25093_North Mangum Street_Decision Memo_20240412

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DECISION MEMORANDUM
DATE: 4/12/2024
FROM: Claire Sorrell TO: BF Assessment File

RE: North Mangum Street Properties II 103, 107, 109 Broadway Street; 601, 603, 605, 607 N Mangum Street; 106, 108 and 110 Hunt Street
Durham, Durham County
Brownfields Project No. 25093-21-032 Based on the following information, it has been determined that the above referenced site, whose intended use is for no uses other than high-density residential, retail,
restaurant, recreation, associated parking, and subject to DEQ’s prior written approval,
other commercial uses, can be made suitable for such uses. Introduction: The Prospective Developer (PD) is Mangum Street Partners, LLC, with its principal
office located at 1805 7th Street, NW, Suite 800, Washington, DC 20001, and its
manager, John D. T. Gerber of the same address. The Brownfields Property is comprised of one 1.58-acre parcel, bordered by Broadway Street to the north, North Mangum Street to the east, Hunt Street to the south, and
commercial property to the west (Durham County Parcel Identification Number (PIN)
0831084988, and REID 233651). At the time of the original Brownfields Property Application to the Brownfields Program on November 4, 2021, the Brownfields Property was comprised of ten parcels with the following Durham County REIDs: 104951, 104952, 104953, 104954, 104955, 104956, 104957, 104958, 104959, 104960. However,
on October 24, 2022, the original parcel references were recombined into Durham
County REID 233651. As of May 2023, there were still two residential structures on the Brownfields Property at 110 Hunt Street and 108 Hunt Street. Currently, in addition to the two residences noted above, the eastern portion of the
Brownfields Property is being used as a storage laydown yard for water and sewer
construction projects. Redevelopment Plans: The Potential Developer plans on building a seven-story, 250-unit multi-family
residential rental community with 10,000 square feet (sf) of retail space and
approximately 260 parking spots. A vapor intrusion mitigation system will be incorporated into the design for this Brownfields Property. The lowest floor of the
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structure will be below grade parking with some residential spaces. A dog run and pet center are planned for this Brownfields Property.

Site History: The Brownfields Property was once ten individual parcels which have since been recombined into one parcel. Previous site uses include auto refueling, radiator service, taxi garage, commercial store and restaurant, residential dwellings, urban farm, and most
recently, as a construction equipment laydown area.
An historical automotive repair shop and a gasoline filling station were identified in the northeastern area of the Brownfields Property (607 and 609 North Mangum Street) from 1937 through at least 1963; however, by 1979, these features are not observed in the
historical record. Some of the past operators of the automotive uses were Longs Service
Station (1930), Whites Service Station (1935), Broadway Taxi Garage (1944), Latta Ess Sales & Service Filling Station (1949), Mangum Street Servicenter (1950s), Mangum Street Esso and Coxs Radiator Service (1963-1969). A Leaking Underground Storage Tank (LUST) was identified at 607 North Mangum Street, which is formerly known as the Ken Martin
Property in the NC DEQ UST regulatory files. The Ken Martin Property (607 North Mangum Street) was placed on the list of leaking
underground storage tanks (LUST list) and Incident Management Database (IMO) for a
release of gasoline in 1988. ATEC Environmental Consultants (ATEC) closed five USTs in 1988 on this part of the Brownfields Property. Groundwater samples were collected from an historic monitoring well on 607 N. Mangum Street in 1989 and 2007, which contained petroleum hydrocarbon constituents and chlorinated compounds. The buildings
associated with this use were removed from the Brownfields Property by 1993 and most
of the remaining land was cleared by 2016. Potential off-site sources of contamination to groundwater include operations with USTs from which releases occurred and that could have impacted the groundwater under
Brownfields Property: 701 North Mangum Street, 120 Broadway Street, 904 North
Roxboro Street, 607 North Mangum Street. Potential Receptors: Potential receptors are future residents, on-site workers, construction workers, visitors,
pets, and recreators/trespassers.
Contaminated Media: DEQ has evaluated data collected from the following media at the subject property: groundwater, soil, exterior soil gas. DEQ relies on the following data to base its
conclusions regarding the subject property and its suitability for its intended reuse. Please
see the Brownfield Agreement’s Exhibit 2 for specific sample locations, dates, and contaminants of concern (COCs). Risk Calculations:
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Risk calculations were performed using the July 2023 DEQ Risk Calculator https://deq.nc.gov/permits-rules/risk-based-remediation/risk-evaluation-resources.
For the purposes of looking at the site spatially, the site was assessed as a whole, using
default assumptions. The risk calculations indicated the following based on available data, including the following media: groundwater, residual soil (based on confirmatory soil data), and
exterior soil gas:

Soil
Soil samples were collected from a depth of two feet below ground surface (ft bgs) to a depth of seventeen feet below ground surface (ft bgs). Arsenic, benzene, hexavalent chromium, heptane, and naphthalene concentrations were detected above their respective Residential Preliminary Soil Remedial Goals (PSRGs) in soil samples that remain at the Brownfields Property. Based on the risk calculator output, the acceptable residential carcinogenic risk (CR) range maximum of 1E-4 was not exceeded for any risk scenario. The threshold noncancer hazard
index (HI) of 1.0 was not exceeded for soil for the residential direct contact soil risk scenario with a HI of 0.83; the risk driver being heptane with a hazard quotient of 0.48. Soil sampling was conducted on June 28 and 29, 2022.
The Phase I Environmental Site Assessment, (Duncklee and Dunham, P.C., August 20, 2019) report identifies two underground storage tanks (USTs) which were removed from the Brownfields Property, 607 N. Mangum Street before the PD took ownership of the Brownfields Property. It was reported that soil from this excavation was aerated and spread
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on the Brownfields Property near the UST excavations. No datapoints from the exported soil were used in the development of the Exhibit 2 or Risk Calculator.
No soil has been exported or imported to the Brownfields Property since the PD has taken ownership of the Brownfields Property.
Groundwater
The depth to groundwater was measured from 6.69 ft bgs to 17.3 ft bgs on June 29, 2022. Sampling occurred on June 14, 1989, August 14, 1989, February 27, 2007, and June 30, 2022; however, only the 2022 groundwater data are available and used on which to base environmental risk calculations. Based on the depths to groundwater recorded on June 28,
2022, the potentiometric groundwater surface elevation indicates that groundwater flows
west across the Brownfields Property. The concentrations of benzene, 1,2-dichloroethane, isopropyl ether, naphthalene, and 2-methylnaphthalene found on the southeastern property line in wells GW-1 and GW-2
exceed their respective NC 2L standard; however groundwater use will be prohibited by
the brownfields agreement for this property. Based on the risk calculator output, the acceptable noncancer hazard index (HI) of 1.0 is exceeded for residential and non-residential worker scenarios with respect to exposure to
groundwater of 78 and 19, respectively. The risk driver is naphthalene with hazard
quotients of 64 and 15, respectively. Based on the risk calculator output, the acceptable carcinogenic risk (CR) value of 1.0E-4 is exceeded for residential and non-residential worker scenarios with respect to exposure
to groundwater, with direct contact groundwater CR of 4.2E-03 and 1.1E-03,
respectively. Additionally, the threshold noncancer hazard index of 1.0 is exceeded for the groundwater to indoor air vapor intrusion pathway for residential and non-residential
worker exposure scenarios, with vapor intrusion hazard indexes of 11 and 2.7,
respectively. The risk drivers for residential and non-residential worker groundwater to indoor air vapor intrusion HIs are hexane (HI of 5.2 and 1.2, respectively), naphthalene (HI of 2.2 and 0.53, respectively), and benzene (HI of 2.1 and 0.49, respectively).
Based on the risk calculator output, the acceptable carcinogenic risk value of 1.0E-04 is
exceeded for the residential groundwater to indoor air pathway, with a value of 3.4E-04. The acceptable risk range for the non-residential worker groundwater to indoor air vapor pathway threshold was not exceeded for carcinogenic risk.

Direct exposure to groundwater is prohibited by the land use restrictions in the BFA; further, municipal water, and not groundwater, is the water source for the redevelopment. There is no ongoing monitoring of groundwater by another DEQ program. It is not expected that the contamination will cause off-site issues.
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Surface Water
Surface water is not located on nor borders the Brownfields Property.
Exterior Soil Gas
Exterior soil gas samples (SG-1 to SG-8) were collected on June 29, 2022, in the unpaved gravel parking lot and vegetated portions of the Brownfields Property, at depths of approximately 6 ft bgs (Figure 1).
For residential exposure scenarios, the risk calculator output shows that the threshold
noncancer HI of 1.0 is met, with a HI of 1.0, with trichloroethylene (HI of 0.4) and naphthalene (HI of 0.28) driving the risk. The source of these contaminants may be related to the historical, on-site automobile service stations.
For non-residential worker exposure scenarios, there is not an exceedance of the
threshold noncancer HI of 1.0, as the threshold noncancer HI is calculated to be 0.081.
For residential and non-residential worker exposure scenarios, the risk calculator output shows that there is not an exceedance of the acceptable CR maximum of 1E-04.

TCE was detected in one sample, SG-2, at a concentration of 28 µg/m3 on July 5, 2022. Based on the planned residential use for the Brownfields Property, the detection of TCE in exterior soil gas, and the HI of 1.0, a vapor intrusion mitigation system (VIMS) that is active, or can be made active, is required for this Brownfields Property. The PD has
agreed to implement a VIMS at this Brownfields Property and a Vapor Intrusion
Mitigation Plan will be forthcoming.
Sub-Slab Vapor Sub-slab vapor samples were not collected. There are two residential structures on the
Brownfields Property, both of which are planned to be demolished as part of the
redevelopment process. A large portion of the Brownfields Property which is planned to be developed is primarily surface grade parking. Indoor Air
Indoor air samples were not collected. There are two residential structures on the
Brownfields Property, both of which are planned to be demolished as part of the redevelopment process. A large portion of the Brownfields Property which is planned to be developed is primarily surface grade parking.
Land Use Restrictions:
LURs will include the standard land use restrictions including approved land uses, land use definitions, specific prohibitions, requirement for an EMP, redevelopment summary reports, demolition requirements, prohibitions on groundwater use, soil disturbance, and known contaminants, access, notification, vapor intrusion, and land use restriction update LURs.

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Based on the site-specific data provided to the Brownfield Redevelopment Section, 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 Branch Issues:
The Environmental Management Plan has yet to be submitted. Redevelopment activities have yet to begin. An approvable VIMS installation work plan is required before installation, and approvable pre-occupancy and post-occupancy work plans and sampling reports are required.
VIMS post-occupancy testing is to be conducted after redevelopment activities conclude. Figure 1. Sample Locations on the Brownfields Property
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