Cliffside PT Work Plan 7-31-20 FINAL

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CAP Pilot Test Work Plan
Cliffside Steam Station (July 2020)
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ENERGY

Introduction/Work Plan Objectives
Selected Remedy Design Overview
Pilot Test Basis of Design
Pilot Test Data Collection Objectives
Implementation Schedule

Pilot test represents a significant (-30%) portion of overall full-scale system corrective action
implementation
Work Plan describes pilot test implementation and data collection objectives and activities
Flow rates, area of hydraulic influence, and well spacing
Constituent of Interest trends
Applied to full-scale system to optimize performance
Ob'ectivr-
Accelerate the corrective action process to meet applicable groundwater standards
Focus the pilot test on the most challenging areas at the Site to make immediate progress
Optimize the full-scale corrective action system performance based on data collected
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Ash excavation source removal part of corrective action
plan
All excavated CCRs to be placed in onsite lined
Industrial Landfill
Ash excavated in 2020 and Q1 2021 to be placed in
active Phases I and II
Phase III construction estimated completion in Q1 2021
Phase IV construction estimated complete in Q2 2021
Area 2 excavation estimated to occur in 2021 (see
figure)
Area 3 excavation estimated to occur 2021 — 2023 (see
figure)
Area 3 — Proximate to groundwater remediation system
Figure 1: Excavation Areas
Cliffside Excavation Plan
May 29, 2020

Proposed Monitoring Well Proposed Source Control Area Extraction
Well
Existing Monitoring Well Approximate Ash Basin Waste Boundary
— ■ ■ Geographic Limitation
Proposed Full Seale Extraction Well - . Cliffside Steam Station Property Line
Pilot TeSA
12 groundwater extraction wells and 10
source control extraction wells
in the vicinity of the Unit 5 Ash Basin
150-ft long shallow French drain and
lining of existing stormwater ditch
Total Combined Extraction Rate: 35 gpm
Full-Scat&-
23 extraction wells, 1 horizontal well,19
new monitoring wells, and 46 infiltration
wells near the Active Ash Basin/Ash
Storage Area
6 new monitoring wells, 22 extraction
wells and a lined ditch in the vicinity of
the Unit 5 Ash Basin
1 new monitoring well and 285 tree wells
by the Former Units 1-4 Ash Basin
Proposed Pilot Test Extraction Well
Proposed Clean Water Infiltration Well
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12 groundwater extraction
wells, 110 to 142 ft total
depth, water level
maintained near top of
bedrock
. i 5
10 source control extraction wells, 35 ft deep,
water level maintained at 25 ft depth
PUM TeO
�* Design is based on the results of dozens of flow and
4 transport simulations including capture zone analysis
` Bedrock depth is shallow (-10 to 40 ft) in southern area
I Node
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near Cooling Tower B.
10 source control wells are designed to capture low pH
plume that is believed to have resulted in mobilization
of COIs.
It is expected that the low pH will be return to
background levels after the source is controlled.
12 groundwater extraction wells are designed to
capture COls near and beyond Geographic Limitation.
p Y
The groundwater extraction wells target the saprolite
and transition zone. The boreholes may extend into
r the upper bedrock to facilitate pump and equipment
installation and maintenance. These wells create a
f cone of depression that is below the elevation of the
h Broad River to ensure capture of COls.
While clean water infiltration is proposed for
remediation of vadose zone boron in the Active Ash
Basin, vadose zone boron does not appear to be an
'I .0 issue in the U5 area, so clean water infiltration is not
,3 proposed at this time
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D_r I . esign Details.—
Remediation Goals Meet applicable groundwater criteria at and beyond the Geographic Limitation. Applicable standards are
North Carolina groundwater standards (02L Standards; IMACs; or BTVs, whichever is greater).
Design Objectives/Approach Achieve groundwater extraction rate of -35 gpm to establish groundwater draw-down/capture zone,
based on modeled extraction well spacing of-30-150 feet.
• Pressure transducers with PLC control set points in each well will automate pump cycling to maintain
targeted draw -down.
• Extracted groundwater pumped to existing conveyance that routes to the Basement Basin, then to the
wastewater treatment system and is ultimately discharged at NPDES Outfall 005.
Instrumentation/Controls Controls Requirements - minimize complexity, include fail safes to prevent spills/equipment damage
and over pressurization, allow for automated operation and remote monitoring.
• Groundwater extraction well pump controls, well level/flow monitoring equipment, water collection tank,
and secondary containment all contained within node buildings to facilitate operations and maintenance,
and winterization.
Vertical Extraction Wells • Pilot test design includes 22 vertical extraction wells, 6" diameter (10" borehole), each including'/2-1 HP
electric submersible pumps and pressure transducers to automate pump cycling.
• Modeled individual extraction well flow rates ranging from 0.6-2.7 gpm.
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Overall goal: Generate data needed to verify and refine the design and operation of the full-scale
groundwater corrective action system
Data collection will focus on performance monitoring to verify conceptual design details, including:
Well Capacity - During development of the newly installed extraction wells, specific capacity (flow rate divided by
drawdown) will be analyzed to select a group of extraction wells for further hydraulic testing.
Area of Hydraulic Influence and Connectivity - Data will be collected within areas of extraction well installation
(focus areas) and select hydraulic testing areas to verify hydraulic parameters, and horizontal and/or vertical
hydraulic gradient control.
C01 Concentration Reduction - C01 concentration data from historical and pilot test monitoring results will be
utilized to evaluate C01 concentration trends and to estimate concentration reduction achieved by hydraulic
influence.
Hydrogeology Verification and Constructability - Data will be collected during the pilot test to verify subsurface
conditions and to test well constructability and will be used to adjust the full-scale extraction well and/or clean
water infiltration well design locations.
s

Permits
■ Erosion and Sediment Control Permit
(June 2020) —Approved
■ Groundwater Recovery Well Permit (July
2020) — 4pproved
■ NPDES Permit (May 2020) —Notification
letter submitted, existing permit in place
Schedule (Estimated Completion Dates
■ Well installation —August 2020
■ System Installation Contracting — September 2020
■ Pilot System Construction complete — March 2021
■ Pilot System Start-up — March 2021
■ EMP Implementation/Pilot Test Data Collection —
on -going following start-up
■ Pilot Test period up to six months
■ Scale -up Activities — TBD
■ Ash excavation must be completed in Active Ash
Basin Area to initiate CAP activities in that area
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