 24.0 < 0.530 < 0.710 < 3.00/< 0.168 < 0.690 < 0.148 < 0.128 < 0.820 < 0.560 < 0.148 < 0.158 < 4.93 < 26.0 < 164 < 153 < 322 < 0.0630
MW5 9/26/22 < 0.130 < 0.410 < 0.500 < 1.60 < 0.220 < 0.200 < 0.760 < 0.700 < 0.630 < 0.193 < 0.190 0.369 < 24.0 < 0.530 < 0.710 < 3.00/< 0.173 < 0.690 < 0.152 < 0.132 < 0.820 < 0.560 < 0.152 < 0.162 < 5.08 < 26.0 < 173 < 162 < 342 3.07
MW6 9/26/22 < 0.130 < 0.410 < 0.500 < 1.60 < 0.220 < 0.200 < 0.760 < 0.700 < 0.630 < 0.197 < 0.190 0.547 < 24.0 < 0.530 < 0.710 < 3.00/< 0.176 < 0.690 < 0.155 < 0.135 < 0.820 < 0.560 < 0.155 < 0.166 < 5.18 26.1 178.3 < 160 21.9+<329 < 0.0630
DW-1 9/26/22 < 0.130 < 0.410 < 0.500 < 1.60 < 0.220 < 0.200 < 0.760 < 0.700 < 0.630 < 0.181 1.36 < 0.229 < 24.0 < 0.530 < 0.710 < 3.00/< 0.162 < 0.690 < 0.143 <0.124 < 0.820 < 0.560 < 0.143 < 0.153 < 4.77 < 26.0 < 167 < 156 9.12+<322 < 0.0630
PW1 9/29/22 < 0.130 < 0.410 < 0.500 < 1.60 < 0.220 < 0.200 < 0.690 < 0.700 < 0.630 < 0.186 < 0.190 < 0.235 < 24.0 < 0.530 < 0.710 - / < 0.760 -< 0.147 < 0.127 < 0.820 < 0.560 < 0.147 < 0.156 < 4.89 < 26.0 < 166 < 155 < 326 -
1 600 600 500 20 70 70 70 70 5 0.4 6,000 4,000 70 25 6 70 1 30 400 400 0.05 0.5 3 400 700 10,000 200 10,000
Gross Contamination Level 5,000 260,000 84,500 85,500 20,000 70,000 6,900 8,500 15,000 5 400 6,000,000 4,000,000 25,000 NE 6,000 30,000 1,000 12,500 28,500 25,000 0.75 0.5 170 NE NE NE NE 10,000,000
Notes:
1. All results in µg/L.
2. BOLD denotes a detection.
3. Shading denotes a 2L Standard violation. Italics indicates a GCL violation.
4. "NE" not established.
5. * Naphthalene reported by 6200B/625 methods.
6. "-" = Indicates compound not tested per that method
7. ** The results listed for the C9-C18 aliphatic carbon fraction class are a summation of the C9-C12 and the C9-C18 classes; likewise, the C9-C22 aromatics are a summation of the C9-C10 and the C9-C22 classes. 1,3,5-TrimethylbenzeneC19-C36 Aliphatics2L Standard Bis(2-Ethylhexyl)phthalateC5-C8 AliphaticsC9-C18 Aliphaticsn-Butylbenzenesec-ButylbenzeneEthanolChryseneDiethyl phthalatetert-Butylbenzene1,2-DichloroethaneIsopropylbenzeneNaphthalene1-MethylnaphthaleneBenzo[k]fluoranthene2-MethylnaphthaleneSUMMARY OF GROUNDWATER SAMPLING RESULTS
Incident Name: Brightwood Incident No.: 30141
Analytical Method
Contaminant of Concern
BenzeneTolueneEthylbenzeneTotal XylenesMTBEIPENitrate as N1,2,4-Trimethylbenzenep-IsopropyltolueneBenzo[b]fluoranthenen-PropylbenzeneC9-C22 AromaticsC9-10 aromatic= 17
C11-22 aromatic = <314
C9-10 aromatic= 21.9
C11-22 aromatic = <329
C9-10 aromatic= 9.12C11-22 aromatic = <322