Memo/Dept. of public Works Enviroment &Energy Division (re-sponses)•
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August 3, 1989
Steve Mielke
Community Development Director
City of Hopkins
1010 First Street South
Hopkins, MN 55343
Dear Mr. Mielke:
Phone: (612) 348 -6846
DEPARTMENT OF PUBLIC WORKS
Environment & Energy Division
822 South Third Street, Suite 300
Minneapolis, Minnesota 55415 -1208
The following are responses to the issues raised from B. A. Liesch and Associates
document review of the Hennepin County Conditional Use Permit application to the
City of Hopkins for temporary storage of HERC process residues at the Bureau of
Public Service facility. The County provides these responses for your review and
distribution to interested parties prior to the August 8, 1989 meeting before the
planning commission.
1. Estimate of truck traffic per day - may be low during load out period...
Is 1/1/90 closure realistic if ash is accepted into December?
Assuming complete use of the facility (20,000 cubic yards capacity), an
average material density of 2000 lbs /cubic yard (1 ton /cubic yard), and a
transport vehicle capacity of 25 tons of material, it is estimated that
800 trips are necessary to completely remove the material from the
facility.
It is anticipated that the ash storage facility at the Woodlake Landfill
in Medina may be available as soon as November 1, which would reduce the
amount of material stored at the Hopkins facility to approximately 12,000
cubic yards. This reduces the number of loadout trips to 480, and could
realistically be accomplished in 15 working days, or approximately three
weeks working eight hours per day on a five day work week, averaging 4
loads per hour. Alternatively, if the number of loads were restricted to
the same frequency as the delivery schedule, or 20 per day, complete
loadout could be accomplished in 24 working days.
Accepting ash up to December 1 would provide approximately 30 days to
close the facility by January 1, 1990, of which 24 days are available to
transport the material using a six day work week. This translates to an
_ HENNEPIN COUNTY
an equal opportunity employer
average of 34 trucks per day, or 4 trucks per hour on a 8 1/2 hour work
day, over a 24 day period to fully accomplish loadout, given the
assumptions used above.
It appears that January 1, 1990 closure would be realizable should
material be accepted up to December 1.
2. Fugitive dust from site during high southwind... What mitigative
measures will be taken or considered?
Wind erosion of exposed ash surfaces are intermittent in nature,
occurring during high wind events. Potential emissions are a function of
moisture content, management practices, and physical characteristics of
the ash after placement. To this end, potential emissions are maximized
by high frequency of high wind speeds, high silt content, high levels of
surfaces exposed to high winds, and low moisture content.
Mitigative measures inherent in this application include elimination of
exposure to winds from all directions except to the south, low silt
content (3 - 5 %) of the material, high expected and designed moisture
content (15 - 22 %; no free moisture) of the material, and low to moderate
amounts of exposed surface available for erosion. Additionally, the
pozzolanic nature of residues from dry scrubbing systems results in
deposited ash forming a hard, nonerodible surface.
It is anticipated that no fugitive emissions will result from high south
wind events due primarily to the physical characteristics of the
material, but the County continues to investigate other mitigative
measures should a fugitive emission be realized, including operational
modifications of the ash handling and conditioning system at the HERC
facility and evaluations of design and installation of a temporary
barrier on the south end of the structure.
3. Leachate Collection
Need description of system. How will it be constructed?
Liner efficiency /calculations /evaluation.
Leachate is not expected to be generated by the storage of the material
since the indoor storage eliminates exposure to precipitation which would
cause leachate formation. Although the material exhibits a moisture
content of 15 - 22 %, there is no free moisture in the material.
Nevertheless, the County intends to construct a small berm - 10" or less
- allowing the transport vehicles and site equipment to gain access to
the facility - on the south side of the facility to help contain any free
liquid or leachate which may be encountered. The general cross section
design is illustrated in Figure 1 below. The liquid will be collected
and contained on site, subjected to appropriate chemical analyses, and
disposed of through approved and permitted methods and facilities.
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- 8 "
10" " � • , � Slope Existing
Base
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Figure 1
South Side Berm Cross - section
Regarding liner efficiencies, liners are designed and intended to control
and minimize the transport of leachate and its associated constituents
out of the containment system. Several factors influence the performance
of a liner system, including the volume of material in place, the
hydraulic head on the liner, the thickness of the liner, the amount of
moisture available and introduced to the waste, the surface area exposed
to precipitation and run -on, the permeabilities of the liner materials,
and the time the leachate is in contact with the liner.
Several aspects of the storage proposal indicate minimum impact on a
liner system. Indoor storage of the material minimizes leachate
formation by eliminating the introduction of moisture to the material.
The material will not be compacted, minimizing any hydraulic head
impinging the bituminous floor. The proposed term of storage is
insufficient to allow transport of any leachate through the floor, as any
free liquids inadvertently present will be discovered with each
subsequent delivery of material, and immediately removed, minimizing the
time liquids or leachate would potentially be in contact with the floor
surface.
Prior to placement of any material in the facility, the County will
conduct a site assessment of the bituminous floor and berm surface, and
perform any necessary repairs to insure the integrity of the surface and
ensure no run -off from the roof or surrounding area enters the storage
area. Following this site assessment and prior to deposition of
material, a sand blanket of up to 4" will be installed, to prevent direct
contact of any material with the floor surface, and facilitate removal
and clean -up efforts after closure. An additional function this sand
blanket will serve is to promote the transport of any free liquids
inadvertently present to the collection point of the facility and
eliminate the possibility of ponding of this liquid on the surface of the
floor.
Calculation of the efficiency of the system is dependent upon the need to
use many assumptions, and most accepted transport models are designed for
systems utilizing natural soil barriers. Furthermore, the application of
some modeling techniques is limited and restrictive, requiring the input
of climatological and geotechnical data presently unavailable to this
project. Additionally, accurate performance of a modeling technique
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requires the measured permeabilities of the materials composing the
liner. Although there is a non - destructive method for applying an ASTM
standard for determining the in -place permeability of bituminous surfaces
(ASTM D 3637), to this date no known applications of this standard for
lining system efficiency studies have been performed in the area. More
traditional permeability studies are less reliable and require
destruction of the in -place surface.
The Minnesota Pollution Control Agency (MPCA) has recognized these issues
regarding the proposal for indoor storage of process residues, and has
also determined that the bituminous floor in the facility is adequate in
construction and design to effectively perform as a lining system to
contain any potential free liquids or leachate from this storage.
Attempts at estimating the performance efficiency of the system would
lead to results which were unreliable and founded on a number of
assumptions.
4. Attachment C Contingency Plan
Need to name emergency coordinators and alternates.
The Attachment C Contingency Plan is the methodology to be followed in
the event of contingency action, and prior to operation of the facility
Emergency Coordinator(s) and alternate(s) will be named and fully trained
in the content and response directives contained in the Plan.
5. Back up facility if Medina is not ready. Is one planned?
Hennepin County continues to explore other alternatives for
storage /disposal capacity, should the Medina facility not be available by
December. The County does not plan at this time to develop a new
facility for this purpose, but rather to utilize (an) existing
facility(ies) capable of providing the necessary services. To this end,
the County is pursuing and maintaining relations with several other
facilities in order to cause a back up facility to be available should
additional capacity be required.
The County does not intend to utilize the Hopkins site for temporary
storage of this material unless they have reasonable expectations that
required approvals and permits will be granted to cause the availability
of another facility by December 1989.
6. Frozen ash - how will it be managed? Will it effect loadout schedule?
The potential for frozen ash having an effect on the loadout schedule is
anticipated to be extremely remote, as operational impacts due to
freezing of the material is expected to be minimal.
Using average climatological data, it is estimated that by January 1 the
exposed surfaces of the material may be permeated by frost to a depth of
approximately twelve to fifteen inches. There are many variables which
will have an effect on the freezing potential of the material, both from
the characteristics of the material as well as the design of the storage
facility. The indoor storage will protect the material from wind and the
elements, eliminate the introduction of precipitation or surface moisture
to the material, provide passive convective heating from the exposure of
sunlight on the expansive black roof surface, and minimize the effects of
phototranspiration from direct exposure to sunlight. The combination of
low surface moisture exposure with moderate temperature buffering will
serve to minimize the degree of freezing. The moisture content of the
material, higher than that of natural soils, will also serve to lower the
frost penetration potential. Additionally, the material possesses
intrinsically high salt concentrations, which inherently lowers the
freezing point below that of natural soils.
In the unlikely event of a freezing problem it is anticipated that the
frozen layer of the material could be easily broken up into manageable
sizes by the use of loadout equipment such as a backhoe.
We thank you for your expeditious review and cooperation in this extremely
important element of the County's solid waste management system, and look
forward to meeting with you on August 8, 1989.
Luther D. Nelson
Division Engineer
cc: Pat Murphy
Tony Jeffries
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7/28/89
Craig Rapp, City Manager
City of Hopkins
- Hopkins, Mn. 55343
JUL 1989
1 1,.._. 31 uLJL)
Dear Craig,
I will not be in Hopkins for the August 7, 1989 storage of ash hearing but
do ,rant to convey to you my feelings about this matter.
I was appalled to read in the Star Tribune that the county is proposing to
temporarily store ash in an open shed on the county grounds adjacent to
our Park Valley neighborhood. According to the paper the "ash contains
toxic substances trapped by the pollution controls and the MPCA requires
it to be disposed of in specially designed landfills."
If it is so dangerous so that it is to be disposed of iri special designed
landfills, why is the county even considering storing it in an open shed,
directly adjacent to a residential neighborhood? The prevailing winds
most of the year are from the north /northwest, which would blow it
directly into our neighborhood. Where does the water drain when the
material is being wetted down 1 would assume into Nine Mile Creek.
The whole proposal is simply bizarre if the MPCA requirements for
disposal of ash are of any significance.
1 also am stunned by Counciimernber Shirley's remark "I em nervous about
always running counter to the county. We need to understand that at times
we need to play a role to do what needs to be done. May 1 remind him he
represents and is responsible to a constituency in Hopkins who depend on
hirrr for protection of health, and property - 1 don't recall that he was
elected by the county to represent the county.
Thank you Craig for your concern and efforts. I would appreciate it if you
would include this letter in your packet to the Hopkins City Council and the
Hennepin County Commissioners.
Sincerely,
Virginia `s Mall
604 5th Ave. S.
Hopkins, Mn. 55343