NCD980602163_19980303_Warren County PCB Landfill_SERB C_Phase II Detoxification Projects - Comments on Draft Preliminary Design Report-OCR

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March 3, 1998
.. NORTH CAROLINA DEPARTMENT OF
ENVIRONMENT AND NATURAL RESOURCES
DIVISION OF WASTE MANAGEMENT
TO: £; Mike Kelly, Deputy Director, Division of Waste Management
FROM:(ifl/ Ed Mussler, P.E., Environmental Engineer, Solid Waste Section
RE: U Comments on Draft Phase II Preliminary Design Report
I have reviewed the draft of the Phase II report on detoxification of the PCB
landfill. The following comments and observations are offered.
1. Page 5-The 60 inches of compacted clay liner was installed according to
the project specifications and the construction quality assurance (CQA)
tests showed the in-place vertical permeability to be less than the specified
lx10·7 cm/sec. It is not of unknown permeability.
2. Page 6-The compacted clay barrier in the cap is not of unknown
permeability. The compacted clay barrier was installed according to the
project specifications and the construction quality assurance (CQA) tests
showed the in-place vertical permeability to be less than the specified
lx1Q·7 cm/sec. Testing performed in the spring of 1997 confirmed the
permeability to be on the order of 1 o-s cm/sec.
3. The report references using the sedimentation basin to hold process water.
Provisions will need to be made to line the basin. In its current state it does
not retain water for any extended period of time.
4. Page 20-The paragraph is awkward and makes no reference to the 12 inch
general fill layer, under the 12 inch vegetative layer, until the next
paragraph. A total of 48 inches of material will be removed and stockpiled.
5.. In reference to the PVC liner, future plans should include invitations to
study the liner. It is unusual that liner is exposed after so long a period of
use. Valuable information could be gained from its study.
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6. It would be interesting to see a break down of the expected number of samples that will
be analyzed and the anticipated cost. Would it be more cost effective to construct a lab on
site or in Warrenton? Savings in result tum around times, transportation, shipping would
be achieved as well as providing training to local residents. Perhaps there is space at a
local community college that would benefit from the program and experience.
Laboratory wastes such as excess soils and solvents could be returned to the site for
treatment in the BCD process, thus eliminating the cost of disposal in a hazardous waste
facility.
7. 3.6.3.1-It is stated that dewatering is not necessary. Previously the report states that
moisture content plays a large role in determining the cost and time of treatment. Would
the site benefit from dewatering, if possible, during the start up period?
8. What will be done with the filter fabric that is removed from the top of the leachate
collection system?
9. Page 41-for final design it is recommended that the design storm for determining the
stormwater separation berms be changed to a 25year-24 hour storm. This is more
conservative, and is required in our MSW rules.
10. 3.7.1-page 44-The bottom liner should be punctured to allow drainage and prevent the
"bathtub" effect.
11. Page 45-With reference to the final cover; If the landfill has been detoxified then
containment would no longer be necessary and just sufficient cover to support vegetation
would be necessary. If it is determined that it would be prudent to put some form of
engineered cover back over the detoxified soil, then the proposed cover is not sufficient.
While it does meet the regulatory minimum for an unlined MSW landfill in North
Carolina, six inches of vegetative cover is inadequate to support a healthy stand of grass.
Since the existing clay barrier and 24 inches of vegetative cover has been removed and
stockpiled, then they should be used to recap the landfill.
12. 5.1-What would be the unit cost to treat additional or excess material? What would be the
parameters to trigger an increase in quantities? What additional site investigations are
envisioned. Is it necessary to put a cost for additional site investigation into the money
request? Will it be necessary to directional drill under the landfill?
13. The cost analysis assumes that 60,000 tons of material are to be treated. Is this a wet
weight, dry weight, and where does the estimate originate from?
14. Appendix G-technical specifications for the synthetics will be needed, as well as CQA for
their installation.
15. Drawing PD3-The top cross section includes a layer of sand and filter fabric which will
be removed and treated. This should be revised.
16. The conceptual plans for using geosynthetics are not permittable. Fabrics would be
·_:_-~d~d on top of the liners. A minimum of three feet of material would likely be
nefessary to prevent damage to the membrane from the heavy equipment traffic. A
"tattletale" of net or sacrificial synthetic should be placed six to nine inches from the top
to indicate when the cover has been diminished. It is likely that a fabric would be
necessary to lay the road coarse base on. Is it necessary to line the clean road?