22008_CLT Aircraft_Decision Memorandum_20190308

DECISION MEMORANDUM DATE: March 8, 2019 FROM: Carolyn Minnich

TO: BF Assessment File RE: Charlotte Aircraft 7705 East W.T. Harris Blvd
Charlotte, Mecklenburg County
BF Project No. 22008-18-060 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, office, recreation, open space,
parking, and with prior written DEQ approval, other commercial uses, can be made suitable for such
uses. Introduction: The Brownfields Property is located at 7705 East W.T. Harris Blvd and comprises three (3) parcels
totaling approximately 26.949 acres (Mecklenburg County Tax Parcel Identification Numbers
10915106, 10915107, and 10915110). The initial application dated January 2018 included one parcel PIN 10915107 and it is 7.92 acres which included the source area of historical contamination. In November 2018, a revised application added two new parcels; Parcel 10915106 is 13.67 acres and Parcel 10915110 is 6.46 acres. The project also shifted into the Redevelop Now Program with
Brownfields.
Redevelopment Plans: The Brownfields Property currently consists of warehouse, workshops, storage buildings, storage sheds, outdoor storage racks, and offices. The existing structures will be demolished and removed. Redevelopment plans include the construction of 12 buildings for high density residential use along with
associated parking, green space, and recreation areas. Site History: Since 1952, the Brownfields Property has been occupied and used by Charlotte Aircraft Corporation
(CAC) as an aircraft part refurbishing facility. Prior to 1952, the Brownfields Property was called Delta
Airbase but was referred to as, and used by, United Aero Service as a flight training school and aircraft maintenance facility. Chlorinated solvents, including trichloroethylene (TCE), were used for parts washing and stripping to
support facility operations. Tetrachloroethylene (PCE) was not explicitly identified in historical reports
as a chemical used in parts cleaning operations, but detections of PCE in the groundwater suggest PCE was likely used. CAC was assigned Groundwater Incident No. 19258 by the Division of Water Quality. In 2007, DEQ
had a reorganization and the incident was moved to the Inactive Hazardous Site Branch (IHSB) and
assigned NONCD0001478 under the name Charlotte Aircraft #3. Potential Receptors: Potential receptors are: construction workers, on-site workers, future residences (adults and youth),
visitors, and trespassers.

Contaminated Media:
DEQ has evaluated data collected from the following media at the subject property: soil, groundwater, and soil vapor. DEQ relies on the following data to base its conclusions regarding the subject property and its suitability for its intended reuse.
Soil
In December 1994, a UST release was reported during the removal of two (2) Underground Storage Tanks (USTs) resulting in the discovery of soil and groundwater contamination. The USTs were located east of building 5 (currently used for office and storage). The incident was assigned UST Incident No.
19164. As part of closure activities, a Limited Site Assessment (LSA) Report was completed. The site
was closed in 1998 by the DEQ UST Section. According to the Environmental Reports, the LSA report listed low concentrations of chlorinated solvents in several monitoring wells. A Comprehensive Site Assessment (CSA) was performed to assess the nature and extent of the chlorinated solvent groundwater contamination and identify a source of trichloroethylene (TCE) and tetrachloroethylene (PCE).

In 2000, CAC retained Duke Engineering and Services to determine the nature and extent of contamination at the CAC Property. During the assessment process, impacted soils indicating a solvent release were detected in the vicinity of the storage building. The primary source of release of TCE is suspected to be an underground concrete sump discovered during a Geoprobe soil sampling assessment.
The sump contained TCE free product and was associated with a former parts washing/stripping
operating conducted at the facility (1950s-1960s). The source of the detected PCE was not identified. In May 2000, Soil Solutions, Inc. (SSI) was retained to thermally treat the contaminated soils on-site. Thermal desorption is an ex-situ process that uses either direct or indirect heat exchange to vaporize
organic contaminates from soil or sludge. SSI mobilized a soil treatment unit to the CAC Property. SSI
thermally treated approximately 140 tons of TCE contaminated soil removed from the source area excavation. After treatment, the soils were transported to SSI soil treatment facility in Winston-Salem for final disposal. Residual TCE concentrations were detected in sidewall and bottom samples collected at the extents of the excavation area. The area was backfilled with clean soil and the final-grade surface
was seeded and mulched.
Phase II ESA activities were conducted in October 2018 which included seventeen soil borings. Soil Boring SB-15 has the most detections and two exceedances for residential PSRGs. This soil boring is near the former excavation area. The following concentrations of trichloroethene (TCE) and
naphthalene were detected above residential PSRGs: a TCE concentrations of 1.79 mg/kg was detected
and the standard is 0.87 mg/kg, and Naphthalene was detected at a concentration of 4.59 mg/kg and the standard is 4.1 mg.kg. Arsenic and hexavalent chromium were detected in several soil boring across the Brownfields Property.
Arsenic concentrations ranged from 1.5 to 4.3 mg/kg, exceeding the residential PSRG of 0.68 mg/kg.
Hexavalent Chromium concentrations ranged from 0.5 to 2.6 mg/kg, exceeding the residential PSRG of 0.31 mg/kg. The detections are across the site and are considered to be naturally occurring and background concentrations.
There were several other compounds detected but not above Residential PSRGs. To evaluate the worst
case scenario, the highest concentration for all detected compounds were used in the risk calculator.o. The results are listed below.
Groundwater
A network for twenty-four (24) monitoring wells and one (1) recovery well have been installed on the
CAC Property. A Corrective Action Plan (CAP) was submitted and recommended Natural Attenuation with semi-annual groundwater sampling of the following monitoring wells:MW5, MW7, MW8, MW9, MW10, MW12, MW16, MW17, MW18, MW21, MW22, DMW2, and RW1. The CAP was approved by DEQ and semi-annual sampling was conducted in 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,
2009, 2010, 2011, 2012, 2014, 2016. In 2005, a portion of the monitoring wells were destroyed during
redevelopment on athletic fields off the CAC Property. The following monitoring wells were replaced (MW16/MW16A, MW17/MW17A, MW18/MW18A. MW20/MW20A). In February 2016, CAC sent a letter to IHSB stating they were having financial hardship and would no
longer be able to fund and conduct additional cleanup activities, assessment work, or semi-annual
groundwater sampling. In April 2016, IHSB contracted with S&ME to conduct groundwater assessment activities including well installation and sampling. In March 2017, IHSB adjusted the site ranking to low priority and CAC Property remains on the Inactive Hazardous Sites and Pollutant -Only Sites Inventory.

Phase II ESA activities were conducted in October 2018. Recent groundwater analytical results indicate the presence of VOCs above 2L standards in groundwater near the former sump (MW-12 and DMW-2) and downgradient of this historical source area (MW-8, MW-9, MW-10, and DMW-4). Specifically, groundwater exceedances during the most recent investigation included:
• PCE exceeded its 2L Standard of 0.7 micrograms per liter (µg/L) in monitoring wells MW-
8, MW-9, MW-10, MW-12, and DMW-4 with the highest concentration of 62.9 µg/L in
DMW-4;

• TCE exceeded its 2L Standard of 3 µg/L in MW-9, MW-12, DMW-2, and DMW-4
with the highest concentration of 1,880 µg/L in MW-12;

• At MW-12 additional 2L Standard exceedances included 1,2-dichlorobenzene, 1,1-
dichloroethane, cis-1,2-dichloroethene, naphthalene, 1,2,4-trimethylbenzene, 1,2-
dichlorobenzene, 1-methylnaphthalene, and 2-methylnaphthalene;

• At DMW-2 additional 2L Standard exceedances included chlorobenzene, 1,2-
dichlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane, 1,1-dichloroethene, cis-1,2-
dichloroethene, naphthalene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene.

Overall, groundwater impacts have decreased or shown natural attention with degradation of parent
VOC compounds to their daughter products.

Surface Water
Surface water is not located on the site.
Soil Vapor In October 2018, six (6) soil gas samples were installed on the northern portion of the Brownfields
Property within the anticipated footprint of the future site buildings. A few of the detected
concentrations were above the DWM Residential Soil Gas Screening Levels (SGSLs), but most were below the SGSLs. Based on the detected concentrations, Buildings 1 and 2 will required a vapor mitigation system. Building 3 will require a sentry well or vapor mitigation system. Please refer to the Groundwater, Soil, and Soil Gas Assessment Report dated November 13, 2018 prepared by Geosyntec
for more details on this future sampling event. The summary table below shows risk calculator results.
Sub-Slab Vapor In February 2010, IHSB Division requested a vapor intrusion study for the CAC Property. The objective was to evaluate the potential for vapor intrusion into occupied building on the CAC Property
and two adjacent residential properties with 100 ft of underlying groundwater plume. Mid-Atlantic conducted sub-slab soil gas and radon testing in the following three building on the CAC Property: the Guard House, the Sales Office, and the Main Office. Indoor air samples were collected in crawl spaces at nearby residential structures. Upon review of the data, calculating attenuation factors, and site conditions, no vapor intrusion pathways were considered to be complete, and the risk from exposure due
to vapor intrusion on the CAC Property is considered to be negligible with regard to the current uses and intended reuses. In October 2018, no sub-slab samples were collected. The existing structures are going to be demolished in preparation for the new construction. See Soil Vapor section for more information.

Indoor Air No indoor air samples were collected. The existing structures are going to be demolished in preparation for the new construction. See Soil Vapor section for more information.Risk Calculations
Indoor air structure risk evaluation for buildings 1, 2, and 3.
Structure Calculated
Carcinogen Risk
Calculated
Non-Carcinogenic Risk
Building 1 1.4 E-05 5.8 E-01
Building 2 1.3 E-05 1.3
Building 3 3.5 E-06 3.0E-01

Required Land Use Restrictions: 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.

• No groundwater usage
• No soil disturbance without DEQ approval
• Soil may not be removed from or soil imported without DEQ approval
• Vapor mitigation in buildings that do not pass DEQ approval for assessment, based on upon current data, two of the new structures on the northern portion of the BF property will require VIMS and proactively on a third building.
• Proper demolition for existing structures
• EMP required prior to redevelopment
• Annual development summary report required
• DEQ shall not be denied access
• Deed conveyance of Notice
• No use of known contaminated on the BF Property
• Abandonment of on-site monitoring wells
• Maintenance of future monitoring wells as needed to remain on site
• LURU submittal