22082_Washington MGP_DM_20211222

DECISION MEMORANDUM
DATE: August 30, 2021/Revised December 22, 2021
FROM: Hayley Irick/Sharon Eckard
TO: BF Assessment File
RE: Washington MGP
211 N Bridge Street
401 W 3rd Street
Washington, Beaufort County
Brownfields Project No. 22082-18-007
Based on the following information, it has been determined that the above referenced
site, whose intended use is for no uses other than institutional, office, public facility,
parking, high density residential, and subject to DEQ's prior written approval, other
commercial uses, can be made suitable for such uses.
Introduction:
The Prospective Developer (PD) is the City of Washington, a local municipality with
offices headquartered at 102 E 2nd Street Washington, NC 27889. Jonathan Russell is the
City Manager. The City of Washington is also led by the Mayor's office and a five -
member City Council. The Planning Administrator, Glen Moore, is the PD's
representative for this project.
The Brownfields Property is comprised of two parcels, 211 N Bridge Street, Tax ID:
5675-79-1209 and 401 W 3rd Street, Tax ID: 5675-79-3303, totaling 3.57 acres. The
Brownfields Property has been vacant as of 2006 with only a few remnant building slabs
and foundations present.
The Brownfields Property is listed with the Manufactured Gas Plant (MGP) Program of
the Federal Remediation Branch of DEQ's Superfand Section under identification
number NCD986197275.
Redevelopment Plans:
The City of Washington plans to redevelop the Brownfields Property as a public safety
and emergency services complex to possibly include a police office, fire station, and/or
other municipal buildings. At this time, no firm redevelopment plans have been
submitted.
Site History:
The Brownfields Property was initially developed as multiple single-family residential
properties prior to 1857 at which time the MGP was initially developed on the
northeastern half -acre of the site. The MGP operation footprint expanded from the years
1857 to around 1958. The MGP operated under the following known owners:
Washington MGP/22082-18-007/Rev22Dec2021

Washington Gas Works, Washington Water and Light Company, Washington Lighting
Company, Washington Gas Company, Carolina Gas and Electric Company, and
Tidewater Power Company. In 1959, natural gas service began in Washington via the
Tidewater Natural Gas Company. Subsequently, by 1962, the majority of the above
ground MGP site structures were no longer present.
By 1948, a bottling plant and private auto repair shop were developed on the
northwestern portion of the Brownfields Property.
In association with HRT, Inc., also known as Tankard Distributing Company, four
underground storage tanks (USTs), previously installed in 1979, were removed from the
northwestern portion of the Brownfields Property in July 1998. These included three
4,000-gallon gasoline USTs and one 8,000-gallon diesel UST. This resulted in the
assigning of Leaking Underground Storage Tanks (LUST) Incident Number 18515 to this
site; this incident was closed out in March 1999.
Pursuant to the November 13, 2001 Administrative Order on Consent (AOC), Docket
Number 00-SF-192, the owner of the Brownfields Property at that time, Carolina Power
& Light Company (later PSNC and currently Duke Energy) committed to assessing and
addressing the contamination at the Brownfields Property associated with the MGP site
through NCDENR's (the predecessor agency of DEQ) Superfund Section, Federal
Remediation Branch. The site was assigned EPA Identification Number NCD986197275.
Assessment commenced at the Brownfields Property with respect to UST closures in
1998. During the 1998 UST removal, 250 cubic yards of observably contaminated soil
was excavated and transported to permitted land farms. The excavation occurred in the
northwest portion of the Brownfields Property at approximately 2 feet below the UST
basin and 2.5 feet horizontally out from the UST basin.
Further assessment and remedial activities commenced at the Brownfields Property in
association with the AOC in 2005. From April to June of 2007, the MGP portion of the
Brownfields Property underwent remedial action in accordance with an approved
Remedial Action Plan (Silar Services, March 2007). Remedial actions included the
removal and breakup of concrete slabs overlying the soil excavation area, stockpiling of
debris (concrete slab, brick, block, and mortar) to be processed for use as backfill,
contaminated soil excavation including the removal of subsurface MGP features (tar
structure, gas holder, piping, and drip pots), and absorption and disposal of free product
light non -aqueous phase liquid (LNAPL), from the surface of encountered groundwater,
and placement of oxygen -releasing compounds in the subsurface. Soil excavation
occurred to the water table, at a depth of approximately six (6) feet below ground surface
(bgs).
In total, approximately 7,907 tons of contaminated soil and MGP related non -hazardous
waste material were exported and disposed of offsite. The MGP-related excavation area
was excavated and backfilled to depths ranging to approximately six feet below ground
surface (bgs), which did not extend below the groundwater table. The excavated areas
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were backfilled with processed debris from the onsite stockpile and native sand and clay
from a local sandpit. Prior to use, both on -site and off -site fill sources were sampled and
analyzed for petroleum hydrocarbon compounds including benzene, toluene,
ethylbenzene, xylenes, and polynuclear aromatic hydrocarbons (PAHs), and metals
according to the procedures described in the approved Remedial Action Plan.
In January 2008, a revised report entitled Remedial Action Final Report (Silar Services,
Inc., January 2008) was completed and submitted to NCDENR. On June 10, 2010, as a
result of the Federal Remediation Branch involvement and remaining contaminants at the
site, a site -specific Declaration of Perpetual Land Use Restrictions was recorded at the
Beaufort County Register of Deeds (Book 1721, Page 615-619); these were revised on
March 17, 2011 (Book 1747, Page 344-350).
Soil samples were collected from the remainder of the Brownfields Property in 2019 as
part of the assessment required for the Brownfields Agreement. These areas were not
associated with the former MGP. The soil samples were analyzed for volatile organic
compounds (VOCs), semi -volatile organic compounds (SVOCs), and metals.
Following soil and MGP source removal in 2007, oxygen -releasing compounds (ORCs)
were placed in the saturated zone at the base of the excavation where significant MGP
residuals remained to promote destruction of the contaminants and bioremediation.
Groundwater has been monitored in accordance with the Groundwater Monitoring Plan,
Former Washington Manufactured Gas Plant Site (Silar Services, Inc., September 2007)
on a semi-annual basis for BTEX, PAHs, and cyanide since 2007. Historically there were
multiple wells at the site, but most have been abandoned as they were removed during
excavation activities or were no longer needed. The following wells are undergoing
continued semi-annual monitoring with the NCDEQ Superfund Section MGP Program:
MW-3SR, MW-5S, MW-6S, MW-9S, and MW-10S.
Potential Receptors:
Potential onsite receptors are: construction workers, on -site workers, visitors, and
trespassers. Potential offsite receptors are: single family residences adjacent in all
directions, and the First United Methodist Church, including its day care facility, adjacent
to the east. A Brownfields Receptor Survey was completed in June 2020.
Contaminated Media:
DEQ has evaluated data collected from the following media at the subject property: soil,
groundwater, and soil gas. DEQ relies on the following data to base its conclusions
regarding the subject property and its suitability for its intended reuse. Refer to the
Exhibit 2 to the Brownfields Agreement for specific sample data that exceeds regulatory
standards or screening levels.
Washington MGP/22082-18-007/Rev22Dec2021

Soil
MGP waste impacted soil - Side wall soil samples from the MGP excavation were
collected every 50 feet along the edge of the excavation pit and were analyzed for
benzene, ethylbenzene, toluene, and xylenes (BTEX), and PAHs. Low level PAHs and
benzene were detected above Residential Preliminary Soil Remedial Goals (PSRGs)
along the perimeter of the excavation.
Based on multiple reports and the results of excavation work performed at the site,
residual MGP-related contaminants may remain in site soil, primarily under the
groundwater table.
Low level arsenic, chromium (VI), and PAHs were detected above their respective
Residential PSRGs.
Groundwater
Historically, there were multiple wells at the site indicating elevated concentrations of
benzene, naphthalene, and other constituents of MGP waste over NCAC 2L groundwater
standards. BTEX and PAH concentrations have been decreasing over time with some
samples now below NCAC 2L groundwater standards.
Groundwater samples were collected from newly installed temporary wells across the
Brownfields Property in 2019 as part of the Brownfields Assessment and analyzed for
VOCs, SVOCs, and metals. No compounds were detected above NCAC 2L groundwater
standards.
Surface Water
Surface water is not located on the Brownfields Property.
Soil Gas
Exterior soil gas samples were collected in March 2021 in the vicinity of the routinely
monitored groundwater wells associated with the former MGP and in the footprint of the
proposed municipal building. Benzene at a maximum of 107 µg/m3, 1,2-dichloroethane
at 4.09 µg/m3, ethylbenzene at a maximum of 67.6 µg/m3, and n-hexane at 5,390
µg/m3were all detected above their respective Residential Vapor Intrusion Screening
Levels (VISLs) in one sample (and its duplicate), SG-1. Sample SG-1 is located in the
northeastern corner of the Brownfields Property, associated with the former MGP and not
in the footprint of the proposed municipal building. Risk calculations are discussed
further below.
Sub -Slab Vapor
No structures except for remnant concrete slabs are present on the Brownfields Property.
Indoor Air
No structures are present on the Brownfields Property.
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Risk Calculations
Risk calculations were performed using the January 2021 DEQ Risk Calculator
hllps:Hdeg.nc.gov/permits-rules/risk-based-remediation/risk-evaluation-resources. The
site risk was calculated looking at the site as a whole.
The risk calculations indicated the following based on available data, including the
following media: groundwater, residual soil, exterior soil gas, and soil gas samples
collected from beneath deteriorated concrete slabs.
Risk for Individual Pathways
Version Date: January 2021
Basis: November 2020 EPA RSL Table
Site ID: 22082-18-007
Exposure Unit ID: Sitewide
DIRECT CONTACT SOIL AND WATER CALCULATORS
Receptor
Pathway
Carciinnogenic
sk
Hazard Index
Ri sk exceeded?
Resident
Soil
8.1E-04
6.0E+00
YES
Groundwater Use*
9.0E-03
1.6E+02
YES
Non -Residential Worker
Soil
7.5E-05
8.4E-01
NO
Groundwater Use*
2.4E-03
3.8E+01
YES
Construction Worker
Soil
1.1E-05
1.0E+01
YES
Recreator/Trespasser
Soil
4.1E-04
2.2E+00
YES
Surface Water*
NC
NC
NC
VAPOR INTRUSION CALCULATORS
Receptor
Pathway
CarcinogenicRisk
Hazard Index
Risk exceeded?
Resident
Groundwater to Indoor Air
5.3E-04
8.3E+00
YES
Soil Gas to Indoor Air
1.2E-05
6.1E-01
NO
Indoor Air
NC
NC
NC
Non -Residential Worker
Groundwater to Indoor Air
1.2E-04
2.0E+00
YES
Soil Gas to Indoor Air
9.2E-07
4.8E-02
NO
Indoor Air
NC
NC
NC
The risk calculator output indicates that remaining soil at the Brownfields Property does
exceed an acceptable carcinogenic environmental risk range and the noncancer hazard
index of 1 for residential, recreator/trespasser, and construction worker exposure
scenarios, but not for a non-residential worker.
Groundwater at the site does exceed an acceptable carcinogenic risk and the noncancer
risk threshold hazard index value of 1 for both direct residential and nonresidential
exposure scenarios. Groundwater use is restricted via the existing DPLURs filed as a
result of the Federal Remediation Branch activities at the Brownfields Property; the
Brownfields Agreement will also reflect a prohibition on groundwater use. It is possible
however, that due to the occurrence of groundwater at about six feet bgs, construction
workers may encounter contaminated groundwater. Precautions for this during the
construction phase will need to be accounted for in the Environmental Management Plan
(EMP), which will be required in the Brownfields Agreement.
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Although groundwater to indoor air vapor intrusion calculations indicate an exceedance
of both acceptable carcinogenic risk and the noncancer risk threshold of 1 for residential
exposures and nonresidential exposures, the soil gas to indoor air calculations suggest
that based on exterior soil gas samples or samples collected below deteriorating concrete
slabs that acceptable cancer risk and noncancer thresholds are not exceeded for either
residential nor nonresidential exposure scenarios.
However, although the soil gas to indoor air calculations appear to reflect that vapor
intrusion would not be a concern for residential or non-residential scenarios, the data
were collected from exterior soil gas or from below deteriorated slabs such that these data
do not reflect what may occur once a building is constructed on top of the land surface.
Particularly in the event that residential use is considered in the future, DEQ should be
consulted and more assessment may be required with vapor intrusion mitigation measures
potentially warranted.
Required Land Use Restrictions:
The Agreement will include the standard land use restrictions regarding land uses,
requirement of an EMP with redevelopment summary report, prohibition on groundwater
use, restrictions on soil, contingencies for vapor intrusion, site access, notification, yearly
land use restriction update, and specific prohibitions on child and adult care, schools, and
residential use unless prior written approval from DEQ is obtained, requirement for the
current owner to ensure safety of the Brownfields Property should the current responsible
parry fail to implement the Remedial Action Plan,
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.
Property Management Unit:
Any proposed residential use should be re-evaluated with respect to vapor intrusion.
Updates or an amendment to the DEQ-approved EMP will be required for future phases
of redevelopment. Possible replacement of monitoring wells required by the MGP
Program during site construction.
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Washington MGP/22082-18-007/Rev22Dec2021