location restrictions summary – coal combustion residuals …€¦ · impoundments 1, 2, 3a, and...
TRANSCRIPT
Report
Location Restrictions Summary –
Coal Combustion Residuals Surface
Impoundments 1, 2, 3A, and 3B
Neal North Energy Center
Project I.D.: 18M014.00
MidAmerican Energy Company
Sergeant Bluff, Iowa
April 2020
Location Restrictions Summary – Coal Combustion Residuals
Surface Impoundments 1, 2, 3A, and 3B
Distribution
No. of Copies Sent To
1 (electronic) Elisa Zappacosta – MidAmerican Energy Company
1 (electronic) Jenny Coughlin – MidAmerican Energy Company
Location Restrictions Summary – Coal Combustion
Residuals Surface Impoundments 1, 2, 3A, and 3B
Project ID: 18M014.00
Prepared for
MidAmerican Energy Company
Neal North Energy Centert
Sergeant Bluff, Iowa
Prepared by
Foth Infrastructure & Environment, LLC
April 17, 2020
Copyright©, Foth Infrastructure & Environment, LLC 2020 390 South Woods Mill Road, Suite 325 • Chesterfield, MO 63017 • (636) 728-1034 • Fax: (636) 728-1035 www.foth.com
REUSE OF DOCUMENTS This document has been developed for a specific application and not for general use; therefore, it may not be used without
the written approval of Foth. Unapproved use is at the sole responsibility of the unauthorized user.
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Location Restrictions Summary – Coal Combustion Residuals
Surface Impoundments 1, 2, 3A, and 3B
Table of Contents
Page
Certification ................................................................................................................................... iii
1 Introduction .............................................................................................................................1
2 Location Restrictions ...............................................................................................................2
2.1 Placement above the Uppermost Aquifer ......................................................................2
2.2 Wetlands ........................................................................................................................2
2.3 Fault Areas .....................................................................................................................3
2.4 Seismic Impact Zones ....................................................................................................3
2.5 Unstable Areas ...............................................................................................................3
3 References ...............................................................................................................................5
Appendices
Appendix A USGS Quaternary Faults
Appendix B USGS Seismic Hazard Tool
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1 Introduction
This Location Restrictions Summary was developed for MidAmerican Energy Company (MEC)
Neal North Energy Center (NNEC) Coal Combustion Residuals (CCR) Surface Impoundments
1, 2, 3A, and 3B in accordance with the CCR Rule (40 Code of Federal Regulations [CFR] Part
257).
Impoundment 1 (north) was previously closed by removal of CCR (Iowa Department of Natural
Resources [IDNR] - Doc #86660). Lined non-CCR wastewater ponds were constructed in the
closure by removal area. Impoundments 1 (south), 2, and 3A were previously closed with a final
cover system over in-place CCR in accordance with the CCR rule (40 CFR 257.102(d)).
Construction of the final cover system for Impoundments 1 (south), 2, and 3A was completed in
December of 2017. Impoundment 3B is in the process of closure in accordance with the CCR
Rule.
Pursuant to IDNR permit (Permit #97-SDP-22-16C) revision issued February 18, 2020 (Doc
#97026), the previously permitted closure for Impoundments 1 (south), 2, and 3A, leaving CCR
in place (40 CFR 257.102(d)), was modified to closure by removal of CCR (40 CFR 257.102(c)).
The closure modification for Impoundments 1 (south), 2, and 3A are incorporated in the closure
of Impoundment 3B.
As described in the Closure Plan for Impoundments 1, 2, 3A and 3B (Revision 1), the closure
design includes removal of CCR from Impoundments 1 (south), 2, 3A, and 3B and consolidation
of CCR in the footprint of Impoundment 3B at an elevation above the high groundwater level
observed in 2019. Clean fill soil will be placed at the base of Impoundment 3B to the high water
elevation prior to consolidation of CCR. The consolidated CCR footprint in Impoundment 3B
will capped with a composite cover system.
The intent of the closure design is to ensure that there will not be an intermittent, recurring, or
sustained hydraulic connection between any portion of the base of the CCR unit (i.e. the
consolidated CCR foot print in Impoundment 3B) and the uppermost aquifer due to normal
fluctuations in groundwater elevations (including the seasonal high water table) following
closure of the impoundments in accordance with the revised Closure Plan.
The CCR Rule includes five location restrictions which are specified in 40 CFR 257.60 through
40 CFR 257.64. A qualified professional engineer is required to certify that the location of
Impoundments 1, 2, 3A, and 3B has been evaluated regarding these location restrictions.
Additionally, the summary is to be placed in the Impoundments 1, 2, 3A, and 3B operating
record.
This summary contains a description of the information available to support the location
restrictions demonstration and the assessment of each location restriction. Based on this
assessment, Impoundments 1, 2, 3A, and 3B meet the wetlands, fault areas, seismic impact
zones, and unstable areas location restrictions, but do not meet the placement above the
uppermost aquifer location restriction.
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2 Location Restrictions
2.1 Placement above the Uppermost Aquifer
40 CRF 257.60 Placement above the uppermost aquifer
“existing CCR surface impoundments…must be constructed with a base that is located no less
than 1.52 meters (five feet) above the upper limit of the uppermost aquifer, or must demonstrate
that there will not be intermittent, recurring, or sustained hydraulic connection between any
portion of the base of the CCR unit and the uppermost aquifer due to normal fluctuations in
groundwater elevations (including the seasonal high water table)…”
The rule defines the uppermost aquifer as, “…the geologic formation nearest the natural ground
surface that is an aquifer, as well as lower aquifers that are hydraulically interconnected with
this aquifer within the facility’s property boundary. Upper limit is measured at a point nearest to
the natural ground surface to which the aquifer rises during the wet season.”
The Annual Groundwater Monitoring and Corrective Action Report for Neal North CCR
Impoundment 3B and the Annual Groundwater Monitoring and Corrective Action Report for
Neal North CCR Impoundments 1, 2, and 3A were reviewed to assess groundwater elevation
data.
The uppermost groundwater elevations were above 1,059 feet above mean sea level (ft amsl) and
are within five feet of the minimum elevation (1,064 ft amsl) where CCR was encountered
within the surface impoundments during previous investigations. Therefore, the impoundments
do not meet the separation requirements of CFR 40 257.60.
2.2 Wetlands
40 CFR 257.61 Wetlands
“…existing CCR surface impoundments…must not be located in wetlands, as defined in § 232.2
of this chapter…”
40 CFR 232.2 defines wetlands as “Wetlands means those areas that are inundated or saturated
by surface or ground water at a frequency and duration sufficient to support, and that under
normal circumstances do support, a prevalence of vegetation typically adapted for life in
saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar
areas.”
40 CFR 232.2 states that “waste treatment systems, including treatment ponds or lagoons
designed to meet the requirements of the Clean Water Act are not Waters of the United States.”
Impoundments 1, 2, 3A, and 3B area part of a wastewater treatment system with a National
Pollution Discharge Elimination System (NPDES) permit. As such, and per 40 CFR 232.2, there
are no jurisdiction wetlands within Impoundments 1, 2, 3A, and 3B.
Therefore, Impoundments 1, 2, 3A, and 3B meet the requirements of 40 CFR 257.62.
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2.3 Fault Areas
40 CFR 257.62 Fault areas
“…existing CCR surface impoundments…must not be located within 60 meters (200 feet) of the
outermost damage zone of a fault that has had displacement in Holocene time…”
Fault areas are defined as “…a fracture or a zone of fractures in any material along which strata
on one side have been displaced with respect to that on the other side.” Halocene time means
“…the most recent epoch of the Quaternary period, extending from the end of the Pleistocene
Epoch, at 11,700 years before present, to present.”
The USGS U.S. Quaternary Faults and Folds Database mapping application provides location
information for Quaternary age faults. The USGS database does not show any Quaternary age
faults within 60 meters (200 feet) of Impoundments 1, 2, 3A, and 3B (Appendix A).
Therefore, Impoundments 1, 2, 3A, and 3B meet the requirements of 40 CFR 257.62.
2.4 Seismic Impact Zones
40 CFR 257.63 Seismic impact zones
“…existing CCR surface impoundments must not be located in seismic impact zones…”
A seismic impact zone is “…an area having a 2% or greater probability that the maximum
expected horizontal acceleration, expressed as a percentage of the earth’s gravitational pull (g),
will exceed 0.10 g in 50 years.”
Utilizing the USGS Unified Hazard Tool, the peak ground acceleration for an earthquake with a
probability of occurrence of 2 percent in 50 years was determined to be 0.039g at the site
(Appendix B). This acceleration is associated with Site Class B/C which corresponds to a weak
rock, based on investigations performed at the site, the site is characterized as a Site Class D.
Since Site Class D material is weaker than Site Class B/C, it will cause amplification of the
seismic acceleration. Per approaches put forward in American Society of Civil Engineers ASCE
7-16, the amplification factor for a Site Class D is 1.6 (Appendix B). Utilizing this factor, peak
ground acceleration for this site, for the design earthquake, is 0.062g.
Based on available information provide by USGS and ASCE methodology, the peak ground
acceleration is below the threshold of 0.10g. Therefore, Impoundments 1, 2, 3A, and 3B meet
the requirements of 40 CFR 257.63.
2.5 Unstable Areas
40 CFR 257.64 Unstable areas
“…existing CCR surface impoundments…must not be located in an unstable area…”
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An unstable area is “…a location that is susceptible to natural or human induced events or forces
capable of impairing the integrity, including structural components of some or all of the CCR
unit that are responsible for preventing releases from such unit. Unstable areas can include poor
foundation conditions, areas susceptible to mass movements, and karst terrains.”
In order to determine if an unstable condition exists, consideration of specific factors is required
(40 CFR 257.64(b)). These factors include:
(1) On-site or local soil conditions that may result in significant differential settling;
(2) On-site or local geologic or geomorphologic features; and
(3) On-site or local human-made features or events (both surface and subsurface).
The following documents provide the structural integrity criteria for existing CCR surface
impoundments and were prepared in accordance the CCR Rule (40 CFR 257.73).
♦ Initial Structural Stability Assessment of Neal North Surface Impoundments 1, 2, and 3A
♦ Initial Safety Factor Assessment for Neal North Surface Impoundments 1,2 and 3A
♦ Initial Structural Stability Assessment of Neal North Surface Impoundment 3B
♦ Initial Safety Factor Assessment for Neal North Surface Impoundments 1,2 and 3A
Based on review of the above documents Impoundments 1, 2, 3A, and 3B are not located in an
unstable area. Therefore, Impoundments 1, 2, 3A, and 3B meet the requirements of 40 CFR
257.64.
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3 References
Burns & McDonnell, 2016 Initial Safety Factor Assessment for Neal North Surface
Impoundment 3B. 10 October 2016
Burns & McDonnell, 2016 Initial Structural Stability Assessment of Neal North Surface
Impoundment 3B. 10 October 2016
Burns & McDonnell, 2018. Initial Safety Factor Assessment for Neal North Surface
Impoundments 1, 2, and 3A. 11 April 2018
Burns & McDonnell, 2018. Initial Structural Stability Assessment of Neal North Surface
Impoundments 1, 2, and 3A. 11 April 2018
GHD, 2019. Annual Groundwater Monitoring and Corrective Action Report for Neal North CCR
Impoundment 1, 2, and 3A. 1 August 2019
GHD, 2020. Annual Groundwater Monitoring and Corrective Action Report for Neal North CCR
Impoundment 3B. 31 January 2020.
United States Environmental Protection Agency, 2015. Hazardous and Solid Waste
Management System: Disposal of Coal Combustion Residuals from Electric Utilities; Final Rule
(40 CFR Parts 257 and 261; Federal Register Vol. 80 No. 74). 17 April 2015.
Foth Infrastructure & Environment, LLC, 2020. Closure Plan – Coal Combustion Residuals
Surface Impoundments 1, 2, 3A and 3B. 17 April 2020.
Foth Infrastructure & Environment, LLC
Appendix A
USGS Quaternary Faults
U.S. Geological Survey Quaternary Faults
USGS, National Geographic, Esri, Garmin, HERE, UNEP-WCMC,USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, increment PCorp.
Fault Areas
Historic (< 150 years)
Latest Quaternary (< 15,000 years)
Late Quaternary (< 130,000 years)
Middle and Late Quaternary (< 750,000 years)
Undifferentiated Quaternary (< 1.6 million years)
Quaternary Faults Database
Historic (< 150 years), well constrained location
Historic (< 150 years), moderately constrained location
Historic (< 150 years), inferred location
Latest Quaternary (<15,000 years), well constrained location
Latest Quaternary (<15,000 years), moderately constrained location
Latest Quaternary (<15,000 years), inferred location
Late Quaternary (< 130,000 years), well constrained location
Late Quaternary (< 130,000 years), moderately contrained location
Late Quaternary (< 130,000 years), inferred location
Middle and late Quaternary (< 750,000 years), well constrained location
Middle and late Quaternary (< 750,000 years), moderately constrained location
Middle and late Quaternary (< 750,000 years), inferred location
3/27/2020, 12:58:21 PM0 90 18045 mi
0 150 30075 km
1:5,020,504
USGSNational Geographic, Esri, Garmin, HERE, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, increment P Corp. | USGS |
Foth Infrastructure & Environment, LLC
Appendix B
USGS Seismic Hazard Tool
Two-percent probability of exceedance in 50 years map of peak ground acceleration
0 500 1,000 KILOMETERS
0 500 1,000 MILES
70°80°90°100°110°120°
45°
40°
35°
30°
25°
Areas where suspected nontectonic
earthquakes have been deleted
0.8
0.4
0.3
0.2
0.14
0.1
0.06
0.04
0.02
0
EXPLANATION
Peak acceleration, expressed as
a fraction of standard gravity (g)
Approximate site location
3/27/2020 Unified Hazard Tool
https://earthquake.usgs.gov/hazards/interactive/ 1/2
Uni�ed Hazard Tool
Input
U.S. Geological Survey - Earthquake Hazards Program
Please do not use this tool to obtain ground motion parameter values for the design codereference documents covered by the U.S. Seismic Design Maps web tools (e.g., theInternational Building Code and the ASCE 7 or 41 Standard). The values returned by the twoapplications are not identical.
Edition
Conterminous U.S. 2014 (v4.0.x)
LatitudeDecimal degrees
42.322
LongitudeDecimal degrees, negative values for western longitudes
-96.371
Site Class
760 m/s (B/C boundary)
Spectral Period
Peak Ground Acceleration
Time HorizonReturn period in years
2475
3/27/2020 Unified Hazard Tool
https://earthquake.usgs.gov/hazards/interactive/ 2/2
Hazard Curve
View Raw Data
Hazard Curves
Time Horizon 2475 yearsPeak Ground Acceleration0.20 Second Spectral Acceleration1.00 Second Spectral Acceleration
1e-2 1e-1
Ground Motion (g)
1e-5
1e-4
1e-3
1e-2
Annu
al F
requ
ency
of E
xcee
denc
e
Uniform Hazard Response Spectrum
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Spectral Period (s)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
Grou
nd M
otio
n (g
)
Spectral Period (s): PGAGround Motion (g): 0.0397
International Building Code (IBC) 2012