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Responsive ■ Resourceful ■ Reliable 1 05157640l12 rev south imp. well cert
GROUNDWATER MONITORING SYSTEM CERTIFICATION -
REVISED
WALTER SCOTT JR. ENERGY CENTER
COAL COMBUSTION RESIDUAL SOUTH SURFACE IMPOUNDMENT
POTTAWATTAMIE, IOWA
Terracon Project No. 05157640
January 30, 2018
1.0 INTRODUCTION
The South Surface Impoundment is an existing coal combustion residual (CCR) surface
impoundment that receives materials from the Walter Scott Jr. Energy Center (WSEC) facility.
Both the WSEC facility and the South Surface Impoundment are located in Pottawattamie
County, Iowa. The location of the WSEC facility and the South Surface Impoundment are
depicted on the attached Figure 1. The impoundment receives and stores wet sluiced CCR
materials which include bottom ash, economizer ash, and boiler slag. Wastewater streams
that are discharged to the impoundment include ash transport water, polisher wastewater,
demineralization neutralizer wastewater, economizer ash hydrovactor water, boiler tube and
air heater cleaning water, and pH adjusted demineralizer water. The impoundment has no
spillways, but water from the impoundment is circulated back to the WSEC facility. The South
Surface Impoundment is classified as an existing, unlined CCR surface impoundment.
On April 17, 2015, the United States Environmental Protection Agency (USEPA) issued the
final version of the CCR rule for regulation and management of CCR materials at coal-fired
units under subpart D of the Resource Conservation and Recovery Act (RCRA). The Federal
CCR rule (40 CFR, Part 257) became effective on October 19, 2015 and applies to the WSEC
South Surface Impoundment.
As required by the Federal CCR rule 40 CFR 257.91 the owner or operator of the CCR unit must install a groundwater monitoring system that consists of a sufficient number of wells, installed at appropriate locations and depths, to yield groundwater samples from the uppermost aquifer that meet the following requirements:
▪ Accurately represent the quality of background groundwater that has not been affected
by leakage from a CCR unit,
▪ Accurately represent the quality of groundwater passing the waste boundary of the
CCR unit.
On October 15, 2017, a Groundwater Monitoring System Certification for the South Surface
Impoundment CCR Unit was placed in the operating record, which included nine monitoring
Groundwater Monitoring System Certification - Revised WSEC CCR South Surface Impoundment ■ Council Bluffs, Iowa January 30, 2018 ■ Terracon Project No. 05157640
Responsive ■ Resourceful ■ Reliable 2 05157640l12 rev south imp. well cert
wells MW-5R, MW-9R, and MW-18 through MW-24. Since submittal of the Groundwater
Monitoring System Certification, evaluation of groundwater analytical data indicate the
possibility that MW-9R may not accurately represent the quality of background groundwater.
Monitoring well MW-133, which is a background well associated with the nearby Monofill CCR
unit, was selected to be incorporated into the monitoring system of the South Surface
Impoundment CCR unit. Incorporation of monitoring well MW-133 into the site monitoring
system meets the requirements of 40 CFR 257.91(a) for a background well for the South
Surface Impoundment CCR unit.
The Groundwater Monitoring System Certification - Revised incorporates the monitoring well
network (MW-5R, MW-9R, MW-18 through MW-24, and MW-133) that will be used during
groundwater sample collection events for monitoring the South Surface Impoundment CCR
unit. The monitoring well network at the South Surface Impoundment meets the general
requirements of the Federal CCR Rule as outlined in 40 CFR 257.91 for groundwater
monitoring system certification. The following sections in this report provide support of the
certification.
2.0 SITE HYDROGEOLOGY SUMMARY
The WSEC South Surface Impoundment (site) is located in the Missouri River Valley near
Council Bluffs, Iowa. A Hydrogeologic Investigation Report (HIR) dated September 2006 was
prepared for the nearby Monofill CCR site (located approximately a half mile to the southwest
of the South Surface Impoundment) which details geology and hydrology for the Monofill CCR
site. As indicated in the HIR, layers of sands, silts, and clays are found at the site which are
consistent with alluvial flood plain deposits. There were no confining units identified in site
borings, and vertical hydraulic gradients were minor in the aquifer. The alluvial aquifer is
considered a contiguous unit with a single water table. Bedrock was not encountered in a
boring that was drilled at the Monofill CCR site to a depth of approximately 117 feet below
ground surface (bgs), however, bedrock at the site is believed to be Pennsylvanian-age shale
or limestone. Based on previous groundwater monitoring event data collected from May 2016
through October 2017, the water table has an average elevation of approximately 960 feet
above mean sea level (amsl) at the site. Groundwater flow at the site is generally to the west
based on interpolation of groundwater elevation data collected during monitoring events from
May 2016 through October 2017.
Groundwater Monitoring System Certification - Revised WSEC CCR South Surface Impoundment ■ Council Bluffs, Iowa January 30, 2018 ■ Terracon Project No. 05157640
Responsive ■ Resourceful ■ Reliable 3 05157640l12 rev south imp. well cert
3.0 GROUNDWATER MONITORING SYSTEM
Based on the hydrogeologic information collected from the site and the location of the CCR
South Surface Impoundment, the groundwater monitoring system consists of one up-gradient
well (MW-9R), three down-gradient wells (MW-5R, MW-18, and MW-19), one cross-gradient
well (MW-21), two cross- to up-gradient wells (MW-22 and MW-23), two cross- to down-
gradient wells (MW-20 and MW-24), and one background well (MW-133). The location of
monitoring wells MW-5R, MW-9R, and MW-18 through MW-24 are depicted on the attached
Figure 2. The location of monitoring well MW-133 relative to the South Surface Impoundment
CCR unit is depicted on the attached Figure 1. Details regarding the groundwater monitoring
system for the South Surface Impoundment CCR unit are summarized on the attached Table
1.
TABLE 1
WALTER SCOTT JR. ENERGY CENTERCOAL COMBUSTION RESIDUAL SOUTH SURFACE IMPOUNDMENT
POTTAWATTAMIE COUNTY, IOWATERRACON PROJECT NO. 05157640
GROUNDWATER MONITORING WELL SYSTEM
Top Bottom
MW-5R 984.46 34.9 959.6 - 949.6 Down-gradientMW-9R 972.26 17.8 964.5 - 954.5 Up-gradientMW-18 978.89 37.7 956.2 - 941.2 Down-gradientMW-19 980.08 37.9 957.2 - 942.2 Down-gradientMW-20 980.59 34.0 961.6 - 946.6 Cross- to Down-gradientMW-21 979.76 40.0 954.8 - 939.8 Cross-gradientMW-22 980.24 27.0 968.8 - 953.8 Cross- to Up-gradientMW-23 986.69 38.6 963.1 - 948.1 Cross- to Up-gradientMW-24 982.30 38.8 958.5 - 943.5 Cross- to Down-gradient
MW-133 970.71 25.5 955.3 - 945.3 Background
Notes:TOC = Top of casing.BTOC = Below top of casing.ft = Feet.ID = Identification.NAVD88 = North American Vertical Datum, 1988.1Installed Depth
Screened Interval
(ft NAVD 88) Classification
Well ID TOC(ft NAVD 88)
TotalDepth (ft
BTOC)1
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