FOURTH FIVE-YEAR REVIEW REPORT FOR
MIDWAY LANDFILL SUPERFUND SITE
KING COUNTY, WASHINGTON
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SEPTEMBER 2020
Prepared by
U.S. Environmental Protection Agency
Region 10
SEATTLE, WASHINGTON
CALVIN
TERADA
Digitally signed by
CALVIN TERADA
Date: 2020.08.28
14:29:33 -07'00'
Calvin Terada, Division Director
Date
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Table of Contents
LIST OF ABBREVIATIONS & ACRONYMS 3
I. INTRODUCTION 4
Site Background 4
FIVE-YEAR REVIEW SUMMARY FORM 5
II. RESPONSE ACTION SUMMARY 7
Basis for Taking Action 7
Response Actions 7
Status of Implementation 10
Systems Operations/Operation and Maintenance (O&M) 14
III. PROGRESS SINCE THE PREVIOUS REVIEW 14
IV. FIVE-YEAR REVIEW PROCESS 16
Community Notification. Community Involvement and Site Interviews 16
Data Review 17
Site Inspection 23
V. TECHNICAL ASSESSMENT 23
QUESTION A: Is the remedy functioning as intended by the decision documents'.' 23
QUESTION B: Are the exposure assumptions, toxicity data, cleanup levels and RAOs used at the time of the
remedy selection still valid'.' 24
QUESTION C: Has any other information come to light that could call into question the protectiveness of the
remedy'.' 25
VI. ISSUES/RECOMMENDATIONS 25
OTHER FINDINGS 27
VII. PROTECTIVENESS STATEMENT 28
VIII. NEXT REVIEW 28
APPENDIX A - REFERENCE LIST
APPENDIX B - SITE CHRONOLOGY
APPENDIX C - SITE HYDROGEOLOGY
APPENDIX D - 2005 DECLARATION OF RESTRICTIVE COVENANT
APPENDIX E - PRESS NOTICE
APPENDIX F - SITE INSPECTION CHECKLIST
APPENDIX G- SITE INSPECTION PHOTOS
APPENDIX H - SELECT FIGURES FROM 2019 HYDROGEOLOGIC ASSESSMENT FOR COMPLIANCE
OF 1.4-DIOXANE
APPENDIX I - DETAILED ARARS REVIEW
APPENDIX J - POTENTIOMETRIC SURFACE MAPS. TIME-SERIES PLOTS AND GROUNDWATER
MONITORING DATA
APPENDIX K - GROUNDWATER ANNUAL NOTICE
Tables
Table 1: Groundwater COCs 7
Table 2: Remedial work implemented under the 1990 Consent Decree 8
Table 3: Groundwater COC Cleanup Goals 10
Table 4: Summary of Planned and/or Implemented Institutional Controls (ICs) 12
Table 5: Protectiveness Determinations/Statements from the 2015 FYR Report 15
Table 6: Status of Recommendations from the 2015 FYR Report 15
Table 7: COCs and 1.4-Dioxane Concentrations in the Upper Gravel Aquifer from this FYR Period 17
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Tabic 8: COCs. 1,4-Dioxane, PCE and TCE Concentrations in the Sand Aquifer from this FYR Period 19
Table 9: COCs and 1,4-Dioxane Concentrations in the Southern Gravel Aquifer from this FYR Period 21
Table 10: Groundwater COC - ARARs Review 25
Table B-l: Site Chronology 1
Table J-1: Groundwater COC ARARs Review 1
Figures
Figure 1: Site Vicinity Map 6
Figure 2: Institutional Control Map 13
Figure 3: Detailed Site Map 18
Figure H-l: Operable or Potentially Operable Water Wells within one mile of the Site 1
Figure H-2: Water Wells in 1 -Mile Radius of the Site 2
Exhibit J-1: Potentiometric Surface Maps 1
Exhibit J-2: Time Series Plots 4
Exhibit J-3: Groundwater Monitoring Data from FYR Period 13
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LIST OF ABBREVIATIONS & ACRONYMS
ARAR
Applicable or Relevant and Appropriate Requirement
CERCLA
Comprehensive Environmental Response. Compensation, and Liability Act
CFR
Code of Federal Regulations
COC
Contaminant of Concern
DCA
Dichloroethane
DO
Dissolved Oxygen
EA
Endangerment Assessment
EPA
United States Environmental Protection Agency
ESD
Explanation of Significant Differences
FYR
Five-Year Review
HOPE
High-Density Polyethylene
IC
Institutional Control
1-5
Interstate 5
MCL
Maximum Contaminant Level
f^g/L
Micrograms Per Liter
mg/L
Milligrams Per Liter
MTCA
Model Toxics Control Act
NCP
National Contingency Plan
NOCOA
Notice of Construction Order of Approval
NPL
National Priorities List
NTU
Nephelometric Turbidity Units
OU
Operable Unit
O&M
Operation and Maintenance
PCE
T etrachloroethylene
PQL
Practical Quantitation Limit
PRP
Potentially Responsible Party
RAO
Remedial Action Objective
RI/FS
Remedial Investigation/ Feasibility Study
ROD
Record of Decision
RPM
Remedial Project Manager
SPU
Seattle Public Utilities
svoc
Semi-Volatile Organic Compound
TCE
Trichloroethylene
voc
Volatile Organic Compound
WAC
Washington Administrative Code
WSDOT
Washington State Department of Transportation
UU/UE
Unlimited Use and Unrestricted Exposure
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I. INTRODUCTION
The purpose of a five-year review (FYR) is to evaluate the implementation and performance of a remedy to
determine if the remedy is and will continue to be protective of human health and the environment. The methods,
findings and conclusions of reviews are documented in FYR reports such as this one. In addition. FYR reports
identify issues found during the review, if any, and document recommendations to address them.
The U.S. Environmental Protection Agency (EPA) is preparing this FYR pursuant to the Comprehensive
Environmental Response. Compensation, and Liability Act (CERCLA) Section 121. consistent with the National
Contingency Plan (NCP) (40 Code of Federal Regulations (CFR) Section 300.430(f)(4)(ii)), and considering EPA
policy.
This is the fourth FY R for the Midway Landfill Superfund site (the Site). The triggering action for this statutory
review is the completion date of the previous FYR. The FYR has been prepared because hazardous substances,
pollutants or contaminants remain at the Site above levels that allow for unlimited use and unrestricted exposure
(UU/UE).
The Site consists of one sitewide operable unit (OU). This FYR addresses the OU.
EPA remedial project manager (RPM) Ashley Groinpe led the FYR. Participants included Min-soon Yim and Jeff
Neuner from Seattle Public Utilities (SPU). Laura Lee and Lisa Gilbert from SPU contractor Parametrix. and
Ryan Burdge and Kelly MacDonald from EPA FYR support contractor Skeo. The review began on 6/20/2019.
Site Background
The Site is located betw een Interstate 5 (1-5) and Highway 99, and between South 252nd Street and South 246th
Street, in Kent. Washington (Figure 1). Currently, the Site includes a fenced 60-acre landfill, a flare station and a
storm water detention pond. Land use in the site vicinity consists of commercial and residential areas. Commercial
establishments and light industry and manufacturing border both sides of Highway 99 in the area. Two upcoming
Washington State Department of Transportation (WSDOT) and Sound Transit 1-5 Corridor transportation projects
will affect the landfill. There are plans to add lanes to 1-5 and extend a light rail track on the eastern edge of the
Site.1 These development actions will require waste removal and replacement with structural fill, relocation of the
eastern edge of the landfill cap and gas control systems, drainage improvements, and other actions. In addition,
the Site is one of several options under consideration for a potential Sound Transit operations and maintenance
facility.
From 1945 to 1966, a gravel pit was operated on site. In 1966, the city of Seattle (the City) began operating an
unlined landfill on site. The City deposited about 3 million cubic yards of solid waste at the Site from 1966 to
1983. The landfill accepted demolition materials, wood waste and other slowly-decomposing materials. Some
hazardous and industrial wastes (including about 2 million gallons of bulk industrial liquids from a single source)
were also placed in the landfill. The Washington State Department of Ecology (Ecology) is responsible for the
oversight management of the Site, as stipulated by an agreement with EPA Region 10, but EPA Region 10 retains
responsibility to complete FYRs.
Groundwater conditions beneath the landfill are complex. Hydrogeologic investigations identified four major
aquifers beneath and impacted by the landfill, in order of shallow est to deepest: Upper Gravel Aquifer. Sand
Aquifer, and the Northern and Southern Gravel Aquifers. The aquifers have unique flow directions and rates, are
interrupted by discontinuous aquitards. and are connected by several vertical flow paths, resulting in a complex
pattern of vertical and lateral groundwater flow. Generally, groundwater flows from the north of the landfill, then
beneath the landfill and to the east and southeast.
1 More information is available on the WSDOT and Sound Transit 1-5 Corridor projects:
https://apps.ecology.wa.gov/gsp/Sitepage.aspx?csid=4729.
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Appendix C provides a more detailed description of site hydrogeology. A well survey was recently conducted and
indicated that there are several domestic and irrigation wells at various depths within one mile of the Site
(Appendix H. Table 1-1).
Appendix A includes a list of documents review ed as part of this FYR. Appendix B includes a chronology of site
events.
FIVE-YEAR REVIEW SUMMARY FORM
SITE IDEM II IC A I ION
Site Name: Midway Landfill
EPA ID: WAD980638910
Region: 10
[
State: WA
City/County: Kent/King
SITE STAT! S
NPL Status: Final
Multiple OUs?
No
Has the Site achieved construction completion?
Yes
REVIEW S I A I I S
Lead agency: EPA
Author name: Ashley Grompe. with additional support provided by Skeo
Author affiliation: EPA Region 10
Rev iew period: 6/20/2019 - 9/23/2020
Date of site inspection: 3/5/2020
Type of rev iew: Statutory
Review number: 4
Triggering action date: 9/23/2015
Due date (fiveyears after triggering action date): 9/23/2020
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Figure 1: Site Vicinity Map
(Seattle
^Bremerton ^
Midway Landfill
Superfund Site
*-%'—l i J* ™ .¦ rT ¦
•Hf
'Jgg
S. 246th Street
m^tomwaterml
lUetehtionlRpndj
T..I
Flare Station
..4 ^ >
Landfill
«
-¦ -
% -
S. 252nd Street
E2 *£
- •*
Sources: Esri, DigitalGlobe, GeoEye, CNES/Airbus DS, USDA,
Earthstar Geographies, USGS, AeroGRID, IGN, DeLorme, AND, Tele
Atlas, First American, UNEP-WCMC, the GIS User Community, the
2000 ROD, the 2015 FYR, the 2019 Hydrogeologic Assessment for
Compliance of 1,4-Dioxane and King County Open GIS Data.
Legend
| Approximate Site Boundary
^ Skeo
Midway Landfill Superfund Site
City of Kent, King County, Washington
Disclaimer: This map and any boundary lines within the map are approximate and subject to change. The map is not a survey. The map is for informational
purpose® only regarding EPA's response actions at the Site.
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II. RESPONSE ACTION SUMMARY
Basis for Taking Action
In 1980, a state-mandated screening process for waste administered by the Seattle-King County Department of
Public Health started. Its goal was to eliminate further disposal of hazardous waste at the Site. When the City
closed the landfill in 1983, it covered the entire surface with a soil cover and began extensive testing of water and
gas in the landfill and its vicinity. Groundwater samples from monitoring wells in and around the landfill and gas
samples from gas probes indicated the presence of organic and inorganic contaminants outside the landfill
boundary. In 1985, Ecology also began investigating the Site and found methane gas in nearby residences.
Before the cleanup work began in 1985, there were several potential exposure pathways. These pathways included
acute hazards to residents due to high levels of methane gas reaching residential basements, and long-term
potential risks from solvents in the groundwater if people had been drinking the groundwater. The risks from
these possible exposures were greater than EPA's and the state of Washington's acceptable risk levels. Other
possible exposures could have occurred through air emissions or through direct contact with the landfill contents.
The City's contractors prepared an Endangerment Assessment (EA) as part of the 1990 remedial investigation and
feasibility study (RI/FS). Because the Rl found little contamination in the surface water, seeps or soil, the EA
concluded that the contaminants detected in these environmental media had not migrated from the landfill. The
EA also found that there was no direct exposure pathway connecting leachate to either human or ecological
receptors. There was concern about the indirect pathw ay of discharge of leachate into the groundw ater system.
A baseline risk assessment that followed EPA Superfund guidance and reflected then-current conditions at the
landfill was not done because the contaminants of concern (COCs). migration routes, and the risks to human
health and the environment were characterized in the 1990 EA. The 2000 Record of Decision (ROD) noted that
while the estimated future risk from drinking groundwater in the vicinity of the landfill following the early
cleanup work was within the acceptable risk range, there was groundwater contamination above federal drinking
water standards (maximum contaminant levels, or MCLs) in two monitoring wells east of the landfill and 1-5.
According to EPA policy, when MCLs are exceeded, action is generally warranted. In addition, state groundwater
cleanup levels under the state of Washington's Model Toxics Control Act (MTCA) were exceeded. Because
drinking this groundwater could result in an imminent and substantial endangerment to human health, remedial
action was needed at the Site. Table 1 lists site COCs for groundw ater.
Table 1: Groundwater COCs
coc
Media
1,2-Dichloroethane (DCA)
Groundwater
Vinyl chloride
Manganese
Response Actions
In October 1984, EPA proposed listing the Site on the Superfund program's National Priorities List (NPL) based
on potential groundwater contamination. Pursuant to a cooperative agreement with EPA. Ecology was designated
as the lead agency for the Site.
In September 1985, the City constructed gas migration control wells on the landfill property and gas extraction
wells beyond the landfill property to control the subsurface migration of gas. Gas was found to have migrated up
to 2,600 feet beyond the landfill prior to installation of the gas extraction system. In 1986, EPA finalized the
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Site's listing on the NPL. In September 1988, the City entered a Response Order on Consent with Ecology to
prepare a RI/FS for the landfill.
In May 1990, prior to completion of the RI/FS. the City and Ecology entered into a Consent Decree pursuant to
MTCA. The Consent Decree set forth Ecology's determination that undertaking certain remedial actions prior to a
Cleanup Action Plan (a MTCA decision document similar to a Superfund ROD) would provide immediate
protection to public health and the environment. In this Consent Decree, the City agreed to finance and perform
specific cleanup work that had four main elements:
• Construction of a landfill cover.
• Completion of a gas extraction system.
• Completion of a surface water management system.
• Preparation of a comprehensive Operation and Maintenance (O&M) Manual.
The Consent Decree also required that the City place a notice in the records of real property kept by the county
auditor stating that the landfill was listed on the NPL, and provide a copy of the Consent Decree to any
prospective purchaser or lessee of the property prior to the transfer of any legal or equitable interest in all or any
portion of the landfill.
Table 2 summarizes the implementation of the work required by the Consent Decree.
Table 2: Remedial work implemented under the 1990 Consent Decree
Consent Decree-required
Remedial Work
Implementation
Landfill gas control
An active gas control system was installed. Construction of the gas migration control
system began in September 1985 and finished in March 1991. It originally included 87
gas extraction wells, 31 of which were located off the landfill in native soil. The off-
landfill wells have since been abandoned or capped. In addition, about 70 off-landfill
gas monitoring probes were installed to provide information on gas concentrations;
about half of these probes have since been abandoned. The gas is extracted through the
control wells at the landfill and routed to a permanent blower/flare system.
Landfill surface filling and
grading
The landfill surface was regraded, which increased the soil cover over the landfill by 2
to 14 feet. The engineered grades improved surface water runoff and decreased
infiltration. The fill was also compacted to reduce permeability and prepare the surface
for the cover system. The work began in August 1988 and finished in June 1989.
Stormwatcr detention pond
construction and associated
dewatering and discharge
system
A lined detention pond was put in north of the landfill. Regrading of the landfill surface
redirected surface water, which previously infiltrated into the landfill, to the new pond.
The detention pond is a 3-acre structure, lined with a 60-inilliincter high-density
polyethylene (HOPE) membrane to eliminate infiltration. The bottom of the pond was
constructed below localized groundwater; therefore, a permanent dewatering system
was also installed, and water is pumped into the pond. Construction of the stormw atcr
detention pond began in August 1988 and was finished in June 1989.
Landfill cap installation
Construction of the final landfill cover began in October 1989 and finished in May
1991. It consists of the following layers from bottom to top: a 12-incli-tliick layer of
low permeability soil/clay material, a 50-millimeter HDPE flexible membrane, a
drainage net. filter fabric, a 12-inch-thick drainage layer, and a 12-inch-thick topsoil
layer.
Linda Heights Park stormwatcr
diversion
The Linda Heights Park drain, a 30-inch culvert that drained directly into the landfill,
was blocked. Stormwatcr is now routed through a pump station and a pipeline to the
detention pond. The old discharge line to the landfill is still in place and functions as an
overflow in the event of a pump station failure. The construction of this rerouting began
in August 1989 and finished in 1991. The pump station and associated diversion of
storm water was activated in January 1992.
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Consent Decree-required
Remedial Work
Implementation
O&M Plan
A comprehensive O&M Manual for short-term and long-term O&M activities for the
systems constructed under the Consent Decree was prepared by the City and approved
by Ecology in April 1992.
Deed notice
The deed notice was implemented; the Institutional Controls section of this FYR Report
provides more information.
Because Ecology had not completed a final remedy selection decision document under the MTCA by early 2000,
the two agencies agreed that EPA should prepare the final remedy selection document under CERCLA instead.
EPA signed the ROD in September 2000 with Ecology's concurrence.
The 2000 ROD stated that containment at the landfill has been successful and reduced site risks. However, the
containment measures already in place needed to be maintained, and institutional controls were necessary to
ensure continued long-term protection of human health and the environment. The 2000 ROD identified the
follow ing remedial action objectives (RAOs) for the response action at the Site:
• To ensure containment is effective and working.
• To ensure containment will be maintained.
• To return groundwater to drinking water standards and state cleanup standards downgradient of the
landfill boundary.
• To ensure no residential exposure to groundwater until groundwater cleanup standards have been met.
The remedy selected in the 2000 ROD included the follow ing remedial components:
• Monitoring to:
o Ensure the remedial systems are working as designed.
o Ensure progress is being made tow ard meeting the groundwater cleanup standards,
o Ensure adequate containment is maintained when and if major changes are approved by Ecology
in site operations such as turning off or scaling dow n the gas collection system.
o Demonstrate that the groundwater cleanup levels have been achieved.
• Continuing to operate and maintain all remedial elements required in the 1990 Consent Decree.
• Implementing three types of institutional controls:
o The City will place a notice in the records of real property kept by the King County auditor,
alerting any future purchaser of the landfill property, in perpetuity, that this property had been
used as a landfill and was on EPA's NPL, and that future use of the property is restricted, per the
1990 Consent Decree.
o The City needs to ensure continued O&M of the containment and monitoring systems if any
portion of the property is sold, leased, transferred or otherwise conveyed, per the 1990 Consent
Decree.
o Notices are needed so that no water supply wells are constructed and used in areas with
groundwater contamination emanating from the landfill, including at minimum:
¦ Annual notices to the Seattle-King County Department of Public Health. Ecology, local
water districts (currently the Kent and High line water districts), and locally active well
drillers of the groundwater conditions in the affected areas downgradient of the landfill.
¦ The City will also annually notify the owner of Well #37 in writing of groundwater
conditions around the well. Alternatively, the City can provide Ecology with adequate
assurances that this well has been properly abandoned.2
The 2000 ROD states that the more stringent of federal drinking water standards and state cleanup standards
under the MTCA are the cleanup levels. Table 3 lists groundwater cleanup goals and their basis. The point of
compliance for the groundwater will be at the edge of the landfill waste as specified in a Compliance Monitoring
2 In the 2000 ROD. Well #37 was identified as being an unused, covered well on privately owned property that was within
1,000 feet of the Site.
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Plan approved by Ecology. All groundwater downgradient of this point of compliance will need to meet these
cleanup goals for contaminants resulting from releases from the landfill before the Site is deleted from the NPL.
Table 3: Groundwater COC Cleanup Goals
Groundwater COC
2000 ROD Cleanup Goal
Basis
1,2-DCA
5 micrograms per liter (ng/L)
Federal Drinking Water Standard (MCL)
Vinyl chloride
0.02 |ig/La
MTCA Method B
Manganese
2.2 milligrams per liter (mg/L)
MTCA Method B
Notes:
Source: Table 8-1, 2000 ROD.
a. Pursuant to Washington Administrative Code (WAC) 173-340-707(2), Ecology will use the
practical quantitation limit (PQL) of 0.2 micrograms per liter (ng/L) to determine compliance with
this cleanup standard because the cleanup standard is lower than the PQL.
Status of Implementation
Several remedial elements were implemented under the 1990 Consent Decree prior to the 2000 ROD. as described
in the Response Actions section of this FYR Report. This section summarizes implementation for the remedy
components of the 2000 ROD.
The City has conducted performance and compliance monitoring since 1989. Monitoring includes fluid level
monitoring, groundwater chemistry monitoring and landfill gas monitoring performed on an ongoing basis. The
current monitoring program is described in the 2000 Midway Landfill Monitoring Plan. Monitoring data are
discussed in further detail in the Data Review section of this FYR Report.
The City continues to conduct O&M activities for the landfill cover system, gas system and surface water
systems. O&M requirements for the Site are described in 1992 Midway Landfill O&M Manual, which includes
short-term and long-term O&M for the systems constructed under the Consent Decree. Ecology continues to
oversee the City's O&M activities. Ecology can approve operational changes when such changes ensure that the
Site and remedy will remain protective. The Seattle-King County Public Health Department has an opportunity to
review requested operational changes.
Institutional Control (IC) Review
The 2000 ROD required several institutional controls, including: 1) a notice on the property alerting any future
purchaser of the landfill property, in perpetuity, that this property had been used as a landfill and was on EPA's
NPL and that future use of the property is restricted; 2) assurance by the City of continued O&M of the
containment and monitoring systems if any portion of the property is sold, leased, transferred or otherw ise
conveyed; and 3) notices so that no water supply wells are constructed and used in areas with groundwater
contamination emanating from the landfill. Site institutional controls are summarized below in Table 4.
The first two of the three institutional control requirements are addressed via a 2005 Declaration of Restrictive
Covenant, which is in place on the landfill parcels (Figure 2). The full covenant is included in Appendix D. The
covenant includes the following restrictions, verbatim:
• Any activity on the Property that may interfere with the Cleanup Action as defined in the ROD. is
prohibited. Any future use of the Property shall not disturb the integrity of the final cover, or any other
components of the containment system. Any future use of the Property shall not disturb, damage, or alter
any component of the landfill gas extraction system, or any of its attendant monitoring probes or wells
except as approved in writing by the Department of Ecology or its successor agency. Any activity on the
Property that may result in the release of a hazardous substance that was contained as part of the Cleanup
Action is prohibited. Any activity on the Property that may results in endangerment to human health or
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the environment by hazardous substances contained on the Property or by gas generated by and emitted
from the Property is prohibited.
• Except for groundw ater monitoring, no groundw ater may be taken for any purpose from any well on the
Property without Department of Ecology ("Ecology") approval. No water supply wells may be installed
on the Property.
• City must give thirty (30) days advance written notice to Ecology of the City's intent to convey any
interest in the Property. No conveyance of title, easement, lease, or other interest in the Property shall be
consummated by the City without adequate provision for continued monitoring, operation and
maintenance of the Cleanup Action.
• City must restrict leases to uses and activities consistent with this Restrictive Covenant and notify all
lessees of the restrictions on the use of the Property.
• City must notify and obtain approval from Ecology prior to any use of the Property that is inconsistent
with the terms of this Restrictive Covenant. Ecology may approve any inconsistent use only after public
notice and comment.
• The City shall allow authorized representatives of Ecology the right to enter the Property at reasonable
times and with reasonable prior notice for the purpose of evaluating compliance with the Cleanup Action
and to inspect records that are related to the Cleanup Action.
• The City reserves the right under WAC 173-340-440 to record an instrument that provides that this
Restrictive Covenant shall no longer limit use of the Property or be of any further force or effect.
How ever, such an instrument may be recorded only if Ecology, after public notice and opportunity for
comment, concurs.
Per the third institutional control requirement, the City must send an annual written notice about the groundwater
quality downgradient from the landfill to the Seattle-King County Department of Public Health, nearby water
districts, locally active licensed well drillers, and Ecology. A map documenting the location of wells with COC
concentrations above ROD cleanup levels was included in annual notices beginning in 2017. These notices are
sent on an annual basis. A copy of the 2020 letter is in Appendix K.
SPU contractor Parametrix completed an updated well survey of private wells in the site vicinity as part of the
2019 1,4-dioxane hydrogeological assessment, which is further summarized in the Data Review section of this
report. Appendix H includes a map of private wells near the Site and a table summarizing well information
including the well type, use status, aquifer and position related to the Site. Downgradient or cross-gradient of the
Site, the survey identified six wells that are in use or potentially in use. Of these, two are domestic wells for
drinking water, and four are irrigation wells. One domestic well is in the Southern Gravel Aquifer, and the other
domestic well is in the Alluvial Aquifer, which is not present in the immediate site area. The Southern Gravel
Aquifer discharges to the Alluvial Aquifer east of the landfill. One of the domestic wells was installed in 2016
within the groundwater quality notification area. The presence of these wells, and the well installed in 2016 in
particular, indicate that there may be an issue with the current groundwater quality notification system for local
regulatory agencies and well drillers. It is currently unknow n whether site-related COCs or 1,4-dioxane are
present in these private wells.
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Table 4: Summary of Planned and/or Implemented Institutional Controls (ICs)
Media, Engineered
Controls, and Areas
That Do Not
Support UIJ/UE
Based on Current
Conditions
ICs
Needed
ICs Called
for in the
Decision
Documents
Impacted
Parcel(s)
IC
Objective
Title of IC Instrument
Implemented and Date
(or planned)
Groundwater, soil.
and remedy
components at the
landfill property
Yes
Yes
2122049014
2122049021
2122049025
2122049026
2122049033
2122049137
2222049168a-b
Assure continued
integrity of the
cleanup action and
provide notice to
land users
2005 Declaration of
Restrictive Covenant
Downgradient
Groundwater
Yes
Yes
Contaminated
groundwater
downgradient
of the landfill
Notify parties of
groundwater quality
to prevent use of
contaminated
groundwater
Groundwater quality notice
to Seattle-King County
Department of Public
Health, nearby
water districts, locally
active licensed well drillers
and Ecology
Notes:
a. The 2005 Declaration of Restrictive Covenant also listed parcel 2122903307. However, this parcel number did
not return any results in an online search in the parcel dataset in May 2020. It was not included in this table or in
Figure 2.
b. The area within the approximate site boundary west of parcel 2122049026 that is not included in the 2005
Declaration of Restrictive Covenant is outside of the fenced landfill area.
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Figure 2: Institutional Control Map
400
800
1,600
Feet
Legend
Sources: Esri, DigitalGlobe, GeoEye, Earthstar
Geographies, CNES/Airbus DS, USDA, USGS,
AeroGRID, IGN, the GIS User Community, King
County GIS Open Data, the 2000 ROD and the
2005 Declaration of Restrictive Covenant.
Parcels under 2005 Declaration
of Restrictive Covenant
^ Skeo
Midway Landfill Superfund Site
City of Kent, King County, Washington
Disclaimer: This map and any boundary lines within the map are approximate and subject to change. The map is not a survey. The map is for informational
purposes only regarding EPA's response actions at the Site.
13
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Systems Operations/Operation and Maintenance (O&M)
Regular operation and maintenance activities at the Site include monitoring, inspection and maintenance of
groundwater, surface water collection and discharge systems, landfill gas collection and transmission systems,
and the landfill cover. Groundw ater monitoring includes groundw ater hydraulic monitoring and groundw ater
quality monitoring as stated in the 2000 Monitoring Plan.
The detention pond is monitored five days per week. If the water level in the pond exceeds 1.0 foot, samples are
collected at the three inlet locations (inflow s from the landfill, Highway 99, and 1-5) and discharge at the
detention pond outlet and tested in the field for pH. temperature, dissolved oxygen (DO), turbidity and
conductivity. Inspections of the surface water collection pipelines using a TV camera are conducted every three
years. The most recent inspection was performed in August 2017, and no abnormalities or defects were noted in
the piping. The next TV inspection will take place in 2020. No significant changes were made to the groundwater
monitoring program or the surface water collection or discharge system during the past five years.
Inspection, maintenance, and monitoring for the landfill gas collection and transmission system are conducted per
the 1992 O&M Plan. Monitoring of the gas extraction system includes daily manifold monitoring and monthly
extraction well monitoring. The flare is continuously monitored to ensure that the mechanical systems are
operating properly. Landfill staff routinely inspect the facility five days a week and respond to off-hour system
alarms such as flame failure or temperatures out of permitted range on the enclosed flare. Landfill gas compliance
probes are monitored weekly, monthly, or quarterly, depending on the compliance status of the probe. Landfill
gas control updates at the flare system during this five-year period include:
• Montrose Air Quality Services source tested the flare on December 14, 2016. The final report for this
source test, dated January 24, 2017, was submitted to the Puget Sound Clean Air Agency. The average
non-methane organic compounds, as hexane, were 5.5 ppm. and when corrected to 3 percent 02. were
10.6 parts per million. The flare temperature, averaged over the period of the test, was 1,245 °F.
• A Notice of Construction Application for Permit Modification was prepared and delivered to the Puget
Sound Clean Air Agency on June 5, 2017, to support modifications to the previous Notice of
Construction Order of Approval (NOCOA) 8517 issued on June 20, 2001. The NOCOA 10440
modifications include lowering the operating temperature restriction based on the most recent successful
source test results and allow ing the in jection of natural gas into the landfill gas stream to ensure stable
flare operation. The Puget Sound Clean Air Agency awarded Order of Approval 11400 on October 11.
2017.
• In the first quarter of 2018, the Startup. Shutdow n, and Malfunction (SSM) Plan for the Landfill Flare
Supplemented with Natural Gas (SPU 2018) was completed to comply with Condition 10 of NOCOA No.
11400 and the requirements of 40 CFR 63.6(e)(3). The final plan is posted at the flare station.
As of 2016, landfill cap and cover integrity inspections are documented monthly in a log sheet based on the O&M
Manual. Several localized areas east of the flare facility were noted to have experienced minor settlement that
resulted in temporary pooling of standing water during periods of high rainfall in the winter of 2020. The
localized areas that have experienced minor settlement will be investigated. Repairs will be conducted in
accordance with the O&M Manual.
Following completion of the transportation construction projects, a revised or new O&M Manual and a revised
Compliance Monitoring Plan (CMP) will be submitted for review and approval. The revised O&M Manual will
reflect changes to the gas extraction system, storm water pond, and groundwater monitoring network.
III. PROGRESS SINCE THE PREVIOUS REVIEW
This section includes the protectiveness determinations and statements from the previous FYR Report as well as
the recommendations from the previous FYR Report and the status of those recommendations.
14
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Table 5: Protectiveness Determinations/Statements from the 2015 FYR Report
OIJ #
Protectiveness
Determination
Protectiveness Statement
Sitewide
Protectiveness Deferred
A protectiveness determination of the remedy at the Midw ay Landfill cannot be
made at this time until further information on the extent of 1,4 dioxane is obtaineu.
Further information will be obtained by additional water quality sampling
downgradient of the site, either at existing and appropriately constructed wells
identified by Ecology or by new wells installed for this purpose and by conducting
a survey of the use of downgradient private wells. It is expected that the
protectiveness determination can be made by September, 2018.
Table 6: Status of Recommendations from the 2015 FYR Report
Issue
Recommendations
Current
Status
Current Implementation Status
Description
Completion
Date (if
applicable)
Upgradient sources of
VOCs in groundwater
will continue to limit
the potential for the
chemicals of concern in
the Southern Gravel
Aquifer to decrease
below the ROD cleanup
levels, especially
because the
concentrations of VOCs
in upgradient well MW-
2IB arc not decreasing.
Ecology will notify property
owners with potential
upgradient sources of
contamination, including
current COCs and 1,4-
dioxane, by September 2016.
Ecology will advise the
property owners on cleanup
requirements. By September
2018, property owners need
to take substantive action on
the upgradient source.
Ongoing
VOC concentrations in MVV-2 IB
remain above MCLs. EPA and
Ecology arc currently convening
on appropriate next steps.
Planned:
9/30/2021
1.4-dioxane has been
found in several wells
at concentrations that
exceed regulatory
levels. The ROD
contains no cleanup
level for 1,4-dioxane.
Additionally , the first
five year review
identified a change to
vinyl chloride cleanup
level.
EPA will write an
Explanation of Significant
Difference to add 1,4-
dioxane as a COG to the
ROD. EPA will consider
whether the vinyl chloride
cleanup level established in
the ROD should be changed,
and if so. it will be
documented in an ESD.
Considered
But Not
Implemented
EPA is still assessing whether
1.4-dioxane is a site-related COC
and determined it was not
necessary to issue an Explanation
of Significant Differences (ESD)
at this time. EPA and Ecology
will examine concentration trends
from further delineation efforts
and reconsider if conditions
worsen. EPA is still considering
whether a cleanup goal change is
needed for vinyl chloride.
Completed:
10/29/2019
15
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Issue
Recommendations
Current
Status
Current Implementation Status
Description
Completion
Date (if
applicable)
The extent of the 1,4-
o.xane plume has not
been delineated.
Ecology will do a search to
determine the location of any
wells constructed within a
one mile radius of Midway
Landfill and 1) identify the
status of those wells (active,
inactive) 2) determine the use
(water
supply/irrigation/monitoring/
etc.) 3) compile well
construction logs as
available. Based on the well
construction logs. Ecology
will determine if any of these
wells arc constructed in a
manner that would allow for
water quality sampling that
would allow further
characterization and
delineation of the
downgradient of the site. If
no existing wells can be
confidently used for this
purpose. Ecology will
identify locations for new
monitoring wells to delineate
the extent of the 1.4-dioxane
plume.
Completed
In 2019, SPU contractor
Paranictrix completed a 1,4-
dioxane hydrogcological
assessment, which included
identifying wells within a 1-mile
radius of the Site and their
statuses. Appendix H provides
information gathered from this
well survey. SPU plans to
conduct a sampling event at 1)
selected currently unused
monitoring wells in the Sand
Aquifer and Southern Gravel
Aquifer to evaluate flow
pathways; and at 2) available
water wells in the Southern
Gravel Aquifer and located
further downgradient of
monitoring wells where 1,4-
dioxane exceeds regulatory
criteria.
Completed:
10/29/2019
The extent of the 1,4-
dioxane plume is
unknown. It is therefore
uncertain whether or
not the ICs prohibiting
water supply well
drilling in "the affected
area" arc protective.
Ecology will send out letters
to all properties in a one mile
radius from Midway Landfill
to determine if they contain a
well, if that well is being
used, and for what purpose
(e.g. drinking water,
irrigation, etc). In the event
that a property owner is
actively using a well,
Ecology will notify the
owner of the potential risks
iinincdiatclv.
Under
Discussion
EPA is still assessing whether
1.4-dioxane is a site-related COC.
Downgradient or cross-gradient
of the Site, the well survey
identified six wells that arc in use
or potentially in use. Of these,
two are domestic wells for
drinking water, and four arc
irrigation wells. The City plans to
provide well users an advisory
letter on 1.4-dioxanc. gather
information on the wells and offer
to sample the wells.
Planned:
12/31/2020
IV. FIVE-YEAR REVIEW PROCESS
Community Notification, Community Involvement and Site Interviews
A public notice was made available by a new spaper posting in the Kent Chronicle print edition and online on
August 7th and August 14th, 2020 (Appendix E). This notice was also added to the EPA site profile page on July
30th, 2020. Both publications stated that the FYR was underway and invited the public to submit any comments to
the EPA. The results of the review and the report will be made available on EPA's Site webpage and at the Site's
information repository, Woodmont Library, located at 6809 Pacific Highway South, in Des Moines. Washington
98198.
16
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Data Review
Annual Groundwater Monitoring
During this FYR period, groundwater was monitored annually in May from 2015 to 2019 in the Upper Gravel
Aquifer, the Sand Aquifer and the Southern Gravel Aquifer. COCs manganese, vinyl chloride, and 1,2-DCA were
monitored, in addition to several other dissolved metals, semi-volatile organic compounds (SVOCs) and volatile
organic compounds (VOCs). Wells monitored during this FYR period are show n on Figure 3. Potentiometric
surface maps for the three aquifers, time-series plots for select contaminants, and historical groundwater data are
included in Appendix J. Overall, as evidenced in the time-series plots in Appendix J. groundwater concentrations
are still above ROD cleanup goals or drinking water standards for some contaminants but have declined from
historical levels (except for upgradient concentrations of trichloroethylene (TCE) and tet rach 1 o roc tin 1 ene (PCE),
which show increasing trends).
Upper Gravel Aquifer
The Upper Gravel Aquifer monitoring well network includes upgradient wells MW-16 and MW-2 1A and
downgradient well MW-7A. MW-7A has been dry since 1992 due to declining groundwater levels in the Upper
Gravel Aquifer. During this FYR period (2015-2019), groundwater was sampled from MW-16 and MW-2 1 A.
Concentrations for COCs and 1.4-dioxane in these wells are summarized in Table 7. Manganese was detected
during this FYR period, but concentrations were always below the cleanup goal, which is consistent with
historical data (see time-series plot in Exhibit J-2, Appendix J). Vinyl chloride concentrations were always non-
detect. but on several occasions the detection limit exceeded the ROD cleanup goal of 0.02 micrograms per liter
(|ig/L); this is consistent with the past 20 years of data for vinyl chloride in the Upper Gravel Aquifer (Exhibit J-2,
Appendix J). Concentrations of 1,2-DCA and 1,4-dioxane were all below detection.
Table 7: COCs and 1,4-Dioxane Concentrations in the Upper Gravel Aquifer from this FYR Period
Manganese (mg/L)
1,2-DCA (ng/L)
Vinyl Chloride (ng/L)
1,4-Dioxane (jig/L)
ROD cleanup goal
2.2
5
0.02
MTC. 1 criterion
-
-
0.4375
5/7/2015
0.092
1.0U
0.020 U
0.4 U
MW-16
(upgradient)
5/5/2016
0.142
1.0U
0.20 U
0.4 U
5/3/2017
0.101
1.00 u
0.20 U
0.4 U
5/8/2018
0.0943
1.00 u
0.020 U
0.4 U
5/7/2019
0.095
1.00 u
0.200 U
0.4 U
5/5/2015
0.001
LOU
0.020 U
0.4 U
MW-21A
(upgradient)
5/3/2016
0.026
LOU
0.20 U
0.4 U
5/2/2017
0.0274
1.00 U
0.20 U
0.4 U
5/9/2018
0.0241
1.00 U
0.020 U
0.4 U
5/8/2019
0.0010 U
1.00 u
0.200 U
0.4 U
Notes:
Source: 2020 Remedial Action Status Report.
U = Indicated the compound was undetected at the reported concentration
17
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Figure 3: Detailed Site Map
MW-8B
® MW-15A
500 1,000
2,000
I Feet
Sources: Esri, DigitalGlobe, GeoEye, Earthstar
Geographies, CNES/Airbus DS, USDA, USGS,
AeroGRID, IGN, the GIS User Community, the
2000 ROD, the 2019 Hydrogeologic Assessment
for Compliance of 1,4-Dioxane and King County
Open GIS Data.
Legend
Approximate Site Boundary
^ Upper Gravel Aquifer Monitoring Well
® Sand Aquifer Monitoring Well
© Southern Gravel Aquifer Monitoring Well
^ Skeo
Midway Landfill Superfund Site
City of Kent, King County, Washington
Disclaimer: This map and any boundary lines within the map are approximate and subject to change. The map is not a survey. The map is for informational
purposes only regarding EPA's response actions at the Site.
18
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Sand Aqui fer
The Sand Aquifer monitoring well network includes upgradient wells MW-8B, MW-17B and MW-21B and
downgradient wells MW-7B, MW-15A, MW-20A and MW-23A. Since the remedial action, water levels in the
Sand Aquifer have declined due to decreased discharge from the Upper Gravel Aquifer, and wells MW-20A and
MW-23A have routinely been dry. During this FYR period, groundwater was sampled in the Sand Aquifer from
wells MW-7B, MW-8B, MW-15A, MW-17B and MW-21B. Concentrations in these wells for COCs, 1,4-
dioxane, and select VOCs that exceed MCLs are summarized in Table 8. Concentrations of 1,2-DCA were all
below detection or below the cleanup goal. Manganese was detected in all wells but concentrations only exceeded
the ROD cleanup goal of 2.2 milligrams per liter (mg/L) in well MW-7B, with relatively stable concentrations
(ranging from 2.29 mg/L to 2.48 mg/L during this FYR period). Concentrations of manganese in MW-7B have
exceeded the cleanup goal since monitoring began in this well (2011), but they overall demonstrate a declining
trend (see time-series plot in Exhibit J-2, Appendix J). MW-7B is at the southeastern, downgradient edge of the
landfill.
Vinyl chloride concentrations exceeded the ROD cleanup goal of 0.02 (ig/L in MW-7B, MW-17B and MW-21B.
In all these wells, vinyl chloride concentrations have declined from historical highs, but concentrations still
oscillated between non-detection and exceeding the cleanup goal (see time-series plot in Exhibit J-2, Appendix J).
In some instances, the detection limit was above the ROD cleanup goal. Concentrations of 1,4-dioxane
consistently exceeded the MTCA Method B cleanup level of 0.4375 (ig/L in wells MW-7B, MW-17B and MW-
21B (Table 8). MW-17B and MW-21B are upgradient of the landfill. MW-7B is downgradient of the landfill. The
1,4-dioxane concentrations between these upgradient and downgradient wells were fairly consistent, but the
highest 1,4-dioxane concentration in this aquifer during this FYR period was found in upgradient well MW-21B
(2.8 (ig/L). While both 1,4-dioxane and vinyl chloride exceedances were present in downgradient well MW-7B,
they were not detected in well MW-15A, which is downgradient of MW-7B.
The 2015 FYR Report noted that upgradient sources of VOCs in groundwater would limit the potential for COCs
to fall below the ROD cleanup goals, as evidenced by VOC concentrations in MW-21B.3 In the last five years,
TCE concentrations in MW-21B have increased above the MCL of 5 j^ig/L to 6.26 (ig/L in May 2019; this appears
to be a slight upward trend when compared to historical TCE concentrations (Exhibit J-2, Appendix J). PCE
concentrations in MW-21B remained significantly above the MCL of 5 (ig/L, ranging from 110 (ig/L to 130 (ig/L
in this FYR period; this is consistent with PCE concentrations from the previous FYR period but is part of an
overall upward trend (Exhibit J-2, Appendix J). TCE and PCE were not detected in monitoring wells
downgradient of the Site during this FYR period in the Sand Aquifer.
Table 8: COCs, 1,4-Dioxane, PCE and TCE Concentrations in the Sand Aquifer from this FYR Period
Manganese
(mg/L)
1,2-DCA
(Mg/L)
Vinyl
Chloride
(Ug/L)
1,4-
Dioxane
(Ug/L)
TCE
(Mg/L)
PCE
(Mg/L)
ROD cleanup goal
2.2
5
0.02
-
-
MTCA criterion or MCL
-
-
-
0.4375
(MTCA)
5
(MCL)
5
(MCL)
MW-7B
(downgradient)
5/6/2015
2.48
1.0U
0.17
1.0
LOU
LOU
5/4/2016
2.44
1.0U
0.02 U
0.6
LOU
LOU
5/3/2017
2.47
1.00 U
0.02 M. U
1.0
1.00 U
1.00 U
5/8/2018
2.29
1.00 U
0.0954
2.0
1.00 U
1.00 U
5/7/2019
2.32
1.00 U
0.200 U
1.3
1.00 U
1.00 U
MW-15A
(downgradient)
5/7/2015
0.002
LOU
0.020 U
0.4 U
LOU
LOU
5/5/2016
0.002
LOU
0.20 U
0.4 U
LOU
LOU
5/4/2017
0.0010 U
1.00 U
0.20 U
0.4 U
1.00 U
1.00 U
3 The 2015 FYR Report issue and recommendation commented on VOCs in the Southern Gravel Aquifer in MW-21B.
However, MW-21B is in the Sand Aquifer.
19
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Manganese
(mg/L)
1,2-DCA
(Mg/L)
Vinyl
Chloride
(Ug/L)
1,4-
Dioxane
(Ug/L)
TCE
(Mg/L)
PCE
(Mg/L)
ROD cleanup goal
2.2
5
0.02
-
-
MTCA criterion orMCL
-
-
-
0.4375
(MTCA)
5
(MCL)
5
(MCL)
5/7/2018
0.00273
1.00 u
0.020 U
0.4 U
1.00 U
1.00 U
5/6/2019
0.0010 U
1.00 u
0.200 U
0.4 U
1.00 U
1.00 U
MW-8B
(upgradient)
5/6/2015
0.087
1.0U
0.02 U
0.4 U
LOU
LOU
5/4/2016
0.047
1.0U
0.20 U
0.4 U
LOU
LOU
5/4/2016
(Duplicate)
0.049
LOU
0.20 U
0.4 U
LOU
LOU
5/4/2017
0.0614
1.00 U
0.20 U
0.4 U
1.00 U
1.00 U
5/8/2018
0.351
1.00 U
0.020 U
0.4 U
1.00 U
1.00 U
5/7/2019
0.275
1.00 U
0.200 U
0.4 U
1.00 U
1.00 U
MW-17B
(upgradient)
5/5/2015
0.046
2.8
0.11
1.5
LOU
LOU
5/3/2016
0.044
2.6
0.20 U
1.0
LOU
LOU
5/2/2017
0.0425
2.11
0.20 U
1.5
1.00 U
1.00 U
5/9/2018
0.0315
2.10
0.0375
0.9
1.00 U
1.00 U
5/8/2019
0.0330
2.14
0.200 U
0.7
1.00 U
1.00 U
MW-21B
(upgradient)
5/5/2015
0.372
LOU
0.031
2.8
4.6
110
5/3/2016
0.342
LOU
0.20 U
1.9
4.6
110
5/2/2017
0.346
1.00 U
0.20 M. U
1.7
5.92
130
5/9/2018
0.341
1.00 U
0.0299
1.9
6.68
128
5/8/2019
0.345
1.00 U
0.200 U
1.5
6.26
118
Notes:
Source: 2020 Remedial Action Status Report.
U = Indicated the compound was undetected at the reported concentration
M = Estimated value for an analyte detected and confirmed by an analyst but with low spectral match parameters
Highlight = Concentration exceeds standard
Southern Gravel Aquifer
During this FYR period, groundwater was sampled in the Southern Gravel Aquifer from wells MW-14B, MW-
20B, MW-23B, MW-29B and MW-30C. Concentrations for COCs and 1,4-dioxane in these wells are summarized
in Table 9. Concentrations of 1,2-DCA were all below detection or below the cleanup goal. Manganese was
detected in all wells but only exceeded the cleanup goal once in MW-20B in May 2015, with a concentration of
2.27 mg/L (just above the cleanup goal of 2.2 mg/L). This appears to be part of an overall downward trend when
compared to historical manganese concentrations (Exhibit J-2, Appendix J).
Concentrations of vinyl chloride exceeded the cleanup goal (0.02 j^ig/L) in all wells during this FYR period. Vinyl
chloride concentrations ranged from non-detect to 0.516 pg/L (Table 9). Concentrations fluctuated between
exceedances and non-detects in well MW-14B and MW-23B, while exceedances were more consistent in wells
MW-20B, MW-29B and MW-30C (Table 9). In some instances, the detection limit was above the ROD cleanup
goal. Exceedances of vinyl chloride in wells MW-29B and MW-30C, which are the wells sampled in this aquifer
that are furthest downgradient of the Site, indicate the extent of vinyl chloride may not be delineated. Overall
concentrations in wells MW-29B and MW-30C have declined from historical levels but remain above the ROD
cleanup goal.
Concentrations of 1,4-dioxane consistently exceeded the MTCA Method B cleanup level of 0.4375 pg/L in all
wells. Concentrations generally trended upward in well MW-14B, downward in MW-20B, remained stable in
MW-23B and MW-30C, and fluctuated in MW-29B. The highest 1,4-dioxane concentrations were found in MW-
20B, with concentration ranging from 27 pg/L in 2015 to 12.9 pg/L in 2019. The extent of 1,4-dioxane is
currently being investigated with the proposed additional sampling events summarized later in this Data Review
section.
20
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Table 9: COCs and 1,4-Dioxane Concentrations in the Southern Gravel Aquifer from this FYR Period
Manganese
(mg/L)
1,2-DCA
Qig/L)
Vinyl Chloride
Gig/L)
1,4-Dioxane
Qig/L)
ROD cleanup goal
2.2
5
0.02
-
MTCA criterion
-
-
-
0.4375
MW-14B
(downgradient)
5/5/2015
0.861
1.0U
0.24
4.1
5/3/2016
0.837
1.0U
0.20 U
5.4
5/2/2017
0.834
1.00 U
0.20 M
6.8
5/8/2018
0.867
1.00 U
0.104
10.3
5/7/2019
0.884
1.00 U
0.200 U
10.3
5/7/2019 (Duplicate, MW-
35)
0.877
1.00 U
0.200 U
9.6
MW-20B
(downgradient)
5/6/2015
2.27
LOU
0.29
27
5/4/2016
2.11
LOU
0.33 M
18
5/3/2017
1.92
1.00 U
0.346
19.9
5/9/2018
1.70
1.00 U
0.257
17.6
5/9/2018 (Duplicate, MW-
35)
1.71
1.00 U
0.266
19.0
5/8/2019
1.61
1.00 u
0.200 U
12.9
MW-23B
(downgradient)
5/7/2015
0.121
1.7
0.098
1.3
5/7/2015, (Duplicate MW-
35)
0.121
1.7
0.099
1.2
5/5/2016
0.123
2.2
0.20 U
1.5
5/4/2017
0.118
1.56
0.20 M
2.0
5/4/17 (Duplicate MW-35)
0.115
1.49
0.20 M, U
2.3
5/7/2018
0.105
1.48
0.0866
2.1
5/6/2019
0.109
1.81
0.200 U
1.8
MW-29B
(downgradient)
5/4/2015
0.858
3.8
0.48
7.9 J
5/4/2015
0.861
3.9
0.44
12 J
5/2/2016
0.830
3.9
0.49 M
11
5/1/2017
0.820
3.54
0.516
13.8
5/1/17 (Duplicate MW-31)
0.817
3.52
0.450
11.7
5/7/2018
0.805
3.37
0.335
12.5
5/6/2019
0.812
3.92
0.337
8.8
5/6/19 (Duplicate MW-31)
0.801
3.91
0.330
9.0
MW-30C
(downgradient)
5/4/2015
0.678
LOU
0.200
4.2
5/2/2016
0.638
LOU
0.210 M
4.4
5/2/16 (Duplicate MW-31)
0.639
LOU
0.200 M
4.7
5/1/2017
0.663
1.00 U
0.241
6.4
5/7/2018
0.644
1.00 U
0.172
5.6
5/7/18 (Duplicate MW-31)
0.691
1.00 U
0.173
5.5
5/6/2019
0.669
1.03
0.200 U
4.8
Notes:
Source: 2020 Remedial Action Status Report.
U = Indicated the compound was undetected at the reported concentration
J = Indicated the compound was detected at an estimated concentration
M = Estimated value for an analyte detected and confirmed by an analyst but with low spectral match parameters
Highlight = Concentration exceeds standard
2019 1.4-Dioxane Assessment
In response to several issues and recommendations from the 2015 FYR Report, SPU contractor Parametrix
completed an assessment of 1,4-dioxane in 2019. The report noted that 1,4-dioxane concentrations were above the
MTCA Method B cleanup level in eight of the currently sampled 12 monitoring wells at the Site, with highest
21
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concentrations occurring in the Southern Gravel Aquifer. The assessment also included an updated well survey of
private wells in the site vicinity (Appendix H). Twelve wells were identified as in use. potentially in use. or not in
use but potentially operable. Of the eight in use or potentially in use wells, six are irrigation wells and two are
domestic wells used for drinking water.
The report recommended the follow ing actions:
1) Additional sampling of downgradient and cross-gradient locations:
a. SPU plans to pursue an incremental approach to further investigate the extent of 1,4-dioxane in
groundwater downgradient of the landfill, including a one-time initial sampling event for 1,4-
dioxane at the follow ing locations: 1) selected currently unused site wells in the Sand Aquifer and
the Southern Gravel Aquifer to further evaluate flow pathw ays; and 2) available water wells in
the Southern Gravel Aquifer and located further dow ngradient of monitoring wells MW-20B,
MW-29B, and MW-30C where 1,4-dioxane exceeds regulatory criteria.
b. If results of the investigation show that 1.4-dioxane is present in further downgradient wells, or if
no wells are available for sampling, additional wells may be selected or installed if concentrations
remain above regulatory criteria.
c. Ow ners of domestic wells that are in use or potentially in use for domestic purposes within 1 mile
of the Site and are located in hydraulically downgradient or cross-gradient locations from the Site
will be contacted to determine if their well is being used, and the City will offer to sample their
well.
2) Evaluation of upgradient sources:
a. Several potential 1,4-dioxane sources were noted upgradient of the Site. The report suggested that
further testing for 1,4-dioxane at these other release sites may be necessary to differentiate and
identify 1,4-dioxane sources.
Surface Water Monitoring
Three hundred seventy observations were made between 2015 through 2019 when the detention pond level
exceeded 1.0 foot. Most of the data were collected from October through early May during the wet season. Most
of the data for the detention pond discharge samples collected at the pond outlet were within compliance criteria.
The exceptions were: 38 of the 353 measurements for DO (criteria >8.0 mg/L). 23 of the 368 measurements for
pH (criteria to be within 6.5 to 8.5 units), and four of the 355 measurements for turbidity (criteria 29
Nephelometric Turbidity Units (NTU)). The average discharge pH was 7.1. the minimum was 6.1 and the
maximum was 9.2. There were no exceedances at the discharge for temperature (criteria <18 degrees Celsius) or
conductivity (criteria <400 (is/cm).
Some of the 2015 through 2019 measurements for these parameters were also out of compliance in the inflow
samples. In general, conductivity and turbidity were higher in the inflow from Highway 99 and 1-5 than in the
detention pond discharge, which was comparable to the landfill inflow.
The pH of the 1-5 and Highway 99 inflow samples was generally higher than the pH of the pond discharge, which
was comparable to the landfill inflow. Measurements of pH exceeding 8.5 units were observed in detention pond
discharge samples between 2015 through 2017, but were not observed during 2018 and 2019.
There is no discernable correlation between the out-of-compliance measurements and the pond level or
precipitation measurements. It is possible that lower DO measurements and the exceedances of pH may be related
to the presence of wildlife such as waterfowl.
After exiting the detention pond, the water flow s through over 1 mile of discharge pipe, undergoing a substantial
gradient drop, and it passes through a baffled outlet structure prior to discharging into the north fork of McSorley
Creek. Over the course of this piped flow , the water is expected to undergo substantial aeration that would
increase its DO to above 8.0 mg/L and deposit excess sediment load to reduce turbidity.
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Gas Monitoring
Landfill gas compliance probes are monitored weekly, monthly, or quarterly, depending on the compliance status
of the probe. There were 5,648 landfill gas measurements between 2015 and 2019. Methane was detected on 214
occurrences. No methane above 5 percent by volume was detected in any of the probes, and the Site remained in
compliance for the five-year period.
Gas probe AM is located in the northeast portion of the Site and is outside of the influence of the current gas
extraction system. This gas probe has three completions. AM-Shallow, AM-Middle, and AM-Deep. Past data for
samples collected from AM-Shallow were above the regulatory value for methane (5 percent, lower explosive
limit) from 2010 through 2012. However, data collected since 2012 in AM-Shallow have been below the
regulatory value ranging from 0 to 4.9 percent methane. Data collected from AM-Middle ranged from 0 to 0.6
percent methane and AM-Deep ranged from 0 to 0.1 percent methane. These probes have not historically
exceeded the regulatory value.
Site Inspection
The site inspection took place on 3/5/2020. Participants included EPA RPM Ashley Grompe. Min-soon Yim and
Jeff Neuner from SPU. Laura Lee and Lisa Gilbert from SPU contractor Parametrix. and Ryan Burdge and Kelly
Mac Donald from EPA FYR support contractor Skeo. The purpose of the inspection was to assess the
protectiveness of the remedy. The site inspection checklist and photographs are available in Appendices G and H.
respectively.
Site inspection participants began the tour on the western side of the landfill. The entrance to the landfill had a
locked gate with signage indicating the area was a landfill and that dumping and unauthorized personnel were not
permitted on site. Site fencing was in excellent condition. The group then inspected the flare/blower station,
which was also in good condition. The storm water detention pond had abundant wetland vegetation, and the
storm water drainages inspected were clear. The group also walked the landfill cap. Overall, it was in good shape.
However, there was evidence that moles had dug into the cap in some areas, and there were a few areas of
settlement and ponding on the cap. Several golf balls were found in one area of the cap. but no site trespassing
was evident. The gas collection systems on top of the cap appeared to be in good condition. The group then
visited the eastern part of the Site, which is the planned location of the rail extension and highway expansion. No
issues were noted.
Skeo visited the site information repository. Woodmont Library, located at 6809 Pacific Highway South in Des
Moines. The library had one site-related document available (the January 2020 public comment period document
from Ecology related to the upcoming 1-5 expansion and light rail extension). It was not sent to the library. A
library patron printed it and placed it in the reference section.
V. TECHNICAL ASSESSMENT
QUESTION A: Is the remedy functioning as intended by the decision documents'.'
Question A Summary:
The remedy is partially functioning as intended. However, private well owners have not yet been notified of the
potential presence of contamination in their wells and offered to have their wells sampled. Without more
information about whether this is a potential exposure pathway (i.e., whether contaminants are present in wells, or
whether wells are confirmed to be in use), a current protectiveness determination cannot be made.
The remedy included a landfill cover, gas extraction, storm water diversion. O&M activities, monitoring and
institutional controls. Overall, the landfill cover remains in good condition, with some minor ponding and
settlement issues noted on the eastern edge. This area will be regraded during the light rail construction. Gas
extraction. O&M activities and monitoring are ongoing. Gas data indicated that no methane above 5 percent by
23
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volume was detected in any of the probes, and the Site remained in compliance for the five-year period.
Stormwater on the landfill is diverted to the storm water detention pond. Most of the surface water sampling data
for the detention pond discharge were within compliance criteria. While some samples did not meet compliance
criteria, after the water exits the detention pond, the water is expected to undergo substantial aeration that would
increase its DO and deposit excess sediment load to reduce turbidity. Institutional controls are in place to prevent
use of contaminated groundwater, ensure continued integrity of the cleanup action and provide notice to land
users of the landfill property.
Groundwater monitoring results indicate no contamination above cleanup goals in the Upper Gravel Aquifer. In
the Sand Aquifer, manganese and vinyl chloride remain above regulatory criteria, but concentrations in
downgradient well MW-15A are either non-detect or below regulatory criteria. Upgradient VOC concentrations in
the Sand Aquifer have remained stable or increased, but this does not appear to be site related. In the Southern
Gravel Aquifer, vinyl chloride exceeded the cleanup goal in the most downgradient wells sampled, indicating the
extent of vinyl chloride may not be delineated. Additional sampling downgradient of these wells may be
warranted. This discussion is ongoing with Ecology and the timing of this sampling will be added in the 2021
technical memorandum.
Concentrations of 1.4-dioxane exceeded the regulatory standard in both the Sand Aquifer and the Southern Gravel
Aquifer. SPU is still investigating 1,4-dioxane in the site vicinity and plans to evaluate upgradient sources and
continue downgradient sampling in water wells or additional monitoring wells as needed. EPA and Ecology will
determine appropriate actions regarding 1,4-dioxane following these actions.
The presence of two domestic and four irrigation wells that are in use or potentially in use and downgradient or
cross-gradient of the Site and the installation of the domestic well in 2016 within the groundwater quality
notification area both indicate issues with the current groundwater quality notification system for local regulatory
agencies and well drillers.
The Site is undergoing redevelopment related to WSDOT and Sound Transit 1-5 Corridor transportation projects
to add lanes to 1-5 and extend a light rail track on the eastern edge of the Site. Ecology completed a Consent
Decree Amendment. Prospective Purchaser Consent Decree. Cleanup Action Plan Amendment, and Public
Participation Plan in early 2020. Following completion of the project, the City of Seattle. Sound Transit, and
WSDOT will make some changes in property ownership. The Sound Transit Federal Way Link Extension rail
alignment property currently owned by WSDOT will become owned by Sound Transit. The new Prospective
Purchaser Consent Decree between Ecology and Sound Transit defines requirements for Sound Transit's long-
term maintenance of their portion of the Site to ensure continued environmental protection. The Consent Decree
Amendment between Ecology and the City of Seattle and the new Prospective Purchaser Consent Decree between
Ecology and Sound Transit will all ensure implementation of the required actions defined in the Cleanup Action
Plan Amendment. These documents are publicly available on Ecology's Site webpage.
Several monitoring wells on the eastern edge of the landfill are expected to be removed during this construction.
The City of Seattle sent the EPA and Ecology a letter with recommendations for necessary well abandonments on
April 9, 2020. The City anticipates that the removed wells will not affect future determinations of compliance
with groundwater cleanup levels. The EPA and Ecology found the proposal was reasonable however the
monitoring well network will be reevaluated by EPA and Ecology follow ing construction to determine whether
current wells remain sufficient or if additional wells need to be added to the netw ork.
QUESTION B: Are the exposure assumptions, toxicity data, cleanup levels and RAOs used at the time of the
remedy selection still valid'.'
Question 6 Summary:
The ROD included the follow ing RAOs: ensure containment is effective and working; ensure containment will be
maintained; return groundw ater to drinking water standards and state cleanup standards dow ngradient of the
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landfill boundary; and ensure no residential exposure to groundwater until groundw ater cleanup standards have
been met.
Containment generally appears effective and maintained, with the exceptions discussed above under Question A.
Groundwater concentrations are still above drinking water standards for some contaminants but have declined
from historical levels (except for upgradient concentrations of TCE and PCE, which are not site COCs). Two
residential wells were found near the Site during the well survey, both of which are downgradient of monitoring
wells where 1.4-dioxane concentrations exceeded regulatory standards in site monitoring wells.4 The City plans to
offer to sample these wells for 1.4-dioxane.
An Applicable or Relevant and Appropriate Requirement (ARARs) evaluation was conducted as part of this FYR
to determine whether any ARARs have changed (Appendix I). As noted in previous FYR reports, the current state
standard for vinyl chloride is less stringent than the cleanup goal selected in the ROD. The current state standard
for manganese is more stringent than the cleanup goal selected in the ROD. and dow ngradient wells have
concentrations of manganese that exceed the current state standard. Table 10 shows the COCs with ARAR
changes. EPA and Ecology will determine if the vinyl chloride and manganese cleanup goals should be changed
to reflect current standards.
Table 10: Groundwater COC - ARARs Review
Groundwater COC
2000 ROD
Cleanup Goal
Basis
Current
Standard'
ARAR Change
Vinyl chloride
0.02 ng/L
MTCA Method B
0.029 |ig/Lb
Less stringent
Manganese
2.2 mg/L
MTCA Method B
0.75 mg/L
More stringent
Notes:
a. Current standards accessed at: httDs://www.eDa.gov/ground-water-and-drinking-water/national-Drimarv-
driiildiig-water-regiilations and
httt>s://www.ezview .wa.gov/Portals/ 1987/Documents/Documents/CLARC Master.Ddf.
b. More stringent MTCA Method B value used between the cancer and noncancer cleanup levels.
On several occasions, the detection limit for vinyl chloride data exceeded the ROD cleanup goal of 0.02 (.ig/L.
While the 2000 ROD indicated that the PQL of 0.2 (.ig/L would be used to determine compliance with this
cleanup goal because the cleanup goal is lower than the PQL. data from this FYR period indicate that in some
cases, a detection limit of 0.02 (ig/L was achieved. EPA and Ecology will determine an appropriate standard with
which to evaluate vinyl chloride data.
The vapor intrusion exposure pathway was considered during this FYR. There were no detections of VOCs in the
Upper Gravel Aquifer during this FYR period. The Upper Gravel Aquifer was the shallowest aquifer sampled
during this FYR period. While VOCs above cleanup goals or regulatory standards are present in the Sand Aquifer
and the Southern Gravel Aquifer, vapor intrusion is generally only considered for the top aquifer.
QUESTION C : Has any other information come to light that could call into question the protectiveness of the
remedy'.'
No other information has come to light that could call into question the protectiveness of the remedy.
VI. ISSUES/RECOMMENDATIONS
4 One well is in the Southern Gravel Aquifer. The other well is in the Alluvial Aquifer. The Southern Gravel Aquifer
discharges to the Alluvial Aquifer east of the landfill.
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I ssncs/ Rocom 111 en (hi t ions
OU(s) without Issues/Recommendations Identified in the FYR:
None.
Issues and Recommendations Identified in the FYR:
OU(s): Sitewide
Issue Category: Monitoring
Issue: The ROD cleanup goals for vinyl chloride and manganese do not reflect
current ARARs.
Recommendation: Determine whether cleanup goal changes are needed for vinyl
chloride and manganese.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party
Responsible
Oversight Party
Milestone Date
No
Yes
EPA/State
EPA/State
9/23/2022
OU(s): Sitewide
Issue Category: Monitoring
Issue: 1.4-Dioxane has been found near the Site. The EPA is still assessing
whether 1,4-dioxane is a site-related COC.
Recommendation: Complete assessment of whether 1,4-dioxane is a site-related
COC and determine appropriate actions to address 1.4-dioxane if needed.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party
Responsible
Oversight Party
Milestone Date
No
Yes
EPA/State
EPA/State
9/23/2022
OU(s): Sitewide
Issue Category: Monitoring
Issue: In the Southern Gravel Aquifer, vinyl chloride exceeded the cleanup goal
by an order of magnitude in the most dow ngradient wells sampled, indicating the
extent of vinyl chloride may not be fully delineated.
Recommendation: Delineate extent of vinyl chloride groundwater contamination
in the Southern Gravel Aquifer.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party
Responsible
Oversight Party
Milestone Date
No
Yes
PRP
EPA/State
9/23/2022
OU(s): Sitewide
Issue Category: Monitoring
Issue: The detection limit for vinyl chloride groundwater data exceeded the ROD
cleanup goal of 0.02 (.ig/L on several occasions. While the 2000 ROD indicated
that the PQL of 0.2 (.ig/L would be used to determine compliance with the cleanup
goal because the cleanup goal is low er than the PQL. data from this FYR period
indicate that in some cases, a detection limit at the cleanup goal was achieved.
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Recommendation: Determine an appropriate standard with which to evaluate
vinyl chloride data.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party
Responsible
Oversight Party
Milestone Date
No
Yes
EPA/State
EPA/State
9/23/2022
OU(s): Sitewide
Issue Category: Institutional Controls
Issue: There are private wells that are in use or potentially in use and
downgradient or cross-gradient of the Site. One domestic well was installed in
2016 within the groundwater quality notification area.
Recommendation: Determine whether modifications to the groundwater quality
notification system are needed to ensure wells are not constructed and used in
areas with groundwater contamination.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party
Responsible
Oversight Party
Milestone Date
No
Yes
EPA/State
EPA/State
9/23/2022
OU(s): Sitewide
Issue Category: Changed Site Conditions
Issue: Downgradient or cross-gradient of the Site, the well survey identified six
wells that are in use or potentially in use. Of these, two are domestic wells for
drinking water, and four are irrigation wells. It is unknown whether these wells
have site-related COC or 1,4-dioxane contamination.
Recommendation: Notify well owners of area groundwater contamination.
Sample private wells for site-related COCs and 1.4-dioxane.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party
Responsible
Oversight Party
Milestone Date
Yes
Yes
PRP
State
9/23/2021
OTHER FINDINGS
Two additional recommendations were identified during the FYR. These recommendations do not affect current
and/or future protectiveness.
• During the site inspection, there was evidence that moles had dug into the cap in some areas, and there
were a few areas of settlement and ponding on the cap. Issues on the cap should be addressed.
• SPU submitted the Remedial Action Status Report (2015-2019) in July 2020. However, in order to
support EPA's FY R. future Five-Year reports should be submitted the year in advance of the FYR. or
annual reports should be submitted for annual review.
• Ensure site repository is updated with appropriate site documents.
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VII. PROTECTIVENESS STATEMENT
Protectiveness Determination:
Protectiveness Deferred
Planned A ddendum
Completion Date:
9/23/2021
Protectiveness Statement:
A protectiveness determination of the remedy at the Site cannot be made at this time until further
information is obtained. Further information will be obtained by: Notifying well owners of area
groundwater contamination and sampling private wells for site-related COCs and 1,4-dioxane. It is
expected that these actions will take approximately one year to complete, at which time a
protectiveness determination will be made.
The next FYR Report for the Midw ay Landfill Superfund site is required five years from the completion date of
this review.
VIII. NEXT REVIEW
28
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APPENDIX A - REFERENCE LIST
Consent Decree, Midway Landfill, Kent, Washington. State of Washington. Department of Ecology vs. City of
Seattle. June 1990.
Declaration of Restrictive Covenant, Midway Landfill Superfund Site. Kent. Washington. City of Seattle and
Washington State Department of Ecology. July 2005.
Five Year Review. Midway Landfill Superfund Site. Kent. Washington. Washington State Department of
Ecology. September 2005.
Five Year Review. Midway Landfill Superfund Site. Kent. Washington. EPA Region 10. September 2010.
Five Year Review. Midway Landfill Superfund Site. Kent. Washington. EPA Region 10. September 2015.
Hydrogeologic Assessment for Compliance of 1.4-Dioxane. Midway Landfill Superfund Site. Kent. Washington.
Seattle Public Utilities. October 2019.
Preliminary Close Out Report. Midway Landfill Superfund Site. Kent. Washington. EPA Region 10. September
2000.
Record of Decision. Midway Landfill Superfund Site. Kent. Washington. EPA Region 10. September 2000.
Remedial Action Status Report 2015-2019. Midway Landfill. Prepared by Parametrix. Seattle. Washington. July
2020
Remedial Investigation. Midway Landfill Superfund Site. Kent. Washington. City of Seattle. Department of
Engineering. Solid Waste Utility. July 1988.
A-l
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APPENDIX B - SITE CHRONOLOGY
Table B-l: Site Chronology
Event
Date
A gravel pit operated on site
1945-1966
The Citv leased the Site for use as a landfill
1966-1983
Seattle-King County Department of Public Health started administering a State-mandated
screening process to eliminate the further disposal of hazardous waste at the Site
1980
The Citv closed the landfill
1983
Methane gas discovered in surrounding residential area
1984
EPA proposed Site for listing on the NPL
October 1984
Ecologv began the RI/FS
March 28, 1985
The Citv began removal action to extract migrating landfill gases
September 1985
EPA placed Site on the NPL
Mav 1986
Ecologv completed the RI/FS
October 3, 1986
The Citv began construction of the stornnvater detention pond
August 1988
The Citv and Ecologv signed Response Order on Consent
September 1988
The Citv completed construction of stornnvater detention pond
June 1989
The Citv began construction of the final landfill cover
October 1989
Ecologv and the Citv entered into Consent Decree
May 1990
The Citv completed construction of gas migration control system
March 1991
The Citv completed construction of landfill cover
May 1991
EPA issued Site's ROD
September 6, 2000
EPA signed Site's Preliminary Close-Out Report and deemed the Site construction
complete
September 21, 2000
EPA completed Site's first FYR Report
September 28, 2005
EPA completed Site's second FYR Report
September 15. 2010
EPA completed Site's second FYR Addendum
Januarv 7, 2013
EPA completed Site's third FYR Report
September 23, 2015
SPU contractor Parametrix completed a 1,4-dioxane hvdrogcological assessment
October 2019
Construction for WSDOT and Sound Transit 1-5 Corridor transportation projects began
2020
B-l
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APPENDIX C - SITE HYDROGEOLOGY
Groundwater movement within and below the landfill has been characterized to an approximate depth of 300 to
350 feet below ground surface (50 to 100 feet above mean sea level). Several groundwater units have been
identified within this interval. From shallowest to deepest these aquifers are: Perched Aquifer; Landfill Aquifer;
Upper Gravel Aquifer; Sand Aquifer; and Northern Gravel and Southern Gravel Aquifer.
Perched Aquifer (also referred to as Shallow Groundwater)
The Perched Aquifer was named during the Rl when it was believed to represent shallow , discontinuous lenses of
groundwater perched on low permeability deposits above the Upper Gravel Aquifer. Field work and data analysis
since completion of the Rl indicate that while this groundw ater is shallow and discontinuous, it is not alw ays
perched. Most of these shallow zones are found north of the landfill. The Perched Aquifer is referred to as
Shallow Groundw ater in some site reports.
Landfill Aquifer (also referred to as Saturated Refuse)
The Saturated Refuse consists of leachate within the landfill. Its occurrence and movement are largely the result
of the former gravel pit topography. Flow in the Saturated Refuse is generally from the north and west toward the
south-central section of the landfill, where the pit excavations were deepest. Leachate likely discharges vertically
throughout much of the landfill base, but the greatest volume of vertical flow is in the south-central area. Leachate
discharging from the landfill enters the underlying Upper Gravel Aquifer.
Upper Gravel Aquifer
The Upper Gravel Aquifer occurs immediately below the base of the landfill, is limited in lateral extent, and is
composed of silty and sandy gravel. The aquifer is typically semi-confined, although some parts are unconfined.
Groundwater flow in the Upper Gravel Aquifer is generally from both the north and south inward toward an area
beneath the southern end of the landfill where the groundwater appears to discharge downward into the
underlying Sand Aquifer. The Upper Gravel Aquifer and Sand Aquifer are separated by the Upper Silt Aquitard. a
discontinuous layer of fine-grained silt, clayey silt, and silty fine sand. Vertical flow from the Upper Gravel
Aquifer into the Sand Aquifer is most pronounced in places where the aquitard is absent.
Sand Aquifer
The Sand Aquifer occurs as a widespread deposit of interbedded sands and silts. Flow in this aquifer in the
vicinity of the landfill is generally from the north and west to the southeast toward an apparent hydraulic sink.
The sink occurs across a broad area beneath the southern part of the landfill and extends several hundred feet to
the east. Groundw ater south of this sink also flow s tow ards the sink. Groundw ater entering this sink appears to
flow dow nward into the Southern Gravel Aquifer. Some vertical flow outside the sink area also occurs from the
Sand Aquifer dow nward into the Southern Gravel Aquifer and Northern Gravel Aquifer.
Southern Gravel Aquifer
The Sand Aquifer and Southern Gravel Aquifer are separated by the Lower Silt Aquitard. Like the Upper Silt
Aquitard. the Lower Silt Aquitard is discontinuous and likely controls dow nward flow from the Sand Aquifer into
the Southern Gravel Aquifer. The deepest stratigraphic units studied are the Northern Gravel Aquifer and
Southern Gravel Aquifer; they occur at about the same elevation, but hydraulic heads in the Northern Gravel
Aquifer are typically 100 feet higher than heads in the Southern Gravel Aquifer. The Southern Gravel Aquifer is
found beneath the southern half of the landfill and extends to the east, south and west. It consists of permeable
sands and gravel interbedded with silts and silty gravel. The Southern Gravel Aquifer appears to be recharged by
the Sand Aquifer and by lateral flow from the south. A groundwater mound in the Southern Gravel Aquifer,
below the hydraulic sink in the Sand Aquifer, is believed to be an expression of flow through the sink.
Groundw ater flow has changed slightly since the Rl. with a more northeast/northwest direction instead of
east/west. Flow to the north is blocked by higher potentiometric heads within the Northern Gravel Aquifer.
Groundw ater in the Southern Gravel Aquifer eventually discharges west to Puget Sound and east to the Green
River Valley.
C-l
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Northern Gravel Aquifer
The Northern Gravel Aquifer is found beneath the northern half of the landfill and extends to the north and
northeast. Like the Southern Gravel Aquifer, the Northern Gravel Aquifer consists of permeable sands and gravel
interbedded with silts and silty gravel. Flow from the Northern Gravel Aquifer is generally from north to south
toward the Southern Gravel Aquifer. Like the Southern Gravel Aquifer, the Northern Gravel Aquifer eventually
discharges to Puget Sound and the Green River Valley.
C-2
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APPENDIX D - 2005 DECLARATION OF RESTRICTIV E COVENANT
5/22/2020
Landmark Web Official Records Search
After Recording Return to:
City of Seattle
Seattle Public Utilities
Real Estate Services
700 s"1 Ave,, Suite 4961
PO Box 34018
Seattle, WA 98124-4018
PECLARATIlJfjl OF RESTRICTIVE COVENANT
MTCA USE RESTRICTIONS (WAC173-340-4401
CITY OF SEATTLE MIDWAY LANDFILL
LOCATED IN KENT, WASHINGTON
Grantor(s): City of Seattle, a Washington Municipal Corporation
Regulatory Agencies; Washington State Department of Ecology
Abbreviated Legal Description of Property: Portions of real properly located in the
northeast and southeast quarters of Section 21 of Township 22 North, Range 4 East and a portion
of the northwest quarter cf Section 22 of Township 22 North, Range 4 Mast, City ot Kent. King
County, Washington
X Additional legal description in. Exhibit A on pages 5 to 6 of document
Auditor's Reference Numbcr(») of documents assigied/releasei/aineiidei: N/A
Assessor's Property Tax Parcel/Account Numbers:
222204-9188-03; 212204-9025-07; 212204-9014-00; 2122-9033-07 (portion); 212204-
9026-05; 212204-9033-07 (portion); 212204-9137-02; and 212204-9021-01.
rjf Restrictive Covenants (Cit\ of Seattle, Midway Lftndfllt) Pag© I
htt|)s:/lfoccra=rarch.kirigcounly.go¥/Lantlmark"fiAffeb/search/index?theme=.blue§lon=searchCriterlaPar£;elW&quickSearchSelectioii=# 1/58
D-l
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5/22/2020
Landmark Web Official Records Search
DECLARATION OF RESTRICTIVE COVENANT
CITY OF SEATTLE - MIDWAY LANDFILL SITE
Tills Declaration ofRcstriclive Covenant is made pursuant to RCW 70. tOSD.llKII 1 Iff)
and (g) and WAC 173-134-440, by the City of Seattle, its successors and assigns, and concerns
the Midway landfill Property located in Kent, Washington, owned in fee simple by the City of
Seattle.
1, PROPERTY DESCRIPTION
The undersigned. City of Seattle ("Seattle"), is the lee owner of real property in King
County, hereinafter referred to affile "Property." The Property is legally described in Exhibit
"A" of this Restrictive Covenant and made a part hereof by reference. For the purposes of this
Restrictive Covenant, the Property refers to the former Midway landfill, located west of
Interstate 5 and cast of Pacific Highway South (Highway 99) at 6outh 248 Street in the City oi
Kent, King County, Washington,
The Property has been used as a municipal landfill. This Property was listed on the
National Priorities List of hazardous waste sites (Superfund) maintained by the United States
Environmental Protection Agency, The Property has been the subject of remedial action under
Federal and State environmental cleanup laws, including Chapter 70.105D RCW. Seattle makes
the following declaration as to limitations, restrictions, and uses as to which the Property may be
put. and specifics that such declarations shall constitute covenants running with the land, as
provided by law, and shall be binding on all parties and all persons claiming under them.
2. DECLARATION OF RESTRICTIVE COVENANT
This Declaration of Restrictive Covenant is made by the City pursuant to the Washington
State Model Toxics Control Act (MTCA), RCW 70,iO5D,O3G(i)(f) and (g) and WAC 173-340-
440, as required hy the State of Washington Department of Ecology, including any successor
agency (hereafter referred to as "'Ecology").
2.1 ' Remedial Action. The remedial action work dune to clean up the Property
(hereinafter the "Cleanup Action") is described in Hie Record of Decision (hereinafter the
"ROD") for the Midway Landfill dated September 6, 2000 and in the Consent Decree with the
Department of Ecology filed under King County, Washington. Superior Court Cause No. 90-2-
13283-8 SEA. A copy of the ROD is attached to this Restrictive Covenant as Exhibit "B."
Copies of these documents and documents describing the Cleanup Action conducted at the
Property are on file at Ecology's Northwest Regional Office, 3190 - 16011' Ave. SR. Bellevue,
WA. Copies of the ROD, Consent Decree and Consent Decree Amendments are also on file in
King County Superior Court, Seattle, WA, under Cause No. 90-2-13283-8 SEA.
Declaration ofRtttriciive CoveunU (City of Seattle. Midway Landfill) . fage 1
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2,2 Purpose of She Restrictive Covenant. This Restrictive Covenant is required by
WAC 173-340-440 to assure the continued integrity of the Cleanup Action and provide notice.
2J Restrictions on Use The City makes the following declaration as to limitations,
restrictions, and uses to which the Property may be put and specifies that such declarations shall
constitute covenants to nui with lite land, as provided by taw, and shall be binding on all parties ^
and all persons claiming under the City, including all current and future owners of any portion of
or interest in the Property:
2.3.1 Any activity on the Property that may interfere with the Cleanup Action as
defined in the ROD, is prohibited. Any future use of the Property shall not
disturb the integrity of the final cover, or any other components of the
containment system. Any future use of the Property shall not disturb,
damage, or alter any component of the landfill gas extraction system, or
any of its attendant monitoring probes or wells except as approved in
writing by the Department of Ecology or its successor agency. Any activity
on the Property that may result in the release of a hazardous substance that
was contained as part of the Cleanup Action is prohibited. Any activity on
the Property that may result in cndongcrment to human health or the
environment by hazardous substances contained on Property or by gas
generated by and emitted from the Property is prohibited.
2.3.2 E.\eepf for groundwater monitoring, no groundwater may be taken for any
purpose from any well on the Property without Department of Ecology
("Ecology") approval No water supply wells may be installed on the
Property.
2.3.3 City must give thirty (30) days advance written notice to Ecology of the
City's intent to convey any interest in the Property. No conveyance of
title, easement, lease, or other interest in the Property shall be
consummated by the City without adequate provision for continued
monitoring, operation and maintenance of the Cleanup Action.
2.3.4 City must restrict leases to uses and activities consistent with this
Restrictive Covenant and notify all lessees of the restrictions on the use of
the Property,
2.3.5 City must notify and obtain approval from Ecology prior to any rise of the
Property that is inconsistent with the terms of this Restrictive Covenant.
Ecology may approve any inconsistent use only after public notice and
comment.
tteelarafi#! of Rutrictive Covenants (City of Seattle, Midwty LaiMlfi.il) Page 3
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2.3.6 The City shall allow authorized representatives of Ecology the right to
enter the Property at reasonable times and with reasonable prior notice for
the purpose of evaluating compliance with the Cleanup Action and to
inspect records that are related to the Cleanup Action.
2.3.7 The City reserves the right under WAC 173-340-440 to record an
instrument that provides that this Restrictive Covenant shall no longer
limit use of the Property or be of any further force or effect. However,
such an instrument may be recorded only if Ecology, after public notice
and opportunity for comment, concurs.
THE CITY OF SEATTLE:
Chuck Clarke
Seattle Public Utilities
STATE OF WASHINGTON
COUNTY OF KING
%
V.
Date Signed
ss.
On this day of
1 for the State of Washingiorf^July
. 2005, before me. the undersigned, a Notary Public
in and for the State of Washingtorf^duly commissioned and sworn, personally appeared Chuck
Clarke, known to me know to be the Director of SEATTLE PUBLIC UTILITIES, the entity that
executed the within and foregoing instrument, and acknowledged the said instrument to be the
free and voluntary act and deed of said entity, for the uses and purposes therein mentioned, and
on oath state that he is authorized to execute the said instrument and that the seal affixed (if any)
is the seal of such entity.
written.
WITNESS my official seal affixed the day and year in this certificate above
it.
£ W WOT/lfiv ^ a
NOTARY PUBLIC in and fafrWe
"tfpy*
I 5
/c
State of Washington, residing at
My commission expires _ f"2U"Pop-1
Declaration of Restrictive Covenants (City of Seattle, Midway Landfill)
Page 4
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Exhibit "A"
MIDWAY LANDFILL LEGAL DESCRIPTION
PARCEL A: Tax lot # 222204-9168-03
That portion of the west half of the soathwsst quarter of the northwest quarter of Section 22, Township 22
North, Range 4 East, W.M.. in King County, Washington, lying westerly of tho Primary State Highway
Number #1 (Interstate Highway No. 5) as condemned in King County Superior Court Cause No. 535003,
and between the north and south lines of the south half of the north half of the southeast quarter of the
northeast quarter of Ssct'on 21, Townsnip 22 North, Range 4 East, W.M., in King County, Washington,
extending easterly to the west margin of Primary Sate Highway #1.
PARCEL B: Tax tot # 212204-9025-07, Wtid #212204-9014-00, and a portion of # 212204-9033-07
The south half of (he southeast quarter of the northeast quarter and tie west half of the west half of the
northeast quarter of the southeast quarter of Section 21, Township 22 North, Range 4 East, W.M., in King
County, Washington, lying westerly of Primary State Highway Number 1 (Interstate Highway No. 5);
EXCEPT that portioi described as follows:
Beginning at the soutnwest comer of the southeast quarter of the northeast quarter of satd section;
thence north. 01e07W east 363.64 feet along the west line of said subdivision;
thence south 87°53'39* east 602,44 feet;
thence south 01°O?W west 202JO feet;
thence south 81 a18*39" west 447.99 feet;
thence south 39*19'39" west 200.00 feet to the west line of the northeast quarter of the southeast quarter
of saitf Section"
thence north OI'OS^S* east 130.03 feet along sa«d west line to the point of beginning;
AND EXCEPT that portion of the north half of the southwest quarter of the southeast quarter of the
northeast quarter of said Section 21, lying north of the south 40 feet and west of the east 60 feet.
AND EXCEPT the north 100 feet of the south 130 feet of the west 95 feet of the west half of the west half
of the northeast cuarte* of the southeast quarter, of said Section 21;
AND EXCEPT the south 30 feet thereof for South 252nd Street,
PARCEL C: Tax lot# 212204-9026-06
Those portions of the southeast quarter of the northeast quarter and the northeast quarter of the
southeast quarter of Section 21, Township 22 North, Range 4 East, W.M.. in King County, Washington,
more particularly described as follows:
Beginning at the southwest corner of the southeast quarter of the northeast quarter of said section; thence
north 01 *07*09" east 363.64 fee' along the west line of said subdivision;
thence south 87°53"3»' east 602,44 feet;
thence south 01°07'09" west 202,70 feet;
thence south 81°19'39" west 447,99 feet;
thence south 39°19'3S" west 280,00 feet to the west line of the northeast quarter of the southeast quarter
of said section;
thence north 01°05'25" east 130.03 feet along said west line to the point of beginning;
EXCEPT that portion, if any, lying north of the south 40 feet and west of the east ©0 feet of the north half
of the southwest quarter of the southeast euarter of the northeast quarter of said Section 21.
Dectaratfon of Restrictive Covenants {City of Seattle, Mxfwty Landfill) P*|* 5
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PARCEL P; Tax lot # 212204-9033-07 (portion)
The north 535,83 feet of the northeast quarter of the southeast quarter of Section 21, Township 22 North,
Range 4 East, W.M.. in King County, Washington, lying wester.y
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Exhibit "B"
RECORD OF DECISION (ROD) FOR THE MIDWAY LANDFILL
[Attached]
Declaration of Restrictive Covenants (City of Seattle, Midway Landfill) -Page *?
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Declaration
SITE NAME AND LOCATION
Midway Landfill
Kent, Washington
CERCT.IS Identification Number: WAD 9806*8910
STATEMENT OF BASIS AfSD IH Rf'OSE
This Decision Document presents the selected remedy tor the Midway Landfill site, located in
the City of Kent, king County, Wasliingt vn, This Record of Decision (ROD) has been
developed in aeeord.mes with the requirements of Comprehensive Environmental, Response.
Compensation, and Liability \ct (CERCXA) of 1980, 42 USC §9601 etseq, (CERCLA), a*
amended hy the Snperfurtd Amendments and Rc authorization Act of 1986 (SARA), and, to
tht- extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan
(NCP), 40 CFR. °arf 300. This decision is based on the Administrative Record for the Site.
The remedy was selected by the U.S. Environmental Protection. Agency. The State of
Washington concurs with the selected remedy.
ASSESSMENT OF THE SITE
The response actiur. selected in this Record of Decision (ROD) is necessary to protect the
public health or welfare or the environment from an actual or threatened release of hazardous
suhb-tances into the environment. Such a release or threat of release may present an imminent
and substantial enJangentieat to public health, welfare, or the environment.
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DESCRIPTION OF THE SELECTED REMEDY
The selected remedy for the Midway Landfill site consists of:
]. Monitoring to:
a) ensure the remedial systems are working as designed,
o) ensure progress Is being made towards meeting the groundwater cleanup standards,
c) ensure adequate containment if maintained when and if major changes are approved
by Ecology in the operation of the site, and
d t demonstrate that the cleanup levels have been achieved.
Monitoring includes, but is not limited to. groundwater monitoring and landfill gas
monitoring
2. Continuing to operate and maintain all remedial project elements required in ihc
EcolngvCity of Seattle 1990 consect decree, including the gas collection system, the
multikyercd can. and the storm water collection system,
3. Implementing, institutional controls, Three types of institutional controls arc included
in the selected remedy: permanent notices in King County's real estate iccords, assurances m
the (990 consent decree that operation and tfuuntenance of the containment and monitoring
systems will continue i: the ownership or control of the property should change; and annual
notices to appropriate agencies, water districts and locally active well drillers so that no water
supply wells arc constructed or used in -ireus with groundwater contamination fiotn the
landfill.
This ROD also establishes cleanup levels fo: the groundwater down gradient from the
landfill.
STATUTORY DETERMINATIONS
The selected remedy is protective of human health and the environment, complies with
Federal anc State requirements thai are applicable or relevant and appropriate for the
remedial action, is cos".~efFeetive, and utilises permanent solutions and alternative treatment
technologies to the maxr-itcr. extent practicable.
The remedy selected iu tins ROD dues satisfy the statutory preference for treatment as a
principal element of Lie remedy, Extracted landfill gas is flared as part of the existing landfill
gas collection system.
Because tills remedy will result in hazardous substances remaining on-site above levels (hat
allow for unlimited use and unrestricted exposure, a statutory review will be conducted under
C£RCLA within five years of this Record of Decision to ensure that the remedy continues to
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be protective of human health and the environment,
DATA CERTIFICATION CHECKLIST
The following information is included in the Decision Summary section of this ROD,
Additional information can be found in the Administrative Record file for this site.
Chemicals of concern (COCs) and their respective concentrations. (See Section 5.)
A baseline risk assessment for current conditions at the landfill was not prepare!
because the contaminants of concern, migration routes, and the risks to human health and the
environment wsre characterized is Rl/FS reports completed in 1990. However, there is s. need
for action because groundwater dowtjgradient from the landfill still contains contaminants of
concern above federal drinking water standards (MCLs.) (See Section 7,}
Cleanup levels established for COCs and the basis for these levels. {See Section 8.)
How the source materials constituting principal threats are addressed. Source
materials constituting principal threats have not been identified at Midway Landfill. (See
Section 4.)
Current and reasonably anticipated future land and groundwater use assumptions used
in the ROD. (See Section 6.)
Potential land uses that will be available at the site as a result of the selected remedy.
(See Sections 6 and 11.3.)
Annual cost estimates for the selected remedy. (See Section 1 i.2.)
Key factors that ted to selecting the remedy. (See Section 11.1)
Acting Regional Administrator. Region 10
United States Environmental Protection Agency
Date
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Decision Summary
Midway Landfill
Kent, Washington
1, Site Name, Location, anil Description
The Midway Landfill is located between. Interstate'5 (1-5) and Highway 99. and between S
252nd Street and S. 246th Street in Kent, Washington, directly east of the city of I)es Moines.
(Figure 1 -1,) The landfill is approximately 60 acres in size with refnse buried on about 40
acres arid at depths over 100 feet. From 1<>66 to :«S3, approximately three million cubic
yards of solid waste were deposited.At Jlie Midway Landfill. The landfill is now owned by lie
City of Seattle,
Because of the remedial work performed by the City of Seattle since 1985. environmental
conditions have greatly improved. The landfill is now covered with a multilaycrcd engineered
cap, with a top layer of grass, "1 he landfill is fenced and access is limited. A gas extraction
system is in place and operating throughout the landfill. Because of these actions, potentially
explosive landfill gas docs not leave the landfill property Mid the quality of the groundwater
leaving the landfill has greatly improved The city's estimate of closure costs amounted to
about $56,5 million as of 1°95.
Lai id use in the landfill viciratj consists primarily of commercial activities and residential
areas. Commercial establishments and light i tdustry and manufacturing border both sides of
Highway W in ilie area. Two elementary schc-pls. Smiiyeiest Elementary School ;ind
Parkside Elementary School, and a city park, Linda Heights Park, are within a half-mile radms
of the site. Most of the nearby residences are detached single-family dwellings, with some
multi-unit residential developments to the south and west. Several mobile tome parks arc
also in the vicinity. A six-acre wetland, the Parkside Wetland, located to the ejst of the
Parkfide Elementary School and west of the landfill is a naturally occurring detention basin
for local surface water runoff, primarily from the west side of Highway 99.
There are no wetlands, flood plains, rare, threatened or endangered species, or sites on or
eligible for the National Registry of Historic places at the site. Storm water from the site
drains into MeSorlcy Creek, which is a salmon-bearing stream containing eoho ar,d chum
salmon, 'teelhead and cutthroat treat Ccho salmon is a candidate for listing under the
Endangered Species Act.
The State of Washington Department of Ecology (Ecology) has been the lead regulatory
agency for the cleanup work at Midway Landfill since the mid-1980's. While the U.S.
Environmental Protection Agency iEPA) has prepared and released a proposed plan and this
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ROD. EPA expects Ecology to continue to "be the lead cleanup regulatory agency overseeing
this remedial action. The work has been, and will cortinae to be, conducted try the City of
Seattle.
2. Site History and Enforcement Activities
2.1. Site History through the 1990 Consent Decree,
Tram 1945 to 1%6, the site of the current Midway Landfill was operated as a gravel pit
Original 1}', the pit was adjacent to a itatjral drainage basin often, used as a settling pone. This
basin, known as Lake Meade, was located northeast from tlic confer of the present landfill. As
the pit was mined, water w;w dnwa from I ako Meade to wash silt and clay from the gravel
and sand, and then returned to the Jal-te. This silt and clay settled on the lake bottom. Near 'he
end of the gravel pit operation, the lake was drained into the southern end of the gravel pit,
depositing a layer of day arid silt into the bottom of the pit. This layer of fine materials
currently underlies much, but not all, of the present landfill.
la 1966, the City of Seattle leased the site and began using it as a landfill. From 1966 to
1983, apfnoMmately three million cubic varels of solid waste were deposited there. Hie
exact dimensions of the bottom of the landfill are hot known. However, existing boreholes
indicate that the solid waste extendi; as deep as "130 feet in some places.
The Midway Landfill was crested primarily to accept demolition materials, wood waste and
other slowly decomposing materials. However, some hazardous wastes and industrial wastes,
including approximately two milhon gallons of bulk industrial liquids from a single source,
were also placed in the landfill In i 980. a state-mandated screening process administered by
the Seattle-King County Department of Public Health was initiated to eliminate the disposal
of any "hazardous waste into Midway Landfill.
When the City closed the landfill in the fall of 1983, it began extensive testing of water and
gas in the landfill and its vicinity. Samples of groundwater from monitoring wells in and
around the landfill and gas samples frotr gas probes, indicated the presence of organic and
inorganic contaminants outside the landfill boundary. In 1(>85, Ecology also began inves-
tigating the site and found methane gas in nearby residences. Beginning in September ly&5,
the City of Seattle cor.strueted gas migration control wells within the landfill property and gas
extraction wells beyond the landfill property to control the subsurface migration of gas. Gas
was found to have migrated up to 2600 feet beyond the landfill prior to installation of (lie gas
extraction system.
In October 1984, Midway Landfill was nominated for inclusion on the federal National
Priorities List (NPL) based on potential groundwater contamination. Fol1 owing that
nomination, Ecoiog} was designated as the lead agency for the Midway Landfill Superlunc
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actior, pursuant io a Cooperative Agreement with EPA. In May 1986, Midway Landfill was
placed on the NFL. In September 19i?i>, the City of Searde. which owns and had operated
Midway Landfill, entered a Response Order oh Consent with Ecology. TMs Response Order
governed the preparation of a Remedial Investigation and a Remedial Action Feasibility Study
i,RJ7FS! for the landfill.
In May 19%, prior to eotr.pletiou of the remedial investigation and feasibility studies, the City
and Ecology entered into a consent decree pursuant to State of Washington Model Toxics
Control Act (MICA,) This legal agreement set forth Ecology's determination that
undertaking certain remedial actions at Midway Landfill, prior to a Cleanup Action Plan (a
M7CA decision document, similar to a Superfotid ROD) would provide immediate
protection to public health and the environment In this consent decree, the City of Seattle
agreed to finance and perform specific cleanup work litis cleanup work, or remedial action,
had four elements:
Construction of a landfill cover. The multi-layered Landfill Cover System ("cap")
was to be comprised of layers (.from bottom to top) of low permeability clayey
silt/silty day, a 50-mil synthetic membrane, a geonet drainage layer, o«e foot of sand
and one loot of topsoil planted with shallow rooted grasses. The landfill cover wai
designed to greatly reduce the amount of rain that would seep into the landfill and to
eoorrol the post-closure escape of hazardous emissions from the landfill.
Completion of a gas extraction system, ir.eluding a Final Gas Manifold System to link
onsite extraction wells to an enhanced motor blower and flare .system. The purpose of
the onsite extraction wells was to create a '"vacuum curtain™ around the closed landfill
to prevent offsite migration otTandilil gas, and to Mp draw previously migrated gas
back to the landfill. The enhanced flares were installed to hum the extracted gas
before cu->chargc to the atmosphere. The gas extraction system also included
approximately 127 offsite gas monitoring probes to provide data on the extent of
landfill gas migration and the effectiveness of the extraction system.
Completion of a surface water management system. This system consisted of site
filling and giading to control surface water drainage to prevent surface water from
infiltrating the landfill, construction of a 10 million gallon storm water detention pond
with a permanent dewatering system, a controlled discharge structure, and rerouting of
storm water front surrounding areas to prevent it from entering the landfill This
rerouting was done by diverting, the Linda Heights Park drain and surface water runoff
from 1-5 to the detention pond.
Preparation of a comprehensive operation and maintenance manual incorporating both
short-term and long-term operation and maintenance requirements for all remedial
actions implemented at the landfill as part of the consent decree.
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The consent decree also required the City to place a notice in the records of real property kept
by the county auditor staling that She landfill was on. the NPL, and serve a copy of the consent
decree upon any prospective purchaser, lessee, transferee- assignee, or other successor in
interest to the property prior to the transfer of any legal or equitable interest in all or any
portion of the landfill.
2.2. Status of the work required by the J WO Consent Decree
Tie City of Seattle etiirroleted construction of the landfill cover, landfill gas extraction
system, and surface water jr.anagetneat system in November 1992. Some of the other
requirements of the consent decree have not jet been completed. As discussed in the
followng section, Ecology and the City of Seattle anticipate amending the 1990 consent
decree after this RO7") is signed.
Construction elements required by the 1£9,0 ConsentDecreg
L.:.k!il)l Gas Control - An active gas control system was installed at the Midway Landfill. It
originally included 8? gas extraction wells, 31 of which were located off the landfill m native
soil. The off-landfill wells have since been abandoned or capped. In addition, Approximately
70 olf-land;tl" gas monitoring probes were installed to provide information on gas
concentrations; about half of these probes have since been abandoned. The gas is extracted
through the control wells at the landfill and routed to a permanent blower/Hare system
Construction of the gas migration control system began in September 1985 and was
completed in March 1991.
Lu'idffit surface filling and grading - The landfill surface was regraded which increased the
soi„ cover over the landfill by ? to 14 feet. The engineered grades improved surface water
runoff and decreased infiltration. The fill was also compacted to reduce permeability and
prepare the surface .or the cover system. The work began in August 19SS and was competed
in June I *>f?f>
Storm Water Detention Pond Construction and Associated Dewatering and Discharge System-
A lined detention pond was constructed to the north of the landfill. Rcgrading of the landfill
surface redirected surface water, which previously infiltrated into the landfill, to the new
detention pond The detention pond is a 3 acre structure, lined with a oO-miliimcter high-
density polyethylene membrane iRDPEj to eliminate infiltration. The bottom of the pond was
constructed below localized groundwater: therefore, a permanent dewatering system was also
installed Construction of the storm water detention pond began in August 1988 and was
completed in June 1989.
Lanclilll Cap Installation - Construction of the final landfill cover began in October 19S9 and
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was completed in May 1991. It consists of far following layers from bottom to top: a 12-ir.ch
thick layer of low permeability (1 x 10-7 cm/sec) soil/thy material; a 50 millimeter KDPE
Eexible membrane; drainage net; filter fabric: 12-inch-thick drainage layer; and a 12-ineh-
thiek lopsoil layer,
Linda Heights Park Storm Water Di\ c-Ktcm - The Linda Heights Park drain, a 30-inch culvert
that drained directly into the landfill, was blocked. Storm water is now routed through a
pump station and ,i pipeline to the detention pond. Hie old discharge line to the landfill is still
in place and Amotions as an overflow in the event of a pump station failure. 'Die construction
of this rerouting began in August 1°S9 aid was completed in Wl, The pump station and
associated diversion of storm water was activated in January i 1>9?,
^fpn-cgnstTUctipr, elements require-*! bv the 1 Vffl consent decree
Operation and maintenance (O&M) plan - A comprehensive operation and maintenance
manual for both short-tain and long-term operation and maintenance for the systems
constructed under the consent decree was prepared by the City of Seattle, and was approved
by Ecology in April 1992.
Deed notice - The deed notice required by Ihe consent decree has not ye! been placed on the
property.
Monitoring and monitoring plan - Monitoring and a monitoring plan are not specifically
identified as required activities in the 1990 consent decree. An amendment to the consent
decree win specify a requirement to implement a compliance monitoring plan approved by
Ecology, as well as to implement an operations and maintenance plan already required to be
prepared under the 1990 consent decree. The City of Seattle and Ecology are still in
negotiations on the long-term monitoring plan. Starting in late ". 989, the City initiated
performance and compliance monitoring programs at the landfill Performance monitoring
0which did not include chemical analysis) was intended to track the response of landfill
leaebate levels and shallow groundwater levels to the implementation actions required by the
consent decree. Quarterly water quality monitoring began in 1990 to develop a database for
water quality in selected groundwater monitoring wells. This monitoring program, which
became the compliance monitoring program, was modified in liTO and again in 1998 with
concurrence from Ecology. Compliance monitoring was intended to track the presence.
ecuicenirctiotK and migration of groundwater contiminants both up gradient and
down gradient cf the landfill, and !o assess the effectiveness of the remedial action. Both
monitoring programs are ongoing and sampling is presently conducted on a twice yearly
tasix I andfill gas monitoring is conducted frequently; it consists of checks for
concentration, composition, temperature, flow and velocity of gaseji in and around the landfill.
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3, Community Participation
Because of The high degree of public interest in the landill, the City of Seattle and the
Washington Slate Department of Ecology first developed a formal community involvement
program: in lyX5 when residents near the landfill became concerned about landfill gas
migration. Public irreettncs were htici at critical points to keep residents informed about
activities at the kndfdi. Also, for about two years, the City ran an information office in the
Midway area 10 give citizens a convenient place to find out about cleanup activities, health
information. aod legal claims. As landfill gas migration was brought under control and
residents* fears subsided, office bouts were reduced arid uvenittully the office closed. During
the same period, a newsletter was sent to about 70U0 area residents. The City and Ecology
also worked with leadeis From focal active community groups to set tip MAG (Midway
Action Group! meetings, which were held monthly at first, and then less frequently. Through
these meetings, community members could express their views and learn about the
investigation and cleanup process.
The City created the Good 'Neighbor Program in 1986 to help the community when concern
over landfill gns was at its peak. The program addressed fears about perceived drops in
property values, The City guaranteed residents that their homes would sell for fair market
value, as if the landfill was not there. The City continued the program until the real estate
market returned to normal.
Very few formal community participation activities took place in the 19Ws, though Ecology
and City of Seattle staff continued to be available to respond to concerns and questions from
the public.
EPA"5 proposed plan was issued in May 2000 and the original public comment period ran
from May 18 to June 16, 2000, Over 2,000 fact sheets summarizing the proposed plan were
sent to all addresses and residents in the three postal carrier routes around the landfill.
Additionally, the fact sheets were mailed to 48 other potentially interested parties (such as the
Cities of Kent and Des Moines) outside the carrier route. Approximately two to three dozen
copies of the proposed plan were sent out, arid additional copies were available from EPA's
Seattle office and at the City of Kent Regional Library. The fact sheet and proposed plan were
also avaikbie on the Region 10 web page. Display notices were published in the Seattle
Times, Seattle Edition on. May 16, in :hc Seattle Times, South Count)' Edition, on May ?>,
sod :n the South County Journal on Ma)- ! 7, The City of Seattle asked for tm extension of the
comment period on June 15. and the end of the public comment period was extended until
July i 7,, 2yu0. Notice? of the extension were published in the Seattle Times, South County
Edition aod the South County Journal on June 21.
The feet sheets, newspaper notices and the proposed pian offered to hold a public meeting if
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sufficient interest was exptesscd by May 31, "QoD. Only four requests for a meeting were
received and thus a public mcetine was not held. EPA staff called each, person who requested
a meeting to make sure ha or she had all the information they v> tinted about the Midway
Landfill and the proposed remedial derision.
Four coRinjerrt letters on the proposed plan were received, EPA's response to tiicse comments
can be found in the attached Responsiveness Summary.
This decision is base J on. the administrative record. 'I he Midway Landfill Administrative
Record is located at the £P A SupcrfimJ Records Center. 120'J Sixth Avenue, Seattle,
WasMngton, and in ths Kern Regkwal Library, 212 2nd Avenue N, Kent, Washington.
4. Scope and Role of this Response Action
This ROD is the final CHRCLA decision for the Midway Landfill site,
The City of Seattle's cleanup work, including the work done in response to the I f>90 consent
decree between Ac City and Ecology, has successfully reduced the environrr.wttal problems at
the landfill, 'The selected remedy incorporates elements required in the 1W consent decree
between City ami Ecology, and adds some elements to ensure long-term protcctivcuess of the
temedy, The selected remedy ako Sets yrour.dwater clean-up standards
The Midway Landfill site has no "principal threat" wastes, as that phrase is defined in EPA
guidance.
For the purpose? of this ROD and potential future deletion of this site from EPA's National
Priorities List, the Midway Landfill '"site'" is the landfill area containing waste, and all
dowrtgradient contaminated groundwater resulting from releases from the landfill. Several
potential up gradient groundwater sources have been identified but are not included within the
•'site" and are not addressed by this ROD.
Ecology has separate responsibilities for derision-making at the Midway T andifi!! site under
the State's Model To\ic Control Act (MTCA). finder MTCA, the decision document that
selects the cleanup action and cleanup levels ii> called a Cleanup Action Plan. Ecology and
the city had been working on a final Cleanup Action Plan for Midway Landfill for many
years. When, in February 2000 it was determined that it was urdikely that such a Cleanup
Action Plan could be .-ompleted >n FY 2i)00. Ecology agreed that CPA could write a
CERCLA ROD for the landfill so that a determination of CERCLA construction completion
could be made. Ecology has decided to utilize the ROD as a Cleanup Action Plan for a final
MTCA remedy, pursuant to WAC 1 ?3-340-3o0(,13'(, This decision will be specified in an
anticipated amendment to the 1°°0 consent decree.
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Ecology lias been the lead regulatory cleanup agency at the Midway Landfill site, EPA
expects Ecology to continue in that capacity.
5. Site Characteristics and Nature and Extent of Contamination
5.1. Conceptual Site .Model and Summitry of Landfill Conditions
Because of the remedial work performed by the City of Seattle at Midway Landfill since
19S5. the environmental conditions at the site have greatly improved.
Potentially explosive methane gas does not leave the landfill property, ami has not
.-since 1990. The gas is collected within the landfill and then burned on the site. The
gas collection system has also helped dry out the landfill contents and further reduce
the contaminaujd groundwater leaving the landfill.
Storm wafer no longer enters the landfill. The entire landfill is covered with an
engineered cap. Clean storm water is collected from the entire surface of the landfill
and the surrounding area and stored ina. lined storm water detention pond north of the
landfill before discharge to McSorley Creek,
There ate multiple layers of sand, or sand and gtuvel, under or around the landfill that
allow subsurface movement of groundwater to and from the landfill. These layers, or
aquifers are called, in order from the surface to the deepest layers studied: the Shallow
Aquifer; Samrated Refuse and Land fill Leneliate; the Upper Gravel Aquifer, the Sand
Aquifer, and the Northern and Southern Gravel Aquifers.
Water in the Shallow Aquifer, the Upper Gravel Aquifer and the Sand Aquifer moves
from outside the landfill inward towards the south end of the Midway Landfill. This
water, along with the leachafe developed within, the landfill itself, then, joins the deeper
Southern Crave! Aquifer. Water from the landfill does not appear to enter the
Northern Gravel Aquifer.
There is now significartly less water within the landfill because of the remedial
actions described above. Many of the shallower monitoring wells in or near the
landfill that used to contain contaminated groundwater are now dry. The water levels
around the landfill in both the Upper Gravel Aquifer and the Sand Aquifer have also
generally dropped. These results mean that much less water is entering the landfill and
the containment systems constructed by the City of Seattle have been successful.
The only downgradient monitoring wells where contamination has been detected over
the past two or three years1 are in the Southern Gravel Aquifer. Two of these wells are
located appioxitnately 600 feet aid 1200 feet east of the south-east corner of the
landfill. Three chemicals, 1 A.-dichloroeth-tne, vinyl chloride, and manganese, have
been detected at levels of concern. The two VOCs were detected at slightly above the
federal drinking water standard. Manganese has also been detected at levels above
background on the west side of the landfill in the Southern Gravel Aquifer.
Another Southern Gravel Aquifer monitoring well that ii closer to the landfill has met
all federal drinking water standards for the past two years. Groundwater monitoring
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conducted during the RI Indicated that this same well had contaminants at levels
arealer than 1U times the federal drinking water standard. Again, these results radicate
that the containment remed) appears tn be successful,
f here Is some groundwater contamination in the Sand Aquifer to the north, northwest
arid west of die landfill that did not come from Midway Landfill Some of the
exouudwater samples in this area arc above both federal and state drinking water
standards and the MTCA cleanup standards. This contamination may be flowing
towards and under the Midway Landfill. No one i> using this groundwater and thus no
one is currently exposed to this contamination.
The following sections provide more detailed summary information about the sftfe
characteristics, hydrogeology, and groundwater quality,
5.2. Geographic Description
The Midway Landfill is located neat the crest of a narrow north-south trending glacier feature
known as the-Des Moines Drift Plain. "Tilts area, referred to as "upland" because of its
locution above adjacent valleys and sea level, is bordered hy Puget Sound on the west and the
Ure«t River valley on the east. Maximum elevations along the crest of the upland generally
range from 400 to 450 feet above mean sea level (MSLj. Puget Sound is at sea level, and the
Gtt.cn River valley floor typically averages about 30 feet above MSL,
The Midway Landfill occupies a shallow, bowl-shaped depression near the crest of the
upland. The surface of the ktndflU generally ranges trcwn 360 to 400 feet above MSL and
slopes upward to the south and east. West of the landfill, tbo land surface is nearly flat across
Highway 91' and then drops steeply downward approximately 100 feet to the Parkside
Wetland,
The upland area is cm with a number of steep-sided stream valleys. Midway Creek is located
northeast of the landfill, and two other streams, the north and south forks of McSorley Creek,
arc located to the weit and southwest, respectively,
I here is no ma:or surface water body in the immediate vicinity of the Midway Landfill. Hie
closest are Lake fen wick. located approximately one mile to the southeast, and Star lake,
located approximately 1.5 miles to the south.
5.3, Geology
Site geology and hydjogeology have had i major influence on the movement of contaminants
in the vicinity of Midway Landfill, the impact of the completed remedial actions, and affect
the .selection of the cleanup remedy.
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The Des Moines Drift Plain is part of the Puget Lowland that lies between the Olympic
Mountains on the west and the Cascade Mountains on the east. The Puget Lowland is
underlain bv a thick, sequence of Quaternary glacial, fluvial (riverine), and lacustrine (lake
beds deposits overlying Tcrtiarv volcanic and sedimentary bedrock. Depth to bedrock is
thought to exceed 1.000 feet near Midway Landfill. Deposits of at least fow gleciations have
hcen identified in the Puget Sound Lowland, Hie most recent glaciation, the Fraser, consisted
of two stages: the Vashnn (oldest) and Stimus (most recent).
Based on earlier studies of fee ttiea aid onah bis of geological samples collected during the
installation of monitoring wells for the RX nine stratigraphically distinct deposits were
identified from the land surface down approximately 400 feet to sediments feat are near
current mean sea level. Because of the complex layering in all the sediments underlying the
landfill, vertical and horizontal permeabilities are highly variable and produce a complex
groundwater flow pattern,
5,4, JIj drogeology and Ground Water Quality
Groundwater movement within and below the landfill has been characterized to an
approximate depth of 300 to 350 feet hclow ground surface {50 to 100 feet above mean sea
level (MSI.)). Several groundwater units have been identified within tins interval. From
shallowest to deepest these aquifers are; Shallow Ground watei; Saturated Refee; Upper
Gravel Aquifer (VGA): Sartu Aquifer f SA); and Southern Gravel Aquifer (SGA) and Northern
Giavel Aquifer (NGA) An east-west cross section is shown ;n Figure 5-1; the Mac of this
cross-section is H-H" on Figure 5-2.
Between October 1986 and January IW0, a total of 56 groundwater monitoring wells were
installed and sampled in 41 locations up gradient and down gradient of the Midway Landfill.
(Many wells have multiple completions at the same location^. Samples from these locations
were analyzed for conventional water quality parameters and EPA's hazardous substance list,
including metals, volatile organic compounds (VOCsO, pesticide? and other potentially
hazardous substances. Hazardous substances detected in tlie groundwater included arsenic,
manganese, benzene, 1.2~diehk>roe thane, vinyl chloride, and methylene chloride.
in addition, the extent of contaminant migration into the groundwater system beneath the
landfill was estimated using specific chemicals as indicators of Icachate movement within the
aquifers. In purieuiar. chloride coiicmratjor.s in the landfill Icachate were several hundred
tmes greater than background groundwater concentrations. Therefore, elevated chloride was
used to delineate the extent of the contaminant plums and as a conservative tracer of
groundwater movement. The concentrations of manganese (a jiaturally-occuiraig metal that is
otter, elevated downaradient of landfills! mid certain chlorinated ethenes and ethanes in the
groundwater wore also used to confirm the extent of the plume.
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A subset of the RI groundwater monitoring network has been used for monitoring the effects
of the work rerpired by the consent decree. Figure S-3 shows the locations of the monitoring
wells still used to monitor groundwater quality, Water levels are monitored in. these and
additional monitoring wells.
Of the hazardous substances identified during the RI, only manganese and two VOCs.
1,2-dichloroeiliane and vinyl chloride, are still considered ground water contaminants of
concern. None of the other hazardous substances have been detected in groundwater at levels
approaching federal thinking water standards downgradiom of the landfill for at least eight
years.
The sections below summarize, by aquifer, the iiydrogeology and groundwater quality
information collected during die past 10 )rears as part of the groundwater monitoring program.
For comparison, averaged contaminant concentration data (arithmetic mean) from, the RJ are
also included. Nondcteets were incorporated into these averages by using half the detection
limit.
5.4.1, shallow Groundwater
5 4 1.1. Shallow Groundwater Hydrogeology
This /one of saturation was described in the RI as shallow, discontinuous Senses of
groundwater perched on low petmeahiliiy deposits above the UGA. Field work and data
analyses since completion of the RI indicate while the groundwater in this unit is shallow and
discontinuous, it is not always perched above low permeability materials. The majority of
these shallow zones are found north and south of the land-fill Die general water elevation of
the shallow groundwater zone adjacent to the landfill is generally at about 325 feet above
MSL north and south of the landfill, and lower, and more discontinuous to the east and west
{Figure 5-4).
The landfill's detention pond dewatering system affects shallow groundwater flow through
areas along the northern periphery of the landfill. Shallow groundwater north of lie landfill
that exists at 320 feet or higher in elevation is captured by the pond's dewatering system and
routed to North McSorley Creek. This system limits the capacity of the shallow groundwater
to discharge into the landfill from the north; however, groundwater deeper than 320 feet in
elevation can and does discharge into the landfill from the north. Shallow groundwater also
occurs in disconnected zones south of the landfill at an elevation of approximately 325 feet,
and diseliaiges, at least seasonally, into the landfill
5.4. S. 1. Shallow Groundwater Water Quality
Shallow groundwater water quality has not been monitored as part of the performance and
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compliance monitoring system. Shallow groundwater flows into the landfill.
_5,iL2 Saturated Refuse and Landfill Leachate
5.4.2.1. Landfill Leachate Hydrogeology
Prior to the remediation required by the 1990 consent decree, the major sources of water to the
landfill were: surface water infiltrating from the landfill surface and from areas north of the
landfill that drained into the landfill; storm water discharge from the Linda Heights
neighborhood, and 1-5 drainage that was routed into the landfill as part of the construction of
1-5; and shallow groundwater from aorth and south of the landfill. Refuse located below
elevations of approximately 325 feet was generally saturated (Figure 5-5).
Flow in the refuse was generally frofli the north and west toward the south-central section of
the landfill, where the pit excavations were deepest, Leachate may have discharged vertically
throughout much of the landfill base, although the rate of discharge was affected by the fine-
grained material deposited during gravel pit operations. Prior to remediation, the greatest
volume of vertical flow was in the south-central area, where leachate discharged to the
underlying Upper Gravel Aquifer.
Since construction of the engineered cap and storm water diversion systems, between 75 and
90 percent of the water that entered the landfill has been diverted and leachate levels have
dropped by as much as 20 feet. This can be seen by comparing water elevations within the
landfill in Figures 5-1 and 5-5, which corresponds to a 90 percent reduction in the amount of
saturated refuse. The only remaining sources of water to the landfill are the shallow,
discontinuous zones of groundwater north and south of the landfill. Water within the landfill
now slowly evaporates into the gas system or leaks through the base of the landfill,
approximately 100 to 150 feet below ground surface, into the underlying Upper Gravel
Aquifer, described below.
5.4.2.2. Landfill Leachate Water Quality
Studies conducted during the SI established that most -of the leachate from the landfill was
aqueous. A small amount of floating light non-aqueous phase liquid (LNAPL) was also
detected in the landfill. Dease non-aqtieous phase liquid (DMA'PL) has never been detected at
the landfill.
Leachate samples were collected as part of the RI and analyzed for conventional water quality
parameters and compounds on the EPA hazardous substance list. Results from these analyses
and related monitoring indicated:
The aqueous leachate contained aromatic and aliphatic hydrocarbons, dissolved salts,
suspended particulates and low levels of YOCs and metals. Polynuclear aromatic
hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were only detected in
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groundwater samples in wells located adjacent to or in direct contact with NAPL pools.
The LNAPL contained metals, VOCs including trans-1,2-dichloroethene and the
BETX group (benzene, ethylbenzcne, toluene and xylene), PAHs commonly detected in
petroleum oil, and PCBs. PCB concentrations ranged from 107 ppm to 1,142 ppm.
Some wells within the landfill had up to 20 feet of NAPL. Monitoring of wells
outside the landfill did not detect any NAPL.
A pumping program was tested as part of the 1990 FS to see if the LNAPL was
extractable. Less than 100 gallons were extracted from the three wells with the greatest
volume of NAPL; recharge into these wells was very slow.
Water quality in the 'andfill leactate has not been monitored as part of the performance
• monitoring system, though water depth and LNAPL have been. By 1998, of the
approximately 18 wells monitored for oil thickness, approximately 13 had either no oil or
only a trace of oil. The remaining 5 bad oil measured between 0.27 feet and 3.96 feet
5.4.3.1. Hydrogeology of the UGA and Upper Silt Aquitard
The Upper Gravel Aquifer consists of fifty to one hundred feet of outwash gravels that
underlie the low permeability layer at the base of the landfill located 100 to 170 feet below
ground surface. These gravels consist of interbedded zones of permeable gravels'and less
permeable mixtures of silt sand, and gravels. Prior (o construction of the actions required by
the 1990 consent decree, discharge from the landfill resulted in significant areas of saturation
within the UGA, especially in water-bearing strata at the base of the unit, where several
monitoring wells were placet!. (See, for example, Figure 5-5.)
Groundwater flow in the UGA is generally from both the north and south inward toward an
area beneath the southern end of the landfill where the groundwater discharges downward into
the underlying Sand Aquifer (SA). The UGA and SA are separated by the Upper Silt
Aquitard, a discontinuous layer of fine-grained silt, clayey silt, and silly fine sand that is
present throughout most of the study area. Vertical flow from the UGA into the SA is most
pronounced in places where the aquitard is absent One of these "windows" in the aquitard
exists beneath the southern end of the landfill, where it allows the discharge from the UGA
into the SA to occur. Discharge through this window was manifested as a distinct
groundwater sink during the RI.
The construction of the remedial actions required by the 1990 consent decree and the
subsequent dewatering of the refuse have greatly reduced'the amount of recharge entering this
unit. Groundwater continues to enter the UGA north and south of the landfill, and the
groundwater and leachate continues to flow toward the sink beneath the southern part of the
landfill.
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However, the response of the UGA to changing conditions at the landfill was strong and rapid
as indicated by the monitoring weils designed to monitor water quality conditions. Within the
landfill footprint and around the perimeter, the UGA monitoring wells have bci.11 dry since
1992. even with rainfall tliat was significantly grra.cr than average during the years from 1997
to 1999. Figure 5-6 shows the current potsjitiometric surface of the UGA, The sink still
exists and appears to have "deepened" due to the loss of recharge from the landfill.
The UGA beneath the landfill i,< under vacuum from the 'andfill gas collection system. Any
leachate leaking through the base of the landfill and infiltrating into this zone moves mostly
by unsaturated flow and is directly exposed to the vacuum under conditions designed to strip
voktiie orgatiics from the infiltrating water. This combination of predominate:}' unsaturated
conditions in the aquifer and the vacuum from the gas extraction system helps to contain
volatile urganics from being released to lite underlying groundwater system.
5.4.3.2. Water Quality in the Upper Gravel Aquifer (UGA)
Prior to construction of the actions requited by the 1990 consent decree, water quality in the
water-bearing strata at the base of the unit, wharf several monitoring weils were placed,
showed significant impacts lion) leachate. However, the KI concluded it was unlikely that
contamination in the Upper Gravel Aquifer existed further than 100 to 200 feet front the
landfill (in the south, west, and east direction) because oi tile strong component of downward
flow in the aquifer into the underlying Sand Aquifer.
Following the remedial work required by the 19^1 consent decree, the monitoring network in
the. UGA included two up gradient wells (MW-2IA and MNV-16) and two downgradient wells
;MW-7A and MW-19B). The down gradient wells were located at points where the saturated
refuse was believed to be discharging leachate downward into the UGA. However, the
downgrading wells MW-7A and MW-19B have not been sampled since 19"2 due to the
declining arouridwatcr levels in tire UGA. In the two or so years prior to going dry. both
wells had no detectable concentrations or any VOCs, except ehluro benzene at concentrations
ranging from non-detected to 4 ppb (the federal drinking water standard or Maximum
Contaminant Level fMCL) is 100 ppb); benzene at concentrations ranging from oon-dctect to
3 ppb (MCL is 5 ppbs: chloroethane at concentrations from non-detected to 3 ppb arid single
hits of ] .2-dichloroethane at 1 ppb and acetone at 25 ppb. During the same years, manganese
concentrations ranged from 3.5 to 5.2 mgf..
5,4.1 The Sand Aquifer i'SAi and the Lower Silt Aqnitard
5,4 4.1. Hydrogeoiogy cf the Sand Aquifer and the Lower Silt Aquitard
The SA occurs as a widespread regional deposit of intcrbedded sands and silts 200 to 300 feet
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below the surface. Plow in this aquifer in. the vicinity of the landfill is generally from the
north, and west to the southeast toward a hydraulic sink, that occurs across a broad area beneath
the southern, part of'.he landfill and extending sev etui htmdred feet to the east (Tigure 5-7).
Groundwater to 4c south and cast of this sink also flows towards the sink. Consequently, the
sink limits the extent that the landfill impacts the SA. and impact1; are not seen beyond, the
sink to : he east. This sink is believed to be located from the southeastern section of the
landfill and up to 800 feet further east. Groundwater entering this sink flows downward into
tbc Southern Gravel Aquifer (SGA),
'Die deepening of lite i»ink ill the UGA as the Saiidfi.il dewatered is also seen in the SA where
the SA sink has also deepened ever the last 5 years. The two SA groundwater flow
monitoring wells within the footprint of the landfill are currently dry, and have been for
several years; the down gradient SA groundwater chemistry monitoring wells, which are
located further front the landfill, only sometimes contain puftteieiit water for sampling
The SA and SGA are separated by the 1 ower Silt Aquitard. Like the Upper Silt Aquitard, the
Lower Silt Aquitard is present as a signifies!!? unit throughout the site, but is discontinuous tn
places. These "windows" in the aquitard allow for the downward flow from the SA into the
SGA. The largest such window identified in the study area exists be.Jow the sink in the SA.
5.4.4.2. Water Quality m ihe Sand Aquifer
The post-1990 monitoring network in the SA iritislly included four up gradient wells
(MW-SB, MV-30B, W-17B, and MW-21B) and three down gradient wells (MW-15A,
MW-20A sad MW-7.3A). MW-^OB was originally installed a? a down gradient well, but the
potentiometrie surface showed that it was actually up gradient of the landfill on the far side of
the groundwater sink formed by SA groundwater discharging into the SGA. The well has
consistently beea dean, and has been deleted from the groundwater monitoring network.
In this aquifer, the groundwater quality situation is complex because of up gradient
contamination flowing towards the landfill. The up gradient wells MW-17B and MW-21B
aw contaminated with chlorinated solvents, as shown below:
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Up Gradient Monitoring Weils In the Sand Aquifer - Recent Concentrations
MW-17B
Recent concentrations
MCt
*. J -dichlorocthane
, 1 -dichloroethene
1,2-diciiloroetIiaiie
90 to 160 ppb
4.8 to 8,2 ppb
8 to 32 ppb
800 ppb*
' Pi'b
5 ppb
MW-21B
1.1-d ichloroethane
I.l-dicMoroethcac
fetraehloroetiieiie
triehioroetfaene
11 to 14 ppb
1.6 to 2.6 ppb
24 to 35 ppb
2.-+ to 3.1 ppb
800 ppb*
7 ppb
5 ppb
5 ppb
* M-JiVoloroethane has r.o MCI, S00 pph is the MICA Method B cleanup Tcvt 1 in She 2/96 CI.ARC
Contamination iti MW-173 has remained fiiiriy constant over tlie last decade, while
contamination at MW-21B has been increasing slightly over the last several years. These two
wells remain the most contaminated wells in the monitoring well network, in terms of number
of ctmtamiaauis fount! in the groundwater. Both Ecology and the City of Seattle have
conducted studies to identify possible source? of this up gradient contamination.
MW- i 5A and MW-23A were selected to provide water quality information in the hydraulic
sink area. MW-23A has not been sampled since W3 due to declining groundwater levels in
the SanJ Aquifer. MW- {5A was act sampled between 1 or»? and 1^97, but has had sufficient
water for sampling from 1997 to the present. Since 10') ? all VOCs have been non-detected
except 1.2-dicMoroetliane with concentrations from 1.1 to 2.1 ppb and manganese
eotweritr&tioDS have ranged from 0.005 to 1.02S tng/L. In the two or so years prior to water
levels getting low, MW-23A had similarly low concentrations of VOCs with 1.1-
dichloroethene from non-detectcd to 2 ppb; 1.2-dichloroethane from 1.9 to 4 ppb; and
trichioroethcne from non-detected to 2 ppb. Manganese concentrations ranged from 1.7 to 4-1
One additional sand aquifer monitoring well (MW-20A) is located just west of the landfill.
TMs well is hydraolicaily down gradient of the up gradient source area near MW-17.
Monitoring well MW-20A is also located hydraulically up gradient of the western edge of the
landfill because water from the Sand Aquifer Cows underneath the landfill and down into the
Upper Gravel Aquifer, Historically, the water quality in die zone monitored by MW-204 was
impacted by both landfill and np gradient sottrce^. MW-20A has been dry and thus not
sampled since 199». It: the two or so .years before going dry. the following concentrations
were found in MW-20A:
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iltable,
mg/L.
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MW-20A - 1 9°2 to 1994 Concentrations
1992 to 1994 Concentrations MCI s
1,1,1 -trichlororthane non-detected to 2.4 ppb 200 ppb
1.1-dichloroeihane 12 to 3? ppb SfX) ppb*
1.2-dichloroeihane 2 to 5.3 ppb 5 ppb
1,2-dichlorocthene noc-detectcd to 2 ppb 70 PPb
benzene non-detected to 1.1 ppb 5 ppb
ehlonxrfhanc ¦ 15 to 20 ppb *' *
manganese " 0.735 to 1,28 mg/L. 2.2
mg'T/'*
4 I J-Jkaloraethane has no MCI.. S,60 ppb is the MTCA Method 3 cleanup level in the 2'9? CLARC
11 tabic.
manganese has. no pi ire are MCL. ' 2 mg'L is the MTC \ MelhoJ B cleanup kve! in thei?fi
CLARC If fable
" chlorocthanc also kisnwn as ethyl chtonde, hai no MCL nor MICA Method B cleanup level in the
:.'96 CLARC [I table.
5.4.5. The Southern :mJ Northern Gravel Aquifers
5.4.5.1. Ilydrogeology of the Southern and Northern Gravel Aquifers
The deepest straugraphic units studied were tht Northern attd Southern Gravel Aquifers
(NO A and SO A, respective'^); :hey occur at jbout the same elevation (300 to 350 feet below
the surfaeei, but livdwulic beads in the NGA are typically 100 feet higher than heads in tic
SGA. During the RI, the NGA was found (o be clean mid nnimpacted.
The SGA is found beceath the southern half at" ihe landfill and extends to the east, south and
west. It consists of permeable sands and gravel interbedded with silts and silty grave!. The
SGA appears to be recharged by the S A arid by lateral flow from the south. A groundwater
mound in the SGA. below the hydraulic sink in the SA, is believed to be an expression of
regional flow through the sink. Groundwater flow from the mound is to the oast and west;
flow to the north is blocked b) Mglier potentiomelrfc heads within the NGA. Groundwater in
the SGA eventually discharges west to Pueet Sound and east to the Green Rivet Valky, The
199S potentioinctric surface of the SGA is shown ir. Figure 5-K, Although the groundwater
mound is still present, water levels along the historical high point (MW-14B, for example)
have dropped by as much as 10 feet from prt-rcmcdial conditions.
Response? to changing recharge conditions have been fairly rapid between the base of the
landfill aisd the SGA, with decreases in the SGA watci lewis occurring in less than 5 years
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from completion of the remedy required by the 1090 consent decree. Once groundwater
enters the SGA, the primary direction of flow shifts from vertically downward to horizontal,
with much lower potentiometric beads driving the flow indicating that water movement within
the SGA horizontally away from the landfill will be much slower than vertical movement
into the SGA,
5.4.5.2, Water Quality in the Southern Gravel Aquifer
Currently, the Southern Gravel Acmfer is the primary aquifer in which groundwater moves
oat and away from "he landfill, ard thus is the primary potential groundwater expostuc
paihwav beyond the landfill property.
The post-1 <>90 monitoring network hi the SGA initially consisted of one up gradient well
(MW-248) and live downgradient wells (MW-14B, MW-20B. MW-23B, MV-23B. and
MW-30C I Weil 24B lias since been removed from the water quality monitoring network
because it has never shown any evidence of groundwater contamination.
Monitoring wells MW-14B, MW-23B, and MW- 29B form a line of monitoring wells to tie
east of the landfill, with MW-14B located at the edge of the landfill, and the other two wells
approximately 600 and 1.500 feet further east, respectively,
the monitoring results for MW-14-B are interesting. (Table 5-1.") Whiie !he average 1,2-
dieMoroetiiane concentration during the R1 was 50 »g/"t, and were generally in the 1ft to 20
ug/L range in the early IQWs, the 2-dichlorocthrmc concentration has been non-detectable
(with a detection limit of • ug/L) in this weH iu the four sampling rounds between May I99H
and November 1999. Similarly, while the .« erage vinyl chloride concentration during the 81
was 4 ug/L. and lie concentrations were generally in the 2 to 4 ug/I range in the early 1990*5.
vinyl chloride concentration has been non-detected (with a detection limit of 1 or 2 ug/L) in
this wel) in these four recent sampling rounds. L is-1,2 -dichloroethene is also found in the 5 to
7,7 ug/L range fthe MOL is "?0 ug'TL} as has been 1,1-dichloroe thane in the 1.6 to 3 ug/L range
(no MCI., hit the MTCA Method B cleanup level is 800 ug/L.) No other monitored VOCs
have been detected ra the past two years. Concentrations of chloride (a leacliate marker) and
manganese (from 4,8 mg/L average in the Ri to approximately 1,5 mg/L in ISW) have shown
similar reductions. Since MNV-14B is located where SA groundwater discharges into the
SGA, aud the SA hits been in compliance since 19q4» this change is interpreted as the
beginning of a "clean front" moving into the SGA,
Concentrations in MW-23B (Table S-.li have also been declining, but,it a slower rate. For
example, average Ri concentrations of 1,2, diehlorcetkuje and vinyl chloride were 13 ug/1
and 5 ugTL respectively. concentrations of these cherr.icals have been around 7 ug/L aud 2
ug/L, respectively, in the four sampling rounds since May • ?98. Manganese concentrations
have always been low in this well, generallv arotaid 0.? mg/L, Cis-1,2-dlchloroethane is also
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defected m this wcjl in the 4,5 to o 4 ug/L range,
Coaoeiuratious are remaiiniig constat in MW-2VB. For example, over the pa^t three yean-,
IJJ-dichlojwih.ne has eonsistsrn'ly been detected in the 5 to It) pph range (as compared to the
R1 average concentration of 5 ppbt with 1.3-didiioroethane detected a single time at 1,2 ppb
and vinyl chloride detected n single time at 1.1 ppb. Manganese concentrations aie low and
have Tanged from 1,05 to 1.24 mc.'L over the past "our years.
The volatile COCf historically have rare.v been detected in downgradient wells ifW-'?0B (to
the west of the landfill) or MW-3QC (to the far southeast of the landf.il).
BactgroiJid manganese concentrations are high in the SGA and the related Noithere Gravel
Aquifer, with the regional background concentration considered to be 1.1 mg/L. MW-24B.
MW-23B. MW-29B. and MW-30C all have manganese concentration!! at or below
background; and manganese concents allots in MW-14B have been decreasing rapidly over
the last few year? as a ''clean front" of less contaminated groundwater enters the SGA.
However, manganese concentrations in MW-20B are above background and increasing. with
concentrations in tie 4.5 to 5.87 mg/L runpe over the past 3 years, as compared to an average
of I , including vinyl chloride, xylenes, toluene, benzene and other solvents.
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fSik City of Seattle
Greg Nickels, Mayor
Seattle Public Utilities
Chuck Clarke. Director
July 13,2005
Subject: Midway Landfill Covenant Fife
City of Seattle, SPU internal R/W # 8415 Drainage and Wastewater Files
NOTE to whom it may concern,
Map exhibits have been removed from this document at this point for recordation due to the
requirements of King County. Some maps were 11" X17" in size and some maps would not
meet the clarity requirements when scanned. The Real Estate Services Office of the
Seattle Public Utilities. The City of Seattle have copies of these exhibits on file (R/W file
#8415} or you may contact the Department of Ecology and ask them for the Midway
covenant map files exhibits under the King County recording number of this document,
Jf you have any further questions, please feel free to contact the Real Estate Office of
Piihlir* I Tho CA1\j nf fipnttlf*
Real Property Services
Seattle Public Utilities
The City of Seattle
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5.6 Surface Water, Seeps and Soil Contamination
Surface water, seeps and soils in areas around the landfill were sampled in the late 1980's as
part of The RI atic no contamination from the Midway Landfill was found.
6. Current aud Potential Future Land and Resource Uses
Land Use: Currently, the landfill is capped and fenced. No public access is allowed, future
land use has been the subject of an extensive but preliminary 1992 study by community
representatives, the City of Kent, and the City of Seattle. Some possible uses considered
desirable by the Midway Citizens Advisory Committee include-ripen space uses such as a
passive park, a sports complex with ball fields, or garden center. Less desirable but
potentially possible future uses would be a golf driving range or a park and ride facility. All
uses would be designed to protect the integrity of the cap and other containment systems.
Groundwater uses: To the test of Ecology's and the City's knowledge, no one is drinking the
groundwater from any aquifer within, almost a mile of tlss landfill, and there are no current
plans to use the groundwater near the landfill for drinking' water. The closest wells currently
in use for drinking water are the Lake Fenwrok wells almost 1 mile southeast of (be Midway
Landfill.
As part of the Midway Landfill Environmental Impact Survey (EIS) in 1*585, the City's
contractor located private wells within a one-mile radius of the landfill, .aid public wells
within five miles of "he landfill by reviewing numerous agency files. Based on this inventory,
the contractor sent questionnaires to approximately 90 households near the landfill in order to
verify she existence and itse of private wells. The list of households was updated during the
Rl. and several key downgrudient wells were re-verified in 199P. Citizens were also
questioned at several public meetings and at meetings of the Midway Action Group regarding
their knowledge of any wells in neighborhoods surrounding the landfill.
From this information, 31 private wells were identified within a one-mile radius of the
landfJl. s'Scc Figure 6-3.) Of the 31 wells, nine are in use, 12 are unused, and 10 are
inoperable. Of the nine wells, five are used for drinking water, including the Lake Penwiek
supply, which services nine homes, and the other four wells are used for irrigation. The five
drinking-water wells are all located over 4,600 feet from the landfill, in the Lake Ten wick
area. Three of the four irrigation wells Eire located over 2.000 feet southwest of the landfill
(out of Lie plume pdth). The fourth irrigation well is located between the groundwater plume
and the Late Fertwick wells.
Monitoring We-i MW-30 in the Southern Gravel Aquifer was added in 1988 to act as an eariy
warning location should any measurable contamination from the landfill move toward the
irrigation well or toward the l.ake Fenwkk wells, MW-30 is still monitored, and lias
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generally remained clean and iiniiKp icted throughout the groundwater monitoring program.
Two other wells were identified within 1,000 feet of the landfill (Weil Nos. 37 and 57), Well
No. 5? is dry and ovraed by the City of Kent. Weil No. 37, on privately owned property, is
unused and co\ ered.
There are three public wells in the Midway Landfill area. Two are operated by the Highiinc
Water District near the two intersections of South 209u' Street and 31" Avenue South, and
South. 208i:' Street and 12"' Avenue South, respectively. These two wells are screened in the
second confined aquifer, at over 120 feet below sea level. Both ate over two miles north and
northwest from the landfill in all atpa that is up .gradient of the landfill, and arc completed in
aquifers that are not connected to the affected aquifers. The third well is operated by the Kent
Water District at South 212* Street and Valley Freeway and is used to satisfy peak summer
demands. None of these municipal wells draw water from affected aquifers, and all are more
distant from the landfill than are the. Lake Fettwick wells.
Finally, neither water district has future plans to develop ground water supplies from any
aquifers within a one-mile radius of the Midway Landfill. The wellhead protection areas
delineated by these utilities do not include the Midway Landfill site.
State regulations (WAC 173-160 -171} do not allow any new private drinking mater wells
within 1000 feet of a solid waste landfill or 100 feet1 of all other sources or potential sources of
contamination, and notice is required to be given to Ecology prior to the construction of any
well. However, the NCP is more stringent and requires EPA to consider all groundwater as
drinking water except directly under a waste management area. The landfill area with refuse
is a waste management area and thus is riot considered a Mure drinking water source by EPA.
All other areas downgradient of tlie landull are considered to be potential future drinking
water sources. However, it is likely that ail future developments lie within water district
sendee areas and, therefore, are not likely to rely on private wells for their potable water
supply.
1. Summary of Site Risks
7,1 Human Health Risks - Prior to the Work Required by the 1990 Consent Decree,
Before the cleanup work began at the Midway Landfill site in 19S5, there were many ways in
which humans could have potentially beest exposed to unacceptable levels of contaminants.
These exposures could have posed acute hazards to residents due to the high levels of methane
gas reaching tesidentiai basements, and long-term potential risks from solvents in the
groundwater if anyone had been drinking the groundwater. The risks from these possible
exposures were greater than SPA's and the State of Washington's acceptable risk levels. For
example, if a wison had been using the groundwater tu MW-14B, one of the most
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contaminated down gradient wells, as their source of domestic rater for 30 years, the
estimated excess cancer risk from vinyl chloride and 1 ,2-dichloroethane alone would have
been approximately 6 x 10-4. Other possible exposures ceroid have occurred through air
emissions or through direct contact with the landfill contents.
1'lie City's contractors prepared an Endangerment Assessment (EA) as part <.»f the 1990 RI/FS
for Midway Landfill Because the RI found little contamination in the surface water, seeps cr
soil, the EA concluded thai the contaminants detected ill these environmental media had not
migrated from the landfill. The EA also found that there was no direct exposure pathway
connecting leaohate to either human or ecological receptors. The only potential exposure
pathways existed through cress-twdia pathways; volatilization of contaminants from Icachate
into [andfili gas or discharge of icachate iiuo the groundwater system. The contaminants in
landfill gas were found to pose a negligible risk leaving leachate to groundwater as the only
migration pathway of concern. it „jr....
7J- Current and Future Human Heafth Kislts
iPTi
A baseline risk assessment that follows corn-it EPA Superfknd guidance on risk assessment
and that reflects current conditions at (he landfill has not been performed on Midway Landfill
because the contaminants of concern, migratioa routes, and the risks to toman health and the
environment were characterized in the 1990 F.A, Based on the success of the containment
actions required by the 1990 consent decree, there a* likely to be no current unacceptable
risks to human health trom the landfill because tlie gas migration has been stopped and no otu
is currently drinking the groundwater VOC contamination in the groundwater downgradiem
of the landfill also appeal's to be decreasing, ax least in the well closest to the landfill. The
only remaining contaminants of concern appear to be vinyl chloride, 1,2-dichloroeth99 concentrations in Well
MW-23B. currently the monitoring well with the highest concentrations of VOC's
Jowngradie.nt of the landfill. This estimate was calculated assuming domestic use of the
groundwater for drinking and showering. EPA's reasonable maximum exposure assumptions
for 30 years. IRIS or Region 9 PRO table toxicity values, and a conservative assumption that
the contaminant concentrations will not change in the future. The excess cancer risk is
estimated to he approximately 1 x 10-4 (with vinyl chloride being the primary ri?k driver"! and
the HI is estimated to be approximately .3 (with manganese being the primaiy risk driver),
both of which are within EPA's acceptable risk range. This cancer risk level is, however, not
within the acceptable risk level under Washington's Model Toxics Control Act, which
requires thai cumulative excess cancer risk be no greater than 1 x 10-5.
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The estimated risk was also calculated for MW-20B, again considering only the maximum
1999 concentrations and using the same assumptions. Well MW-20B is currently the
monitoring well wiLi the highest concentration uf manganese downgradieni of the landfill
The Hazard Quotient for manganese in this well is approximately 6.
These estimated risks are potential future risks only, because there are no drinking water
wells within the down gradient plume of the landfill, nor are there any plans to place any
drinking wells in this area in the future. (See Section 6.)
73 Ecological Risks
No ecological risks to plants or animals ate expected now or in the future because there will
be co exposure to the contaminants at or from the site. The site is covered and capped with
dean material, and the groundwater from the site does not impact any surface water bodies or
seeps. Surface water discharging from the site is monitored for conventional pollutants such
pH, dissolved oxygen and turbidity. No hazardous substances are expected to be in tie
surface water discharge from the landfill because the remedial actions under the 1990 consent
decree have eliminated surface water contact with, the refuse..
7,4. Basis for Action
Q
While the estimated ftittire risk from drinking groundwater downgradient from Midway
Landfill is within the NOP acceptable risk range, there is groundwater contamination above
federal drinking water standards, or MCLs, in two monitoring wells east of the landfill and I-
5. According to EPA policy, when MCLs are exceeded, action is generally warranted, to
addition, state groundwater cleanup levels under MTCA are exceeded. Because drinking this
groundwater could result in an imminent and substantial e-ndangerment to human health,
remedial action is needed at Midway Landfill.
S. Remedial Action Objectives
Midway Landfill is an example of a site where containment has been successful and has
reduced the risks posed by the site. However, the containment measures already in olaca must
he maintained and institutional controls are necessary to ensure continued long-term
protection of human, health and the environment.
The remedial action objectives of this response action arc:
To ensure containment is effective and working
To ensure containment will he maintained
To return groundwater to drinking writer standards end state cleanup standards
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down gradient of the landfill boundary
To ensure no residential exposure to groundwater until groundwater cleanup
standard? have been met
Cleanup Standards
For groundwater that is a potential future source of drinking water, the more stringent of
feder.il drinking water standards falso known as Maximum Contaminant Levels or MCLs) and
State of Washington cleanup standards under the Model Toxics Control Act (MTCA) are the
cleanup levels, r or the groundwater contaminants at this site, the cleanup levels and their
bass are shown in Table 1. tr
Tabic 8-1; Groundwater Cleanup Standards
Contaminant
Cleanup Level
Basis of the Cleanup Level
1.2-dicliloroethafie
5 ug/L , ,
:
Federal Drinking Water Standard
(MCL)
vinyl chloride
.0^.
MTCA Method B,
manganese
2.2 mg/L
%
^ thod B
1 Pursuaa.1 to WAC i 73-340-707(2). Ecology will utilize the practical quantitation limit
(PQL) of 0.2 ug/L to determine compliance with this cleanup standard because the cleanup
standard is lower than the PQI„
1,2-Diehlorotthane and vinyl chloride are solvents. Vinyl chloride can also be formed in
groundwater during the natural breakdown of other solvents, Manganese is a natural mineral
in sail that dissolves into the groundwater because of the chemistry of the water leaving the
landfill.
If other contaminants resulting iron; releases from the landfill are -found in any downgradient
monitoring well, cleanup levels, if necessary, will he established for these additional
contaminants using the federal drinking water standards and MTCA.
f he point of compliance for the groundwater will be at the edge of the landfill waste, as
specified in a Compliance Monitoring Plan to be appro\ ed by Ecology. Under MTCA, this
location is considered a "conditional point of compliance." All groundwater downgradient of
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this poiol »f compliance will need to meet these cleanup levels for contaminants resulting
from releases from the landfill before the Midway Landfill is removed from the Superfund
National Priorities List,
9. Summary of Remedial Alternatives
Two remedial alternatives were considered for the Midway Landfill site,
No Action Alternative;
Under the "No Action alternative, EPA would not require any additional action at the Midway
Landfill site T&e City of Seattle would still have to fulfill its responsibilities under its 1990
consent decree with Ecology, as weii as any other requirements established under state or
local regulations for dosed landfills. Monitoring could he required under this alternative.
EPA would not set cleanup levels nor points of compliance under this alternative.
Limited Action Alternative:
This alternative does not require any significant additional remedial construction because the
actions taken by the City of Seattle since 1985 have eliminated or greedy reduced the
contaminants leaving the landfill. Instead, this alternative focuses on maintaining and
monitoring the constructed containment remedy to ensure it is and will continue to be
effective and protective. This alternative would also set groundwater cleanup levels aid
points of compliance. This approach is consistent with EPA's presumptive remedy for
municipal landfills.
The main elements of the limited action alternative are:
1. Monitoring to :
a) ensure the remedial systems are working as designed,
b) ensure progress is being made towards meeting the groundwater cleanup standard
e) ensure adequate containment is maintained when and if major changes are approved
by Ecology m the operation of die site, such as taming off or scaling down the gas collection
system, and
d) demonstrate that the cleanup levels ha\e been achieved,
2 " Contimfnj to operate and maintain all remedial elements required in the 1990
Ecology,''City of Seattle consent decree,
t. Implementing institutional controls. Institutional controls are legal or administrative
actions that help cnsuie the long-term protect] veaess of the remedy. At this site, tike limited
action alternative includes tlrrec types of institutional controls. The first type of institutional
control would be a legal notice the City would place in King County's records, alerting any
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mture purchaser of the property, in perpetuity, that this property had been used as a landfill
and was an EPA's National Priorities list, and that future use of the property is restricted.
The second tyae of institutional control is a requirement that the City ensures continued
operation and maintenance of the containment and monitoring systems if ownership of the
property should change. Both of these institutional controls are required as part of the 1990
consent decree between F-cology and the City of Seattle, though the legal notice has not yet
been placed in the County's records. The third type of institutional control is an annual
written notice about the groundwater quality down gradient train the landfill The City of
Seattle would be required to notify the Seattle-King County Department of Public Health,
uearhy water districts, locally active licensed well drillers and Ecology. As an additional
protection, state regulations forbid my private drinking water wells within 1.00ft feet of a
municipal landfill or within 100 feet from all other sources of potential contamination.
The remedy would also he reviewed no less often than every five years to ensure that the
remedial action remains protective of human health and the environment.
10. Comparative Evaluation of Alternatives
EPA evaluated the two alternatives using the nine criteria established in EPA's National Oil
and Hazardous Substances Pollution Contingency Plan. The nine criteria are divided into
three categories: threshold, balancing, and modifying criteria. To be eligible for selection, on
alternative must meet the first two threshold criteria. The next five criteria are the balancing
criteria which weigh trade-oifs among the alternatives. The last two modifying criteria are
considered aftei the public comment period during the final selection of the remedy.
Overall Protection of Human Health anil the Environment
Both alternatives are protective, because the City of Seattle would continue to operate and
maintain the cap, and the gas and storm water systems under both alternatives.
Compliance with Applicable or Relevant and Appropriate Requirements
Federal and state drinking water standards and MTCA groundwater cleanup standards are the
primary applicable or rrlevuit and appropriate requirements under the Limited Action
Alternative, "f he cleanup standards listed above would need to be met in the downgradient
monitoring wells before the remedial action st the Midway Landfill could be considered
complete No cleanup standards would be set by EPA under the No Action Alternative,
though Ecology could decide to set cleanup standards separately under MTCA at a later time.
Long-term Effectiveness and Permanence
The Limited Action Alternative has greater long-term effectiveness and permanence than the
No Action Alternative because it would requite annual notice to water districts and well
permit regulators, which would provide: slightly greater assurance that no one would drink the
groundwater leaving the landfill It would also clarify the need to adjust monitoring
requirements as site conditions chiinge,
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Reduction of Toxicity, Mobility and Volume of Contaminants through. Treatment
Neither alternative includes any additional treatment. Extracted landfill gas is flared as part of
file existing landfill gas collection system.
Short-term Effectiveness
Both alternatives have the same short-term effectiveness. Neither alternative includes
construction nor will either alternative affect the time needed for all groundwater leaving the
site to meet cleanup standards.
Impleinentabilitv
Both alternatives are equally iiipljpentaMe.
' lMe
Cost %_#. ....
The costs for the two alternatives are exjsxted to be very similar. The monitoring costs for
the Limited Action Alternative may be'slightlv higher than the monitoring costs for the No
Action Alternative.
Hi •
Stale Acceptance
Ecology was consulted on the proposed plan and itesiewed this ROD. Ecology concurs with
the selected limited action remedy.
Community Acceptance
Four comment letters have been received. Two letters, from the Seattle-King County
Department of Public Health and from a local resident, supported the Limited Action
Alternative. The second iet'.er, from the City of Des Moines, docs not express any opinion
about the alternatives, but is concerned about turbidity that may be leaving the landfill cap and
discharging into North McSorley Creek. The City of Des Moines asked the City of Kent and
the City of Seattle to prepare a storm water pollution plan for turbidity frcw this outfall, and
a-ked for specific monitoring. The City of Seattle supported the Limited Action Alternative,
but requested certain changes and clarifications. A longer summary of these comments and
EPA's responses can he found in :he attached Responsiveness Summary.
EPA staff also received infumial comments through phone calls. In these calls, five members
of the puWic >upj\trtcd thv limited action alternative.
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11, The Selected Remedy
11.1 Summary of the Rationale for the Selected Remedy
FPA's selected remedy is the Limited Action Alternative, Of the alternatives considered, this
alternative will provide the best long-term protectivcness at the Midway Landfill site. It sets
groundwater cleanup standards and it ensures long-term operation, maintenance, and
monitoring of the containment systems at the Midway Landfill site. It would also clarify the
need for. and types ot". institutional controls that are necessary to ensure long-term
profectiveness of the remedy.
Additionally, this alternative will best ensure long-term protectiveness of the containment
remedy currently in place. While EPA believes no new remedial construction (as EPA
guidance defines the term) is needed, it is important that the City of Seattle continue to
operate and maintain the gas collection system, the cap that was constructed over the landfill,
and the storm water collection system. The City also needs to continue to monitor the
effectiveness of these actions, and to regularly Sample the groundwater until groundwater
cleanup standards have been met. The City seeds to establish permanent, legally binding,
controls on the landfill property to ensure that the cap and containment systems are not
damaged as long as the cap and gas and storm water systems are required. The less formal
institutional control requirements, in the form of notices to agencies, water districts, and
active well drillers, for the off-property groundwater contamination are appropriate For this
site considering that the area is fully served by community water systems, no private wells are
known to be in use, and the relatively low levels of remaining contamination in the
dovngradier.it monitoring wells. Also, groundwater cleanup levels for the groundwater
downgradient of the landfill need to be established.
In order for Ecology to utilize this ROD as a Cleanup Action Plan, the cleanup action
established through the ROD must meet the MTCA remedy selection requirements of WAC
173-340-36(X2) (threshold requirements) and (3) (requirementto utilize permanent solutions
to the maximum extent practicable; requirement to provide for a reasonable icstoration time
frame; requirement to consider concerns raised daring public comment.) WAC 173-340-
36(X IB). The threshold requirements for remedy selection are Cut the remedy shall protect
human health and the environment, comply with cleanup standards, comply with applicable
state and federal laws, arid provide for compliance monitoring. Ecology has determined that
the selected remedy, as described hi the ROD, satisfies those threshold requirements.
With respect to MTCA's preference for permanent solutions. Ecology has determined that the
following remedies for individual components, taken together, are permanent to the maximum
extent practicable m that they prevent oi n:::iimize the migration of hazardous substances into
tne environment and provice for a net redaction in the amount of hazardous substances
31 ¦
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released from the source area. First, with respect to the Midway Landfill refuse itself,
Ecology has determined that the isolation and containment remedy of the 1990 consent decree
and this ROD is the preferred amiable cleanup technology, See WAC l?3-340-360(9)(c)
(describing Ecology's expectations of sites with. large volumes of materials with relatively
low levels of hazardous substances where treatment is impracticable.) With respect to landfill
gas generated by the refuse. Ecology litis determined that the treatment, of such gas, as
specified under die 3990 consent decree and this ROD, constitutes "destruction or
detoxification" which is the highest preference cleanup technology under MTCA. With
respect to groundwater contaminated by landfill Jeadiate, Ecology has determined that the
incremental benefit to be realized from implementing additional remedial engineering
measures (e.g. treatment) is substantially and disproportionately outweighed by the cost of
inch measures, This determination is based upon the facts that: 1) the actions taken by the
City of Seattle since 1985 have eliminated or greatly reduced the contaminants leaving the
landfill; 2) the levels of contamination that remain in the groundwater are low and trending
towards compliance with, cleanup standards: and 3) the groundwater does not have any current
human or environmental receptors. Therefore, Ecology has determined that institutional
controls and monitoring, as required under fiiis ROD. constitute an appropriate remedy for
crotnidwater until cleanup levels are achieved.
With respect to a reasonable restoration time frame, EPA and Ecology agree that the remedial
actions implemented have created conditions under which groundwater will achieve
compliance with Elte cleanup standards over time, Based on the results of the groundwater
monitoring to date, it is apparent that groundwater down gradient of the landfill is very near
compliance with the cleanup standards, Ecology concludes that.based on present trends, it is
likely that groundwater down gradient of the landfill will reach compliance with cleanup
standards in approximately five years. Based upon the facts that institutional controls aimed
at preventing the use of contaminated groundwater as a drinking water source are a
component of this ROD, that the contaminant levels ate already low; and that a documented
trend towards compliance exists. Ecology has concluded that this constitutes a reasonable
restoration time frame.
Finally, Ecology has determined that the ROD has considered concerns raised during public
comment. (Sec ROD Section 13 and EPA Responsiveness Summary.)
11,2. Detailed Description of the Selected Remedy
The selected remedy consists of:
I. Monitoring to ;
ai ensure the remedial systems are working as designed,
b) ensure progress is being made towards meeting the groundwater cleanup standards,
c) ensure adequate containment is maintained when aid if major changes are approved
by Ecology in the operation of the site,
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system, anil
d) demonstrate thai the cleanup levels have been achieved.
The monitoring will be done by the City of Seattle, while Ecology will continue to be the lead
cleanup regulatory agency at the site. The details of the monitoring requirements have been
set out by the City of Seattle in an Ecology-approved compliance monitoring plan.
Monitoring, including installation of new monitoring wells, are among the activities EPA
expects at site? e\en after EPA determines that construction has been "completed" at a site.
Through the procedures outlined in the agreements between Ecology and the City of Seattle,
Ecology may require the City of Seattle to install and monitor new monitoring wells if
needed.
If necessary, the monitoring program may also address the issue of the source of turbidity in
North McSorloy Creek raised by the City of Des Moir.es in their comment letter on the
proposed plan. The City of Des Moines requested thai the City of Seattle continue to monitor
the S 250th Street outfall for turbidity during storm events (on a periodic basis) and provide
the results to the City of Des Moines Engineering Department.
2. Continuing to operate and maintain all remedial elements required in the 1990 consent
decree. Ecology will continue to oversee the City's operation and maintenance activities.
Operational changes can be approved by Ecology wheti such changes ensure that the site and
remed}' will remain protective, "lhe Seattle king Count) Public Health Department should
be given the opportunity to review requested operational changes.
3, Implementing institutional controls. Institutional controls are legal or administrative
actions that help ensure the long-term protectiveness of the remedy. At this site, the selected
remedy consists of three types of institutional controls. Variations of the first two types of
institutional controls are already required in the 1990 consent decree.
First, the City of Seattle will place a notice in the records of real property kept by the
King Coimty auditor, alerting any future purchaser of the landfill property, in perpetuity, that
this property had been used as n landfill and was oil EPA's National Priorities List, and that
future use of the property is restricted. The use restriction skill comply with the post-closure
use restrictions under the State of Washington's Criteria for Municipal Solid Waste Landfills
(WAC 173 -351-500( 1X1} and {2)(c)(ii.). The City has not yet placed any legal notice in the
County's records even though a foim of this nonce was required by the 1990 consent decree.
EPA understands that this is a subject that will be addressed through an amendment to the
>090 consent decree. EPA expects the City to place this notice on the deed within sis months
of the dale of effective date of the consent decree amendment, unless the City has negotiated
an alternative enforceable schedule with Ecology.
Second, "lie City needs io ensure continued operation and maintenance of die
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containment and jaoniroring systems if any portion of the property is sold, leased, transferred
or otherwise conveyed.. This requirement is an element of the 1990 consent decree.
Tlilrd. notices arc needed so that no water supply wells are constructed and used in
areas with groundwater contamination emanating from the landfill. These notices shall
include at a miniraum the following:
The City will annually notify the Seattle-King County Department of
Public Health, Ecology, the local water districts (currently, the Kent and Highline Water
Districts) and locally active well drillers in writing of groundwater conditions in the affected
areas downgradfent of the landfill. This notice will include a map showing the location of the
affected areas and indicate which aquifers arc, affected and their elevations. This information
shall he updated annually and can he part of mi annual groundwater monitoring report.
Locally active well drillers are all well drillers that have drilled wells within King County in
the Year orior to the notice. Ecology will provide the list of locally active well drillers to the
City, llils requirement for annual notices can he removed or modified by Ecology after
groundwater cleanup standards have been .net in the groundwater monitoring wells
downgradient front the landfill.
The City of Seattle will also annually notify owner of Weil W17 (See
figure 6-1) in writing of groundwater conditions in the area of the well. Alternatively, the
City of Seattle can provide to Ecology adequate assurances that this well has been properly
abandoned.
As an additional protection, state regulations forbid any private drinking water wells within
1.000 feet of a municipal landfill or 100 feet from all other sources or potential sources of
contamination (WAC 173-160-171). State regulations (WAC 173-160-151) also requires a
property owner, agent of that owner, or a water well operator to notify Ecology of their intent
to begin well construction prior to beginning work. This notification can provide notice to
Ecology ifanyone plans to build a new water well too near Midway Landfill.
Ecology will continue to be the lead regulatory agency overseeing the performance of the
selected remedial action by the City of Seattle, However, if necessary, EPA could use its
statutory authority to ensure that actions selected by this ROD are implemented.
The groundwater cleanup standards for the current contaminants of concern can be found in
Table 8-1. If other contaminants resulting from releases from the landfill are found in any-
down gradient monitoring well, cleanup levels, if necessary, will he established for these
additional contaminants using the federal drinking water standards mid EvlTCA.
The point of compliance lor the groundwater will be at the edge of the landfill waste as
specified in a Compliance Monitoring ?!ac to be approved by Ecology. Under MTCA, this
locution is considered a "'conditional point of compliance." Ail groundwater downgradient of
this point of compliance will need to meet these cleanup levels for contaminants resulting
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from releases from the landfill before the Midway Landfill is removed from the Snperfund
National Priorities List.
One of the City of Seattle's concerns is that contaminated groundwater is coming into the
landfill from up gradient sources, and that this ir.-coining contaminated groundwater will
never allow the groundwater leaving the landfill to meet the groundwater cleanup standards.
Because of the major inipnwemenis ill dowagradient water quality in the last ten years, EPA
believes it is possible that the groundwater leaving the landfill will eventually meet the
groundwater cleanup standards. However, if in the future the City wants to demonstrate that it
is technically impracticable for them to meet the cleanup standards at every downgrading
well because of the up gradient soun.es, EPA and Ecology will work together with the City to
determine what information is needed to support such a demonstration.
Because the selected rented}' will result in hazardous substances remaining on-site above
levels that allow for unlimited use and unrestricted exposure, a statutory review will be
conducted under CERCLA within five years of this Accord of Decision to ensure that the
remedy continues to be protective of human health and the environment. Because Ecology is
expected to continue to he the lead regulatory agency for this cleanup, EPA would expect
Ecology to perform the five year review at this site.
The City of Seattle estimates that the closure costs of Midway Landfill amounted to about
$56.5 million as of 1995. This does not include the ancillary costs associated with the landfill
such as the "Good Neighbor Policy" (See Section 3.) in recent years, the budgeted and actual
operation and maintenance costs have ranged ftum $435,000 to $535,600 annually. This
amount includes monitoring costs.
113 Expected Outcomes of the Selected Remedy
This section presents the expected outcomes of the selected remedy in terms of resulting land
and groundwater uses.
AO future land use at the landfill mast be designed and implemented in a manner that will
maintain the integritv of the remedy required tmoer the 1990 consent decree. A number of
future land uses have been suggested by Midway Citizens Advisory Committee, working with
the Cities of Kent aid Seattle in 1992. While this selected remedy clarifies the legal notices
that need to be in place to ensure the long-term effectiveness of the containment systems, the
selected remedy does not place any additional limits on future land use at the Midway
Landfill site arid does not change the feasibility of the possible future uses suggested by the
Advisory Committee.
Groundwater use directly under the landfill will always he restricted, Once the groundwater
dovrasyadient from the landfill meets the cleanup standards established in this ROD, nothing
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ill this selected remedy would forbid use of this groundwater for drinking water, 'The cleanup
levels selected in this ROD are either equal to or more stringent than the federal MCLs.
However, state and local regulations place oilier limits on the use of the groundwater. For
example, state regulations forbid any new private drinking water wells within 1000 feet of a
municipal landfill,
12. Statutory Determinations
12.1 Protection of Hainan Health and the Environment
The selected remedy will protect human health and the environment by a combination of-
engineering and institutional controls. The engineering controls that have been constructed at
Midway Landfill by the City c.f Seattle have been effective in containing gas migration and
kachate release from the landfill This effectiveness is demonstrated by the City's gas
monitoring results and by iie decreasing water levels in and below the landfill and the
decreasing concentration of hazardous substances in the groundwater dowrigradient from the
landfill The selected remedy will ensure long-term protectivencss by requiring that the
containment systems remain effective, that monitoring will continue and be adjusted as
necessary, and by clarifying and improving the institutional controls associated with the site
and the remedy to ensure that no one will be exposed to the contents of the landfill nor to
contaminated groundwater, Implementation of the selected remedy will not pose
unacceptable short-term risks or cross-media impacts..
12.2 Compliance with Applicable, or Relevant and Appropriate Requirements
The selected remedy for Midway Landfill will comply with all federal and state APARs, The
chemical-, action-, rod Ioeation-speeitlc ARARs .ire as follows:
The Washington Model Toxics Coiitroi Act (MTCA) Cleanup Regulations (Chapter 173-340
WACt are applicable. In particular, MTCA is> applicable to the determination of the order of
preference of cleanup technologies (WAC 173-3 40-360(4)), to require the provision of a
reasonable restoration time fame (WAC 173-340-360(6)), the establishment of groundwater
cleanup levels (WAC 173-340-720^3')), selection of the point of compliance (WAC 173-340-
720(5;)» the determination o f attainment of the groundwater cleanup level when the practical
quantitation lirmt is greater than the cleanup level (WAC 173-340-707), and the format of the
institutional controls (WAC 173-340-440.)
Certain landfill cloture and post-closure requirements in the Washington Criteria for
Municipal Solid Waste Landfills iChapter 173-35! WAC) and in the Washington Minimum.
Functional Standards for Solid Waste Handling (Chapter 173-304 WAC) are relevant and
appropriate. Specifically. the notation on the deed requirement in WAC 173-351-500 (1)(I)
arid the minimum functional standard for explosive landfill gas in WAC l73-304-160(2Xh)
are relevant and appropriate.
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The primary federal drinking water standards (40 CFR 141), known as the MC'ls, established
under the Safe Drinking Water Act, are relevant and appropriate to the establishment of the
groundwater cleanup standards downgradient of the landfill.
12.3 Cost-Effectiveness
The costs of the selected remedy are proportional to its overall effectiveness. The costs of this
remedy are similar to the costs of the no action alternative, but provide better long term
proteciiveness.
12.4 Utilize Permanent Solutions and Alternative Treatment Technologies to the
Maximum Extent Practicable
The selected remedy utilizes permanent solutions to the maximum extent practical. HPA's
presumptive remedy for municipal landfills is containment. Ten years of monitoring data
show that the containment remedy has been successful in reducing the risks and exposures
from the site. The selected remedy helps ensure that trie containment remedy will continue to
he protective.
1 lie selected remedy at Midway Landfill satisfies the statutory preference for treatment as a
principal element of the remedy. Extracted landfill gas is flctred as part of the existing landfill
jzas collection system. Dieting the XT, numerous hazardous substances were found in the
extracted landfill gas including vinyl chloride, xylenes, toluene, benzene and other solvents.
12.6 Five year reviews
Because this remedy will result in hazardous substances remaining above levels that allow for
unlimited use and unrestricted exposure, a statutory review will be conducted within five
years of this Record of Decision to ensure that the remedy continues to be protective of
human health aid the environment.
13, Documentation of Significant Changes from the Preferred Alternative in the
Proposed Plan
There are no significant changes between the preferred alternative described in the proposed
plait and the remedy selected in this ROD
The following mhioi changes !\ave been made from the preferred altera drive in the proposed
plan:
12.S, Preference for Treatment as a
.PrinciptC^w
ient
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- An additional RAO has been added to clarify that returning groundwater down gradient of
the landfill to drinking water and state cleanup standards Is a goal of this remedial action,
- The ROD clarifies that details of the landfill monitoring program have been established by
Ecology and the City of Seattle in a compliance monitoring plan. The proposed plan implied
that Ecology would establish die details unilaterally.
- The selected remedy includes a minor changes to the institutional control requirements for
notification of well drillers. The notice will be provided to well drillers that have been
recently active in King County, Ecology will provide the list of locally active well drillers to
the City of Seattle,
- The ROD does not contain the statement that Ecology determines when the site meets
eleamts levels. The City can contact both Eco'ogy and EPA when the City believes the site
has met all of the requirements of this ROD and thus could be considered for deletion from
tbeNPL
- Tic remedy selected in this ROD lias an added requirement that the City annually notify the
owner of one off-property well, unless the ,€ity provides Ecology adequate assurances thai
this well has been properly abandoned.
These changes are a logical outgrowth of the information presented in the proposed plan and
in the administrative record.
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Table 5-1
Southern Gravel Aquifer, Downgradient Well
Moniioriufc, Well 14B
Report
Number
J Sampling Date
Chloride
fmg/L)
Manganese
(rn&'Ll
1.2 Di-
chloroethane
(ug/L)
Vinyl
Chloride
(ugfL)
31 Average
219
4,8
50
4
]
February 19*50
2801
3.9
27
1 U
2
May 1990
175
3.6
1 U
1 u
3
August 1991
ISO
5
25
1 u
4
January 1991
ISO
4
31
3
5
April 1991
190
.3.6
20
'"J
6
July 1991
170
20
4
7
October 1991
212
29
3
a
March 1992 J 22
3.5
19
1 U
9
3 me 19Q2
146
3.9
19
4
10
September 1992
201
3.7
16
1 U
11
December 1992
153
3.86
13
2.6
12
April 1993
lt>2
3,4^
2.3
1 U
13
June 1993
159
3.3S
12
3.1
14
September 1993
168 '
3.45
10
3.3
Deceinbet 1993
127
3.49
S.8
3.4
16
March 1994
165
344
I? •
May 1994
154
3.19
6 ' i
IS
September 199*1
140 i
}
3.SS
19 j
December 1994
160 j
3.0ft"
6 J
1 U
20
March 1995
190
3.3
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21
May 1995
140
3.26
20
2 2
1
22 September 1995
180
3.22
23
December 1995
170
3.14
9.2
2.7
24
March 1996
150
3.19
25
May 1996
180
3,07
6.6
'2.5
26
September 1996
170
2.96
2?
December
130
2.8
2.7
2.3
28
March 199?
,140
2.58
29
May 199?
120
2.73
11
20
30
September 1997
97
2.57
31
December 1997
85
2.23
I 3
2,2
32
March 1998
1
71
1.86
33
__
May 1998
51
1 U
2U
34
November 1998
29
1.
1 U
2 U
35
April 1999
27
1.48 '
1 u
1 U
36
October 1990 37
1.49
1 u
1 IJ
L' •= Indicates cumpound was no! detected above the specified reporting limit.
J = Indicate? that concentration is an estimate because all QC criteria were not met
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Table 5-2
Southern Gravel Aquifer, Downgradient Well
Monitoring Well 23 B
Report
Number
Sampling Date
Chloride
(mg/L)
Manganese
(ing/L)
,1,2 Di-
cHoroctbane
(ug/L)
Vinyl
Chloride
(ug/L)
R! Average
68
0.2S
13
5
1
February 1990
140 J
0.37
11
1 U
2
May 1990
50
(i33
14
1 LI
3
August 1991
61
.
0.48
10
1 U
4
January 1991
60
0.41
12
5
April 1991
58 ^
Ji4
10
4
6
July 1991
50
0.38
' 13
S
1
October 1991
61
0.35
11
1
i
8
March 1992
54
0.39
9
6
9
June i1 j Dcccnbsr " g94
4^
0,35
8.7 ' 1 TJ
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20
March 1995
. 41
0.343
71 '
May 1995
39
0.323
S.i '
3.2
22
September J 995
39
0,309
23
December 1995
40
0.311
7.1
3.5
24
Match 1996
40
0.32
25
May 1996
39
0.302
8.5
3
26
September 1996
40
0.317
27
December 1 ^96
38
0.304
6,8
2.7
28 1 March 1997
38
0.28?
29 j May 199?
38
0.284
7.7
2.4
30 : September 1997
36
n 312
31
December 1997
35
0.278
9.7
4
3 '2
March W8 , 36
'0.281
1
33
May 1998
36
0.295
7 ' 2.4
34
November 1998
36
0.275
6.6 | 2
35
April 1999
25
0.259
7.1 1 1.2
36
October 1999 ' 28
0.258
7.5 ! 2
U = Indicates compound was aot detected above the specified reporting limit.
J - Indicates that concentration is an eMimate because all QC criteria were not met.
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Water Quality in the Sand Aquifer
Up Gradient Monitoring Wells
MW17-B Recent concentrations ¦ MCL
1,1-dicUoroefnane 90 to 160 ug/L 800 ug/L*
1.1-dicMoroeth.eiie 4 8 to 8.2 ug/L 7 ug/L
1.2-dichIoroathice 8 to 12 ug/L 5 ug/L
MW 21-A ¦
1.1-dichloToethanc ' 1 ) 1 to 14 ug/L 800 ug/L*
I.l-dichloroethene • ~ —> 1,6 to 2.6 ug/L 7 ug/L
tetrachloroetbene ¦ 24 to 35 ug/L 5 ug/L
Irichloroethene , 2.4 to 3.1 ug/L 5 ug/L
* 1,1 -dichloroethane has no MCL, 800 ug/L is the MICA Method B cleanup level in the 2/96
CLARC II tabic.
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APPENDIX A
RESPONSIVENESS SUMMARY
MIDWAY LANDFILL
The responsiveness aimmary addresses public comments on the proposed plan for the
remedial action under CERCLA for Midway Landfill NPf. site in Kent, Washington. EPA's
proposed plan was issued in May 2000 and '.he original public comment period ran from May
18 to Juris 16. 2000. The City ot* Seattle asked for an extension of the comment period on
June 15. and the end of the public comment period was extended 30 days until. July 17, 2000.
EPA's notices and fact sheets offered to hold a public meeting if sufficient interest was
expressed by May 31, 2000. Only font requests were received and thus a public meeting was
not held.
-
Written eammenfa
• Four written comment letters-were received.
Comrnrnf: I received your tact sheet about the Midway Landfill in Kent Washington and I'm
writing (his letter to recommend that EPA implement their Limited Action Plan. Monitoring
wells 23 B and 29B arc in a neighborhood and a church parking lot and should be monitored
until signs of contamination no longer exist.
Response; Thank yon for your comment and your support of EPA's preferred alternative.
Comment: The City of Dcs Moines has just completed a 5 year stream water quality
monitoring program, which included the monitoring of McSorlcy Creek, the receiving stream
of the runoff from Midway Landfill. The monitoring of the drainage outfall showed elevated
levels of turbidity above water quality standards for a Class AA stream. McSortey Creek is a
salmon-bearing stream containing echo and ehmn salmon, steelhead and cutthroat trout.
Although not conclusive, mainly because the treatment ponds on the Landfill also receive
runoff from nearby Pacific Highway South, the turbidity may he the result of nuttoff from the
Landfill clay cap. In order to full)' remedy the situation, the City of Pes Moines believes that
the City of Seattle and the City of Kent, the owner of the Pacific Highway right-of-way in this
area, need to jointly prepare a storm water pollution control plan for controlling the turbidity
eormng from this outfall The City wot:id like to have the opportunity to review such a plan.
'i he City of Des Moines also requests that, as pan of EPA's monitoring proposal, Seattle
continue to monitor the outfall for turbidity during storm events (on a periodic basis ) and
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provide the results of the tests to the City of Des Moines Engineering Department.
Response; EPA forwarded a copy of the City of Des Moines's letter to the City of Seattle
aid 10 Ecology. In response, the City of Seattle has begun discussions with both the City of
Des Moines and the City of Kent 10 address the turbidity issue. The City of Seattle lias sent
the City of Des Moines all of the 1999 storm water detention pond monitoring data. This
data, as we?l as the earlier years of data, appear to indicate that the main source of turbidity is
the pond inflow from Pacific Highway South. Also, the City of Kent has now started to
identify the City of Kent's options regarding requiring the private property owners to improve
the quality of water discharged from their site.
EPA's description of the selected remedy (Section 11,2) acknowledges your request for
additional monitoring. Details of the monitoring program will be established by Ecology and
the City under their existing agreements,, or, if necessary, unilaterally by Ecology using state
regulatory authority.
Comment: Public. Health-Seattle & Kirig.CouRty supports EPA's limited action alternative.
Outstanding groundwater issues in proximity to the landfill need to be addressed in order to
protect both the environment and the public health of tbe impacted community.
. Response; Thank you for your comment and your support of EPA's preferred alternative.
Comment; The City of Seattle supports the 'limitcdjictbn remedy" alternative proposed in
the plan for the ROD.
Response: Thank you for your support of the limited action alternative.
Comment: The City has reached a tentative agreement with the Washington Department of
Ecology ('"Ecology") concerning this issue; Ecology will adopt the EPA ROD in its entirety,
and the existing Consent Decree ("CD") between Ecology and the City will be formally
amended to reflect EPA'f limited action remedy. Thus, Ecology will not issue a Cleanup
Action Plan ("CAP**) for the Midway Landfill, since the RuD will serve that same purpose.
The City is pleased to announce this approach with Ecology because it will save both the City
and Ecology the staff arsd budget resources necessary to issue and implement a separate CaP.
Response: When EPA was wtitirig the proposed plan, Ecology had tentatively decided that
Ecology would prepare a Cleanup Action Plan under MTCA. In accordance with EPA's
understanding of Ecology's current position, the ROD lias beer, changed to reflect the fact that
after this ROD is completed. Ecology will use this EPA ROD, at' allowed under MTCA. EPA
has worked with Ecology to incorporate language into this ROD tu reflect the necessary
2
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M I"CA requirements.
Comment: Proposed Plan page 1 • delete "Additional groundwater wells may need to be
installed." The City has been monitoring groundwater through an existing network described
in fr.e CMP, ll is the City's understanding that Ecology will review and approve the CMP,
which sets forth, the well network and monitoring schedule, as previously submitted. There is
neither a pending requirement nor a technical justification for additional wells beyond the
network in the submitted CMP.
Response- The detai's of the monitoring requirements have been set out by the City of
Seattle in a compliance monitoring plan recently approved by Ecology, Through lite
procedures outlined in the agreement? between Ecology and the City of Seattle, Ecology may
require the City of Seattle to install and monitor new monitoring wells if needed.
Comment: Proposed Han, page 2 - the last paragraph needs to be re-written to reflect that
Ecology will adopt the ROD and will not issue a CAP.
Response: Please see EPA's response to the City's second uomrnert, above.
Comment: Proposed plain page 5 - add the word 'tniaT to the first paragraph. The edited
sentence will read: "This lejfsl agreement set forth Ecology's determination thai certain final
remedial actions.,,This edit reflects the wording of the existing CD that the remedial
actions performed under the CD were final actions and riot interim actions.
Response: The referenced sentence from the proposed plan has not been repeated in the ROD.
A sentence that begins with the same phrase cau be found in Section 2.1, but concludes with
Ecology's determination that undertaking certain remedial actions would provide immediate
protection to public health and the environment. This determination can be found in
Paragraph 6, Page 9 of the 1 WO Consent Decree.
Comment; Proposed plan, page 5 - re-write the paragraph above "Site Characteristics" to
state that Ecology will amend the CD and adopt the ROD in its entirety, including the limited
action remedy, which addresses long-term monitoring through the CMP,
Response: As a result of discussions and reviews between the time of the proposed plan and
EPA's completion of the ROD, Ecology has decided to utilize the ROD as a Cleanup Action
Plan pursuant to MICA, and so approve the CMP. The ROD reflect? these recent Ecology
decisions.
Comment: Proposed plan, page 7 third full paragraph from the top of the page. Delete
"'most likely*" from the first sentence. Based on the voluminous technical data, groundwater
contamination in the Said Aquilet to the north, northwest and west ofthe landfill does not
3
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come from the landfill. The present sentence is inaccurate.
Response: The phrase has been removed from the Summary of Landfill Conditions in Section
5.1. ¦¦ •
Comment: Proposed plan, page « - Tabic 1. Proposed Groundwater Cleanup Standards.
These proposed standards are acceptable to the City, with the exception of vinyl chloride, it is
the City's understanding that Ecology will agree to use the practical quantification limit
(PQU for vinyl chloride as allowed by previously published Ecology directive.
Response; The concentration for determining compliance with the vinyl chloride cleanup
ievel is 0.2 ug/L and lias not changed from the proposed plan. This concentration reflects
Ecology's consideration of the PQL issues for vinyl chloride, consistent with WAC 173-340-
707 and the Department of Ecology's Implementation Memo No. 3, November 24, 1993.
Comment: Proposed plan, page 10 - the fUli paragraph under "#I Monitor to." Delete this
first sentence: "The moniiorirg will be done..and insert a sentence that states that
monitoring will be done pnraiant to the CMP approved by Ecology.
Response: This sentence has been modified. The selected remedy reflects the City of Seattle
and Ecology recent agreement on the details of the monitoring plan.
( omatnt: Proposed plan, page 1! - this sentence describing the third type of institutional
control needs to be edited: The reference to notifying "local licensed we'll drillers" should be
deleted because Ecology has dropped this requirement, further, the City proposes satisfying
the notification requirement to the health department and nearby water districts by sending
them die annual groundwater monitoring reports. This paragraph should state this as well.
Response; Ecology has not dropped the requirement that local licensed well drillers be
notified. However, this element of the selected rented}' lias been changed in two ways. First,
the notice requirement has been re-focused to limit Ihe notice to those licensed well drillers
who have drilled wells in King County in the year just prior to the notice. This change
reflects the competitive state-wide nature of tht well drilling business while not requiring
notices to drillers that may no longer be active. Second. Ecology will provide the list of
•names and address to the City of Seattle. Ecology's Office of Water Resources maintains a
database that can provide this information.
The selected remedy allows the City to satisfy the notification requirements through
distribution of the annual groundwater monitoring report, as long as the report contains the
required information.
Comment: Proposed plan., page 12 - "State Acceptance" This sentence should be edited to
4
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reflect that Ecology intends to accept ike limited action remedy and adopt the ROD in :ts
entirety.
Response; Trie ROD now says that Ecology concurs with the selected remedy and that
Ecology has decided to utilize the ROD as a Cleanup Action Plan pursuant to WAC 173-viO-
3&0{'li).
Comment; Proposed plan, page 13 - delete the last two sentences of the last paragraph, which
begin: "For example, fc'eologv believes it may be necessary to identify..." As discussed
above, it is the City's understanding that Ecology will approve the previously submitted CMP.
This CMP sets outfits scope of the City's uroundwuter monitoring obligation under the CIl
and amended CD., The CMP dcutt act address groundwater entering the landfill from off-sire
sources located oa the north and northwest of the landfill.
Response; The two sentences have been deleted from the description of the selected remedy.
The intent of the sentences was to provide an example of the type of information that may be
necessary if the City of Seattle wishes to demonstrate it is technically impracticable to meet
the cleanup standards at every down gradient well because of the up gradient sources. I!" in
the future the city would want to mate a demonstration that it is technically impracticable to
meet the cleanup standards, it is possible that EPA arid Ecology would require monitoring that
is act part of a monitoring plan already approved by Ecology. As stated in the ROD, in this
situation, EPA and Ecology would work together wiiiabe City of Seattle to determine what
information would he needed to support such a demonstration.
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5
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APPENDIX E - PRESS NOTICE
(b)(4) Copyright
EwrtSapevtar Frfcta^ August 7,2020 7
(b)(4) Copyright
SEPA EPA Reviews Cleanup at Midway
IC'1.!,""!!!.!. IjinHfill Superfund Site in Kent-
Public Input Welcome
The fourth five-Year Review of the environmental cieanup at Mtfway
Landfill, a Superfund site m Kent, Washington, Is underway. EPA must
review Superfund sites every five years when contaminants remain an ate
to ensure that the cieanup continues to protect human health and the
environment.
The Qty cr Seattle fasdftfll accepted demolition mate nay, wood waste and
industrial wastes from 1966 to 19E3. LaniJfllllng activities contaminated
groundwater and ar with hazardous chemicals. The cleanup tor the
Mdway Landfill included gas and stormwater control, capping, and
instttirtloru! controls. The cleanup- was compacted in 3992 and
groundwater monitoring ts ongoing. Mu:h of the landM area remains
undeveloped and the Federal Way Link Extension light rati ts being
constructed on the cast per, meter.
Feedback welcome: As someone from the area and familiar wih the site,
you may know things that can heap our review team. If you have
observations, information, or concerns about EPA's review., please contact
Ashley Grornpe, Pra|ect Manager at SflO 424 4372 ex112S4, or 206 553-
12B4. More information and documents related to this site are available at:
https://www.cpa.gov/superfund/ m tdway a ndfi ii.
To submit comments: E mail
Mall: Ashicy Grampe, M5 12D12 1,U.S. EPA Region la 1200 Swth
Avenue, Suite 155, Seattle, WA 98101.
TOO/TTY users may call the Federal Malay Senfe* at BD0477 8339.
Then please give the operator #206- 55312S4.
E-l
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(b)(4) Copyright
(b)(4) Copyright
EPA Reviews Cleanup at Midway
Landfill Superfimd Site fcn Kent
Public Input Welcome
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E-2
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APPENDIX F - SITE INSPECTION CHECKLIST
FIVE-YEAR REVIEW SITE INSPECTION CHECKLIST
I. SITE INFORMATION
Site Name: Midway Landfill
Date of Inspection: 3/5/2020
Location and Region: Seattle. WA 10
EPA ID: WAD980638910
Agency, Office or Company Leading the Five-Year
Review: EPA
Weather/Temuerature: 50s and overcast
Remedy Includes: (check all that apply)
Landfill cover/containment ~ Monitored natural attenuation
~ Access controls ~ Groundwater containment
Institutional controls ~ Vertical barrier walls
~ Groundwater pump and treatment
~ Surface water collection and treatment
m Other: gas collection
Attachments: Q Inspection team roster attached ~ Site map attached
II. INTERVIEWS (check all that apply)
1. O&M Site Manager Jeff Neuner (Seattle Program Manager 3/5/2020
Public Utilities) Title Date
Name
Interviewed at site ~ at office ~ by phone :
Problems, suggestions ~ Report attached:
2. O&M Staff Jeff Neuner and M in-soon
Yim (Seattle Public
Utilities)
Name
Interviewed at site ~ at office ~ by phone : __
Problems/suggestions ~ Report attached:
EPA staff interviewed Jeff Neuner and M in-soon during 3/5/2020 site walk. Information gathered during
interview is reflected in this FYR report. No significant deficiencies were noted.
3. Local Regulatory Authorities and Response Agencies (i.e., state and tribal offices, emergency
response office, police department, office of public health or environmental health, zoning office, recorder of
deeds, or other city and county offices). Fill in all that apply.
Agency Washington State Department of Ecology
Contact Mark Adams Cleanup
Name Project
Manager
Title
Problems/suggestions ~ Report attached:
EPA and Ecology have been in regular communication regarding upcoming site construction projects
and will continue to coordinate based on 2020 FYR Recommendations.
Agency
Contact Name
Title Date Phone No.
Program Managers 3/5/2020
Title Date
6/11/2020 (425) 649-7107
Date Phone No.
G-l
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Problems/suggestions [~~l Report attached:
4. Other Interviews (optional) Report attached:
Laura Lee and Lisa Gilbert from SPU contractor Parametrix were also present on the 3/5/2020 site inspection and
made available for technical questions regarding landfill performance and groundwater conditions over the past
years. No issues were noted during the interview.
III. ON-SITE DOCUMENTS AND RECORDS VERIFIED (check all that apply)
1. O&M Documents
~ O&M manual ^ Readily available
^ Up to date
~ N/A
~ As-built drawings ~ Readily available
~ Up to date
M N/A
~ Maintenance logs |3 Readily available
13 Up to date
~ N/A
Remarks: O&M manual and maintenance logs on-site
2. Site-Specific Health and Safety Plan
^ Readily available
13 Up to date
~ n/a
~ Contingency plan/emergency response plan
~ Readily available
~ Up to date
0N/A
Remarks: Jeff Neuner provided EPA and Ecology with H&S Update and Continuitv of Operations Plan on
3/9/2020 to reflect current site conditions.
3. O&M and OSHA Training Records
~ Readily available
~ Up to date
0N/A
Remarks:
4. Permits and Service Agreements
1^ Air discharge permit
^ Readily available
13 Up to date
~ n/a
~ Effluent discharge
~ Readily available
~ Up to date
13 N/A
~ Waste disposal, POTW
~ Readily available
~ Up to date
13 N/a
n Other permits:
~ Readily available
~ Up to date
13 N/A
Remarks:
5. Gas Generation Records
13 Readily available
13 Up to date
~ n/a
Remarks:
6. Settlement Monument Records
~ Readily available
~ Up to date
13 N/A
Remarks:
7. Groundwater Monitoring Records
13 Readily available
13 Up to date
~ n/a
Remarks:
8. Leachate Extraction Records
~ Readily available
~ Up to date
13 N/a
Remarks:
9. Discharge Compliance Records
~ Air ~ Readily available
~ Up to date
~ N/A
~ Water (effluent) ~ Readily available
~ Up to date
13 n/a
G-2
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Remarks:
10. Daily Access/Security Logs
Remarks:
Readily available Up to date ~ n/a
IV. O&M COSTS
1. O&M Organization
~ State in-housc
1^1 PRP in-housc
~ Federal facility in-house
~
O Contractor for state
~ Contractor for PRP
~ Contractor for Federal facility
2. O&M Cost Records
~ Readily available ~ Up to date
~ Funding mechanism/agreement in place £3 Unavailable
Original O&M cost estimate: ~ Breakdown attached
Total annual cost by year for review period if available
To:
From:
From:
From:
From:
From:
Date
Date
Date
Date
Date
Date
Total cost
To:
Date
Total cost
To:
Date
Total cost
To:
Date
Total cost
To:
~ Breakdown attached
~ Breakdown attached
~ Breakdown attached
~ Breakdown attached
~ Breakdown attached
Date
Total cost
3. Unanticipated or Unusually High O&M Costs during Review Period
Describe costs and reasons:
V. ACCESS AND INSTITUTIONAL CONTROLS ^ Applicable ~ N/A
A. Fencing
1. Fencing Damaged ~ Location shown on site map Gates secured Q N/A
Remarks:
B. Other Access Restrictions
1. Signs and Other Security Measures
Remarks:
~ Location shown on site map ^ N/A
C. Institutional Controls (ICs)
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1. Implementation and Enforcement
Site conditions imply ICs not properly implemented ~ Yes M No ~ N/A
Site conditions imply ICs not being fully enforced Q Yes m No ~ N/A
Type of monitoring (e.g., self-reporting, drive by):
Frequency:
Responsible party/agency:
Contact
Name Title
Reporting is up to date
Reports arc verified by the lead agency
Specific requirements in deed or decision documents have been met
Violations have been reported
Other problems or suggestions: ~ Report attached
Date
Phone no.
[~l Yes
~
No
IKlN/A
l~l Yes
~
No
IEI n/a
M Yes
~
No
~ n/a
[~l Yes
No
~ n/a
2. Adequacy [3 ICs arc adequate ~ ICs arc inadequate ~ N/A
Remarks:
D. General
1. Vandalism/Trespassing ~ Location shown on site map No vandalism evident
Remarks:
2. Land Use Changes On Site ~ N/A
Remarks: A light rail and highway expansion is planned for the eastern part of the Site by the end of 2020.
WSDOT is working with the Citv and Ecology to ensure continued remedy protectiveness.
3. Land Use Changes Off Site ^ N/A
Remarks:
VI. GENERAL SITE CONDITIONS
A. Roads [3 Applicable ~ N/A
1. Roads Damaged ~ Location shown on site map ^ Roads adequate ~ N/A
Remarks:
B. Other Site Conditions
Remarks:
VII. LANDFILL COVERS Applicable ~ N/A
A. Landfill Surface
1. Settlenient (low spots) ~ Location shown on site map ~ Settlement not evident
Area extent: Settlement was visible on the eastern part of the landfill Depth:.
outside of the fence. This area will be disturbed by the redevelopment
project and will be addressed at that time.
Remarks:
2. Cracks ~ Location shown on site map Cracking not evident
Lengths: Widths: Depths:
G-4
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Remarks:
3. Erosion Q Location shown on site map
[x] Erosion not evident
Area extent:
Depth:
Remarks:
4. Holes ~ Location shown on site map
~ Holes not evident
Area extent: there were some holes on the cap from moles burrowing
Depth:
Remarks:
5. Vegetative Cover ^ Grass
Cover properly established
E3 No signs of stress Q Trccs/shrubs (indicate size and locations on a diagram)
Remarks:
6. Alternative Cover (e.g., armored rock, concrete)
M N/A
Remarks:
7. Bulges ~ Location shown on site map
13 Bulges not evident
Area extent:
Heieht:
Remarks:
8. Wet Areas/Water Damage O Wet areas/water damage not evident
l~l Wet areas O Location shown on site map
Area extent:
E3 Ponding ~ Location shown on site map
Area extent: There was some
Bonding in the northwest Dart of
the landfill, near the stornnvater
pond. Site operators indicated
that this would flow into the
stornnvater pond if enough water
was present.
l~l Seeps O Location shown on site map
Area extent:
l~l Soft subgrade O Location shown on site map
Area extent:
Remarks:
9. Slope Instability O Slides
~ Location shown on site map
1^ No evidence of slope instability
Area extent:
Remarks:
B. Benches ~ Applicable ^ N/A
(Horizontally constructed mounds of earth placed across a steep landfill side slope to interrupt the slope in order
to slow down the velocity of surface runoff and intercept and convey the runoff to a lined channel.)
C. Letdown Channels [3 Applicable ~ N/A
(Channel lined with erosion control mats, riprap, grout bags or gabions that descend down the steep side slope of
the cover and will allow the runoff water collected by the benches to move oil of the landfill cover without
creating erosion gullies.)
1. Settlement (Low spots) ~ Location shown on site map
^ No evidence of settlement
G-5
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Area extent:
Remarks:
2. Material Degradation
Material type:
Remarks:
~ Location shown on site map
Depth:
No evidence of degradation
Area extent:
3. Erosion
Area extent:
Remarks:
~ Location shown on site map
No evidence of erosion
Depth:
4. Undercutting
Area extent:
Remarks:
~ Location shown on site map
^ No evidence of undercutting
Depth:
5. Obstructions
~ Location shown on site map
Si/c:
Remarks:
Type:.
^ No obstructions
Area extent:
6. Excessive Vegetative Growth Type:
No evidence of excessive growth
1^ Vegetation in channels docs not obstruct flow
~ Location shown on site map Area extent:
Remarks:
D. Cover Penetrations
13 Applicable ~ N/A
1. Gas Vents O Active
E3 Properly secured/locked Functioning
~ Evidence of leakage at penetration ~
Remarks:
~ Passive
Routinely sampled 13 Good condition
Needs maintenance ~ N/A
2. Gas Monitoring Probes
E3 Properly secured/locked Functioning M
~ Evidence of leakage at penetration ~
Remarks:
Routinely sampled 13 Good condition
Needs maintenance ~ n/a
3. Monitoring Wells (within surface area of landfill)
~ Properly secured/locked ~ Functioning ~
~ Evidence of leakage at penetration ~
Remarks:
Routinely sampled
Needs maintenance
~ Good condition
13 n/a
4. Extraction Wells Leachate
[~l Properly secured/locked ~ Functioning ~
~ Evidence of leakage at penetration ~
Routinely sampled
Needs maintenance
~ Good condition
13 n/a
G-6
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Remarks:
5. Settlement Monuments
l~l Located
O Routinely surveyed
§N/A
Remarks:
E. Gas Collection and Treatment
[3 Applicable
~ N/A
1. Gas Treatment Facilities
E3 Flaring O Thermal destruction O Collection for reuse
1^1 Good condition ~ Needs maintenance
Remarks: The gas extraction system has reached an asymptotic extraction stage. In the first quarter of 2018. the
Startup. Shutdown, and Malfunction (SSM) Plan for the Landfill Flare Supplemented with Natural Gas (SPU
2018) was completed to comply with Condition 10 of NOCOA No. 11400 and the requirements of 40 Code of
Federal Regulations (CFR) 63.6(e)(3).
2. Gas Collection Wells, Manifolds and Piping
E3 Good condition ~ Needs maintenance
Remarks:
3. Gas Monitoring Facilities (e.g., gas monitoring of adjacent homes or buildings)
~ Good condition ~ Needs maintenance N/A
Remarks:
F. Cover Drainage Layer ~ Applicable N/A
G. Detention/Sedimentation Ponds [3 Applicable ~ N/A
1. Siltation Area extent: Depth: Ek]N/A
~ Siltation not evident
Remarks:
2. Erosion Area extent: Depth:
E3 Erosion not evident
Remarks:
3. Outlet Works Functioning O N/A
Remarks:
4. Dam Q Functioning ^ N/A
Remarks:
EL Retaining Walls ~ Applicable ^ N/A
VIII. VERTICAL BARRIER WALLS ~ Applicable 13 N/A
IX. GROUNDWATER/SURFACE WATER REMEDIES ^ Applicable ~ N/A
A. Groundwater Extraction Wells, Pumps and Pipelines ~ Applicable N/A
B. Surface Water Collection Structures, Pumps and Pipelines ~ Applicable O N/A
C. Treatment System ~ Applicable ^ N/A
D. Monitoring Data
1. Monitoring Data
G-7
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n Is routinely submitted on time Is of acceptable quality
2. Monitoring Data Suggests:
~ Groundwater plume is effectively contained Contaminant concentrations arc declining
E. Monitored Natural Attenuation
1. Monitoring Wells (natural attenuation remedy)
~ Properly secured/locked ~ Functioning ~ Routinely sampled
[~l All required wells located ~ Needs maintenance
Remarks:
X. OTHER REMEDIES
If there arc remedies applied at the site and not covered above, attach an inspection sheet describing the physical
nature and condition of any facility associated with the remedy. An example would be soil vapor extraction.
XI. OVERALL OBSERVATIONS
A. Implementation of the Remedy
Describe issues and observations relating to whether the remedy is effective and functioning as designed. Begin
with a brief statement of what the remedy is designed to accomplish (e.g., to contain contaminant plume,
minimize infiltration and gas emissions).
The remedy appears to be functioning as designed. Site waste has been capped, landfill gas is addressed via the
flare station and site access is limited. Institutional controls are in place. The need to address 1.4-dioxane is
JB. Adequacy of O&M
Describe issues and observations related to the implementation and scope of O&M procedures. In particular,
discuss their relationship to the current and long-term protcctivcness of the remedy.
O&M activities at the Site appear to be adequate. Site fencing, the cap, the gas collection infrastructure and flare
station were all in good condition during the inspection. There were some limited areas of ponding and settlement
on the cap that should continue to be monitored and corrective action taken as needed.
C. Early Indicators of Potential Remedy Problems
Describe issues and observations such as unexpected changes in the cost or scope of O&M or a high frequency of
unscheduled repairs that suggest that the protcctivcness of the remedy may be compromised in the future.
N/A
D . Opportunities for Optimization
Describe possible opportunities for optimization in monitoring tasks or the operation of the remedy.
N/A
~ Good condition
IK|n/a
G-8
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APPENDIX G - SITE INSPECTION PHOTOS
Locked entrance gate on western side of landfill with signage
Seattle Public Utilities
Landfill signage
NflDWAY LANDFILL CLOSURE
LANDFILL GAS FLARE FACILITY
ONSITE GRADING AND DETENTION POND
STORMWATER PIPELINE TO SMITH CREEK
H-l
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Flare station
Flare station
H-2
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Area of ponding on landfill that requires regrading
Gas collection infrastructure on landfill
H-3
-------
Landfill, facing west
Landfill, facing east
H-4
-------
Evidence of burrowing into landfill cap by rodents
Stormwater pond
H-5
-------
Monitoring well MW-21
Stonnwater conveyance on landfill
H-6
-------
Monitoring well MW-14
Area of settlement on landfill cap in area of future redevelopment
H-7
-------
Area of future rail line and highway expansion, facing north
Area of future rail line and highway expansion, facing south
H-8
-------
Site fencing along 1-5
Gate on eastern side of landfill
H-9
-------
APPENDIX H - SELECT FIGURES FROM 2019 HYDROGEOLOGIC
ASSESSMENT FOR COMPLIANCE OF 1,4-DIOXANE
Figure H-l: Operable or Potentially Operable Water Wells within one mile of the Site^
Operable or Potentially Operable Water Wells within one Mile of Midway Landfill
Well
Name
Well Type
Likely
Aquifer
Use
Operable?
Hydraulic Position with
Respect to Landfill
21C1
(b)(6)
Group D
SA
Not in use
Covered but
operable
Cross-gradient
21F1
Marcus Whitman
Church
Group D
SA
Not in use
Covered but
operable
Cross-gradient to
Downgradient
21P1
(b)(6)
Group D - Irrigation
UGA
Potentially in use
Likely
Upgradient
22A2
war
Group D
AA
Potentially in use
New well
Cross-gradient to
Downgradient
22H1
(b)(6)
Group D
SGA
In use
Yes
Cross-gradient to
Downgradient
22J2
Kent Riverbend
1R
Group A - Irrigation
AA
In use
Yes
Downgradient
22Q1
wmm
Group D - Irrigation
SGA
Potentially in use
Unknown
Downgradient
22Q2
mm
Group D - Irrigation
SA
Potentially in use
Unknown
Downgradient
22Q3
(b)
Group D - Irrigation
SA
Potentially in use
Likely
Downgradient
27A3
mm
Group D - Irrigation
SGA
Not in use
Yes
Cross-gradient to
Downgradient
28G6
(b)(6)
Group D
UGA
Not in use
Yes
Upgradient
29A2
(b)(6)
Group D - Irrigation
UGA
In use
Yes
Upgradient
AA = Alluvial Aquifer
SA = Sand Aquifer
SGA = Southern Gravel Aquifer
UGA = Upper Gravel Aquifer
5 From section 5.3 of the Parametrix October 2019 Hydrogeologic Assessment for Compliance of 1,4-Dioxane.
1-1
-------
Figure H-2: Water Wells in 1-Mile Radius of the Site-
DES
MOINES
Section Key (USGS Standard Labels)
Frager Rd I Reitti Rd Area
Midway Upland
/rnilh
Miilw
KENT.
L>ES
MOINES
\\ iMNlmiiiii
He at'lt
ehsiA
SEATTLE PUBLIC UTILITIES
MIDWAY LAND-ILL
14-DKMANL LVALUE ION
h. HuEASTtlOySE
**<**12381
rr hi BRADY
..-aj«t>rt 07/23/19
SLR-ER
MIDWAY LANOFtL PARCELS WITH REFUSE
MIDWAY LAMDnU. PARCELS WITH NO REFUSE
0' 2,000'
0
C
B
A
E
F
G
H
M
L
K
J
N
p
Q
R
-ESEND
VW-XX M-SWAVMONITORIMQ
wpu oc*r<3«. io
- -i.e..*-
Lake Far wick Area
i/s+mfr
¦ // f i i a*T» tr: " |_^p
MAP SOURCE: USGS DES MOINES AND POVERTY BAY 7.5-MIN QUADRANGLES
Parametrix
INUNE9IIM& PtANNiNfc tWKWNMEhTAiSCIiNCtS
Figure 9
1-Mile Radius Water Well
Location Map
Midway Landfill
Kent, Washington
6 Figure is from the Parametrix October 2019 Hydrogeologic Assessment for Compliance of 1,4-Dioxane.
1-2
-------
APPENDIX I - DETAILED ARAMS REVIEW
The 2000 ROD stated that for groundwater that is a potential future source of drinking water, the more stringent
of federal drinking water standards (MCLs) and state cleanup standards under the MTCA are the cleanup levels.
Table J-l provides a comparison of the ROD cleanup goals to current standards. As noted in previous FYR
reports, the current standard for vinyl chloride is less stringent than the cleanup goal. The current standard for
manganese is more stringent than the cleanup goal. EPA will determine if the vinyl chloride and manganese
cleanup goals should be changed to reflect current standards.
Table J-l: Groundwater COC ARARs Review
Groundwater COC
2000 ROD
Cleanup Goal
Basis
Cu rrent
Standard'
ARAR Change
1.2-DCA
5 ng/L
Federal Drinking
Water Standard (MCL)
5 ng/L
None
Vinyl chloride
0.02 ng/L
MTCA Method B
0.029 |ig/Lb
Less stringent
Manganese
2.2 ing/L
MTCA Method B
0.75 ing/L
More stringent
Notes:
a. Current standards accessed at: https://www.eDa.gov/ground-water-and-drinking-water/ncitioncil-Drimarv-
drinking-water-regulations and
httDs://www.ezview.wa.eov/Portals/ 1987/Documents/Documents/CLARC Master.Ddf.
b. More stringent MTCA Method B value used between the cancer and noncancer cleanup levels.
J-l
-------
APPENDIX J - POTENTIOMETRIC SURFACE MAPS, TIME-SERIES PLOTS
AND GROUNDWATER MONITORING DATA
Exhibit J-l: Potentiometric Surface Maps2
Parametrix
twnweratiw iiAhH-'vc e mvi maw i* -al somch
Figure 11
Upper Gravel Aquifer
Potentiometric Surface Map
Midway Landfill
Kent, Washington
7 Figures are from the Parametrix October 2019 Hydrogeologic Assessment for Compliance of 1,4-Dioxane.
K-l
-------
lirtway Creek
DES
MOINES
Section Key [LJSGS Standard Labels)
CwMmjMl i
Wfl
Mldwdj
/cnilh
vK'-1—
WiHidmuiit'
Star
I ilkl-
I ti.?
iiwrwif
ehsim*
SEATTLE PUBLIC UTILITIES
I/IIDWAV LANDULL
1 4-DIOXAHE EVALUATION
mb K rASTHQUSE
mn.«-Qe&7
auw.P M BRADV
07/2 3f19
raw-n SURFER
HI^QI
3A WATER WELL
XXXX 3A WELL LOCATION / WATER
O lEV&L ELEVATION
vvv GROUWWVATER CONTOIS
'iilr I POTENTIQMETRJC SURfACQ
SURFACE F LOW DIRECTION
GROUNDWATER FLOW DIRECTION
midway ;.anofil i parcels Wi t» i refusP *
N
MIDWAY LANDFILL PARCELS WITH NO REFUSE
0' 2,000"
Parametrix
ENGINEERING . PLANNING. ENVIRONMENTAL SCIENCES
Figure 12
Sand Aquifer
Potentiometric Surface Map
Midway Landfill
Kent, Washington
K-2
-------
Figure 13
Northern and Southern Gravel Aquifer
Potentiometric Surface Map
Midway Landfill
Kent, Washington
Parametrix
ENGINEERING . PLANNING. ENVIRONMENTAL SCIENCES
K-3
-------
Exhibit J-2: Time Series Plotss
Upper Gravel Aquifer
-MW-16{lKiA-Up)
-MW-21A {JGA-Up}
-ROD Cleanup Level (a)
Sand Aquifer
-fr-
Ki:
k
3.5
3
2.5
* ,
1.5
1
0.5
~
.A
lat=t
*Ba-
¦Ett 'KB
QO^^^Qinorr.^-ru-11/-, vOi£ii-.r--u;cccv. 0-'CO'-''-OQ.-4--trMrs[nrri->r-4Lnknu3j3r^r^«jK30
CTi 0"> C* CT> cr CT'C^'O"' 0 cn CT' c^1 *J" O CT< C C"' cn O O O O O O O O O O COO O O O O O O O ¦"! r-t «-« «—l «--<*-* S-H i-« »-« H n r* ri r4 1^ H r,
is dpja aaij mjj anil ecii doi ii a>ij mxj sj-u scia wA od-q inA eoja tSeia wij wij lic^i eo_i gi_n tail ttojb »ii &j,o eeja &>jj
4l3#3(i3«3#3»3S3«3«3«3i3«3«3«3#3#3#3#3«3o3«l34l3«l3#3ll3v3«3»3it3#
• MW-7B (5A-Down)
MW-17S (SA-Up)
-WW-SB (5A-Up)
- MW-21B (SA-Up)
MW-15A (SA-Up)
—— ROD Geanup Level (a)
3
- MW-14B (SGA-Oown) - ~- MW-20B (SGA-Dowo) — I— MW-23B (SGA-Oown)
¦ MW-296 (SGA-Qown) -O- MW-30C (S6A-Down| ROD Cleanup level (a)
i Non dUKWdviiims<>i«iww*h vjo>tMKtMiiiwi Manganese by Aquifer
|al Cleanup laval aitabluhad in thafxwl EPA RaeonJ of D«ckMon forth# M«hvay Landfill, S»pUmb«r6, Midway Landfill, Kent, Washington
8 Time-series plots are from the Remedial Action Status Report 2015-2019, except forthe 1,4-dioxane time series plots,
which are from the Parametrix October 2019 Hydrogeologic Assessment for Compliance of 1,4-Dioxane.
K-4
Southern Gravel Aquifer
-------
•1
:
MW-16 (UGfl-Up)
2,5
MW-21A (UGA-Up)
2
iiiiiisiiiiiiisiijin'iinnij
3.5
3
2.5
2
MW-7B (SA-Down)
I't.
0,5
nnnnnnnnninninnn
25
MW-8B (SA-Up)
•
:
jisiiiiiiiiiiiiiiiiiisssiiisii
MW-15A (SA-Up)
b\
t ;
0
\
N-. •••
immmmmmmmmi
2.5
2
MW-17B (SA-Llp)
1
0.5
mi
HunnnnnnnniituHiit
2.5
2
MW-21B (SA-Up)
K
0
IllllllllllHIlHIIIiillUIill
MW-14B (SGA-Down)
* •
4
11II1!1I!HI1!!!ISIIS1IISIIIIS
- ROD Cleanup Level (a) — - Avg Rl
(i)Ow
Rl = R<
Midway Landfill, Kent Washington
MW-20B (SGA-Down)
§S5B!S3t83!5;S$SSgg S88&88S:S!5JSStS2
MW-23B (SGA-Down)
2.5 -
2
-
tmmmmmmmmm
K-5
-------
i Upper Gravel Aquifer
i
0.8
gji 0.6
0.4
0.2
0
-MW-16 (UGA-Up)
- MW-21A {UGA-Up)
-ROD Cleanup Level (a)
Sand Aquifer
-xxx-x-
|it t t
Iff
i i
i 1!»
l Ifr
if
i
0.5
f
Jmh
¦ f « »*\ ¦ b ¦
¦a feL_x-
.J*'*****.
jj UDii tiuJi sdxj tlfljj tin A uo-u to—i riflaj U£_o »¦" <¦'¦¦ tin ¦'; uojj ^ "
r3dl3(j3ti3l|l3i|)3«3(|J3tt3t393«3t'3«i3(i3i|i3li3li3il3ili3ill3»i3«3»3#34(3(li3iK3il)2a
< II — MW-30C (S6A-Qown) SOD Cleanup Level {a}
Southern Gravel Aquifer
ji rinji ccxs dd_q anj^ apxj co_d m_o upij m>su mjd apis opx; mxi apj3 SP-Q bojo ap_o npxs W.Q apii m_q apij ep_o opij ripi} apii sp_o opjo ep_a
I|jti39i3(!3g|3iii3i|3ti3u3di3iii3gi3ii3i|i3i|3i|j3ii3j3i;3iii3gi3i|i3ii3u3y3t/3ti3gi3ai3j
K-6
-------
MW-16 (UGA-Up)
-*v~y
liilillilililllllillliuillill
MW-15A (SA-Up)
m
llllllllllllllllllllilllliiill
MW-2Q B (SGA-Down)
Illlllilllllllllllllllilllllll
| "
a 04
5
"V-V
niiiuili
t 1i
linillllllllilllllllliillllll
iiiiiiiiiiiiiiiiiiiiiiiiiinn
0.35
MW-7B (SA-Oown)
0.3
0.25
"t
0.2
4 °ot
\
0
illlllllllillllillllllllilSIlI
MW-21B (SA-Up)
mmmmmimmmm
mmmmnmimnmm
06
1 0,
0.2
m
mimmimmnmimm
M4B (SGA-Down)
unillllllllillilllllllllSiil
' v\
Hinmnnminnriisunii
- ROD Cleanup Level (a) Avg Rl
s 1/2 the detection timet.
p-fna:rPA Riscnt) af 3ecis
Vinyl Chloride
Miaway Lanarm, i\eni, vvasnington
K-7
-------
Upper Gravel Aquifer
5 T
4 -
c
Sj? S! oti-O opx: ap_c 3a<3gi3iii3'j
-MW-16 (UGA-Up)
- MW-21A {UGA-Up)
-ROD Cleanup Level (a)
Sand Aquifer
^NNmtflg5unfig^h.NfflffiCTig}oo-H^Q(mrTi^^iiiLn^o^KcostifficiaO'"«-"(Nfti!nm'tf-U iln r't »ln r> 6fl_t
3v3(l3v3v3t3«31 <11 1 < >l <11 < 1 • <11 < U. < 1. < •! <11 <1 < I I < .4 < U < l» < II
MW-7B {SA-Down}
-¦*¦• MW-17B(SA-Jp)
MW-8B (SA-Up)
MW-21B (SA-Up)
-•X- MW-15A (SA-Up)
' ROD Cleanup Level (a)
- MW-23B (SuA-Down)
¦ROD Cleanup Level {a}
1,2-Dfchloroethane by Aquifer
Midway Landfill, Kent. Washington
Notes Nwi-dertectfld values are shown as 1/2 the dflfiection limit
(a) C lifts it up !»v»l attahlithad i?i rSie fina I EPA flacard of Decision for the Md»av Landfill, BApTarrbar 6,
2000
rn MW-14B
-------
mmmimmmmm
IIIIISIIIIIIIISIIIIIISIIIIIIII
MW-21A(UGA-Up)
lllllllllllllllllllllulllllli
liiiiiiiniiiiiiiiiiiiisniiii
nnnnnmninnnnnnu
lllllllllllllliilllliliilllill
IllllllllllllllllillllllliliU
IllIIlIlIllIlIIlIllllUSIIIul
- ROD Cleanup Level (a) Avg Rl
iai Cleanup level established in thefiial EPA fleeo'd of Deds-onforthe Midway landfall, Seprtemoe> 6, 20(10.
Rl = Remedia Investicjetion
Sar>d Acjuifer
Sail hern Gfavel Aquifer
1,2-Dichloroethane
Midway Landfill, Kent, Washington
K-9
-------
_q dr.xi gcxs rajij mx* riiixj w_d apxi apxi opi apja dpx) on_c apxi aji-Q «>x> apxi gp_a w>-C apx» apxi m_q opx) spxi opja apx> opij gpx: mjq «j_a
U"v2^3u3ill3ili3u3gi3«3di3u3ii3ii.3iu3{u3g|3li3ii3ai3iii3n3ii|j«i"ii3t|3di3ljJ||>3ii|3ii
-MW-16 {Up) —i?r—MW-21A (Uo)
Sand Aquifer
S
MW-7B(Qown) —O-MWSB(Up) — X- MW-lSA(Up) ••¦*¦• WW 17B (Up) I MW-21B (Up) MTCAB
Southern Gravel Aquifer
3.S
3
2-5
' 2
1.5
1
0.5
xi xj eyJxi &xi «3xi atsA aeis «5flxs Wxi qsji nfixi foxi ooxi eoxi wis OCX! ufiii isflxi Wxi Wxs
-------
Upper Gravel Aquifer
gpii wii mxi apja co_d qojo sp_q oaa 311.0 boxj oojd ma 311-0 ssjd bojo op-a on-G ap.Q dpi 4p_a apij 50_n ooia npx> oti-O opx: ap_c 3a<3gi3iii3'j
<£*i
OQ-l-fNr>Jrr,m25i;iuiOy5!vNai«!2'3iOO^^rvifH{ri",i*J5^in^gPvNCC«l2ffiQO''-'N'N-Tnr|'J"1iriinUD^NN»ffi£ri
tncntniTCniTXJlCriO'TiPffiCnCr.inPinffiCr.TlOOQOCOOOOOQOOOOOOOOOHrlr.rtrtrtririrlrtHrirtrtrtririnH
A lifljj tlfczs iloji ailjIi tiflxi tkioj qdjj ijdjj dajj tip.,ci 4ajL o3_u taa_o tk)_u ikijj iiB-sb ttoJi odxj tlfljj tin A 00.44 to^j dojj ilojj »¦" <¦'¦¦ 61)-Li uoja (kijj
r3«3v3«3q)3ai3«3«3(|i3«3«3«3i|/3«39i3i|i3w3ii3«3iv3i|l3i|i3ii3ti3g/3iv3i!/3v3ni3^
< 11 <11 <11 < 11
Notes Sfcw-detecftWi vslu.es are shewn as 1/2 the detection llmtl
MFC A e = Vied aI Tostlcs Central Act |Wi£ 173-340) Matheri 3 dmn up [aval.
Tetrachloroethene by Aquifer
Midway Landfill, Kent. Washington
K-11
-------
Upper Gravel Aquifer
i if S i- 8 S
z 2 z 2 z 2
-~—MW-SA (UGA-Up)
->^MW-27B »:»>.>>¦•»>•»>•»>.»»• V1*"** ¦*.
® If 3 :M- S M J8 :S c «p o * o a
2Sz|z5z52525z52
—O— MW-SB (Up) ' » MW-11A {Up)
• • *•• MW-17B (Up) —~— MW-18A (Up)
-O— MW-28 lUp) GWQS
- «~- MW-7B (Down)
—X- MW-15A (SA-Up)
—t— MW-21B (Up)
MTCA Method 8 Cleanup Level
Southern Gravel Aquifer
r o 5" o 5 o o S" o 5" o «* S
Z5i=525z5z5z5z
-MW-14B {Down} MW-20B (Down)
¦ MW-29B (Down) —O-MW-30C (Down)
-MTCA Method B Cleanup Level
£v rM R r3
S" O O *3
5 z 5 * 5
—+— MW-23B (Down)
GWQS
Parametrix Figure 4
L1,4-Dioxane Results by Aquifer
Midway Landfill
Kent, Washington
K-12
-------
Exhibit J-3: Groundwater Monitoring Data from FYR Period-
Table A3-1. Minimum Functional Standard and Organic Parameters in Groundwater, M id way Landfill, Upper Gravel Aquifer, 2015-2019 Data Summary
im .'isini-'i
R 62
R-63
- "
R66
R-62
R-63
R-6&
i mp'tjnil
Urals
smxns
rfy2Qfg
5-3,'20^7 5lBCbi%
Cm2Q19
rf5/2015
SI3I2016
5/2/2017
s®wa
5/8/2019
Fh 'si F r irm ti fs
7.98
«.../a 6. y 1
8.74
6.94
6.90
371 315
649 3
296.0
«- 1,!' 1T
1 1
ti a
11.4
12 0
r y
ns
11.6
^ iirj»\ in in 111' u r
Chloride
780
p..-,
611
6.15
STS
^ *?,7
Sulfate
7
21 1
r.
30 7
29.2
3fc7
28,1
Chemical Cfcyien Oerrwu?
.
' ¦
... i . t <
0.60
0.51
0 52
f'h
!|
0 14
0116
0 0&2S
0081©
oos
• •• ••
. , ¦
*1. ivy
0.142
0.101
0.0943
C.0950
0.001
C.026
0.0274
0,0241
vn i Jiilsithiirp mm
MWtmm
«A
¦ ••
s iVk^I c '
i' n> 1 r ^
¦
,ii "in ^
MS't
.
L u r / . i"
tfU'L
• -
Ch!dittet?iani2
¦
T ncbrorofiwororriethane
Ut/l
180
187
1.58
' I t 1 f Mi 111, 1
Mi/l
•• :
iig/L
. ••
U-DidiloroetKen©
t 1. 1. P 1 1 IK i
- .
Carton Oftuiftce
l-tg/L
'
t ra r,$ • 1,2-D»cblo roelhe re
pj/'L
• •
Vinyl Acetate
- ••
1,1-Diiiiloroefhsne
uu/i
2«8us«ror.e
•• •
. .
i 'Li,t! i U <
• .. :
1 12
> 1 >i ii
Hfi/L
¦
- •
~ , 1 1 r -- i ii
ug/l
. •
> 1 E j H M 1 I in
: :
1 H ...V|jte
Ug/L
• " • :
TncNoroethene
1 ! 1 II -
•
Pi, i . afl3 i
(jg/L
.. -
i< .i. t! 1 ir 'i i
\igfl
4-M«hvl-2-Pent»rone (M:BK
•
.1. - ' m M 1 M' 1- '¦*
MS/L
. -
- n. i
' •
t "in itAf f f f r
Mg/l
. :
_ l"> H
M|/t
.. ~. " '
' i M i r.
••
i" i U .^ufi
•; :
1 1 > ¦ I 1 1 t , r.
Chterabenzene
\itfl
¦
MU ,l Zi. >
.
n i 1 Ii n
• .
Gyrene
MI/'L
Bramoforrr.
• '
1 T'tf- i t t'-h i
¦ ^ I
9 Groundwater monitoring data tables are from the Remedial Action Status Report 2015-2019.
K-13
-------
Table A3-2. Minimum Functional Standard and Organrc Parameters in Groundwater faraway Landfill, Sand Aquifer, 2016-2019 Data Summary
VI,'
u«i
MV-'i^lPOWN)
R-63
R~ ¦*<
R-CC"
R-«;r
H'U?
R-S4
R-65
R-S6
*«*
R-S3
«"«. : R-i5
R-se
Dupiic
Ccr«j«oHni Urit*
b'hKUib
V4?2tPSr
,*
fi'Mf-l'J
*f4*Jcu h'4;.',n.j
ti4/VU* *
*w:oi9
5/7/2015
smmm
5(4/2017
5/7/2018
5*6/2019
Fwn ni T« H
1'!' ' i-l
8 ?3
0 68 8 /6
6iw
a. so
i,
8.64
HM
6 70
8®
6 66
Corduct-vity (J mhos/cm
528
S06
492
48S.8
478.6
¦J f / 2 3
347
363
39-
406 3
390 2
Temperatare C
12.9 13 5
¦¦j •. /i
12.2
171
12.3
12 3
Oiwo « -sn -« »-> tt^'nciOTs
1 ii. i ^ mp/L
12 ?
11.8 11.6
14.9
13 1
®:s
;¦¦¦; .•) 1
9.22
5.8
5.3
5.7B
5 99
5,96
* - . '1
33 4
2B7 27 3
27 D
39 8
29.4
»7
24.9
24?
2e.§
I 1 ».| 1 > 1 1 -u
IBS 221
. •••
. . •-
T. r_ > »i/L
0.98
1.02
0 9?/
0.80
4.1C 1.0® ZfW
1.26 [ > .:
0.79
0.75
0 86
0.60
LA m,c'o*:: Met , , ?NB. pg/._
' •:'
'
•: '¦
¦
)
- •'
«.
•
¦
Wft.
: •
M't
-
m>'-
:
UjJfL
' ^
li>. <<-•.. (19ft.
Ml
" '
' •' "
Mil
. • ' .
|jg)t.
• .
.
MB'-
it , ' ' ran.
t 0/2
K-14
-------
Table A3-2. Minimum Functional Standard and Organic Parameters Hi Groundwater, Midway Landfill, Sand Aquifer, 2016-2019 Data Summary
uompou'ia Units
BfUP]
MW-218 (UP)
R-62
R"63
R-64
R-«5 • R-66
R-62
R-63
R-64
R-65
R-68
5/3/2016
5/2/2017
*SK20' 5#8'2019
5/5/2015
5/3/201S
5/2/2017
VS/2018
5/8/2G19
Fvldf
ph i.i
G7t
e.ss
a&e
70» 7 OD
e 93
Si)S 7 02
I 20
i:;
- i •1 'i ymhosfcm
'328
348
345
745.e 342.4
604
589 S71
1206
566. S
C
121
124
11.9
12 2 ' 12.0
113
r ,
!1 a
it :¦:>
ccmvc'rr ; ivl K^nrttrs
hit mo'L
1.Q8
113
121
1-0.7 11.3
12.3
11 3
1 ¦:.
984
10 i
ti'Bi: m$\.
319
52 2
23 3
23 2 - 20.8
nz
mn
02 4
S2 9
$3.3
tmiL
¦ - =
Total Organ-c Ca/foon mc/L
1.01
101
0.97 ' 1,03
1.10
¦¦¦
1.09
i.i:
DsscUee f'let.ls
¦
m&il
0.04S
0 044
0CW25
0.0315 ' 003-30
0.372
0.342 0 346
0.541
0.345
i vol mie O'j mmcc-
MifL
1 5
1 0
15
0.9 - 0,7
2.8
-
i 0
¦^ni i!j>« Oi Mri t s
Mg<<~
-
1 , 1 1 r 1 - M(L
011
0.0373 :
0.031
0.0298
Wli1,.
wt
¦ '
USft.
19
¦¦; n
1 52
P0fL
pg^l
1 4
1.4
1 10
103 ' 119
25
si
3.04
2 85
f » ' ,!e n Hm ms-L
yg'-
M0'-
1. *¦ -DicNoroethane pgt
20
1©
131
12.9 14.8
2.G
2.4
2 30
2.06
2.39
hi I i.i-
cis-i .2-Owhs-oroethwt® yqn.
2 S
2.5
2SD
2,38 ' 2.58
pg.'L
1,1 1-i'fidl-itofa^an©
1 /
1 £
i >.y.
1 0B
pgM.
1 h I Mlh,
2 S
2.6
211
2.10 ' 2.14
&***» m.
' •
W-
4.6
ie:
5 68
'i:::¦
t jinl t hi t-iU . >
pgi'l
U I Ml ' - 1 i -11- II" ,)
n'~
T io,
1' ¦ i'. P |. »«,
PUB.
2 i ncWoroethaiw pg-L
¦
1 eUachtoroethetie
1 is
ID
1 1
1 1H
1i@/~
L M 1 1 ^g/l.
M9^
M9'-
MS^
W'-
Iig.li.
1 , ¦¦ 2,2 -T et ?®chto* wslftane (jigft,.
^ t n H Il'-i-" jr,«- 2 of 2 S5
Rametfe Acliors Stall, s Report
K-15
-------
Table *3-3. Minimum Funcllonal Standard and Organic Paratmetere, In Sfounclwaler, Midway Landfill, Southern Qrasel AquWw, 2015-201» Data Summary
«*-U8;basW)
-»¦«
-------
I'urnjjojm?
f icfd Pjr.smeti'f-
Temperalure
„or*crttioml in ^
Cfoforisfe
Sulfas®
Total Organic Carbon
Manganese
Saqi Vu.Afk- Orsj.in e-.
1.4-D»o*ane
Vo jt '<< Orcj.Tmcs-
Tfvctfiarofijcromei
1,1,2-TficWorc-l,:
wi.u-r
1.1-D»chtoroeth«i=
Methylene Of-tone
rl>- ' >1= * r-
tmns-1,2-Dichteo
rfinv
Drchloroethane
1,2-Diciioroether>'
Carbon Tefr&c-bloi
l,2-D«c*ilorcethan
Benzene
T ftchiora^thene
>-Di
4-hm\f^2-PmunQm {MB
ds-l^ichto-opnapene
Difcwomochloi
Chtoroberze
Table A3-3, Minimum Functlonal Standard and Organic Parameters In groundwater) Midway Landfill, Southern ®ra»el Aqu»w, 201S-TO18 Otto Summary
-mwm
___
Duplicate
CMW-35) !
~T5l 1 1 . ¦ ¦
35)
~R^r
•w
5/7/15 I 5/5/2016 I 5/4/2017 5W2017 J 3TH2G18 ! 5/6/2019
" R-62
&ALHni> Wt*>
21 ©
22.4
Tif
12 S
C.S81
~r^t
uupm.
fMW-31)
5/1/2017
¦ R-65
"W
Du plicate
fMW-31)
mm'is
S7?
608 6
' V, '
13.S
lid'.
Ren
2 of 3
$S3" ?
>: it, "i
K-17
-------
Table A3-3. Minimum Function.?! SuiiHanJ and Oripmc Parameters u> Groundwater Midway Landfill, Southern Gmv«?I Aquifer, 2015*2018 Oati Summary
C-impGord
H'li< P~l T»v f i
ration: on.t1 P tnmpter^
b-t ii vu dti1> Of (.t
1,4-Diovane
Volatile Organlcs
f- f i - .rtttiane
jdfcWoK^nemaiw
5?oethyf vinyl ethe
D»bri:irt«c:h?Q:'
Cfiterebenzsi
Ethyihenz&M
i I' «¦ >
Bromc'orn
1,1,2,2-Tet
__
naf
R-l
Dupfenfe | duplicate
(MW-31J 1 M
?i '•?.Wi:nii mtmn saamr i aroma -r :i ,,ji
I i i f.TH
II , :v
-------
Table A3-4. Minimum Functional Standard and Organic Parameters in Groundwater, Midway Landfill, Field and Trip Blanks, 2015-2019 Data Summary
romf Kl
Units
®5=
trip StanSts
R.S2
R-63
nm
' R-85 nm
Rjte
R-63
R-64
R-65
R-66
S«®1S
5*5/2016
5/3/2017
6/8/2018 5/7/2019
5/4/2015
5/5/2015
s#Mids?i20i3
5/2/2016
aimis
5/4/2016 5/5/2016
5/1/2017
r
512/201?; mm-n 5/4/2017
51712018
5/8/2018 5/9/2018
5/6/2019 5/7/2019
5/8/2019
Mmii«s,<"em
? enperature
c;
Cor 'smior^i ^rjm&Ws
ng/L
Sulfate
ng/L
Chsmtcs! Oxygen Deman-s
mg/L
'• . ••
Total Organic Carbon
ngf't
1 15
:
Dissolved Metais
i
ng/L
'
Manganese
ng/l
o CO?
' .=
Sy Hi volri'iiy Cr.winis'-v
1 (5. J"
11 M.'i
.. : .
»j-1! f C>'ii ' H« s.
ChkromeHNan©
M #L
• - !
Vinyl Chfcnde
Mil/1
•• " !
Srowcsnielbarie
MIJll
Chic'oetftare
M»'t
• . =
i I "1 S '
|J0!1
;
1. l.2-7ricWoro-1.2:2-fciRuatccffcjru
Ml
• 5
Acetone
MB/l
• =.
l.t-Dteh^oethene
MS*
.' J
< 1 !> n , 1.
tiSlL
79
i
Carbon Disuffide
PtIt
: *
¦
trana-l .2-Dichtoroetherw
MS*.
j
Vinyl Acetate
Mgil
=
: =: •.
: "1 .
1,1-DichiOfoethaie
ug/L
• =
¦
!
2-3ul3Rone
p glt-
;•
cis-t,2*Djchtoroe?hefle
Mg/L
• ' .=
• • • .
Chiccform
Ui»t
' =
¦
I.VUrichioroethane
• •
Carbon Tetrachloride
MB'l
§
'
.•/ ¦
1,2Mi>o«orthame
M3«-
. J
V • -•
Benzene
MB>t
¦ ' :
THCtvometbeie
MSl/i
' ' :
1,2»Dich;0-ropnopane
MSlI
!
•
¦
Bromodichforometrane
M#.
2-Chloroplhyl vinyl ether
PSd
• ¦ =
¦ ¦- '
• = ;. = ¦
4-fc*eihyl-2- Pwtarow (MiBKj
M9t
'
•
ct»-t>Dwhtofopfopent
|J»fi
i
trws-1 5-Dichbmprr.pp^
m'l
=
2~*temwm
Mi*
l,t,2-TricWeraethan®
MB*.
'
T«tiacMofcetfH?re
CfycmochSoromethafliS
" • • '
Chicioben^t'fie
MS*
Bhyfceraew
Mgil
*
rn.p-Xylem?
mti
*
: =;•.= .•
o-Xyten*
m-
Styren©
wa'L
¦
• .
Bromcform
IMgil
1,1,2,2-Tetrae-hlofoethsne
MS .1
..- .-
K-19
-------
Table A-3 Notes:
UP or DOWN in column title denotes whether the well is located upgradient or down gradient of the landfills influence,
U = Indicated the compound was undetected at the reported concentration
J = Indicated the compound was detected at an estimated concentration
M = Estimated value for an analyte detected and confirmed by an analyst but with low spectral match parameters.
This flag is used only for GC-MS analyses
Q = Indicates a detected analyte with an initial or continuing calibration that does riot meet established acceptance
criteria (<20%RSD, <20%Drtft or minimum RRF)
- - = Not analyzed
R-62 = Round 62, May 2015
R-63 = Round 63, May 2016
R-64 = Round 84, May 2017
K-65 = Round 65, May 2018
R-66 = Round 66, May 2019
K-20
-------
APPENDIX K - GROUNDWATER ANNUAL NOTICE
City of Seattle
Seattle Public Utilities
TRANSMITTAL
June 2, 2020
TO: Mark Adams, Washington State Department of Ecology
Yolanda Pon, Public Health Seattle King County
Highline Water District
Lakehaven Utility District
Active Well Drillers in King County (Washington State Department of Ecology list)
Owner of Well 37
Re: Midway Landfill Annual Groundwater Conditions Report
Informational - No Action Required
Enclosed is the annual notice of groundwater conditions in affected areas downgradient of
the Midway Landfill for 2019. This is being sent to you pursuant to the requirements in the
Midway Landfill Record of Decision (ROD) between the City of Seattle and the United States
Environmental Protection Agency, and in compliance with a Consent Decree between the
City of Seattle and the Washington State Department of Ecology (Ecology).
The City of Seattle is required to annually notify the Seattle-King County Department of
Public Health, Ecology, the local water districts, and locally active well drillers of
groundwater conditions in the affected areas downgradient of the Midway Landfill. You are
hereby notified that no water supply wells are to be constructed or used in the areas of
known groundwater contamination listed in Table 1 and shown on Figure 2.
If you have any questions or require additional information, please contact me at
ieff.neuner@seattle.gov or at 206-684-7693.
Sincerely,
Jeff Neuner
Midway Landfill Manager
Enclosure
Mami Hara, General Manager/CEO
Seattle Public Utilities
PO Box 34018
Seattle, WA 98124-4018
h tta:/Vwww.seattle.aov/util
Tel (206) 684-5851
Fax (206) 684-4631
TDD (206) 233-7241
L-l
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City of Seattle
Seattle Public Utilities
2019 ANNUAL NOTICE OF GROUNDWATER CONDITIONS IN
AFFECTED AREAS DOWNGRADIENT OF THE MIDWAY LANDFILL1
For Informational Purposes Only—No Action Required
The City of Seattle is the owner and previous operator of the Midway Landfill, located north
of South 252nd Street between SR-99 and 1-5 in Kent, Washington (Figure 1).
Extensive testing of groundwater within and surrounding the landfill area has indicated the
presence of various contaminants that do not meet federal drinking water standards
(Maximum Contaminant Levels [MCLs]) or state groundwater standards (Model Toxic
Control Act [MTCA; WAC173-340] Method B cleanup levels].
Cleanup levels for contaminants of concern (COCs) were established in a Record of
Decision (ROD) between the City of Seattle and the United States Environmental Protection
Agency.
A summary of the concentrations of COCs and additional parameters in groundwater with
concentrations greater than MCLs or MTCA B cleanup levels are presented in Table 1. The
locations of wells with concentrations of COCs above ROD cleanup levels are shown on
Figure 2.
In compliance with a Consent Decree between the City of Seattle and the Washington State
Department of Ecology (Ecology), and in accordance with the ROD, Ecology and all
appropriate local health districts, water districts, and certified well drillers are hereby
notified that no water supply wells are to be constructed or used in the areas of known
groundwater contamination as indicated on Table 1 and shown on Figure 2.
This is an annual notification.
1 The City will annually notify the Seattle-King County Department of Public Health, Ecology, the local water districts, and locally
active well drillers in writing of groundwater conditions in the affected areas down gradient of the landfill.
Mami Hara.SPU General Manager/CEO
Seattle Public Utilities Tel (206] 684-5851
700 5th Avenue, Suite 4900 Fax [206] 684-4631
PO Box 34018 TDD (206] 233-7241
Seattle, WA 98124-4018 ten://www.seattie.nnv/utri
L-2
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P*w«9
"HSFSq
S 2J4TH ST
-
r
t '
tlf~r ffill
.
Vjl1. ". 'til
TvsSr*
5 HT
: .
& *.:
Parametrix
ENGINEERING . PLANNING . ENVIRONMENTAL SCIENCES
A
City of Seattle, Seattle Public
Utilities Owned Parcel Boundary
That Includes Midway Landfill
250 500 750
Figure 1
Site Location Map
Midway Landfill
Kent, Washington
Feet
L-3
-------
Image Source PagleViewTechrologes.
ffi, MW-16
. «
-ID
-iM't
„ __ - ,^$p *3
MW-30C
F • JBC-
i *
9
ff; *-
- a.«
W Jut:
' ¦
Li
¦ ti'r % ? r.\
, r..^-r; s**^ .*'« 'Af| *. Vt^r
oiV-'
*• tWrtf *?P Vs j_
Figure 2
Comparison of Contaminants of
Concern to ROD Cleanup
Levels, May 2019
Midway Landfill
Kent, Washington
Manganese
® Exceeds CUL (2.2 mg/L)
(J) Does Not Exceed CUL
Vinyl Chloride
® Exceeds CUL (0.29 ug/L)
® Does Not Exceed CUL
1,2-Dichloroethane
0 Exceeds CUL (5 ug/L)
0 Does Not Exceed CUL
A
N
350 700 1.050
Feet
Parametrix
ENGINEERING . PLANNING. ENV! SON MENTAL SO ENCES
L-4
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Table 1, Groundwater Concentrations of Contaminants of Concern and Additional Parameters Not Included in the ROD, Midway landfill, May 2019
Upper Gravel Aquifer
Sand Aquifer
Southern Gravel Aquifer
MW-16
UP
MW-21A
UP
MW-7B
DOWN
MW-8B
UP
MW-15A
DOWN
MW-17B
UP
MW-21B
UP
MW-14B
DOWN
MW-20B
DOWN
MW-23B
DOWN
MW-29B
DOWN
MW-30C
DOWN
Compound
Units
Comparison Standards
5/7/2019
5/8/2019
5/7/2019
5/7/2019
5/6/2019
5/8/2019
5/8/2019
5/7/2019
5/8/2019
5/6/2019
5/6/2019
5/6/2019
Contaminants of Concern
ROD Cleanup Level3
Manganese
Vinyl Chloride
1,2-Dichloroethane
lit
2,2
0.29b
5
0,0950
J. 32
0.275
0,0330
2,14
0.345
0,884
1.61
0.109
O0A n
1.81
0.S12
0.337
3,92
0.669
1.03
Parameters Not Included In the ROD c
MCLd MTCA Be
Dissolved Metals
iron
mg/L
0,3**
0.0816
1.76
0.0677
/>
4,27
os'ltg/
Semi-Volatile Organics
1,4-Dioxane
Hg/L
0.44
13
0.7
15
10.3
12,9
1.8
8.8
4,8
Volatile Organics
1,1-Dichloroethane
Trichloroethene
Tetrachloroethene
Hg/L
Hg/L
Hg/L
7.7
5* 4
5* 5
1,35
¦
2.39
,LA'; U
i.06 u
J CO u
.t 00g;
:.00 is
AO,- U
:
Notes:
ROD - Record of Decision
UP or DOWN in column title denotes whether the well is located upgradientor downgradient of the landfill's influence.
3 = CltMNu > KhedufipFiw CPA POD M dway L-mdfi <•> !p StMlPrrih 6 2000,
= The icvisnd c u lup lovel for v ny cnlo dt. c 0 29 ng/L ymglnc MTCA adiUstcd canccii i ,<.ofr le~5.
- n i > in idf-.riramf-lf s I i it h-wt- to ur n1i jlmn<- g eakr fh n MCL o MTCABieiii, e^e
= MCL/Federal maximum contaminant levei.
= MTCA B/Modei Toxics Control Act (WAC 173-340) Method B Cleanup Level. CLARC II Database, Ecology.
- Cn^eds cleanup level established in the Final EPA ROD for the Midway Landfill Site, September 6, 2000 for COCsor exceeds Federal MCLor MTCA Method B Groundwater Cleanup Level for
paramete s net ncuded nticFft i u1 irds, EPA H if r ia| Primary Drinking Water Regulations {40 CFR 141 59 FR 34322).
2019 Annual Notice of Groundwater Conditions in
Affected Areas Downgradient of the Midway Landfill
May 2020 | 553 1550-063 01.02
L-5
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