4101_Guilford_CityHighPoint_Riverdale_MSWLF_Seaboard_MonitoringComments_FID1832781_20240329

SEABOARD GROUP II AND THE CITY OF HIGH POINT
March 29, 2024
Mr. Kim Caulk, Supervisor Facility Management Branch
North Carolina Department of Environmental Quality
Division of Waste Management
1646 Mail Service Center
Raleigh, North Carolina 27699-1646
Re: Response to Comments - 2023 Annual Monitoring Report
Former Seaboard Chemical and Riverdale Drive Landfill Site
Jamestown, Guilford County, North Carolina
EPA ID No. NCD071574164/ Solid Waste Permit No. 4101-MSWLF-1979
Dear Mr. Caulk:
In response to NC DEQ comments on the 2023 Annual Monitoring Report dated February 29,
2024 and follow up email comments on March 20, 2024, the Seaboard Group/City of High Point
(Parties) provide the following response:
1. Comment: Table 1 spans 30 pages and lists groundwater elevations obtained at the site back
to 2000. Action Item: In future reports documenting annual monitoring events, edit the table
to list only data from well gauging events back to 2010. (Most wells appear to have at least a
few groundwater elevations from gauging events between 2010 and 2012, when most site
monitoring wells were sampled). At the bottom of the table, include a note directing the
reader to the 2023 report to obtain groundwater level measurements prior to 2010.
Response: This comment appears to address the length of Table 1 and suggests limiting the
historical data. As discussed during our call on March 11, 2024, we propose to modify the
format of the field data presented in the Annual Water Quality Monitoring Reports. The
basic monitoring well information (ID, construction date, depth, TOC elevation, water level
elevation, lat/long, etc) will be summarized on a single table to present the information
collected during the current monitoring event. The field measurements (pH, conductivity,
temperature, dissolved oxygen) will also be summarized on a single table for the current
monitoring event. This will allow the reader to review all pertinent data for the monitoring
event without referencing multiple pages.
The analytical summary tables for groundwater and surface water will remain unchanged to
allow for evaluation of data trends for each monitoring location.
2. Comment: Well PW-SF-1 and its associated contaminant concentrations are not shown on
any of the isoconcentration maps. This well has the highest concentration of 1,4-dioxane and
vinyl chloride among the wells sampled during the 2023 annual event. Action Item: Revise
the five isoconcentration maps to include the results from sampling of well PW-SF-1.

Response: Well PW-SF1 is an active extraction well located hydraulically downgradient of
the Pond 3 Area on the former Seaboard property. The data from this well wasn't used for
development of isoconcentration maps as it is not representative of static groundwater quality
conditions.
3. Comment: The isoconcentration maps do not show the results for contaminants of concern
(COCs) detected in the samples from each monitoring well installed as part of a well cluster.
A comparison of the lab results table with each isoconcentration map indicates that Babb &
Associates labeled the well in each well cluster that had the highest concentration. Action
Item: Place a note on each figure indicating that this approach was used for displaying the
results.
Response: As the isoconcentration maps represent the contaminant concentration in plan
view, using the highest value at each monitoring location was deemed appropriate to
represent the lateral extent of contaminants. A note will be added to future reports to indicate
the data used at nested wells for preparation of the maps.
4. Comment: The contaminant plumes for total volatile organic compounds (VOCs),
chlorobenzene and vinyl chloride in bedrock extend beneath the Deep River and under the
land within the regulated buffer of the Piedmont Triad Regional Water Authority (PTRWA).
This contamination is evidenced by concentrations above the NC Groundwater Quality
Standards (2L Standards) at PW-15D and PW-16D. The concentrations and total VOCs in
groundwater have decreased in the wells since the remediation system became fully
operational in 2017. However, the concentrations for chlorobenzene and vinyl chloride
remain above the 2L Standards.
Additional Email Comments Received on March 20, 2024: At the meeting on Monday,
March I Ith there was some discussion about a potential future requirement to sample PW-19
or possibly another new monitoring well. We requested that information be provided from
Seaboard Group II (letter dated 2/29/2024) about the sampling potential for well PW-19
across the impounded river (now Randleman Lake) to evaluate its condition for potential
sampling. The well was non -detect when it was last sampled in 2015.
We have prepared a spreadsheet to review trends in concentrations of chlorobenzene, 1,4-
dioxane and vinyl chloride in selected monitoring wells adjacent and on both sides of the
lake. The concentrations of chlorobenzene and 1,4-dioxane have been going down in AW-3
and AWB-4 since the improved extraction wells came online on 6/30/2022. The
concentration of vinyl chloride generally went down between June 2022 and April 2023 but
since has increased slightly. The deep bedrock wells east of the southern intermittent stream
have shown increases in 1,4-dioxane in the well just south of the lake (PW-6D) and increases
in both chlorobenzene and vinyl chloride in the well north of the lake (PW-16d). Both wells
are screened in rock at depths of 169 - 179 feet (PW-16D) and 260-275 feet (PW-6D).
Well PW-19 is located about 920 feet east-northeast of well PW-6D, generally in the
direction of the elongated plumes for chlorobenzene, 1,4-dioxane and vinyl chloride that are
shown in the figures of the 2023 annual report. In addition to evaluating the condition of PW-
19, review information about the site -specific and local geology that may guide installation

of a future bedrock well in the area of PW-19 or a more suitable location northeast of PW-
16D. The HWS intends to closely monitor the trends in contaminant concentrations in
samples collected from wells on both sides of the lake.
A new comment with regard to the 2023 annual report was generated by this review work.
The historical laboratory results table should be expanded to include the technical memo E-
II monitoring wells that were monitored during 2023. Wells AW-3 and AWB-4 are not
included in the 2023 annual report historical table.
Response: The Parties have also noted the increasing contaminant trend in the deeper
monitoring wells east of the Southern Intermittent Stream. As shown on the graphs provided
below, the slight increases in contaminant concentrations appear to correlate with reduced
extraction volume from PW-DR1. These reduced extraction volumes are likely related to
dewatering of the bedrock fractures which may be influenced by seasonal recharge rates to
the aquifer.
PW-16D (screened 169'-179')
100
80
60
G
bo
40
20
0 'w-
May-19 Dec-19 Jun-20 Jan-21
300
250
200
150
100
50
6000
5000
4000
c
3000 2
�o
C7
2000
1000
ti 0
Jul-21 Feb-22 Aug-22 Mar-23 Oct-23 Apr-24
Chlorobenzene—*-1,4-Dioxane Vinyl Chloride -*FPW-DR1 Extraction
PW-6D (screened 270'-300')
6000
5000
4000
c
3000 2
m
C7
2000
1000
0 0
May-19 Dec-19 Jun-20 Jan-21 Jul-21 Feb-22 Aug-22 Mar-23 Oct-23 Apr-24
Chlorobenzene—o-1,4-Dioxane Vinyl Chloride -4<--PW-DR1 Extraction

To further evaluate this relationship, the extraction rate for PW-DR1 was increased to lower
the water level within PW-DR1 by 10 additional feet on December 19, 2023. We plan to
collect a groundwater sample from PW-6I/6D, PW-15D, and PW-16D in late June 2024.
These four wells will be sampled again in the fall during the Annual Water Quality
Monitoring event. This will allow for an evaluation of the effects of lowering the extraction
set -point in PW-DR1 on contaminant concentrations over time in the deeper monitoring
wells.
Also, as requested in the March 20, 2024 email, the Parties will include the groundwater data
from the Extraction System Evaluation and the limited quarterly monitoring program in
Table 2 of the Annual Water Quality Monitoring Report. The Extraction System Evaluation
consisted of four quarterly sampling events which were conducted on September 2022 and
January/March/July 2023. The limited quarterly monitoring program began with Q4 2023
and includes two monitoring wells (AW-3/AWB-4) and the on -site surface water monitoring
locations.
5. Comment: A November 2007 figure produced by ERM NC, PRC (Figure 2, Site Map and
Monitoring Locations), shows a bedrock monitoring well (PW-19) located about 920 feet
east-northeast of well pair PW-6i/6D. This property is labelled as owned by the City of High
Point and the "Former Stone Property". The PW-19 well location appears potentially
downgradient of the northeasterly plume orientations shown on the maps. Action Item:
Document the condition of well PW-19 and access to the well for potential future sampling.
Response: Monitoring well PW-19 is currently located on the former Stone property and is
secured with an above -grade locked protective casing.
6. Comment: On December 11, 2023 the HWS requested that the SG parties update the
receptor survey for the Site. The findings from the updated receptor survey are anticipated in
late March 2024. Action Item: In the receptor survey text, document the current occupancy
and ownership status of the properties on the other side of the PTRWA buffer where the
former property owners once provided access to sample monitoring wells PW-18 and PW-
19. These wells were last sampled in January 2019 and 2015, respectively.) Total VOCs in
the sample collected from PW-18 were measured at an estimated concentration of 24 J ug/l
("J" qualified by the lab). A common laboratory contaminant, acetone, composed 17 of the
24 ng/1 (sic). Contaminants were not detected above the quantitation limit in the sample
collected in 2015 from PW-19.
Response: The updated receptor survey was submitted to DEQ on March 22, 2024.
Monitoring well PW-18 is located on property owned by Mr. John T. Crutchfield. According
to public records reviewed for the receptor survey, Mr. Crutchfield's mailing address is: 6007
Emsley Rd, Greensboro, NC 27407. Mr. Crutchfield had repeatedly denied access to his
property We understand from past conversations with the property owner that the land is not
occupied with a permanent resident; however, without Mr. Crutchfield's cooperation we
cannot verify the current use of the property. Past sampling results have not shown Site
COCs to be present in PW-18.

Please contact us if there are any questions or comments regarding this correspondence.
Respectfully,
Seaboard Group II and City of High Point
Mr. Gary D. Babb, P.G.
Babb & Associates, P.A. ,Z*Iz—z "s'E
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cc: Jackie Drummond - NCDEQ Division of Solid Waste
Craig Coslett — de maximis, inc. Project Coordinator