NC0003417_HF Lee Accellerated remediation 12_4_15 Draft_20160502

H.F. Lee — Accelerated Remediation for Offsite Groundwater Impacts
December 4, 2015 - DRAFT
Background
Groundwater sampling performed for the H. F. Lee active and inactive ash basins CSA found
exceedances of 2L Standards or IMAC for arsenic and boron in monitoring wells east of the active ash
basin and for cobalt, iron and manganese north of the inactive ash basins. The monitoring wells are
located near the property lines in these areas. The CSA also included sampling of groundwater seep
locations along the perimeter ditch east of the active ash basin. Samples collected at these locations
showed exceedances of 2L Standards or IMACs for arsenic, boron, iron, manganese, thallium and
vanadium, and elevated concentrations of total dissolved solids.
Groundwater flow direction is from the active ash basin to the south towards the Neuse River and from
the inactive ash basins to the east to the Neuse River. The receptor survey (included in the CSA)
indicates: 1) there are no private water supply wells located to the east of the active ash basin, and 2)
there are no private water supply wells located between the ash basins and the river, 3) public water lines
service the area.
Additional groundwater monitoring wells and assessment to fully delineate the extent of impacted
groundwater around the active and inactive basins is planned.
Proposed Accelerated Remediation Actions
To address the requirement for accelerated remediation in the recent NCDEQ and Duke Energy
agreement, the following steps are recommended.
• Accelerate installation, sampling and analyses for the data gap wells in these areas.
• Initiate preliminary siting and design for a hydraulic capture (i.e., remediation) system to be
installed to the east of the active ash basin to prevent the migration of impacted groundwater
offsite.
• Abandon the water supply wells located on properties adjoining the north side of the inactive
basins.
• The following hydraulic capture scenarios may be considered for the east side of the active basin.
• Installation of an intercept trench/culvert along the east side of the active basin. Water collected
from the trench would be pumped into the active basin and thereby join the discharge pathway
covered by the site NPDES permit until the closure activities for the active basin begin. At that
time an alternate NPDES discharge option would need to be implemented. The system would be
designed to intercept migration of groundwater in the surficial deposits as it moves from
underneath the ash basin. An existing pump station installed in the perimeter ditch might be
utilized as part of the system.
• Installation of a series of groundwater extraction wells along the east side of the active basin.
Again, the concept is to collect groundwater in the surficial deposits as it migrates from
underneath the ash basin. The option includes long term operation and maintenance of down -well
pumps as well as a system to convey extracted water to the active basin or an alternative outfall
location.
Permits required for these remedial approaches include: Wetlands permitting, NCDEQ recovery well
permits, erosion & sediment control permit, and modification of the NPDES permit.
The conceptual hydraulic control area for the east side of the active basin is shown on the figure
attached.

00
♦/ , INTERCEPTOR TRENCH
APPROXIMATELY 2,850 FT LONG
4
♦� , EXISTING DITCH
14 EQUALLY SPACED EXTRACTION WELLS
(APPROXIMATELY 203.5 ft APART)
--� � ♦ ! III
ACTIVE ASH BASIN
a�
LAY OF LAND AREA (LOLA)
EXISTING PUMP STATION Q
(180 GPM)
'
00
(SOURCE:
APRIL 17, 2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSP
GRAPHIC SCALE FIGURE 1
300 0 300 600
IN FEET ACCELERATED REMEDIATION OPTIONS
148 RIVER STREET, SUITE 220 ACTIVE ASH BASIN
GREENVILLE, SOUTH CAROLINA 29601
PHONE [phone] H.F. LEE ENERGY COMPLEX
www.sRAWNB JOHNCHAST IN 1199 BLACK JACK CHURCH RD
Terra PROJECT MANAGER:
ASTAIN DATE 11/09/2015 GOLDSBORO NORTH CAROLINA
PROJECT IG 1 (ACCEL RE MAHAN
LAYOUT. FIG 1 (ACCEL REMED OPTIONS �
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