A
quarterly inspection of the Marjol Battery Site was conducted on June 27, 2012.
Based upon the inspection, Lackawanna County Conservation District (LCCD)
approved moving forward with conversion of the sedimentation basin at the Site
to a stormwater management basin.
Construction activities associated with conversion of the basin
began on July 9, 2012, and were completed on September 12, 2012.
Why did
basin conversion need to be done? The temporary
sedimentation basin was designed to manage sediment that was picked
up in stormwater during construction activities by using structures
such as a baffle and skimmer to encourage sediment to drop out and
stay in the basin. The basin also always had a few feet of water in
it. Once construction activities were complete and vegetation was
sufficiently established at the Site, sediment was no longer picked
up by the stormwater runoff and the controls were no longer needed.
This meant that the basin could be converted to a permanent stormwater management basin which slows down the water but does not
retain it. The sediment control structures are no longer present in
the stormwater management basin.
What was involved
in basin conversion? Basin conversion involved several
steps:
1) The first step was to dewater the sedimentation basin.
2) Once the water was removed from the sedimentation basin, a ramp
was constructed into the basin so that the sediment could be
removed.
3) During basin conversion, the sedimentation basin was
backfilled with about 4 feet of soil to an elevation of 752 ft. The
permanent stormwater management basin was designed as required by
state and local regulations to manage a 2 through 100-year, 24-hour
storm event. In addition, the permanent stormwater basin meets the
Throop Borough Stormwater Management Ordinance that requires that a
minimum 1-foot freeboard is maintained for a 2 through 100-year
storm event.
4) The skimmer was removed from the outlet structure, two
permanent bottom orifice plates were installed on the outlet
structure to allow water to discharge from the basin at a
controlled rate, some additional gabion mattresses were installed
as energy dissipaters at the bottom of both the north and south
channels with additional riprap was placed at the bottom of the
north channel.
5) Finally, topsoil was placed over all disturbed areas and the
areas were seeded and fertilized in order to establish
vegetation.
Was contaminated material disturbed during basin conversion?
During the basin conversion process, disturbance of the contaminated material
that is inside the capped area did not occur. Construction activities for basin
conversion only involved activities in areas and with materials
(soils/sediments) that are “clean” (average lead levels below 500
mg/kg).
How was stormwater managed during the basin conversion process?
During basin conversion, when there was a heavy storm and discharge
from the basin occurred, a turbidity measurement was taken as soon
as practicable (i.e., during the next scheduled working hours). It
was expected that if there was stormwater discharge during the basin
conversion activities, the turbidity level would exceed the 250 NTU
standard that was set for the Site as an indirect measurement of
dissolved lead while contaminated materials were being handled. LCCD,
PADEP, and USEPA were all aware that the turbidity level for the Site
would likely be exceeded when stormwater discharge occurred before
vegetation was established in the basin. It was agreed that while construction
activities were occurring for basin conversion, stormwater discharge
samples would be collected and analyzed for total and dissolved lead
if there was a turbid discharge. (Note: As approved by PADEP, if
there was a multi-day turbid discharge event, a sample would only be collected on the first day of turbid discharge.) Once earth moving
activities were complete and the topsoil was seeded with erosion
control mat in place, no discharge monitoring would take place.
Note: During basin conversion, a discharge sample was collected
on July 27, 2012. See the Stormwater Management System July
calendar page for sample results.
(Click here
to go to the Stormwater Management System July calendar page.)
What happens after
basin conversion (including, how will stormwater be managed post
basin conversion)? Now that basin conversion is completed,
erosion inspections focusing on erosion and sedimentation controls
will continue until permanent vegetation is established on the newly
seeded areas. Once that vegetation is established, Gould will
request an inspection by LCCD to close out the NPDES permit for the
Site. The earliest that this will occur is after the fall growing
season 2012. Until that time, Gould has elected to continue basin
discharge sampling for total and dissolved lead on a monthly basis,
as possible, following heavy rain events. With the change from a
sedimentation basin to a stormwater management basin, stormwater is
no longer stored in the basin and the water can discharge on its own
such that discharge from a storm event may be completed by the time
personnel report to the Site and consequently we may not be able to
obtain samples. Please note, no sampling will take place during a
rain event.
