DERR-2024-006541

Technical Memorandum
Date: February 22, 2024
To: Leigh Anderson, Project Manager
Division of Environmental Response & Remediation
Utah Department of Environmental Quality
195 North 1950 West
Salt Lake City, Utah 84114-4840
From: Brad Glisson, Assistant Vice President, Project Manager
WSP USA Environment & Infrastructure Inc.
RE: Proposed Corrective Action Level for 1,4-Dioxane in Off-Site Groundwater
Former General Electric (GE) Facility at 130 East 1100 North
North Salt Lake, Utah
VCP No. C102
A summary of the exposure setting for 1,4-dioxane in shallow groundwater at the Site
and surrounding area is provided in the text below including the identification of
potential receptors and exposure routes. Based on the evaluation of the potential for
human receptors to be exposed to 1,4-dioxane in shallow groundwater, a proposed
corrective action level is presented.
General Background
1,4-Dioxane was widely used as a stabilizer for chlorinated solvents such as 1,1,1-
trichloroethane (TCA) and is often found at solvent release sites. 1,1,1-TCA was identified
as an ozone-depleting material in 1995 in accordance with the Montreal Protocol and
production declined significantly along with the use of 1,4-dioxane as a solvent
stabilizer (USEPA, 2017; ITRC, 2021a). Recent studies have also demonstrated that 1,4-
dioxane is a relatively common contaminant in association with trichloroethylene (TCE)
in groundwater, independent of the presence of 1,1,1-TCA. (USEPA Region 5, 2019).
The US Environmental Protection Agency (USEPA) has not established a maximum
contaminant level (MCL) for 1,4-dioxane. The drinking water equivalent for 1,4-dioxane is
1 milligram per liter (mg/L) or 1,000 µg/L, with a lifetime health advisory of 0.2 mg/L
(200 µg/L) in drinking water (USEPA, 2018). USEPA has calculated a Regional Screening
Level (RSL) of 0.46 µg/L for residential use of tap water based on a 1E-06 lifetime excess
cancer risk. The residential tap water RSL based on noncancer hazard (HQ=1) is 57 µg/L
(USEPA, 2023a). State standards for 1,4-dioxane in drinking water and/or groundwater
range from 0.3 µg/L (Massachusetts and Vermont) to 200 µg/L (Iowa). Utah is one of
eight states with no established drinking water standard or screening criterion for 1,4-
dioxane. The World Health Organization has a suggested drinking water threshold of
50 µg/L (ITRC, 2021b).
Technical Memorandum
Proposed Corrective Action Level for 1,4-Dioxane in Off-site Groundwater
Former GE Facility, VCP No. C102
February 22, 2024
2
Potential Receptors and 1,4-Dioxane in Groundwater
Information regarding potential human receptors and use of groundwater in the
vicinity of the Site has been presented in previous documents and is briefly
summarized below along with data on current concentrations of 1,4-dioxane in
groundwater through December 2023.
Land use within a 0.5-mile radius of the Site consists of industrial/commercial facilities
to the north, west, and south. A mobile home park, Colonial Woods II Mobile Home
Park, borders the Site to the east which is upgradient of the groundwater flow
direction. The property to the west of the Site includes a railroad easement (4 tracks
total), followed by 3D Storage property, a self-storage facility. Also, the North Salt Lake
Municipal Well is located approximately 200 feet west of the Site boundary.
There are no residential receptors located downgradient of the Site to the west, and
based on the 2023 Zoning Map, the closest downgradient residential district is
approximately one (1) mile west of the Site (City of North Salt Lake, 2023). The Site, as
well as the off-site downgradient properties to the west, are zoned for manufacturing-
distribution (MD) use. A residential development is located approximately one-half mile
to the northwest of the Site across Highway 2600S. Property between the Site and the
residential development is zoned Light Industrial/Business Park Zone (I-1) and is also in
industrial/commercial use (Woods Cross City, 2021).
A current water well search on the Utah Division of Water Rights well log dataset (2024)
indicates that four well borings were started east of the mobile home park in 2009.
Three wells were completed, one to a finished well depth of 70 feet with a well intake
depth at 50 feet, one to a finished well depth of 65 feet with a well intake depth of 45
feet, and the third well was installed to a finished well depth of 50 feet with a well
intake depth of 50 feet. The well log records for these three wells identify them as “test”
wells and the wells were abandoned in September 2023.
Six well logs were identified within approximately one-half mile downgradient of the
Site. Three wells were located generally southwest of the Site, including: (1) a
nonproduction well (Holly Energy) bored to 280 feet but not completed with no
finished well depth or well intake depth noted; (2) a well (no owner identified) installed
to 390 feet with a well intake depth of 305 feet, a pump intake depth of 200 feet; and
(3) a well (Bountiful East Stake) finished to 221 feet, with a water intake depth of 211 feet.
A fourth well, identified as an irrigation well owned by Lynn Trenbeath, is located to the
west and was installed to 157 feet with a well intake depth of 147 feet. The remaining
two locations are associated with the municipal well located approximately 200 feet
west of the Site. The one location is identified as a boring to 320 feet that was
subsequently abandoned. The remaining well, the municipal well, is identified to have a
finished well depth of 300 feet with a well intake depth of 180 feet.
Technical Memorandum
Proposed Corrective Action Level for 1,4-Dioxane in Off-site Groundwater
Former GE Facility, VCP No. C102
February 22, 2024
3
There are 22 monitoring wells at the Site (MW-1 through MW-8 and MW-10 through
MW-23) constructed to depths that range from 9.5 ft below top of casing (ft below TOC)
(MW-17) to 20.0 ft below TOC (MW-8). Based on data collected at the Site from 2017
through December 2023, the average depth to water is 8.06 ft below TOC.Groundwater
flow at the Site is generally to the west/northwest and toward the municipal well;
however, the municipal well is located in a separate confined aquifer, with the water-
bearing zone identified as 80 to 130 feet below ground surface (bgs).
Two deep soil borings were advanced near the Site’s western property boundary in
September 2023 to complete vertical delineation of on-site subsurface geologic soil
conditions and to evaluate for the presence of a deeper water bearing zone. Prior to
installation of the borings, WSP first completed a review of available soil boring logs
from wells located on adjoining properties to evaluate the deeper lithologic soil
conditions. These logs identify the presence of a clay layer extending from as shallow as
5 ft to 100 + ft-bgs. The results of the vertical delineation assessment conducted near
the Site boundary indicated soil conditions consisted of approximately 20 feet of
predominantly clay soil with no water bearing zone at depth. In addition, there was no
evidence of volatile organic compounds at depth (WSP, 2023).
There is no use of shallow groundwater on-site or directly downgradient. The N. Salt
Lake municipal well, as noted above, is associated with a water-bearing zone located
80 to 130 feet bgs. An environmental covenant has been developed for the Site which
restricts groundwater use for monitoring purposes only. The on-site building is not
currently occupied and if redevelopment of the Site occurs in the future, the
environmental covenant and Site Management Plan will restrict the property to
industrial/ commercial use only. Analytical results for 1,4-dioxane in on-site groundwater
range from non-detect (MW-20) to 132 µg/L (MW-3) based on the December 2023
monitoring event and are well below the corresponding vapor intrusion screening level
(VISL) for industrial properties of 12,500 µg/L and the VISL for residential properties of
2,860 µg/L (USEPA, 2023b; TR=1E-06). Concentrations of 1,4-dioxane in groundwater in
the monitoring wells along the western property boundary (MW-15 through MW-19)
ranged from 1.57 (MW-16) to 11.4 µg/L (MW-17) based on the December 2023 data.
Two monitoring wells were installed off-site on the 3D Storage property to depths of 20
feet (offsite A-1 and offsite A-2), with an average depth to groundwater over four (4)
quarterly sampling events of 8.76 feet below TOC. Groundwater on the 3D Storage
property, as well as on the GE Site, is shallow in nature and there is no evidence of any
connection to the deeper water bearing zone from which the municipal well draws
water.
There are no residential receptors downgradient of the Site and, as noted above, no
known use of off-site shallow groundwater. During the four quarters of groundwater
monitoring conducted at the off-site wells, 1,4-dioxane ranged from 1.0 µg/L (offsite A-2
in September 2022) to 5.2 µg/L (offsite A-1 in December 2022). The most recent
monitoring event conducted at the off-site wells in December 2023 reported
concentrations of 1,4-dioxane at 5.76 µg/L in offsite A-1 and 5.06 µg/L in offsite A-2.
Technical Memorandum
Proposed Corrective Action Level for 1,4-Dioxane in Off-site Groundwater
Former GE Facility, VCP No. C102
February 22, 2024
4
These off-site concentrations are at the midpoint of the acceptable cancer risk range
for 1,4-dioxane based on groundwater being used as a potable water supply (4.6 µg/L)
and are well below the residential tapwater RSL based on noncancer hazard, as well as
the VISLs for both residential and industrial receptors.
Shallow groundwater at and in the vicinity of the Site is not used as a source of potable
water supply. Communication with the City of North Salt Lake has indicated drinking
water is obtained from the confined aquifer at depths of approximately 80 to 130 feet
bgs, and the water quality is not currently impacted by 1,4-dioxane or any VOCs, and
based on the vertical delineation studies, is unlikely to be impacted in the future. The
groundwater quality of the North Salt Lake Municipal Well located approximately 200
feet to the west of the Site is routinely monitored and according to the North Salt Lake
water department representatives there have been no issues identified with the Site
related constituents of concern (COCs).
Proposed Corrective Action Level
The USEPA RSL for 1,4-dioxane in residential tap water of 0.46 µg/L is appropriate for an
initial screening criterion, but as noted on the USEPA RSL website, the RSLs are not
cleanup standards and should not be used as cleanup levels (USEPA, 2023a). The RSLs
are initial screening criteria to determine whether a site may require further
investigation. These criteria are modified to incorporate site-specific information,
including property use to develop cleanup goals or corrective action levels. For this
specific situation, the residential tapwater RSL of 0.46 µg/L is overly conservative for a
corrective action level for off-site shallow groundwater as it does not take into
consideration the use of the off-site property which is industrial/commercial. There are
no residential receptors located downgradient to either the west or northwest of the
Site.
Use of the residential tapwater RSL also does not consider the fact that off-site shallow
groundwater is not a source of potable water supply; therefore, there is no potential for
Industrial/commercial worker exposure to groundwater through ingestion or dermal
contact. The only pathway for potential exposure is associated with volatilization to
indoor air and as discussed previously, both on-site and off-site measured
concentrations of 1,4-dioxane in shallow groundwater are well below both industrial
and residential VISLs.
The Utah Division of Environmental Response & Remediation (UDERR) and USEPA
utilize an acceptable cancer risk range of 1E-06 to 1E-04 with a preference for achieving
the more protective end of the risk range. For noncancer hazards, the UDERR utilizes an
acceptable hazard quotient of 1.0 to represent the level at which an individual could be
exposed on a daily basis with no appreciable risk of adverse effects during a lifetime.
The concentrations of 1,4-dioxane in groundwater that represent the acceptable cancer
risk range based on groundwater use as a potable water supply are 0.46 µg/L to 46 µg/L
and the concentration that represents an acceptable hazard quotient of 1 is 57 µg/L
(USEPA, 2023a). These values are not appropriate for off-site corrective action levels due
Technical Memorandum
Proposed Corrective Action Level for 1,4-Dioxane in Off-site Groundwater
Former GE Facility, VCP No. C102
February 22, 2024
5
to the industrial/commercial use of the property as well as the lack of exposure to
groundwater. Therefore, WSP, on behalf of GE, is proposing an off-site corrective action
level of 10 µg/L. This value is conservative and within the acceptable cancer risk range
(equivalent to a residential cancer risk of 2E-05); and is equivalent to a residential
noncancer hazard quotient of 0.2 which is less than the acceptable noncancer hazard
level of 1. The proposed value of 10 µg/L is also orders of magnitude less than the
residential VISL of 2,860 µg/L.
The proposed corrective action level for 1,4-dioxane in off-site groundwater is
conservative as it remains within the acceptable residential cancer risk range for 1,4-
dioxane in groundwater used as a potable water supply, but provides some flexibility
given:
The off-site property(s) to the west are zoned manufacturing-distribution, and to
the northwest are zoned Light Industrial/Business Park Zone, and are in
industrial/commercial use,
Based on the current zoning maps for North Salt Lake and Woods Cross City
there are no residential receptors (i.e., residential districts) within one-half mile
of the Site in either the west or northwest direction,
Review of available well boring logs located on adjoining properties identified
the presence of a clay layer extending from as shallow as 5 ft to 100 + ft-bgs,
There is no use of shallow groundwater as a source of drinking water supply
near the Site.
The municipal well located to the immediate west of the Site is located in a
separate confined aquifer, with the water-bearing zone identified as 80 to 130
feet below ground surface (bgs).
In summary, based on the exposure setting described above and the lack of potential
exposure to 1,4-dioxane in shallow groundwater, it is proposed that 10 µg/L be
established as the corrective action level for 1,4-dioxane in off-site shallow groundwater
downgradient from the Former General Electric (GE) Facility. This value is conservative
for a non-residential property with the only potential for exposure to shallow
groundwater being through volatilization to indoor air.
Technical Memorandum
Proposed Corrective Action Level for 1,4-Dioxane in Off-site Groundwater
Former GE Facility, VCP No. C102
February 22, 2024
6
References
City of North Salt Lake, 2023. Zoning Map, adopted February 21.
ITRC, 2021a.Fact Sheet: History of Use and Potential Sources - 1,4-Dioxane, March.
ITRC, 2021b.Fact Sheet: Regulatory Framework - 1,4-Dioxane, February.
USEPA, 2019. Memorandum entitled “Procedures for Addressing Potential 1,4-Dioxane
Contamination at Region 5 Superfund Remedial Sites”, from Douglas Ballotti, Director,
Superfund & Emergency Management Division to Remedial Project Managers,
December 12.
USEPA, 2017.Technical Fact Sheet – 1,4-Dioxane, Office of Land and Emergency
Management, EPA 505-F-17-011, November.
USEPA, 2018. 2018 Edition of the Drinking Water Standards and Health Advisories
Tables, Office of Water, March.
USEPA, 2023a. Regional Screening Level (RSL) Summary Table (TR=1E-06; HQ=1),
November.
USEPA, 2023b. Vapor Intrusion Screening Level Calculator (TR=1E-06; HQ=1), November.
Utah Division of Water Rights, 2024. On-line search of water well records at:Utah Well
Logs | Utah Well Logs | Utah’s State Geographic Information Database (AGRC), February
7, 2024.
Woods Cross City, 2021. Zoning Map for Woods Cross City, Utah, last amended March 16,
2021.
WSP USA Environment & Infrastructure, Inc., (WSP) 2023. Memorandum from WSP to
General Electric Company on Exploratory Soil Boring Findings, October 5, 2023.