HAZARD RANKING SYSTEM (HRS) DOCUMENTATION RECORD COVER SHEET
Name of Site:
East Basin Road Groundwater
EPA ID No.:
DEN000304044
Date Prepared:
September 2022
Contact Person:
Lorie Baker
U.S. Environmental Protection Agency
Philadelphia, Pennsylvania
(215)814-3355
Baker.Lorie@,epa.gov
Pathways. Components, or Threats Not Scored
The surface water migration pathway, soil exposure and subsurface intrusion pathway, and air migration
pathway were not scored in this Hazard Ranking System (HRS) documentation record as they are not
expected to contribute significantly to the overall Site score as noted below. The subsurface intrusion
component of the soil exposure and subsurface intrusion pathway is of concern to the U.S. Environmental
Protection Agency (EPA) and may be considered during a future evaluation.
Surface Water Migration Pathway: The surface water migration pathway was not scored. The source
being evaluated is a per- and polyfluoroalkyl substances (PFAS) and chlorinated volatile organic compound
(CVOC) groundwater plume with no one identified source(s).
Soil Exposure and Subsurface Intrusion Pathway - Soil Exposure Component: The soil exposure
component of the soil exposure and subsurface intrusion pathway was not scored because the source being
evaluated is a PFAS and CVOC groundwater plume with no one identified source(s).
Soil Exposure and Subsurface Intrusion Pathway - Subsurface Intrusion Component: The subsurface
intrusion component of the soil exposure and subsurface intrusion pathway was not scored. This component
of the soil exposure and subsurface intrusion pathway is a concern at the Site due the presence of CVOCs
in groundwater samples (Section 3.1.1 of this HRS documentation record) and may be considered during
a future evaluation.
Air Migration Pathway: The air migration pathway was not scored because the source being evaluated is
a PFAS and CVOC groundwater plume.
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HAZARD RANKING SYSTEM (HRS) DOCUMENTATION RECORD
Name of Site:
Date Prepared:
EPA ID No.:
EPA Region:
Street Address of Site*
County and State:
East Basin Road Groundwater
September 2022
DEN000304044
3
410 E. Roosevelt Ave.
New Castle, New Castle County, Delaware 19720
General Location in the State: Northeast Delaware
Topographic Map: Wilmington South, DE
Latitude: * 39.673092° North
Longitude: *- 75.597211° West
The reference point for the site latitude and longitude coordinates corresponds to the intersection of School
House Lane and Route 13/N. Dupont Highway in New Castle, Delaware, as shown on Figures 1 and 2 of
this Hazard Ranking System (HRS) documentation record (Refs. 3; 4; 5, p. 2; 92, pp. 1, 2).
* The street address, coordinates, and contaminant locations presented in this HRS documentation record
identify the general area the Site is located. They represent one or more locations EPA considers to be part
of the Site based on the screening information EPA used to evaluate the site for NPL listing. EPA lists
national priorities among the known "releases or threatened releases" of hazardous substances; thus, the
focus is on the release, not precisely delineated boundaries. A Site is defined as where a hazardous substance
has been "deposited, stored, disposed, or placed, or has otherwise come to be located." Generally, HRS
scoring and the subsequent listing of a release merely represent the initial determination that a certain area
may need to be addressed under the Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA). Accordingly, EPA considers that the preliminary description of facility boundaries at the
time of scoring will be refined as more information is developed about where the contamination has come
to be located.
Scores
Ground Water1 Pathway
Surface Water Pathway
Soil Exposure and Subsurface Intrusion Pathway
Air Pathway
HRS SITE SCORE 50 00
100.00
Not Scored
Not Scored
Not Scored
1 "Ground water" and "groundwater" are synonymous; the spelling is different due to "ground water" being codified
as part of the HRS, while "groundwater" is the modern spelling.
1
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WORKSHEET FOR COMPUTING HRS SITE SCORE
East Basin Road Groundwater
1. Ground Water Migration Pathway Score (Sg)
(from Table 3-1, line 13)
2a. Surface Water Overland/Flood Migration Component
(from Table 4-1, line 30)
2b. Ground Water to Surface Water Migration Component
(from Table 4-25, line 28)
2c. Surface Water Migration Pathway Score (Ss)
Enter the larger of lines 2a and 2b as the pathway score.
3. Soil Exposure and Subsurface Intrusion Pathway Score (Ssessi)
(from Table 5-1, line 22)
4. Air Migration Pathway Score (Sa)
(from Table 6-1, line 12)
S
100.00
Not Scored
Not Scored
Not Scored
Not Scored
Not Scored
s!
10,000
5.
Total of Sg2 + Ss2 + Ssessi2 + Sa2
10.000
6. HRS Site Score Divide the value on line 5
by 4 and take the square root
50.00
2
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GROUND WATER MIGRATION PATHWAY SCORESHEET
East Basin Road Groundwater
GROl \l> WATER MIGRATION PATHWAY
Eaclor Categories and Eaclors
MAMMl M
YAH i:
YAH i:
ASSIGNED
Likelihood of Release
1. Observed Release
550
550
2. Potential to Release
2a. Containment
10
Not scored
2b. Net Precipitation
10
Not scored
2c. Depth to Aquifer
5
Not scored
2d. Travel Time
35
Not scored
2e. Potential to Release
[lines 2a(2b+2c+2d)l
500
Not scored
3. Likelihood of Release
550
550
Waste Characteristics
4. Toxicity/Mobility
*
10,000
5. Hazardous Waste Quantity
*
100
6. Waste Characteristics
100
32
Targets
7. Nearest Well
50
50
8. Population
8a. Level I Concentrations
**
256,487
8b. Level II Concentrations
**
NE
8c. Potential Contamination
**
NE
8d. Population (lines 8a+8b+8c)
**
256,487
9. Resources
5
0
10. Wellhead Protection Area
20
20
11. Targets (lines 7+8d+9+10)
**
256,557
12. Aquifer Score (lines 3x6x11 divided by 82,500)
100
100.00
13. Ground Water Migration Pathway Score (SKW)
100
100.00
* Maximum value applies to waste characteristics category.
* * Maximum value not applicable.
NE Not Evaluated
3
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REFERENCES
Reference
Number Description of the Reference
1. U.S. Environmental Protection Agency (EPA). Hazard Ranking System, Title 40 Code of Federal
Regulations (CFR) Part 300, Appendix A (55 Federal Register [FR] 51583, Dec. 14, 1990, as
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1, 2019, with two attachments. Attachment A: FR Vol. 55, No. 241. December 14, 1990. Hazard
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75.563940&pText=New%20Castle.%20Delaware April 11.3 Pages.
4
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5
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27. TestAmerica. 2018. Analytica Report. Job Number: 460-165183-1. Job Description: DE-0363 O
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30. Eurofins 2021. Analytical Report. Job Number: 460-246600-1. Job Description: New Castle Ave
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31. Tetra Tech. 2022. Project Note to East Basin Road Groundwater Site File. Subject: Artesian
Water Company Laboratory Analytical Data (with attachments, Eurofins, and Suburban Testing
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32. Tetra Tech. 2022. Project Note to East Basin Road Groundwater Site File. Subject: New Castle
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33. Environmental Data Services, LTD. 2022. Data Validation Report. August 2017-2021 Sampling.
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34. Tetra Tech. 2021. Electronic Mail Correspondence with Carl Armbruster, Eurofins, Regarding
Reporting Limit and Method Detection Limit. (Lab Quality Manual Definitions). February. 4
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35. Tetra Tech. 2022. Project Note to East Basin Road Groundwater Site File. Subject:
Public Well Elevations. Artesian Public Supply Wells & New Castle County Municipal Public
Well Supply. May 2. 2 Pages.
36. EPA. 2020. National Functional Guidelines for Organic Superfund Methods Data Review.
November. 190 Pages.
37. EPA. 1996. Using Qualified Data to Document an Observed Release and Observed
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38. EPA. 2020. Method 537.1. Determination of Selected Per- and Polyfluorinated Alkyl Substances
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39. Tetra Tech. 2022. Electronic Mail Correspondence with Stephanie Gordan, DNREC, Regarding
Well Permit Applications and/or Completion Reports for New Castle Public Wells (with attached
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40. State of Delaware. 2003. Public Water Supply Source Water Assessment for Artesian Water Co.
(Collins Park). Department of Natural Resources and Environmental Control. December 31. 39
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6
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41. State of Delaware. 2003. Public Water Supply Source Water Assessment for Artesian Water Co.
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December 31. 34 Pages.
42. State of Delaware. 2003. Public Water Supply Source Water Assessment for Artesian Water Co.
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43. State of Delaware. 2003. Public Water Supply Source Water Assessment for City of New Castle
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44. State of Delaware. 2003. Public Water Supply Source Water Assessment for Artesian Water Co.
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45. State of Delaware. 2003. Public Water Supply Source Water Assessment for Artesian Water Co.
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46. DNREC. 2013. Site Inspection of New Castle County Airport. DE-0357. December. 224 Pages.
47. Environmental Alliance, Inc. 2020. Remedial Investigation Report, New Castle County Airport,
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49. AECOM. 2014. Remedial Investigation Report and Feasibility Study. IRP Site 2. Delaware Air
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50. Wood. 2021. Final Groundwater Long-Term Monitoring Program Report, Second Semi-Annual
Event. Environmental Restoration Program. New Castle Air National Guard Base. August 12.
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51. AECOM. 2017. October 2016 Poly- and Perfluoroalkyl Substance Groundwater Sampling
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Contract#: W9133L-14-D0001. May. 526 Pages.
52. Amec Foster Wheeler. 2019. Final Report FY16 Phase 1 Regional Site Inspections for Per and
Poly Fluoroalkyl Substances. Volume I of XII. Delaware Air National Guard Base. Contract #:
W9133L-14D-0002. March. 2,597 Pages.
53. EA. 2022. Final Site Inspection Report, Duncan Readiness Center and Army Aviation Support
Facility. Per- and Polyfluoroalkyl Substances Impacted Sites ARNG Installations, Nationwide.
Contract No. W912DR-19-D-0005. March. 198 Pages.
7
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54. Brightfields, Inc (Brightfields). 2014. Final Brownfield Investigation Report, 600 North Dupont
Highway (DE-1539). September. 316 Pages.
55. Brightfields. 2017. LTS Groundwater Sampling Report - Second Quarter 2017. 600 North
Dupont Highway (DE-1539). June 21. 538 Pages.
56. Brightfields. 2019. Quarterly Groundwater Sampling Report. Jackson Ave. and N. DuPont
Highway Groundwater Plume (DE-1678). February 19. 727 Pages.
57. Brightfields. 2012. Phase II-B Groundwater Investigation. Community Plaza Shopping Center.
April 16. 87 Pages.
58. Brightfields. 2013. Phase II-D Supplemental Groundwater Investigation Report. Community
Plaza Shopping Center. July. 129 Pages.
59. Brightfields. 2015. Remedial Investigation Report. Community Plaza (DE-1567). September.
3,882 Pages.
60. Brightfields. 2021. Long-Term Stewardship Inspection Report, Community Plaza Site, Operable
Unit 2. February. 83 Pages.
61. EPA. 2014. Emerging Contaminants - Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic
Acid (PFOA) Fact Sheet. EPA 505-F-14-001. March. 10 Pages.
62. EPA. 2021. "Multi-Industry Per- and Polyfluoroalkyl Substances (PFAS) Study - 2021
Preliminary Report." EPA-821-R-21-004. September. 81 Pages.
63. EPA. 2021. Addressing PFOA and PFOS in the Environment: Potential Future Regulation
Pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act and
the Resource Conservation and Recovery Act. 40 CFRPart 302 [EPA-HQ-OLEM-2019-0341;
FRL-10019-13-OLEM] RIN 2050-AH09. 6560-50-P. January. 30 Pages.
64. EPA. 2022. Our Current Understanding of the Human Health and Environmental Risks of PFAS.
Accessed April 4, 2022. Available at: https://www.epa.gov/pfas/our-current-understanding-
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65. ATSDR. 2019. Toxicological Profile for Tetrachloroethylene. June. Available at:
https://www.atsdr.cdc.gov/ToxProfiles/tp 18.pdf. 435 Pages.
66. ATSDR. 2019. Toxicological Profile for Trichloroethylene. June. Available at:
https://www.atsdr.cdc.gov/toxprofiles/tp 19.pdf. 511 Pages.
67. ATSDR. 1996. Toxicological Profile for 1,2-Dichloroethene. August. Available at:
https: //www .atsdr. cdc. gov/T oxProfiles/tp 8 7 .pdf. 198 Pages.
68. ATSDR. 2006. Toxicological profile for Vinyl Chloride. July. Available at:
https://www.atsdr.cdc.gov/ToxProfiles/tp20.pdf. 329 Pages.
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69. ATSDR. 2019. Toxicological profile for 1,1-Dichloroethene - April 2022.. Available at:
https://www.atsdr.cdc.gov/ToxProfiles/tp3 9.pdf. 240 Pages.
70. ATSDR. 2022. Toxicological profile for 1,2 - Dichloroethane - Draft for Public Comment.
January. Available at: https://www.atsdr.cdc.gov/toxprofiles/tp38.pdf. 253 Pages.
71. EAWAG Biocatalysis/Biodegradation Database. Tetrachloroethene Pathway Map (Anaerobic).
Accessed January 31, 2017. Available at http://eawag-bbd.ethz.ch/tce2/tce2 map .html 3 Pages.
72. Tetra Tech. 2022. Project Note to East Basin Road Groundwater Site File. Subject:
Car Washes in New Castle. June 6. 2 Pages.
73. BB&E, Inc. 2016. Final Perfluorinated Compounds Preliminary Assessment Site Visit Report.
Delaware Air National Guard Base, New Castle, Delaware. January. 1,513 Pages.
74. AECOM. 2019. IRP Site 4B Site Closure Report, Delaware Air National Guard Base, New
Castle, Delaware. Contract #: W9133L-14-D0001. August. 57 Pages.
75. DNREC. 2022. Delaware Environmental Navigator Facility Search. Accessed June 2. Available
at:
https://den.dnrec.delaware.gov/Search/FacilitvSearch.aspx?results=Y&tvpe=advanced&facname
=Drv+clean+Central&pitvpes=&picount=0&zip=&citv=50800&countv=&house=&senate=&sch
ool=&watershed=&basin=. 3 Pages.
76. Tetra Tech. 2022. Project Note to East Basin Road Groundwater Site File. Subject: Map of Public
Supply Wells in New Castle, Delaware (with attached figure depicting public well locations).
June 21.2 Pages.
77. Artesian Resources. 2021. Letter from Administration Engineer, to Mr. Steve Smailer, P.G.
Water Supply and Coordinating Council, Department of Natural Resources and Environmental
Control. Regarding: Self-Sufficiency Act of 2003 (with attached Report of Consumer Water
Conservation Plan and Certification of Adequate Water Supply). June 23. 68 Pages.
78. EPA. 2022. Safe Drinking Water Information System. Water System Search Results - Chester
Water Authority. Information Accessed: June 2. Available at:
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79. EPA. 2022. Safe Drinking Water Information System. Water System Search Results - Elkton
Water Department. Information Accessed: March 24. Available at:
https://0rdspub.epa.g0v/0rds/sfdw/sfdw/r/sdwis fed reports public/200. 1 Page.
80. EPA. 2022. Safe Drinking Water Information System. Water System Search Results - Artesian
Water Company. Information Accessed: July 26. Available at:
https://0rdspub.epa.g0v/0rds/sfdw/sfdw/r/sdwis fed reports public/200. 1 Page.
9
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Reference
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81. Tetra Tech. 2022. Electronic Mail Correspondence with Mr. Steven Repole, Finance Director,
Town ofElkton, Regarding: Elkton Water System. March 29. 3 Pages.
82. Tetra Tech. 2022. Electronic Mail Correspondence with Supervisor of Water Quality, Artesian
Water Company, Regarding: Artesian Well in New Castle (with attachments and Allocation Well
Limits). April 6. 6 Pages.
83. EPA. 2022. Safe Drinking Water Information System. Water System Search Results - Municipal
Services Commission. Information Accessed: March 15. Available at:
https://0rdspub.epa.g0v/0rds/sfdw/sfdw/r/sdwis fed reports public/200. 1 Page.
84. Tetra Tech. 2022. Electronic Mail Correspondence with Water Utility Manager, Municipal
Services Commission, Regarding: New Castle Public Water System (with attachments and
Annual Pumping Data). June 7. 48 Pages.
85. State of Delaware. Wellhead Protection Program. Undated. 40 Pages.
86. DGS. 2022. Delaware Geologic Information Resource (DGIR) Map Viewer. Information
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application. Accessed June 8. 2 Pages.
87. Municipal Services Commission. 2022. MSC Water System Overview - 2022, High Level
Description of the Municipal Services Commission Water System. 2 Pages.
88. EPA. 2020. Memo Regarding Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid
(PFOA) as a CERCLA Pollutant or Contaminant from Lorie Baker, HRS Coordinator, Region 3
to East Basin Road Groundwater site Hazard Ranking System documentation record. June 20.
4 Pages.
89. EPA. 2022. Technical Fact Sheet: Drinking Water Health Advisories for Four PFAS (PFOA,
PFOS, GenX chemicals, and PFBS). Office of Water. EPA-822F-22-002. June. 7 Pages.
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I Page.
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95. EPA. 1998. Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in
Ground Water. September. 248 Pages.
96. Tetra Tech. 2022. Project Note to East Basin Road Groundwater Site File. Subject: New Castle
Municipal Services Commission Apportioned Population. July 26. 1 Page.
97. EPA. 1989. Preliminary Assessment New Castle County/Greater Wilmington Airport, New
Castle, Delaware. June. 55 Pages.
11
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SS-Site Summary
SITE SUMMARY
The East Basin Road Groundwater Site (the Site) consists of a groundwater plume with no identified source
located in the City of New Castle, New Castle County, Delaware (Refs. 3 and 4). The geographic
coordinates at the Site are 39.673092° north latitude and -75.597211° west longitude, based on the
Intersection of School House Lane and Rte. 13/N Dupont highway (Figure 1; Refs. 3; 4; 92). The site
consists of groundwater contaminated with per- and polyfluoroalkyl substances (PFAS) and chlorinated
volatile organic compounds (CVOCs) as identified by groundwater samples collected from municipal and
monitoring wells that meet the criteria for an observed release, as further discussed in Section 3.1.1 of this
HRS documentation record and shown on Figure 2 provided in Reference 5. The Delaware River is located
approximately 1 mile east-southeast from the eastern edge of the plume. Land use within the plume includes
an airport in the north and west sections and is a prominent land feature within the plume. Other land uses
within the plume include densely populated residential areas in the south, east, and west with mixed
commercial land uses including dry cleaners, manufacturing facilities, and automobile repair shops (Refs.
5, p. 2; 11, pp. 1,2).
The groundwater samples collected from the plume were withdrawn from the Interconnected Columbia and
Potomac Aquifers (Section 3.0.1 and Tables 4 through 23 of the HRS documentation record). Actual
contamination at Level I concentrations of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid
(PFOA), and tetrachloroethylene (PCE) have been documented in nine public supply wells that supply
drinking water to an apportioned population of approximately 25,648 persons; two public wells have
exceeded the maximum contaminant level for PCE and eight public wells have exceeded the noncancer risk
screening concentration for PFOS and/or PFOA (Section 3.3 of this HRS documentation record).
A 2002 report prepared by the Department of Natural Resources and Environmental Control (DNREC) and
Delaware Health and Social Services Division of Public Health identified the presence of volatile organic
compounds (VOCs) in several Artesian Water (Artesian) public supply wells in New Castle, Delaware: (1)
Collins Park Well, (2) Llangollen Well Field, and (3) Airport Industrial Park Wells (Ref. 6, pp. 18, 33-43).
VOCs detected in raw, untreated water samples included: tetrachloroethylene (PCE), trichloroethylene
(TCE), cis-l,2-dichloroethylene (cis-l,2-DCE), 1,1-dichloroethane (1,1-DCA), 1,2-dichloroethane (1.2-
DCA), carbon tetrachloride, 1,1-dichloeoetheylene (1,1-DCE), and 1,1,1-trichloroethane (TCA) (Ref. 6,
pp. 34, 36, 38, 39, 40, 41, and 42). Contaminants present in the Llangollen wells were associated with two
National Priorities List (NPL) Superfund Sites: (1) Delaware Sand and Gravel and (2) Army Creek Landfill,
and two state Superfund Sites: (1) Former Amoco Polymer Plant and (2) the Denton Landfill located within
0.5 miles north and northeast of the Llangollen Wellfield, each with documented groundwater
contamination by VOCs, semivolatile organic compounds (SVOCs), and metals (Ref. 6, pp. 37, 40). The
source of the VOCs in the Collins Park well and the Airport Industrial Park (AIP) wells was not definitively
identified; however, the report indicated nearby former dry cleaners, an industrial park, auto repair facilities,
and the airport as possible sources (Ref. 6, pp. 34 and 40).
In 2011, DNREC conducted a Preliminary Assessment (PA) of the Artesian AIP Wells #1 and #2 to
determine the likely sources of contamination in the wells (Ref. 10, p. 5). The PA provides analytical history
of the two wells from 1984 to 2010 that show AIP Well #1 had its highest detection of PCE in 1999 at a
concentration of 19 micrograms per liter (jj.g/1) and had its highest detection of TCE in 1993 at 9.4 jj.g/1.
AIP Well #2 had its highest detection of PCE in 2009 at 21 jj.g/1 and had its highest detection of TCE in
1984 at 2.7 jj.g/1. Both wells also had detections of 1,1-DCE, 1,1-DCA, cis-l,2-DCE, and 1,1,1-TCA (Ref.
10, pp. 12, 96, and 97). The PA identified numerous possible sources of the CVOCs including the Delaware
Air National Guard (Tenant) Wilmington Airport Site (DANG) (EPA ID: DE0000306286/DE0572824274)
- 1950-Present, which has known PCE and TCE contamination; the New Castle County Airport (NCCA),
which has several tenants that may have used PCE or TCE for cleaning, degreasing, or paint stripping of
aircraft; several landfills; and a number of dry cleaners (Ref. 10, pp. 7, 8, 9, 10, 92-94). Investigations have
12
-------
SS-Site Summary
been conducted at several of the possible sources of VOCs by DNREC or the property owners; detailed
information about these investigations is provided in the Attribution section of this HRS Documentation
record.
In 2013 and 2014, as part of the federal Third Unregulated Contaminant Monitoring Rule (UCMR 3),
drinking water samples were collected from public supply wells in New Castle, Delaware. Concentrations
of PFOS and PFOA exceeded the EPA 2009 provisional health advisory levels (HALs) of 200 nanograms
per liter (ng/1) and 400 ng/1, respectively (Note: June 2022 HAL update indicates 0.02 ng/1 for PFOS and
0.004 ng/1 for PFOA [Ref. 89, p. 4]), in five public supply wells: (1) Artesian Wilmington Manor Well #3,
(2) Jefferson Farms Well #1, (3) the City of New Castle Municipal Services Commission (NCMSC) Basin
Road Well, (4) Schoolhouse Lane Well, and (5) Frenchtown Road Well (Refs. 7, p. 12; 8, pp. 82, 83).
PFOA was detected at a maximum concentration of 940 ng/1 and PFOS was detected at a maximum
concentration of 2,300 ng/1 (Refs. 7, p. 12; 8, pp. 82, 83). In addition to the five public wells that contained
PFOA and or PFOS above EPA's 2009 provisional HAL, there were several other wells owned by either
Artesian or NCMSC that contained concentrations of PFOA and or PFOS investigated as part of the PA
(Ref. 8, pp. 64, 82, 83).
In 2015, DNREC conducted a PA to identify the likely source(s) of PFAS (formerly referred to as
perfluorinated compounds [PFCs]) groundwater contamination of the public supply wells in New Castle,
Delaware (Ref. 8, pp. 1, 2). The PA investigated an approximately 7 square mile area (referred to in the PA
as an area of interest [AOI]) surrounding the five public wells that contained PFOA or PFOS at
concentrations in exceedance of EPA's 2009 provisional HAL (Ref. 8, pp. 8, 18, 29, 31). The PA identified
16 Areas of Potential Concern (AOPC) that may have used, produced, dispensed, or disposed of compounds
products that may contain PFAS (Refs. 7, p. 66; 8 pp. 8-12). The identified areas included several industrial
complexes and carpet facilities near contaminated public supply wells; Harry Wood Landfill; several fire
training areas for local firefighters, the airport, and military; and airplane or helicopter crashes at the airport
as possible sources of PFAS in the groundwater (Refs. 8, pp. 9-12, 32). Extensive investigations have been
conducted at DANG and portions of NCCA that document the presence and release of PFAS and CVOCs
at these locations as presented in the Attribution section.
In 2017, 2018, and 2020, DNREC conducted a Site Inspection (SI) that included the installation and
sampling of monitoring wells at six of the 16 AOPC, as well as at locations throughout the AOI, to
investigate the presence of hazardous substances in groundwater (Ref. 7, pp. 25, 70, 71, 87). As further
documented in Section 3.1.1, analytical results of the groundwater samples collected from the monitoring
wells installed as part of the SI showed the presence of PFOA, PFOS, and VOCs such as TCE, PCE, 1,2-
DCA, and vinyl chloride (Ref. 7, pp. 99, 100, 101, 104, 106, 107, 113, 114, 120, and 121).
In 2021, DNREC conducted an Expanded Site Inspection (ESI) that included the installation and sampling
of monitoring wells in the northeast portion of the AOI, the sampling of select existing monitoring wells,
and the sampling of two Artesian public supply wells and two NCMSC public supply wells (Ref. 9, pp. 26,
28, 29, 121, 124). As further documented in Section 3.1.1, analytical results of the groundwater samples
collected from the monitoring wells as part of the ESI showed the presence of PFOA, PFOS, and VOCs
such as TCE, PCE, 1,2-DCA, cis-l,2-DCE, and vinyl chloride (Ref. 9, pp. 68, 69, 72, 73, 74, 75, 78, 79,
80, 81, 84, 122, and 124).
In 2022, the Agency for Toxicological Substances (ATSDR) published a PFAS Exposure Assessment
Report for New Castle County, Delaware (Ref. 12, p. 1). This Exposure Assessment assessed PFAS levels
in the blood and urine of New Castle area residents. Test results were compared to PFAS levels in a
nationally representative sample. Tap water and indoor dust samples from a subset of households were also
analyzed for PFAS (Ref. 12, p. 6). The report found that the levels of several PFAS in the blood of residents
13
-------
SS-Site Summary
living in the New Castle area were higher than the national average and that the increase may be associated
with drinking contaminated water (Ref. 12, p. 8).
The Site is being evaluated as a groundwater plume site with no identified source. As shown on Figure 3
provided in Reference 5, there are too many known or possible sources for the PFAS and CVOCs in
groundwater to reasonably attribute the groundwater contamination to one or more specific source(s), as
further discussed in the Attribution section of this HRS documentation record (Section 3.1.1 of this HRS
documentation record). A review of the EPA Envirofacts database identified numerous facilities in New
Castle, Delaware listed as plastics or resin manufacturing or recycling facilities (approximately 24), auto
repair facilities (approximately 9), metal coating, fabrication, or smelting facilities (approximately 6),
current dry cleaners (approximately 5), chemical plants or manufacturers (approximately 3), electronics
manufacturers (approximately 2), and textiles facilities (approximately 2), as well as several others facilities
that may have used, produced, dispensed, or disposed of compounds and products that may contain PFAS
or CVOCs (Refs. 5, p. 3; 11, pp. 1, 2). As shown on Figure 4 of Reference 5, there are 23 public supply
wells located within a 4-mile radius of the Site. The wells are completed in the Columbia and Potomac
aquifers (Refs. 40, p. 7; 41, p. 7; 42, p. 7; 43, p. 7; 44, p. 7; 45, p. 7). Releases of PFAS and CVOCs from
multiple possible sources likely have comingled over time; particularly considering the impacts to local
groundwater flow direction as a result of the pumping history of the municipal wells (Ref. 18, pp. 17, 36,
37, 38; Section 3.0.1),
14
-------
Wm
SS-Site Suninian
'Power plant
Cherry
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=^C^UAilMGTON
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kiLlcohook
NATIONAL WMA
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Legend
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Site Reference Point
Baltimore
Figure 1
Site Location
Annapolis
Note: References 3, p. 1; 92, p. 1 of this HRS
documentation record.
TETRA TECH
Imagery: ESRI Mapping Service
The source of the map image is ESRI, used by the EPA with ESRI's permission.
Prepared For: EPA R3 START
Prepared By: M. Kelly
Coordinate System: NAD 1983 2011 StatePlane Delaware FIPS 0700 Ft US
Date Saved: 07/25/22
EPA Contract No: 68-HE-032-D0003
TD No: TD603-21-11-001
15
-------
SD-Containment
Source No.: 1
SOURCE DESCRIPTION
2.2
SOURCE CHARACTERIZATION
Number of the source:
1
Source Type:
Other
Name of the Source:
Contaminated Groundwater Plume with no identified source
Description and Location of Source (with reference to a map of Site):
The East Basin Road Groundwater Site is a groundwater plume with no identified source ("Source 1").
Under the HRS, a contaminated groundwater plume can be evaluated as a source when the origin of
hazardous substances that have contributed to the plume cannot be reasonably identified (Ref. 1, Section
1.1). The area of the plume shown on Figure 2 of Reference 5 is based on available sample locations that
meet the criteria for an observed release to groundwater (Section 3.1.1).
For the purpose of this HRS documentation record, analytical data used to document an observed release,
Section 3.1.1, was limited to groundwater samples collected as part of the SI and ESI conducted by EA
Engineering, Science, and Technology, Inc. (EA) under contract with DNREC and analytical data of the
public supply wells collected by the public water suppliers Artesian and NCMSC. Analytical data of
groundwater samples collected by other entities at locations and facilities throughout New Castle, Delaware
that show the presence of PFAS and CVOCs in groundwater is provided as additional supporting data (Refs.
46, pp. 51, 67; 47 pp. 81, 82, 83, 97, 98; 48, pp. 16, 18, 19; 49, pp. 65-67, 71, 73, 98, 99, 101, 102; 50, pp.
35, 52-58; 51, pp. 35, 41; 52, pp. 72, 73, 85-88, 746, 747, 753, 124-142, 1402, 1405, 1406, 1407, 1426,
1427, 2098, 2101, 2102, 2103, 2108; 53, pp. 65, 66; 54, pp. 109; 55, pp. 9, 10, 97, 112, 123, 132, 145, 158,
536; 56, pp. 12, 17, 270, 279, 283, 295, 324, 336, 359, 390, 399, 408, 435; 57, pp. 4, 18, 22; 58, pp. 13, 29;
59, pp. 142, 143, 1895, 1930, 1961, 1990, 2020, 2027, 2054, 2061, 2100, 2852, 2853; 60, pp. 17, 34, 37,
In 2017, 2018, and 2020, DNREC conducted a SI that included the installation and sampling of monitoring
wells to investigate the presence of hazardous substances in groundwater (Ref. 7, pp. 25, 70, 71, 87). As
further documented in Section 3.1.1, analytical results of the groundwater samples collected from the
monitoring wells installed as part of the SI documented an observed release to groundwater of PFOA,
PFOS, and VOCs such as TCE, PCE, 1,2-DCA, and vinyl chloride (Section 3.1.1, Tables 4 through 15).
In 2021, DNREC conducted an ESI that included the installation and sampling of additional monitoring
wells, the sampling of select existing monitoring wells, and the sampling of two Artesian public supply
wells and two NCMSC public supply wells (Ref. 9, pp. 26, 28, 29, 121, 124). As further documented in
Section 3.1.1, analytical results of the groundwater samples collected from the monitoring wells installed
as part of the ESI documented an observed release to groundwater of PFOA, PFOS, and VOCs such as
TCE, PCE, 1,2-DCA, cis-l,2-DCE, and vinyl chloride (Section 3.1.1, Tables 4 through 15).
Samples collected by Artesian and NCMSC have shown concentrations of PFAS since 2013 and 2014,
respectively (Refs. 7, p. 12; 8, p.82). Most recent available analytical data for samples collected by Artesian
documented an observed release to groundwater of PFOA, PFOS, and VOCs such as TCE, PCE, and cis-
1,2-DCE (Section 3.1.1, Tables 16 through 23).
42, 43).
16
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SD-Containment
Source No.: 1
PFOA and PFOS are fluorinated organic man-made compounds that are chemically and biologically stable
in the environment and resist typical environmental degradation processes. As a result, these chemicals are
very persistent in the environment. PFOS and PFOA are water-soluble and migrate readily from soil to
groundwater, where they can be transported long distances (Ref. 61, pp. 1-3). PFAS, in particular PFOS
and PFOA, are associated with a wide variety of industrial and commercial processes such as (Refs. 61, pp.
1,2; 62, p. 13; 63, pp. 7, 8):
Aviation operations (North American Industry Classification System [NAICS] code 488119)
Carpet manufacturers (NAICS code 314110)
Car washes (NAICS code 811192)
Chrome electroplating, anodizing, and etching services (NAICS code 322813)
Coatings, paints, and varnish manufacturers (NAICS code 325510)
Firefighting foam manufacturers (NAICS code 325998)
Landfills (NAICS code 562212)
Municipal fire departments and firefighting training centers (NAICS code 922160)
Paper mills (NAICS codes 322121 and 322130)
Petroleum refineries and terminals (NAICS codes 324110 and 424710)
Photographic film manufacturers (NAICS code 352992)
Polish, wax, and cleaning product manufacturers (NAICS code 325612)
Polymer manufacturers (NAICS code 325211)
Printing facilities where inks are used in photolithography (NAICS codes 323 111 and 325910)
Textile mills (textiles and upholstery) (NAICS codes 313210, 313220, 313230, 313240, and
313320)
Wastewater treatment plants (NAICS code 221320).
PFOA and PFOS are two of the most widely used compounds in the PFAS group and are used in fire
extinguishing foam (aqueous film-forming foams [AFFF]) and are used to extinguish flammable liquid-
based fires. Such foams are used in training and emergency response events at airports, shipyards, military
bases, firefighting training facilities, chemical plants, and refineries (Refs. 61, p. 2; 62, pp. 58, 59; 64, p.
1).
PCE is primarily used as a dry cleaning solvent, where it is released as fugitive emissions or as liquid waste
(Ref. 65, pp. 24, 31, 288). In addition to being used as a dry cleaning solvent, it also has uses as a metal
degreasing solvent and as a chemical intermediate (Ref. 65, pp. 23, 283). PCE partitions primarily to the
atmosphere when released into the environment, but when present in soil, it can leach and migrate to
groundwater (Ref. 65, pp. 24, 288, 294, 295). PCE breaks down into TCE, cis-l,2-DCE, 1,1-DCE, and
vinyl chloride, and to a lesser extent trans-l-2-DCE in the environment (Ref. 71, pp. 2 - 3).
TCE is used as a solvent to remove grease from metal parts and as a chemical that is used to make other
chemicals. TCE has also been used as an extraction solvent for greases, oils, fats, waxes, and tars; by the
textile processing industry to scour cotton, wool, and other fabrics; in dry cleaning operations; and as a
component of adhesives, lubricants, paints, varnishes, paint strippers, pesticides, and cold metal cleaners
17
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SD-Containment
Source No.: 1
(Ref. 66, p. 23). When released to the environment, TCE migrates readily through soil to groundwater and
may occur as an original contaminant or as a result of the breakdown of PCE (Ref. 66, pp. 24, 336).
1,2-DCE is most often used to produce solvents and in chemical mixtures (Ref. 67, p. 17). 1,2-DCE has
also been used as a solvent for waxes, resins, acetyl cellulose, perfumes, dyes, lacquers, thermoplastics,
fats, and phenols. 1,2-DCE released into the environment can readily evaporate into the atmosphere;
however, in the subsurface, 1,2-DCE may dissolve in water, seep deeper into the soil, and possibly
contaminate groundwater. Once in groundwater, 1,2-DCE takes approximately 13-48 weeks for half of a
given amount to break down (half-life in water). 1,2-DCE can eventually break down into vinyl chloride,
which is believed to be a more hazardous chemical (Ref. 67, pp. 17, 94). The majority of 1,2-DCE present
in groundwater involves biodegradation processes related to primary pollution from TCE or PCE (Ref. 67,
p. 103).
Vinyl chloride is a manufactured substance that does not occur naturally; however, it can be formed in the
environment when other manufactured substances such TCE, TCA, and PCE are broken down by certain
microorganisms (Ref. 68, p. 22). Vinyl chloride is used to make a polymer called polyvinyl chloride (PVC),
which consists of long repeating units of vinyl chloride. PVC is used to make a variety of plastic products
including pipes, wire and cable coatings, and packaging materials. Other uses include furniture and
automobile upholstery, wall coverings, housewares, and automotive parts (Ref. 68, pp. 22, 186). Vinyl
chloride can migrate to groundwater and can also be in groundwater due to the breakdown of other
chemicals (Ref. 68, pp. 23, 189, 194).
The primary use of 1,1-DCE is as a chemical intermediate to make other products such as plastics,
packaging materials and flexible films such as plastic wrap, and flame-retardant coatings for fiber and carpet
backing (Ref. 69, p. 11). However, it is also found in landfills as the result of breakdown of polyvinylidene
chloride products and as the degradation products of other chemicals such as PCE, TCE, and 1,2-DCA in
the environment by dehydrochlorination reactions (Ref. 69, pp. 98, 104). 1,1-DCE primarily exists in a
vapor phase, although it migrates readily through soil and groundwater when found in these media (Ref.
69, p. 105).
1,2-DCA is primarily used in the production of vinyl chlorides, though it is also used as a dispersant in
rubber and plastics, and as a solvent in organic synthesis. 1,2-DCA was previously used as an insect and
soil fumigant, in cleaning products (especially for use on textiles), and in adhesives (Ref. 70, p. 145). Up
until the ban of leaded gasoline in the 1990s, 1,2-DCA was used as a lead scavenger; however, even after
the ban of leaded gasoline, 1,2-DCA has been used in leaded fuel for aviation (Ref. 70, p. 152). It is slightly
soluble in water and is expected to be very mobile in the environment (Ref. 70, p. 146).
Documentation of the observed release sample analyses is presented in Section 3.1.1 Observed Release,
Chemical Analysis. The rationale for the lack of an identifiable source for the groundwater contamination
(i.e., that the significant increase in contaminant concentrations cannot be attributed to a release from any
individual facility) is presented in Section 3.1.1 Observed Release, Attribution.
18
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SD-Containment
Source No.: 1
2.2.2 Hazardous Substances Associated with the Source
The following hazardous substances are associated with the source (Section 3.1.1 of the HRS
documentation record):
Perfluorooctanesulfonic acid (PFOS)
Perfluorooctanoic acid (PFOA)
Tetrachloroethylene (PCE)
Trichloroethylene (TCE)
cis-l,2-Dichloroethylene (cis-l,2-DCE)
trans-1,2-Dichloroethylene (trans-1,2-DCE)
1,2-Dichloroethane (1,2-DCA)
Vinyl Chloride
2.2.3 Hazardous Substances Available to Pathway
Analytical results for groundwater samples collected from monitoring wells and public supply wells
indicate that a release of hazardous substances has occurred to the groundwater migration pathway, as
documented in Section 3.1.1 of this HRS documentation record. Based on this evidence of hazardous
substance migration, a containment factor value of 10 is assigned for the ground water migration pathway,
as shown in Table 1 (Ref. 1, Section 3.1.2.1, Table 3-2).
TABLE 1
SOI RCE NO. 1 CONTAINMENT 1 ACTORS
C Oil t;i i n moil 1 Description
Containmcnl Eaclor Value
References
Gas release lo air
NS
NA
Particulate release to air
NS
NA
Release to groundwater: based on
evidence of hazardous substance
migration (contamination detected in
groundwater samples delineating the
plume), a containment factor of 10 is
assigned.
10
1, Section 3.1.2.1, Table 3-2;
Section 3.1.1 of this HRS
documentation record
Release via overland migration and/or
flood
NS
NA
Notes:
NA = Not applicable
NS =Not scored
19
-------
SD-Hazardous Waste Quantity
Source No.: 1
2.4.2 Hazardous Waste Quantity
Insufficient information exists to evaluate hazardous constituent quantity and hazardous waste stream
quantity. Therefore, the hazardous waste quantity value is calculated using Tier C, the volume of the plume,
and source type other (Ref. 1, Section 2.4.2.1) for Source No. 1.
2.4.2.1.1 Hazardous Constituent Quantity (Tier A)
The hazardous constituent quantity for Source No. 1 could not be adequately determined according to the
HRS requirements; that is, the total mass of all CERCLA hazardous substances in the source and releases
from the source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section
2.4.2.1.1). There are insufficient historical and current data (manifests, potentially responsible party [PRP]
records, state records, permits, waste concentration data, etc.) available to adequately calculate the total or
partial mass of all CERCLA hazardous substances in the source and the associated releases from the source.
Therefore, there is insufficient information to evaluate the associated releases from the source to calculate
the hazardous constituent quantity for Source No. 1 with reasonable confidence. Scoring proceeds to the
evaluation of Tier B, hazardous waste stream quantity (Ref. 1, Section 2.4.2.1.1).
Hazardous Constituent Quantity (C) Value: Not scored
2.4.2.1.2 Hazardous Waste Stream Quantity (Tier B)
The hazardous waste stream quantity for Source No. 1 could not be adequately determined according to the
HRS requirements; that is, the mass of the hazardous waste streams plus the mass of any additional
CERCLA pollutants and contaminants in the source and releases from the source is not known and cannot
be estimated with reasonable confidence (Ref. 1, Section 2.4.2.1.2). There are insufficient historical and
current data (manifests, PRP records, state records, permits, waste concentration data, etc.) available to
adequately calculate the total or partial mass of the waste stream plus the mass of all CERCLA pollutants
and contaminants in the source and the associated releases from the source. Therefore, there is insufficient
information to evaluate the associated releases from the source to calculate the hazardous waste stream
quantity for Source No. 1 with reasonable confidence. Scoring proceeds to the evaluation of Tier C, Volume
(Ref. 1, Section 2.4.2.1.2).
Hazardous Waste stream Quantity (W) Value: Not scored
2.4.2.1.3 Volume (Tier O
The exact volume for Source 1 could not be adequately determined according to the HRS requirements
(Ref. 1, Section 2.4.2.1.3). Monitoring wells and public supply wells located within the plume contained
PCE, TCE, cis-l,2-DCE, trans-1,2-DCE, 1,2-DCA, and vinyl chloride as well as PFOS and PFOA at
concentrations significantly above background (Section 3.1.1), However, the boundaries and total depths
of the plume are not sufficiently defined to reasonably estimate a volume. Therefore, based on the presence
of hazardous substances in the observed release samples, the volume of the groundwater contamination is
at least greater than 0 cubic yards (yd3), but the exact volume is unknown (Ref. 1, Section 2.4.2.1.3, Table
2-5; Sections 2.2 and 2.2.2 of this HRS documentation record).
Dimension of source in cubic yards (yd3): greater than (>) 0 yd3
Volume (V) Assigned Value: (> 0)/2.5 = > 0
20
-------
SD-Hazardous Waste Quantity
Source No.: 1
2.4.2.1.4 Area (Tier D)
The volume of the source has been determined; therefore, the Tier D - area is assigned a hazardous waste
quantity value of 0 (Ref. 1, Section 2.4.2.1.3).
Area (A) Assigned Value: 0
2.4.2.1. 5 Source Hazardous Waste Quantity Value
The source hazardous waste quantity value for Source 1 is > 0 for Tier C - Volume (Ref. 1, Section
2.4.2.1.5).
Source Hazardous Waste Quantity Value: >0
21
-------
SD-Summary
i Alii.i: 2
Sl l i: SI MMARY ()l SOI R( i: DESCRIPTIONS
Source
\ ii in her
Source
1 lii/iirilous
W ;isle
Qiiitiilitx
\ :illie
Source 1 lii/iirilous
C Oust it uent
Qiiitiililx Complete
0
iN
10
iNS
iNS
iNS
Votes:
> = greater than
Y = Yes
N = No
NS =Not scored
22
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GW-General
3.0 GROUND WATER MIGRATION PATHWAY
3.0.1 General Considerations
Regional Geology:
The Site is in northern Delaware, in New Castle, east of the New Castle County Airport, and lies within the
Coastal Plain Physiographic Province (Ref. 15, p. 1). The Coastal Plain consists of a sequence of
unconsolidated gravels, sands, silts, and clays that form a southeast-dipping wedge resting on older
metamorphic, igneous, and consolidated sedimentary basement rocks (Refs. 15, p. 1; 16, pp. 17, 19, 20).
Sediments range from Cretaceous Age to Holocene Series of Quaternary Age and were deposited in fluvial,
deltaic, and marine environments. Later reworking by modern and ancestral streams and rivers has resulted
in the downcutting of Cretaceous age sediments and the deposition of new channel and terrace deposits
(Ref. 16, p. 17). The Coastal Plain sediments thicken from a thin line along the edge of the Fall Line with
the Piedmont Physiographic Province to the northwest near Newark, Delaware, to more than 800 feet thick
to the southeast near Delaware City, Delaware (Refs. 16, p. 19; 17, p. 55).
The uppermost stratigraphic unit underlying the site is the Quaternary Age, Pleistocene Series Columbia
Formation (Refs. 15, p. 1; 18, pp. 15, 23) The Columbia Formation is fluvial in origin and is composed
primarily of poorly sorted fluvial sands with some interbedded gravels, silts, and clays (Ref. 19, p. 1). The
Columbia Formation occurs as channel fillings and thin isolated patches in New Castle County in northern
Delaware where the Site is located and as abroad sheet across most of Kent and Sussex Counties in southern
Delaware that were deposited by streams entering Delaware from the northeast and spread south and
southeast across Delaware (Ref. 20, p. 15). Pleistocene Age paleochannels (extensive erosion of the
underlying Potomac sediments) are present in New Castle and resulted from a lowering of sea level during
the Pleistocene era and the subsequent downcutting of Pleistocene rivers into the underlying Potomac
sediments (Refs. 18, pp. 28, 33; 19, p. 1). The Columbia Formation ranges from less than 10 feet thick to
over 100 feet and is characterized by fine to coarse, yellowish- to reddish-brown, sand with varying amounts
of gravel. Scattered beds of tan to reddish-gray clayey silt are common. Near the base of the unit, clasts of
cobble to small boulder size found in gravel beds ranging from a few inches to three feet thick (Ref. 15, p.
1).
The Cretaceous Age Potomac Formation underlies the Columbia Formation at the Site (Ref. 19, p. 1). The
Potomac Formation was deposited in a fluvial setting with the resulting sediment distribution dominated
by small-scale, fining-upward sequences, characterized by irregular sand bodies in a silty clay matrix. Sand
was separated from the clay and silt fractions by stream action and was deposited mainly in stream channels.
The sand bodies, because they were generally confined to the channels of the depositing streams, are
elongated and tabular rather than sheet-like (Ref. 18, pp. 17, 18). Individual beds of sand, silt, and clay
generally are restricted in areal extent and thickness. Because of the lithologic variability in both the
horizontal and vertical direction, it is considered a single stratigraphic unit in Delaware (Ref. 18, p. 12).
The Potomac Formation is characterized by dark-red, gray, pink, and white silty clay to clayey silt and very
fine to medium sand beds. Beds of gray clayey silt to very fine sand that contain pieces of charcoal and
lignite are common. The Potomac ranges in thickness from 20 feet at the up dip to over 1600 feet thick in
southern New Castle County (Ref. 15, p. 1).
Regional Hydrogeology:
The hydrogeologic framework of the Columbia and Potomac Formations underlying the Site is complex
and the heterogeneity of hydraulic properties of aquifers contained within these formations is enhanced by
channel geometry and discontinuous confining layers. Paleochannels and flood-plain deposits from braided,
23
-------
GW-General
anastomosed, and meandering fluvial system environments are also found within the formations, further
complicating interpretation of the connections between aquifer sand layers (Ref. 16, p. 26). As documented
below, the aquifers in the region in descending order are the surficial/water table (i.e., the Columbia
Aquifer) and Potomac Aquifers.
The sediments of the Columbia Formation comprise the Columbia aquifer (Ref. 18, p. 28). The Columbia
aquifer functions as a water table aquifer and is capable of yielding large quantities of water where thickness
is greater than 40 feet (Ref. 18, p. 14, 33; 20, p. 19). The saturated part of the Columbia Formation forms a
surficial aquifer. Groundwater in the surficial aquifer is recharged by direct infiltration of precipitation.
Flow is generally from higher to lower land-surface elevations, resulting in groundwater discharge to small
streams and creeks (Ref. 16, pp. 18, 20). The Columbia aquifer is recharged from the surficial aquifer and
is Delaware's most important ground water resource (Ref. 20, pp. 8, 46). The aquifer is composed
principally of sands that occur as channel fillings in northern Delaware, where the Site is located, and as a
broad sheet across central and southern Delaware (Ref. 20, p. 14). The saturated thickness of the aquifer
ranges from a few feet in many parts of northern Delaware to more than 180 feet in southern Delaware
(Ref. 20, p. 17). The transmissivity of the aquifer varies greatly reflecting local changes in lithology (from
fine sand to coarse sand and gravel) and changes in saturated thickness. However, the hydraulic data
indicate that the Columbia deposits effectively act as a medium to coarse sand aquifer (Ref. 20, p. 6).
Transmissivity values have been estimated for the New Castle area to be between 2,400 and 8,000 feet
squared per day (ft2/d) (Ref. 20, p. 39). Vertical hydraulic conductivity for the Columbia sediments have
been reported to range from 1.7x10-6 feet per second (ft/s) for silty sand to 3.8x10-4 ft/s for sand and
3.3x10-5 ft/s for silty sand and 3.3x10-2 for gravel beds (Ref. 18, p. 33). The Columbia aquifer, and the
flow system within this aquifer, is unconfined and conceptualized as being controlled mainly by topography
and the location of surface-water features (Ref. 16, p. 18).
Underlying the Columbia aquifer is the Potomac aquifer (Ref. 18, pp. 15, 18, 19, 21-25). The source of
groundwater for the Potomac aquifers is recharge from the overlying Columbia aquifer. Most of the
recharge occurs near the updip extent of the aquifers where sandy zones of the Potomac Formation crop out
at, or near, the land surface and from the Columbia aquifer where confining units are thin or absent (Refs.
16, p. 18; 18, p. 36). During pre-pumping conditions, much of the water in the Columbia aquifer discharges
as base flow into local streams or lakes. The remainder of the groundwater flows into the deeper Potomac
aquifers (Ref. 18, p. 36). Reported recharge into the Potomac aquifers from the Columbia aquifer was from
0.1 to 2.0 inches per year (in/yr), including in the confined Potomac aquifers in northern Delaware (Ref.
18, p. 36). Reported transmissivity values of the Potomac Formation range from 454 to 8,480 ft2/d (Ref. 18,
p. 26).
The vertical and horizontal variability of sediment distribution in the Potomac Formation makes aquifer
correlation complex (Ref. 18, p. 18). The formation has been differentiated into sub-aquifers: an upper,
middle, and lower, comprised of discontinuous sandy units separated by silty clay confining layers (Refs.
16, pp. 19, 20; 18, pp. 14, 15, 18, 21, 22, 23, 24, 25, 26, 27). The sediment variability of the Potomac
Formation is reflected in the wide range of values for aquifer properties. The range in values is primarily a
function of the lithology, thickness, lateral extent, and degree of interconnection of sand bodies within a
localized area (Ref. 18, p. 26). The regional flow system within the aquifers of the Potomac Formation is
characterized by relatively slow downdip (southeast) flow, controlled mainly by hydrostratigraphy (Ref.
16, pp. 18-20).
The downward erosion of river channels during Pleistocene era resulted in the removal of underlying
Cretaceous sediments. The channel-fill sediments deposited after the erosional episodes consisted of sand
and gravel of the Columbia Group and Holocene sediments. These sediments have a greater permeability
than the Potomac confining unit that had overlain the Potomac aquifers. Therefore, the paleochannels will
influence groundwater in the Potomac aquifer and may act as a conduit for water to leak out of or into the
24
-------
GW-General
Potomac aquifer units (Refs. 18, pp. 33, 34; 19, p. 1). The sediments of the Columbia Formation fill that
eroded surfaces within the underlying Potomac Formation formed a paleochannel that trends northeast to
southwest with a thickness of approximately 70 ft. within the vicinity of the Site (Ref. 7, pp. 13, 68). Due
to erosion, the Upper Potomac clay may be discontinuous or missing entirely within the paleochannels. As
presented below, the Upper Potomac clay is absent in places from the NCCA, as documented in boring logs
from select monitoring wells (Ref. 7, p. 13). Groundwater in the Columbia Formation (with public supply
wells located in the paleo-channel filled with Columbia Formation sediments) is rapid and expected to be
in the hundreds of feet per year based on a fate and transport assessment of PFAS compounds in
groundwater at NCCA and DANG and at the public supply wells located in and around the paleochannel
(Ref. 9, pp. 58, 132).
The hydraulic gradient between the aquifers and the Delaware River is affected by pumpage from the
aquifers. In areas where the aquifers are relatively unstressed, potentiometric heads are above the altitude
of the river, resulting in groundwater discharge to the river. Conversely, gradients are from the river to the
aquifers in areas where pumping has lowered potentiometric heads below the river level (Ref. 18, p. 17).
Water in the Potomac aquifer units not affected by pumpage flows southeast and eventually discharges into
overlying sediments and the Delaware River (Ref 18, p. 36).
Site Geology/Hydrogeology and Aquifer Descriptions:
The aquifers evaluated for this HRS evaluation are the interconnected Columbia Aquifer and Potomac
Aquifer that comprise the Columbia/Potomac Aquifer System. Well logs of monitoring and public supply
wells throughout the Site and New Castle, Delaware, demonstrate the variability in the subsurface material
indicative of the formations that comprise the Columbia/Potomac Aquifer System such as the Columbia
and Potomac formations (Refs. 7, pp. 70, 71, 240-247, 252, 258, 261, 262, 299-305, 316-321; 9, pp. 121,
129-131, 164-167; 39, pp. 6, 9, 11, 15, 31, 34; 76. p. 2). The wells logs and cross-sections show intervals
of clay, sand, gravel, sandy-gravel, sandy-clay, silty-clay, silty-gravel, silty-sand, silty, sandy-gravel
ranging in thickness from just a few feet to tens of feet thick.
In the vicinity of the Site, groundwater flow within the Columbia and Potomac Aquifers is influenced by
pumping from public supply wells, as wells as a possible surficial groundwater divide across the NCCA
(Ref. 8, p. 16). Surface elevations at the airport reach 85 feet at the airport and lessen to sea level at the
Delaware River located approximately 2 miles to the east-southeast and at the Christina River located
between 0.5-mile west and 1 mile north of the airport (Ref. 8, pp. 16, 30, 47, p. 28). Based on review of
groundwater gauging over a nine year period, an apparent groundwater divide in the surficial aquifer is
present north of the east-west runway at the NCCA (Ref. 7, pp. 55, 77). Along the east side of the NCCA,
surficial groundwater flows to the east-southeast toward the Delaware River while on the west side of the
NCCA surficial groundwater is likely to flow to the west-northwest toward the Christina River. The
presence of the groundwater divide may be related to the thinning of the Columbia Aquifer at the NCCA
(Ref. 7, pp. 14, 77). Additionally, a groundwater mound has been observed in the southeastern portion of
the DANG facility located in the northeast portion of the NCAA with shallow groundwater flowing in a
west-southwesterly direction (Refs. 7, p. 77; 52, pp. 25, 81). A northerly groundwater flow direction is also
inferred radiating from the groundwater mounding at the DANG facility (Refs. 7, p. 77; 52, p. 84). The
apparent groundwater divide was also noted at a facility just north of the airport with shallow groundwater
flow observed to be towards the northwest on the western portion of the facility and towards the southeast
on the eastern portion of the facility (Ref. 56, pp. 4, 11).
Aquifer 1 - Columbia Aquifer:
A hydrogeologic cross section prepared from boring logs Cc55-18, Cd 51-8, and Cd 52-27,13 (section D
to D') in the vicinity of the Site in New Castle illustrates the thickness of the Columbia aquifer (Ref. 18,
25
-------
GW-General
pp. 15, 23). The cross section shows the presence of the Columbia Aquifer overlying the Upper Potomac
Aquifer. The maximum local thickness of the aquifer is approximately 70 feet (Ref. 18, p. 23). Wells
completed in a paleochannel of the Columbia aquifer indicate that the aquifer has a thickness of
approximately 70 feet, and the aquifer is present at elevations of 40 feet above sea level to approximately -
30 feet below sea level (boreholes Cd42-16, 17) (Refs. 18, pp. 15, 25; 19, p. 1). In the northern portion of
the Site, underlying the Castle Hills and Collins Park well fields, south of the Delaware Memorial Bridge,
a hydrogeologic cross section prepared from borings logs Cd42-16, 17, Cd43-4, Cd-43-16, Cd43-1, and
Cd-43-2 (section F to F') illustrates the approximate thickness of the Columbia aquifer ranging from 30
feet to 70 feet and is present at elevation of 40 to -40 feet (Refs. 18, pp. 15, 25; 19, p. 1). In this area, the
Columbia the Potomac aquifer. The cross-section illustrates a possible paleochannel cutting into the middle
Potomac aquifer (Ref. 18, pp. 25, 26). To the south of New Castle, in the southern portion of the Site, the
Columbia aquifer is fairly thin and overlies the upper Potomac aquifer (Ref. 18, pp. 15, 21, 22). However,
a paleochannel is present at the Llangollen well field where the Columbia aquifer is approximately 50 feet
thick (Ref. 19, p. 1).
Aquifer 2 - Potomac Aquifer
The vertical and horizontal variability of sediment distribution in the Potomac Formation makes aquifer
unit correlation difficult; the Potomac aquifer is considered a single stratigraphic unit in Delaware, but
regionally it has been subdivided into an upper, middle, and lower aquifer units separated by discontinuous
layers of fine-grained sediments (Refs. 16, pp. 19, 20; 18, pp. 12, 14, 15, 18, 21, 22, 23, 24, 25, 26, 27).
Underlying the Columbia aquifer in the vicinity of the Site in New Castle is the discontinuous upper
Potomac confining unit; where this confining unit is present it can range in thickness from about 15 feet
(borehole Cc55-18) to approximately 90 feet (borehole Dc24-19) (Ref. 18, pp. 21, 23, 27). The upper
confining unit is not present adjacent to the Delaware River just south of New Castle (borehole Dd21-1), to
the west of the New Castle in boreholes (Dcl4-3 and Dcl4-42), or in monitoring well boreholes NCPW-
MW18 and NCPW-MW21 where the Columbia aquifer is in direct contact with the sands of the upper
Potomac (Ref. 7, pp. 299-303, 316-321; 18, pp. 15, 22, 27; 19, p. 1). Vertical hydraulic conductivities of
the upper Potomac confining unit, where present, range from 3.3xl0"10 to 4.9xl0"6 ft/s (Ref. 18, p. 28).
The upper Potomac unit is present in the western and southern portions of New Castle but becomes thin
and discontinuous or is absent completely in the vicinity of the Delaware River and in the northern portion
of New Castle (Refs. 18, pp. 15, 20, 21, 22, 23, 24, 25; 21, p. 1; 22, p. 1).
The base of the upper sand in the Potomac Aquifer unit increases in depth towards the east and reaches a
depth of approximately 160 feet below mean sea level (msl) at the Delaware River (Ref. 21, p. 1). The
thickness of the upper sandy zone in New Castle ranges from 20 to 120 feet thick (Ref. 22, p. 1). In the
vicinity of the Site, the thickness of the upper Potomac aquifer unit ranges from approximately 18 feet to
42 feet beneath the western part of the New Castle (boreholes Dcl5-13, Ccl5-16, and Ccl5-18), but is
approximately 10 feet thick under the eastern part (borehole Cd52-27) (Refs. 18, pp. 15, 23; 21, p. 1; 22, p.
1).
A discontinuous confining unit overlying the middle Potomac aquifer is present in eastern New Castle
(borehole Cd52-27) and northeast of New Castle (Ref. 18, pp. 15, 23, 25, 27). The middle Potomac
confining unit, where present, ranges greatly in thickness and has intervals of sand bodies (Ref. 18, pp. 15,
23, 24, and 25).
In the vicinity of the Site, in east New Castle, the middle Potomac aquifer is present at approximately 100
feet below sea level (borehole Cd52-27) and has a thickness of approximately 30 feet (Ref. 18, pp. 15, 20,
23). The middle Potomac aquifer is continuous to the northwest, at a depth of 48 to 60 feet below sea level,
26
-------
GW-General
with a thickness of about 20 to 30 feet (Ref. 18, pp. 25). A Columbia paleochannel is likely documented at
borehole Cd43-16 located north of New Castle at 60 to 76 feet below sea level based on a mineral analysis
of the sand and supports that the Columbia aquifer is in direct contact with the sand unit of the Middle
Potomac Aquifer (Ref. 18, pp. 15, 18, 25, 26).
All wells at this Site are finished in the Upper or Middle Potomac aquifer units and therefore the Lower
Potomac aquifer unit is not described. While discontinuous confining units can be found within the Potomac
Aquifer system, no local or continuous confining units restrict the movement of water between the Potomac
aquifer units and these units act as one aquifer (Ref. 7, pp. 299-303, 316-321; 18, p. 12; Ref. 19, p. 1).
3.0.1.1 Target Distance Limit
The target distance limit defines the maximum distance from the source(s) at the Site over which targets
are evaluated. In accordance with HRS Section 3.0.1.1, the targets associated with the ground water
migration pathway are evaluated within a 4-mile radius from the source(s) at the Site. Figure 4 in Reference
5 of this HRS documentation record depicts the 4-mile radius target distance limit based on center of the
plume.
3.0.1.2 Aquifer Boundaries
3.0.1.2.1 Aquifer Interconnections
The absence of discernible continuous clay layers, both locally and regionally, demonstrates that a
continuous (greater than 2 miles) confining layer is not present in the formations that comprise the
Columbia/Potomac Aquifer System in the vicinity of the groundwater plume (Refs. 9, 129-131; 19, p. 1;
47, p. 100). The upper Potomac aquifer units are not laterally continuous, and to the northeast of the airport
much of the Potomac formation has been eroded and filled with Columbia sediments of the Pleistocene Age
(Refs. 21, p. 1; 22, p. 1). Boreholes (Dcl4-3 and Dcl4-42) establish that the Columbia Aquifer is in direct
contact with the sands of the Upper Potomac Aquifer (Ref. 19, p. 1). Monitoring wells located within the
boundaries of the groundwater plume further demonstrate that there is no continuous confining unit;
boreholes logs for wells NCPW-MW18 and NCPW-MW21 indicate that no HRS qualifying confining unit
is present down to a depth of approximately 90 feet below msl (Ref. 7, pp. 299-303, 316-321; 9, p. 130).
There is also evidence that sand of the Columbia formation are also in direct contact with sand of the middle
Potomac where a paleochannel eroded the Potomac formation and created a paleochannel with deposited
sands of the Pleistocene Age Columbia Group as shown in boreholes Cd43-4 and Cd-43-16 (Ref. 18, pp.
18, 25, 26). The Pleistocene erosion removed the overlying Potomac confining unit which resulted in
deposition of more permeable sediment and provided a conduit for water to leak out of or into the Potomac
aquifers (Ref. 18, p. 33).
The migration of non-naturally occurring contaminants through the fine-grained sediments and the
subsequent presence of contamination throughout the Columbia/Potomac Aquifer System to a depth of at
least -103 feet in elevation demonstrates that the interbedded fine-grained units do not act as a local barrier
to groundwater flow within the Columbia/Potomac Aquifer System. Site contaminants, such as PFOS,
PFOA, and CVOCs, have been detected in groundwater monitoring and public supply wells screened within
sands of the Columbia and Upper Potomac Aquifers as documented in Section 3.1.1 (wells screened at
depths ranging from an elevation of 5.2 feet to elevation of -103.25 feet as shown on Figure 2 in Reference
5 and Tables 4 through 23 of this HRS documentation record). Vertical distribution has likely been
influenced by the many active public groundwater pumping wells located within the vicinity of the Site,
and has likely caused a downward vertical migration from the numerous source areas to production well
screens over 100 ft. bgs. Rapid horizontal and vertical transport of contaminants has been observed within
27
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GW-General
the generally more permeable paleochannel sands and gravels, where the production wells are generally
located (Ref. 7, pp. 56, 77).
For HRS scoring purposes, as described above, and consistent with the HRS, the Columbia and Potomac
Aquifers are interconnected (evidence of observed migration of hazardous substances and no continuously
present confining units) and evaluated as a single hydrologic unit (Ref. 1, Section 3.0.1.2.1).
Both Artesian and the NCMSC public supply wells withdraw water from the Columbia/Potomac Aquifer
System (Tables 18 and 22 of this HRS documentation record).
3.0.1.2.2 Aquifer Discontinuities
For HRS scoring purposes, an aquifer discontinuity occurs when a geologic, topographic, or other structure
or feature entirely transects an aquifer within the 4-mile target distance limit, thereby creating a continuous
boundary to groundwater flow within this limit (Ref. 1, Section 3.0.1.2.2).
As shown on the Geologic Map for the New Castle County, Delaware, there are no aquifer boundaries, such
as mountain ranges, deep rivers, continuous HRS qualifying confining units, or faults, within 4 miles from
the Site that entirely transects any portion of the aquifer within the 4-mile TDL and would constitute an
aquifer discontinuity (Ref. 15, p. 1; Figure 4 in Reference 5 of this HRS documentation record). The
Christina River is relatively shallow and does not form a hydrological divide (Refs. 16, pp. 19 and 20; 19,
p. 1).
i Alii.i: 3
SI MM ARY ()l AQ1 ll-'KK(S) liKINd EYAI.l ATE I)
Aquifer
No.
Aquifer Name
Is Aquifer
Interconnected with
I pper Aquifer within 2
miles? (Y/N/NA)
Is Aquifer
Continuous within
4-mile 1 1)1.? (Y/\)
Is Aquifer
Kiirst? (Y/\)
1
Columbia Aquifer
Y
Y
N
2
Potomac Aquifer
Y
Y
N
Notes:
> = greater than
Y = Yes
N = No
NA = Not applicable
NS =Not scored
TDL = Target distance limit
28
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GW-Observed Release
3.1 LIKELIHOOD OF RELEASE
3.1.1 Observed Release
Aquifer Being Evaluated: Columbia/Potomac Aquifer System
As discussed in Section 3.0.1, the Columbia Formation ranges in depth from 10 to 100 feet below ground
surface (bgs), below which is the Potomac Formation that has a maximum thickness of 1,600 feet. As shown
on Tables 6, 7, 10, 11, 14, 15, 18, 19, 22, and 23 of this HRS documentation record, samples containing
PCE, and PCE breakdown products, as well as PFOS and PFOA, were collected from monitoring and public
supply wells to a maximum depth of 137 feet bgs (-110 feet elevation); therefore, an observed release in
the Columbia/Potomac Aquifer System is documented.
Direct Observation
The aquifers are not evaluated for observed release by direct observation.
Chemical Analysis
An observed release by chemical analysis is established by demonstrating that the hazardous substance in
release samples is significantly greater in concentration than in the background samples, and by
documenting that at least part of the significant increase is due to a release from the Site being evaluated.
The significant increase can be documented in one of two ways for HRS purposes. If the background
concentration is not detected, an observed release is established when the sample measurement in a similar
sample equals or exceeds the appropriate quantitation limit. If the background sample concentration equals
or exceeds the detection limit, an observed release is established when the sample measurement in a similar
sample is three times or more the background concentration and above the appropriate quantitation limit
(Ref. 1, Section 2.3). Tables 4 through 23 of this HRS documentation record provide the hazardous
substances concentrations and additional sample and well information for the groundwater samples used to
establish observed releases. Background and Observed Release sample locations are shown on Figure 2 in
Reference 5 of this HRS documentation record (Ref. 5, p. 2).
Groundwater samples from monitoring wells were collected by EA, under contract with DNREC, as part
of the SI in 2017, 2018, and 2020 (Ref. 7, pp. 28, 33, 232, 351-364). EA, under contract with DNREC,
collected additional groundwater samples from monitoring wells and four public supply wells in 2021 as
part of the ESI (Ref. 9, pp. 28, 29, 154-158, 182-190). Sample collection included the collection of quality
assurance (QA) and quality control (QC) samples which consisted of field duplicates, matrix spike
(MS)/matrix spike duplicates (MSDs), field blanks, rinsate blanks, and trip blanks (Refs. 7, p. 35; 9, p. 29).
Samples were analyzed for VOCs by EPA Method SW846 8260 and for PFAS by modified version of EPA
Method 537 (for monitoring well samples), and by EPA Method 537.1 (for drinking water samples) (Refs.
7, p. 35; 9, p. 31). Analytical results were validated by a third-party contractor, Environmental Data
Services, Ltd., according to Data Review and Validation Guidelines for Perfluoroalkyl Substances (PFASs)
Analyzed Using EPA Method 537, EPA 910-R-18-001 (November 2018) and EPA Contract Laboratory
Program National Functional Guidelines for Organic Superfund Methods Data Review, OLEM 9240.0-51,
EPA-540-R-20-005 (November 2020) (Ref. 33, pp. 2, 21, 45, 59, 79, 113, 125, 143, 155, 223).
Water samples were collected from the public supply wells by the respective public supply facilities,
Artesian, and NCMSC for PFAS and VOCs by EPA Methods 537 (and 537.1) and 524.2, respectively,
(Refs. 31, p. 1; 32, p. 1).
29
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GW-Observed Release
S el ecti on of B ackground
In general, hazardous substances associated with the Site, particularly PFAS compounds, were detected in
all groundwater samples collected during the SI, ESI, and recent sampling of the public supply wells by the
water authorities. Wells chosen to document background conditions are wells located on the farthest edges
of the plume and show that groundwater samples collected to document an observed release are greater
than three times (or more) the concentrations detected in the background sample locations. Therefore, the
observed release wells delineate an area of significant increase. For background similarity, and to meet the
criteria for establishing an observed release, wells are separated into five categories, as described below.
This ensures that background wells are screened within the same relative depth within the
Columbia/Potomac Aquifer and have similar construction as the contaminated wells with which they are
being compared:
Shallow monitoring wells are screened at depths ranging from 50.84 to 10.97 feet elevation (Tables
4 and 6)
Intermediate monitoring wells are screened at depths from 5.2 feet msl to -23.38 feet elevation
(Tables 8 and 10)
Deep monitoring wells are screened at depths ranging from -45.34 to -87.91 feet elevation (Tables
12 and 14)
Public supply wells are only compared with other public supply wells, due to longer screen lengths
and larger casing diameters than the monitoring wells; however, to ensure similar screened intervals
within the aquifer, public supply wells are evaluated as:
o Intermediate public supply wells, screened at depths from ranging from -15 to -69.75 feet
elevation (Tables 16 and 18)
o Deep public supply wells, screened at depths ranging from -50.5 to -141.2 feet elevation
(Tables 20 and 22)
Background levels for each analyte in each well category are identified in bold.
1 Alii.I!4
IJU kdROl M) SHALLOW \1()\IT()RI\(; WELL INFORMATION
Well II)
(l)NRIX
permit ID)
Ele\ at ion
I-eel1
Completed
Well
Depth
li-'C I lliJS
(ck\ alion-
kvl in msl)
Screened Intenal
l ee I liijs
(ck\alion-kvl in
msl)
Well
Diameter
(in)
Litholo^v
Referenced)
NCPW-MW24
(275657)
50.20
30 (20.2)
14.71 to 29.71
(35.49 to 20.49)
2
Intervals of
sand and clay
9, pp. 67, 131,
166, 167, 170
Notes:
Elevation based on ground surface. Elevation based on NAVD88.
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
MW= Monitoring well
NAVD88 = North American Vertical Datum
NCPW = New Castle Public Wells
30
-------
GW-Observed Release
i Alii.i: 5
liAC KdkOl M) SHALLOW MOM lORINd W'KLI. CONCENTRATIONS
Well II)
(Siimple ID)
Siimplo
Ditto
1 In/melons
Suhsl since
Conccnlnilion
(ntj 1 or utj 1)1
RL (ihj 1
or
uu 1)1
Rcl'crcncc(s)
NCPW-MW24
(NCPW-
MW24-
11032021)
11/03/21
PFOS
0.52 L
i.yi
PP
3185
157, No, 3d, pp Uo(),
33, pp.176-182, 219
PFOA
4.33
1.91
9, PP
3185
157, 190; 30, pp. 1656,
33, pp. 176-182,219
trans-1,2-DCE
0.24U
1.0
9, PP
3173
157, 190; 30, pp.461,
33, pp.223-230, 271
cis-1,2-DCE
0.22U
1.0
9, PP
3173
157, 190; 30, pp.461,
33, pp.223-230, 271
TCE
0.31U
1.0
9, PP
3173
157, 190; 30, pp.461,
33, pp.223-230, 271
PCE
0.25U
1.0
9, PP
3173
157, 190; 30, pp.461,
33, pp.223-230, 271
Notes:
^nits for PFOS and PFOA are ng/1 and for VOCs are fig/1.
RL = Reporting limit. The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a
specified degree of confidence (Refs. 32, p. 24; 34, p. 2).
The samples were analyzed by a non-CLP laboratory. RLs presented above are most equivalent to the SQL as defined by HRS Section 1.1 (Ref. 1,
Sections 1.1 and 2.3).
U = Indicates the analyte was analyzed for but not detected (Ref. 9, p. 242).
jig/1 = micrograms per liter
ng/1 = nanograms per liter
1,1-DCA= 1,1-dichloroethane
cis-l,2-DCE = cis-l,2-dichloeroethylene
trans-1,2-DCE = cis-l,2-dichloeroethylene
PCE = Tetrachloroethylene
TCE = Trichloroethylene
PFOS = Perfluorooctanesulfonic acid
PFOA = Perfluorooctanoic acid
CLP = Contract Laboratory Program
ID = Identifier
MW= Monitoring well
NCPW = New Castle Public Wells
VOC = Volatile organic compound
31
-------
GW-Observed Release
i Alii.i:
OBSKRYKI) RELEASE SHALLOW MOMTOKIVi WELL l\l ORM Yl l()\
Well II)
(l)\RE( permit
ID)
Ele\ nlioii
I-eel1
Completed
Well Depth
kvl liijs
U'k\ alioil-
kvl in nisi)
Screened
Inten ill
kvl litjs
U'k'\ alioil-kvl
in nisi)
Well
Diiimeler
(Ml)
Litholo^y
Reference! s)
NCPW-A9-MW05
(259014)
42.97
35
(7.97)
17 to 32
(25.97 to 10.97)
1.5
Intervals of clay
and sand
7, pp. 80, 87,
244,245, 273
NCPW-A11-MW06
(259018)
68.87
47
(21.87)
37 to 47
(31.87 to 21.87)
1.5
Intervals of silty
sand, sand and
gravel; little clay
7, pp. 80, 87,
246, 247, 276
NCPW-A13-MW12
(259003)
74.80
50
(24.8)
40 to 50
(34.80 to 24.80)
1.5
Intervals of silty
sand, sand, and
sandy clay
7, pp. 80, 87,
252,253,283
NCPW-A13-MW13
(259005)
61.33
40
(21.33)
29 to 39
(32.33 to 22.33)
1.5
Intervals of sand
and sandy clay
7, pp. 80, 87,
254, 255, 286
NCPW-A13-MW14
(259002)
70.69
50
(20.69)
40 to 50
(30.69 to 20.69)
1.5
Intervals of sand
and clayey sand
7, pp. 80, 87,
256-258, 289
NCPW-A14-MW16
(259016)
69.84
37
(32.84)
19 to 29
(50.84 to 40.84)
1.5
Intervals of sand
and sandy clay
7, pp. 80, 87,
261,262, 294
NCPW-MW23
(275658)
60.74
50
(10.74)
39.6 to 49.6
(21.14 to 11.14)
2
Sand; limited
intervals of clay
9, pp. 67, 132,
164, 165, 169
Notes:
Elevation based on ground elevation. Elevation based on NAVD88.
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
MW = Monitoring well
NAVD88 = North American Vertical Datum
NCPW = New Castle Public Wells
32
-------
GW-Observed Release
TABU-! 7
()ijsi:r\ i:i) rlllasi: shallow momtoriv; well concentrations
Well II)
(Siimplc ID)
Siimplo
Diile
1 lil/il I'll (MIS
Suhsl since
C'oncenlnKion
(iiij 1 or utj 1)1
RL (ihj 1
or
u» 1)1
Kelerence(s)
NCPW-A9-MW05
(NCPW-A09GW-05)
9/17/18
PFOS
262
1.68
26, pp. 338, 821; 33, pp. 113-
119, 123
PFOA
162
1.68
26, pp. 338, 821; 33, pp. 113-
119,123
NCPW-A11-MW06
(NCPW-A11GW-06)
8/9/17
PFOS
15.4
1.94
25, pp. 270, 652; 33, pp. 79-
85, 87
PFOA
24.1
1.94
25, pp. 270, 652; 33, pp. 79-
85, 87
NCPW-A13-MW12
(AREA 13 -MW12-
11012021)
11/01/21
PFOS
18
1.80
30, pp. 1189, 3182; 33, pp.
176-184, 189
PFOA
71.1
1.80
30, pp. 1189, 3182; 33, pp.
176-184, 189
trans-1,2-DCE
2.9
1.0
30, pp. 326, 3171; 33 pp. 223-
232, 237
cis-1,2-DCE
2.3
1.0
30, pp. 326, 3171; 33 pp. 223-
232, 237
TCE
19
1.0
30, pp. 326, 3171; 33, 223-
232, 237
PCE
2.8
1.0
30, pp. 326, 3171; 33, 223-
232, 237
NCPW-A13-MW13
(NCPW-A13GW-13)
9/19/18
PFOA
71.3
1.73
27, pp. 270, 761; 33, pp. 143-
149, 151
NCPW-A13-MW14
(AREA 13-MW 14-
11022021)
11/2/21
PFOS
28.3
1.94
30, pp. 1447, 3183; 33, pp.
176-184, 206
PFOA
107
1.94
30, pp. 1447, 3183; 33, pp.
176-184, 206
NCPW-A14-MW16
(NCPW-A14GW-16)
9/17/18
PFOS
111
1.76
26, pp. 316, 821; 33, pp. 113-
119,121
PFOA
67.6
1.76
26, pp. 316, 821; 33, pp. 113-
119,121
NCPW-MW23
(NCPW-MW23-
11032021)
11/03/21
PFOS
8.35
1.87
30, pp. 1696, 3185; 33, pp.
177-184, 222
PFOA
39.1
1.87
30, pp. 1696, 3185; 33, pp.
177-184, 222
Notes:
^nits for PFOS and PFOA are ng/1 and for VOCs are fig/1.
Data was validated in accordance with EPA Contract Laboratory Program National Functional Guidelines (NFG) for Organic Superfund Methods
Data Review, OLEM 9240.0-51, EPA-540-R-20-005, November 2020 (Ref. 33, pp. 125, 132, 137).
RL = Reporting limit. The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a
specified degree of confidence (Refs. 32, p. 24 34. 2).
The samples were analyzed by a non-CLP laboratory. RLs presented above are most equivalent to the SQL as defined by HRS Section 1.1 (Ref. 1,
Sections 1.1 and 2.3).
jig/1 = micrograms per liter
ng/1 = nanograms per liter
cis-l,2-DCE = cis-l,2-dichloeroethylene
trans-1,2-DCE = cis-l,2-dichloeroethylene
33
-------
GW-Observed Release
PCE = Tetrachloroethylene
TCE = Trichloroethylene
PFOS = Perfluorooctanesulfonic acid
PFOA = Perfluorooctanoic acid
CLP = Contract Laboratory Program
ID = Identifier
MW = Monitoring well
NCPW = New Castle Public Wells
VOC = Volatile organic compound
TABLES
liACKCROl M) INTERMEDIATE MOMTORINd W'EI.I. INFORMATION
Well II)
(l)\REC permit ID)
Election
loot1
Completed
Well
Depth
I ccl lliJS
(ck'\ at ioii-
ll.vl in nisi)
Screened lnlcr\;il
led lliJS
(ck'\iilion-ltvl in
nisi)
Well
Diiimeter
(in)
l.ilh()lo»\
Referenced)
NCPW-MW22
(275659)
17.10
24
(-6.9)
13.74 to 23.74
(3.36 to-6.64)
2
Intervals of
clay, sand, and
clay with sand
9, pp. 67, 131,
162
Notes:
Elevation based ground surface. Elevation based on NAVD88.
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
NAVD88 = North American Vertical Datum
34
-------
GW-Observed Release
i Alii.i:4)
liACKCROl M) INTERMEDIATE monitoriv; \\t:i.i. concentrations
Well II)
(Sumpic ID)
Sninplo
Dsile
1 l;iz:irilous
Substitute
CoiHTiilnilion
(iiij 1 or utj 1)1
RL (ihj 1
or
u» 1)1
RcI'civiut(s)
NCPW-MW22
(NCPW-
MW22-
11032021)
11/03/21
PFOS
0.51U
1.90
9, pp. 157, 188; 30, pp. 1625,
3185; 33, pp. 176-182,217
PFOA
41.5
1.90
9, pp. 157, 188; 30, pp. 1625,
3185; 33, pp. 176-182,217
1,2-DCA
0.43U
1.0
9, pp. 157, 188; 30, pp. 455,
3173; 33, pp.223-230, 269
cis-1,2-DCE
0.22U
1.0
9, pp. 157, 188; 30, pp. 455,
3173; 33, pp.223-230, 269
TCE
0.31U
1.0
9, pp. 157, 188; 30, pp. 455,
3173; 33, pp.223-230, 269
Notes:
^nits for PFOS and PFOA are ng/1 and for VOCs are fig/1.
RL = Reporting limit. The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a
specified degree of confidence (Refs. 32, p. 24; 34, p. 2).
The samples were analyzed by a non-CLP laboratory. RLs presented above are most equivalent to the SQL as defined by HRS Section 1.1 (Ref. 1,
Sections 1.1 and 2.3).
U = Indicates the analyte was analyzed for but not detected (Ref. 9, p. 242).
jig/1 = micrograms per liter
ng/1 = nanograms per liter
1,2-DCA= 1,2-dichloroethane
cis-l,2-DCE = cis-l,2-dichloeroethylene
trans-1,2-DCE = cis-l,2-dichloeroethylene
PCE = Tetrachloroethylene
TCE = Trichloroethylene
PFOS = Perfluorooctanesulfonic acid
PFOA = Perfluorooctanoic acid
CLP = Contract Laboratory Program
ID = Identifier
MW = Monitoring well
NCPW = New Castle Public Wells
VOC = Volatile organic compound
35
-------
GW-Observed Release
TAB LI! 10
OBSKRYKI) RKI.KASK INTKKMKDIATK MOMTORIVI WELL I\l ORM Yl l()\
Well II)
(l)\RL( permit
II))
Ele\ nlion
leet'
Completed
Well Depth
led lliJS
(ck\ alion-
kvl m msl)
Screened
lnler\ ;il
led lltJS
(ck\alion-kvl in
msl)
Well
Diiimeter
(in)
l.itholo^v
Rcl'crcnce(s)
NCPW-A8-MW01
(259009)
3.26
12
(-8.74)
2 to 12
(1.26 to -8.74)
1.5
Sand, silty sand
7, pp. 80, 87, 240, 264
NCPW-A8-MW02
(259010)
5.99
15
(-9.01)
5 to 15
(0.99 to -9.01)
1.5
Sand, silty sand;
little clay
7, pp. 80, 87, 241,267
NCPW-A8-MW03
(259011)
10.15
15
(-4.85)
5 to 15
(5.15 to-4.85)
1.5
Sand, silt
7, pp. 80, 87, 242, 269
NCPW-A9-MW04
(259013)
25.20
30
(4.8)
20 to 30
(5.2 to-4.8)
1.5
Intervals of sand
and clay
7, pp. 80, 87, 243,271
NCPW-MW19s
(270406)
49.88
68.17
(-18.29)
57.92 to 67.92
(-8.04 to -18.04)
2
Sand, silty sand
7, pp. 81, 87, 304-307,
323
NCPW-MW20s
(270409)
42.04
65.67
(-23.63)
55.42 to 65.42
(-13.38 to-23.38)
2
Sand, silty sand;
little clay
7, pp. 81, 87, 309-312,
324
Notes:
Elevation based on ground elevation. Elevation based on NAVD88.
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
MW = Monitoring well
NAVD88 = North American Vertical Datum
NCPW = New Castle Public Wells
36
-------
GW-Observed Release
table 11
OBSERVED RELEASE INTERMEDIATE MONITORING WELL CONCENTRATIONS
Well II)
(Siimplo ID)
S:i m pic
D:iU>
1 lil/il I'll (MIS
SubsliiiUT
CoiHTiilmlion
(iiij 1 or iiij 1)1
RL
(IlL! 1 or
uu 1)1
RcI'civiut(s)
NCPW-A8-MW01
(NCPW-A08GW-01)
8/8/17
PFOS
97.8
2.68
7, p. 351; 24, pp. 421, 1831;
33, pp. 45-51, 53
PFOA
177
2.68
7, p. 351; 24, pp. 421, 1831;
33, pp. 45-51, 53
NCPW-A8-MW02
(NCPW-A08GW-02
DL for PFOS and
PFOA;
NCPW-A08GW-02
for CVOCs)
8/8/17
PFOS
3400
47.8
7, p. 352; 24, pp. 448, 1831;
33, pp. 45-51, 55
PFOA
560
47.8
7, p. 352; 24, pp. 448, 1831;
33, pp. 45-51, 55
cis-1,2-DCE
2.7
1.0
7, p. 352; 24, pp. 105, 1831;
33, pp.59-66, 69
TCE
5.7
1.0
7, p. 352; 24, pp. 105, 1831;
33, pp.59-66, 69
NCPW-A8-MW03
(NCPW-A08GW-03)
8/8/17
PFOS
34.5
2.5
7, p. 353; 24, pp. 459, 1831;
33, pp. 45-51, 56
NCPW-A9-MW04
(AREA09-MW04-
11012021)
11/1/21
PFOS
729
17.77
9, pp. 154, 183; 30, pp. 14,
3182; 33, pp.176-182, 192
PFOA
170
1.77
9, pp. 154, 183; 30, pp. 1218,
3182; 33, pp.176-182, 191
NCPW-MW19s
(NCPW-MW19S-
081720201450)
8/17/20
PFOS
59
1.7
7, pp. 232, 362; 28, pp. 435,
1465; 33, pp.2-7, 20
NCPW-MW20s
(NCPW-MW20S-
11022021)
11/2/21
PFOS
152
1.90
9, pp. 155, 187; 30, pp.1493,
3184; 33, pp.176-184, 209
1,2-DCA
4.7
1.0
9, pp. 155, 187; 30, pp. 395,
3172; 33, pp.223-332, 257
Notes:
^nits for PFOS and PFOA are ng/1 and for VOCs are fig/1.
Data was validated in accordance with EPA Contract Laboratory Program National Functional Guidelines (NFG) for Organic Superfund Methods
Data Review, OLEM 9240.0-51, EPA-540-R-20-005, November 2020 (Ref. 33, pp. 59, 223).
RL = Reporting limit. The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a
specified degree of confidence (Refs. 32, p. 24; 34, p. 2).
The samples were analyzed by a non-CLP laboratory. RLs presented above are most equivalent to the SQL as defined by HRS Section 1.1 (Ref. 1,
Sections 1.1 and 2.3).
MDL = Method detection Limit. This is the minimum measured quantity of a substance that can be reported with 99 percent confidence that the
concentration is distinguishable from method blank results, consistent with 40 CFR Part 136 Appendix B, August 2017 (Ref. 34, p. 2).
jig/1 = micrograms per liter
ng/1 = nanograms per liter
1,2-DCA= 1,2-dichloroethane
cis-l,2-DCE = cis-l,2-dichloeroethylene
trans-1,2-DCE = cis-l,2-dichloeroethylene
PCE = Tetrachloroethylene
TCE = Trichloroethylene
PFOS = Perfluorooctanesulfonic acid
PFOA = Perfluorooctanoic acid
CLP = Contract Laboratory Program
ID = Identifier
MW = Monitoring well
NCPW = New Castle Public Wells
QAPP = Quality Assurance Project Plan
VOC = Volatile organic compound
37
-------
GW-Observed Release
TABLE 12
liAC KCROl M) DEEP MOMTORINd WELL l\l ORMATION
Well II)
(DNREC permit ID)
Election
loot1
Completed
Well
Depth
l ed lliJS
U'k'\ illloil-
llvl in nisi)
Screened lnlcr\;il
led lliJS
U'L'\alion-llvl in
nisi)
Well
Diiimeter
(in)
Lilh()lo»\
Reference! s)
\CPW-\IW'IX
(270431)
11.uy
(-87.91)
SW |o WW
(-77.91 to-87.91)
2
liilci v ;ils ol"
sand and silt
7, pp. X 1, X7,
299-303
Notes:
Elevation based on ground elevation. Elevation based on NAVD88.
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
MW = Monitoring well
NAVD88 = North American Vertical Datum
NCPW = New Castle Public Wells
38
-------
GW-Observed Release
TABLE 13
backcroi M) deep monitoring well concentrations
Well II)
(Sjimple ID)
Siimple
l):ile
1 lii/iirdoiis
Substance
CoiHTiilnilion
(ntJ 1)
RL (n-l)
Rcl'crcnce(s)
NCPW-MW18
(NCPW-
MW18-
11022021)
11/2/21
PFOS
7.14
1.82
30, pp. 1288, 3182; 33, pp.
176-184, 196
Notes:
RL = Reporting limit. The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a
specified degree of confidence (Refs. 32, p. 24; 34, p. 2).
The samples were analyzed by a non-CLP laboratory. RLs presented above are most equivalent to the SQL as defined by HRS Section 1.1 (Ref. 1,
Sections 1.1 and 2.3).
ng/1 = nanograms per liter
CLP=Contract Laboratory Program
ID = Identifier
MW = Monitoring well
NCPW = New Castle Public Wells
PFOS = Perfluorooctanesulfonic acid
TABLE 14
OBSERVED RELEASE DEEP MONITORING WELL INIORMA 1 ION
Well II)
(DNREC permit
ID)
Ele\ nt i on
I-eel'
Completed
Well Depth
kvl liijs
(ck\ alion-
kvl in nisi)
Screened
lnter\ ;il
led lliJS
(ck\ alion-kvl in
111 si)
Well
Diiimeter
(Ml)
Lilhol()»\
Refcrenc
e(s)
NCPW-MW21
55.41
111
(-55.59)
100.75 to 110.75
(-45.34 to-55.34)
2
Intervals of sand,
silty sand,
gravel; little clay
7, pp. 81,
87, 316-
321, 325
Notes:
Elevation based on ground elevation. Elevation based on NAVD88.
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
MW= Monitoring well
NAVD88 = North American Vertical Datum
NCPW = New Castle Public Wells
39
-------
GW-Observed Release
TABLE 15
OBSERVED RELEASE l)EEI» MOMTORINC WEI L CONCENTRATIONS
Well II)
(Sumpic ID)
Sample
Diile
1 lii/iirdoiis
Substance
CoiHTiilnilion
(iiiJ 1)
RL (ihj 1)
Rcl'crcncc(s)
NCPW-MW21
(NCPW-MW21-
081720200933)
8/17/20
PFOS
99
1.9
7, p. 364; 28, pp. 309, 1465;
33, pp. 2-7, 12
Notes:
RL = Reporting limit. The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a
specified degree of confidence (Refs. 32, p. 24; 34, p. 2).
The samples were analyzed by a non-CLP laboratory. RL presented above is most equivalent to the SQL as defined by HRS Section 1.1 (Ref. 1,
Sections 1.1 and 2.3).
ng/1 = nanograms per liter
CLP=Contract Laboratory Program
ID = Identifier
MW = Monitoring well
NCPW = New Castle Public Wells
PFOS = Perfluorooctanesulfonic acid
TABLE 16
BACkCROl Nl) INTERMEDIATE PI BI.IC W EI L INIORMA I ION
Well II)
(l)NREC permit
ID)
Elc\ iilion
I-eel1
Completed
Well
Depth
I'eel bijs
(ele\ alum-
reel in nisi)
Screened lnler\;il
l ee I liijs
(ele\alion-feel in
nisi)
Well
Diameter
(in)
Litholo^v
Rcl'crcncc(s)
Midvale Well 1R
(259062)
57
87
(-30)
72 to 84
(-15 to-27)
10
Intervals ui'sill
and sand; little
clay/Columbia-
Potomac
35, pp. 1, 2;
39, pp. 10,
11; 82, p. 5
Midvale Well 2R
(259060)
45
77
(-32)
60 to 75
(-15 to-30)
10
Intervals of silt,
sand and clay/
Columbia-
Potomac
35, pp. 1, 2;
39, pp. 41,
42; 82, p. 5
Collins Park Well
1
(40146)
55.25
100-125
(-44.75 to -69.75)
10
Potomac Group
35, pp. 1,2;
40, p. 7
Notes:
Elevation based on ground surface. Elevation based on NAVD88.
Indicates could not be documented with available information,
bgs = Below ground surface
ID = Identifier
in = inch
msl = mean sea level
NAVD88 = North American Vertical Datum
40
-------
GW-Observed Release
table 17
liAC KdROl M) INTERMEDIATE I'l lil.K W'EI.I. CONCENTRATIONS
Well II)
(Siimplo ID)
Siimplo
Dsile
1 lit/itidous
Suhsl since
Concent mtion
(iiij 1 or iiij 1)1
MRL/RL2
(iiij 1 or
uu 1)1
RoI'civiut(s)
Collins Park
(4427323 for
PFOS and
PFOA;
9094439-01 for
CVOCs)
9/18/19
PFOS
24
2
31, pp. 56, 58
PFOA
72
2
31, pp. 56, 58
9/30/19
TCE
<0.5
0.5
31, pp. 62, 65, 66, 67
PCE
0.6
0.5
31, pp. 62, 65, 66, 67
Midvale 1R
(7121398-01)
10/15/19
PFOS
11
2
31, pp. 144, 145
PFOA
53
2
31, pp. 144, 145
12/13/17
TCE
<0.5
0.5
31, pp. 124, 130, 131,
132
PCE
<0.5
0.5
31, pp. 124, 130, 131,
132
Midvale 2R
(10038 Well 2
for PFOS and
PFOA;
8014661-01 for
CVOCs)
10/15/19
PFOS
14
2
31, pp. 144, 145
PFOA
46
2
31, pp. 144, 145
1/30/18
TCE
<0.5
0.5
31, pp. 136, 138, 139,
140
PCE
<0.5
0.5
31, pp. 136, 138, 139,
140
Notes:
^nits for PFOS and PFOA are ng/1 and for VOCs are fig/1.
2 MRLs are associated with the PFOS and PFOA data and RLs are associated with the VOC data.
The MRLs and RLs presented above are most equivalent to the SQL as defined by HRS Section 1.1 (Ref. 1, Sections 1.1 and 2.3). However, it
cannot be documented with available information whether the above noted MRLs and RLs are sample-specific.
MRL = Minimum reporting limit - The minimum concentration that can be reported as a quantitated value for a method analyte in a sample
following analysis. This defined concentration can be no lower than the concentration of the lowest calibration standard for that analyte and can
only be used if acceptable QC criteria for this standard are met. (Ref. 38, p. 6). In accordance with EPA Method 537, laboratories are required to
demonstrate they can meet the MRL (Refs. 31, pp. 55, 143; 38, pp. 3, 18, 19).
RL = Reporting limit - The concentrations of a compound below which results are reported as nondetect or less than for this sample set (Ref. 91,
P. i).
< = less than
jig/1 = micrograms per liter
ng/1 = nanograms per liter
cis-l,2-DCE = cis-l,2-dichloeroethylene
PCE = Tetrachloroethylene
TCE = Trichloroethylene
PFOS = Perfluorooctanesulfonic acid
PFOA = Perfluorooctanoic acid
CLP=Contract Laboratory Program
ID = Identifier
QC = Quality criteria
SQL = Sample Quantitation Limit
VOC = Volatile organic compound
41
-------
GW-Observed Release
i Alii.i: is
obskryki) ri:i.i: \si: i\ti:rmi:diati: i»i iji.ic \vi:ll information
Well II)
(DNRIX permit ID)
Kle\ ;il ion
I-eel1
Completed
Well
Depth
Iccl lliJS
(dc\ at ioii-
1'v.vl in msl)
Screened
Inten :il
led lliJS
(clc\alion-ltvl in
msl)
Well
Diiimeler
(in)
Borehole
l.ithol()»\/
Screened
l-'orniiition
Rcfcrcnce(s)
Airport Industrial
Park 1
(48941)
60
122
(-62)
100 to 112
(-40 to -52)
10
Layers of
clay with
intervals of
sand and
gravel/
Potomac
Group
35, pp. 1,2;
39, pp. 5, 6;
41, p. 7
Airport Industrial
Park 2
(52445)
63.75
126
(-62.25)
104 to 114
(-40.25 to -50.25)
10
Interval of
sand
beneath
layers of
clay/Potoma
c Group
35, pp. 1,2;
39, pp. 8, 9;
41, p. 7
Jefferson Farms 2R
(241858)
44
105
(-61)
90 to 100
(-46 to -56)
12
Columbia-
Potomac
35, pp. 1,2;
39, p. 45; 82,
p. 5
Wilmington Manor 3
(10041)
24
92
(-68)
48 to 72
(-24 to -48)
17
Columbia
Group
35, pp. 1,2;
39, pp. 12,
13; 42, p. 7
Basin Road
(10060)
21.5
68 to 83
(-46.5 to-61.5)
10
Potomac
Group
35, pp. 1,2;
43, p. 7
Notes:
Elevation based on ground elevation. Elevation based on NAVD88.
Indicates could not be documented with available information
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
NAVD88 = North American Vertical Datum
42
-------
GW-Observed Release
TABLE 1')
OBSERVED RELEASE INTERMEDIATE I'l lil.K WELL CONCENTRATIONS
Well II)
(Siimplo ID)
Siiinplo
Dale
1 hi/iirdoiis
Subsl:iiUT
CoiHTiilnilion
(iiij 1 or utj 1)1
MRI./RL2
(IlL! 1 or
IIU 1)1
Rcl'crcncc(s)
Airport Industrial Park 1
(NCPW-AIPW1-
11032021)
11/3/21
PCE
7.5
1.0
30, pp. 426,3172;
33,223-232, 261
Airport Industrial Park 2
(52445 Well 2 for
PFOS;
9042776-01 for
CVOCs)
10/29/19
PFOS
90
2
31, PP. 5, 7
4/25/19
PCE
20.7
0.5
31, pp. 19,21,22,
23
TCE
1.1
0.5
31, pp. 19,21,22,
23
Jefferson Farms 2R
(NCPW-JF2R-
11032021)
11/3/21
PFOS
203
1.88
30, pp. 1590, 3184;
33, pp.176-184,
215
Wilmington Manor 3
(00552/10041 Well 3 for
PFOS.
0034348-03 for
CVOCs)
4/16/20
PFOS
1,700
2
31, pp. 158, 160
4/3/20
PCE
2.2
0.5
31, pp. 150, 152,
153
Basin Road
(NCPW-BASIN-
11022021)
11/2/21
PFOS
3,240
32.3
30, pp. 1413, 3183;
33, pp.176-184,
204
PFOA
269
1.62
30, pp. 1396, 3183;
33, pp.176-184,
203
Notes:
^nits for PFOS and PFOA are ng/1 and for VOCs are fig/1.
2 MRLs are associated with the PFOS and PFOA data and RLs are associated with the VOC data.
Data was validated in accordance with EPA Contract Laboratory Program National Functional Guidelines (NFG) for Organic Superfund Methods
Data Review, OLEM 9240.0-51, EPA-540-R-20-005, November 2020 (Ref. 33, p. 223).
Qualified data were used in accordance with EPA's fact sheet "Using Qualified Data to Document an Observed Release and Observed
Contamination". No adjustment factor for J qualified data was needed or used (Ref. 37, pp. 4, 8).
MRL = Minimum reporting limit. The minimum concentration that can be reported as a quantitated value for a method analyte in a sample
following analysis. This defined concentration can be no lower than the concentration of the lowest calibration standard for that analyte and can
only be used if acceptable QC criteria for this standard are met (Ref. 38, p. 6). In accordance with EPA Method 537, laboratories are required to
demonstrate they can meet the MRL (Refs. 31, pp. 4, 157; 38, pp. 3, 18, 19).
RL = Reporting limit - The concentrations of a compound below which results are reported as nondetect or less than in this Suburban laboratories
analysis (Ref. 91, p. 1). In the Eurofins laboratories analyses, reporting limits are the minimum levels, concentrations, or quantities of a target
variable (e.g., target analyte) that can be reported with a specified degree of confidence (Refs. 32, p. 24; 34, p. 2).
The samples were analyzed by a non-CLP laboratory. The MRLs and RLs presented above are most equivalent to the SQL as defined by HRS
Section 1.1 (Ref. 1, Sections 1.1 and 2.3). However, it cannot be documented with available information whether the above noted MRLs and RLs
are sample-specific.
jig/1 = micrograms per liter
ng/1 = nanograms per liter
PCE = tetrachloroethylene
TCE = trichloroethylene
PFOS = Perfluorooctanesulfonic acid
PFOA = Perfluorooctanoic acid
CLP=Contract Laboratory Program
ID = Identifier
QC = Quality criteria
SQL = Sample Quantitation Limit
VOC = Volatile organic compound
43
-------
GW-Observed Release
TABLE 20
l!A( KCkOl M) DEEP l»l BMC WELL INEOKMATION
Well II)
(l)NREC permit
ID)
Ele\ iilion
loci1
Com plot
eil Well
Depth
l ee I bij s
(ele\ aim
n-leel in
nisi)
Screen oil
lutein ill
l ee I bij s
(ele\alum-reel in
msl)
Well
Diiimeter
(in)
Borehole
Lilhol()»\/
Screened
I'o nil ii (ion
kel'erencets)
Llangollen Well 6R
(259051)
53.6
172
(-118.4)
105 to 145
(-51.4 to -91.4)
12
Intervals of sand,
silt, gravel,
clay/Upper
Potomac
35, pp. 1, 2;
39, pp. 46-
49; 82, p. 5
Llangollen Well 2
(35081)
61.5
164
(-102.5)
122 to 160
(-60.5 to -98.5)
10
Intervals of
sandy clay, sand,
gravel,
clay/Upper
Potomac
35, pp. 1, 2;
39, p. 50; 44,
p. 7; 82, p. 5
Llangollen Well 7
(10049)
45
180
(-135)
115 to 175
(-70 to-130)
12
Intervals of
coarse sand and
gravel, clay, fine
sand/Upper
Potomac
35, pp. 1, 2;
39, p. 51; 49,
p. 51; 44, p.
7; 82, p. 5
Wilmington
Airport 3R
(108453)
44
160
(-116)
135 to 154
(-91 to-110)
12
Intervals of fine
to medium sand
and
clay/Potomac
35, pp. 1, 2;
39, pp. 52,
53; 82, p. 6
Llangollen G3R
(240617)
15.8
160
(-144.2)
102-157
(-86.32 to -141.2)
12
Medium to
coarse sand,
some gravel and
clay
intervals/Upper
Potomac
35, pp. 1, 2;
39, pp. 54,
55; 82, p. 5
Wilmington
Airport 1
(10029)
70.5
187 to 197
(-116.5 to-126.5)
8
Potomac Group
35, pp. 1,2;
45, p. 7
Notes:
Elevation based on ground elevation. Elevation based on NAVD88.
Indicates could not be documented with available information
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
NAVD88 = North American Vertical Datum
44
-------
GW-Observed Release
TABLE 21
liAC KCROl M) DLLP PI liLIC WELL CONCENTRATIONS
Well II)
(Snmple ID)
S;imple
l):ile
1 hiznrilous
Substance
CoiHTiitriilion
(nu 1 or uu 1)1
MRL
-------
GW-Observed Release
1 Alii.i: 22
OBSKRYKI) RKI.AKSK DKIT I>1 lil.lC W'KI.L INFORMATION
Well II)
(D\r i:c
permit ID)
Kle\ nt i on
I-cot1
Completed
Well Depth
feel lliJS
(ele\ alion-
I'eel in nisi)
Screened
lnler\ ;il
I'eel liijs
(ele\alum-feel in
nisi)
Well
Diiimete
r (in)
Borehole
l.ilh()lo»\/
Screened
l-'orm;ilion
Rcl'crcnce(s)
Jefferson I'ann
1R
(237552)
36.75
140
(-103.25)
92 lo 140
(-55.25 to-
103.25
12
Sand, minimal
clay/Potomac
35 QQ. 1 2
39^pp.56-'
58; 82, p. 5
Frenchtown
Road
(35665)
40
135
(-95)
99-125
(-59 to -85)
12
Intervals of
sand and clay/
Potomac
Group
35, pp. 1,2;
39, p. 15; 43,
p. 7
Schoolhouse
Lane
(137)
37.5
88 to 128
(-50.5 to -90.5)
12
Intervals of
sand and clay/
Potomac
Group
35, pp. 1,2;
39, pp. 34,
35; 43, p. 7
Crossroads
(242100)
27
137
(-110)
100 to 130
(-73 to -103)
12
Intervals of
sand and clay
35, pp. 1,2;
39, p. 30, 31
Notes:
Elevation based on ground elevation. Elevation based on NAVD88.
Indicates could not be documented with available information
bgs = Below ground surface
DNREC = Delaware Department of Natural Resources and Environmental Control
ID = Identifier
in = inch
msl = mean sea level
NAVD88 = North American Vertical Datum
46
-------
GW-Observed Release
TABLE 23
OBSERVED RELEASE l)EEI» PI lil.K WELL CONCENTRATIONS
Sample ID
Siimplo
Dale
1 lazardous
Suhsl since
Conccnlmlion
(nu or u» 1)1
MRL/RL/
LOQ (iiij 1)
Rclcivncc(s)
Jefferson Farm
1R
(3044531)
6/18/14
PFOS
200
401
31, pp. 175, 177
Frenchtown
Road
(GW 9975950)
1/28/19
PFOS
520
182
32, pp. 11, 15
Schoolhouse
Lane
(NCPW-
SCHOOL-
11022021 DL)
11/2/21
PFOS
878
8.493
30, pp. 1369, 3183; 33,
pp. 176-184, 201
Crossroads
1/28/19
PFOS
680
172
32, pp. 10,15
PFOA
290
OO
32, pp. 10, 15
Notes:
1 Indicates the value is an MRL.
2 Indicates the value is a limit of quantitation.
3 Indicates the value is an RL.
The samples were analyzed by a non-CLP laboratory. The MRLs, LOQs, and RLs presented above are most equivalent to the SQL as defined by
HRS Section 1.1 (Ref. 1, Sections 1.1 and 2.3). However, it cannot be documented with available information whether the above noted MRLs,
LOQs, and RLs are sample-specific (Ref. 1, Sections 1.1 and 2.3).
LOQ = Limit(s) of quantitation Reporting Limit: The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that
can be reported with a specified degree of confidence (Ref. 34, p. 2).
MRL = Minimum reporting limit - The minimum concentration that can be reported as a quantitated value for a method analyte in a sample
following analysis. This defined concentration can be no lower than the concentration of the lowest calibration standard for that analyte and can
only be used if acceptable QC criteria for this standard are met (Ref. 38, p. 6). In accordance with EPA Method 537, laboratories are required to
demonstrate they can meet the MRL (Refs. 31, p. 174; 38, pp. 3, 18, 19).
RL = Reporting limit. The minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a
specified degree of confidence (Refs. 32, p. 24; 34. p. 2).
jig/1 = micrograms per liter
ng/1 = nanograms per liter
CLP=Contract Laboratory Program
ID = Identifier
PFOS = Perfluorooctanesulfonic acid
PFOA = Perfluorooctanoic acid
QC = Quality criteria
SQL = Sample Quantitation Limit
VOC = Volatile organic compound
47
-------
GW-Observed Release
Additional Supporting Data
Groundwater investigations for VOCs and PFAS have been conducted by various entities at several
properties throughout New Castle, Delaware. The data from these numerous investigations were not used
to score the Site because sufficient data presented above document a significant increase in the
contaminated plume with no identified source scored in this HRS documentation record (Tables 7 to 23 of
this HRS documentation record). However, analytical data does exist that shows PFAS and VOC
groundwater contamination throughout New Castle, Delaware. The discussion of the below properties, and
their use and handling of hazardous substances associated with the Site, are provided as additional
supporting data. The data also provides support for evaluating the Site as a contaminated groundwater
plume with no identified sources because the significant increase cannot be attributed to specific source.
NCCA
VOCs, such as PCE, TCE, and cis-l,2-DCE, have been detected in monitoring wells installed at New Castle
County Airport (NCCA) as early as 2012 (Ref. 46, pp. 31, 51, 67). Monitoring wells containing
concentrations of CVOCs are primarily located along the southeastern and southwestern corner of the
property (Ref. 46, pp. 51, 67). The contaminated monitoring wells are screened at depths ranging from 12
to 22 feet bgs (55.52 to 45.52 msl) to 100 to 110 feet bgs (-38.62 to-48.62 msl) (Ref. 46, pp.31, 198-223).
Lithology of the wells show intervals of sand, silt, and clay (Ref. 46, pp. 198-223). Groundwater samples
collected in 2017, 2018, and 2019 from the NCCA monitoring wells in the southwestern portion of the
property continued to show concentrations of PCE (up to 650 jj.g/1), TCE (up to 45 jj.g/1), cis-l,2-DCE (up
to 10 jj.g/1), and vinyl chloride (up to 2 jj.g/1) (Ref. 47, pp. 81, 82, 83, 97). The monitoring wells are screened
in the Columbia and Upper Potomac formations (Ref. 47, pp. 78, 79, 98-102).
In 2015, EPA collected groundwater samples from eleven monitoring wells located along the northern,
western, and southern boundaries at the NCCA for PFAS (formerly referred to as PFCs [perfluorinated
compounds]) (Ref. 48, pp. 16, 18). Analytical results showed the presence of PFOS and PFOA at
concentrations up to 268 ng/1 (equivalentto 0.268 jj.g/1) and 96 ng/1 (equivalent to 0.096 jj.g/1), respectively.
The monitoring wells are screened at depths ranging from 16 to 6 feet bgs (52.27 to 62.87 ft msl) to 100 to
110 feet bgs (-38.86 to -48.86 ft msl) (Ref. 48, pp. 16, 18). Additionally, a sample collected in 2014 from a
residential drinking water well north of the airport contained 41 ng/1 PFOA (equivalent to 0.041 jj.g/1) (Ref.
48, pp. 12, 18). Groundwater collected from one monitoring well, MW-10, was also analyzed for VOCs.
Analytical results showed the presence of cis-l,2-DCE (5.2J jj.g/1), PCE (290 jj.g/1), and TCE (15 jj.g/1) (Ref.
48, pp. 16, 19).
DANG
In 2014, the Delaware Air National Guard (Tenant) Wilmington Airport Site (DANG) (EPA ID:
DE0000306286/DE0572824274) - 1850-Present, which occupies the northeast portion of the NCCA,
conducted a Remedial Investigation/Feasibility Study to investigate numerous identified areas of
contamination on the property (Ref. 49, pp. 9, 93). Groundwater samples collected from direct-push borings
and from existing and newly installed monitoring wells contained concentrations of cis-l,2-DCE (up to 3.7
jag/1), TCE (10.3 up to jag/1), and PCE (5.8 up to ng/1) (Ref. 49, pp. 65-67, 71, 73, 98, 99, 101, 102).
Monitoring wells installed as part of the RI/FS are screened at depths ranging from 19 to 45 feet bgs (ground
surface elevations ranging from 32.34 to 12.26 msl) (Ref. 49, pp. 46, 113-136, 237-248). Lithology of the
wells show primarily sand with some gravel, minimal intervals of clay (Ref. 46, pp. 114, 116, 118, 120,
122, 124, 126, 128, 130, 132, 134, 136). Groundwater samples collected from monitoring wells at DANG
from 2015 to 2020 continued to show concentrations of cis-l,2-DCE, TCE, and PCE, as well as vinyl
48
-------
GW-Observed Release
chloride (up to 14 jj.g/1), with MW 403 containing the highest and most consistent concentrations of CVOCs
(Ref. 50, pp. 52-58, 35). Monitoring well 403 is screened between 75 and 105 feet bgs (Ref. 50, p. 35).
In 2016, DANG began monitoring groundwater at the facility for PFAS in an effort to identify potential
sources of PFAS in public water supply wells in the area surrounding the base (Ref. 51, p. 9). PFOS and
PFOA were detected in all groundwater samples collected from monitoring wells located on the base, with
the exception of one well located on the eastern boundary of the property, at concentrations up to 4,600 ng/1
(equivalent to 4.6 jj.g/1) for PFOA and 11,000 ng/1 (equivalent to 11 jj.g/1) for PFOS (Ref. 51, pp. 35, 41).
The monitoring wells at the facility are completed within the Columbia and Potomac Formations ranging
in depth from shallow (less than [<] 60 ft bgs), intermediate (75 to 105 ft bgs), and deep (> 200 ft bgs) (Ref.
18, pp. 21, 23, 27; 51, pp. 35, 41). In 2017, DANG conducted a PFAS site investigation to assess PFAS in
groundwater at the base and investigate potential on-base release locations (Ref. 52, p. 13). Groundwater
samples were collected from both existing monitoring wells at the base, as well as newly installed temporary
wells (Ref. 52, p. 36). PFOS was detected up to 16,900 ng/1 (equivalent to 16.9 jj.g/1) and PFOA up to 1,240
ng/1 (equivalent to 1.24 jag/1) (Ref. 52, pp. 72, 73, 85-88, 746, 747, 753, 124-142, 1402, 1405, 1406, 1407,
1426, 1427, 2098, 2101, 2102, 2103, 2108). The newly installed temporary wells were installed to depths
of 15 to 40 feet bgs (Ref. 52, pp. 108-114). Lithology of the wells show intervals of sand and clay (Ref. 52,
pp. 108-114).
DEARNG
In 2021, the Delaware Army National Guard, Duncan Readiness Center and Army Aviation Support
Facility (ARNG) - 1971-Present conducted an SI to determine the presence or absence of PFOA, PFOS,
and other PFAS at the Duncan Readiness Center (RC) and Army Aviation Support Facility (AASF) located
along the northwest boundary of the NCCA; the Delaware ARNG (DEARNG) leases the property from the
NCCA (Ref. 53, pp. 9, 23). Groundwater samples were collected from temporary monitoring wells and one
existing monitoring well (Ref. 53, pp. 48, 55). Analytical results of groundwater samples showed PFOS up
to 150 ng/L and PFOA up to 280 ng/1 (Ref. 53, pp. 65, 66). Temporary wells were installed between 20 and
45 ft bgs (33.25 feet elevation to 19.79 feet elevation) (Ref. 53, p. 53, 137-143, 154, 174, 176, 178, 180,
182, 184, 186). Lithology of the wells show intervals of sand, silty sand, sandy clay (Ref. 53, pp. 137-143,
173, 175, 177, 179, 181, 183, 185).
600 Dupont Highway/Jackson Ave, and North Dupont Highway
In 2014, a Brownfields investigation was conducted for an automobile service station property located at
600 Dupont Highway (Ref. 54, pp. 8, 9, 82). The property is located adjacent to a dry cleaners (Ref. 54, p.
83). As part of the investigation, four monitoring wells were installed to depths of 15 to 30 ft bgs (42 to
26.71 feet elevation) (Ref. 54, pp. 94, 241-244). Cross-sections and boring logs wells show the lithology is
intervals of sands, silts, and clays (Ref. 54, pp. 86 87, 218, 219, 222, 223, 224, 229, 230). Analytical results
of groundwater samples contained concentrations of cis-l,2-DCE (up to 4.4 jj.g/1), TCE (up to 1.1 jj.g/1),
and PCE (up to 35 jj.g/1) (Ref. 54, pp. 109). Groundwater samples collected from the existing monitoring
wells throughout 2014, 2015, and 2016 continued to contain concentrations of cis-l,2-DCE, TCE, and PCE,
as well as some detections of 1,2- DCA (Ref. 55, pp. 10). Analytical results from the samples collected in
2017, from both existing and newly installed monitoring wells contained concentrations of cis-l,2-DCE
(up to 4.8 jag/1), TCE (up to 15 jag/1), and PCE (up to 970 jag/1) (Ref. 55, pp. 9, 10, 97, 112, 123, 132, 145,
158, 536). The newly installed wells were installed at similar elevations and similar lithology as the existing
wells (Ref. 55, pp. 9, 12-18, 19-21, 23). In 2018, two additional wells were installed, and groundwater
samples were collected from the nine monitoring wells (Ref. 56, pp. 10, 721). Analytical results of the
monitoring well samples showed concentrations of cis-l,2-DCE (up to 6.6 jj.g/1), TCE (up to 150 jj.g/1), PCE
(up to 450 jag/1), and 1,2-DCA (up to 0.83 jag/1) (Ref. 56, pp. 12, 17, 270, 279, 283, 295, 324, 336, 359,
49
-------
GW-Observed Release
390, 399, 408, 435). The newly installed wells were installed at similar elevations and similar lithology as
the existing wells (Ref. 56, pp. 28-30, 32-33, 48).
287 Christiana Road - Community Plaza
Since 2012, VOCs, such as PCE, TCE, and cis-l,2-DCE, have been detected in monitoring wells at installed
the Community Plaza at 287 Christiana Road, that contains a dry cleaners (Refs. 57, pp. 4, 11, 18, 22; 58,
pp. 13, 29). In 2014, analytical results of the groundwater samples collected as part of an RI from existing
monitoring wells and newly installed monitoring wells contained concentration of cis-l,2-DCE (up to 290
jj.g/1), trans-l,2-DCE (58 up to jj.g/1), TCE (up to 17 jj.g/1), PCE (up to 180 jj.g/1), and vinyl chloride (up to
0.77 jig/1) (Ref. 59, pp. 142, 143, 1895, 1930, 1961, 1990, 2020, 2027, 2054, 2061, 2100, 2852, 2853).
Monitoring well at the property are screened between 11 and 38 feet bgs (34.7 to 11.9 feet elevation (Refs.
57, pp. 38-40; 58, pp. 53-55; 59, pp. 129, 192-196). The lithology of the wells shows intervals of sand, silt
and clay (Refs. 57, pp. 31-36; 58, pp. 46-51; 59, pp. 159-190). The most recent available groundwater
samples collected from a select number of monitoring wells in 2020 showed concentrations of cis-l,2-DCE
(up to 240 jj.g/1), TCE (up to 130 jj.g/1), PCE (up to 1,200 jj.g/1), and vinyl chloride (up to 0.47 jj.g/1) (Ref.
60, pp. 17, 34, 37, 42, 43).
50
-------
GW-Observed Release
Attribution
The East Basin Road Groundwater Site is a documented release of PFOA, PFOS, and CVOCs that include
PCE, TCE, cis-l,2-DCE, trans-1,2-DCE, 1,2-DCA, and vinyl chloride. Observed releases to groundwater
have been established resulting in the contamination of nine active municipal wells (Section 3.1.1 Tables
19 and 23 of this HRS documentation record). The specific source(s) causing the significant increase of the
contamination at the East Basin Road Groundwater Site cannot reasonably be attributed at this time because
of the presence of multiple known and possible sources of PFAS and CVOCs and the mixing of
groundwater.
In an effort to identify the source(s) of PFAS and CVOCs in groundwater in New Castle, Delaware, DNREC
has conducted or overseen investigations at the following locations:
NCCA
DANG
DEARNG
BMX Fire Training Area
600 Dupont Highway/Jackson Ave. and North Dupont Highway
Community Plaza
NCCA
In 1941, the New Castle County Airport Commission (NCCA) acquired the land for use as a civilian airport
(Ref. 97, p. 6). From 1941 to 1946, the NCCA was occupied and operated as the U.S. Army, New Castle
Army Airfield (EPA ID: DEN000305948) under the War Department (known today as the Department of
Defense) (Refs. 47, p. 17; 97, p. 6). The U.S. Army utilized the property as an airbase and training facility
from 1941 to 1946 (Refs. 47, pp. 17, 18; 97, pp. 6, 9). After World War II, from 1946 to 1949, the War
Department transitioned the airfield back to New Castle County as a civilian airport [In 1947, the Army Air
Corps split from the Department of the Army and became the Department of Air Force - U.S. Air Force,
New Castle Army Airfield (EPA ID: DEN000305948)] (Ref. 97, p. 9). However, the military, including
the Delaware Air National Guard (DANG) and the Delaware Army National Guard (DEARNG), has
continued to maintain a presence at the airport (Ref. 47, p. 18; 97, pp. 9, 10). The Site remains an active
airport facility, which is currently owned by NCC and since 1995 the Site has been operated and leased by
Delaware River and Bay Authority (DRBA) (Ref. 47, pp. 17, 18). A Preliminary Assessment (PA) was
conducted by EPA Region III in 1988 at the then New Castle County/Greater Wilmington Airport. The
EPA was investigating formerly owned DOD facilities to determine the historic use and disposal of
hazardous substances. The EPA PA indicates that materials and fuels containing hazardous substances had
been managed at the Site during World War II under the DOD and following the development of the
municipal airport thereafter (post-1946). The materials listed in the EPA PA included solvents, paints, and
paint strippers composing of unknown constituents. Past tenants were also reported to have used cleaning
solvents and paint removers that potentially contained hazardous substances. The former tenants listed in
the EPA PA and known current tenants subsequent to the EPA PA include Atlantic Aviation, Aero-Taxi,
Hawker Beechcraft Services, Dawn Aeronautics, Rollins, Hercules, and Rapidgear Repair (Ref. 47, p. 18).
In addition to the use and possible releases of chlorinated solvents at the NCCA, many of the airport
buildings and hangars contain foam fire suppressant systems (Ref. 8, pp. 12, 48, 77, 210, 211, 223, 232,
237). Since the properties use as a military airbase, there have been several plane and helicopter crashes at
51
-------
GW-Observed Release
the airport. The last crash occurred in 2007, which showed the use of foam (Ref. 8, pp. 12, 48, 92, 93).
Additionally, there is a fire training area located on the north end of Runway #19 that airport personnel
have confirmed this area was used by the airport for fire training activities and that aqueous film forming
foam (AFFF) may have been used (Ref. 8, pp. 11, 41).
As presented in Additional Supporting Information, CVOCs and PFOS and PFOA have been detected
in groundwater samples collected from monitoring wells located at the NCCA. However, shallow and deep
soil samples collected in 2013 (34 samples) and 2016 (two samples) did not contain concentrations of
CVOCs (Refs. 46, pp. 45-47, 67; 47, pp. 80, 96). Collected soil samples have not been analyzed for PFAS
(Refs. 46, p. 16; 47, pp. 44, 45).
DANG
DANG occupies approximately 57 acres at the northeast corner of the NCCA (Ref. 7, p. 70). A PA
conducted by DNREC in 2015 indicated a possible fire training area located on the DANG property (Ref.
8, pp. 11, 16). However, in 2016, DANG conducted a separate PA that indicated there is no evidence that
a fire training area is, or was located, within the current footprint of the DANG property boundary and that
DANG utilized the fire training area located on NCCA property, north of the runway (Ref. 73, p. 13). A SI
conducted by DEARNG indicates that DANG uses an area to the south of the DEARNG property for fire
training (Ref. 53, pp. 32, 35). The DANG PA did indicate several areas where AFFF has been stored or
released and may include crash sites, hangars, fuel spill areas, hazardous waste storage facilities,
firefighting equipment testing areas, and others (Ref. 73, pp. 15, 16, 33). Of particular note is the Wash
Rack area which is a concrete area, approximately 175 feet by 120 feet. The area is not sheltered and there
is a central drain. According to fire station personnel, annual nozzle testing using AFFF was conducted at
the Wash Rack until approximately two years ago. The Wash Rack has one drain that is equipped with a
valve that can divert drainage to either the storm water system or the sanitary sewer. AFFF was likely
diverted into the sanitary system; however, had the potential to drain to the South Stormwater Retention
Basin (Outfall 2) if the valve in the drain was not diverted. Gaps between the concrete were visible in the
Wash Rack area (Ref. 73, pp. 16, 33, 36, 37). The DNREC PA indicates that two buildings on the DANG
property contain AFFF and that at one of the buildings, a full systems check dispensed its entire contents
of AFFF after installation (Ref. 8, pp. 11, 42). However, the DANG PA indicates these two buildings do
not contain AFFF but rather high expansion foam (HEF) suppression systems (Ref. 73, pp. 16, 17 18, 33).
Soil samples collected in 2017, contained concentrations of PFOS and PFOA at several areas (Ref. 52, pp.
70, 71, 85, 86, 87). As presented in Additional Supporting Information, PFOS, and PFOA have been
detected in groundwater samples collected from monitoring wells located at DANG.
An area of CVOC contaminated soil was documented on the DANG property, referred to as IRP Site 4B,
where the improper disposal of waste solvents, particularly the burial of an aircraft fuel cell containing
spent solvent, resulted in contamination of soil and groundwater with the CVOCs such as PCE, TCE, and
their daughter products cis-l,2-DCE and vinyl chloride (Ref. 74, pp. 10, 24, 26). CVOCs were detected in
soil samples at this location as early as 2004 with one soil sample collected in 2011 containing PCE at 3,000
(ig/kg, TCE at 120,000 (ig/kg, and cis-l,2-DCE at 22,000 (ig/kg (Ref. 74, pp. 28, 32). In 2011 and 2012,
approximately 100 tons of contaminated soil was removed and a soil vapor extraction system (SVE) was
installed (Ref. 74, pp. 10, 28). Additionally in 2011 and 2012, bioremediation was conducted of the
groundwater in the vicinity of IRP Site 4B (Ref. 74, p. 10). As presented in Additional Supporting
Information, CVOCs, such as PCE, TCE, and cis-l,2-DCE have been detected in groundwater samples
collected from monitoring wells located at DANG.
52
-------
GW-Observed Release
DEARNG
DEARNG encompasses approximately 17.3 acres adjacent to the NCCA (Ref. 53, pp. 9, 23). Soil samples
collected on the property as part of a SI conducted by DEARNG in 2021, showed concentrations of PFOS
and PFOA (Ref. 53, pp. 55, 64). Soil samples were not analyzed for VOCs as part of the SI (Ref. 53, pp.
45). The PFOS and PFOA detected in soil on the DEARNG property are possibly associated with a
helicopter crash that occurred in the 1970s and the fire suppression system in the hangar, which was
discharged in 2011 when it was retrofitted with Jet-X 2 percent high expansion foam (Ref. 53, p. 31). As
presented in Additional Supporting Information, PFOS and PFOA were also detected in groundwater
samples collected from monitoring wells located at DEARNG.
BMX Fire Training Area
The BMX Fire Training Area (referred to as Area 9) is owned by New Castle County (Ref. 8, p. 10). Local
fire fighters confirmed that the area was used as a fire training area but could not confirm whether AFFF
containing PFAS was used during fire training exercises. Historically, the property contained a three-story
incinerator and two ammunition bunkers used by the military (Refs. 7, p. 19; 8, p. 40). The BMX fire
Training Area was one of the locations investigated by DNREC in 2017 as part of the SI conducted by
DNREC. Soil samples, primarily surface soil (0 to 2 feet bgs), collected from the BMX fire training area
did not contains concentrations of CVOCs (Ref. 7, pp. 46, 69, 73, 89, 90, 94, 95). Soil samples collected
by DNREC as part of the SI were not analyzed for PFAS (Ref. 7, p. 26). As presented in Section 3.1, PFOS
and PFOA were also detected in groundwater samples collected from monitoring wells located at the BMX
Fire Training Area as part of the DNREC SI.
600 Dupont Highway/Jackson Ave, and North Dupont Highway
The 600 Dupont Highway property has been used as an automobile service station, gas station, and towing
facility since the early 1960s (Ref. 54, p. 9). In 2014, as part of a Brownfields investigation, soil samples
were collected from the property; two of the collected samples showed detections of PCE at 0.04 milligrams
per kilogram (mg/kg) and 0.011 mg/kg (Ref. 54, pp. 83, 91, 104, and 105). A dry cleaners is across Jackson
Ave from the property (Ref. 54, p. 83).
To further investigate chlorinated solvent contamination detected in groundwater monitoring wells in the
vicinity of the 600 North DuPont Highway property, sampling was conducted at a property directly adjacent
to the dry cleaners (Ref. 56, pp. 1, 9, 10). One of two collected soil samples, which was collected near the
corner of the dry cleaners, contained concentrations of PCE at 0.1 mg/kg (Ref. 56, pp. 10, 16).
As presented in Additional Supporting Information, CVOCs, such as PCE, TCE, and cis-l,2-DCE have
been detected in groundwater samples collected from in monitoring wells located on these properties in the
vicinity of the dry cleaners.
A search of Delaware's Environmental Navigator Database did not provide any results for the dry cleaning
facility (Ref. 75, pp. 1,2).
Community Plaza
An RI was conducted at Community Plaza, a strip mall that contains a dry cleaners, at 287 Christiana Road
in New Castle, Delaware in 2014 (Ref. 59, pp. 8, 111). Three soil samples collected from two soil borings
closest to the dry cleaners contained concentrations of PCE (0.14 mg/kg), TCE (0.075 mg/kg), cis-l,2-DCE
(up to 0.074 mg/kg), and trans-l,2-DCE (0.75 mg/kg) (Ref. 59, pp. 120, 139). As presented in Additional
53
-------
GW-Observed Release
Supporting Information, CVOCs, such as PCE, TCE, cis-l,2-DCE, trans-1,2-DCE, and vinyl chloride
have been detected in groundwater samples collected from monitoring wells located on this property.
Other Possible Sources
As shown in Reference 5, there are too many known or possible sources within the vicinity of the Site to
reasonably attribute the significant increase in the PFAS and CVOCs in the groundwater to one or more
specific source (s).
Industrial facilities that manufacture organic chemicals, plastics, and synthetic fibers may have PFAS at the
facility for numerous reasons such as: to specifically manufacture PFAS through electrochemical
fluorination, telomerization, or other processes in production of such products; as a polymerization
processing aid; for the production of plastic, rubber, and resin; and in the manufacturing of commercial
chemical products (e.g., carpet cleaning sprays, cleaning agents, protective coatings) (Ref. 62, pp. 13, 32).
Twenty seven facilities in the vicinity of the Site are identified in the EPA Enviromapper database as
plastics or resin manufacturing facilities, or chemical plants or manufacturers (Ref. 5 p. 2; 11).
PFAS are found in chemicals used as wetting agents, mist and fume suppressants to prevent air emissions
of toxic metal fumes, agents to reduce mechanical wear, and surface coatings to impart certain
characteristics (e.g., reduced corrosion, enhanced appearance) at a variety of metal finishing facilities such
as electroplating, electroless plating, anodizing, coating, printed circuit board manufacturing, and chemical
etching and milling (Ref. 62, pp. 13, 42). Eight facilities in the vicinity of the Site are identified in the EPA
Enviromapper database as metal coating, fabrication, or smelting facilities, or as electronic manufacturers
(Ref. 5, p. 2; 11).
Textile mills use PFAS chemicals to impart outdoor gear, clothing, household, and other textile products
with water, oil, soil, and heat resistance (Ref. 62, pp. 13, 54). Two facilities in the vicinity of the Site are
identified in the EPA Enviromapper databased as textile facilities (Refs. 5, p. 2; 11).
PFAS lower the surface tension and improve wetting and rinse-off in a variety of industrial and household
cleaning products, including car wash products, as they reduce streaks and improve reflection of cleaned
glass (Refs. 93, p. 3; 94, pp. 3, 4). Approximately 15 car washes are located within New Castle Delaware
(Ref. 72, p. 2).
PCE, which breaks down into TCE, cis/trans-1,2-DCE, DCE, and vinyl chloride, is a commercially
important chlorinated hydrocarbon solvent and chemical intermediate. It is used as a dry cleaning and
textile-processing solvent and for vapor degreasing in metal-cleaning operations (Ref. 65, pp. 279, 302; 95
p. 39). Historically, the most important use of TCE has been vapor degreasing of metal parts, which is
closely associated with the automotive and metals industries (Ref. 66, p. 324). TCE has also been used by
the textile processing industry to scour cotton, wool, and other fabrics, as well as in waterless drying and
finishing operations (Ref. 66, p. 324). TCE has been used as a solvent or a component of a solvent blend
for adhesives, lubricants, paints, varnishes, paint strippers, pesticides, and cold metal cleaners and in the
production of polyvinyl chloride (Ref. 66, p. 324). The EPA Enviromapper databased identified a total of
26 facilities that fell into the category of metal coating and fabrication, dry cleaning, auto repair, chemical
plants or manufacturers, and textiles facilities (Refs. 5, p. 2; 11).
Summary
As presented above, many known or possible current and historical users of PFAS and CVOCs are located
in the area of the Site. Any releases of PFAS, PCE, or other CVOCs to the Columbia/Potomac Aquifer
System from known or possible users in this area would likely have co-mingled over time (Section 3.1.1
54
-------
GW-Observed Release
of the HRS documentation record). This co-mingling could be the result of changes in local groundwater
flow directions caused by pumping groundwater from the aquifer from the numerous public supply wells
located within the area ofthe Site (Ref. 18, pp. 17, 36, 37, 38). The specific source(s) causing the significant
increase of the contamination at the East Basin Road Groundwater Site cannot reasonably be attributed at
this time because of the presence of multiple known and possible sources of PFAS and CVOCs and the
mixing of groundwater. PFAS and CVOCs have been commonly used for many purposes and released to
the environment from numerous sources where they persist for long periods of time in groundwater (Refs.
61, pp. 1, 3; 65, pp. 23, 294; 66, pp. 23, 24, 327; 67, pp. 17, 103; 68, pp. 22, 23, 189; 69, pp. 11, 105; 70,
pp. 10, 154, 155; 71, pp. 2, 3; 95, p. 39 ). The persistence of PFAS and CVOCs in groundwater contribute
to the difficulty in attributing the PFAS and CVOC contamination in groundwater to a specific source.
Hazardous Substances Released
Tetrachloroethylene (PCE)
Trichloroethylene (TCE)
cis-l,2-Dichloroethylene (cis-l,2-DCE)
trans-1,2-Dichloroethylene (trans-1,2-DCE)
1,2-dichloroethane (1,2-DCA)
Vinyl Chloride
Perfluorooctanesulfonic acid (PFOS)
Perfluorooctanoic acid (PFOA)
Ground Water Observed Release Factor Value: 550
55
-------
GW-Waste Characteristics
3.2 WASTE CHARACTERISTICS
3.2.1 Toxicitv/Mobilitv
TOXICITY AM) N
TABLE 24
OUII.ITY-WASTE CHARACTERISTICS
1 hi/iiriloiis Substitute
Source
Nil m hers
Toxicity
I'iiclor
\ :illie
Mobility
Tudor
Ysilue1
Toxicity/
Mobility
References
Tetrachloroethylene
(PCE)2
1, OR
100
1.0
100
1, Section
2.4.1.1; 2, p.
17
Trichloroethylene
(TCE)2
1, OR
1,000
1.0
1,000
1, Section
2.4.1.1; 2, p.
20
cis-1,2-
Dichloroethylene
(cis-1,2-DCE)2
1, OR
1,000
1.0
1,000
1, Section
2.4.1.1; 2, p. 5
trans-1,2-
Dichloroethylene
(trans-1,2-DCE)2
1, OR
100
1.0
100
1, Section
2.4.1.1; 2, p. 8
1,2-dichloroethane
(1,2-DCA)2
1, OR
100
1.0
100
1, Section
2.4.1.1; 2, p. 1
Vinyl Chloride2
1, OR
10,000
1.0
10,000
1, Section
2.4.1.1; 2, p.
23
Perfluorooctanesulfonic
acid (PFOS)2
1, OR
10,000
1.0
10,000
1, Section
2.4.1.1; 2, p.
11; 88, pp. 1-
3
Perfluorooctanoic acid
(PFOA)2
1, OR
10,000
1.0
10,000
1, Section
2.4.1.1; 2, p.
14; 88, pp. 1-
3
Notes:
OR = Observed Release
1 Hazardous substances meeting the criteria for an observed release by chemical analysis to an aquifer underlying a source are assigned a mobility
factor value of 1 (Refs. 1, Section 3.2.1.2).
2As presented in Sections 2.2 and 3.1.1 of this Hazard Ranking System (HRS) documentation record, PCE, TCE, cis-l,2-DCE, trans-1,2-DCE,
1,2-DCA, vinyl chloride, PFOS, and PFOA were detected in the contaminated groundwater plume, also evaluated as the source at this Site.
56
-------
GW-Waste Characteristics
3.2.2 Hazardous Waste Quantity
TABLE 25
1 IA/AKDOI S WASTE Ql AM ITY
Source Number
Source Hazardous Waste
Quantity (IIWQ) Value
(Ref 1 Scclion 2 4 2 15)
Is source hazardous
constituent quantity data
complete? (Yes \n)
1
>0
No
Sum of Values:
> 0, rounded to 1 (Ref. 1, Section 2.4.2.2)
The sum corresponds to a hazardous waste quantity factor value of 1 in Table 2-6 of the HRS (Ref. 1,
Section 2.4.2.2). However, because the hazardous constituent quantity is not adequately determined
(Section 2.4.2.1.1 of this HRS documentation record) and targets are subject to Level I concentrations
(Section 3.3.2.2 and Table 27 of this HRS documentation record), a pathway hazardous waste quantity
factor value of 100 is assigned if it is greater than the hazardous waste quantity value from Table 2-6 (i.e.,
1) (Ref. 1, Section 2.4.2.2). Therefore, a hazardous waste quantity factor value of 100 is assigned for the
ground water migration pathway (Ref. 1, Section 2.4.2.2).
Hazardous Waste Quantity Factor Value: 100
3.2.3 Waste Characteristics Factor Category Value
PFOS, PFOA, and vinyl chloride correspond to the toxicity/mobility factor value of 10,000, as shown
previously (Section 3.2.1 of this HRS documentation record).
Toxicity/Mobility Factor Value (10,000) x Hazardous
Waste Quantity Factor Value (100): 1 x 106
The product (1 x 106) corresponds to a Waste Characteristics Factor Category Value of 32 in Table 2-7 of
the HRS (Ref. 1, Section 2.4.3.1).
Hazardous Waste Quantity Factor Value: 100
Waste Characteristics Factor Category Value: 32
57
-------
GW-Targets
3.3 TARGETS
The Artesian Water Company supplies drinking water to 209,706 persons (Ref. 80, p. 1). Artesian's water
supply system consists of 19 wellfields and 53 groundwater supply wells in New Castle County, Delaware
(Refs. 90; 77, pp. 9, 40-42; 82, pp. 4-6). Artesian also purchases 0.5 million gallons of water per day from
Chester Water Authority, whose source water is surface water (Ref. 77, pp. 10, 11; 78, p. 1). The system is
a single interconnected distribution system with no one well or purchased water source providing more than
40 percent of the total volume of supplied water (Refs. 77, p. 9; 82, pp. 1, 4, 5, 6). Artesian also maintains
interconnections with several additional adjacent water utilities for emergency purposes only and are not
regularly used (Ref. 77, pp. 10, 11). These interconnections were not considered when evaluating the
capacity of the system. In addition to the population served by the Artesian system in Delaware, Artesian
also supplies water to the Town of Elkton (Refs. 77, p. 11; 81, p. 2). The purchased water from Artesian
(8.77 million gallons) is mixed with Elkton's finished surface water (35.46 million gallons) and
groundwater from four wells (9.96 million gallons) in a reservoir (Ref. 81, p. 2). Nineteen of Artesian's 53
public supply wells, are located within a 4-mile radius of the Site (Figure 4 in Ref. 5). The public supply
wells located within a 4-miles radius of the Site are completed in the Columbia/Potomac Aquifer System
[Refs. 39, pp. 4, 5, 6, 7-13; 40, p. 7; 41, p. 7; 42, p. 7; 44, p. 7; 45, p. 7; 82, pp.4-6]. As documented in
Section 3.1.1, five of Artesian's public supply wells completed within the Columbia/Potomac Aquifer
System have contamination meeting the observed release criteria.
New Castle Municipal Services Commission (NCMSC) has four groundwater supply wells in New Castle
and supplies drinking water to 6,000 persons (Refs. 83, p. 1; 84, p. 2). MSC uses one well at a time for
water supply, resting the other wells. However, within the last 2 years, MSC has stopped using the Basin
Road well due to the high concentrations of PFAS contamination. This well is actively maintained and
annually tested for PFAS contamination levels but will not be used for water supply except in an emergency.
The remaining three active water supply wells are rotated on a monthly basis then rested for approximately
60 days. All water is pumped to the only water treatment facility for treatment and pumped into the
distribution system (Ref. 84, pp. 2). MSC does not purchase or sell well to other entities but does maintain
an interconnection with Artesian for emergency purposes (Ref. 84, pp. 2, 3). NCMSC wells are completed
within the Potomac Group Aquifer (Refs. 43, p. 7; 87, p. 1). The Frenchtown Road well has cumulatively
provided more than 40 percent of the total volume of water annually over the past 5.5 years; therefore, each
well's contribution is apportioned by percentage contributed to the total supply (Refs. 84, pp. 12, 21, 30,
38, 46, 48; 96, p. 1). Of the total 792,559,876 gallons of water pumped from 2017 through 2022 to date, the
approximate percentages contributed by the four NCMSC wells to that total are as follows:
Basin Road Well - (43,695,900 gallons / 792,559,876 gallons) = 0.055132617
Frenchtown Road Well - (347,242,150 gallons / 792,559,876 gallons) = 0.43812734
School Lane Well - (282,670,100 gallons / 792,559,876 gallons) = 0.35665457
Cross Roads Well - (118,951,726 gallons / 792,559,876 gallons) = 0.15008548
(Ref. 84, pp. 12, 21, 30, 38, 46, 48; 96, p.l).
The target population is apportioned as follows:
For the Town of Elkton, because the surface water intake contributes more than 40 percent to the total
volume of the system, the population is apportioned by percentage contributed to the total supply (Refs. 1,
Section 3.3.2; 81, p. 2):
8.77 million gallons (purchased water from Artesian) divided by 54.19 million gallons (total water
supply of the City of Elkton) = 0.16, times 15,625 (total population served by the Town of Elkton)
= 2,500 persons (Refs. 79, p. 1; 81, p. 2).
58
-------
GW-Targets
For Artesian, because no one well or purchased water source contributes more than 40 percent of the total
water supply, the target population is apportioned evenly among the 54 water sources (53 wells and 1
purchased water source) (Refs. 1, Section 3.3.2; 77, pp. 9, 10, 11, 40-42; 82, pp. 1, 4, 5, 6):
209,706 persons plus 2,500 (persons apportioned to purchased Artesian water in Elkton) = 212,206
(total persons supplied water by Artesian) divided by 54 (53 wells plus 1 purchased water source)
= 3,929.74 persons per well (Refs. 77, pp. 9, 10, 40-42; 79, p. 1; 80, p. 1; 81, p. 2).
For NCMSC, the Frenchtown Road well has cumulatively provided more than 40 percent of the total
volume of water annually over the past 5.5 years; therefore, the population is apportioned by percentage
contributed to the total supply (Refs. 1, Section 3.3.2; 84, pp. 12, 21, 30, 38, 46, 48):
Based on the approximate percentages contributed by the four NCMSC wells described above, the
population apportioned to the four NCMS wells is as follows:
Basin Road Well - 0.055132617 x 6,000 persons = 330.80 persons
Frenchtown Road Well - 0.43812734 x 6,000 persons = 2,628.76
School Lane Well - 0.35665457 x 6,000 persons = 2,139.93 persons
Cross Roads Well - 0.15008548 x 6,000 persons = 900.51 persons
(Refs. 83, p. 1; 84, pp. 12, 21, 30, 38, 46, 48; 96, p. 1).
Table 26 lists the applicable benchmarks against which analytical results of the observed release samples
were compared.
i;
TABLE 2(>
:\( 'IIMARKS
Suhsl since
MCL/MCLC
(IIU 1)
CRSC
( utj 1 or ntj 1)
\( RSC
Uiij 1 or iil: 1)
Rcfcrcncc(s)
PCE
5
37.1
120
2, p. 17
TCE
5
1.19
10
2, p. 20
Cis-1,2-DCE
70
NA
40.1
2, p. 5
Trans-1,2-DCE
100
NA
401
2, p. 8
1,2-DCA
5
0.856
120
2, p. 2
Vinyl Chloride
2
0.0214
60.2
2, p. 23
PFOS
NA
NA
40.1
2, p. 11
PFOA
NA
1,110
60.2
2, p. 14
Notes:
1 Units are presented in jug/1 for consistency with reported data.
2Units are in fig/1 for VOCs and ng/1 for PFAS.
jig/1 = micrograms per liter
ng/1 = nanograms per liter
CRSC = Cancer Risk Screening Concentration
MCL = Maximum Contaminant Level
MCLG = Maximum Contaminant Level Goal
NCRSC = Non-cancer Risk Screening Concentration
1,2-DCA= 1,2-Dichloroethane
cis-l,2-DCE = cis-l,2-dichloroethylene
PCE = Tetrachloroethylene
PFOA = Perfluorooctanoic acid (PFOA)
PFOS = Perfluorooctanesulfonic acid (PFOS)
TCE = Trichloroethylene
trans-1,2-DC = Trans-1,2-dichloroethylene
VOC = Volatile organic compound
59
-------
GW-Targets
The following public supply wells are subject to Level I and each is assigned a population as calculated
above. Per HRS Section 2.5.2, if more than one benchmark applies to a hazardous substance, Level I is
assigned if the concentration of the hazardous substance equals or exceeds the lowest applicable benchmark
concentration. The benchmarks listed below in Table 27 represent the lowest applicable benchmark for
PFOS, PFOA and PCE (see Table 26 of this HRS documentation record).
i abi.i: 2-7
I.I.M.I. 1 ( ()N( I N I K \ 1 IONS
Well
Substance
Concent radon
(fi«>/l or ii*»/l)'
Benchmark
(fi«>/l or ii"/!)1
Reference(s)
Jefferson
Farm 1R
PFOS
200
40.1 (NCRSC)
2, p. 11; 31, p. 175
Jefferson
Farm 2R
PFOS
203
40.1 (NCRSC)
2, p. 11; 30, p. 1590
Airport
Industrial
Park 1
PCE
7.5
5 (MCL)
2, p. 17; 30, p. 426
Airport
Industrial
Park 2
PFOS
90
40.1 (NCRSC)
2, p, 11; 31, pp. 5, 7
PCE
20.7
5 (MCL)
2, p. 17; 31, p. 19,21
Wilmington
Manor 3
PFOS
1,700
40.1 (NCRSC)
2, p. 11; 31, pp. 158,
160
PFOA
180
60.2 (NCRSC)
2, p. 14; 31, pp. 158,
160
Basin Road
PFOS
3,240
40.1 (NCRSC)
2, p. 11; 30, p. 1413
PFOA
269
60.2 (NCRSC)
2, p. 14; 30, p. 1396
Schoolhouse
Lane
PFOS
878
40.1 (NCRSC)
2, p. 11; 30, p. 1369
Crossroad
PFOS
680
40.1 (NCRSC)
2, p. 11; 32, p. 10
PFOA
290
60.2 (NCRSC)
2, p. 14; 32, p. 10
Frenchtown
Road
PFOS
520
40.1 (NCRSC)
2, p. 11; 32, p. 11
Notes:
1 Units are in fig/1 for VOCs and ng/1 for PFAS.
jig/1 = micrograms per liter
ng/1 = nanograms per liter
MCL = EPA Maximum Contaminant Level.
NCRSC = Non cancer risk screening concentration
PCE = tetrachloroethylene
PFOA = Perfluorooctanoic acid
PFOS = Perfluorooctanesulfonic acid
60
-------
GW-Targets
1 Alii.1. 2X
i \kc;i:i wi l ls
Well
Distance
from
Source
(mi.)
Popn hit ion
l.e\el 1
Documented
Rcl'crcnce(s)
Arlcsinn Wells
Jefferson Farm 1R
1-2
3,929.74
Y
5, Figure 4; 2, p. 11; Sections
3.1.1 and 3.3 of this HRS
documentation record
Jefferson Farm 2R
1-2
3,929.74
Y
5, Figure 4; 2, p. 11; Sections
3.1.1 and 3.3 of this HRS
documentation record
Airport Industrial
Park 1
0.5-1
3,929.74
Y
5, Figure 4; 2, p. 17; Sections
3.1.1 and 3.3 of this HRS
documentation record
Airport Industrial
Park 2
0.5-1
3,929.74
Y
5, Figure 4; 2, pp. 11, 17;
Sections 3.1.1 and 3.3 of this
HRS documentation record
Wilmington Manor 3
0.5-1
3,929.74
Y
5, Figure 4; 2, pp. 11, 14;
Sections 3.1.1 and 3.3 of this
HRS documentation record
NC'MSC Wells
Basin Road
0.5-1
330.80
Y
5, Figure 4; 2, pp. 11, 14;
Sections 3.1.1 and 3.3 of this
HRS documentation record
Schoolhouse Lane
0.5-1
2,139.93
Y
5, Figure 4; 2, p. 11; Sections
3.1.1 and 3.3 of this HRS
documentation record
Fenchtown Road
0.5-1
2,628.76
Y
5, Figure 4; 2, p. 11; Sections
3.1.1 and 3.3 of this HRS
documentation record
Crossroad
1-2
900.51
Y
5, Figure 4; 2, p. 11, 14;
Sections 3.1.1 and 3.3 of this
HRS documentation record
Notes:
1 Distances are measured from Source (Figure 4 of Ref. 5).
mi = mile
N = No
Y = Yes
61
-------
GW- Nearest Well/Population
3.3.1 Nearest Well
As identified in Section 3.3 of this HRS documentation record, nine public supply wells are subject to Level
I concentrations. Therefore, a nearest well factor value of 50 is assigned (Ref. 1, Section 3.3.1, Table 3-11).
Nearest Well Factor Value: 50
3.3.2 Population
3.3.2.2 Level I Contamination
As identified in Section 3.3 of this HRS documentation record, nine public supply wells (five Artesian and
four NCMSC) are subject to Level I concentrations. The populations assigned to the wells are also explained
in Section 3.3 of this HRS documentation record.
TABLE 29
LEVEL 1 POPl I.ATION TARGETS
Lcm'I 1 Wells
Population
Rel'erence(s)
Jefferson Farm 1
3,929.74
Section 3.3 of this HRS
documentation record
Jefferson Farm 2
3,929.74
Airport Industrial Park 1
3,929.74
Airport Industrial Park 2
3,929.74
Wilmington Manor 3
3,929.74
Basin Road
330.80
Schoolhouse Lane
2,139.93
Crossroad
900.51
Frenchtown Road
2,628.76
The total population served by drinking water from points of withdrawal subject to Level I concentrations
is 25,648.7 (Ref. 1, Section 3.3.2). This population is multiplied by 10 to determine the Level I
concentrations factor value, as shown below (Ref. 1, Section 3.3.2.2).
Total Level I Population: 25,648.7
Level I Concentration Factor Value: 25,648.7 x 10 = 256,487
(Ref. 1, Section 3.3.2.2)
3.3.2.3 Level II Concentrations
As documented in sections 3.3 and 3.3.1 of this HRS documentation record, all drinking water wells
evaluated as targets were documented to contain Level I concentrations; therefore, per HRS Section 3.3.2.3,
no wells were evaluated as subject to Level II contamination. Also, Level I concentrations result in a
maximum score of 100.00 forthe groundwater migration pathway; therefore, the Level II Factor Value was
not scored.
Level II Concentration Factor Value: Not Evaluated
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GW- Nearest Well/Population
3.3.2.4 Potential Contamination
Level I concentrations result in a maximum score of 100.00 for the groundwater migration pathway;
therefore, the Potential Contamination Factor Value was not scored.
In addition to the five AWC public wells and four NCMSC public wells that contain Level I concentrations
(see Section 3.3, Table 27), AWC has an additional 14 public supply wells within a 4-mile radius of the
Site (Figure 4 of Ref 5). The potential target population served by these wells were not evaluated as it
would not impact the overall site score.
Potential Contamination Factor Value: Not Evaluated
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GW-ResourcesAVellhead Protection Area
3.3.3 Resources
The Resources Factor Value was not scored because it would not significantly contribute to the overall Site
score.
Resources Factor Value: 0
3.3.4 Wellhead Protection Area
The contaminated groundwater plume lies within AWC and NCMSC Well head Protection Areas (Ref. 86,
pp. 1,2; Figure 2 in Reference 5 ofthisHRS documentation record). Wellhead protection areas in Delaware
are designated by EPA in accordance with Section 1428 of the Safe Drinking Water Act (Ref. 85, pp. 1, 2).
Therefore, the Wellhead Protection Area Factor Value of 20 is assigned (Ref. 1, Section 3.3.4).
Wellhead Protection Area Factor Value: 20
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