WI0300345_Monitoring (Report)_20191010 (2)

%k1 WithersRavenel
SIX MONTH POST INJECTION GROUNDWATER AND
SURFACE WATER MONITORING REPORT
Trex Properties
3114 and 3124 Cullman Avenue
Charlotte, North Carolina 282o6
EPA Site ID #: NCD 049 773 245
Prepared for-
Trex Properties, LLC
1515 Des Peres Road, Suite 300
St. Louis, Missouri 63131
Prepared By.•
WithersRavenel, Inc.
219 Station Road, Suite 1o1
Wilmington, North Carolina 28405
[phone]
WR Project #: 02080048.10
October 2019
Brian J. Belli , RSM
Senior Hydrogeologist
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40- WithersRavenel
1. Our People. Your Success.
October 10, 2019
Trex Properties, LLC
1515 Des Peres Road, Suite 300
St. Louis, Missouri 63131
Attention: Mr. Matthew Dostal
Subject: Six Month Post Injection Groundwater and Surface Water Monitoring Report
Trex Properties
3114 and 3124 Cullman Avenue
Charlotte, North Carolina 28206
EPA Site ID #: NCD 049 773 245
WR Project No. 03130430.12
Dear Mr. Dostal:
WithersRavenel, Inc. (WR) has prepared this Six Month Post Injection Groundwater and
Surface Water Monitoring Report to document the groundwater and surface water sampling
events that followed the injection of activated persulfate into the surficial aquifer that
underlies the subject site and downgradient properties. The injection work was completed
in January 2019 and post injection monitoring events were conducted in February and July of
2019 in accordance with the North Carolina Department of Environmental Quality (NCDEQ)
Underground Injection Control (UIC) Program Permit No. WI0300345 issued for the Trex
Properties site on July 21, 2017.
We appreciate the opportunity to be of service to Trex Properties, LLC. Should you have any
questions regarding this report, please do not hesitate to contact me at (pzo) 2569277or at
bbellisna withersravenel.com.
Sincerely,
WithersRavenel
Brian J. Bettis, PG, RSM
Senior Hydrogeologist
Project Manager
219 Station Road, Suite 101, Wilmington, NC 27511
t: 910.256.9277 1 www.withersravenel.com I License No. C-0832
Cary I Greensboro I Pittsboro I Raleigh I Wilmington

Trex Properties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # 031304 30.1z
TABLE OF CONTENTS
1.0 INTRODUCTION...................................................................................... 1
2.0 INJECTION OF IRON -ACTIVATED SODIUM FERSULFATE..................... 2
3.0 WATER QUALITY MONITORING.............................................................. 2
3.1 GROUNDWATER SAMPLING PROCEDURES....................................................................... 2
3.2 GROUNDWATER SAMPLING RESULTS.............................................................................. 3
3.2.1 Tetrachloroethylene(PCE)......................................................................................... 4
3.2.2 Trichloroethylene(TCE)............................................................................................. S
3.2.3 Cis 1,2 Dichloroethene (Cis 1,2 DCE)....................................................................... 6
3.3 SURFACE WATER SAMPLING PROCEDURES..................................................................... 7
3.4 SURFACE WATER ANALYTICAL RESULTS........................................................................ 7
4.0 OBSERVATIONS ...................................................................................... 9
Figures
Figure 1
General Location Map
Figure 2
Monitoring Well Location and Topographic Map
Figure 3
Trex Injection Strategy
Figure 4
Water Table Elevation Contour Map Quly 2019)
Figure 5
Tetrachloroethene in Groundwater Quly 2019)
Figure 6
Trichloroethene in Groundwater Quly 2019)
Figure 7
Cis 1,2 Dichloroethene in Groundwater Quly 2019)
Figure 8
Geologic Cross Section A -A'
Figure 9
Geologic Cross Section B-B'
Figure 10
Geologic Cross Section C-C'
T_LI_..
Table 1
Summary of Monitoring Well Construction Information
Table 2
Summary of Groundwater Analytical Results
Table 3
Summary of Surface Water Analytical Results
Appendices
Appendix A
Injection Event Records and Photo Documentation
Appendix B
Groundwater and Surface Water Sampling Forms
Appendix C
Laboratory Reports and Chain of Custody Records
Appendix D
Graphs of Contaminant Concentrations versus Time
Appendix E
IET 12o-Day Data Evaluation
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Trex Properties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # 031304 30.12
1.0 INTRODUCTION
This report has been prepared as required by NCDEQ UIC Program Injection Permit No.
WI0300345, specifically Part IV — Monitoring and Reporting Requirements. The permit was
issued to Trex Properties, LLC (Trex) on July 21, 2017 in response to an Application for Permit
to Construct and/or Use a Well(s) for Injection, for In Situ Groundwater Remediation dated
January 18, 2017. The injection and monitoring work is being conducted by Trex to satisfy
environmental remediation requirements of the NCDEQ Hazardous Waste Section (HWS).
The Trex site consists of two properties that together comprise + 1.68 acres and
accommodate two warehouse type structures each approximately 11,000 square feet in size
that were constructed in the early 196os. The building at 3114 Cullman Avenue was
previously used by Detrex, Inc. to treat and recycle several types of hazardous waste under
a Resource Conservation and Recovery Act (RCRA) Part B permit issued in 1983. Products,
storage containers, and non-RCRA/non-hazardous solid wastes such as used oil were
previously stored at the adjacent building located at 3124 Cullman Avenue. Both properties
were acquired by Trex on June 18, 2013 and are located east of but within the limits of the
City of Charlotte. All of the hazardous and non -hazardous wastes were removed from the
two buildings in 2014 and both are currently unoccupied.
The general locations of the properties and surrounding topography, roads and railways are
shown in Figure 1. The aerial photograph in Figure 2 shows the general land use within the
immediate vicinity of the properties, local topography, and the locations of permanent
monitoring wells installed as part of the RCRA Facility Investigation. Past incidental spills of
solvents resulted in contamination of unsaturated materials occurring beneath and
adjacent to the two buildings, and underlying groundwater. Over the years, solvent
contaminated groundwater migrated to vacant downgradient properties to the north, and to
a perennial stream known as Little Sugar Creek.
Recommended soil and groundwater remediation activities for the site are described in the
Conceptual Approach to Remediation (CAR) prepared by WR and dated July 15, 2o16. The
NCDEQ HWS provided approval to commence with these activities in a letter dated October
24, 2o16. Accordingly, a soil vapor extraction (SVE) system consisting of 3o extraction wells
was constructed within the two Trex buildings and began operating in August 2017. The SVE
system has operated since that time resulting in significant reduction of soil contaminant
concentrations, and alleviation of vapor intrusion issues at adjacent properties. Trex
provides biweekly reports to the NCDEQ HWS to document and track the soil remediation
process.
The CAR recommended injection of iron -activated sodium persulfate at locations on the Trex
properties and adjacent properties to the north. Figure 3 illustrates the UIC Program
approved injection strategy and the approximate locations where 20 injection wells were to
be installed by Innovative Environmental Technologies, Inc. (IET) on behalf of Trex in 2o18.
Description of the injection activities are provided in Section 2 of this report, and the results
of post injection groundwater and surface water monitoring activities are discussed in
Section 3.
Page 1

Trex Properties, Charlotte NC October2019
Six Month Post Injection 6roundwaterand Surface WaterMonitoring Report WR Project # o 313o4 3o.12
2.0 IN]ECTION OF IRON -ACTIVATED SODIUM PERSULFATE
Between January 7" and 17", 2oi9 and on behalf of Trex, IET implemented the injection
strategy described in the UIC application and permit for the site. The remedial strategy
utilized the oxidation remediation product "Ferric Oxide activated Persulfate". According to
IET, this product combines a self -activating oxidation persulfate chemistry while providing
components for a longer lasting biological attenuation process following the initial
oxidation event. A copy of the Injection Event Record (IER) dated January 24, 2019 that IET
submitted to the UIC Program is included in Appendix A. A copy of IET's Technology
Discussion and Field Report dated January 2019 is also included in Appendix A, as are
photographs taken by WR to document the event.
Details of the injection event including descriptive logs for each injection point are included
in IET's January 2o19 reports. In summary, a total of approximately 159,000 pounds of
sodium persulfate were mixed with approximately 14,000 pounds of ferric oxide powder and
municipal water to create about 69,500 gallons of injectant that was introduced into 19 of
the 20 injection wells referenced previously. Several attempts were made to install
injection well IW-16, however subsurface obstacles encountered prior to reaching the
targeted injection depth prevented installation of that well. Additionally, daylighting of
injectant in the vicinity of wells IW-1 and IW-2 to the south of the building at 3114 Cullman
Avenue caused IET to utilize direct push machinery to inject the prescribed amount of
injectant into the subsurface at seven nearby locations. More detailed descriptions and
information regarding the injection event are included in Appendix A.
3.0 WATER QUALITY MONITORING
3.1 Groundwater Sampling Procedures
In accordance with the monitoring plan contained in the UIC application and permit, pre -
injection groundwater and surface water were collected between the dates of November 261h
and 29th, 2o18. Groundwater samples were obtained from 20 permanent monitoring wells,
specifically: PMW-1A & 1B, PMW-2A & 213, PMW-3A, PMW-4A, PMW-5A, PMW-6A, PMW-7A &
713, PMW-8A & 813, PMW-9A, 913, & 9C, PMW-ioA & 1oB, PMW-iiA & i1B, and PMW-13B. The
sampling locations are shown on Figure 2. Post injection samples from these wells were
collected approximately one month following the injection event (February 191h and 2oth,
2o19), and approximately six months following the injection event (July 23" and 24th, 2019).
The following procedures were utilized during each of the three sampling events.
After confirming each well's identity and location, the depth to the static groundwater level
within the well to be sampled was measured from the top of the well casing. Field
measurement of volatile organic vapors in the air space at the well head was then measured
using a calibrated Photo Ionization Detector (PID). The PID reading was recorded on the
sampling form for the well. The well was then purged according to the EPA -approved low -
flow method using a peristaltic pump equipped with a variable speed flow controller
capable of limiting the purge rate to less than one-half liter per minute. Field parameters
including; water level during purging, volume of water removed, dissolved oxygen (DO),
temperature CC), electrical conductivity (or EC in mS/cm), pH, oxidation-reduction potential
(ORP), and turbidity were monitored during purging and recorded on the sampling forms
included in Appendix B. The post injection groundwater samples were also field tested for
persulfate content, and the test results were also recorded on the sampling forms.
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TrexProperties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # o 313o4 3o.12
After parameter measurements were observed to stabilize (less than 10% variance over
three consecutive readings), groundwater samples were decanted directly into laboratory -
prepared containers in the order shown below, stored on ice, and transported under
standard chain -of -custody protocol to the Pace Analytical Services laboratory located in
Huntersville NC (Pace). Each sample was analyzed as follows:
• Volatile Organic Compounds (VOCs) via EPA Test Method 826oD
• Ethene via RSK 175 Method
• Iron via EPA Method 6o1oD with Preparation Method EPA 3oioA
• Chloride and Sulfate by EPA Method 300.o Rev 2.11993
• Total Organic Carbon via Standard Method 531oB-2011
Table 1 provides construction information for all of the active monitoring wells at the site
and depth to groundwater measurements obtained on July 22, 2019 from the 20 monitoring
wells referenced in this section. The depth to groundwater measurements were used to
determine the groundwater elevations shown on Table 1 and in Figure 4. The contours of
equal shallow groundwater elevation shown in Figure 4 imply that the direction of
groundwater flow is northerly towards Little Sugar Creek. This makes intuitive sense and is
consistent with previous determinations of groundwater flow direction at the site.
uroundwater Sampling itesuRs
Table 2 provides a summary of the laboratory analytical results for the pre -injection
monitoring event in November 2018, and the two post injection monitoring events
conducted in February and July 2oi9. The laboratory analytical reports and chain of custody
records for these events are included in Appendix C. According to the results for the July
2019 samples, concentrations of nine VOCs currently exceed their respective North Carolina
Groundwater Standards established in Title 15A of the NC Administrative Code Subchapter
2L (2L Standards) at one or more locations. These VOCs and the locations where their
concentrations exceed their 2L Standards are shown in the table below:
VOC
Location where Concentration Exceeds 2L Standard
1,1,2,2-Tetrachloroethane
PMW-1A, PMW-3A, PMW-4A
1,1,2 - Trichloroethane
PMW-3A
1,1 Dichloroethane
PMW-1A,
1,1 Dichloroethene
PMW-9C
Benzene
PMW-4A, PMW A, PMW B
Cis 1,2 Dichloroethene
PMW-1A, PMW-1B, PMW-4A, PMW-5A, PMW-6A, PMW-7A, PMW-9A,
PMW B, PMW C, PMW-1oA, PMW-ioB,
Tetrachloroethene
PMW-iA, PMW-113, PMW-2A, PMW-2B, PMW-3A, PMW-4A, PMW-5A,
PMW-6A, PMW-7A, PMW-7B, PMW-8A, PMW-8B, PMW-9B, PMW-9C,
PMW-1oA, PMW-1oB, PMW-11A, PMW-11B, PMW-13B
Trichloroethene
PMW-1A, PMW-1B, PMW-2A, PMW-2B, PMW-3A, PMW-4A, PMW-5A,
PMW-6A, PMW-7A, PMW-7B, PMW-8A, PMW-8B, PMW-9A, PMW-9B,
PMW-9C, PMW-ioA, PMW-1oB, PMW-iiA, PMW-1iB, PMW-13B
Vinyl Chloride
PMW-iA, PMW-9A, PMW-9B
The VOCs Tetrachloroethene (PCE), Trichloroethene (TCE) and Cis 1,2 Dichlorothene (Cis 1,2
DCE) are present at most monitoring well locations and are therefore considered to be the
main contaminants of concern (COCs) at the site. The extent and concentrations of these
VOCs in groundwater is discussed in the following sections.
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TrexProperties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # o 313o4 3o.1z
3.2. 1 TETRACHLOROETHYLENE (PCE)
PCE is considered to be a primary COC in groundwater at the site. During the July 2019
monitoring event, PCE was detected at concentrations that exceeded its 2L Standard of 0.7
ug/L at 19 of the 20 groundwater monitoring locations. The July 2019 PCE concentrations
are shown in Table 2 and are depicted spatially on Figure 5.
The PCE concentrations that exceeded the 2L Standard of 0.7 µg/L ranged from 39.5 µg/L
(PMW-8B) to 34,000 µg/L (PMW-6A). The highest PCE concentrations are present in the
central portion of the site near wells PMW-5A and PMW-6, and in the northern portion near
the PMW-9 and PMW-io well clusters. Concentration versus time graphs for each VOC
detected at a concentration exceeding its 2L standard are included in Appendix D. Graphs
of PCE concentrations vs time in shallow and deep groundwater from Appendix D are
reproduced below:
Page 4

TrexProperties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # o 313o4 3o.1z
The graphs of PCE concentration versus time for shallow groundwater imply stable or
decreasing concentration trends in all cases. The PCE concentration versus time graphs for
deeper groundwater imply stable concentration trends in all cases except that for deep
downgradient monitoring well PMW-9C.
3.2.2 TRICHLOROETHYLENE (TCE)
TCE is also considered to be a primary COC in groundwater at the site. During the July 2019
monitoring event, PCE was detected at concentrations that exceeded its 2L Standard at all
20 groundwater monitoring locations. The July 2019 PCE concentrations are shown in Table
2 and are depicted spatially on Figure 6.
The TCE concentrations that exceeded the 2L Standard of 3 µg/L ranged from 17.4 µg/L
(PMW-9A) to 98,9oo µg/L (PMW-5A). Like PCE the highest TCE concentrations are present in
the central portion of the site near wells PMW-5A and PMW-6, and in the northern portion
near the PMW-9 and PMW-10 well clusters. Graphs of TCE concentrations vs time in shallow
and deep groundwater from Appendix D are reproduced below:
Page 5

Trex Properties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # 031304 30.1z
The graphs of TICE concentration versus time for shallow groundwater imply stable or
decreasing concentration trends in all cases except that for PMW-5A, which shows an
increasing trend. The PCE concentration versus time graphs for deeper groundwater imply
stable concentration trends in all cases except that for location PMW-9C.
3.2.3 CIS 1,2 DICHL❑R❑ETHENE (CIS 1,2 DCE)
PCE and TCE daughter product Cis 1,2 DCE was detected at concentrations that exceeded its
2L Standard at 12 of the 20 groundwater monitoring locations. The July 2019 Cis 1,2 DCE
concentrations are shown in Table 2 and are depicted spatially on Figure 7.
The Cis 1,2 DCE concentrations that exceeded the 2L Standard of 70 pg/L ranged from 92
pg/L (PMW-1B) to 2,710 pg/L (PMW-6A). The highest Cis 1,2 DCE concentrations are present
in the central portion of the site near wells PMW-5A and PMW-6, and in the northern portion
near the PMW-9 and PMW-10 well clusters. Graphs of PCE concentrations vs time in shallow
and deep groundwater from Appendix D are reproduced below:
Page 6

Trex Properties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # 031304 30.12
The graphs of Cis 1,2 DCE concentration versus time for shallow groundwater imply stable or
decreasing concentration trends in all cases except that for PMW-1A, which shows and
increasing trend. The PCE concentration versus time graphs for deeper groundwater imply
stable concentration trends in all cases except for deep downgradient locations PMW-9B
and PMW-9C. Concentration versus time graphs for the all of the VOCs detected in site
groundwater by individual well location are also included in Appendix D.
3.3 Surface Water Sampling Procedures
During the pre and post injection monitoring events, WR personnel collected three surface
water samples (SW-1 through SW-3) from Little Sugar Creek at the locations shown in Figure
2. Each sample was collected by submerging a laboratory -cleaned, non -preserved, one liter
glass container into the stream and then decanting the water into the laboratory -prepared
bottleware containing the appropriate amount of preservative for the analysis to be
conducted.
The samples were stored on ice and transported under standard chain -of -custody protocol
to Pace for analysis of VOCs by EPA Method 826oD. The post injection surface water
samples were field tested for: persulfate, temperature, pH, electrical conductance,
dissolved oxygen, and redox. The field readings are included on the sampling forms in
Appendix B and are summarized in Table 3.
3.4 Surface Water Analytical Results
PCE concentrations in excess of its North Carolina Surface Water Standard established in
Title 15A of the NC Administrative Code Subchapter 2B (2B Standard) of 3.3 pg/L were
detected in the July 2019 surface water samples from locations SW-2 and SW-3 (see Table
3). The detected PCE concentrations in surface water samples from these locations were
11.6 pg/L (SW-2) and 7.9 ug/L (SW-3).
TCE concentrations exceeding the 2B Standard of 30 ug/L were also identified in the surface
water samples from location SW-2 (48.9 ug/L) and SW-3 (35.2 ug/L). The concentration of
TCE at upstream surface water location SW-1 (28.2 ug/L) was slightly less than the 2B
Standard of 30 ug/L. Detectable concentration of Cis 1,2 DCE were also identified in all
three of the surface water samples, however all of the concentrations were below the EPA
Tap Water Screening level of 36 ug/L. A 2B Standard for Cis 1,2 DCE has not been
established.
The surface water sampling locations and analytical results are also illustrated on Figures 2
through Figure 7. Table 3 summarizes the current and historic surface water analytical
results. Copies of the laboratory analytical reports and chains of custody are included in
Appendix C. Graphs of pre and post injection PCE, TCE and Cis 1,2 DCE concentrations
versus time for each of the surface water samples are included in Appendix D, and are
reproduced on the following page of this report.
Page 7

VOC Concentrations (ug/L) vs Time - SW-1
ao.D
—1,z-Dia,ln.oetnene —Te<aenlo—nene
fi0.0
�TridibrceMene ---•Linear leis-1,2-0idtlarcethene)
50.0
Li near(retrnchloraethenej — — --Linear jrd&l.,—then.)
40.0
`
30.0
20.0
—
MO
0.0
10/22/2018
12/16/2018
2/4/2019 3/26/2019 5/15/2019 7/4/2019
VOC Concentrations (ug/L) vs Time - SW-2
leo.D
14D.D
—d,L2-0ichl.—hene —T—hl—here
120.0
—Tdchl.—hene ----Linear (cis-1,2-0iddoroethene)
100.0
`
etrachl—thene — Linear unearR j --- (Tridibrnethene)
80.0
`
W-0
40.0
20.0
`
0.0
10/27/2019
12/16/2018
2/4/2019 3/26/2019 5/15/2019 7/4/2019
VOC Concentrations (ug/L) vs Time - SW-3
IM.0
—
100.0
—cis-1,2-Dichlamethene—Tehnchl—here
—Trirh.—hene ----Linear icis-1,2-0idI—here)
80.0
elraW—thene ---dl.—hene •DneatiT j -Linear n� n)
fi0.0
8/23/2019
9/23/2019
10/27/2018 12/16/2018 2/4/2019 3/26/2019 5/1512M 7/4/2019 W2312019

Trex Properties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # 031304 30.1z
The graphs of VOC concentrations versus time for the three surface water samples indicate
decreasing or stable concentrations over the post injection monitoring period thus far.
4.0 OBSERVATIONS
Tables 2 and 3 provide comparisons of pre and post injection total VOC concentrations at all
of the groundwater and surface water sample locations. The results of these comparisons
are summarized below.
Sample Location
Identity
Total VOC Concentration
Increase or Decrease
(Nov 2o18 to Feb 201 )
Total VOC Concentration
Increase or Decrease
(Nov 2o18 to July 201 )
PMW-1A
3%
125%
PMW-1B
26%
52%
PMW-2A
12%
26%
PMW-213
76%
13%
PMW-3A
6 %
1%
PMW- A
56%
25%
PMW-5A
35%
17%
PMW-6A
2%
0%
PMW-7A
21%
7%
PMW-713
8 %
27%
PMW-8A
%
%
PMW-813
0%
1%
PMW-9A
18%
28%
PMW- B
%
275%
PMW- C
3%
255%
PMW-1oA
6 %
%
PMW-1oB
83%
2%
PMW-11A
75%
66%
PMW-11B
1%
o%
PMW-13
27%
0%
SW-1
62%
57%
SW-2
73%
62%
SW-3
63%
65%
The majority of total VOC concentration comparisons indicate substantial concentrations
decreases, presumably a result of the injection activities documented in this report.
Rebound of total VOC concentrations was observed at locations PMW-1A, PMW-213 and
PMW-5A, which are within the treatment zone. Locations PMW-7A, PMW-8A, PMW-913 and
PMW-9C are located near the lateral limits of the treatment zone, which apparently have not
been affected by the injection event at this time.
Graphs of total VOC concentrations versus time since groundwater monitoring began at the
site in 2012 are included in Appendix D. Overall decreasing concentration trends over time
are apparent at all 20 of the groundwater monitoring locations that are part of the post
injection monitoring program for the site.
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Trex Properties, Charlotte NC October2019
Six Month Post Injection Groundwater and Surface Water Monitoring Report WR Project # 031304 30.1z
Geologic cross sections showing monitoring and injection wells within the treatment area
are provided as Figures 8, 9 and io. The total VOC concentrations detected in the November
2oi8 pre -injection samples, and those detected in the July 2019 samples are shown by
monitoring well location on these cross sections. The contours of equal total VOC
concentration shown on the cross sections imply that the magnitude and extent of total
VOCs in site groundwater have decreased as a result of the injection event.
A copy of IET's 12o-day data evaluation report to Trex is included as Appendix E. IET's
report contains more detailed discussion of the results of the injection in terms of chemical
parameter changes observed in the post injection analytical results. The July 2019 post
injection sulfate concentrations at locations PMW-1A, PMW-3A, PMW-5A, PMW-6A, PMW-
1oA, PMW-1oB and PMW-11A were still elevated over an order of magnitude above the pre -
injection sulfate concentrations as were the ORP measurements at these locations.
According to IET, this indicates that the chemical oxidation via production of sulfate free
radicals and hydroxyl radicals is continuing to occur at these locations.
The concentrations of sulfate in the July 2019 samples from locations PMW-1A, PMW-3A,
PMW-5A, and PMW-6A remain above the 2L Standard of 250 mg/L for sulfate. According to
the UIC injection permit requirements, monitoring of injection related byproducts should
continue until their concentrations attenuate to pre -injection conditions or to below the
applicable 2L Standard, whichever is greater.
In accordance with the monitoring plan contained in the UIC application and permit, Trex
will return to the site six months following the second post injection monitoring event to
collect additional groundwater and surface water samples. Accordingly, the next post
injection monitoring event will occur in January 202o, approximately one year after the
injection event. Trex will prepare a one-year post injection groundwater and surface water
monitoring report approximately two months following receipt of the analytical results for
the January 2020 monitoring event.
Page 10