23022_Chapel Hill Police_DM_20240614

DECISION MEMORANDUM
DATE: June 14, 2024
FROM: Sharon Eckard
TO: BF Assessment File
RE: Chapel Hill Police Property
828 Martin Luther King Jr Blvd
Chapel Hill, Orange County
BF Project No. 23022-19-068
Based on the following information, it has been determined that the above referenced
site, whose intended use is for no uses other than municipal service center, office, retail,
recreational, associated parking uses, and with prior written approval from DEQ, other
commercial uses, can be made suitable for such uses.
Introduction:
The Prospective Developer (PD) is the Town of Chapel Hill (Town), 405 Martin Luther
King Jr. Blvd, Chapel Hill, Orange County. The Town is led by the Mayor and an eight -
member town council. The Town Manager is Christopher C. Blue. The Brownfields
contact person is John Richardson, Community Resilience Officer, Town of Chapel Hill.
The Brownfields Property is a 10.24-acre parcel, assigned tax ID 9789413949, which is
currently occupied by the Town's Police Station and associated parking lots. There is an
elevated portion of the Brownfields Property on which the police station was constructed
and a lower portion along an urban stream, Bolin Creek, that includes a portion of the
Bolin Creek Trail. There is a steep embankment to the south that separates these two
areas. Bolin Creek forms the southern boundary of the Brownfields Property.
Bolin Creek is classified as a Class WS-V, Nutrient Sensitive Waters (NSW) surface
water body, and is part of the Cape Fear River Basin. Bolin Creek eventually discharges
to Little Creek, which discharges to Jordan Lake, a drinking water and recreational
reservoir, about six to eight miles downgradient of the Brownfields Property.
The site is currently zoned R-2 Residential 2 (4 units/acre) as is the adjacent property
except for as noted below. The Brownfields Property lies within a mixed commercial and
residential area of Chapel Hill. Properties to the southwest and southeast are zoned as R-4
medium density residential (10 units/acre) and properties to the south are zoned as NC
Neighborhood Commercial. Commercial properties to the south that border Bolin Creek
include a gasoline station site (Mobil/Run-In-Jim's convenience store) and an automotive
repair facility (Lloyd Tire & Alignment).
The Town maintains a website dedicated to information about the redevelopment of the
Brownfields Property, including historical environmental assessment, risk assessment,
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and interim remedial measures (IRM) documents. Those documents can be found at the
following link: Municipal Services Center Project I Town of Chapel Hill, NC
Redevelopment Plans:
The Town initially evaluated a combined municipal service center with retail and high
density residential with a portion as affordable housing for this site. The Town has since
decided to forgo residential use in favor of redeveloping the Brownfields Property with a
municipal service center to replace the current police station that is situated on the
Brownfields Property and continued recreational use. The land use restrictions in the
brownfields agreement will reflect the Town's chosen land uses.
Only conceptual redevelopment plans are available at this time; engineering design
documents are not yet available but will be necessary prior to redevelopment as a
component of the land use restrictions in the agreement.
Site History:
The Brownfields Property was originally a borrow pit in the 1950s to early 1960s.
Reportedly, the pit was filled by the individual owner/operator of the borrow site
(Richard W. Sparrow) from the mid- 1960s through the mid- 1970s with fill material
including construction and demolition debris (concrete, wood, metals), and fill soil with
coal combustion products (CCP) as structural fill. The understanding is that the CCP
originated from the UNC-Chapel Hill's power generation facilities. The Town of Chapel
Hill purchased the Brownfields Property in 1980 and constructed the existing police
station facility shortly thereafter.
Regulatory History:
The Town has conducted multiple environmental assessments, including risk assessment
and screening ecological risk assessments at the Brownfields Property since 2013. Prior
to 2019, the Town was conducting work under the jurisdiction of the NC DEQ Inactive
Hazardous Sites Branch (IHSB) under ID NONCD0001486. At that time, IHSB's
analysis had indicated that the environmental risks associated with the coal ash structural
fill were not commensurate with risks associated with a site that would be placed on the
Federal Superfund National Priorities List (NPL) nor would be considered an NPL-
caliber site.
The Town's stated desire to safely redevelop the Brownfields Property led the Town to
apply to the NC Brownfields Program (now, the Brownfields Redevelopment Section
(BRS)). The Chapel Hill Police Property site was made eligible for continued evaluation
of a brownfields agreement on October 1, 2019 under the standard brownfields option.
The first priority for the Town was to evaluate and conduct interim remedial measures
(IRMs) in 2019 through 2020 to remove CCP material that was encroaching on the Bolin
Creek Trail, which was performed under a DEQ-approved Environmental Management
Plan (EMP).
Once the IRMs had been completed, the Town performed additional environmental
assessment of the Brownfields Property to fill Brownfields-identified assessment data
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gaps under guidance from the Brownfields Program. The report on these additional
assessment activities was provided in late 2022. Information about the assessments
conducted at the Brownfields Property and a discussion of the environmental risks posed
by contaminants in various media at the Brownfields Property is provided below.
Work on the Brownfields Agreement (BFA) documents started shortly after assessment
was deemed complete in 2023 and the Town had determined that they would focus only
on non-residential uses at the Brownfields Property. BFA document production
continued into 2024. Over the course of this project, DEQ management, Brownfields,
and State Superfund DEQ representatives have been in contact with U.S. Environmental
Protection Agency (EPA) staff over this Brownfields Property due to the concerns raised
by community groups in the area, particularly with respect to the Town's initial plan for
residential use at the Brownfields Property.
The Town conducted IRM maintenance activities at the Brownfields Property in April
2024. This included regrading drainage at the top of the slope, excavating and relocating
CCP material to another area of the site, adding silt fencing, pruning of vegetation, and
hydroseeding.
Public Engagement:
The Brownfields Redevelopment Section has engaged with the public regarding the
Chapel Hill Police Property in advance of the Brownfields statutory 30-day public
comment period. Persons and groups, including Town Council member, Mr. Adam
Searing; Friends of Bolin Creek (FOBC) represented by Ms. Julie McClintock and Mr.
Nick Torrey (also of Southern Environmental Law Center (SELL)); and local university
personnel have expressed concern over the coal ash particularly if the redevelopment
contained a residential component. Other residents living near the Brownfields Property
expressed support for its redevelopment as long as it was done safely. Information from
these residents has come in the form of emails, letters, and shared presentations.
In May 2022, Sharon Eckard, Eastern Branch Head with the BRS, participated in a
virtual meeting with representatives of FOBC, and in a virtual presentation hosted by the
Town to discuss the Brownfields process and communicate the status of the work on the
Chapel Hill Police Property BFA. DEQ later provided responses to the Town to address
specific additional questions not covered during the meeting due to time constraints.
In January 2024 (letter states 2023 in error), SELC sent a letter to the newly elected
Town of Chapel Hill Mayor Jessica Anderson and Sharon Eckard highlighting two draft
(at that time) technical documents related to their claims about the environmental risks
posed by the coal ash fill at this Brownfields Property. The first document listed below
has now been published in a red -lined, final version. Those two documents are:
1) U.S. EPA, Risk Assessment of Coal Combustion Residuals: Legacy Impoundments and
CCR Management Units, October 2023, Draft. Available at:
https://www.regulations.gov/document/EPA-HQ-OLEM-2020-0107-0887
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2) U.S. EPA, Draft Integrated Risk Information System (IRIS) Toxicological Review of
Inorganic Arsenic, Available at https://regulations.gov/document/EPA-HQ ORD-2012-
0830-0056
DEQ staff have reviewed these two draft documents, and the final, red -lined version of
the October 2023 Risk Assessment draft that was finalized in April 2024. A brief
discussion of these risk documents is provided below in this document.
In October 2023, after discussing the site and our respective programs with Mr. Bill
Hunneke, Section Chief for State Superfund Section and Sharon Eckard separately, Mr.
W. Perrin de Jong with the Center for Biological Diversity, Asheville, NC, filed a
CERCLA petition ("Petition") with the EPA requesting that the federal agency conduct a
Preliminary Assessment (PA) at this Brownfields Property for its possible inclusion on
the National Priorities List (NPL) under CERCLA. Shortly after being made aware of the
existence of the two draft EPA documents that SELC shared in their letter of January
2024, the Center for Biological Diversity requested that EPA incorporate these
documents into the Petition that had been filed the prior October.
The EPA conducted the PA over the last several months. In their response letter to the
CERCLA petition entitled Abbreviated Preliminary Assessment Letter Report (U.S. EPA,
Region 4, May 1, 2024), EPA concluded the following:
"The Town of Chapel Hill and the NCBP [North Carolina Brownfields
Program] are negotiating a BFA. In addition to the assessment and IRM
activities already conducted, the BFA will outline the need for additional
assessment and remediation, if any, based on the intended future
reuse/redevelopment plans, which does not include residential use. The
Town of Chapel Hill anticipates that a draft of the agreement will be
available for public comment in Spring 2024. As a result, the EPA
recommends that future activities at the site be conducted under the
purview of the NCBP. "
Environmental Assessment History:
The reports that were reviewed for the evaluation of the Brownfields Property data are
listed in the Brownfields Agreement. Technical reports were primarily prepared on behalf
of the Town by Falcon Engineering, Inc. and Hart & Hickman, PC. A preliminary human
health and ecological risk assessment for the site was performed by Duncklee & Dunham
(now Synterra) and Dr. Ken Rudo of Rudo Toxicological Consultants; they focused
primarily on recreational use along the Bolin Creek Trail and Bolin Creek. Synterra and
Rudo Toxicological Consultants identified data gaps and suggested additional assessment
with respect to ecological risk, which was conducted by Hart & Hickman. Some key
points from the various technical reports are presented below:
Falcon Engineering, Inc.
Earlier in the assessment phase, from 2013 through 2016, the site was characterized by
Falcon Engineering through scopes of work discussed in six separate reports. Initial
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groundwater monitoring attempts were hampered by high turbidity readings in some of
the wells (MW-1, MW-3, and MW-4); these wells were subsequently replaced with wells
MW-lA (H&H) and MW-3A/MW-4A (Falcon). Wells MW-3 and MW-4 were
abandoned. Falcon analyzed soil, CCP (referred to as sediment in early reports), surface
water, and groundwater for volatile organic compounds (VOCs) and semi -volatile
organic compounds (SVOCs), and metals.
Hart & Hickman, PC
Hart & Hickman, PC (H&H) began assessment activities at the Brownfields Property in
2016. Relevant information from the environmental reports is provided below:
Phase II (H&H August 2017)
• Evaluated shallow soil for presence of CCPs (47 shallow soil borings on approx.
50 ft grid— embankment, 6 borings upper level, 4 borings — lower level)
• Analysis of shallow soil in upper level
• CCP sample leachate analysis
• Evaluated chromium (Cr) detections in shallow soil
• Collected background soil samples (5 borings)
• Installed additional wells (3)
o MW-5 actually offsite background across Bolinwood Drive in bedrock
o MW-6 — hollow stem auger (HSA) to 17.5 ft below ground surface (bgs);
perched water at 10 ft
o MW-7 — bedrock at 15 ft bgs and well installed to 69.5 ft bgs
• Collected Bolin Creek surface water and stream sediments (5 locations)
• Aquifer slug tests (6 MWs) that measured an average hydraulic conductivity (K)
at 0.2 ft/day
• Underlying bedrock identified as meta -granitic rock
• Later revised the CSM based on further lithologic information
Results Data Gap Sampling (H&H, May 2019)
• Background soil data
• Stream sediment and surface water data
• GW data
• Radon (Rn) — five samples collected in existing police station; Rn not detected
(ND) in 3 of 5 samples, and was at the detection limit of 0.4 picoCuries per liter
(pCi/L) in 2 of 5 samples, one -tenth below the EPA radon action level of 4 pCi/L.
Data gap assessment (H&H 2O20)
• Drainage pathway soil and soil/CCP sampling — some of the data in this report
reflects soil that has now been removed from the BF Property.
• Installation of wells MW-IA (near MW-1 installed by Falcon and for which no
boring log was available/elevated turbidity), MW-8 (near GP-6 to verify location
of CCPs relative to the water table), MW-9 (near GP-2/GP-3 to verify location of
CCPs relative to water table), and temp well TMW-10 near GP -I I to verify
location of CCPs relative to the water table (September 2019):
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o Roto-sonic drilling within the fill areas
o Perched water zones noted
o MW-I ID installed in Feb 2020 to evaluate perched water conditions &
groundwater data in bedrock below fill
■ HSA/air rotary drilling — 6-inch casing to 45 ft bgs; well installed
to 56 ft bgs
■ Adjacent to MW-9
■ Grout inspections performed by Orange Co Health Dept
o Investigation -derived waste (IDW) containerized onsite & transported to
A&D Env Service permitted facility
o Analysis — metals; gw from MW-9 (reducing) and MW-I ID
(oxidizing/higher pH & SC than MW-9) in Feb 2020 analyzed for
alkalinity, Na, Ca, Mg, and K for geochemical purposes between perched
and bedrock water.
• Provides updated cross-section in Figure 4 and transect location map Fig 3 —
different conceptual model for CCP occurrences based on additional data (pdf pgs
29 and 30/159)
• Geochem parameters different between MW-9 and MW-11D
Fill Area: > 70 samples over assessment period
Based on observations during assessment, the fill material was found to consist of
construction and demolition debris with fill soil intermixed with zones of CCP:
• Fill material identified to depths of about 40 ft bgs
• CCP zones from 1-3 ft thick with some zones up to 10 ft thick
• CCP was observed in MW-1 as deep as 29 ft bgs
• In upper level, CCPs capped with clayey silt (<1 to 1 Oft thick); mostly >2 ft cap
• CCP exposed during assessment on the eastern and central areas embankment
• CCPs in western portion soil <2 ft thick
• Erosion of this layer resulted in deposition along Bolin Creek Trail; this was what
was removed during the IRMs discussed below
The IRMs (IRM Report, H&H, April 19, 2021) included the following:
• Excavation and off -site disposal of soil and exposed CCP (1,004 tons) along
Bolin Creek Trail — Areas G & H — North of Trail; Area I — south of Trail; and
Area F
0 Included erosion & sediment control measures
0 Removed brush and 57 smaller trees
0 Air knife vacuum excavation performed "soft digging" around mature
trees in Areas H&I; CCPs embedded into root matrix
0 Soil/CCP composite samples from Areas G, H & I - TCLP, RCRA metals,
sulfur, sulfate, and pH for off -site waste characterization — deemed
nonhazardous and disposed of at Republic's Uwharrie Environ Landfill
0 Geotechnically unsuitable soil deemed non -hazardous and disposed of at
Upper Piedmont Env Landfill
0 Air monitoring upwind and downwind and ambient in work area for
elevated dust levels
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0 CCPs excavated to depths of 1.5 ft bgs and up to 3 ft bgs in Areas F & H
■ Soil represented by prior samples HH-7, SS-1, SS-2, SS-3, SS-3A,
SED-16, SED-17 (Area H), HH-6, SS-4, SS-5, SS-6, SED-11,
SED-14, SED-15 (Area I), and HH-5 (storm diversion channel)
excavated from property; therefore, these sample results are not
used for Exhibit 2 nor in the DEQ risk calculations.
• Stabilization and cover of exposed CCP along the embankment — Area F — eastern
and Area D - central
• 725 tons of quarry fill and 145 cubic yards (cy) of topsoil imported to backfill
excavations
• Temporary measures to address stormwater and erosion control along the
embankment, and restrict access:
0 Installation of super silt fencing (350 linear ft (If)-LM3000) and
hydroseeding including a biodegradable growth medium along the
embankment for erosion resistance; standard silt fence (301f) and super
silt fence (150 If) installed downgradient of the SE corner of Area F along
the southern portion of the chain link fence
0 Installation of a new stormwater diversion channel along the top of the
slope
0 Installation of fencing and signage notifying trail users not to cross the
fencing and that this was a coal ash remediation area.
0 Maintenance — periodic fertilization, inspections, removal and disposal of
accumulated CCPs, Park Maintenance Superintendent with Town in
accordance with guidance in Erosion and Sediment Control Planning and
Design Manual (DEQ, May 2013)
• Noted that permanent measures would be instituted with the redevelopment of the
Brownfields Property
• CCPs, drainage pathway soil, and shallow soil contaminants of concern (COCs) —
arsenic (As), barium (Ba), manganese (Mn), mercury (Hg), and selenium (Se)
• An additional 1,120.1 tons of soil from outside the Areas G, H & I generated
during excavation of new portions of the trail transported offsite for disposal at
Republic's Upper Piedmont Landfill (no CCPs present)
• Post -excavation soil sampling — 0-1 ft bgs before fill placement (G-1, H-1-H-7, I-
1 — I-3) — composited with grabs for VOCs and SVOCs; areas were backfilled
after confirmation data received.
• Import fill material from Wake Stone Knightdale Quarry — 725 tons and 145 cy
virgin topsoil from Sand & Soils a landscape supply com in Durham/Town's risk
assessor provided approval in 2020 for use at site.
• Stormwater management — installed stormwater controls to divert surface water
runoff towards an existing outfall channel east of the parking lot on the upper
level
0 Lined with polypropylene turf reinforcement matting and seeded
0 Enhancement of existing outfall channel with riprap, #57 stone, and a
filter weave geotextile fabric
0 Approved by Town's Stormwater Management Div, September 2020
0 Installed October to November 2020
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0 12 cy of CCPs were removed and disposed of at Republic's Uwharrie
Landfill (included in the 1,004.27 ton figure above)
0 Stormwater as-builts were approved by the Town in Appendix D.
The conclusion of the Human Health and Ecological Risk Assessment (HHERA)
(Synterra, May 2021) with respect to human health was that the greenway trail was safe
for users following the 2020 IRMs. The conclusion of the HHERA with respect to
ecological risk was that eco-risk was likely minimal but recommended additional
evaluation and further study in this regard. In response to that conclusion, H&H
performed additional risk assessment activities in 2021 that covered the entirety of the
Brownfields Property. Some of their conclusions related to risk are addressed below.
In order to address remaining data gaps, H&H performed additional assessment activities
in 2022 at the Brownfields Property, in accordance with a Brownfields Assessment Work
Plan, which was approved on August 30, 2022. The scope of work consisted of
performing a Brownfields Receptor Survey, and collecting additional data on soil,
groundwater, sub -slab vapor, and exterior soil gas. The report from that assessment scope
of work is presented in Brownfields Assessment Report (Hart & Hickman, December 13,
2022):
• A potential private well was identified at 3 Mt. Bolus Road, about 500 ft north of
the Brownfields Property; however, this location is connected to public water and
sewer; it is unknown if this well is in use for irrigation or other purposes.
• Bolin Creek is identified as a Water Supply (WS-V) water body and a Nutrient
Sensitive Water (NSW); there are recreational trail users that use the paved
recreational Bolin Creek Trail that passes by the Brownfields Property.
• Additional soil assessment was performed in the proposed stormwater pond area
and the existing diesel fuel above -ground storage tank (AST) area.
• Groundwater data collected from within the structural fill was consistent with
prior sampling events in which elevated concentrations of metals are associated
with CCP in the structural fill; groundwater data collected from below the
structural fill in bedrock do not suggest impact from the structural fill material
• VOCs and SVOCs are not detected above method detection limits in the onsite
monitoring wells.
• Vapor intrusion risk was evaluated through exterior soil gas and sub -slab vapor
samples in the existing police building. No VOCs were detected that exceeded
non-residential VISLs; however, TCE was detected in exterior soil gas samples in
excess of its residential VISL. Mercury was not detected in the vapor samples.
Methane concentrations and static pressures did not indicate a concern regarding
methane at the Brownfields Property.
Potential Receptors:
Potential receptors are construction workers, on -site workers, visitors, recreators,
trespassers, and Bolin Creek.
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Health Risk Assessments
As mentioned above, human health risk assessments were conducted at the Brownfields
Property by Synterra Corporation and Rudo Toxicological Consultants, LLC in 2019,
pre-IRM, and in 2021 after the IRMs were completed. These risk assessments were
performed to address concerns about the recreational use of the Bolin Creek Trail in the
vicinity of the structural fill site, and by H&H in 2021 as a follow-up to the original
health risk assessment. Information about those risk assessments follows:
Synterra's HHERA (Maw)
• Two assessments:
o Preliminary risk eval 2019 for IRMs would be protective of trail users
o Post-IRM risk assessment update
o Used 2018 version DEQ risk calculator for HH risk assessment which was
current at that time
o Discusses hazard identification process and exposure assessment
processes
o Used max values for COCs
o Used 2014 and 2016 as baseline conditions for the site
o Evaluated two completed exposure scenarios: Human recreators and
construction workers
o Default parameters provided in Appendix A
o Assumptions about age of child only to 6 yrs
o Assumed Cr+6 unless speciated
o Used max concentrations in 2019 without consideration of background
conc
o "Background COI concentrations contribute to the risk of persons exposed
on the Site and should be considered in the risk management and risk
communication."
o For post-IRM assessment, used January 2021 DEQ risk calculator that was
available at the time:
■ Exposure duration — 0.5 hr
■ 195 day/yr exposure
■ For construction worker post-IRM concentrations used (max)
■ Excluded thallium from SW as not detected/not representative
o Screening Level Ecological Risk Assessment (SLERA) performed as part
of post-IRM
■ Surface Water (Bolin Creek) — no COCs
■ Sediment — Ba, Cr
■ Soil — As, Pb, Hg, Sr, Tl, V, Zn
■ Excluded data collected from below 4 ft and under impervious
surfaces
o Conclusions:
■ IRM effective in reducing risk to trail users
■ "Ecological risk is minimal"; final remedy design should include
ecological risk assessment
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■ Town needs to continue to monitor Site conditions until final
remedy in place
■ If new areas of CCP exposure noted, additional data collection
should occur
■ Update HH risk calcs
■ Construction activities — site worker training, use of PPE,
additional sampling with change in site conditions or exposure, for
example, based on the nature of the construction activities
■ Potential unacceptable risk: future construction worker (As & Mn,
and recreational user (As) — implement PPE and other safety
measures — in Site Construction Plan
Human Health Risk Assessment (H&H, 2021)
H&H used exposure unit designations of EU #1 (Upper Level), EU#2 (Lower Level, i.e.,
Bolin Creek & Trail area), EU#3 (Embankment), and potential for erosion on the
embankment to transport CCP into the trail area on which to generate a series of risk
calculations for the site, some of which varied from the DEQ risk calculations presented
above.
To develop exposure point concentrations for the risk screening, H&H used the following
approach:
• Soil samples excavated during 2020 IRMs were excluded as they are no longer
located on the Brownfields Property
• Only used most recent sample for those media sampled more than once
• Soil samples collected at depths of 2 ft or less used for residential, nonresidential
works, & greenway users
• Soil samples collected at depths of 10 ft or less used for construction workers
• If impacted soil or CCP at deeper depths are exposed during site redevelopment,
additional risk evaluation should be performed
• BRS would require confirmatory sampling and risk evaluation of areas where
impacted soil or CCP not covered by impervious surfaces or at least 2 ft of clean
fill
• Surface water — used only those collected in 2016 and 2019
• Stream sediment — used only the 2019 data as representative of current conditions
• Used maximum concentrations based on the datasets above
• After initial risk calculations, removed metals at concentrations below site -
specific background soil values (BSVs).
• BSVs: 95% UTL with 95% coverage for background soil and the lower of 2x the
mean or the maximum detected concentration for background surface water and
sediment (Appendix C)
• Default exposure parameters for residential, non-residential work, construction
worker — reasonable maximum exposure (RME) — within 90ffi to 99ffi percentiles
• Greenway users — used polling data collected by the Town, i.e. used values equal
to or more conservative than the 98ffi percentile of responses — worst -case
• List of exposures on p 25/294 of Risk Assessment Report (RAR) & in Appendix
C - used 6 yrs child and 20 yrs adult
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• Toxicity factors — default in risk calculator (includes possible effects for pregnant
women)
For Ecological Risk Assessment — H&H (2021)
• Initial screening
• Compare to ESV (Region 4)
• not a full SLERA
• EU# 1 -wooded area surrounding the facility; surface soil exposure
• EU#2 -highest likelihood of potential ecological receptors to surface soil,
sediment, and surface water
• EU#3 — moderate potential; surface soil exposure
• Need permanent measures to stabilize embankment
• Results:
o EU#1 — conc above ESVs and BSV in S-4 (Cd, Co, Cu, Mn, Ni) and MW-
7 (outlier Cu conc)
o EU#2 — only in SED-13 above ESV & BSV (Ba, Se, Sr)
o EU#3 — above ESV and BSV in all four samples (S-7, H-9, H-10, and H-
11) for As, Ba, Be, Hg, Se, and Sr — remediation recommended to address
exposed CCPs in this area (performed in concert with final remedial
actions and site redevelopment)
• Stream sediment:
o Exceedances of ESVs for Ba and Cr are less than BSVs and similar to
upstream samples
o Also used EPA Region 4 Refinement Screening Values (RSVs) for
sediment — less conservative ecological effects data — used as a second -tier
screening where ESVs exceeded; RSVs not exceeded.
• Surface water:
o No concentration exceeded EPA Region 4 Acute and Chronic Surface
Water ESVs, NC 2B Surface Water Standards, or In -Stream Target Values
H&H conclusions from this risk assessment include:
• If developed for residential use, H&H recommends remediation or other actions
(excavation, impervious cover, resampling) to address impacts in the area of S-4
• Reference to the EMP for construction worker safety; however, important to
clarify that an EMP can inform construction workers, but it does not take the
place of the contractor's H&S Plan and occupational safety requirements
• LUR preventing groundwater use
Regarding the risk assessments, Brownfields conferred with Dr. Frances Nilsen, Ph.D.
Environmental Toxicologist for DEQ, who specializes in metals toxicology, among other
areas. The HHERA studies and other site data were shared with Dr. Nilsen. Based on the
analysis conducted over the years and the mitigation steps that had been taken at the site,
Dr. Nilsen stated that the Town had taken appropriate measures to prohibit access to
areas impacted by coal ash material, that the CCP presents less of a risk for non-
residential purposes under consideration than for residential uses. Further, Dr. Nilsen
indicated that based on collected onsite stream data, that the concentrations detected in
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the stream do not seem to be having an impact on the ecosystem at the site. Dr. Nilsen
further indicated that if the forested area of the site is to remain as -is, with barriers in
place to prevent human exposure and environmental disturbance, combined with the
required monitoring of the site to ensure the receptor pathway remains disconnected, that
an ecological risk assessment would not be necessary. Therefore, we do not anticipate
requiring any further work with respect to ecological risk assessment unless an
unforeseen change of conditions poses a threat to Bolin Creek.
Interim Remedial Measures Maintenance Activities (Spring 2024)
The Town recently completed interim remedial measures maintenance activities under an
approved Environmental Management Plan to further stabilize the slope and protect
against access to the CCP until the final remedy is implemented. These activities included
modifying the drainage at the top of the slope, adding silt fencing, removing trees that
could de -stabilize the material, and hydroseeding.
Contaminated Media:
DEQ has evaluated data collected from the following media at the subject property:
groundwater, soil, CCP, exterior soil gas, sub -slab vapor, drainage pathway sediment,
Bolin Creek surface water, and Bolin Creek sediment. DEQ relies on the data from these
media to base its conclusions regarding the subject property and its suitability for its
intended reuse. Please see the Brownfield Agreement's Exhibit 2 and the assessment
reports for specific sample locations, dates, and COCs.
Soil and CCP — Due to the past history of the Brownfields Property, the site is underlain
by soil and CCP, intermixed in areas, and construction debris. Several risk calculators
were generated to address constituents that were detected in site soil (excluding data that
represents soil that has been removed from the property during the IRMs) across the site,
and in the drainage pathway, the planned stormwater pond area, and the AST area, and
the CCP samples across the site (excluding the CCP removed from the property during
the IRMs).
Groundwater - Groundwater at the Brownfields Property occurs in the existing
monitoring wells in the fill area at depths of 30-40 bgs; additional information about
groundwater and how the data from each zone was used in the risk calculators is provided
below:
• Zones of perched water appear within the fill area, an effect that may be, at least
in part, created by the pozzolanic reaction between the CCP and the soil, which
would tend to form layers of relatively impermeable material in the subsurface in
addition to the uncontrolled formation of layers of different permeabilities during
initial placement, such as sand and gravel vs demolition debris vs clay/silty layers
of soil.
• Groundwater wells are completed in the following units; data from these units
was used to evaluate environmental risk in a corresponding risk calculator:
o MW-5 (background well located across Bolinwood from the Brownfields
Property) - screened in bedrock
12
Chapel Hill Police Property/23022-19-068/14Jun2024

o MW-I, MW-IA, MW-2, MW-8, MW-9 —perched groundwater zones in
fill area
o MW-3, MW-3A, MW-4, MW-4A, MW-6 — lower elevation outside of the
fill area
o MW-7 — immediately east of the stormwater pond area in bedrock
o MW-11D —constructed within the fill area, but screened below the fill
into bedrock
• Data suggest that the contaminated groundwater plume is generally stable within
the fill material with most COCs either decreasing in concentration or remaining
stable over the time monitoring has been conducted.
Risk Calculations:
Risk calculations were performed using the February 2024 DEQ Risk Calculator
https:Hdeq.nc.goy/permits-rules/risk-based-remediation/risk-evaluation-resources. The
DEQ Risk Calculator is an Excel -based, menu -driven program. The risk evaluation
procedures, equations, and default parameters used to create the calculator follow current
U.S. EPA risk assessment guidance. It incorporates a database that contains toxicity
values and other chemical -specific parameters obtained directly from the USEPA
Regional Screening Level (RSL) tables and is updated when U.S. EPA updates the RSL
tables. Additional information on use of the DEQ Risk Calculator can be found at the
link noted above.
For the purposes of looking at the site spatially, the site was divided into multiple risk
calculators by different types of media and using the maximum concentrations site -wide.
The following risk calculators were developed by Brownfields staff using the data noted:
1. Soil Samples — max concentrations of contaminants (excluding soil removed
during IRMs)
2. CCP Samples — max concentrations of contaminants (excluding CCP removed
during IRMs)
3. Drainage Pathway soil samples
4. Stormwater Pond Area soil samples — 2022
5. AST Area soil samples — 2022
6. Leachate samples collected by H&H in 2016
7. Background groundwater — well MW-5 (max concentrations)
8. Groundwater samples from within the fill material - 2022
9. Groundwater samples from below the fill in bedrock well MW-11 D - 2022
10. Groundwater samples downgradient of the fill - 2022
11. Bolin Creek stream sediment and surface water (max concentrations, 2013-2019)
12. Exterior soil gas samples - 2022
13. Police Building sub -slab vapor samples — 2022
14. Site -Wide using historical maximum concentrations in groundwater, CCP/soil,
and exterior soil gas samples
The calculated HI risk results based on the DEQ risk calculators for various site media
are compared in the summary tables below. Additional information about the data and
the risk calculator output for each media type are presented in the pages following these
summary tables.
13
Chapel Hill Police Property/23022-19-068/14Jun2024

Soil and Fill/CCP Various Locations (Risk Calculators (RC) Nos. 1, 2, 3, 4, & 5):
Residential -
Non-
Construction
Recreator/
Direct Contact
Residential-
Worker Direct
Trespasser
Type of Media
Direct Contact
Contact
Direct Contact
CR
HI
CR
HI
CR
HI
CR
HI
Soil RC No. 1
1.8E-05
3.3
3.4E-06
0.22
1.4E-06
7.9
9.8E-06
1.8
Fill/CCP (RC
1.5E-04
6.2
3.2E-05
0.43
6.9E-06
12
8.4E-05
3.4
No. 2
Drainage
Pathway Soil
2.3E-05
2.1
4.9E-06
0.15
1.3E-06
7.9
1.3E-05
1.2
RC No. 3
Stormwater
Pond Soil (RC
4.7E-06
0.65
7.5E-07
0.044
3.7E-07
2.0
2.6E-06
0.36
No. 4
AST Area Soil
4.3E-06
0.84
6.2E-07
0.057
6.3E-07
1.1
2.4E-06
0.47
RC No. 5
Bold - Exceeds CR of 1E-04 or HI of 1
CR - Cancer risk
HI - Non -cancer hazard index
Leachate Samples Derived from Surface Soil (Risk Calculator No. 6):
Type of Media
Residential -Direct Use
Non -Residential -Direct Use
CR
HI
CR
HI
Leachate Samples
3.5E-04
7.3
7.0E-05
1.1
Bold - Exceeds CR of 1E-04 or HI of 1
CR - Cancer risk
HI - Non -cancer hazard index
Groundwater Screened in the Fo lowing Media Risk Calculators Nos. 7, 8, 9 & 10):
Type of Media
Residential -Direct
GW Use
Non -Residential -
Direct GW Use
CR
HI
CR
HI
Back round-MW-S RC No. 7
4.8E-06
1.8
9.7E-07
0.3
Fill/CCP RC No. 8
7.2E-04
22
1.4E-04
3.7
Bedrock-MW11D RC No. 9
1.1E-05
1.7
2.1E-06
0.25
Downgradient Fill-
MW-3A, MW-4A, MW-6 (RC
No. 10
7.4E-06
4.4
1.5E-06
0.75
Bold - Exceeds CR of 1E-04 or HI of 1
CR - Cancer risk; HI - Non -cancer hazard index
GW - Groundwater
Note: Groundwater is not used as a source of water to the Brownfields Property and
direct groundwater use is prohibited under the Brownfields Agreement.
14
Chapel Hill Police Property/23022-19-068/14Jun2024

Bolin Creek Stream Sediment & Surface Water (Risk Calculator No. 11):
Type of Media Recreator/Tres asser
CR III
Sediment RC No. 11 3.2E-06 0.58
Surface Water (RC No. 11) 1.7E-06 0.13
Bold — Exceeds CR of 1E-04 or HI of 1
CR — Cancer risk
HI — Non -cancer hazard index
Exterior Soil Gas and Sub -slab Vapor Samples (Risk Calculators Nos. 12 and 13):
Residential
Non- Residential
Type of Media
Soil Gas to
Indoor Air
Soil Gas to Indoor
Air
CR
HI
CR
III
Exterior Soil Gas o. 12
2.1E-05
1.2
1.5E-06
0.094
Sub -Slab Vapor — Police
Station (No. 13)
2,9E-07
0.096
2.2E-08
0.0076
Bold — Exceeds CR of 1E-04 or HI of 1
CR — Cancer risk
HI — Non -cancer hazard index
15
Chapel Hill Police Property/23022-19-068/14Jun2024

Risks Calculated based on Site -Wide Maximum Concentrations by DEQ Compared
to H&H Risk Calculations performed in 2021 based on H&H EU Designations (Risk
Calculator No. 14)
Type of Exposure
DEQ
Wide
H&H
EU#1
H&H
EU#2
H&H
EU#3
DEQ
side
H&H
EU#1
H&H
EU#2
H&H
EU#3
CR
HI
Residential -
Soil/CCP
1.6E-04
2.4E-06
NC
9.4E-05
8.3
3.6
NC
3.1
Residential - GW
3.6E-03
NC
NC
NC
83
NC
NC
NC
Residential - GW to
Indoor Air
0.0
NC
NC
NC
0.0
NC
NC
NC
Residential - Soil
Gas to Indoor Air
2,15E-05
NC
NC
NC
1.2
NC
NC
NC
Non -Residential
Soil/CCP
3.3E-05
4.8E-06
NC
2.0E-05
0.57
0.24
NC
0.22
Non -Residential
Groundwater
6.3E-04
NC
NC
NC
12
NC
NC
NC
Non -Residential GW
to Indoor Air
0.0
NC
NC
NC
0.0
NC
NC
NC
Non -Residential Soil
Gas to Indoor Air
1.5E-06
NC
NC
NC
0.094
NC
NC
NC
Construction
Worker Soil
7.7E-06
7.0E-06
1.4E-06
4.4E-06
11
11
3.6
8.8
Recreator/Trespasser
- Soil
g 9E-05
NC
8.4E-06
3.4E-06
4.6
NC
0.41
0.46
Bold - Exceeds CR of 1E-04 or HI of 1
CR - Cancer Risk
EU - Exposure Unit
HI - Hazard Index
GW - Groundwater
NC - Not calculated
Relevant conclusions from the BRS's review of these environmental reports, a discussion
of calculated environmental risk values summarized in the above tables, and the risk
drivers based on these data for these various site media are provided below.
16
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator I — Soil Samples:
• Based on physical description and an evaluation of constituents, particularly
metals, CCP is confirmed to occur as structural fill reportedly mixed in with
construction and demolition debris in the elevated portion of the site.
• Metals that exceed Residential Preliminary Soil Remedial Goals (PSRGs) in site
soil are: arsenic (As), hexavalent chromium (Cr+6), cobalt (Co), manganese (Mn),
thallium (Tl), and vanadium (V); however, residential use of the site is not
contemplated at this time.
• Only one metal in site soil, As, exceeds its Industrial/Commercial PSRG, though
the concentrations that do are generally single digit values and are consistent with
site -specific and literature background concentrations for NC soil. One metal
detected at its Industrial PSRG is thallium in soil collected from well MW-5; it
should be noted that well MW-5 is not located on the Brownfields Property, but is
located just off -site and serves as a background well screened in bedrock.
• Based on maximum values of constituents in soil samples characterized as soil
that was not identified as being mixed with CCP, the calculated noncancer HI
values for direct residential exposure to soil (3.3), direct construction worker
exposure to soil (7.9), and direct exposure for a recreator/trespasser (1.8) exceed
the noncancer threshold hazard index (HI) of 1. None of the calculated risk
values for these exposures exceed the acceptable cancer risk (CR) maximum of
1 E-04.
• The calculated CR and HI for non-residential worker exposure does not exceed
the acceptable CR risk range nor the threshold HI of 1.0.
• The risk drivers for residential exposure to soil are thallium (Tl), cobalt (Co), Mn,
and As. The risk drivers for construction worker exposure to soil are Mn, Co, Ni,
and As. The risk drivers for recreator/trespasser scenarios are Tl, Co, and Mn.
See the risk calculator output for maximum concentrations of contaminants in site soil
below; the maximum concentrations in soil used in the risk calculator represent soil that
was obtained from the depths of 0 to 3 feet bgs.
17
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk for Individual Pathways for
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID• Soil
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Riskexceeded?
Resident
Soil
1.8E-05
3.3E+00
YES
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
3.4E-06
2.2E-01
NO
Groundwater Use*
NC
NC
NC
Construction Worker
Soil
1.4E-06
7.9E+00
YES
Recreator/Trespasser
Soil
9.8E-06
1.8E+00
YES
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
18
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 2: Coal Combustion Product (CCP) — includes samples that are mixed
soil and CCP
• CCP has been exposed at the surface, particularly in very steep areas. During the
IRMs, the Town stabilized the slopes where these exposures occurred and is
required to monitor routinely and abate any daylighted areas caused by storm or
other events to minimize exposure risk prior to the implementation of a final
remedy.
• Metals that exceed Residential PSRGs in CCP or mixed CCP and soil are:
aluminum (Al), As, Ba, cadmium (Cd), hexavalent chromium (Cr+6), Co, iron
(Fe), Mn, and Hg.
• Similar to the soil samples profile discussed above, primarily As exceeds its
Industrial/Commercial PSRG, although there is one detection of Hg that exceeds
its Industrial/Commercial PSRG. The concentrations of As in CCP samples
ranges from 3.37 milligrams per kilogram (mg/kg) to as high as 95.9 mg/kg. One
analysis of Al in this material from 2013 was at the I/C PSRG of 23,000 mg/kg.
• Direct contact calculated risk values for CCP indicate an exceedance of an
acceptable cancer risk of 1E-04 (1.5E-04) and an exceedance of the noncancer
hazard index threshold of 1.0 (6.2) for direct residential exposure; and a HI of 12
for construction worker and 3.4 for recreator/trespasser by ingestion and
inhalation.
• Calculated risk values for direct exposure to soil (CCP) under a non-residential
worker scenario do not exceed either the regulatory acceptable CR nor the
noncancer HI of 1.
• The risk drivers for direct contact to soil (in this case CCP) for residential
scenarios are As, Co, Hg, Mn, Al, Ba, and Cd by ingestion, dermal contact, and/or
inhalation. The risk drivers for construction workers are Mn, As, Hg, Al, Co, and
Ba by ingestion and inhalation. The risk drivers for recreator/trespasser scenarios
are As, Co, Hg, and Mn by ingestion.
See the risk calculator output for maximum concentration in CCP samples below; the
maximum concentrations in CCP used in the risk calculator are obtained primarily from
the depths of 0 to 4 ft, but includes certain samples collected to a depth of 12 or 15 feet
bgs.
19
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk for Individual Pathways for
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: Coal Combustion Product (CCP) Samliles
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Soil
1.5E-04
6.2E+00
YES
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
3.2E-05
4.3E-01
NO
Groundwater Use*
NC
NC
NC
onstruction Worker
Soil
6.9E-06
1.2E+01
YES
Recreator/Trespasser
Soil
8.4E-05
3.4E+00
YES
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
20
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 3: Drainage Pathway Soil
• The results for the drainage pathway soil indicate that Residential PSRGs are
exceeded by concentrations of As, Cr+6, Co, and Mn; however, no residential use
is planned for this Brownfields Property.
• Only arsenic concentrations ranging from 3.97 mg/kg to 14.5 mg/kg exceeds its
Industrial/Commercial PSRG.
• The calculated risk values from the drainage pathway soil samples, collected from
the upper six inches along drainages at the Brownfields Property, do not exceed
an acceptable CR for any exposure pathway, but do exceed the noncancer HI of 1
for direct residential exposure (2.1), for direct construction worker exposure (7.9),
and for the recreator/trespasser scenario (1.2). The threshold HI of I is not
exceeded for the non-residential worker exposure pathway.
• The risk drivers for direct residential exposure to soil are principally from the Co,
As, and Mn concentrations through ingestion routes. The construction worker
exposure is principally from Mn, Ni, and As through the inhalation route. The
recreator exposure route risk drivers are Mn, Co, and As.
See the risk calculator output below for the drainage pathway soil samples collected from
the upper six inches of soil; maximum concentrations were obtained from samples HH-2,
HH-3, HH-4, HH-12, SED-9, and SED-13.
Risk for Individual Pathways 1
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: Drainage Pathway Soil
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
sk
Hazard Index
Riskexceeded?
Resident
Soil
2.3E-05
2.1E+00
YES
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
4.9E-06
1.5E-01
NO
Groundwater Use*
NC
NC
NC
Construction Worker
Soil
1.3E-06
7.9E+00
YES
Recreator/Trespasser
Soil
1.3E-05
1.2E+00
YES
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Risk exceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
21
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 4: Stormwater Pond Area Soil
• The shallow soil samples collected from the upper 2 ft within the area of the
planned redevelopment stormwater pond indicates that only As concentrations in
two of the three samples (HH-13 and HH-14) exceed the Residential PSRG for
As; the Industrial Commercial PSRG for As is not exceeded.
• The risk calculator output for these soil samples indicates that an acceptable CR
and the threshold HI are not exceeded for any exposure scenario except direct
contact for a construction worker with a HI of 2.0.
• The risk driver for the construction worker scenario is principally Mn through
inhalation.
See the risk calculator output below for the stormwater pond soil samples collected from
the upper two feet of soil (1-11-1-13 & HH-14).
Risk for Individual Pathways r$71 91171M
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Ex sure Unit ID: Stormwater Pond Soil September 2022
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
sk
Hazard Index
Riskexceeded?
Resident
Soil
4.7E-06
6.5E-01
NO
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
7.5E-07
4.4E-02
NO
Groundwater Use*
NC
NC
NC
Construction Worker
Soil
3.7E-07
2.0E+00
YES
Recreator/Trespasser
Soil
2.6E-06
3.6E-01
NO
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Risk exceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
22
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator S: AST Area Soil
• The AST Area soil was assessed through one boring, HH-12, in 2022 from a
depth of 4-5 ft bgs. The results from the analysis conducted on the sample from
HH-12 indicate that the concentrations of As, Cr+6, and Co exceed their
respective Residential PSRGs, but there are no exceedances of
Industrial/Commercial PSRGs.
• There were very low values of VOCs detected below the reporting limits, i.e.,
estimated (J) values of chlorobenzene, ethylbenzene, and toluene, and one
detection of total xylenes.
• The calculated risk values for the AST area soil indicate no exceedances of an
acceptable CR nor the threshold HI of 1 for any exposure scenario, except for the
construction worker pathway. The risk drivers for this pathway are Mn and Ni.
See the risk calculator output below for the AST Area soil sample collected from the
depth of 4-5 ft bgs.
Risk for Individual Pathways
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: AST Area, HH-12
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
CarcinogenicRisk
Hazard Index
Risk exceeded.
Resident
Soil
4.3E-06
8.4E-01
NO
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
6.2E-07
5.7E-02
NO
Groundwater Use*
NC
NC
NC
Construction Worker
Soil
6.3E-07
1.1E+00
YES
Recreator/Trespasser
Soil
2.4E-06
4.7E-01
NO
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
23
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 6: Leaching Potential from CCP (2016 Samples)
Several samples of CCP material from the upper eight feet of ground surface in 2016
were subjected to leaching potential testing using the Synthetic Precipitation Leaching
Procedure (SPLP) to evaluate whether leachate generated from groundwater percolating
through the CCP could impact groundwater in such a way as to exceed NC 2L
groundwater standards. The maximum concentrations used in the risk calculator
originated from samples HH-1 through HH-3.
• The results indicate that leachate samples from the collected CCP samples
exceeded the respective NC 2L groundwater standard for the following COCs:
antimony (Sb), As, Ba, Co, lead (Pb), Mn, Se, strontium (Sr), and vanadium (V).
• SPLP leachate from the CCP samples resulted in a direct contact groundwater CR
of 3.5E-04 and HI of 7.3, both exceeding acceptable regulatory risk thresholds for
direct residential exposures (drinking, bathing), but just exceeds an acceptable HI
of 1.0, with the calculated HI of 1.1 for nonresidential direct exposures.
• The risk drivers for the exceedance of direct residential exposure to leachate for
CR is the ingestion of arsenic. The risk drivers for the noncancer HI are As, Se,
Co, Mn, Ba, V, and Sr.
See the risk calculator output below for the leachate samples collected from the upper
eight feet of soil.
Risk for Individual Pathways U
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: Leachate Samples H&H 2O16
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
CarcinogenicHazard
Risk
Index
Risk exceeded?
Resident
Soil
NC
NC
NC
Groundwater Use*
3.5E-04
7.3E+00
YES
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
7.0E-05
1.1E+00
YES
Construction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
NC
NC
NC
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
CarcinogenicRisk
Hazard Index
Risk exceeded?
Resident
Groundwater to hidoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
24
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 7: Off -site Upgradient (Background) Groundwater (MW-5)
• The off -site upgradient (background) groundwater well, MW-5, has had
detections of the following COCs above their respective NC 2L groundwater
standard: manganese (Mn) and selenium (Se). Lithium (Li) and Molybdenum
(Mo) were also detected in this well, but there are not NC 2L groundwater
standards established for Li and Mo.
• The risk calculations indicate that acceptable CR and HI are not exceeded based
on the background bedrock groundwater results in MW-5 except for direct
residential use with an HI of 1.8. This groundwater is not used for water supply
• The calculated groundwater to indoor air risk values for both residential and non-
residential scenarios was zero as no volatile compounds have been detected in this
background bedrock well.
See the risk calculator output below for the August 2022 groundwater sample collected
from the bedrock interval in background bedrock well MW-5.
Risk for Individual Pathways
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: MW-5 Background Bedrock Well
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
CarcinogenicRisk
Hazard Index
Risk exceeded.
Resident
Soil
NC
NC
NC
Groundwater Use*
4.8E-06
1.8E+00
YES
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
9.7E-07
3.0E-01
NO
Construction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
NC
NC
NC
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
25
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 8: Groundwater within the Fill (Perched GW) (Wells MW-1, MW-IA,
MW-2, MW-3, MW-4, MW-8, & MW-9)
• Groundwater concentrations of the following constituents are detected in wells
constructed within the fill in excess of NC 2L groundwater standards: Sb, As, Ba,
beryllium (Be), total Cr, Co, copper (Cu), Fe, Pb, Mn, Hg, Se, Sr, sulfate, Tl, V,
and zinc (Zn).
• The calculated risk values based on maximum concentrations of contaminants in
Aug 2022 groundwater samples within the fill exceeds both the regulatory
acceptable range for cancer risk and the threshold HI of 1 with respect to direct
groundwater use in residential scenarios at 7.2E-04 and 23 respectively, and
nonresidential direct groundwater use at 1.4E-04 and 3.7, respectively.
• The risk drivers for these values in groundwater for direct residential use are Mn,
As, Li, Co, Ba, Hg, and Sr by ingestion, dermal, and/or inhalation routes. The risk
drivers in groundwater for direct non-residential use are Mn, As, and Li by
ingestion and dermal routes.
• No VOCs nor SVOCs were detected in groundwater collected from within the fill
material. Therefore, the calculated groundwater to indoor air risk values indicate
no exceedances of the regulatory risk threshold values for CR nor HI for both
residential and nonresidential scenarios.
See the risk calculator output below for the maximum concentrations of contaminants in
the most recent (August 2022) groundwater sample event (from wells MW-IA, MW-8,
and MW-9) collected from the wells located within the CCP/structural fill (Perched GW):
Risk for Individual Pathways 1
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Ex sure Unit ID: Max Concentrations GW in CCP Aug2022
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
sk
Hazard Index
Riskexceeded?
Resident
Soil
NC
NC
NC
Groundwater Use*
7.2E-04
2.2E+01
YES
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
1.4E-04
3.7E+00
YES
Construction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
NC
NC
NC
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Risk exceeded?
Resident
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
26
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 9: Groundwater below the Fill in Bedrock (MW-IID)
• No COCs are detected in MW-11D in excess of established NC 2L groundwater
standards; the Li and Mo concentrations detected in MW-11D are included on
Exhibit 2 as there are no established NC 2L standards for Li or Mo.
• No VOCs nor SVOCs are detected above method detection limits in any
monitoring well; COCs were only metal constituents.
• Groundwater concentrations in the last round of sampling were consistent with
previous results; additional parameters were included in the most recent analytical
program (for example, Li and Boron (B). Boron, though detected, was not found
at a concentration that exceeds its NC 2L groundwater standard, and as noted
above Li does not have an established NC 2L groundwater standard.
• The risk calculations based on the recent data for well MW-11D indicate an
exceedance of acceptable CR and noncancer HI thresholds only for the HI for
direct residential use of groundwater at 1.7. However, groundwater at the
Brownfields Property shall not be used for water supply and its use is prohibited
in the Brownfields Agreement.
• The risk driver for the direct residential use of groundwater in MW-I ID is Li by
ingestion.
• Groundwater wells MW-5 (background), MW-7, and MW-11D are all completed
in bedrock, with MW-11D completed in bedrock below the structural fill material
containing debris and CCP. Compounds identified in MW-5 are primarily Ba,
Mn, Se, Sr, chloride, fluoride, and sulfate with J values of As, Co, Li, Mo, and V.
Well MW-7, located east of the structural fill, has similar compounds, but
generally at lower concentrations than MW-5. MW-11D is also similar in the type
of compounds detected, but has generally lower concentrations than MW-5, with
the exception of B, Mo, and Sr. However, none of the metals detected in
groundwater from well MW-11D are at concentrations that exceed their NC 2L
standard, if one has been established.
See the risk calculator output below for the August 2022 groundwater sample collected
from the bedrock interval screened below the CCP in well MW-11D.
27
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk for Individual Pathways for
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: MW-11D, Onsite Bedrock Well
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Soil
NC
NC
NC
Groundwater Use*
1.1E-05
1.7E+00
YES
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
2.1E-06
2.5E-01
NO
nstruction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
NC
NC
NC
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
28
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 10: Groundwater downgradient of the CCP/Structural fill (MW-3A, MW-
4A, MW-6)
• Contaminants that have been detected in excess of NC 2L groundwater standards
in the groundwater wells downgradient of the structural fill material are As, Ba,
Cr+6, total Cr, Pb, Li, Mn, Mo, Se, Sr, sulfate, and Tl.
• The data for the most recent sample event conducted in August 2022 for wells
MW-3A, MW-4A, and MW-6 were used in the risk calculator to evaluate the risk
posed by groundwater downgradient of the structural fill area after the IRMs had
been conducted in this area.
• The calculated risk values for the August 2022 groundwater in this area indicates
that acceptable CR and HI threshold values are not exceeded except for direct
residential groundwater use HI of 4.4. The risk drivers for direct residential use
are Li and Mn. Groundwater will not be used for water supply at this Brownfields
Property.
See the risk calculator output below for the August 2022 groundwater sample collected
from the groundwater wells downgradient of the structural fill (MW-3A, -4A, & 6).
Risk for Individual Pathways
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: GW downgradient of Structural Fill (MW-3A, 4A, -6)
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
CarcinogenicRisk
Hazard Index
Risk exceeded?
Resident
Soil
NC
NC
NC
Groundwater Use*
7.4E-06
4.4E+00
YES
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
1.5E-06
7.5E-01
NO
Construction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
NC
NC
NC
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
29
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 11: Bolin Creek Samples - Surface Water
• Collected in 2013, 2014, 2016, and 2019
• 3 — upstream location; 3 locations adjacent; and 3 downstream (Note:interpret SW
sample 5, noted as being downgradient in reports, as onsite and therefore not
interpreting for the sake of risk calculations that this sample is downstream).
• Surface water samples collected adjacent to and downstream of the Brownfields
Property do not appear to be appreciably different in metals concentrations in
samples collected between 2014 and 2019.
• In some cases, NC 2B standards do not exist for certain contaminants. In that
case, the EPA National Recommended Water Quality Criteria for Aquatic Life &
Human Health, or the NC In -Stream Target Values for Surface Waters are used
for comparison purposes.
• Of the surface water samples, no constituents analyzed for in the surface water of
Bolin Creek were detected at a concentration that exceeded its specific NC 2B
surface water standard; only manganese at 100 ug/L (an outlier) exceeds the EPA
National Recommended Water Quality Criteria for Aquatic Life & Human
Health. It should be noted however, that due to high natural occurrence of
manganese in NC surface waters, the EPA approved the removal of NC human
health standards as part of the 2007-2016 Triennial review for Mn.
• These risk calculations indicate that there is no human health risk concerns from
exposure to the surface water of Bolin Creek at the Brownfields Property.
Risk Calculator 11: Bolin Creek Sediment
• Collected in 2016 and 2019
• 2 upstream locations; 3 adjacent; 2 downstream (assuming sample SED-5 is
interpreted to be onsite and not a downstream sample). Note Exhibit 2 only
contains the sample results for the locations that are within the Brownfields
Property's boundaries.
• Stream sediment in three samples (SED-3, SED-4, and SED-5) had concentrations
that exceeded their respective Residential PRSGs: As, Cr+6, Co, and Mn;
however, none of these concentrations exceeded the Industrial/Commercial
PSRGs for these COCs.
• These risk calculations indicate that there is no human health risk concerns from
exposure to the sediment of Bolin Creek at the Brownfields Property.
The risk calculator output indicates that there are no exceedances of an acceptable CR nor
HI for the maximum concentrations of contaminants in the Bolin Creek sediment or
surface water based on a recreator/trespasser exposure to creek sediment or surface water.
30
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk for Individual Pathways for
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: Bolin Creek Stream Sediment & Surface Water
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Soil
NC
NC
NC
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
NC
NC
NC
Construction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
3.2E-06
5.8E-01
NO
Surface Water*
1.7E-06
1.3E-01
NO
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
NC
NC
NC
Indoor Air
NC
NC
NC
31
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 12: Exterior Soil Gas
• Exterior soil gas samples were collected across the elevated portion of the
Brownfields Property in 2022. The contaminants in exterior soil gas samples that
exceeded their respective Residential Vapor Intrusion Screening Levels (VISLs)
were bromodichloromethane, chloroform, 1,2-dichloroethane (1,2-DCA), cis-1,2-
dichloroethene (cis-1,2-DCE), ethyl acetate, and trichloroethylene (TCE). The
compounds 4-ethyltoluene, and trichlorofluoromethane do not have established
VISLs. For those contaminants that have established VISLs, no contaminant
concentration exceeded its respective Non -Residential VISL.
• The only exceedance was in the calculated residential soil gas to indoor air HI of
1.2 as there were some detections of VOCs in exterior soil gas, including TCE.
The HI for nonresidential exposures was much less, at 0.094.
• The risk drivers for the soil gas to indoor air HI exceedance are principally TCE
with cis-1,2-dichloroethylene (cis-1,2-DCE) and ethyl acetate.
• Based on these values, the BRS would recommend VI mitigation for any
residential uses at the property, should such use be contemplated in the future.
Based on the calculated HI for non-residential worker exposure pathways, we
would not recommend a VI mitigation for non-residential uses of the Brownfields
Property.
The risk calculator output below indicates that there is one exceedance — the HI of 1.2 for
the soil gas to indoor air calculation for residential uses, which are not contemplated at
this time.
Risk for Individual Pathways 1
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: Exterior Soil Gas
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
sk
Hazard Index
Riskexceeded?
Resident
Soil
NC
NC
NC
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
NC
NC
NC
Construction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
NC
NC
NC
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Risk exceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
2.1E-05
1.2E+00
YES
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
1.5E-06
9.4E-02
NO
Indoor Air
NC
NC
NC
32
Chapel Hill Police Property/23022-19-068/14Jun2024

Risk Calculator 13: Sub -Slab Vapor — Police Station
There were two sub -slab vapor samples collected from the existing police station building
in 2022. There were low detections of several VOCs in these samples; however, there
were no compounds for which their concentrations exceeded Residential nor
Nonresidential Vapor Intrusion Screening Levels (VISLs).
The calculated risk values for CR and HI based on the sub -slab vapor samples from the
police building did not indicate an unacceptable CR or noncancer risk from vapor
intrusion for neither a residential nor a non-residential exposure pathway.
Risk for Individual Pathways
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: Sub -Slab Vapor - Police Station Building
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Ri sk exceeded?
Resident
Soil
NC
NC
NC
Groundwater Use*
NC
NC
NC
Non -Residential Worker
Soil
NC
NC
NC
Groundwater Use*
NC
NC
NC
Construction Worker
Soil
NC
NC
NC
Recreator/Trespasser
Soil
NC
NC
NC
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
Carcinogenic
Risk
Hazard Index
Riskexceeded?
Resident
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
2.9E-07
9.6E-02
NO
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
NC
NC
NC
Soil Gas to Indoor Air
2.2E-08
7.6E-03
NO
Indoor Air
NC
NC
NC
Risk Calculator 14: Site Wide GW, CCP/Soil, Ext Soil Gas
When comparing the maximum concentrations of COCs in site -wide groundwater,
CCP/soil, and exterior soil gas, direct exposure to CCP/soil and groundwater for all
scenarios exceeds either one or both the acceptable CR or HI values, except for non-
residential worker direct soil exposures, which don't exceed acceptable values for CR nor
HI.
It is important to note that although this risk analysis uses the maximum concentrations of
site contaminants, that the engineering controls put in place by the Town during the
implementation of the IRMs largely prevent exposure to the areas of contamination for
users of the Brownfields Property. The final remedy is necessary to minimize exposure to
the extent possible for users of the Brownfields Property.
Regarding VI risk, the HI for residential exposures based on exterior soil gas sample
results exceeds an HI of 1, but the HIS for non-residential exposure pathways is 0.094 for
33
Chapel Hill Police Property/23022-19-068/14Jun2024

the soil gas to indoor air value. Based on this HI, vapor intrusion mitigation would not be
recommended nor required for non-residential uses at the Brownfields Property.
Risk for Individual Pathways
Version Date: February 2024
Basis: November 2023 EPA RSL Table
Site ID: 23022-019-068
Exposure Unit ID: Site Wide: Max Cone: GW, CCP/soil, Ext Soil Gas
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Risk exceeded?
Resident
Soil
1.6E-04
8.3E+00
YES
Groundwater Use*
3.6E-03
8.3E+01
YES
Non -Residential Worker
Soil
3.3E-05
5.7E-01
NO
Groundwater Use*
6.3E-04
I 1.2E+01
YES
Construction Worker
Soil
7.7E-06
1.1E+01
YES
Recreator/Trespasser
Soil
8.9E-05
4.6E+00
YES
Surface Water*
NC
NC
NC
dF—VAPOR
INTRUSION CALCULATORS
Receptor
Pathway
CarcinogenicRisk
Hazard Index
Risk exceeded?
Resident
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
2.1E-05
1.2E+00
YES
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
0.0E+00
0.0E+00
NO
Soil Gas to Indoor Air
1.5E-06
9.4E-02
NO
Indoor Air
NC
NC
NC
Indoor Air
Based on the lack of exceedances of VOC constituents in the sub -slab vapor sampling
conducted at the existing police station building against non-residential VISLs paired
with the knowledge that this building will be demolished in the future, and either not
replaced with an enclosed building or one that would be solely for non-residential uses at
this time, indoor air sampling was not conducted other than the radon testing discussed
below.
Radon Testing
Radon testing was conducted in 2019 in the existing police station building to evaluate
for the presence at the surface of the natural decay of radium in subsurface materials.
Radon was either not detected or was detected only at the detection limit of 0.4 pCi/L,
indicating that the risk from radon is negligible.
Methane Gas Screening
Out of an abundance of caution, methane gas screening was conducted within the
footprint of the proposed redevelopment activities in accordance with the Brownfields
Program methane protocol. There was only one detection of methane, which was in
exterior soil gas monitoring point SG-3, centrally located in the parking lot south of the
existing police station building. Methane detections at SG-3 were 0.1% and 0.2% by
volume, which were within the accuracy range of the monitoring instrument. Methane
was not detected in any other sample; static pressure measured at these points was below
the accuracy limits of the field instrumentation and is therefore considered negligible.
34
Chapel Hill Police Property/23022-19-068/14Jun2024

These methane screening results suggest the site is not a methane risk and would meet the
threshold criteria for methane site development for both residential or non-residential
uses.
Toxici . and Exposure Pathway Review
The toxicity of COCs is taken into account in the risk assessment process by entering
site -specific chemical data into the DEQ Risk Calculator. The toxicological data is
derived directly from the U.S. EPA RSL database as noted above. The results quantify
the environmental risk in terms of carcinogenic risk and noncancer hazard index. These
values are compared to acceptable regulatory risk values, which are a maximum of 1 E-04
for CR and a threshold value of 1.0 for HI. If site COCs cause exceedances of these risk
values then appropriate actions are to be taken to make the site safe for its reuse. These
calculations have been performed and are discussed above in the Risk Calculations
section of this document.
The next step is to then evaluate the various exposure pathways to known contamination
and identify if they are complete. A completed exposure pathway is the way in which
human exposure to COCs can occur. An incomplete exposure pathway means that human
exposure is not possible because one of the following is true: 1) COCs are not present at
concentrations that are deemed harmful; 2) receptors are not present, or 3) COCs are not
accessible to receptors.
Discussion of U.S. EPA Risk Assessment Documents:
1. U.S. EPA, Risk Assessment of Coal Combustion Residuals: Legacy Impoundments and
CCR Management Units, October 2023, Draft. Available at:
hltps://www.regulations.gov/document/EPA-HQ-OLEM-2020-0107-0887
Note: EPA finalized this document in April 2024, and published a red -lined final version
along with the announcement of the publication of the final rule entitled Hazardous and
Solid Waste Management System: Disposal of Coal Combustion Residuals from Electric
Utilities; Legacy CCR Surface Impoundments (Federal Register, Vol. 89, No. 90, May 8,
2024/Rules and Regulations). The red -line, final version of the risk assessment document,
which EPA revised to include additional information and to address public comments, is
available in the Docket Documents tab at this link and directly at Regulations.gov or
athttps://www.regulations.gov/document/EPA-HQ-OLEM-2020-0107-1064. Section and
page references for this document below refer to the red -lined final version.
This document is a report of a comprehensive risk assessment modeling effort to evaluate
the environmental risks from other types of coal ash sites that are not specifically related
to the federal rules that were established in 2015 for management of coal combustion
residuals (CCR) generated at coal-fired electric utilities, known as the CCR Rule. As
U.S. EPA states on page 1-1,
"This rule established minimum national standards under Subtitle D of
RCR,4 for the design, operation, and closure of landfills and surface
35
Chapel Hill Police Property/23022-19-068/14Jun2024

impoundments that accept CCR after the effective date of the rule on
October 19, 2015. "
The purpose of this risk assessment modeling effort is to evaluate the potential for risk
from placement of CCR in legacy impoundments and Coal Combustion Residual
Management Units (CCRMUs) that fell outside the scope of the 2014 Risk Assessment.
EPA notes that they started from the same methodology and data sources as in the 2014
Risk Assessment for selecting appropriate data and characterizing facility environmental
setting, CCR waste properties, contaminant transport, and receptor exposure; however,
EPA notes that they adjusted the methodology as necessary to better reflect an updated
conceptual model for smaller CCRMUs placed for purposes other than disposal and to
incorporate more recent data. EPA also considered the potential for additional, non -
groundwater exposures specific to smaller CCRMUs.
Based on the site characteristics of the Brownfields Property, the onsite coal ash
structural fill seems to resemble most clearly the description of the CCRMU Fill used in
the risk assessment document. The risk evaluation for this model type is presented in
Section 4, CCRMU Fill Groundwater Risk (pg 4-1 through 4-19), and Section 5,
CCRMU Fill Soil Risk (pg 5-1 through 5-8) of this document. However, it's important to
understand that the risk management decisions made on the Brownfields Property are
based on actual site data collected over a decade of time and are not based on estimates of
site parameters that are used in the EPA models.
Section 4, CCRMU Fill Groundwater Risk — EPA's modeling efforts were focused on
whether exposures may result if contaminated groundwater is used as a source of
drinking water by future residents stemming from the placement of CCR in a smaller area
than that of a large facility disposal area or landfill. EPA assumed that a hypothetical site
would be redeveloped in the future for residential use and that as part of that
redevelopment any engineering controls have been disturbed. EPA further assumed that
there will be some type of soil or other cover placed over the CCR so that it is not
exposed to the open air.
This conceptual model does not contemplate a scenario in which protective measures,
other than soil cover, would be required through institutional controls and stewardship
such as an executed Brownfields Agreement, which would be put in place on this
Brownfields Property to mitigate the environmental risk associated with the coal ash.
For their modeling efforts, EPA used what is thought to be the best available data from a
range of site -based, regional, and national datasets based on a combination of government
sources and peer -reviewed journal articles, many of which were used in the 2014 Risk
Assessment. The result of the model run as described in Section 4 indicates that there
could be long-lasting impact to groundwater from arsenic concentrations in CCR within
the range considered for regulation.
In contrast to the EPA modeled results, while we do see arsenic in groundwater at the
Brownfields Property, site -specific data from groundwater samples collected at the
36
Chapel Hill Police Property/23022-19-068/14Jun2024

Brownfields Property indicate that maximum concentrations of arsenic in groundwater
within the CCR fill area itself ranged up to 140 µg/L; however, the most recent arsenic
concentrations collected from wells screened within the CCR fill area are in the range of
22.9 µg/L to 37 µg/L, and that recent concentrations of arsenic in groundwater wells
located downgradient of the CCR are less than the arsenic NC 2L groundwater standard
of 10 µg/L. Furthermore, groundwater concentrations in on -site bedrock wells below the
CCR do not exhibit arsenic concentrations in excess of its NC 2L standard of 10 µg/L
Additionally, the land use restrictions proposed in the Brownfields Agreement, and which
would run with the land once the Brownfields Agreement was fully executed and
recorded, prohibit groundwater use for any purpose.
Section 5, CCRMUFill Soil Risk
EPA conducted modeling to estimate the exposure to radiation that may result from
residing on a home built on or around a CCRMU fill site. The evaluation considered the
potential for exposure to gamma radiation and radon gas from CCR placement within the
soil of a residential site. EPA did not model direct ingestion or inhalation of CCR or
uptake of contaminants to crops and livestock, nor separate leaching to groundwater;
however, EPA states that the contributions from these additional pathways to overall
exposures is expected to be low compared to those that are modeled in the risk
assessment.
With respect to their results in Section 5, EPA concluded the following on page 5-8:
and
"Available data indicate the potential for radon emanation and
associated risk from CCR is not distinguishable from that of background
soils. Therefore, this exposure route was not retained for further
consideration. The remaining modeled risks from gamma radiation for
future residential receptors were modeled with the EPA PRG Calculator
under the assumption that some level of cover separates the CCR and the
receptor. Modeled high -end risks ranged from 4x10-6 at a cover thickness
of 60 cm to Ix10-4 at a cover thickness of 20 cm. "
"The parameter with the greatest influence on risk is the amount of cover
soil separating the CCR and the receptor. This is because the soil serves
as a shield and limits exposure to gamma radiation."
An engineered cap including a minimum of two (2) feet of demonstrably clean fill soil in
addition to an earth retention system is a requirement of this Brownfields Agreement if
the CCR remains in place. Such a thickness of clean fill soil is consistent with the 60 cm
(60 cm is about 24 inches) of soil cover that EPA used in its modeling run that equated to
EPA's modeled risk of 4x10-6 for residential reuse. Such a risk value is within the
acceptable regulatory cancer risk range of up to 1x10-4, and is therefore protective with
respect to gamma radiation. Further, the risk values would be lower for non-residential
scenarios not modeled by EPA, but that are intended for the Brownfields Property.
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As we noted above with respect to radon, the radon testing performed within the police
station on the Brownfields Property did not indicate the presence of radon gas in indoor
air; hence, this exposure pathway is incomplete at the Brownfields Property.
Section 6, Uncertainty and Sensitivity Analyses
In Section 6, EPA discusses the uncertainty and sensitivity analyses for the model runs
that they conducted. With respect to post -closure exposures, EPA further states on pages
6-22 and 6-23:
"The main model and sensitivity analyses identified potential risks
resulting from gamma radiation and radon gas if CCRMUfills are
disturbed ... In the absence of residential receptors, a reasonably
maximally exposed receptor under a future land use scenario might be an
individual who uses the open area for recreation."
Further EPA noted that with respect to gamma radiation in a recreational setting, the
worst case scenario equivalent identified a cancer risk attributed to gamma radiation of
around 3x10-6, which is within the acceptable cancer risk range of 1x10-6 to 1x104. EPA
further notes that this scenario is expected to overestimate risk for multiple reasons.
EPA's final conclusion in Section 6 (page 6-24) states:
"The results of all these analyses reinforce the conclusions from previous
modeling that disposal in historical and inactive landfills and surface
impoundments, as well as placement in CCRMUfills, have the potential to
result in risk to future receptors that warrant regulatory action."
One such regulatory action is the use of the State Brownfields process to identify the site -
specific risks and put in place the institutional controls necessary to render the site safe
for its reuse. As part of that process, the Brownfields statute allows the use of land use
restrictions, including as in the case restrictions against disturbance of soil and CCR at
the site and the design and implementation of an engineered cap and earth retention
system if material is left in place, as part of a site remedy to render incomplete an
otherwise completed exposure pathway, thereby ensuring full protection of public health
and the environment and to enable the long-term stewardship of a brownfields property.
2. Notice, Availability of the Draft IRIS Toxicological Review of Inorganic Arsenic, U.S.
Environmental Protection Agency, Federal Register, October 16, 2023
http:llwww.regulations.gov, Docket ID No. EPA—HQ—ORD-2012-0830
This Notice states:
"This draft assessment is not final as described in EPA's information
quality guidelines, and it does not represent, and should not be construed
to represent Agency policy or views."
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The draft of this document clearly indicates a warning in the footer that one should not
reference this document, i.e.,"DRAFT-DO NOT CITE OR QUOTE". Therefore, we are
not opining on this particular document at this time.
Based on known concentrations at this Brownfields Property and current toxicological
input and risk equations, arsenic is accounted for in the risk calculations and is already
considered a risk driver for environmental risk management decisions at the site. Final
remedy designs will already have mitigation of exposure to the contaminants in the CCP
and impacted soil as a primary objective. Should EPA modify any of the toxicological
parameters associated with arsenic, that would be taken into account in the final remedial
designs for the Brownfields Property through an updated risk calculator.
Land Use Restrictions:
For all the risk exceedances noted above in the risk analyses will be mitigated or
eliminated through the land use restrictions that would be set forth through the
recordation of the Notice of Brownfields Property at the Orange County Register of
Deeds. Such land use restrictions would run with the land in perpetuity.
The land use restrictions (LURs) for this Brownfields Property will include site -specific
LURs related to requirements for a final remedy design and implementation prior to
construction, excavation or utility installation; design and construction of an engineered
cap and slope stabilization of impacted soil/CCP if remaining at the Brownfields
Property. The Notice of Brownfields Property shall also set forth LURs pertaining to land
use limitations, including prohibitions on use of the property for childcare centers, adult
care centers, schools, or residential use; prohibitions on all groundwater use; prohibitions
on soil disturbances without approval; requirements for Environmental Management
Plans, final grade sampling to confirm surface soil quality, demolition, and
redevelopment summary report(s); prohibitions on community gardens, ground -contact
sports, kennels, agriculture; and further requirements for property access; abandonment
of monitoring wells except for certain key sentinel wells to be monitored, addressing
construction damage to wells, deed notification upon transfers of property, separating old
from new contamination, and the annual Land Use Restriction Update that certifies
compliance with land use restrictions; and.
Based on the site -specific data provided to the Brownfield program, the site reuse is
suitable for the site as long as the agreed upon land use restrictions in the BFA are abided
by, and the final remedy for the CCP area is designed, implemented, and maintained so
that the site can be made safe for this proposed reuse.
Issues For Continued Property Management
The design of the final remedy for the site's CCP will need to be reviewed as well as a
final grade sampling workplan and report(s). A vapor intrusion issue has not been
identified at this site and therefore no vapor intrusion mitigation system is planned at this
time for non-residential uses at the Brownfields Property.
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Monitoring wells MW-3A, 4A, and -6A are to be maintained as sentinel wells to
evaluate trends in groundwater downgradient from the structural fill as per a written plan
and schedule prepared to DEQ's prior written satisfaction.
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