[Federal Register Volume 84, Number 141 (Tuesday, July 23, 2019)]
[Proposed Rules]
[Pages 35360-35365]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-15658]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 300
[EPA-HQ-SFUND-1990-0011; FRL-9997-03-Region 8]
National Oil and Hazardous Substances Pollution Contingency Plan;
National Priorities List: Deletion of the Mystery Bridge Rd./U.S.
Highway 20 Superfund Site
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule; notice of intent.
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SUMMARY: The Environmental Protection Agency (EPA) Region 8 is issuing
a Notice of Intent to Delete the Mystery Bridge Rd./U.S. Highway 20
Superfund Site (Site) located in Evansville, WY, from the National
Priorities List (NPL) and requests public comments on this proposed
action. The NPL, promulgated pursuant to the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) of
1980, as amended, is an appendix of the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP). The EPA and the State of
Wyoming, through the Wyoming Department of Environmental Quality
(WDEQ), have determined that all appropriate response actions under
CERCLA, [other than maintenance of institutional controls and five-year
reviews], have been completed. However, this deletion does not preclude
future actions under Superfund.
DATES: Comments must be received by August 22, 2019.
ADDRESSES: Submit your comments, identified by Docket ID no. EPA-HQ-
SFUND-1990-0011, by one of the following methods:
http://www.regulations.gov. Follow on-line instructions
for submitting comments. Once submitted, comments cannot be edited or
removed from Regulations.gov. The EPA may publish any comment received
to its public docket. Do not submit electronically any information you
consider to be Confidential Business Information (CBI) or other
information whose disclosure is restricted by statute. Multimedia
submissions (audio, video, etc.) must be accompanied by a written
comment. The written comment is considered the official comment and
should include discussion of all points you wish to make. The EPA will
generally not consider comments or comment contents located outside of
the primary submission (i.e. on the web, cloud, or other file sharing
system). For additional submission methods, the full EPA public comment
policy, information about CBI or multimedia submissions, and general
guidance on making effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.
Email: Andrew Schmidt ([email protected]).
Mail: Andrew Schmidt, Remedial Project Manager, 8SEM-RB-
SA, Environmental Protection Agency, Region 8, 1595 Wynkoop Street,
Denver, CO 80202.
Hand delivery: Andrew Schmidt, Remedial Project Manager,
8SEM-RB-SA, Environmental Protection Agency, Region 8, 1595 Wynkoop
Street, Denver, CO 80202.
Instructions: Direct your comments to Docket ID no. EPA-HQ-SFUND-
1990-0011. EPA's policy is that all comments received will be included
in the public docket without change and may be made available online at
http://www.regulations.gov, including any personal information
provided, unless the comment includes information claimed to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Do not submit information that you
consider to be CBI or otherwise protected through http://www.regulations.gov or email. The http://www.regulations.gov website is
an ``anonymous access'' system, which means EPA will not know your
identity or contact information unless you provide it in the body of
your comment. If you send an email comment directly to EPA without
going through http://www.regulations.gov, your email address will be
automatically captured and included as part of the comment that is
placed in the public docket and made available on the internet. If you
submit an electronic comment, EPA recommends that you include your name
and other contact information in the body of your comment and with any
disk or CD-ROM you submit. If EPA cannot read your comment due to
technical difficulties and cannot contact you for clarification, EPA
may not be able to consider your comment. Electronic files should avoid
the use of special characters, any form of encryption, and be free of
any defects or viruses.
Docket: All documents in the docket are listed in the http://www.regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material,
[[Page 35361]]
will be publicly available only in the hard copy. Publicly available
docket materials are available either electronically in http://www.regulations.gov or in hard copy at: U.S. EPA Region 8, Superfund
Records Center and Technical Library, 1595 Wynkoop Street, Denver, CO
80202. Viewing hours: 8 a.m. to 4 p.m., Monday through Thursday,
excluding holidays; Contact: Andrew Schmidt; (303) 312-6283, email:
[email protected] and Natrona County Public Library, Reference
Desk, 307 East 2nd Street, Casper, WY 82601-2593, (307) 577-7323,
Hours: Monday through Thursday: 9 a.m. to 7 p.m., Friday and Saturday:
9 a.m. to 5 p.m.
FOR FURTHER INFORMATION CONTACT: Andrew Schmidt, Remedial Project
Manager, U.S. Environmental Protection Agency, Region 8, SEM-R8-SA,
1595 Wynkoop St., Denver, CO 80211, (303) 312-6283, email:
[email protected].
SUPPLEMENTARY INFORMATION:
Table of Contents
I. Introduction
II. NPL Deletion Criteria
III. Deletion Procedures
IV. Basis for Intended Site Deletion
I. Introduction
EPA Region 8 announces its intent to delete the Mystery Bridge Rd./
U.S. Highway 20 Superfund Site from the National Priorities List (NPL)
and requests public comment on this proposed action. The NPL
constitutes appendix B of 40 CFR part 300 which is the National Oil and
Hazardous Substances Pollution Contingency Plan (NCP), which EPA
promulgated pursuant to section 105 of the Comprehensive Environmental
Response, Compensation and Liability Act (CERCLA) of 1980, as amended.
EPA maintains the NPL as the list of sites that appear to present a
significant risk to public health, welfare, or the environment. Sites
on the NPL may be the subject of remedial actions financed by the
Hazardous Substance Superfund (Fund). As described in 40 CFR
300.425(e)(3) of the NCP, sites deleted from the NPL remain eligible
for Fund-financed remedial actions if future conditions warrant such
actions.
EPA will accept comments on the proposal to delete this site for
thirty (30) days after publication of this document in the Federal
Register.
Section II of this document explains the criteria for deleting
sites from the NPL. Section III discusses procedures that EPA is using
for this action. Section IV discusses the Mystery Bridge Rd./U.S.
Highway 20 Superfund Site and demonstrates how it meets the deletion
criteria.
II. NPL Deletion Criteria
The NCP establishes the criteria that EPA uses to delete sites from
the NPL. In accordance with 40 CFR 300.425(e), sites may be deleted
from the NPL where no further response is appropriate. In making such a
determination pursuant to 40 CFR 300.425(e), EPA will consider, in
consultation with the State, whether any of the following criteria have
been met:
i. Responsible parties or other persons have implemented all
appropriate response actions required;
ii. All appropriate Fund-financed response under CERCLA has been
implemented, and no further response action by responsible parties is
appropriate; or
iii. The remedial investigation has shown that the release poses no
significant threat to public health or the environment and, therefore,
the taking of remedial measures is not appropriate.
Pursuant to CERCLA section 121(c) and the NCP, EPA conducts five-
year reviews to ensure the continued protectiveness of remedial actions
where hazardous substances, pollutants, or contaminants remain at a
site above levels that allow for unlimited use and unrestricted
exposure. EPA conducts such five-year reviews even if a site is deleted
from the NPL. EPA may initiate further action to ensure continued
protectiveness at a deleted site if new information becomes available
that indicates it is appropriate. Whenever there is a significant
release from a site deleted from the NPL, the deleted site may be
restored to the NPL without application of the hazard ranking system.
III. Deletion Procedures
The following procedures apply to deletion of the Site:
(1) The EPA consulted with the State before developing this Notice
of Intent to Delete.
(2) The EPA has provided the State 30 working days for review of
this notice prior to publication of it today.
(3) In accordance with the criteria discussed above, EPA has
determined that no further response is appropriate;
(4) The State of Wyoming, through the WDEQ, has concurred with
deletion of the Site, from the NPL.
(5) Concurrently with the publication of this Notice of Intent to
Delete in the Federal Register, a notice is being published in the
Casper Star-Tribune.
(6) The EPA placed copies of documents supporting the proposed
partial deletion in the deletion docket, made these items available for
public inspection, and copying at the Site information repositories
identified above.
If comments are received within the 30-day public comment period on
this document, EPA will evaluate and respond appropriately to the
comments before making a final decision to delete. If necessary, EPA
will prepare a Responsiveness Summary to address any significant public
comments received. After the public comment period, if EPA determines
it is still appropriate to delete the Site, the Regional Administrator
will publish a final Notice of Deletion in the Federal Register. Public
notices, public submissions and copies of the Responsiveness Summary,
if prepared, will be made available to interested parties and in the
site information repositories listed above.
Deletion of a site from the NPL does not itself create, alter, or
revoke any individual's rights or obligations. Deletion of a site from
the NPL does not in any way alter EPA's right to take enforcement
actions, as appropriate. The NPL is designed primarily for
informational purposes and to assist EPA management. Section
300.425(e)(3) of the NCP states that the deletion of a site from the
NPL does not preclude eligibility for future response actions, should
future conditions warrant such actions.
IV. Basis for Intented Site Deletion
The following information provides EPA's rationale for deleting the
Site from the NPL:
Site Background and History
The Site is in Natrona County, Wyoming northeast of Casper, Wyoming
and one mile east of Evansville. The Site is bordered on the north by
the North Platte River, on the west by the Sinclair Refinery (formerly
known as the Little America Refining Company or LARCO), on the south by
U.S. Highway 20 and on the east by Mystery Bridge Road. The northern
two thirds of the Site contain residential housing units built
primarily between 1973 and 1983. The Tallgrass Energy Partners, LP
facility (formerly owned by KN Energy and KM Upstream LLC and referred
to as the former KMI Property) and the adjacent DOW/DSI property
comprise the southern third of the Site. The site is underlain by two
aquifers, a shallow alluvial aquifer and a deeper bedrock aquifer.
Activities at the site impacted the shallow alluvial aquifer, which was
historically utilized by residences downgradient for domestic water
supply purposes.
[[Page 35362]]
Site investigations, initiated due to resident complaints of poor
water and air quality, were completed in 1986 and 1987 and identified a
benzene, toluene, ethylbenzene and xylenes (BTEX) plume originating
from the former KMI Property and a volatile halogenated organic
chemicals (VHOs) plume originating from the DOW/DSI property moving
northeast towards the North Platte River. The Site was proposed for
listing on the National Priorities List (NPL) June 24, 1988 (53 FR
23978), and was listed on the NPL on August 30, 1990 (55 FR 35502). The
former KMI property was partially deleted from the NPL on August 29,
2017 (82 FR 29764). Potential releases at the Sinclair Refinery
(formerly LARCO) facility are currently being addressed under a
Resource Conservation and Recovery Act (RCRA) 3008(h) order.
KM Upstream LLC and its predecessors operated a natural gas
fractionation, compression, cleaning, odorizing, and transmission
facility at the Site beginning in 1965. During the plant start-up, an
underground pipe burst, injecting 5,000 to 10,000 gallons of absorption
oil into the subsurface. In addition, an earthen flare pit was
initially used to collect spent material generated by the facility.
Absorption oil, emulsions, anti-foulants, and anti-corrosive agents,
crude oil condensate, liquids accumulated in the flare stack, potassium
hydroxide treated waste, and lubrication oils and blowdown materials
from plant equipment were all possibly collected in the flare pit. In
1984, a concrete-lined flare pit was constructed and put into
operation. Leaks from the earthen flare pit, the initial absorption oil
spill, and a catchment area that collected surface water run-off from
the facility are all believed to have contributed to the BTEX soil and
groundwater impacts.
The DOW/DSI facility conducted oil and gas production enhancement
services starting in the 1950's. Contamination originating from the
DOW/DSI facility is believed to have come from the truck wash water
disposal system (believed to have contained chlorinated solvents) and
the toluene storage area on the northern end of the facility.
EPA is the lead agency for the Site and WDEQ is the support agency.
Pursuant to the 1991 Consent Decree, KN Energy, its successor KMI, and
DOW/DSI have jointly conducted and funded the remediation work at the
Site. The former KMI Property is in continued operation as mid-stream
gas processing facility and is now owned and operated by Tallgrass
Energy Partners.
Removal Actions
In August 1986, nearby residents complained of poor air and water
quality. The Agency for Toxic Substances and Disease Registry (ATSDR)
then issued an advisory after VHOs were detected in area drinking water
wells. Studies determined that a contaminated groundwater plume from
the nearby industrial facilities was responsible for the poor water
quality.
Starting in 1987, EPA searched to identify potentially responsible
parties (PRPs) for the contaminated groundwater. EPA also oversaw a
removal action in January 1987 for immediate installation of 25
groundwater monitoring wells and alternative drinking water provisions
for area residents until permanent alternatives could be established.
By July 1987, EPA identified KMI and Dow/DSI as the companies
responsible for generating the contaminated plumes emanating from the
industrial area. By December 1987, KMI and Dow/DSI entered separate
Administrative Orders on Consent (AOCs) to perform immediate removal
actions to control the sources of contamination and inhibit further
migration of the existing groundwater plumes into the residential
subdivision. Each PRP was required to prepare an Engineering
Evaluation/Cost Analysis (EE/CA) of its property to document the extent
and nature of the contaminants present and to support proposals of
expedited removal actions.
EPA's initial response actions also included extending a water
transmission line from the Town of Evansville and connecting residents
after detecting elevated levels of contaminants in drinking water
wells. In addition, the Evansville water treatment plant received a new
water intake and related upgrades. This work was completed in January
1989.
KMI Property
An investigation was conducted as part of the EE/CA for removal
actions at the KMI property. The investigation included a soil vapor
survey and borings to collect soil and groundwater samples. The soil
vapor survey was conducted near the flare pit and soil and groundwater
samples were also collected. The investigation lead to the discovery of
impacted soil, groundwater, and light non-aqueous phase liquids
(LNAPLs) in the subsurface.
The EE/CA prepared by KMI evaluated removal technologies and
recommended a removal action. KMI began the recommended removal action
in November 1989. The removal action consisted of groundwater pump and
treat (PAT) and soil vapor extraction (SVE) systems to remove BTEX
contaminants in three phases: LNAPL, groundwater, and soil vapor. The
SVE system extracted vapor phase hydrocarbons from the unsaturated
interval between the water table and the ground surface. The PAT system
pumped groundwater to the surface where volatile hydrocarbons were
removed by air stripping. LNAPL, when present, was removed from the
groundwater extraction wells when the PAT system was in operation.
The removal actions on the KMI property were also selected as part
of the OU1 remedy in the Record of Decision (ROD); thus, operation of
the PAT and SVE systems continued into the remedial phase. The
completion of removal activities for the KMI parcel, including
confirmation sampling data and QA/QC activities are documented in the
OU2 Phase I Report, KN Energy Gas Compressor Station, dated June 27,
1995.
DOW/DSI Property
In accordance with the AOC, DOW/DSI prepared an EE/CA report to
document the nature and extent of the releases of contaminants, and to
support proposals of expedited removal actions to control migration of
contaminants and eliminate sources of contaminants beneath and adjacent
to the property. As a result of the investigative activities conducted
to support the EE/CA at the DOW/DSI property, several volatile
halogenated organic (VHO) soil contaminants were identified in the
groundwater and soil near the abandoned chlorinated gravel leach sump
area.
The EE/CA prepared by DOW/DSI evaluated removal technologies and
recommended a removal action. Beginning in late 1987 and continuing
through part of 1988, the removal action was conducted by DOW/DSI. The
removal action consisted of removals of a buried wash water disposal
system, an empty and out-of-service underground storage tank (UST), and
approximately 440 cubic yards of soil and debris from an older
abandoned sump area. The excavations were backfilled with clean sand
and gravel. In addition, two SVE systems were installed on the property
to remove volatile halogenated organic (VHO) chemicals from the
abandoned sump area and aromatic hydrocarbons (toluene, xylenes and
ethylbenzene) from the former toluene storage area.
Confirmatory subsurface soil sampling prior to shutdown of the SVE
systems in 1988 showed that the SVE systems had lowered in-situ
[[Page 35363]]
concentrations of soil contaminants below the Soil Action Levels (SALs)
developed by EPA for the Site in support of the expedited removal
actions. The completion of removal activities for the DOW/DSI parcel,
including confirmation sampling data and QA/QC activities are
documented in the Phase I Summary Report for the DSI Property under OU2
of the Brookhurst/Mystery Bridge Superfund Site, dated February 22,
1994.
Remedial Actions
In December 1987, the AOC signed by DOW/DSI and KMI also required
the two PRPs to perform a Remedial Investigation/Feasibility Study (RI/
FS) of the Brookhurst Subdivision, which is located north and east of
the KMI and DOW/DSI properties and hydrologically downgradient. The RI/
FS report, which was completed in June 1990, concluded that two plumes
of contaminated groundwater originated in the industrial area south of
the subdivision and were migrating through the subdivision in a
northeast direction. The first of these plumes was contaminated with
VHO compounds (referred to as the VHO plume) and extended from the DOW/
DSI property to the North Platte River. The second plume was
contaminated with BTEX compounds (referred to as the BTEX plume) and
extended from the KMI property to the adjacent Burlington Northern Rail
Road property and possibly into the subdivision directly north of the
KMI property. In addition, LNAPL originating at the KMI property and
extending slightly into the subdivision, was found floating on the
groundwater. The RI/FS suggested that VHO and BTEX plumes were not
commingled in the area downgradient from the DOW/DSI and KMI
facilities.
As part of the RI/FS, a Baseline Risk Assessment (BRA) was
conducted in 1989. The BRA assessed carcinogenic risks and the
potential for non-cancer health effects of eleven chemicals resulting
from direct ingestion of contaminated groundwater under residential
homes. Risks were also calculated for the hypothetical scenario where
the DOW/DSI and KMI facilities were redeveloped for residential use.
The BRA concluded that ecological risks due to the releases from the
industrial areas were not expected to be significant, but that human
health cancer risks presented by the VHO and BTEX plumes in alluvial
groundwater under the residential scenario were unacceptable. Human
health non-cancer risks due to the VHO and BTEX plumes were determined
to be below a level of concern.
The Site was divided into two OUs, OU1 was designated to address
contaminated groundwater, and OU2 was designated to address contaminant
source areas on the industrial properties. The creation of the two OUs
was done to ensure that the principle threat to human health and the
environment, groundwater (OU1), was dealt with immediately, and to
allow further assessment of the soil source areas to ensure adequate
cleanup.
The OU1 ROD was signed on September 24, 1990. The remedial action
objectives (RAOs) were to: Prevent ingestion of water containing trans-
1,2 dichloroethylene (DCE), 1,1,1 trichloroethane (TCA),
trichloroethylene (TCE), tetrachloroethylene (PCE), benzene, toluene,
ethylbenzene, or xylene at concentrations that either a) exceed MCLs or
proposed MCLs, or b) present a total carcinogenic risk greater than 1 x
10-4-1 x 10-6; and restore the alluvial aquifer
to concentrations that both a) meet the MCLs or proposed MCLs for
trans-1,2 DCE, 1,1.1 TCA, TCE, PCE, benzene, toluene, ethylbenzene, and
xylene, and b) present a total carcinogenic risk less than 1 x
10-4-1 x 10-6.
The agency selected a combination of alternatives to address the
VHO plume and the BTEX plume. Common elements included source area
groundwater treatment, soil removal and soil vapor extraction,
monitoring of groundwater, and implementation of institutional
controls.
KMI Property (BTEX Plume)
The selected remedy included continued operation of the KMI removal
action. Specifically, the selected remedy included extraction of ground
water with concentrations of BTEX compounds above MCLs or proposed MCLs
throughout the plume; treatment of contaminated groundwater with an on-
site air stripping facility; and reinjection of treated water into the
aquifer to provide additional hydraulic control of the BTEX plume and
to minimize any potential impact from the BTEX remediation efforts on
the RCRA and VHO plumes.
DOW/DSI Property (VHO Plume)
The selected remedy included continued operation and enhancements
to the DOW/DSI removal actions. The remedy included extraction of
groundwater with concentrations of VHOs above MCLs or proposed MCLs in
the upgradient portion of the plume (i.e., on and/or near the DOW/DSI
facility); treatment of contaminated groundwater with an on-site air
stripping facility; reinjection of treated water into the aquifer to
provide additional hydraulic containment of the upgradient portion of
the VHO plume being extracted, minimize any impact from the VHO
remediation efforts on the RCRA plume and BTEX plume, and enhance the
natural attenuation process in the downgradient portions of the VHO
plume; and reliance on natural processes for reduction of VHO levels in
downgradient portions of the VHO plume.
The OU2 ROD was signed on September 30, 2010 and determined that
removal actions taken at each parcel treated or excavated all soils
exceeding industrial use standards. The soils at these properties are
acceptable for industrial uses. The remedy selected for OU2 is
institutional controls to limit the use of KMI and DOW/DSI parcels to
industrial use, to govern the handling of excavated soils on each
parcel and to restrict groundwater use.
Remedy Implementation
Following the OU1 ROD, a Consent Decree (CD) was signed with both
DOW/DSI and KMI in October 1991, in which the parties agreed to
implement the OU1 ROD remedy.
Requirements for the KMI Industries BTEX plume remedial design (RD)
included groundwater monitoring to determine whether additional
groundwater extraction or monitoring points downgradient of the KMI
facility were needed. During the RD, it was determined that
contamination above MCLs had not migrated beyond the facility boundary
and no system expansion was needed. Since no expansion was needed, no
addition remedial construction was performed.
Requirements for the DOW/DSI VHO plume included construction of a
groundwater extraction and treatment system. The system installation
was completed in August 1993 and included three extraction wells, a
water treatment unit, and an infiltration gallery.
In conjunction with the OU2 ROD, a special warranty deed was
recorded for the KMI property, and a restrictive covenant was recorded
for the DOW/DSI property in Natrona County in September 2010. Both the
KMI warranty deed and the DOW/DSI restrictive covenant limit use of the
properties to industrial use, govern the management of excavated soils
on each property, prevent the use of groundwater on each property for
any use other than sampling and monitoring, and ensure that no use of
the properties will jeopardize the selected remedies.
[[Page 35364]]
Attainment of Cleanup Levels
KMI Property
The October 1991 CD for remedial design and remedial action entered
by the Court required the following groundwater performance standards
for the KMI property:
1. Remediate groundwater so that concentrations shall not exceed
MCLs and proposed MCLs, as set forth in the ROD for BTEX.
2. The area of attainment shall include the entire BTEX plume,
including those areas of the plume inside and outside the KMI facility.
Concentrations of ethylbenzene, toluene, and xylenes were not
historically measured above the MCLs. As a result, the groundwater
remediation evaluation focused on benzene as the indicator contaminant
of concern.
A KMI Groundwater Monitoring Plan (GWMP) was developed in 1993 to
evaluate the effectiveness of the Remedial Action (RA), to evaluate
groundwater post-RA and determine compliance with the performance
standards. Specifically, the KMI GWMP established that following shut
down of the remediation system and after 12 months of groundwater
sampling with results below the MCL, post-RA monitoring would begin.
The KMI remediation system operated continuously between November
1989 and August 1996 when EPA approved KMI's request to cease active
remediation. The pre-certification inspection was completed on July 16,
1997, and approval of Remedial Action Completion was provided on August
20, 1997. After active treatment was shut down, attainment monitoring
was conducted to evaluate post remediation conditions. Achievement of
RAOs under post-RA monitoring was determined to have been met after a
minimum of eight quarterly sampling events were conducted in which, for
each well, the 90 percent one-tailed upper confidence limit (UCL90)
concentrations for benzene, ethylbenzene, toluene and total xylenes
were below the MCLs for each chemical. Compliance with RAOs for the KMI
plume was achieved in November 2009. The completion of remedial
activities, including statistical analyses of groundwater data were
documented in The Completion Report for Groundwater Remediation
Activities at the Casper Compressor Station letter report dated June
22, 2010, and the Summary of the Previous Eight Quarters of Post
Remedial Action Groundwater Monitoring at the Casper Compressor
Station, Technical Memorandum, dated February 12, 2010.
Because the KMI parcel met RAOs for the source area and in
groundwater, and because the necessary institutional controls were in
place to prevent unacceptable exposure to site contaminants, the KMI
property was partially deleted from the NPL on August 29, 2017.
DOW/DSI Property
The October 1991 CD for remedial design and remedial action
required the following performance standards for the DOW/DSI parcel:
1. Remediate groundwater so that concentrations shall not exceed
MCLs and proposed MCLs, as set forth in the ROD for VHOs.
2. The area of attainment shall include the entire VHO plume,
including those areas of the plume inside and outside the DOW/DSI
facility.
Similar to the KMI property, a Groundwater Monitoring Plan (GWMP)
was developed in 1993 to evaluate the effectiveness of the Remedial
Action (RA) and to evaluate groundwater post-RA and determine
compliance with the performance standards. In accordance with post-RA
groundwater monitoring requirements, RAOs would not be achieved until
the 85 percent upper confidence limit (UCL85) of the arithmetic mean
for four consecutive quarters of groundwater monitoring data did not
exceed the remedial performance goals. The test would be performed for
each monitoring well in the contaminant plume.
The DOW/DSI remediation system operated continuously between
November 1993 and April 2001 when EPA approved DOW/DSI's request to
cease active remediation. The request was based on the appearance of a
temporary petroleum sheen entering the groundwater treatment equipment
and measurable light non-aqueous phase liquid (LNAPL) near the north
boundary of the DOW/DSI property, which the treatment system was not
designed to handle. The observance of LNAPL in some of the wells was
temporary and in subsequent sampling events was not observed.
On September 18, 2015, DOW/DSI submitted a letter detailing
achievement of RAOs for the VHO plume based on requirements detailed in
the 1993 DOW/DSI GWMP. Due to the age of the document and new guidance,
EPA asked DOW/DSI to evaluate groundwater data using a more stringent
statistical test. In October 18, 2017, DOW/DSI submitted a report
detailing achievement of RAOs for the VHO plume based on using a more
stringent 95% upper confidence level on the mean and using a minimum of
eight data points. Completion of the remedial action was documented in
the Completion of Remedial Action and Completion of Work Report,
Mystery Bridge Rd./US Highway 20 Superfund Site Consent Decree for
Remedial Design and Remedial Action (OU1) and Administrative Order for
Removal Action on Consent (OU2), dated October 18, 2017.
Additional sampling was conducted in 2018 to confirm conclusions
made in the 2017 Completion of Remedial Action and Completion of Work
Report. Sampling results confirmed that concentrations of dissolved
phase VHOs were below MCLs in the wells sampled. Results of additional
confirmation sampling are documented in the Revised 2018 Well
Redevelopment and Groundwater Sampling Report, Mystery Bridge Rd/US
Highway 20 Superfund Site Consent Decree for Remedial Design and
Remedial Action (OU1), dated September 28, 2018. The Completion of
Remedial Action and Completion of Work Report, Mystery Bridge Rd./US
Highway 20 Superfund Site Consent Decree for Remedial Design and
Remedial Action (OU1) and Administrative Order for Removal Action on
Consent (OU2), was subsequently updated on April 5, 2019.
Operation and Maintenance
No operation or maintenance is required for the Site; however, the
effectiveness and presence of the environmental covenants will be
evaluated every five years as part of the Five-Year Review process.
Five-Year Review
Five Year Review Reports (FYR) are required for the Mystery Bridge
Site. FYRs are required because hazardous substances, pollutants, or
contaminants remain at the site above levels that allow for unlimited
use and unrestricted exposure (UU/UE). The next FYR is due five years
from the signing of the July 2019 FYR.
The last (5th) FYR was completed in July 2019. The 5th FYR
concluded that the remedies at OU1 and OU2 are protective of human
health and the environment, and there were no Issues or Recommendations
noted. The FYR noted that Institutional Controls (ICs) are in place
restricting the use of drinking water beneath the industrial
properties, governing the management of soils on each of properties,
and limiting future development to industrial use.
[[Page 35365]]
Community Involvement
Public participation activities have been satisfied as required in
CERCLA Section 113(k), 42 U.S.C. 9613(k) and CERCLA Section 117, 42
U.S.C. 9617. Documents in the deletion docket, which the EPA is relying
on for the proposed deletion from the NPL, are available to the public
in the information repositories, and a notice of availability of the
Notice of Intent to Delete has been published in the Casper Star-
Tribune to satisfy public participation procedures required by 40 CFR
300.425(e)(4).
Determination That the Site Meets the Criteria for Deletion in the NCP
The EPA and the State have followed procedures detailed in 40 CFR
300.425(e) in order to propose deletion of this Site from the NPL. The
Site has achieved all Remedial Action Objectives specified in the ROD
for both soil and groundwater, and all RAOs are consistent with EPA
policy and guidance. EPA in consultation with the State of Wyoming has
determined that no further Superfund response action is necessary in
order to protect human health and the environment.
List of Subjects in 40 CFR Part 300
Environmental protection, Air pollution control, Chemicals,
Hazardous substances, Hazardous waste, Intergovernmental relations,
Penalties, Reporting and recordkeeping requirements, Superfund, Water
pollution control, Water supply.
Authority: 33 U.S.C. 1321(d), 42 U.S.C. 9601-9657; E.O. 13626,
77 FR 56749, 3 CFR 2013 Comp., p. 306; E.O. 12777, 56 FR 54757, 3
CFR, 1991 Comp., p. 351; E.O. 12580, 52 FR 2923, 3 CFR, 1987 Comp.,
p. 193.
Dated: July 15, 2019.
Gregory E. Sopkin,
Regional Administrator, Region 8.
[FR Doc. 2019-15658 Filed 7-22-19; 8:45 am]
BILLING CODE 6560-50-P