FOURTH FIVE-YEAR REVIEW REPORT FOR
MONSANTO CHEMICAL CO. (SODA SPRINGS PHOSPHOROUS PLANT)
SUPERFUND SITE
CARIBOU COUNTY, IDAHO
STA.
Prepared by:
cli 2m-
Boise, Idaho
Prepared for:
U.S. Environmental Protection Agency
Region 10
Seattle, Washington
^ (1 ^ 2-0 [g
Sheryl Bftorey, Director Date
Office of Environmental Cleanup
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TABLE OF CONTENTS
LIST 01 ABBREVIATIONS & ACRONYMS 3
I. INTRODUCTION 4
Site Background 4
FIVE-YEAR REVIEW SUMMARY FORM 5
II. RESPONSE ACTION SUMMARY 6
Basis for Taking Action 6
Response Actions 6
Remedial Action Objectives 7
Remedy Components 7
Status of Implementation 9
III. PROGRESS SINCE THE LAST REVIEW 10
IV. FIVE-YEAR REVIEW PROCESS 13
Community Notification, Involvement & Site Interviews 13
Data Review 13
Groundwater Quality 13
Surface Water Quality 19
Sediments in Soda Creek and Alexander Reservoir 20
Offsite Soils 21
Site Inspection 22
V. TECHNICAL ASSESSMENT 23
QUESTION A: Is the remedy functioning as intended by the decision documents? 23
Question A Summary: 23
QUESTION B: Are the exposure assumptions, toxicity data, cleanup levels, and remedial action
objectives (RAOs) used at the time of the remedy selection still valid? 24
Question B Summary: 24
Changes in Applicable or Relevant and Appropriate Requirements (ARARs) and To Be
Considered (TBCs) Criteria 24
New Contaminants or Contaminant Sources 24
Changes in Toxicity and Other Contaminant Characteristics 24
Changes in Risk Assessment Methods 24
Changes in Exposure Pathways and Land Use 24
Changes in Remedial Action Objectives 24
QUESTION C: Has any other information come to light that could call into question the
protectiveness of the remedy? 24
VI. ISSUES/RECOMMENDATIONS 25
VII. PROTECTIVENESS STATEMENT 27
VIII. NEXT REVIEW 27
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TABLE OF CONTENTS (CONTINUED)
List of Tables
1 Concentrations of COCs and Remedial Goals for Groundwater and Soil 7
2 Summary of Planned and/or Implemented ICs 9
3 Protectiveness Determinations/Statement from the 2013 FYR 10
4 Status of Recommendations from the Third FYR 11
5 Short-term Constituent Concentration Trend at Point-of-Compliance Wells and Soda Creek 16
6 Short-term Constituent Concentration Trends at Other Wells and Springs 17
List of Figures
1 Monsanto Plant Vicinity Map
2 Monitoring Well Locations, Springs, Groundwater Elevation and Flow Direction in the Upper
Basalt Zone (June, 2017)
3 Soda Creek and Springs Sample Locations
4 Cadmium Concentrations in the Upper Basalt Zone (June 2017)
5 Fluoride Concentrations in the Upper Basalt Zone (June 2017)
6 Manganese Concentrations in the Upper Basalt Zone (June 2017)
7 Nitrate Concentrations in the Upper Basalt Zone (June 2017)
8 Selenium Concentrations in the Upper Basalt Zone (June 2017)
9 Cadmium and Selenium in Production Wells (UBZ-4)
10 Cadmium, Selenium, and Manganese in Northwest Pond Wells (UBZ-4 Source Area)
11 Selenium and Cadmium Trends in Old Underflow Solids Pond Area Wells (UBZ-2 Source Area)
TW-22 -24, -37
12 Selenium and Cadmium Trends in South Fenceline and Southwest Corner POC Wells (UBZ-1
and 2 Downgradient) TW-10, -20, -39
13 Selenium Trends in UBZ-2 Wells at South Property Line (UBZ-1 and 2 Downgradient)
14 Selenium Concentrations in Springs and Surface Water (Distribution)
15 Selenium Trends in Mormon A, B, and C Springs and Mormon Creek
16 Locations of the Sediment Sample Reaches in Soda Creek
17 Arsenic Concentrations in Soda Creek Sediment
18 Beryllium Concentrations in Soda Creek Sediment
19 Cadmium Concentrations in Soda Creek Sediment
20 Copper Concentrations in Soda Creek Sediment
21 Nickel Concentrations in Soda Creek Sediment
22 Polonium-210 Concentrations in Soda Creek Sediment
23 Selenium Concentrations in Soda Creek Sediment
24 Silver Concentrations in Soda Creek Sediment
25 Vanadium Concentrations in Soda Creek Sediment
26 Soil Sampling Parcels and Radium-226 Concentrations
Appendixes
A References
B Public Notice
C Site Inspection Checklist
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LIST OF ABBREVIATIONS & ACRONYMS
l-ig/L
microgram per Liter
ARAR
Applicable or Relevant and Appropriate Requirement
CERCLA
Comprehensive Environmental Response, Compensation, and Liability Act
CFR
Code of Federal Regulations
cfs
cubic feet per second
CH2M
CH2M HILL, Inc.
City
City of Soda Springs
coc
contaminant of concern
CSM
Conceptual Site Model
DEQ
Idaho Department of Environmental Quality
EPA
U.S. Environmental Protection Agency
ESD
Explanation of Significant Differences
FYR
Five-Year Review
Golder
Golder Associates, Inc.
IC
Institutional Control
IDAPA
Idaho Administrative Code
ISM
Incremental Sampling Methodology
KMCC
Kerr-McGee Chemical Corporation
LBZ
Lower Basalt Zone
MCL
maximum contaminant level
mg/L
milligrams per liter
MNA
Monitored Natural Attenuation
NCP
National Contingency Plan
NPL
National Priorities List
O&M
operation and maintenance
POC
point of compliance
PRP
potentially responsible parties
RAO
Remedial Action Objectives
RG
remedial goals
RI/FS
Remedial Investigation/Feasibility Study
ROD
Record of Decision
SOP
standard operating procedure
SRI
Supplemental Remedial Investigation Report
UBZ
Upper Basalt Zone
UFS
underflow solids
WQS
water quality standards
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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) prepared this FYR pursuant to the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) Section 121 (42 U.S.C § 9621), consistent
with the National Contingency Plan (NCP) (40 Code of Federal Regulations [CFR] Section 300.430(f)(4)(ii)) and
considering EPA policy.
This statutory review is the fourth FYR for the Monsanto Chemical Corporation Superfund Site (Site), and its
completion was triggered by the completion date of the previous FYR in 2013. FYRs are required for this Site
because hazardous substances, pollutants, or contaminants remain at the Site above levels that allow for unlimited
use and unrestricted exposure. The Idaho Department of Environmental Quality (DEQ) is a support agency for
this Site and was involved in the development of this report. CH2M HILL, Inc. (CH2M) provided support to EPA
in the data analysis and overall evaluation of the remedy for this FYR.
This FYR was led by Kathryn Cerise at EPA Region 10, with assistance from the CH2M technical team including
Greg Warren/Geologist, Jeff Schut/Risk Assessor, Allan Erickson/Hydrogeologist, and Margaret O'Hare/
Senior Technical Consultant. Monsanto was notified of the initiation of the FYR, which began in May 2018.
Site Background
The Site is located in Caribou County, Idaho, approximately 1 mile north of the City of Soda Springs (City)
(Figure 1) (all figures are included at the end of this report). Soda Springs has a population of 3,058 (U.S. Census
Bureau, 2010). Land use within the phosphorous plant boundary is industrial. The adjacent land to the north, west,
and south of the phosphorous plant is primarily agricultural, including cultivation and pasture. East and southeast
of the plant along Hwy 34 is a light and heavy industrial zone. Land use within the city limits is mostly residential
with some commercial, agriculture, and light industrial zones.
Monsanto purchased the property in 1952 to use local phosphate-rich ore to manufacture elemental phosphorus.
The Site comprises approximately 800 total acres that include the 540-acre operating area and an additional
approximate 260 acres of buffer area owned partly by Monsanto and partly by various farmers. The buffer area
contains contaminants of concern (COC) in offsite surface soils that originated from Site operations and is
therefore part of the Site (defined by the extent of contamination). The Site is subject to Institutional Controls (IC)
required by the 1997 Record of Decision (ROD) (USEPA, 1997) and 1998 Consent Decree. ICs are
nonengineered instruments (for example, administrative and legal controls) that help to minimize the potential for
human exposure to contamination and/or protect the integrity of a remedy. The industrial chemical manufacturing
facility originally owned by Kerr-McGee Chemical Corporation (KMCC) is directly east of the Site, across State
Route 34.
The Site is located at approximately 6,000 feet above mean sea level in elevation in a broad, relatively flat valley.
The valley is bordered by the Blackfoot Lava Field to the north, the Soda Hills on the west, and the Aspen Range
on the east. Surface drainage in the valley is predominantly to the south. The closest surface water body is Soda
Creek, located approximately 2,000 feet west of the facility. Soda Creek flows south and enters Alexander
Reservoir, south and west of the City. The major river in the vicinity is the Bear River, located approximately
2 miles south southwest of the Site. The Bear River also flows into Alexander Reservoir.
The regional groundwater flow is generally north to south, with a more westerly component under Soda Springs.
Natural springs are important hydrologic features of the basin, and emerge at several locations to the ground
surface as result of discharge from the underlying groundwater aquifer. Groundwater is the main source of
drinking water in the area, with Formation Spring and Ledger Spring complex serving as the sources of drinking
water for the City. The Monsanto Plant has constructed four production wells to supply process water to the plant.
Additionally, domestic water wells may be located in the Site vicinity.
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Groundwater is found within two primary hydrostratigraphic zones beneath the Site, known as the Upper Basalt
Zone (UBZ) and the Lower Basalt Zone (LBZ). Each of the two zones has been broken down into four
subsections based on natural hydrogeological controls such as fault boundaries, and also production well pumping
that alters groundwater flow, and groundwater quality (UBZ-1 through 4 and LBZ-1 through 4). Groundwater
contamination plumes are primarily within the UBZ. The UBZ-1 and UBZ-2 discharge to springs and surface
water south and southwest of the plant boundary (Figure 2).
The ROD concluded that no floodplain zones, endangered species, or historical or archeological sites are known
to exist in the immediate vicinity of the Site. The Canada lynx is the only species on the threatened list for
Caribou County (IDFG, 2018), although habitat at or surrounding the Site is not suitable to support lynx.
Monsanto has approximately 360 employees and approximately 100 contract employees working at the facility.
Land use within the fenced operating area was agricultural before the plant was built; land use was designated
industrial once the plant was built and is expected to remain industrial for the reasonably anticipated future.
FIVE-YEAR REVIEW SUMMARY FORM
SITE IDENTIFICATION
Site Name: Monsanto Chemical Co. (Soda Springs Plant)
EPA ID: IDD081830994
Region: 10
State: ID
City/County: Soda Springs/Caribou
NPL Status: Final
Multiple OUs?
No
Has the site achieved construction completion?
Yes
Lead agency: EPA
Author name: Kathryn Cerise
Author affiliation: EPA Region 10
Review period: 5/29/2018 - 8/19/2018
Date of site inspection: 6/6/2018
Type of review: Statutory
Review number: 4
Triggering action date: 9/10/2013
Due date (fiveyears after triggering action date): 9/10/2018
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II. RESPONSE ACTION SUMMARY
The following sections provide a summary of the response actions conducted at the Site.
Basis for Taking Action
The basis for taking action was the complaint from a landowner immediately south of the Site that livestock
drinking water from several nearby springs experienced problems related to excess fluoride exposure. In 1984,
Monsanto hired Golder Associates, Inc. (Golder) to characterize groundwater impacts from past and current
operations.
The pre-CERCLA investigation showed that groundwater under the Site contained elevated levels of fluoride,
cadmium, selenium, and sulfate in monitoring and production wells at the Site. As a result of potential human
health and environmental exposures from contaminated groundwater flowing south from the Site towards Soda
Springs, and also because of documented environmental and likely human exposures to excess fluoride from at
least one local well, EPA listed the Site on the National Priorities List (NPL) in 1990.
Pursuant to a March 19, 1991, Administrative Order on Consent issued by EPA, Monsanto completed a Remedial
Investigation/Feasibility Study (RI/FS) under EPA oversight between March 1991 and April 1996. The Remedial
Investigation included groundwater, soil, source materials, surface water, air, biota, and sediments.
The list of potential exposure concerns identified during the RI/FS included the following:
• Radionuclide (Radium-226) exposures from slag and source materials in the operating area, primarily to
Monsanto employees
• Potential residential exposures to metals (arsenic and beryllium) and radionuclides in groundwater, soil, and
air immediately outside the operating area if future residential development were not controlled, specifically
along the southern and northern Monsanto plant fence lines
• Potential exposures to other hazardous substances in soil inside the operating area to current and future
workers
The final ecological assessment concluded that ecological impacts were unlikely and that ecological risk-based
cleanup levels should not be used to set remediation goals, however, potential aquatic effects in Soda Creek
were noted.
Response Actions
Monsanto performed Site improvements and initial response actions to reduce the threats to groundwater prior to
EPA signing a ROD in 1997. These included the following (Golder, 2008):
• August 1985. Removal of the Old Hydroclarifier suspected of impacting groundwater and replacement with a
new unit.
• 1986. Replaced four underground fuel storage tanks with aboveground tanks equipped with concrete sumps.
• 1987. Abandoned four of the original monitoring wells (TW-3, 4, 5, and 6) that created hydraulic connection
between upper and lower aquifers.
• 1983 to 1988. Took the old Underflow Solids (UFS) Ponds out of service, removed contaminated soil,
backfilled, then filled with molten slag and sealed with a bentonite cap.
• 1988. Closed and excavated the Northwest Pond and sealed the bottom with bentonite. This area is permitted
by DEQ to receive plant sanitary solid waste.
• 1985 to 1989. Installed recovery wells around the Old Hydroclarifier and used these to intercept contaminated
groundwater. The groundwater was pumped into the New Hydroclarifier between 1985 and 1989. Pumping
ceased in the spring of 1989 and was never resumed.
• 1993. Connected plant sewage evaporation ponds to municipal wastewater system.
• 1995. Began pilot scale projects and engineering controls to reduce fugitive dust from on-site source piles.
• 2012. In response to recommendations made in the third FYR, Monsanto conducted a Phase I source area
characterization to identify if sources of COCs remained buried in ponds and could be affecting MNA
progress (Golder, 2013).
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EPA signed a ROD for the Site on April 30, 1997. The ROD identified the potential COCs for soil and sediment
as well as COCs for groundwater based on exceedances of EPA risk-screening criteria, and documented the
selected remedy for environmental media affected by operations at the plant (EPA, 1997). The remedy addressed
the multiple pathways of concern: groundwater, soils, and source piles, air, surface water, and sediments. The
ultimate goal is to eliminate groundwater contamination sources and restore, through natural attenuation (within 5
to 30 years), the groundwater aquifers affected by past releases from the Site.
Remedial Action Objectives
The remedial action objectives (RAO) for the Site as specified in the ROD (EPA, 1997) are as follows:
• Prevent human ingestion of, inhalation of, or direct contact with groundwater at levels exceeding the
maximum contaminant level (MCL) defined under the Safe Drinking Water Act for cadmium, fluoride,
nitrate, and selenium, or risk-based concentrations for manganese
• Prevent external exposure to radionuclides in soils at levels that pose cumulative estimated risks above
3 x 10-4, corresponding to a dose equivalent of approximately 15 millirems per year.
• Prevent the ingestion or inhalation of soils containing radionuclides at levels posing cumulative estimated
risks exceeding 3 x 10-4, or metals (arsenic, beryllium) at levels posing cumulative estimated carcinogenic
risks exceeding 1 x 10-5.
Remedy Components
The remedy selected in the ROD addressed six media at the Site: groundwater, offsite soils, source piles, air,
sediments, and surface water.
Groundwater
The selected remedy for groundwater is Monitored Natural Attenuation (MNA) with ICs to prevent use of
contaminated groundwater for drinking purposes, until such time as cadmium, fluoride, selenium, nitrate, and
manganese concentrations in groundwater decline to a level lower than the MCLs or risk-based concentrations for
those substances. Example ICs include legally enforceable prohibition on drinking water wells in the affected area
to prevent human exposure. In addition, it was believed that the old ponds suspected as source areas (UFS Pond
and Northwest Pond) had been closed and lined with impermeable material to eliminate ongoing COC sources
which would allow natural attenuation to occur.
Except for the annual monitoring of groundwater, springs and the discharge outfall, no further action was deemed
necessary because (at the time) there were no drinking water users of the affected groundwater and because the
combination of past remediation actions and natural attenuation was predicted to restore groundwater to levels
that would allow for unrestricted use within 30 years. The ROD states "if groundwater recovery appears to
significantly differ from model projections, the model and the need for additional groundwater remedial actions
should be re-evaluated."
The ROD established groundwater remedial goals (RG) for the COCs. These are the MCLs for cadmium,
fluoride, nitrate, and selenium, and a risk-based concentration for manganese. Table 1 provides a summary of the
groundwater COCs and RGs. The ROD also established points of compliance (POC) for groundwater RG
monitoring. The POCs generally downgradient and are highlighted in yellow on Figures 2 and 3.
Table 1. Concentrations of COCs and Remedial Goals for Groundwater and Soil
COC
Groundwater
RG (mg/L)
Regulatory Source
Highest Concentration from
RI/FS to Present (mg/L), Year,
Location3
June 2017 Highest
Concentration (mg/L)
(Percent Decrease)
Cadmium
Fluoride
Nitrate as
NOs/Nitrate as N
0.005
4
44/10
MCL
MCL
MCL
70.4, 1985, TW-40
16, 1997, TW-37
20.7, 2006, TW-20
2.67 (-96)
9.55 (-40)
19.9 (-4)
Selenium
0.05
MCL
0.935, 1993, TW-37
0.220 (-76)
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Highest Concentration from June 2017 Highest
Groundwater RI/FS to Present (mg/L), Year, Concentration (mg/L)
COC RG (mg/L) Regulatory Source Location3 (Percent Decrease)
Manganese 0.18 Risk-Based 3.17,2013, TW-17 3.08 (-3)
Concentration
Soil RG (pCi/g)
Radium-226 3.7 Risk-Based
Concentration
Note:
a Highest concentrations listed are based on 2017 Water Quality Report, Table 14 (Golder, 2018a)
mg/L = milligram per Liter
pCi/g = picoCuries per gram
Surface Water
The remedy for surface water is NFA, and no surface water RGs were established under the ROD. However, Soda
Creek was identified as a POC location because the plants effluent is discharged into Soda Creek.
Several sample locations have been established to monitor and evaluate discharges of groundwater to surface
water, and effects of discharges on surface water quality.
When the ROD was finalized in 1997, there was no aquatic surface water quality standard for selenium in effect.
In 2003, the State of Idaho established an aquatic chronic standard for selenium of 0.005 mg/L. (IDAPA
58.01.02.210).
Source Piles
The selected remedy for source piles (on-plant solid waste piles that consist of underflow solids and tailings) and
materials within the plant is No Further Action, because Monsanto's past cleanup actions, institutional and
engineering controls (fugitive dust emissions) have reduced potential sources of worker exposure and contaminant
migration to surrounding soils to acceptable levels. However, the source piles are comprised of fine-grained soil-
like particles that have migrated off-site via wind transport and impacted surrounding soils, e.g. the "offsite soils".
Therefore, the offsite soils have ICs and are required to be sampled every five years (see following section).
Offsite Soils
The solid waste on-site piles have in the past been sources of contaminant migration to off-Plant soils. The
remedy for offsite soils is Institutional Controls (IC) in the form of land use restrictions placed in deeds. ROD
specifies the offsite soil sampling be conducted at least every 5 years to determine the concentration of COCs for
that year, and to verify that engineering controls used for the source piles are effectively preventing spread of soils
from the source piles, and/or recontamination of offsite soils and that the remedy remains protective.
The Remedial Goal for offsite soils is 3.7 picocuries per gram for Radium-226 (Table 1). Upon receipt of results
from the FYR offsite soil sampling programs, a title search or equivalent will be conducted to verify that any
property parcels with soil concentration greater than the RG for offsite soils are under IC, if applicable. If such
properties are present that are not covered by existing ICs, then action will be taken to implement the selected soil
remedy for that property. The ROD states that the selected remedy for offsite soils containing Radium-226 above
the RG is an election of the affected property owners to have their property either (1) cleaned via excavation,
containment, and replacement of contaminated soils (none of the property owners elected this option), or
(2) rendered under an IC in the form of an environmental easement placed in their deed to prevent
residential uses.
Air
The ROD concluded that No Further Action (NFA) was necessary for air emissions under CERCLA.
Sediments
The ROD concluded that No Further Action (NFA) was necessary for sediments. However, the ROD specified
that sediments should be sampled in Soda Creek in support of each FYR to confirm whether COC concentrations
in the sediments are decreasing (as predicted), increasing, or remaining stable. Thus, sediment sampling in Soda
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Creek is required every 5 years. The ROD states: "If sediment concentrations are shown to be increasing or
evidence of health impacts are identified, the protectiveness of the remedy should be re-evaluated."
Status of Implementation
Remedial actions include groundwater, surface water, sediment, and off-site soil monitoring.
Groundwater and Surface Water Monitoring include:
• Execution of annual groundwater, springs, and Soda Creek surface water quality sampling to assess the extent
of contamination relative to applicable regulatory levels, remediation goals, and groundwater plume
boundaries with respect to RGs selected for the Site, RAOs, and groundwater MNA modeling projections.
• Assessment of contaminant trends in groundwater and surface water to determine if COC levels are declining
at an acceptable rate. As stated in the ROD, evaluate the need for additional groundwater modeling and
remedial actions "if actual groundwater recovery appears to significantly differ from model projections".
• Ensure ICs remain in place and are effective.
Sediment Sampling includes:
• Collection of sediment samples every 5 years using Incremental Sampling Methodology (ISM) to obtain
representative samples over a given reach of the creek to support each FYR assessment of whether sediment
contaminant concentrations are stable or declining as predicted.
Off-Site Soil Sampling includes:
• Because the fine-grained material in the on-site source piles are known to have migrated to offsite soils via
wind transport, soil sampling is conducted every five years on surrounding off-site soils to measure
concentrations of COCs in order to verify that source control [of the on-site source piles] is effectively
preventing the further spread of site contaminants. Monsanto continues to test engineering controls such as
plot-testing cover materials to replant the source piles.
• Confirming that ICs are in place for all soil grids surrounding the Site that contain Radium-226 concentrations
greater than the remediation goal of 3.7 picocuries per gram and 15 millirems per year for radionuclides,
based on a statistically valid sampling program. Evaluate need to implement additional ICs or removal actions
and identify possible recontamination of soils from on-site source piles or spread to additional areas through
ground disturbance and airborne dispersal.
Maintenance and Operation include:
• Verifying that facility operations continue to be in compliance with environmental and worker health and
safety requirements so that potential releases and exposures remain adequately controlled, and the remedy
remains effective. Evaluate COC concentrations in off-site soils to ensure that engineering controls on the
source piles (on-site soils) are preventing spread to offsite soils.
Table 2. Summary of Planned and/or Implemented ICs
Media, engineered controls,
and areas that do not support
Unlimited Use and
ICs called for
Title of IC Instrument
Unrestricted Exposure based
ICs
in Decision Impacted
Implemented and Date
on current conditions
Needed
Documents Parcels
IC Objectives
(or planned)
Soils
YES
YES ; Offsite Soils
Prevent Ingestion and
Environmental Protection
i surrounding
inhalation of
Easements and
i Monsanto
radionuclides
Declaration of Restrictive
Plant (see
Covenants; 1998,1999,
: Figure 26)
and 2002.
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Media, engineered controls,
and areas that do not support
Unlimited Use and
Unrestricted Exposure based
on current conditions
ICs
Needed
ICs called for
in Decision
Documents
Impacted
Parcels
IC Objectives
Title of IC Instrument
Implemented and Date
(or planned)
Groundwater
YES
YES
Domestic
Wells
potentially
located in
Soda Springs
Prevent ingestion and
use of contaminated
groundwater for
drinking purposes until
groundwater recovers
by enacting legally
enforceable prohibitions
on drinking water
Not implemented.
III. PROGRESS SINCE THE LAST REVIEW
This section includes the protectiveness determinations and statements from the last five-year review as well as
the recommendations from the last five-year review and the current status of those recommendations. The remedy
for the Site was identified as not protective during the third FYR (USEPA, 2013) conducted in 2013. That
protectiveness statement is as follows:
Table 3. Protectiveness Determinations/Statement from the 2013 FYR
OU#
Protectiveness Determination
Protectiveness Statement
Sitewide
Not Protective
The remedy for the Monsanto Site is currently not protective because
concentrations of COCs in groundwater remain above MCLs and RGs,
contaminated groundwater plumes above the MCLs and RGs extend beyond
the IC boundaries, the contamination in groundwater plumes has not been
fully characterized which poses risks to domestic wells downgradient of the
Monsanto Site, and monitoring trends indicate that the groundwater
performance standards will not be met in the foreseeable future.
Contaminated groundwater appears to be impacting surface water and
sediment in nearby creeks. In addition, sources on the Monsanto facility may
be contributing to groundwater contamination.
Table 4 includes the issues, recommendations, and status of recommendations from the third FYR. Table 4 lists
also additional work conducted to fill data gaps identified during annual review of submittals (EPA 2017), testing
aquifer properties, and selenium removal pilot testing.
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Table 4. Status of Recommendations from the Third FYR
Issue
Recommendations/
Follow-up Actions
Concentrations of COCs in
groundwater and surface water
remain above RGs/MCLs, exceed
RGs/MCLs beyond the Monsanto
property boundary, nature and
extent of groundwater plume(s)
of site-related COCs are not well
defined, and trends indicate that
groundwater RGs will not be met
in the 5- to 30-year time frame
anticipated in the ROD.
Define the full nature and extent of
groundwater contamination by
identified COCs by implementing a
supplemental focused Remedial
Investigation.
When that Remedial Investigation is
completed, execute a supplemental
focused Feasibility Study to evaluate the
current remedy and the need to add
additional remedial actions to achieve
RAOs. If necessary execute a ROD
amendment or ESD to achieve RAOs.
Continue monitoring groundwater and
surface water annually to observe
changes in COC concentrations.
Registered and possibly
unregistered domestic and
irrigation wells downgradient of
the Monsanto Site may be
exposed to the COCs that exceed
the RGs.
Investigate current usage of
registered/unregistered domestic wells
downgradient of the Monsanto Site and
the relationship to the fully defined
groundwater plume(s).
Develop an institutional control plan for
areas where groundwater COCs have
migrated beyond current southern
property boundary.
Current Status
Current Implementation Status Description
Completion
Date
(if applicable)
Ongoing
Completed
Focused Rl in progress. This has included, In Progress
through 2018:
Monsanto installed wells at southwest property
line in 2018 to define the full southwestern
extent of selenium plume.
Monsanto is presently (2017 to 2018) conducting
pumping tests and treatability pilot studies to
evaluate capture of plume near the plant
boundary and selenium removal from effluent.
This is anticipated to continue
Monsanto installed monitoring wells in 2018 to
evaluate groundwater COCs east of monitoring
wells and evaluate groundwater capture zone
and potential migration to UBZ-3.
Monsanto also installed wells on the east side of
Primary Fault to evaluate hydraulic boundary
conditions near groundwater pumping
capture zone.
Currently Monsanto is evaluating data for draft
Remedial Investigation report. Awaiting
submittal of data to EPA.
Completed April 2015 - Monsanto conducted an Well Survey
offsite well survey and located four domestic Completed
wells and one spring in a residential basement. i on April 31,
Sample results from these wells and spring 2015
indicated that concentrations of all constituents | (Monsanto,
of concern were below the respective Monsanto i 2015)
remediation goals.
No progress on IC plan.
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Issue
Recommendations/
Follow-up Actions
Current Status
Current Implementation Status Description
Completion
Date
(if applicable)
Potential sources of COCs to
groundwater remain in the old
UFS Ponds, UFS Piles, Northwest
Pond, and Old Hydroclarifier
Areas.
Conduct the next phase of the Source
Characterization to evaluate current
sources and update the conceptual site
model to evaluate if current remedies
are appropriate.
Complete
Monsanto investigated potential source areas by
installing wells, excavating test pits, and
conducting leaching and mobility analyses during
2013 through 2015. This investigation positively
identified remaining sources of COCs in the plant
boundaries with potential to release into
groundwater. Therefore, the updated CSM
indicates that the assumptions made in the
current remedy are not appropriate.
Source Area
Report
submitted in
2016
(Golder,
2016)
Concentrations of contaminants
in sediments in Soda Creek are
elevated downstream of facility
in the flow-diverted reaches.
Continued monitoring of sediments to
compare results against new sampling
protocol and determine if remedial
action may be needed.
Complete
Sediment sampling has been conducted every 5
years as part of the FYR. For this fourth FYR,
sampling was performed in July 2017. The 2017
sampling was the second event using ISM. In this
FYR report, results are compared against the
2012 sample results. The third ISM sample will
be conducted in 2022, after which trends in
concentrations may be observed.
Complete
(Golder
2018b)
12
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IV. FIVE-YEAR REVIEW PROCESS
Community Notification, Involvement & Site Interviews
EPA published a notice announcing the performance FYR for the Site in the Caribou County Sun on June 7,2018.
This announcement stated there was a five-year review underway, and invited the public to submit any comments
to the EPA project manager. As of the date of this report, no comments from the community had been received. A
copy of the public notice is included as Appendix B to this FYR report.
CH2M HILL interviewed the Monsanto O&M project manager as part of the FYR process. The interview was
conducted to identify Monsanto Site conditions and issues, successes or problems related to the remedy, and status
of O&M activities that has occurred since the third FYR.
The following individual was interviewed:
1. Jason Maughan, Regulatory Specialist, Monsanto Chemical Company, Soda Springs, Idaho.
Mr. Maughan is Monsanto's CERCLA/O&M Project Manager for the Soda Springs facility. He indicated
that EPA, its contractors, and also Monsanto's contractors have fulfilled their duties, and kept him
informed and supplied him with appropriate levels of information regarding Monsanto Site activities. He
also stated that the remedial actions coincide with the objectives of Monsanto - soil migration from on-site
source piles is being minimized through engineering controls and plot testing, off-site soil ICs are in place
and additional remedial actions have been identified that will move the overall project in compliance with
CERCLA requirements. Some small-scale Monsanto Site-related projects are being constructed unrelated
to CERCLA activities, but these will not impact the future Monsanto Site remedial activities. Monsanto is
conducting the additional Focused RI based on recommendations from last FYR, including constructing
additional wells, characterizing source areas, and conducting ongoing aquifer pump testing to evaluate
groundwater capture and water quality changes. Several supplemental RI activities have been completed,
and some are ongoing such as the pumping test/groundwater capture evaluation. These data will steer
decisions for a focused Feasibility Study.
Data Review
Groundwater, surface water, soils, and sediment data trends pertinent to this FYR period are discussed in the
following text. COCs for the Site include cadmium, fluoride, nitrate, manganese, and selenium. Other constituents
that are monitored in the groundwater include chloride, molybdenum, and sulfate.
Table 1 lists the ROD RGs for groundwater. No surface water RGs were established under the ROD. However, a
State of Idaho Cold Water Standard for selenium was established in 2003 by reference to the National Toxics Rule.
Figures 2 and 3 show the locations of groundwater monitoring wells, groundwater flow directions, springs, and
surface water sampling locations. Discussions of individual COC trends in each medium are provided in the
following sections. Figures and tables, adapted from data reports prepared by Golder for Monsanto are included to
illustrate data trends.
Groundwater Quality
In accordance with the 1997 ROD (USEPA, 1997), "If groundwater recovery appears to significantly differ from
model(ed) projections, the model and the need for additional groundwater remedial actions should be
re-evaluated."
Overall, monitoring results show that groundwater concentrations of COCs have decreased at most monitoring
locations in the time since implementation of the source control actions performed by Monsanto in the mid-1980s
and 1990s. However, over the last decade in some wells the downward trends have stabilized at concentrations
above RGs, and, at other locations, concentrations of COCs have been increasing near and downgradient of source
areas during the last review period. COCs are thus not declining at rates predicted during the ROD preparation.
The selenium plume has expanded above RGs at the southern IC boundary.
Based on long-term monitoring, COC concentrations in the deeper LBZ aquifers are generally stable and below
RGs, which indicates that the deeper groundwater is currently not significantly impacted by source areas at the
Site. However, COC concentrations in the shallow UBZ aquifers exhibit exceedances of the RGs. Therefore, the
following discussion is limited to potential impacts to the UBZ aquifers based on data collected from monitoring
13
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wells located in UBZ-1, UBZ-2, UBZ-3, and UBZ-4. Data for COC concentrations and trends are available
through 2017.
Source Area Wells. COC Distribution
UBZ-1 and 2 Source Areas
The suspected primary source areas for the UBZ-1 and 2 groundwater plumes are the old UFS and Tailings Ponds,
on the west-northwest side of the plant (Figure 2). COCs in the near-source groundwater plumes include cadmium,
fluoride, manganese, nitrate, and selenium. The groundwater also contains elevated levels of non-COC monitored
analytes chloride, molybdenum, and sulfate that are monitored to evaluate water quality and used as indicator
constituents.
In general, the groundwater plumes in UBZ-1 and 2 travel southward. However, the downgradient extent of each
constituent varies as a result of varying mobilization and transport mechanisms (such as source intensity,
subsurface geochemical/retardation processes), and structural controls (such as faulting of the basalt flows).
UBZ-3 and 4 Source Areas
The suspected source areas for the UBZ-3 and 4 Plumes include the former Northwest Pond and the Old
Hydroclarifier (Figure 2). COCs in these plumes also include cadmium, fluoride, nitrate, manganese, and selenium.
Elevated levels of chloride, molybdenum, and sulfate have also been detected in these plumes.
Each COC exceeds its RG within at least some portions of UBZ-3 and 4. In general, groundwater plumes from the
Northwest Ponds and the Old Hydroclarifier would be expected to travel toward the south, consistent with the
general direction of groundwater flow at the Site. However, groundwater with elevated COCs within the UBZ-4
plume is largely captured by the plant production wells that supply industrial water for the plant. In addition, the
Primary fault separates UBZ-2 from UBZ-4 (Figure 2) and is interpreted to be a hydraulic barrier that prevents
migration of COCs from UBZ-4 to UBZ-2. It is uncertain how the plume might migrate if the production wells
were to be shut down for any length of time.
Because the UBZ-4 plume is generally contained by the plant production wells, no monitoring wells have been
constructed within the southern portion of UBZ-4, near the boundary with UBZ-3. However, in 2017, data gaps
were identified east of the production wells and in the southern part of UBZ-4 and northern part of UBZ-3 (EPA,
2017). At the request of the EPA, monitoring wells were installed to delineate plumes east and south of the
production wells.
Elevated concentrations of molybdenum and vanadium in groundwater have been identified along the east and
southeast sides of the plant. Elevated molybdenum has also been identified in springs within Soda Springs south of
the plant (Big Springs and City Park Spring, Figure 2). These areas of elevated molybdenum and vanadium in the
shallow groundwater and springs originate from source areas at the former Kerr-McGee plant on the east side of
Highway 34.
Source Area Well COC Distribution
The 2017 distributions of each of COC in groundwater (plume maps) are illustrated in Figures 4 through 8,
respectively. COCs including fluoride and manganese exceed RGs in plant area wells near the suspected source
areas (NW pond and UFS ponds) but generally do not extend beyond the south fenceline and are limited to the
plant area (Figures 5 and 6).
Nitrate as N is detected above the RG of 10 mg/L in the immediate vicinity of source areas including the old UFS
ponds and Old Hydroclarifier, and also southwest of the plant (Figure 7) Note that on Figure 7, elevated nitrate
concentrations in wells southeast of the Plant appear to originate from source area(s) outside the Plant based on
groundwater flow directions and the absence of any source areas in the UBZ-3 on the Plant (Golder, 2018a).
Elevated nitrate levels in wells TW-63 and TW-64 and Homestead Spring are attributed to agricultural fertilizer
applications in the area south of the plant and west of Government Dam Road (Golder, 2017a).
In the POC plant production wells PW-01, -02, and -03, cadmium is detected above the RG of 0.005 mg/L, with a
maximum concentration of 0.0669 at PW-01 (Figure 4 shows cadmium concentrations). Selenium increased to
above the RG of 0.05 mg/L in PW-01 at a concentration of 0.0992 mg/L (Figure 8 shows selenium concentrations).
In the Northwest Pond wells, cadmium is above the RG in TW-16 and 17 at concentrations of 0.484 mg/L and
0.0134 mg/L, respectively. Selenium is above the RG in these two wells at concentrations of 0.279 mg/L and
14
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0.206 mg/L, respectively. In Old Hydroclarifier wells TW-40 and 43, cadmium is above the RG at concentrations
of 2.16 and 1.73 mg/L. Selenium is above the RG in these two wells at concentrations of 0.897 and 0.727 mg/L,
respectively. In UFS Pond wells TW-22, 24 and 37, cadmium concentrations are above the RG in these three wells
at concentrations of 0.0391 mg/L, 0.352 mg/L, and 0.514 mg/L, respectively
Newer monitoring wells drilled near suspected source areas in 2014 (since the last FYR) include TW-70 through
TW-76. All of these wells exceed the RGs for cadmium except for TW-76. TW-71 is the highest in cadmium at a
concentration of 0.949 mg/L. Selenium is above the RG in these three wells at concentrations of 0.219 mg/L,
0.314 mg/L, and 0.220 mg/L, respectively. Selenium also exceeded the RG in all of the newer monitoring wells
(TW-70 through TW-76). TW-76 shows the highest selenium at a concentration of 0.64J mg/L (estimated value).
South Fenceline POC Wells COC Distribution
POC wells TW-20, 34, 35, and 39 are located along the plant's southern fenceline (Figure 2). All COCs except
manganese are above RGs in well TW-39. Selenium exceeds the RG in wells TW-20 and 39, with a maximum
concentration of 0.364 mg/L (Figure 8). TW-10 is not a POC well, but is located at the southwest corner of the
plant and exceeds the RG for selenium at a concentration of 0.089 mg/L.
South of Plant POC Wells COC Distribution
POC wells TW-53, 54, 55 and the Harris Well are located south of the south fenceline. These are largely free of
COCs above the RGs, except for selenium, which was detected in 2017 at concentrations above the RGs in all four
of these wells, with a maximum concentration of 0.179 mg/L at TW-54 (Figure 8).
Source Area and Point-of-Compliance Wells. COC Trends since the last FYR
The trends of COCs observed since the last FYR are discussed in this subsection, and are based on a visual
interpretation of time-concentration graphs and interpretations presented in the annual water quality report (Golder,
2018a). Table 5, excerpted from the Golder summary report on groundwater conditions (2018a), shows the short-
term (since the last FYR) constituent concentration trends at POC wells and surface water sites. Table 5 (Golder,
2018a) shows the short-term constituent concentrations at other wells and springs, generally grouped by location at
the Site. Figures 9 through 15 provide time-concentration history graphs of COCs that are of importance because
of exceedences of RGs, and either stable or increasing trends. These largely focus on cadmium and selenium. As
noted previously, fluoride, manganese, and nitrate appear to be largely stable and limited in extent to within the
plant area. Exceptions are noted below.
Source Area Well COC Trends:
Figure 9 shows the time concentration history of cadmium and selenium in POC plant production wells PW-01
and 02. It appears that these COC have been increasing in these two wells since 2015. Figure 10 shows the time-
concentration history of cadmium, selenium, and manganese in the Northwest Pond wells TW-16 and TW-17. The
selenium in TW-16 and 17 has been increasing since 2007; the most notable increased has occurred in TW-17,
which was non-detect for site COCs prior to 2007. Manganese has been increasing in TW-17 since the early 1990s.
Cadmium has been increasing in TW-17 since a low level in approximately 2010. In the Old Hydroclarifier wells
TW-40 and 43, cadmium and selenium concentrations exhibit stable trends.
Figure 11 shows the time concentration history of selenium and cadmium in the old UFS and Tailings Pond source
area wells (TW-22, TW-24, and TW-37). The selenium concentrations have been increasing in TW-22 and 24
since low levels in 2007, and stable in TW-37. Concentrations in these wells are all above the RGs. Cadmium is
decreasing in TW- 37 since a high in 2011, but remains well above RGs. In new wells near the old UFS ponds
TW-70 through 76), selenium is increasing in TW-71 and 76, but decreasing in wells TW-72, and 73. Cadmium
concentrations are increasing in TW-71, 75, decreasing in wells TW-72 and 73.
South Fenceline and South of Plant Wells COC Trends
POC wells TW-20, 34, 35, and 39 exhibit generally stable trends for COCs, with some fluctuations over the years
(Figure 12). However, cadmium has shown a steady increase since approximately 2007 in TW-39 (Figure 12).
Selenium levels declined in TW-20 and 39 over the past 5 years but are above the RGs. Nitrate appears to be
increasing in TW-20 and 39 after a low concentration in 2015. As Table 5 illustrates, POC wells TW-53, 54, and
the Harris Well show primarily stable or decreasing COC trends since about 2015, with the exception of a slight
increase of selenium in TW-55 to above the RG. Nitrate concentrations have decreased in TW-53, but exhibited a
sharp increase in TW-54.
15
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Table 5. Short-term Constituent Concentration Trend at Point-of-Compliance Wells and Soda Creek
Constituents of Concern
Location
Formation
Cadmium
Fluoride
Manganese
Nitrate as N
Selenium
Groundwater
Production Wells
PW-01
UBZ.LBZ-4
U- N
4 Y
o Y
Y
ft N
PW-02
UBZ.LB2-4
« N
4 Y
O Y
H- Y
» Y
PW-03
UBZ.LBZ-4
« N
o Y
O Y
ft Y
1> Y
Southern Plant Fence Line
TW-20
UBZ-2 y4
<» Y
Y
O Y
t N
O N
TW-34
UBZ-2 y3
O Y
Y
<» Y*
O Y
Y
TW-35b
UBZ-2 y3
<» Y
<» Y
Y*
« Y
<» Y
TW-39
UBZ-2 y4
N
O N
O Y
ft N
O N
South of Plant (Former Harris Propert
/)
TW-53
UBZ-1 y5
<» Y
Or Y
O Y
¦a y
4 N
TW-54
UBZ-2 y4
O Y
<» Y
O- Y
t N
4- N
TW-55
UBZ-2 y3
<» Y
Y
O Y
1} Y
ft N
Mormon A Springc
UBZ-1 y5?
O Y
O Y
O Y
t N
-0 N
Harris Well
UBZ-2 y4
Y
4 Y
O Y
<» Y
¦0- N
Soda Creek
Soda Up Station (SC^01]_
-
<» Y
o Y
O Y*
Y
<» Y
Soda Down Station (SC-04)
-
<» Y
4 Y
O Y
Y
» Y
Non-Contact Cooling Water Discharge
Non-Contact Cooling Water Discharge
4Y
OY
*Y
*Y |
Notes:
a. Constituents included for illustrative puiposes only, no remediation goal
b_ Proposed alternative point of compliance for Harris Well
c„ Not a Point of Compliance location
d. TW-35 could not be sampled, short-term trend is 2012 to 2016
* Natural background for manganese
«¦ Concentrations relatively stable overall in the past 5 years (2013 to 2017)
-0- Concentrations decreased overall in the past 5 years (2013 to 2017)
•ft- Concentrations increased overall in the past 5 years (2013 to 2017)
Y Equal to or less than EPA Remediation Goal in June 2017
N Greater than EPA Remediation Goal in June 2017
Source: Golder, 2018a
16
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Table 6. Short-term Constituent Concentration Trends at Other Wells and Springs
Location
Formation
Constituents of Concern
Cadmium
Fluoride
Manganese
Nitrate as N
Selenium
NW Pond
TVV-29 (background)
UBZ^t y3
o
o
o
ft
o
TW-16
UBZ-4 y3
o
o
o
ft
ft
TW-17
UBZ-4 y3
ft
o
o
ft
ft
TW-I8
LBZ-4
o
o
ft
o
o
Old UFS Ponds
TW-57 (background)
UBZ-2 y5?
o
o
4
o
TW-37
U'BZ-2 y4
ft
a
o
o
TW-45
LBZ-2 y2
<£>
o
o
o
o
TW-71
UBZ-2 y4
ft
<=>
ft
ft
ft
TW-72
UBZ-2 y4
o
nr
nr
nr
TW-73
UBZ-2 y4
ft
o
u
TW-77
UBZ-4 y2
o
o
o
o
TW-78
UBZ-4 y3
ft
ft
ft
4
d
Tailings Pond
TW-22
UBZ-2 y4?
ft
o
4
o
ft
TW-24
UBZ-2 y4
o
o
o
o
ft
TW-75
UBZ-2 y43
ft
o
a
ft
o
TW-76
UBZ-2 v4a
o
«-
nin
nr
hp
UFS Piles
TW-46
UBZ-4 y3
o
o
o
ft
o
TW-49
UBZ-4 y3
o
JJ
o
ft
TW-50
UBZ-4 y3
o
o
ft
o
Old Hydroclarifier and Plant Area Wells
TW-30
UBZ-4 y3
o
o
o
ft
ft
TW-40
UBZ-4 y3
o
o
o
o
o
TW-41
UBZ-4 y3
o
o
o
o
o
TW-43
UBZ-4 y3
o
o
o
o
o
TW-26
LBZ-4
o
o
o
o
TW-44
LBZ-4
o
o
o
o
17
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Location
Formation
Constituents of Concern
Cadmium
Fluoride
Manganese
Nitrate as N
Selenium
Southwest Corner Wells
TW-07
UBZ-1 y4
o
4
o
o
o
TW-08
UBZ-1 y3
o
o
o
o
o
TW-10
UBZ-1 y5
o
o
o
0
TW-87
UBZ-1 y4
o
-------
Downgradient Wells, COC Distribution
In general, COCs including cadmium, manganese, and fluoride were not detected above RGs south of the plant
fenceline. Two interpreted nitrate plumes are identified south and southwest of the plant, with maximum
concentrations at TW-85 at a concentration of 34.8 mg/L (Figure 7). Most of the other wells in these plumes have
nitrate concentrations between 10 and 20 mg/L; compared with the RG of 10 mg/L (Figures 4 through 7).
Figure 8 indicates that selenium is the only COC that exceeds its RG outside of the southern Monsanto property
boundary, at TW-65 with a 2017 concentration of 0.059 mg/L. Selenium was detected in TW-66, the deeper well
adjacent to TW-65, at a concentration of 0.028 mg/L, below the RG. The selenium plume has migrated southward
past the southern and property line (IC boundary) within the UBZ-1 and 2 aquifers. This plume appears to be
following a southerly preferential flow path in the three shallowest water-bearing zones beneath the Site (gamma
zones 3, 4, and 5). As reported in the 2017 water quality report (Golder, 2018a), data from downgradient
monitoring wells installed by Kerr McGee show that selenium concentrations appear to be very low south of the
southern property line and TW-65 (i.e. further downgradient), ranging from 0.0028 mg/L at KM-46, and 0.0017 at
KM-39.
The next upgradient shallow wells from the south property line, TW-59, 62 and 64, have selenium concentrations
above the RGs at 0.084, 0.147, and 0.084J mg/L, respectively. Additional monitoring wells installed in 2018
should define the southwest extent of the selenium plume west of Government Dam Road.
Downgradient Wells, COC Trends
Selenium concentrations in southern property line wells TW-65 and TW-66 are stable overall (Figure 13, Table 6)
although the selenium concentration has decreased slightly since 2011 in TW-65. However, selenium
concentrations are interpreted to be increasing in the next upgradient wells TW-59, 62, and 70 (Table 6).
Surface Water Quality
Figure 3 shows the principal surface water bodies affected at the site including Soda Creek (downstream from the
effluent discharge) and Mormon Creek (fed by discharging impacted groundwater). EPA requested that Monsanto
analyze surface water discharges to Soda Creek for hazardous substances at a level of detail consistent with
ongoing groundwater data reporting. Thus, upstream and downstream sample locations were added to Soda Creek
in 2001, and Mormon Creek sampling was added in 2002 (EPA, 2008).
Surface Water - Springs
Total recoverable selenium has exceeded the chronic WQS of 0.005 mg/L at several springs during the monitoring
period beginning in 1980. Mormon A, B, and C Springs (Figure 14) are groundwater discharge from UBZ-1 and 2.
Selenium has historically exceeded the groundwater RG and surface water chronic WQS (0.005 mg/L). In 2017,
the selenium concentration in Mormon A Spring (alternate POC location) was 0.228 mg/L. The concentrations of
total recoverable selenium in Mormon B and C springs ranged from 0.136J mg/L to 0.08 mg/L in 2017.
At Mormon A, B and C springs, the selenium concentrations are above the groundwater RG, but have exhibited
decreasing trends in the short-term since approximately 2014-2015 (Table 6, Figure 15). Nitrate is above the
groundwater RG and increasing in Homestead and Mormon A, B, and C springs in the short-term. Other COCs
(including fluoride, and manganese) are below the groundwater RGs and are interpreted to be stable.
Cadmium concentrations have been stable above the groundwater RG of 0.005 mg/L and surface water chronic
WQS of 0.0006 mg/L in alternate POC location Mormon A Spring. The cadmium concentrations in Mormon A
Spring have decreased from peaks in the 1980s but appear to have stabilized since the 1990s at concentrations
around 0.015 mg/L. Cadmium was detected at SW spring above its confluence with Soda Creek at a concentration
of 0.0083 mg/L.
At Southwest and Homestead springs, total recoverable selenium concentrations (0.019 mg/L and 0.039 mg/L,
respectively) are below the groundwater RG of 0.05 mg/L, but above the chronic WQS of 0.005 mg/L.
Surface Water - Creeks
Soda Creek
Fifteen surface water sampling stations have been established on Soda Creek (Golder, 1998; EPA, 2008), from
upstream of the Site to approximately 2 miles downstream where Soda Creek intersects US Highway 30 (Figure 3).
Soda Creek is flow-impaired between power canal diversions at the Soda Weir (SC-2) and the Soda upstream
19
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power return (SC-7), and below the irrigation diversion (SC-9). In 2017, the flow ranged from 67 cubic feet per
second (cfs) at the diversion weir (SC-2) down to less than 1 cfs below the diversion. The flow increased to
approximately 3.2 cfs in the diverted reach because of inflow from Southwest and Mormon springs, and other base
flow, and then was measured at 62 cfs below the power return (SC-7).
Of significance in the flow-impaired reach of Soda Creek is that the springs and seeps that feed this reach are
surface water expressions of groundwater discharging from the UBZ-1 and UBZ-2 aquifers. Also of significance is
that a majority of the flow is diverted upstream then returned downstream, and thus the COC concentrations in the
flow-impaired portion of Soda Creek are more pronounced.
Station SC-01 is upstream of the spring inflow into the flow-impaired section, and SC-04 is downstream. In the
flow-impaired reach, total recoverable selenium exceeded the chronic aquatic standard (IDAPA 58.01.02) of
0.005 mg/L at Soda Creek sample stations SC-4, SC-6 and SC-7 in 2017, with concentrations of 0.0121 J, 0.124J
and 0.0130J, respectively (Figure 14). However, below the power canal return, at Stations SC-08 through SC-11,
dilution from the return flow results in the downstream selenium concentrations to drop below the Idaho chronic
criteria. In addition, the selenium concentrations at stations SC-04 and SC-06 have decreased since 2010 (Golder,
2018a, Figure E-7). The noncontact cooling water discharge sampling location on Soda Creek has exhibited an
increase in nitrate and selenium concentrations in the short-term.
Cadmium levels were above the WQS of 0.0006 mg/L in the flow-diverted reach at Stations SW Spring, SC-3,
SC-4, SC-6 and SC-7 at concentrations of between 0.0012 and 0.008 mg/L). However, below the power canal
return flow, cadmium is non-detect due to dilution.
Mormon Creek
Mormon Creek is a tributary to Soda Creek that is fed by discharge from the UBZ-1 and 2 aquifers (Mormon A, B,
and C Springs, Calf Spring, and diffuse groundwater seepage). Flow in Mormon Creek was measured at 0.4 cfs in
2017. The sampling station on Mormon Creek (MC-1) is located immediately above its confluence with Soda
Creek. Selenium concentrations at MC-1 have exceeded the groundwater RG and chronic WQS of 0.005 mg/L
since monitoring at this station began in 2002, with a 2017 estimated concentration of 0.172J mg/L. Cadmium
concentrations in Mormon Creek were 0.0101 mg/L in 2017.
However, selenium concentrations decreased between 2014 and 2015 at the three Mormon Springs sampling
stations that feed Mormon Creek, likely in response to reduced flows and groundwater capture during aquifer pilot
testing upstream. The selenium concentration at Station MC-1 dropped between 2011 and 2015, then increased
from 2015 to 2017 (Figure 15).
As identified in the ROD, Soda Creek is the only natural stream which is nearby and potentially affected by the
Site. Exceedances of selenium and cadmium WQS were noted within the flow impaired reaches of Soda Creek and
upgradient surface water expressions (i.e., springs). The upper portions of Soda Creek do not support a fisheries
resource due to naturally-occurring carbon dioxide concentrations in the water. The lower reach of Soda Creek,
just above its confluence with the Alexander Reservoir, provides suitable conditions to support fisheries.
Exceedances of selenium and cadmium WQS have not been observed in these lower reaches.
Sediments in Soda Creek and Alexander Reservoir
During the Phase I and Phase II or the RI, sediments were sampled in Soda Creek upstream and downstream of the
plant outfall, and the non-contact cooling water was also sampled and analyzed. Statistical analyses were
performed on the water and sediment data to determine which downstream parameters were elevated with respect
to upstream concentrations (Golder, 2018b). Sediments collected from Soda Creek downstream of the Soda Weir
were found to contain elevated levels of arsenic, cadmium, copper, nickel, selenium, silver, vanadium, and
polonium-210. Each elevated constituent was subjected to a preliminary risk-based screening to identify the
constituents of potential concern (COPCs) in sediment. Additional sediment sampling was conducted and included
toxicity testing on benthic invertebrates. The results of the toxicity testing results on the sediments were
inconclusive.
The ROD did not specify a remedy for sediments, but required sediment sampling in Soda Creek every five years
to evaluate if concentrations of COCs are increasing, decreasing, or stable. Monsanto conducted sediment
sampling in 2017 to support the fourth FYR (Golder, 2018b) using Incremental Sampling Methodology (ISM).
Figure 16 shows the locations of the Sediment Sample Reaches in Soda Creek. Figures 17 through 25 show the
20
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constituent concentrations in sediment and variations in concentrations from upstream to downstream in the 11
reaches sampled. Both the 2017 and previous 2012 ISM data are shown for comparison to observed increases or
decreases.
The following text provides a summary of the apparent changes (increases/decreases) since 2012 in each COC
throughout the system (note that Reach 10 was not sampled in 2017 because of high flows). The changes are based
on visual interpretations of the concentrations between 2012 and 2017 and also interpretations provided in Golder
(2017b).
• Arsenic: No apparent trend with time except a higher concentration at Control Reach 01 since 2012
(Figure 17).
• Beryllium: Very slight increase since 2012 in reaches 01, 05, 06, 07, and 11 (Figure 18).
• Cadmium: Slightly higher concentrations since 2012 in reaches 07, 08, and 11 (Figure 19).
• Copper: No apparent trend with time except slightly lower concentrations in reach 07 and Region 11, also
called the Soda Creek Arm (Figure 20).
• Nickel: No apparent trend with time in nickel concentration, except for higher concentration in reach 01, and
lower concentration in Reach 08 (Figure 21).
• Polonium 210: Slightly higher concentrations than 2012 in reaches 01, 02, 05, 07, and Soda Creek Arm.
However, the highest concentration overall was upgradient in Reach 01 (Figure 22).
• Selenium: Slightly higher than 2011 in Reaches 02, 05 and 07, but same as 2011 in Soda Creek Arm
(Figure 23).
• Silver: Higher than 2012 in the flow-diverted reaches (05 through 08), but similar to upstream reaches and
non-detect in the Soda Creek Arm (Figure 24).
• Vanadium: Slight decrease in concentrations between 2012 and 2017 (Figure 25).
Overall, in the downstream reaches, cadmium concentrations decrease from Reach 07 to the Soda Creek Arm, but
are slightly higher than the upstream control reaches. Concentrations of arsenic, beryllium, cadmium, nickel,
selenium, silver, and vanadium all decrease from Reach 08 (in the flow-diverted portion of Soda Creek) to the
Soda Creek Arm (Region 11). The copper concentration in sediments is slightly higher in the Soda Creek Arm than
in Reaches 05, 06, 07, and 08. COC concentrations are lower than observed in the upstream control reaches except
for cadmium and copper.
The ISM results are compared to Freshwater Sediment Screening Benchmarks (EPA, 2006), which are based on
ecological risk. These are not legally enforceable but are used to guide decisions regarding site specific
investigations for ecological risk.
Cadmium concentrations exceed the sediment screening benchmark of 0.99 mg/Kg in reach 05 through 11.
Selenium concentrations exceed the sediment screening benchmark of 2 mg/kg in all reaches in Soda Creek, at
concentrations between 4.2 and 57 mg/kg. Arsenic, nickel, and silver concentration exceed sediment screening
benchmarks in almost all reaches. Copper concentrations are below screening benchmarks in all reaches.
Beryllium, polonium-210, or vanadium do not have sediment screening benchmarks. In summary, in the flow-
diverted reaches, cadmium and selenium concentrations increase markedly in reaches 06 and 07. It is interpreted
that cadmium and selenium enter Soda Creek from Mormon Creek and baseflow of groundwater from UBZ-1
and 2. However, concentrations of these two COCs in sediment decline downstream from Reach 08, when the
power return flow enters Soda Creek.
The constituent concentrations in Soda Creek sediments appear to be generally stable and did not increased
markedly between 2012 and 2017. The third sediment ISM sample will be conducted in 2022. The results of this
sample event will enable evaluation of trends in sediment concentrations.
Offsite Soils
As required by the ROD, Monsanto collected offsite soil samples for the fourth FYR to determine the
concentrations of COCs in soil grids surrounding the plant. Soil sampling results indicated that offsite soils were
all below the remediation goal of 3.7 picocuries per gram for Radium-226, except in Parcels 1, 2, and 6 (these
parcels had concentrations of 4.41, 3.82, and 4.1 picocuries per gram, respectively) (Figure 26). These parcels are
on the southeast side of the plant and Radium-226 concentrations from these parcels exceeded the RG in the third
FYR. These parcels have previously been identified as exceeding the RGS, and those parcels are under appropriate
21
-------
ICs (Golder, 2018c). Because no new areas with RG exceedances were identified, no title or other searches will be
conducted as no new ICs are needed.
Decision Units 21, 22 and 25, located northeast of the plan, showed Radium-226 concentrations above the RG
during the third FYR. However, samples from these decision units had Radium-226 concentrations below the RG
during the fourth FYR.
Site Inspection
The FYR site inspection was conducted on June 6, 2018. Jason Maughan of Monsanto and Greg Warren of CH2M
(representative of EPA) were in attendance. The purpose of the inspection was to visually assess the protectiveness
of the remedy and ongoing Site O&M, including the condition and sampling of the monitoring wells, and
engineering controls of the source piles.
No significant findings were observed during the inspection. The monitoring wells inside and outside of the plant
were all in acceptable condition. Monsanto continues fugitive dust control on plant roads, and has been plot-testing
cover materials for plants on the on-site source piles. The checklist is included in Appendix C and provides
additional details regarding the condition and performance of the remedy.
22
-------
V. TECHNICAL ASSESSMENT
QUESTION A: Is the remedy functioning as intended by the decision documents?
Question A Summary:
No. The ROD (1997) indicates that modeling predicted that "without further action concentrations of constituents
in groundwater at the southern Plant boundary will be restored to background levels within 5 to 30 years"
(depending on the contaminant and it rate of degradation). In addition, the combination of source control and
remedial actions and natural attenuation "is projected to restore the groundwater to [contaminant] levels which
allow for unrestricted use and exposure within 30 years". Finally, the ROD states "If groundwater recovery
appears to significantly differ from model projections, the model and the need for additional groundwater
remedial actions should be re-evaluated".
Based on a review of current groundwater data and source area conditions, the groundwater remedy (MNA) is not
performing as intended. Groundwater monitoring data reveal that after initially decreasing, some COC
concentrations have been increasing over the last several years in some of the monitoring locations, and at some
locations appear relatively stable above the RGs. In addition, the COC selenium has been detected at the southern
property boundary in monitoring well TW-65 at concentrations that exceeded its RG. Monitoring wells upgradient
from the southern property line are interpreted to be increasing in the short-term (Figure 8; Table 6; Golder,
2018a). These trends indicate the selenium is not attenuating at the previously-estimated rate.
The RI concluded that remaining source areas such as the Northwest Pond and UFS Ponds had been adequately
controlled by taking the ponds out of service and lining them with impermeable barriers to prevent any
contaminant migration. However, investigations conducted since the last FYR (Golder, 2016) revealed that more
than 40,000 tons of source materials are estimated to remain in the UFS and Tailing Ponds. Moreover, these
potential source areas are covered with crushed slag and other permeable materials that allow infiltrated
precipitation to flow vertically downward and reach the groundwater aquifer; thus contributing to ongoing
contamination in groundwater.
Attenuation rates have proved to be slower than originally predicted, for selenium in particular. These issues raise
the uncertainty of the ability of the implemented remedy of MNA to achieve the goal of groundwater restoration
within the 5- to 30- year timeframe. Groundwater cleanup performance standards have not been achieved as of
2017, and data suggest that those standards will not be achieved in the foreseeable future, particularly now that
leaching from remaining COC sources has been positively identified.
Uncertainties in the Conceptual Site Model have been identified (Golder, 2016). Data gaps were identified at the
southwest property line along Government Dam Road where the selenium plume has not been completely
delineated; and east and southeast of the plant production wells, where the extent of groundwater capture and the
relationship to the Kerr-McGee plume has not been fully characterized. Monitoring wells were installed in 2018
to address these data gaps, but at the time of this report preparation, these data are not available. Other unknowns
include the full extent and thickness of the UFS source materials remaining buried on site, the spatial distribution
of precipitation infiltration, the source of elevated chloride that could result in increased cadmium leaching, the
source of nitrate and manganese within the UBZ-2 area that results in groundwater concentrations above the RG,
and the potential for COC transport downgradient of UBZ-4 outside control by production wells.
A domestic well survey and sampling event was conducted in 2015 (Golder, 2015) to investigate the presence of
domestic wells and current usage. The area of the study included all areas where wells that could have been
potentially impacted by the plume from the Site. No drinking water wells were discovered to exceed the RGs for
any site COCs (Golder, 2015). However, no specific safeguards or legally enforceable restrictions are in place to
prevent use of groundwater in locations where site-related COCs exceed RGs within Soda Springs, south of
Monsanto's property line.
23
-------
QUESTION B: Are the exposure assumptions, toxicity data, cleanup levels, and remedial action
objectives (RAOs) used at the time of the remedy selection still valid?
Question B Summary:
Yes. Exposure assumptions, ARARs, RGs, and RAOs used at the time of the remedy are still valid. Changes to
toxicity factors and EPA guidance are not significant enough to affect the remedy or require additional
monitoring. The narrative below describes changes that have occurred since the remedy was selected, and whether
those changes affect the validity of the remedy.
Changes in Applicable or Relevant and Appropriate Requirements (ARARs) and To Be Considered
(TBCs) Criteria
The 1997 ROD did not identify Idaho surface water quality standards as ARARs. Monitoring data indicates that
total recoverable selenium has exceeded the current Idaho chronic WQS of 0.005 mg/L in areas where
contaminated groundwater discharges to springs and creeks. EPA should consider whether a decision document is
needed to incorporate the Idaho WQS as an ARAR and the selenium WQS as an RG. No other changes were
identified for ARARs or TBCs.
New Contaminants or Contaminant Sources
No new contaminants have been identified at the Site.
Changes in Toxicity and Other Contaminant Characteristics
Human health toxicity factors for several contaminants evaluated during the risk assessment have changed since
the time of remedy selection, although the changes to these toxicity factors were minor. The inhalation toxicity
factors used during the risk assessment are outdated because guidance for estimating risk from the inhalation
pathway has changed since the time of the risk assessment (EPA, 2009). The impact of these changes on baseline
risk is unknown, although these methodology changes are unlikely to affect the remedy because exposures via the
dust inhalation pathway are much less than through ingestion.
Changes in Risk Assessment Methods
EPA has published many new risk assessment guidance documents since the ROD. No new guidance documents
that would affect the assessment of risks at this site have been issued in the last five years. The methodology used
during the human health and ecological risk assessments was sufficient to evaluate risk in those areas of the Site
that were evaluated at that time. Methodology changes provided in new or updated guidance documents are not
anticipated to be significant enough to result in changes to RGs or to affect the validity of previous remedial
action decisions at the Site.
Changes in Exposure Pathways and Land Use
Since the last FYR, domestic well survey and water quality sampling reports were completed for the Soda Springs
area south (downgradient) of the Site, where the plume may have migrated (Golder, 2015). The survey identified
only four domestic wells and one spring that are operational in the study area. Three of the wells are used for
drinking water, while the fourth well is used for irrigation and stock watering. Sample results collected in 2015
(Golder, 2015) from the four domestic wells identified showed that COC concentrations are all below the RGs
identified in Table 1. Additionally, potable water is provided by the City for the citizens of Soda Springs.
Considering this, along with the results of the well survey and water quality sampling report, groundwater
contamination related to the Site is not believed to pose an unacceptable risk under the current conditions.
Changes in Remedial Action Objectives
There have been no changes to the existing RAOs, and the RAOs remain valid.
QUESTION C: Has any other information come to light that could call into question the
protectiveness of the remedy?
No.
24
-------
VI. ISSUES/RECOMMENDATIONS
Issues itihI Recommendations 1 cloutilied in (ho Fi\e-Year Rcxicw:
OU(s): N/A
Issue Category: Remedy Performance
Issue: Concentrations of COCs in groundwater exceed RGs beyond the Monsanto
property boundary, nature and extent of groundwater plume(s) of site-related COCs are
not well defined, and trends indicate that groundwater RGs will not be met in the 5- to
30-year time frame anticipated in the ROD.
Recommendation: Complete the supplemental focused Remedial Investigation and
execute a focused Feasibility Study to evaluate the current remedy and the need to add
additional remedial actions to achieve RAOs. If necessary execute a ROD amendment
or ESD to achieve RAOs. Continue monitoring groundwater annually to observe
changes in COC concentrations.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party Responsible
Oversight Party
Milestone Date
No
Yes
PRP
EPA
3/13/2020
Issues and Recommendations Identified in the Fi\e-Year Rexiew:
OU(s): N/A
Issue Category: Institutional Controls
Issue: No restrictions are in place to prevent installation and/or use of domestic or
irrigation wells downgradient of the Monsanto Site where COCs exceed the RGs.
Recommendation: Develop an institutional control plan for areas where groundwater
COCs have migrated beyond current property boundary. Enact enforceable restrictions
on groundwater use beyond southern property boundary to prevent exposure where
plume has migrated to Soda Springs.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party Responsible
Oversight Party
Milestone Date
No
Yes
PRP
EPA
9/6/2019
Issues and Recommendations Identified in the Fi\e-Year Rexiew:
OU(s): N/A
Issue Category: Remedy Performance
Issue: Potential sources of COCs to groundwater remain in the old UFS Ponds, UFS
Piles, Northwest Pond, and Old Hydroclarifier Areas.
Recommendation: Fully define the extent of remaining on-site sources and address
leaching of COCs into groundwater.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party Responsible
Oversight Party
Milestone Date
No
Yes
PRP
EPA
9/6/2019
25
-------
Issues itihI Recommendations 1 cloutilied in (ho l"i\e-Year Kc\ic\\:
OU(s): N/A
Issue Category: Remedy Performance
Issue: Concentrations of contaminants in sediments in Soda Creek are elevated based
on statistical analyses and relative to ecological risk benchmarks downstream of facility
in the flow-diverted reaches.
Recommendation: Continue monitoring the sediments every five years. Consider
whether remedial action is necessary to address ecological risks due to elevated
contaminant concentrations in sediments.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party Responsible
Oversight Party
Milestone Date
No
Yes
PRP
EPA
8/18/2023
Issues and Recommendations Identified in (he l"i\e-Year Rexiew:
OU(s): N/A
Issue Category: Remedy Performance
Issue: Concentrations of surface water in location where groundwater discharges to
several streams and creeks exceed Idaho WQS.
Recommendation: Continue monitoring surface water annually. Execute a ROD
amendment or ESD to add surface water RAOs, ARARs, and RGs, and require any
necessary remedial action.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party Responsible
Oversight Party
Milestone Date
Yes
Yes
PRP
EPA
8/18/2023
Issues and Recommendations Identified in the l"i\e-Year Rexiew:
OU(s): N/A
Issue Category: Remedy Performance
Issue: Uncertainties have been identified in the CSM that raise questions to the
appropriateness of the remedy.
Recommendation: Execute the recommendations from the focused supplemental RI
and source area characterization (Golder, 2016) to fully characterize source materials,
COC transport mechanism, evaluate chloride, nitrate and manganese sources, and
evaluate water quality data from wells installed in 2018.
Affect Current
Protectiveness
Affect Future
Protectiveness
Party Responsible
Oversight Party
Milestone Date
No
Yes
PRP
EPA
3/13/2020
26
-------
VII. PROTECTIVENESS STATEMENT
Sitewide Protectiveness Statement
Protectiveness Determination:
Not Protective
Protectiveness Statement:
The remedy for the Monsanto Site is not protective because concentrations of surface water in locations where
groundwater discharges to several streams and creeks exceed Idaho WQS. The following actions need to be
taken to ensure protectiveness: execute a ROD Amendment or ESD to add surface water RAOs, ARARs, and
RGs, and require any necessary remedial action.
In addition, the following issues need to be taken in order to ensure long-term protectiveness: Complete the
supplemental focused Remedial Investigation and execute a focused Feasibility Study to evaluate the current
remedy and the need to add additional remedial actions to achieve RAOs. If necessary execute a ROD
amendment or ESD to achieve RAOs. Continue monitoring groundwater, sediments, and surface water to
observe changes in COC concentrations. Fully define the extent of remaining on-site sources and address
leaching of COCs into groundwater. Develop and implement an institutional control plan for areas where
groundwater COCs have migrated beyond current property boundary.
VIII. NEXT REVIEW
The next FYR report for the Site is required 5 years from the completion date of this review.
27
-------
Figures
-------
Tfrrttefntie
Knot)
fwmufion
Institutional — 1
Control Boundary j
Monsanto
Plant Boundary
Chtster
Hill
Institutional
Conjtrol Boundary
, * • «*
Soda Springs
Plant
Alexander
Jkserpoif
LEGEND
— - Institutional Control Boundary
Monsanto Plant Boundary
REFERENCE(S)
1. SERVICE LAYER CREDITS: COPYRIGHT© 2013 NATIONAL GEOGRAPHIC SOCIETY,
l-CUBED
1,250
2,500
FEET
5,000
3
Source: Golder Associates Inc. 2017. 2017 Off-site Soil Sampling Report, Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company.
FIGURE 1
Monsanto Plant Vicinity Map
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
AX0629180941BOI
CtlM
-------
i Old Hydroclarifier
Former Underflow
Solids Ponds
k/lW-49
r#: 5929.35
5977.54
"tW-17
t'TW-30
KM-21 f
5983.44
TW-37S
5894.43
TW-31 =
5954.57i
iTW-78 j
|5§23.40«
„ KM-44
® 5991.90
TW-331
TW-26
v jJtW-79 '(
15918.50,
iA\i
TW-24
5883.50
-TW-22A
Primary Fault
—TW-34 I ;i
«58«8^i»-.5880i
-TW-50 ]|
5868.04 ill
TW-81 J
>.,^'5672.14"~ ]
m^V-TW-19 I
5867.35 . 68e7.77*J
* TW-88-fij;
5881.18 ii V
TW-oNflji'
5670.02 -:-l
TW-08 "'E
5870.28.
—TW-83
[SPRING
MAUGHANfl
IMARSH SPRINGI
in on-contoctxoMngwter POND INLETS
A [HARRIS WELL
VlSMliO
1 _A tw-53 js Tw-54
V" 5882.80 5864.05
Jon a spring—'5860
"non-contact COOLING watef
¦sill v !
-KM-37
5967.77
SPRING 2-
TW-55
5861.43-
rSQ02 SODAVVETR;
5910
|SWSPRING (ABOVE SODA)*
¦^^¦SO03SODA MIDS^"
[SPRING 3]
Points of Compliance
Locations are highlighted
in Yellow
1C-1 MORMON CREEK
KM-41
5854.78
(HUMBLE SPRING'
(LEWIS)
JjDGERASPRING I
) 'LEDGER B SPRING
fa, LEDGERC SPRl N G
. P
. S. \
^SPRING BOX1
TW-59
5848.43
KELLY P
ISQ06 SODA AT PROPERTY
tPR-1 POWER RETURN CANALl
-07 SODA UPSTREAM POWER RETURN
TW-67
^Stle spring pond up
1TTLE SPRING POND DOWN.
ISC-08 SODA AT OCTAGON PARK?
»SQ10 SODA AT RAILROAD BRIDGE'
ISC-09 SODA ABOVE DIVERSI ON,
CSC-11 SODA AT HIGHWAY 30
(tIGERT EAST
City park spring"
-INDEPENDENT WELL
jHGERT SOUTH
KM-40
5775.03
3IG SPRING]
LEGEND
I MORMON A
SPRING LOCATION WITH NAME (WHERE KNOWN)
SPRING LOCATION (NOT SAMPLED) WITH NAME
(WHERE KNOWN)
DOC
# MORMON CREEK SURFACE WATER LOCATION WITH NAME
-EjHNM) well location in soda springs with name
GROUNDWATER FLOW DIRECTION
5840—.^ GROUNDWATER CONTOUR (10 FOOT INTERVAL)
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
<^> TW-60
TW-59
TW-56
+ TW-28
^>PW-1
MONITORING WELL LOCATION WITH NAME IN ? ?_u_? ? PAIIIT
GROUNDWATER ZONE UBZ-1 D
MONITORING WELL LOCATION WITH NAME IN FISSURE
GROUNDWATER ZONE UBZ-2 , .
UBZ-1 GROUNDWATER ZONE
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-3 INSTITUTIONAL CONTROL BOUNDARY
MONITORING WELL LOCATION WITH NAME IN pRFFk"
GROUNDWATER ZONE UBZ-4 OKttK
POWER CANAL
PRODUCTION WELL LOCATION WITH NAME
IRRIGATION CANAL
TRONOX WELL LOCATION WITH NAME IN UBZ
— GROUNDWATER FLOW REGION BOUNDARY
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
0 600
1" = 600' "
AX0629180941BOI
FIGURE 2
Monitoring Well Locations, Springs, Groundwater
Elevation and Flow Direction in the Upper
Basalt Zone (June 2017)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
cfoZm
-------
Points of Compliance
Locations are highlighted
in Yellow
LEGEND
I MORMON A
SPRING LOCATION WITH NAME (WHERE KNOWN)
*
DOC
• MORMON CREEK SURFACE WATER LOCATION WITH NAME
SPRING LOCATION (NOT SAMPLED) WITH NAME
(WHERE KNOWN)
-EfHNM)
WELL LOCATION IN SODA SPRINGS WITH NAME
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
? ?-U-? ?— FAULT
D
•> -) -) -) -)->-> -) -) -) ¦) -> -) -) -) -) -> - FISSURE
UBZ-1 GROUNDWATER ZONE
INSTITUTIONAL CONTROL BOUNDARY
— . . . . . . — CREEK
POWER CANAL
IRRIGATION CANAL
groundwater FLOW REGION BOUNDARY
0 600
1" = 600' "
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
FIGURE 3
Soda Creek and Springs Sample Locations
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
cUZm
-------
SS02 LANDFILL NORTH
0.0009U
iPW-04
0.0009U
TW-48
'0.0009U
S02 LANDFILL SOUTFH
,0.0009.U
TW-28
0.0Q09U
:TW-29 -
0.0009J
TW-15?
0.0009U
TW16|
PlP-4844
jTW-57 1
0.0008U
(TW-74
0.0009U
KM-32
TW50
'0.0056-
U-TW-30
V0.0010J
JjhTW-42
®NS l
®TW40 v
Ikie J
i V^TW-77
•o^00|U
KM-24
NS
¦ NS
[TW-33-
0.0008U
TW-26
0.0015JJ
TW-76
0.0009J
! TW-79 f
\0.0008J'
\ TW-75-
' V 0.196
TW-68 /
0.0008U /
TW-38 /
0.0009U
m m
TW-87-^i
0.0010J Ui
COOPER SPRING^ 1 V
^ w ¦
'• MARSH SPRING
J^T^^O.0009U J
* M . HI ¦<..
—TW-34
---0.0009^
\-TW-20
\ 0.0045
=TW-35.
NS
' TW-88-
0.0009J
TW-07-
0.009U
-TW-08''
0.0010 J,
—TW-83
>j0.0008Ui
KM-33-
NS
jsPRINGlB
Ins
TW-12
0.0008U
.TW-81
:0.0009Ul
=TW-85 .
0.0009U
-TW-80
.0.0423
-TW-82
0.0010J
(HARRIS WELL
0.0009U
TW-19
0.0009J
-TW-58 \
0.00960* \
-TW-10
0.0009U 1
DOC SPRING^
NS
. ;SW SPRING AT GOVERNMENT DAM ROAD^f
BlL. flaagJI
^NON-CONTACT COOLING WATER POND INLET^'
I , 0.0059 \
' "SC-01 SODA UP—j \l
0.0009U \
nSC-02 SODA WEIR
0.0009U
1 SC-05 SODA BELOW WEIR "—'
0.0009U
SWSPRING (ABOVE SODA)—-
0.0083 _
¦SC-03 SODA MID—^
¦ n 'Bj
-NON-CONTACT COOLING WATER
0.0058
CALF SPRING-
0.0063"
TW-86
.0.0009U
KM-37
NS
SPRING 2-
I NSi
TW54
0.0032
TW-53
0.0009U
TW-55
0.0008J
TW-56
0.0008U
/|—MORMON A SPRING
"l ;0.0149
-MORMON B SPRING
ip.0009U , 3
KM-45
NS
'VjgFINCH SPRING!
-SPRING 3
Ins . _
-MORMON C SPRING
0.0009U
TW61
0.0008U
—TW-70
0.0008U
TW62
0.0008U
TW-63-
0.0008U
-MC-i MORMON CREEK
¦0.0101
KM-41
NS
HUMBLE SPRING
0.0009U
SPRING 4
Ins I
TW64-
0.0008U
TW60
0.0012J
BOYSCOUT SPRINGHkI;
IB
¦I "'-Ma
H ^SPRING BOX—*
NslWl
SC-04 SODA DOWN-
0.0012 J
-LEWIS-
0.0009U
r^LEDGER A SPRING
5 NS
^Ledger b spring
Bmlns I
HOMESTEAD SPRING
0.0009U
TW-59
0.0009U
KELLY PARKSPRIN!
C SPRING
L.jB^SC-06 SODA AT PROPERTY LINE
/ 0.0021
/
PR-1 POWER RETURN CANAL
-0.0009U _ /•
jSC-07 SODA UPSTREAM POWER RETURN
10.0015J
KM-38-
NS
-TW-65
0.0009U
TW-67
0.0008U
TW-66 '
0.0009U
LEGEND
MORMON A
(0.015)
DOC
SPRING LOCATION WTH NAME (WHERE KNOWN)
SPRING LOCATION (NOT SAMPLED) WITH NAME
(WHERE KNOWN)
I MORMON CREEK SURFACE WATER LOCATION WITH NAME
-EfHNM)
(<0.041)
WELL LOCATION IN SODA SPRINGS WITH NAME
SAMPLE: CHEMICAL CONCENTRATION (mg/L) WITH
QUALIFIER (IF ANY)
(,..U)= NOT MEASURED
(,..J)= ESTIMATED
(J+)= ESTIMATED WITH HIGH BIAS
A TW-60
V (<0.002 U)
TW-59
(<0.002 U)
fa TW-56
"T"(<0.002 U)
TW-28
*(<0.002 U)
4K pW-1
(<0.041)
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-1
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-2
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-3
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-4
PRODUCTION WELL LOCATION WITH NAME
TRONOX WELL LOCATION WITH NAME IN UBZ
-CHEMICAL ISOPLETH (mg/L)
DASHED WHERE APPROXIMATE
, „.0.005/.
* . - - - £ at- ? WHERE UNKNOWN
A> Jp
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
3. YELLOW/GREEN SHADED AREAS EXCEED CADMIUM RG OF 0.005 MG/L.
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
? ?-U-? ?— FAULT
D
FISSURE
UBZ-1 GROUNDWATER ZONE
INSTITUTIONAL CONTROL BOUNDARY
— . . . . . . — CREEK
POWER CANAL
IRRIGATION CANAL
. ? .? •? ? GROUNDWATER FLOW REGION BOUNDARY
0 600
1" = 600' "
AX0629180941BOI
FIGURE 4
Cadmium Concentrations in the Upper Basalt
Zone (June 2017)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
cUZm
-------
KM-37
NS
SPRING 2-
3 NSl
KM-45 \
Ins _J 11
\ v i 1 \
AJcFINCH SPRINGl' fk. —SPRING 3
KM-41
NS
[SPRING 4]
Ins J
BOYSCOUT SPRINGHv,
NS Xp'J
^ \
ml JHkoI
« SPRING BOX^ • * •
NS
j—Ledger a spring
3 NS
8S|ledger b spring
H£ NS
KELLY PARKSPRINt
^LEDGER C SPRING
Ins
jS02 LANDFILL NORTH
10.405
S02 LANDFILL SOUTH-
,0.207.
iLl.OS -%ao
[TW-57
0.406 \\
, TW-50
goj5U I
£,jW-42
iNSw
rTW-40 v
13.60 M
KM-44
Ins_j
L TW-26]
r i.4o_
m
! TW-79f,
\10.10 %
A\l*
\J TW-75
\ 4.46
TW-68
0.348J+
TW-87-
0.503
^HOOPER SPRINGfftf 'MHft
¦
m MARSH SPRING
JUfp^,0.488J
=TW-35.
NS
KM-33-
NS
o lLTW80
| 1 4.15J-!
| '—TW-82
0 1.49
fHARRIS WELL
B.72J-
DOC SPRINGk
NS
SW SPRING AT GOVERNMENT DAM ROADf#-
0.800J-1
-NON-CONTACT COOLING WATER
0.469J
CALF SPRING-
2.05J-1
KM-37
NS
SPRING 2-
3 NSl
0.197J-
'' SC-02 SODA WE IR
0.289J-
SC-05 SODA BELOW WEIR
0.220J-
SWSPRING (ABOVE SODA)-
0.454
•SC-03 SODA MID—-
¦ 0240J-W
TW54 J, TW-55°
1.85J- "r^ 0.476 y
KM-45 \
Lns _J 11
ffrjfl—MORMON A SPRING
PtET
-MORMON B SPRING
HJ9J-
\ v | 1
"-.V jCFINCH spring! 7j&
-SPRING 3
NS
-MORMON C SPRING
11.22 J-
—TW-70
0.10U
TW62
TW61
0.250
-MC-1 MORMON CREEK
11.99J-
KM-41
NS
HUMBLE SPRING
0.498J-
iSPRING 4
Ins J
TW64-
0.617
TW60
0.209
BOYSCOUT SPRINGHv,
NS Xp'J
^ \
ml JHkoI
« SPRING BOX^ • * •
NS
SC-04 SODA DOWN-
0.309J-
jLEWIS
0.235J-
j—Ledger a spring
3 NS
jEs^ledger b spring
NS
HOMESTEAD SPRING
0.228J-
KELLY PARKSPRINt
^LEDGER C SPRING
Ins
^SjLjSC-06 SODA AT PROPERTY LINE
f^Hff0.303J-
( «J
PR-1 POWER RETURN CANAL, U
I0.223J- Hi
jSC-07 SODA upstream power return
I0.302J-
KM-38
NS
NON-CONTACT COOLING WATER POND INLET-
0.237±1
,c;r.ni Qnna i ip—
LEGEND
jP A SPRING LOCATION WITH NAME (WHERE KNOWN)
nnr SPRING LOCATION (NOT SAMPLED) WITH NAME
/JJ' (WHERE KNOWN)
# MORMON CREEK SURFACE WATER LOCATION WITH NAME
-^INDEPENDENT WELL LOCATION IN SODA SPRINGS WITH NAME
(<0 0411 SAMPLE: CHEMICAL CONCENTRATION (mg/L) WITH
( ' QUALIFIER (IF ANY)
(,..U)= NOT MEASURED
(,..J)= ESTIMATED
(J+)= ESTIMATED WITH HIGH BIAS
-CHEMICAL ISOPLETH (mg/L)
DASHED WHERE APPROXIMATE
? WHERE UNKNOWN
A TW-60
V (<0.002 U)
TW-59
(<0.002 U)
fa TW-56
"T"(<0.002 U)
TW-28
*(<0.002 U)
4K pW-1
(<0.041)
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-1
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-2
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-3
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-4
PRODUCTION WELL LOCATION WITH NAME
TRONOX WELL LOCATION WITH NAME IN UBZ
? ?-U-? ?— FAULT
D
FISSURE
UBZ-1 GROUNDWATER ZONE
INSTITUTIONAL CONTROL BOUNDARY
— . . . . . . — CREEK
POWER CANAL
IRRIGATION CANAL
. ? .? •? ? GROUNDWATER FLOW REGION BOUNDARY
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
0 600
1" = 600' "
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
3. YELLOW-SHADED AREA EXCEEDS FLUORIDE RG OF 4.0 MG/L.
AX0629180941BOI
FIGURE 5
Fluoride Concentrations in the Upper Basalt
Zone (June 2017)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
cUZm
-------
SS02 LANDFILL NORTH
0.0049U
iPW-04
0.0049U
TW-48
'0.0049U
S02 LANDFILL SOUTFH
_0.0049JJ
lTW-28|ite
1 0.158 ,'i#7
'TW-29 '\j
0.0049U ^
\-M- TW"49
,:*r0.0049U
TW-15?
0.0049U
| TW-16J
~0.0049Uj|
* TW-57 ~l
0.0049U',
S, KM-32
jf 0.0087
TW-50
' iyU«J
L-TW-30 •
5>0.0057J'" %
o ft y/
ISiTW42
"ns
—tW-40 \M)
5"i0.0073MB/
TW-41-
^0.0049U
V 77 TW"431
,4 0.0073J]
KM-5
0.00088
-KM-22
0.00077
KM-23—
L NSi -
PW-01
0.0049U
[TW-33-
0.0049U
TW-26]
0.487,
KM-4
0.0909
PW-02
'0.0049U.
aim ;n~A /
PW-03 J
0.0049L)!
Yellow/green shaded
areas exceed manganese
RG of 0.18 mg/L
1TW-79
\0.343
\ TW75-
' \ 0.540
M. i
TW-68
0.0049U
TW-38 /
I0.0049U
J |\ TW-69—>¦
» ' \\ \ 0.0049U/
m /to L'f//
Ki^HOOPERSPRrNGi'fc I I ^TW-84;
H^T UW36
^ BMARSlfSPRING W/
0.505 Y /
TW-87'
' 0.341
TW-39—
'0.0049U
—TW-34
¦-"0.173 ——
->TW-20
0.0049U
JW-81
^^0.0049Ui
yc\
P^TW-19 -
/} 0.0049U |
-TW-58 I
0.0049U \ '
=TW-35,
'NS
KM-33-
0.0179
jsPRINGlB
Ins
TW-12
0.0053J
^TW-85;
r 0.054 ?
/' / \
;TW-10 ^
0.0049U\
6 X1^TW-80
[/1/ 0.063 '
L y^7TW-82
Z P"1-70 1
[HARRIS WELL
|0.0049U
DOC spring!
NS ' 1
[SW SPRING AT GOVERNMENT DAM ROAD^t"
I _ 0.0115 I
'NON-CONTACT COOLING WATER POND INLET—
0.0049U
.-""SC-01 SODA UP^^i j
0.149
n SC-02 SODA WEIR Lj
0.286
1 SC-05 SODA BELOW WEIR
0.176
:SWSPRING (ABOVE SODA)-
0.044
SC-03 SODA MID—-
¦ 0.116
-NON-CONTACT COOLING WATER/
0.0049U
CALF SPRING-
0.208f
'TW-86
0.0049U
KM-37
0.0276
SPRING 2-
I NSI
TW54 j
0.0049Lr
TW-53
0.0049U
TW-55
0.0049U-
KM-45 \
0.00095 1
JIP-MORMON A SPRING
/i)U/0.0049U
-MORMON B SPRING
I0.0049U , "I
'Vj§FINCH SPRING!
-SPRING 3
Ins . _
;MORMON C SPRING
0.0049U
—TW-70
0.0049U
TW62
0.0049U
TW61
-0.477
j// TW-63'
j / 0.0049U
¥/ / / . ..
-MC-1 MORMON CREEK,
10.0077J
KM-41
0.0175
HUMBLE SPRING
'0.291
SPRING 4
Ins I
/ TW64-
0.0049U,
,TW60
4.59
BOYSCOUT springhkI;
IB
¦I V-
^ ^SPRING BOX—*
NslWl
SC-04 SODA DOWN-
0.0756
-LEWIS-
0.0049U
r^LEDGER A SPRING
5 NS
^Ledger b spring
Bmlns I
HOMESTEAD SPRING
'0.0049U
TW-59
0.0049U
KELLY PARKSPRIN!
:dger c spring
L.jB^SC-06 soda at property line
/ 0.0748
bSfSKBbXIl V 3ff& 1
rPR-1 power return canal jt
.0.139 HK
jSC-07 SODA UPSTREAM POWER RETURN
10.072
KM-38-
0.0025
-TW-65
0.0049U
TW-66 j
0.0077J
LEGEND
jP A SPRING LOCATION WITH NAME (WHERE KNOWN)
nnr SPRING LOCATION (NOT SAMPLED) WITH NAME
/JJ' (WHERE KNOWN)
# MORMON CREEK SURFACE WATER LOCATION WITH NAME
^INDEPENDENT WELL LOCATION IN SODA SPRINGS WITH NAME
(<0 041) SAMPLE: CHEMICAL CONCENTRATION (mg/L) WITH
( ' QUALIFIER (IF ANY)
(,..U)= NOT MEASURED
(,..J)= ESTIMATED
(J+)= ESTIMATED WITH HIGH BIAS
CHEMICAL ISOPLETH (mg/L)
DASHED WHERE APPROXIMATE
? WHERE UNKNOWN
A TW-60
V (<0.002 U)
TW-59
(<0.002 U)
fa TW-56
"T"(<0.002 U)
TW-28
*(<0.002 U)
4K pW-1
(<0.041)
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-1
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-2
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-3
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-4
PRODUCTION WELL LOCATION WITH NAME
TRONOX WELL LOCATION WITH NAME IN UBZ
= FAULT YZ/77S7J,
FISSURE
UBZ-1 GROUNDWATER ZONE
INSTITUTIONAL CONTROL BOUNDARY
— . . . . . . — CREEK
POWER CANAL
IRRIGATION CANAL
. ? .? •? ? GROUNDWATER FLOW REGION BOUNDARY
AREA OF UPWARD COMPONENT TO
VERTICAL HYDRAULIC GRADIENT
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
3. YELLOW/GREEN SHADED AREAS EXCEED MANGANESE RG OF 0.18 MG/L.
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
FIGURE 6
Manganese Concentrations in the Upper
Basalt Zone (June 2017)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
cUZm
-------
NITRATE IN
IS
"ED TO
: FROM
'VjgFINCH SPRING!
-SPRING 3
Ins . _
PLANT
2018a)
KM-41
NS
SPRING 4
Ins I
BOYSCOUT SPRINGHkI;
ns n
¦I "'-Ma
H ^SPRING box—^
NslWl
r^LEDGER A SPRING
5 NS
^Ledger b spring
Bmlns I
KELLY PARKSPRIN!
:dger c spring
>S02 LANDFILL NORTH
S02 LANDFILL SOUTH^
6.79.
jTW16^7Tf-
P 6.55J
TW-57 '-f;
0.20
TW-50
•v'0.292J+(
^^yrw-42
tyfij NS
]l—fW-40 v
&17.5J+#
I TW-77
0.058J+
KM-24
NS
¦ NS
TW26J
4Q9
! TW-79
\1.58
\ TW-75-jjh'
' \8.63J+ i|J
TW87-
0.05U
jH 00 P E R SPRING I | 9
«NS _ -) V\
fill
O MARSH SPRING
J-W^,0.05UJ
-TW-34
-0.251J+'
-TW-20
19.9J+
TW-35.
NS
KM-33-
NS
o\ T TW-80
10.5
J.? —TW-82
°J 1.23J+
IHARRIS WELL
7.68 J
DOC SPRING
NS
SW SPRING AT GOVERNMENT DAM ROAt
'NON-CONTACT COOLING WATER POND INLET—
6.22J
SO01 SODA UP^\^
0.758J
n SC-02 SODA WEIR Lj
0.829J
1 SC-05 SODA BELOW WEIR
0.712
:SWSPRING (ABOVE SODA)-
Ifr 2.41J+
SC-03 SODA MID—-
¦ n iW
-NON-CONTACT COOLING WATER
6.11J
~ CALFSPRING-
/ 10.1J.
KM-37
NS
SPRING 2-
I NSl
TW54
20.1J+
f\r-j-MORMON A SPRING
ill / 14.2J
-MORMON B SPRING
14.6J \
KM-45
NS
^ELEVATED NITRATE IN
VTHIS AREA IS
INTERPRETED TO
ORIGINATE FROM
SOURCE AREA(S)
OUTSIDE THE PLANT
(GOLDER, 2018a)
'VjgFINCH SPRING!
-SPRING 3
Ins . _
-MORMON C SPRING
12.1 J
—TW-70
4.28J+
TW62
7.41J+
TW61
0.84J
-MC-1 MORMON CREEK
11.6J
KM-41
NS
HUMBLE SPRING
2.64J
SPRING 4
Ins I
TW64-
16.7
TW60
0.05U
BOYSCOUT SPRiNGflH
i n
¦I "'-Ma
± ^SPRING BOX—*
NslWl
SC-04 SODA DOWN-
1.47J
LEWIS
10.8J
r^LEDGER A SPRING
5 NS
^Ledger b spring
S®ns I
HOMESTEAD SPRING
17.8J
KELLY PARKSPRINt
:dger c spring
\ ^ SO06 SODA AT PROPERTY LINE
/ . 1.65 J I
IJXtZr. ——3—|I1W V WR K
PR-1 POWER RETURN CANAL fr1 %
ISC-07 SODA UPSTREAM POWER RETURN-
11.66 J
KM-38
NS
LEGEND
fP (0015)ON A SPRING LOCATION WITH NAME (WHERE KNOWN)
nnr SPRING LOCATION (NOT SAMPLED) WITH NAME
/JJ' (WHERE KNOWN)
# MORMON CREEK SURFACE WATER LOCATION WITH NAME
^INDEPENDENT WELL LOCATION IN SODA SPRINGS WITH NAME
(<0 041) SAMPLE: CHEMICAL CONCENTRATION (mg/L) WITH
( ' QUALIFIER (IF ANY)
(,..U)= NOT MEASURED
(,..J)= ESTIMATED
(J+)= ESTIMATED WITH HIGH BIAS
-CHEMICAL ISOPLETH (mg/L)
DASHED WHERE APPROXIMATE
? WHERE UNKNOWN
A TW-60
V (<0.002 U)
TW-59
(<0.002 U)
fa TW-56
"T"(<0.002 U)
TW-28
*(<0.002 U)
4K pW-1
(<0.041)
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-1
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-2
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-3
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-4
PRODUCTION WELL LOCATION WITH NAME
TRONOX WELL LOCATION WITH NAME IN UBZ
? ?-U-? ?— FAULT
D
FISSURE
UBZ-1 GROUNDWATER ZONE
INSTITUTIONAL CONTROL BOUNDARY
— . . . . . . — CREEK
POWER CANAL
IRRIGATION CANAL
. ? .? •? ? GROUNDWATER FLOW REGION BOUNDARY
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
3. YELLOW-SHADED AREAS EXCEED NITRATE (AS N) RG OF 10.0 MG/L.
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
0 600
1" = 600' "
AX0629180941BOI
FIGURE 7
Nitrate Concentrations in the Upper Basalt
Zone (June 2017)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
cUZm
-------
IS02 LANDFILL NORTH
0.0032J I
pW-04
0.0038J
TW-48
'0.0043J
S02 LANDFILL SOUTH-
0J3028J
jTW-16^:
pLO.279 "J
jTW-57 »
0.0017J
KM-32
0.0021
, TW-50
/''0.02081
AA\N-42{
j|NS. |
fTW-40 v
"o.897_ M,
TW-77
0.0036J
iTW-33-
0.0039J
TW-26.:
0.304J
KM-4
0.0046
1 TW-79
\0.150J'
A\ b/
V TW-75-
/ \ 0.384
f V
KM-3-
0.00057
KM-16\
0.0025"°
A TW-68 / /
Vj 0.0005J/ /
TW-87-^j
0.0004UJ h
[HOOPER SPRING!
,NS I
=TW35_
NS
TW-88-
0.0004UJ
-TW-08'
0.0004U
—TW-83,
)f]0.049J:
KM-33-
0.0023
^SPRING 11
MARSH SPRING
S5-.0.0004U
TW-12
0.0041 J
o I TW-80
| 0.364
| '—TW-82
° 0.014
I HARRIS WELL
b.165
C \s\N SPRING AT GOVERNMENT DAM ROAD^f-
0.0172|f
'NON-CONTACf COOLING WATER POND INLET®'
i 0.0322JTt
^SC-01 SODA UP ) \
0.0004UJ \
SC-02 SODA WEIR
0.0011 J
1 SC-05 SODA BELOW WEIR "—"
0.0005J
SW SPRING (ABOVE SODA)—
0.0192 ,
¦SC-03 SODA MID—'—
¦ n nn^-i iW
/ y. vf, v
-non-cont/ct cooling water
I0.0356
, f / CALFSPRING-
J I 0,196;
EV-3
0.0024o
KM-37
0.00064
SPRING 2-
I Nsl
TW54
0.179
TW-56
0.0021J
KM-45 \
0.0045 1
/J—MORMON A SPRING
-0.228
-MORMON B SPRING
0.136J
'VjgFINCH SPRING!
yf ^0.0013 _l
-SPRING 3
Ins . _
-MORMON C SPRING
iO-0803J
TW61
0.0004UJ
-MC-i MORMON CREEK
10.172J .
KM-41
0.0022
HUMBLE SPRING
0.0381
SPRING 4
Ins I
TW64-
0.0840J
TW60
0.0004UJ
BOYSCOUT SPRINGHkI;
ns n
¦I "'-Ma
H ^SPRING BOX—*
NslWl
SC-04 SODA DOWN-
0.0121 J
v^LEWIS
* 0.0226
r^LEDGER A SPRING
5 NS
^Ledger b spring
S®ns I
HOMESTEAD SPRING
0.0397
KELLY PARKSPRIN!
:dger c spring
L.jB^SC-06 soda at property line
nJBo.0124J__
I v-' - \
PR-1 POWER RETURN CANAL\
;0.0021J \
jSC-07 SODA UPSTREAM POWER RETURN
*0.0130J
KM-38-
0.0068
TW-67
0.0051 J
LEGEND
jP A SPRING LOCATION WITH NAME (WHERE KNOWN)
nnr SPRING LOCATION (NOT SAMPLED) WITH NAME
/JJ' (WHERE KNOWN)
# MORMON CREEK SURFACE WATER LOCATION WITH NAME
-^INDEPENDENT WELL LOCATION IN SODA SPRINGS WITH NAME
(<0 041) SAMPLE: CHEMICAL CONCENTRATION (mg/L) WITH
( ' QUALIFIER (IF ANY)
(,..U)= NOT MEASURED
(,..J)= ESTIMATED
(J+)= ESTIMATED WITH HIGH BIAS
A TW-60
V (<0.002 U)
TW-59
(<0.002 U)
fa TW-56
"T"(<0.002 U)
TW-28
*(<0.002 U)
4K pW-1
(<0.041)
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-1
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-2
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-3
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-4
PRODUCTION WELL LOCATION WITH NAME
TRONOX WELL LOCATION WITH NAME IN UBZ
CHEMICAL ISOPLETH (mg/L)
DASHED WHERE APPROXIMATE
? WHERE UNKNOWN
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
? ?-U-? ?— FAULT
D
FISSURE
UBZ-1 GROUNDWATER ZONE
INSTITUTIONAL CONTROL BOUNDARY
— . . . . . . — CREEK
POWER CANAL
IRRIGATION CANAL
. ? .? •? ? GROUNDWATER FLOW REGION BOUNDARY
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
3. YELLOW/GREEN SHADED AREA EXCEEDS SELENIUM RG OF 0.05 MG/L.
0 600
1" = 600' "
AX0629180941BOI
FIGURE 8
Selenium Concentrations in the Upper
Basalt Zone (June 2017)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
cUZm
-------
o>
E
c
o
'+->
CO
+¦>
c
a>
a
c
o
o
+->
c
a>
D
(0
c
o
o
0.25
0.20
0.15
0.10
0.05
0.00
m
? PW-01
I
u
<
ft
c o
—J
a)T-comr^a)T-comr^a)
NMWoooocoroarooJO)
(T)(D(D(D(D(D(D(D(D(D(D
(35
T-comr^c35T-com
OOOOO-t-T-T-T-T-
oooooooooo
C\IC\IC\IC\IC\IC\IC\IC\IC\IC\I
Cadmium
0.6
0.5
0.4
0.3
0.2
0.1
0.0
PW-01
i i i rv-^rN-> | "i i i i i i^i i i i i i i i i i i i i i i i i i i i i i i i i i i i
CD
CD
CO LO
CD
CO LO
CD
COCOCOCOCOCDCDCDCDCD
0}0}0}0}0}0}0)0>0>0>
T— CO LO
o o o
o o
o
o
CD
o
o
CO LO
CD
CM CM CM CM CM CM CM CM CM CM
Selenium
LEGEND
—•— Constituent Concentration (mg/L)
O Non-Detects
• Cadmium Remediation Goal (0.005 mg/L)
Selenium Remediation Goal (0.05 mg/L)
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions,
Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
0.05
0.04
0.03
0.02
0.01
PW-02
COCOCOCOCDCDCDCD
CD(7)(7)(7)(7)(7)(7)(7)
CM CM CM CM CM CM
O
CM
O O O
CM CM CM
Cadmium
0.6
0.5
0.4
0.3
0.2
0.1
0.0
PW-02
CD
CD
CO
CD
CO LO
CD
CO LO
COCOCOCOCDCDCDCD
CD(7)(7)(7)(7)(7)(7)(7)
CD
CD
CD
O
O
CO
O
O
LO
O
O
o
o
CD
o
o
CO LO
CM CM CM CM CM CM
O
CM
O O
CM CM
CD
O
CM
Selenium
Figure 9.
Cadmium and Selenium in Production Wells (UBZ-4)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
chM-
-------
o>
E
c
o
'+->
CO
+¦>
c
a>
a
c
o
o
+->
c
a>
D
(0
c
o
o
0.88 mg/L
TW-17
CD
T
CO
LO
CD
T—
CO
LO
CD
T—
CO
LO
CD
T—
CO
LO
CD
CO
CO
CO
CO
CO
CD
CD
CD
CD
CD
o
O
O
o
o
T
T
T
T
T
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
o
O
O
o
o
o
o
o
o
o
¦*-
¦*-
¦*-
¦*-
¦*-
¦*-
¦*-
C\l
C\l
C\l
C\l
C\l
C\l
C\l
C\l
C\l
C\l
Cadmium
0.6
0.5
0.4
0.3
0.2
0.1
0.0
TW-16
<
>
o
J
k-r.
T
# I/
CD
T—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
CO
CO
CO
CO
CO
CD
CD
CD
CD
CD
o
O
O
o
o
t—
t—
t—
t—
t—
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
o
O
O
o
o
o
o
o
o
O
¦«—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM
Selenium
LEGEND
—•— Constituent Concentration (mg/L)
O Non-Detects
— — — Selenium Remediation Goal (0.05 mg/L)
• - Cadmium Remediation Goal (0.005 mg/L)
Manganese Remediation Goal (0.18 mg/L)
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions,
Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
¦*-comr^o)T-com
OOOOOOOOOOCDCDCT)
CD(7)(7)(7)(7)(7)(7)(7)
r^cr>T-cOLnr^cr>T-
CDCDOOOOO^-
CDCDOOOOOOOOOO
t-t-CMCMCMCMCMCMCMCMCMCM
Manganese
COCOCOCOCOa>a>
03(T>0}0}(T>(7>0)
co lo h- a> <<-
OOOOOt-t-t-t-t-
oooooooooo
CNCNCNCNCNCNCNCNCNCM
Selenium
Figure 10.
Cadmium, Selenium, and Manganese in Northwest
Pond Wells (UBZ-4 Source Area)
Monsanto Site 2018 4th Five-Year Review
Caribou County, Idaho g
CM2 W:
-------
o>
E
c
o
'+->
CO
+¦>
c
a>
a
c
o
o
+->
c
a>
D
(0
c
o
o
0.6
0.5
0.4
0.3
0.2
0.1
0.0
TW-22
1
i | i | i | i | i | i i i i i i i i i i i i i i i i i i i |-
co lo h-
CD
O^COLDNO^COLnNO^COLDNO)
r^cococococoa>a>a>a>a>ooooo
CDCDCDCDCDCDCDCDCDCDCDOOOOOOOOOO
^^^^^^^^^^^-CMCMCMCMCMCMCMOJCMCM
Selenium
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
i
TW-37
J
~
L
T
\a .Am
i
....J*.,
CD
co lo cd
COCOCOCOCOCDCDCDCDCD
CO LO
CD
CDCDCDCDCDCDCDCDCDCDCD
O
O
CO LO
O O
o
o
CD
o
o
CO LO
CD
C\J CM CM CM CM CM CM CM CM CM
Selenium
LEGEND
—•— Constituent Concentration (mg/L)
O Non-Detects
— — — Selenium Remediation Goal (0.05 mg/L)
• - Cadmium Remediation Goal (0.005 mg/L)
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions,
Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CD
T—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
CO
CO
CO
CO
CO
CD
CD
CD
CD
CD
o
O
O
o
o
t—
t—
t—
t—
t—
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
o
O
O
o
o
o
o
o
o
O
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM
Selenium
2.0
1.5
1.0
0.5
0.0
CD
T—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
CO
CO
CO
CO
CO
CD
CD
CD
CD
CD
o
O
O
o
o
t—
t—
t—
t—
t—
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
o
O
O
o
o
o
o
o
o
O
¦*-
t-
¦*-
t-
t-
t-
t-
t-
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM
Cadmium
TW-24
I
A/
•
V
/
I
v
1
f
\!
% *
TW-37
v
1
*
Figure 11.
Selenium and Cadmium Trends in Old Underflow Solids
Pond Area Wells (UBZ-2 Source Area) TW-22, -24, -37
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho g
CM2 W:
-------
o>
E
c
o
'+->
CO
+¦>
c
a>
a
c
o
o
+->
c
a>
D
(0
c
o
o
0.4
0.3
0.2
0.1
0.0
TW-10
T-coLor^cDT-coLor^cDT-coLor^cDT-
COOOOOOOOOCDCDCDCDCDOOOOO^-^-^-'?-^-
CDCDCDCDCDCDCDCDCDCDOOOOOOOOOO
t-^-t-t-t-t-t-t-t-t-CMCNJCNJCNJCNCNCMCNCNJCM
Selenium
CD(T)(T)(T)(7)(7)(7)(7)(7)(7)(7)
CM CM CM CM CM CM C\l C\l C\l CM
Cadmium
LEGEND
—•— Constituent Concentration (mg/L)
O Non-Detects
_ _ _ Selenium Remediation Goal (0.05 mg/L)
Cadmium Remediation Goal (0.005 mg/L)
Source: Goldef*Associates Inc. 2018. 2017Summary Report on Groundwater Conditions,
Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
¦!-comr^CT)-!-com
0000000000050505
0)0)0)0)0)0)0)0)
^ fO LO N O) ^
ooooo^— t—
oooooooooo
CMCMCMCMCMCMCMCMCMCM
Selenium
1.0
0.8
0.6
0.4
0.2
i
>
TW-39
i
t
IAa*\ t
I
L
> ?
0.0
CD
CD
CO LO
CD
CO LO
CD
COCOCOCOCOCDCDCDCDCD
03(T>0}0}(T>(7>(T>
-5- CO LO
o o o
o o
o
o
CD
o
o o o
CO LO
CMCMCMCMCMCMCMCMCM
CD
O
CM
Selenium
Figure 12.
Selenium and Cadmium Trends in South Fenceline and Southwest
Corner POC Wells (UBZ-1 and 2 Downgradient) TW-10, -20, -39
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho g
CM2 W:
-------
0.20 -r
TW-65
0.15
0.10
"5)
& 0.05
c
o
'+->
CO
c 0.00
d>
o
c
o
<-> Selenium
+->
c
a>
3 °-20 i
« TW-67
c
o
o
CD
T—
00
LO
CD
t—
00
LO
CD
t—
00
LO
CD
t—
00
LO
CD
CO
00
00
CO
00
CD
CD
CD
CD
CD
o
O
O
o
o
t—
t—
t—
t—
t—
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
o
O
O
o
o
o
o
o
o
O
¦«—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM
0.15
0.10
0.05
o.oo yy
lo h- cd v
G) G) G) C
0}
-------
s T—KM-15
\ 0.0025
TW-87-^j
0.0004UJ ty
vHOOPER SPRING]
Ins
TW-88-^ji
0.0004UJ jji l
TW-07—
0.0075
-TW-08"
0.0004U
—TW-83,
)ii0.049J
KM-33-
0.0023
*- MARSH SPRING
^>,0.0004U
TW-12
0.0041J
0 I TW-80
| 0.364
1 'TW82
° 0.014
[HARRIS WELL
0.165
DOC SPRING^
\m
ISW SPRING AT GOVERNMENT DAM ROAD;
0.01721
[NON-CONTACT COOLING WATER POND INLET*
0.0322J
SC-01 SODA UP^pMW
0.0004UJ
SC-02 SODA WEIR J
0.0011 J
SC-05 SODA BE LOW WEIR—
0.0005J
SWSPRING (ABOVE SODA)]!
0.0192
SC-03 SODA MID—
J- 0.0031 J
-NON-CONTACT COOLING WATER
0.0356
/ CALF SPRING
K i 0.196
TW-53
0.134
TW-56
0.0021 J
KM-45 \
0.0045 1
m. /if—MORMON A SPRING
' \1 — li * "Q. 228
— ^^MORMON B SPRING
0.136J
-MORMON C SPRING \
!q.0803J \
TW-63-—A- TW-61 \
n ms.i ^ 0.0004UJ t
\c:finch spring!
HMti I
-MC-1 MORMON CREEK
|o.172J
HUMBLE SPRING
0.0381 I
TW-64-
0.0840J
BOYSCOUT SPRIN(
TW-60
0.0004UJ
SC-04 SODA DOWN-
0.0121 J
.LEWIS!
0.0226
NSMk
awH
m = -p
SPRING BOX^|i
NS
HOMESTEAD SPRING
0.0397
TW-59
0.084
KELLY PARK SPRING-
NSi
Y _• ^SC-06 SODA AT PROPERTY LINE
FJg0.0124J
I 1 \
'PR-1 POWER RETURN CANAL\
SO. 0021J . \
jSC-07 SODA UPSTREAM POWER RETURN
0.0130 J
KM-38-
0.0068
TW-67
0.0051 J
LITTLE SPRING POND UP
0.0011 J
LITTLE SPRING POND DOWN
0.0015 J
ISC-08 SODA AT OCTAGON PARK
0.0041 J
\ Hi' ' -
fsc-io SODA AT RAILROAD BRIDGE1*,
10.0034J I
KM-46
0.0028
jSC-09 SODA ABOVE DIVERSION
0.0045J
KM-39
0.0017
KM-42
0.0087
KM-47
0.00013U
iSC-11 SODA AT HIGHWAY 30
0.0033J
KM-43
0.0045
CITY PARK SPRING
0.0036J
rtn INDEPENDENT WELL
"Ho. 0021J
mKMA0
K 0-0048
KM-48
0.00013U
BIG SPRING
0.0027J _
LEGEND
fP (0015)ON A SPRING LOCATION WITH NAME (WHERE KNOWN)
nnr SPRING LOCATION (NOT SAMPLED) WITH NAME
/JJ' (WHERE KNOWN)
# MORMON CREEK SURFACE WATER LOCATION WITH NAME
-^INDEPENDENT WELL LOCATION IN SODA SPRINGS WITH NAME
(<0 0411 SAMPLE: CHEMICAL CONCENTRATION (mg/L) WITH
( ' QUALIFIER (IF ANY)
(...U) = NOT MEASURED
(,..J)= ESTIMATED
(J+)= ESTIMATED WITH HIGH BIAS
A TW-60
V (<0.002 U)
TW-59
(<0.002 U)
fa TW-56
"T"(<0.002 U)
TW-28
*(<0.002 U)
4K pW-1
(<0.041)
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-1
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-2
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-3
MONITORING WELL LOCATION WITH NAME IN
GROUNDWATER ZONE UBZ-4
PRODUCTION WELL LOCATION WITH NAME
TRONOX WELL LOCATION WITH NAME IN UBZ
-CHEMICAL ISOPLETH (mg/L)
DASHED WHERE APPROXIMATE
-? WHERE UNKNOWN
^—0.05,,
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions, Monsanto
Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
? ?-U-? ?— FAULT
D
FISSURE
UBZ-1 GROUNDWATER ZONE
INSTITUTIONAL CONTROL BOUNDARY
— . . . . . . — CREEK
POWER CANAL
IRRIGATION CANAL
. ? .? •? ? GROUNDWATER FLOW REGION BOUNDARY
NOTES
1. NAD83 IDAHO STATE PLANES, EAST ZONE, US FOOT.
2. AERIAL PHOTO FROM GOOGLE EARTH (8/2/2013).
0 600
1" = 600' "
FIGURE 14
Selenium Concentrations in Springs and
Surface Water (Distribution)
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Ctl2m:
-------
o>
E
c
o
'+->
CO
+¦>
c
a>
a
c
o
o
+->
c
a>
D
(0
c
o
o
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Mormon A Spring
¦ ¦
_
l/U
A Ml
: i
•
ITV
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CD
CT>-!-eomr^CT>-!-eomr^CT>-!-eomr^CT>-!-eom
h-oooooooooocncncncncnooooo-i-T-T-T-T-
05050505050505050505050000000000
t-t-t-t-t-t-t-t-t-t-t-CMCMCMCMCMCMCMCMCMCM
Mormon C Spring
CD
CO LO
CD
CO LO
CD
cococococoa>a>a>a>
CDCDCDCDCDCDCDCDCDCDCJ)
o
o
CO LO
o o
o
o
CD
o
o
CO LO
CD
C\J CM CM CM C\J CM CM CM CM CM
LEGEND
—•— Constituent Concentration (mg/L)
O Non-Detects
—¦— Dissolved Constituent Concentration (mg/L)
~ Dissolved Non-Detect (mg/L)
— — — Selenium Remediation Goal (0.05 mg/L)
Source: Golder Associates Inc. 2018. 2017Summary Report on Groundwater Conditions,
Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CD
^—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
CO
CO
CO
CO
CO
CD
CD
CD
CD
CD
o
O
O
o
o
t—
t—
t—
t—
t—
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
o
O
O
o
o
o
o
o
o
O
¦«—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
¦*—
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CD
T—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
t—
CO
LO
CD
CO
CO
CO
CO
CO
CD
CD
CD
CD
CD
o
O
O
o
o
t—
t—
t—
t—
t—
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
CD
o
O
O
o
o
o
o
o
o
O
¦*-
¦*-
¦*-
¦*-
¦*-
¦*-
¦*-
¦*-
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM
Mormon B Spring
"i i i i i i i i i i i i i i i i i i i i i i i i r~
Mormon Creek
-I I i I i I i I i I i I i I i I i I i I i I i I i I i o i o i o i o i o i o r
Figure 15.
Selenium Trends in Mormon A, B, and C Springs and
Mormon Creek
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Clfl2W:
-------
Soda
Springs
Plant
MonsantQiSoda
Springs Plant/
Ho'operjSprinq
Hooper.
. ¦
spnng
[Southwest
^Spring
Marsh|Sprinqi
Kackley
Spring, 1
fS.WjSpririq
power
return
SW Spring
confluence
te™Spriifig(
jjfabp.vei
^Mormon)
2nd power
diversion
Mormonml
Creek
confluence
iHomesteaci
[Spring^
Station
SC-4
2nd power
returnjB&
SSB3EJ
<®37Q3
SC-Q9?Sbda
Diversion
^SC-08Soda
'at Octagon'
Park
iSGrlQ Soda
'at Railroad
Irrigation
diversion
'Socla'at
Highway 30
©^©Soda Springs aaa3®
QdHMa
Reservoir
confluence
a as©
LEGEND
Spring
Soda Creek
tT
Reach ID
Sampling Reach Boundary
Sampling Region Boundary
Irrigation Canai
Power Diversion Canal
Power Return
Plant Boundary
Institutional Control Boundary
REFERENCE(S)
1. SERVICE LAYER CREDITS: ESRI, HERE, DELORME, MAPMYINDIA, ®
OPENSTREETMAP CONTRIBUTORS
SOURCE: ESRI, DIGITALGLOBE, GEOEYE, EARTHSTAR GEOGRAPHICS,
CNES/AIRBUS DS, USDA, USGS, AEROGRID, IGN, AND THE GIS USER COMMUNITY
500
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
1,000
2,000
FEET
AX0629180941BOI
FIGURE 16
Locations of the Sediment Sample Reaches in Soda Creek
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho m
cfoZm
-------
Control Reaches
Flow-Diverted Reaches
Downstream
100
90
80
70
oo
"So
£ 60
<
0£
o
u
50
40
30
20
10
-> <-
Reach 01
Reach 02
Reach 03
Reach 05
Reach 06
Reach 07
Reach 08
Reach 10
Region 11
SEDIMENT LOCATIONS
LEGEND
~ 2017 Sediment Concentration (mg/kg)
2012/13 Sediment Concentration (mg/kg)
Sediment Benchmark - (EPA 2006) (mg/kg)
Note - Samples were not collected in 2017 from Reach 3 and 10 due
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
FIGURE 17
Arsenic Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
Control Reaches
Flow-Diverted Reaches
Downstream
1.5
oo
"So
E
<
0£
1.0
O 0.5
u
0.0
Reach 01
Reach 02
Reach 03
Reach 05
Reach 06
Reach 07
Reach 08
Reach 10
Region 11
SEDIMENT LOCATIONS
LEGEND
~ 2017 Sediment Concentration (mg/kg)
» 2012/13 Sediment Concentration (mg/kg)
No Sediment Benchmark - (EPA 2006)
Note - Samples were not collected in 2017 from Reach 3 and 10 due
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
FIGURE 18
Beryllium Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
Control Reaches
Flow-Diverted Reaches
Downstream
00
"So
E
<
0£
45
40
35
30
25
20
O 15
u
10
Reach 01 Reach 02 Reach 03 Reach 05 Reach 06 Reach 07
Reach 08
Reach 10
Region 11
LEGEND
SEDIMENT LOCATIONS
Note ¦
— 2017 Sediment Concentration (mg/kg)
2012/13 Sediment Concentration (mg/kg)
- Sediment Benchmark - (EPA 2006) (mg/kg)
Samples were not collected in 2017 from Reach 3 and 10 due
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
FIGURE 19
Cadmium Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
Control Reaches
Flow-Diverted Reaches
Downstream
M>
"So
E
<
0£
o
u
35
30
25
20
15
10
Reach 01
Reach 02
Reach 03
Reach 05
Reach 06
Reach 07
Reach 08
Reach 10
Region 11
LEGEND
SEDIMENT LOCATIONS
2017 Sediment Concentration (mg/kg)
2012/13 Sediment Concentration (mg/kg)
Sediment Benchmark - (EPA 2006) (mg/kg)
¦ Samples were not collected in 2017 from Reach 3 and 10 due
Note
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
FIGURE 20
Copper Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
Control Reaches
Flow-Diverted Reaches
Downstream
140
120
100
oo
"So
E
<
0£
o
u
80
60
40
20
Reach 01 Reach 02 Reach 03 Reach 05 Reach 06 Reach 07
SEDIMENT LOCATIONS
Reach 08
Reach 10
Region 11
LEGEND
~ 2017 Sediment Concentration (mg/kg)
2012/13 Sediment Concentration (mg/kg)
Sediment Benchmark - (EPA 2006) (mg/kg)
Note - Samples were not collected in 2017 from Reach 3 and 10 due
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
FIGURE 21
Nickel Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
Control Reaches
Flow-Diverted Reaches
4.0
3.5
3.0
m 2.5
<
0£
2.0
u 1.5
O
u
1.0
0.5
0.0
>
-------
Control Reaches
Flow-Diverted Reaches
Downstream
60
50
^ 40
E
<
0£
o
u
30
20
10
Reach 01
LEGEND
Reach 02
Reach 03
Reach 05
Reach 06
Reach 07
Reach 08
Reach 10
Region 11
SEDIMENT LOCATIONS
2017 Sediment Concentration (mg/kg)
2012/13 Sediment Concentration (mg/kg)
Non-Detect
¦ - Sediment Benchmark-(EPA2006) (mg/kg)
Samples were not collected in 2017 from Reach 3 and 10 due
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
Note
FIGURE 23
Selenium Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
2.5
2.0
oo
"So
E
<
0£
1.5
1.0
O
u
0.5
0.0
Control Reaches
Flow-Diverted Reaches
Downstream
Reach 01
Reach 02
Reach 03
LEGEND
Reach 05 Reach 06 Reach 07
SEDIMENT LOCATIONS
Reach 08
Reach 10
Region 11
2017 Sediment Concentration (mg/kg)
2012/13 Sediment Concentration (mg/kg)
O Non-detect
¦ - Sediment Benchmark-(EPA2006) (mg/kg)
Samples were not collected in 2017 from Reach 3 and 10 due
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
Note -
FIGURE 24
Silver Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
Control Reaches
Flow-Diverted Reaches
Downstream
Reach 01
Reach 02
Reach 03
Reach 05
Reach 06
Reach 07
Reach 08
Reach 10
Region 11
LEGEND
SEDIMENT LOCATIONS
Note ¦
— 2017 Sediment Concentration (mg/kg)
2012/13 Sediment Concentration (mg/kg)
No Sediment Benchmark - (EPA 2006)
Samples were not collected in 2017 from Reach 3 and 10 due
to unsafe sampling conditions. Reach 4 and 9 samples were
not collected in either event due to unsafe sampling conditions.
FIGURE 25
Vanadium Concentrations in Soda Creek Sediment
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho
Source: Golder Associates Inc. 2018. Soda Creek Sediment Sampling and Analysis Fourth CERCLA Five-Year
Review, Monsanto Company Soda Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
-------
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LEGEND
I I PARCEL
ITl PLANT BOUNDARY
— SODA CREEK
NOTE(S)
1. THE MONSANTO PLANT OWNS THE PROPERTIES WITH THE OWNER NAMES
OF P4 PRODUCTIONS
REFERENCE(S)
1. SERVICE LAYER CREDITS: SOURCE: ESRI, DIGITALGLOBE, GEOEYE,
EARTHSTAR GEOGRAPHICS, CNES/AIRBUS DS, USDA, USGS. AEROGRID, IGN. AND
THE GIS USER COMMUNITY
1.81
3.82
NS
20
T
Radium-226 Fourth FYR (pCi/g) Result
Radium-226 Fourth FYR (pCi/g) Result
Concentrations > remediation goal (3.71 pCi/g)
P4 PRODUCTIONS
010000067810
35.9
PARCEL OWNER INFORMATION
PARCEL IDENTIFICATION NUMBER
PARCEL AREA (ACRES)
1,000
2,000
4.000
Not sampled
PARCEL IDENTIFICATION NUMBER
TRIPLICATE SAMPLES COLLECTED
Source: Goider Associates Inc. 2018, Off-site Soil Sampling Report
Fourth CERCLA Five-Year Review, Monsanto Company Soda
Springs, Idaho Plant. Prepared for Monsanto Company. May.
AX0629180941BOI
FEET
FIGURE 26
Soil Sampling Parcels and Radium-226 Concentrations
Monsanto Site 2018 Fourth Five-Year Review
Caribou County, Idaho _
cfoZm
-------
Appendix A: References
-------
Golder Associates, Inc. (Golder). 1998. May 1998 Groundwater Status - Solutia Soda Springs Site, prepared for
Monsanto Chemical Company by Golder Associates, Inc., Redmond, WA.
Golder Associates, Inc. (Golder). 2008. Second Five-Year Review Report for Groundwater Conditions at the
Monsanto Soda Springs Plant. July.
Golder Associates, Inc. (Golder). 2013. Source Area Characterization - UBZ-2, Phase 1, Monsanto Soda Springs
Idaho Plant. July.
Golder Associates, Inc. (Golder). 2015. Report on Domestic Well Survey and Water Quality Sampling, Monsanto
Soda Springs Plant, ID. April.
Golder Associates, Inc. (Golder). 2016. Phase II UBZ-1 Source Area Characterization, Monsanto Soda Springs
Idaho Plant. May.
Golder Associates, Inc. (Golder). 2018a. 2017 Summary Report on Groundwater Conditions, Monsanto Company
Soda Springs, Idaho Plant. May.
Golder Associates, Inc. (Golder). 2018b. Soda Creek Sediment Sampling and Analysis, Fourth CERCLA Five-
Year Review. May.
Golder Associates, Inc. (Golder). 2018c. Off-Site Soil Sampling Report, Fourth CERCLA Five-Year Review. May.
Idaho Department of Fish and Game (IDFG). 2018. Caribou County Observation List. Accessed July 11, 2018.
https ://idfg .idaho. gov/species/taxa/list/countv/caribou.
U.S. Census Bureau. 2010. United States Census Bureau. Accessed June 11, 2018. http://www.census.gov/.
U.S. Environmental Protection Agency (EPA). 2017. Technical Review Comments, 2016 Summary Report on
Groundwater Conditions at the Monsanto Soda Springs Idaho Plant. Submitted to Monsanto Chemical
Company. July.
U.S. Environmental Protection Agency (EPA). 2013. Third Five-Year Review Report For Monsanto Chemical
Co. (Soda Springs Phosphorous Plant) Superfund Site Caribou County, Idaho. Prepared by CH2M HILL,
Boise, Idaho. Prepared for U.S. Environmental Protection Agency, Region 10, Seattle, Washington,
August.
U.S. Environmental Protection Agency (EPA). 2008. Second Five-Year Review Report for Monsanto Chemical
Co. (Soda Springs Plant). EPA ID: IDD081830994. Caribou County, Idaho. Prepared by U.S. EPA
Region 10, Seattle, Washington. August.
U.S. Environmental Protection Agency (EPA). 2006. Freshwater Sediment Screening Benchmarks.
https://www.epa.gov/sites/production/files/2015-Q9/documents/r3 btag fw sediment benchmarks 8-
06.pdf.
U.S. Environmental Protection Agency (EPA). 2003. Guidance for Developing Ecological Soil Screening Levels
(Eco-SSLs). OSWER Directive 92857-55.
U.S. Environmental Protection Agency (EPA). 1997. EPA Superfund Record of Decision: Monsanto Chemical
Co. (Soda Springs Plant) EPA ID: IDD081830994, OU 01, Soda Springs, Idaho. 04/30/1997.
-------
Appendix B: Public Notice
-------
® FPA Cleanup Review Underway
Monsanto Chemical Go. Soda Springs Plant
Public Input Welcomed
EPA Would Like Your Feedback
The 2018 review for Monsanto Seda Springs Plant is now underway and scheduled to be completed
by September. EPA reviews Super-fund sites every five years to assess cleanup progress and identify
any additional actions that might be needed. As part of the review, EPA would like to hear from the
community. If you have anything you would like us to consider during our review or if you have
questions, please contact Kathryn Cerise, EPA Project Manager, no later than July 1,2018.
Evaluation of Cleanup Measures
The Monsanto Soda Springs Plant is an active phosphate processing facility. Soils and groundwater
were contaminated with hazardous chemicals including radium-226 in soil, and fluoride, cadmium,
manganese, nitrate, and selenium in groundwater. The cleanup actions for the soil contamination
at the site are complete. The plan for groundwater is to control the suspected-sources of
contamination, then allow the groundwater to recover naturally. Regular sampling and monitoring
of groundwater track the results. This is referred to as "monitored natural attenuation." Data show
decreasing levels of contamination but not as fast as expected. Since the last review in 2013,
additional studies have been done to learn why contaminants in groundwater are not decreasing
at the rates originally expected. Information from these studies will be included in the 2018
Monsanto Five-year Review Report out in September.
Contact EPA: Kathy Cense EPA Project Manager, at cerise.kathryn@epa.gov
or 206-553-2589 or toll free 800-424-4372 ext. 2589.
For. more information:
Visit the site page: https://www.epa.gov/superfund/morisanto-soda-spririgs
2017 EPA Selenium Fact Sheet: https://semspub.epa.gov/src/document/10/100049057
2013 Monsanto 3rd Five-Year Review: https://semspub.epa.gov/src/document/lp/690731
Visit the library: Soda Springs Public Library, 149 S. Main, 208-547-2606
TDD and/or TTY users may call the Federal Relay Service at 800-877-8339.
Please give the operator phone number 206-553-2589, for Kathryn Cerise.
-------
Appendix C: Site Inspection Checklist
-------
Five-Year Review Site Inspection Checklist
I. SITE INFORMATION
Site name: Monsanto Chemical Company, Soda
Springs Phosphorous Plant
Date of inspection: June 6,2018
Location and Region: Soda Springs, ID, Region X
epa id: IDD08180994
Agency, office, or company leading the five-year
review: EPA/CH2M Hil l
Weather/temperature: Sunny, 70s
Remedy Includes: (Check all that apply)
~ Landfill cover/containment
~ Access controls
X Institutional controls
~ Groundwater pump and treatment
~ Surface water collection and treatment
~ Other
Attachments: ~ Inspection team roster attached ~ Site map attached
II. INTERVIEWS (Check all that apply)
1. O&M site manager Jason Maughan Regulatory Specialist June 6,2018
Name Title Date
Interviewed X at site ~ at office ~ by phone Phone no. 208-240-1540
Problems, suggestions; ~ Report attached
4. Other interviews (optional) ~ Report attached.
III. ON-SITE DOCUMENTS & RECORDS VERIFIED (Check all that apply)
1.
O&M Documents
~ O&M manual ~ Readily available ~ Up to date
~ As-built drawings ~ Readily available ~ Up to date
~ Maintenance logs ~ Readily available ~ Up to date
Remarks: O&M I ncludes annual surface water and groundwater sampling
~ N/A
~ N/A
~ N/A
2.
Site-Specific Health and Safety Plan ~ Readily available ~ Up to date
X Contingency nlan/cmcnicncv rcsnonsc nlan ~ Readilv available ~ Ud to date
Remarks: Monsanto plant (active facility) has ERP.
~ N/A
~ N/A
3.
O&M and OSHA Training Records X Readily available ~ Up to date
Remarks: Site is active nhosnhorous nlant. No rcnortablcs.
XN/A
X Monitored natural attenuation
~ Groundwater containment
~ Vertical barrier walls
C-l
-------
OSWER No. 9355.7-03B-P
4.
Permits and Service Agreements
X Air discharge Dermit X Readilv available
X Ud to date
~ N/A
X Effluent discharge X Readilv available
X Ud to date
~ N/A
X Waste disposal, POTW X Readily available
~ Other permits ~ Readily available
Remarks
~ Up to date
~ Up to date
~ N/A
~ N/A
5.
Gas Generation Records ~ Readilv available ~ Up to date X N/A
Remarks
6.
Settlement Monument Records ~ Readily available
Remarks
~ Up to date
XN/A
7.
Groundwater Monitoring Records X Readilv available ~ Up to date ~ N/A
Remarks: CoDies of annual GW and SW annual reDorts keDt on site and available for review.
8.
Leachate Extraction Records ~ Readily available
Remarks: Manage solids from environmental control svstem.
~ Up to date
XN/A
9.
Discharge Compliance Records
X Air ~ Readilv available
~ Ud to date
~ N/A
X Water (effluent) ~ Readilv available
~ Ud to date
~ N/A
Remarks: KeDt on site and available for review
10.
Dailv Access/Securitv Logs X Readilv available ~ Up to date ~ N/A
Remarks: Site is active 24-7. fenced/gated, and has sign in/sign out and full-time securitv staff
C-2
-------
IV. O&M COSTS
1.
O&M Organization
~ State in-house ~ Contractor for State
X PRP in-house X Contractor for PRP
~ Federal Facility in-house ~ Contractor for Federal Facility
~ Other
2.
O&M Cost Records
~ Readily available ~ Up to date
X Funding mechanism/agreement in place
Original O&M cost estimate: Not Available
From_ Jan2013_ To Dec. 2013 $165,159.61 ~ Breakdown attached
Date Date Total cost
From_ Jan2014_ ToDec. 2014 $136,057.20 ~ Breakdown attached
Date Date Total cost
From Jan 2015 To _Dec2015_ $148,166.29 ~ Breakdown attached
Date Date Total cost
From_Jan2016 To_Dec2016 $119,509.00 ~ Breakdown attached
Date Date Total cost
From_Jan2017 ToDec. 2017 $171,000.00 ~ Breakdown attached
Date Date Total cost
3.
Unanticipated or Unusually High O&M Costs During Review Period
Describe costs and reasons: None to reDort
V. ACCESS AND INSTITUTIONAL CONTROLS ~ Applicable ~ N/A
A.
Fencing
1.
Fencing damaged ~ Location shown on site map ~ Gates secured X N/A
Remarks: Monsanto maintains fences.
B.
Other Access Restrictions
1.
Signs and other security measures ~ Location shown on site map X N/A
Remarks: Monsanto maintains signs. Onlv access is through front sate via securitv guards.
C-3
-------
OSWER No. 9355.7-03B-P
C. Institutional Controls (ICs)
1. Implementation and enforcement
Site conditions imply ICs properly implemented X Yes ~ No ~ N/A
Site conditions imply ICs being fully enforced X Yes ~ No ~ N/A
Type of monitoring (e.g., self-reporting, drive by) Self monitored. Restrictive Deeds in Place,
conducted domestic well survey to confirm no use of impacted groundwater.
Frequency: Continuous
Responsible party/agency: PRP (Monsanto), Greenfield Environmental Trust, DEQ, EPA.
Contact Jason Maughan Regulatory Specialist June 6,2018
Name Title
Date
Phone no.
Reporting is up-to-date
~ Yes
~
No
XN/A
Reports are verified by the lead agency
~ Yes
~
No
XN/A
Specific requirements in deed or decision documents have
been met
~ Yes
~
No
XN/A
Violations have been reported
~ Yes
~
No
XN/A
Other problems or suggestions: ~ Report attached
2. Adequacy X ICs are adequate ~ ICs are inadequate ~ N/A
Remarks
D. General
1. Vandalism/trespassing ~ Location shown on site map X No vandalism evident
Re marks
2. Land use changes on site X N/A
Remarks: The site is an active phosphorous processing facility, continued production will result in
additional UFS, slag, SQ2, treater dust, coke as part of processing. Otherwise, plant continues
normal operations.
3. Land use changes off siteD N/A
Remarks: Still farming surrounding buffer property within IC boundary.
VI. GENERAL SITE CONDITIONS
A. Roads X Applicable ~ N/A
1. Roads damaged ~ Location shown on site map X Roads adequate L N/A
Remarks
C-4
-------
B.
Other Site Conditions
Remarks Continue fugitive dust control, discontinued MsCL for dust control, plot tested
cover materials for plants on UFS piles.
VII. LANDFILL COVERS ~ Applicable
XN/A
A.
Landfill Surface
1.
Settlement (Low spots) ~ Location shown on site map
Areal extent Depth
Remarks
~ Settlement not evident
2.
Cracks ~ Location shown on site map
Lengths Widths Depths
~ Cracking not evident
Remarks
3.
Erosion ~ Location shown on site map
Areal extent Depth
Remarks
~ Erosion not evident
4.
Holes ~ Location shown on site map
Areal extent Depth
Remarks
~ Holes not evident
5.
Vegetative Cover ~ Grass ~ Cover properly established ~ No signs of stress
~ Trees/Shrubs (indicate size and locations on a diagram)
Remarks
6.
Alternative Cover (armored rock, concrete, etc.) ~ N/A
Remarks
7.
Bulges ~ Location shown on site map
Areal extent Height
Remarks
~ Bulges not evident
C-5
-------
OSWER No. 9355.7-03B-P
8.
Wet Areas/Water Damage
~ Wet areas
~ Ponding
~ Seeps
~ Soft subgrade
Remarks
~ Wet areas/water damage not evident
~ Location shown on site map Areal extent
~ Location shown on site map Areal extent
~ Location shown on site map Areal extent
~ Location shown on site map Areal extent
9.
Slope Instability ~ Slides
Areal extent
Remarks
~ Location shown on site map ~ No evidence of slope instability
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.)
1.
Flows Bypass Bench
Remarks
~ Location shown on site map ~ N/A or okay
2.
Bench Breached
Remarks
~ Location shown on site map ~ N/A or okay
3.
Bench Overtopped
Remarks
~ Location shown on site map ~ N/A or okay
C.
Letdown Channels ~ 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 off of the landfill
cover without creating erosion gullies.)
1.
Settlement ~ Location shown on site map ~ No evidence of settlement
Areal extent Depth
Remarks
2.
Material Degradation ~ Location shown on site map ~ No evidence of degradation
Material type Areal extent
Remarks
3.
Erosion ~ Location shown on site map ~ No evidence of erosion
Areal extent Depth
Remarks
C-6
-------
4.
Undercutting ~ Location shown on site map ~ No evidence of undercutting
Areal extent Depth
Remarks
5.
Obstructions Type
~ Location shown on site map
Size
Remarks
~ No obstructions
Areal extent
6.
Excessive Vegetative Growth Type
~ No evidence of excessive growth
~ Vegetation in channels does not obstruct flow
~ Location shown on site map Areal extent
Remarks
D.
Cover Penetrations ~ Applicable ~ N/A
1.
Gas Vents ~ Active ~ Passive
~ Properly secured/locked ~ Functioning ~ Routinely sampled ~ Good condition
~ Evidence of leakage at penetration ~ Needs Maintenance
~ N/A
Remarks
2.
Gas Monitoring Probes
~ Properly secured/locked ~ Functioning
~ Evidence of leakage at penetration
Remarks
~ Routinely sampled ~ Good condition
~ Needs Maintenance ~ N/A
3.
Monitoring Wells (within surface area of landfill)
~ Properly secured/locked ~ Functioning ~ Routinely sampled ~ Good condition
~ Evidence of leakage at penetration ~ Needs Maintenance ~ N/A
Remarks
4.
Leachate Extraction Wells
~ Properly secured/locked ~ Functioning
~ Evidence of leakage at penetration
Remarks
~ Routinely sampled ~ Good condition
~ Needs Maintenance ~ N/A
5.
Settlement Monuments ~ Located ~ Routinely surveyed ~ N/A
Remarks
C-7
-------
OSWER No. 9355.7-03B-P
E.
Gas Collection and Treatment ~ Applicable ~ N/A
1.
Gas Treatment Facilities
~ Flaring ~ Thermal destruction ~ Collection for reuse
~ Good condition^ Needs Maintenance
Remarks
2.
Gas Collection Wells, Manifolds and Piping
~ 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
1.
Outlet Pipes Inspected ~ Functioning ~ N/A
Remarks
2.
Outlet Rock Inspected ~ Functioning ~ N/A
Remarks
G.
Detention/Sedimentation Ponds ~ Applicable ~ N/A
1.
Siltation Areal extent Depth ~ N/A
~ Siltation not evident
Remarks
2.
Erosion Areal extent Depth
~ Erosion not evident
Remarks
3.
Outlet Works ~ Functioning ~ N/A
Remarks
4.
Dam ~ Functioning ~ N/A
Remarks
C-8
-------
H. Retaining Walls ~ Applicable ~ N/A
1.
Deformations ~ Location shown on site map ~ Deformation not evident
Horizontal displacement Vertical displacement
Rotational displacement
Remarks
2.
Degradation ~ Location shown on site map ~ Degradation not evident
Remarks
I. Perimeter Ditches/Off-Site Discharge ~ Applicable ~ N/A
1.
Siltation ~ Location shown on site map ~ Siltation not evident
Areal extent Depth
Remarks
2.
Vegetative Growth ~ Location shown on site map ~ N/A
~ Vegetation does not impede flow
Areal extent Type
Remarks
3.
Erosion ~ Location shown on site map ~ Erosion not evident
Areal extent Depth
Remarks
4.
Discharge Structure ~ Functioning ~ N/A
Remarks
Vm. VERTICAL BARRIER WALLS ~ Applicable XN/A
1.
Settlement ~ Location shown on site map ~ Settlement not evident
Areal extent Depth
Remarks
2.
Performance MonitoringType of monitoring
~ Performance not monitored
Frequency ~ Evidence of breaching
Head differential
Remarks
C-9
-------
OSWER No. 9355.7-03B-P
IX. GROUND WATER/SURFACE WATER REMEDIES ~ Applicable UN/A
A.
Groundwater Extraction Wells, Pumps, and Pipelines ~ Applicable X N/A
1.
Pumps, Wellhead Plumbing, and Electrical
~ Good condition^ All required wells properly operating ~ Needs Maintenance ~ N/A
Remarks: Extraction wells operating as part of RI/FS activities; continue to collect data on water quality
improvements.
2.
Extraction System Pipelines, Valves, Valve Boxes, and Other Appurtenances
~ Good condition^ Needs Maintenance
Remarks
3.
Spare Parts and Equipment
~ Readily available ~ Good condition^ Requires upgrade ~ Needs to be provided
Remarks
B. Surface Water Collection Structures, Pumps, and Pipelines ~ Applicable X N/A
1.
Collection Structures, Pumps, and Electrical
~ Good condition^ Needs Maintenance
Remarks
2.
Surface Water Collection System Pipelines, Valves, Valve Boxes, and Other Appurtenances
~ Good condition^ Needs Maintenance
Remarks
3.
Spare Parts and Equipment
~ Readily available ~ Good condition^ Requires upgrade ~ Needs to be provided
Remarks
C-10
-------
C. Treatment System ~ Applicable X N/A
1. Treatment Train (Check components that apply)
~ Metals removal ~ Oil/water separation ~ Bioremediation
~ Air stripping ~ Carbon adsorbers
~ Filters
~ Additive (e.g., chelation agent, flocculent)
~ Others
~ Good condition ~ Needs Maintenance
~ Sampling ports properly marked and functional
~ Sampling/maintenance log displayed and up to date
~ Equipment properly identified
~ Quantity of groundwater treated annually
~ Quantity of surface water treated annually
Remarks
2. Electrical Enclosures and Panels (properly rated and functional)
~ N/A ~ Good condition^ Needs Maintenance
Remarks
3. Tanks, Vaults, Storage Vessels
~ N/A ~ Good condition^ Proper secondary containment ~ Needs Maintenance
Remarks
4. Discharge Structure and Appurtenances
~ N/A ~ Good condition^ Needs Maintenance
Remarks
5. Treatment Building(s)
~ N/A ~ Good condition (esp. roof and doorways) ~ Needs repair
~ Chemicals and equipment properly stored
Remarks
6. Monitoring Wells (pump and treatment remedy)
~ Properly secured/locked ~ Functioning ~ Routinely sampled ~ Good condition
~ All required wells located ~ Needs Maintenance ~ N/A
Remarks
D. Monitoring Data
1. Monitoring Data
X Is routinely submitted on time X Is of acceptable quality
2. Monitoring data suggests: some COCs are stable, some are migrating
~ Groundwater plume is effectively contained ~ Contaminant concentrations are declining
C-ll
-------
OSWER No. 9355.7-03B-P
D.
Monitored Natural Attenuation
1.
Monitoring Wells (natural attenuation remedy)
X ProDerlv secured/locked X Functioning X Routinely samDled X Good condition
X All reauired wells located ~ Needs Maintenance ~ N/A
Remarks: Monitoring well network samDled and maintained annually.
X. OTHER REMEDIES
If there are remedies applied at the site which are 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.
No other remedial actions for soils, air, surface water, sediment. 5YR monitoring required for
sediment and off-site soil.
XL 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 to accomplish (i.e., to contain contaminant plume,
minimize infiltration and gas emission, etc.).
Remedy is in place to monitor migration of COCs downgradient and to evaluate if COC
concentrations are declining (attenuating) and groundwater plumes are stable or decreasing.
Concentrations of some COCs have not decreased as originally expected and continue to migrate.
In particular, selenium has been identified in southern property wells at concentrations above the
MCL. In addition, remaining sources of COCs were identified during source area investigations.
These could be contributing to ongoing COC detections. Additional remedies appear to be
warranted to address remaining source areas and also COC behavior in groundwater. Pilot testing
and groundwater aquifer testing are being conducted to evaluate the effectiveness of a change in
the remedy.
B.
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 protectiveness of the remedy.
No issues identified with O&M. Annual surface water and groundwater monitoring continues to
track COC trends.
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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 protectiveness of the remedy may be
compromised in the future.
No issues identified with O&M
D.
Opportunities for Optimization
Describe possible opportunities for optimization in monitoring tasks or the operation of the remedy.
PRP added additional water level monitoring points i.e transducers, and constructed
additional monitoring wells to characterized COC distribution and optimize data
collection.
C-13
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