GROUND WATER & SOURCE WATER
PROTECTION:
STRUCTURAL & NON-STRUCTURAL CONTROLS FOR
EFFECTIVE MANAGEMENT OF SALT STORAGE PILES
Presented to the Ground Water
Protection Council Annual Forum
September 25, 2001 - Reno, NV
BRUCE M. BERTRAM
Salt Institute
JIM M. WOLF, P.E.
IMC Salt, Inc.
Overland Park, KS
Bruce Bertram
became the Technical Director of the Salt Institute in 1985. His responsibilities include
environmental-regulatory, safety & health, production and transportation, highway
deicing, standards and specifications, and other technical issues affecting the salt
industry. Mr. Bertram began his career with
the International Salt Company serving in a number of engineering, plant management, and
regulatory affairs positions with International Salt and its successor, Akzo Nobel Salt. He has a B.S. in geological engineering from
Michigan College of Mining & Technology and a M.S. in business administration from
Michigan Technological University. Mr.
Bertram has written a number of technical papers about salt issues. He participates in committee activities as a
member of several professional societies and industry associations, including American
Chemical Society, American Public Works Association, American Society for Testing and
Materials, American Water Works Association, National Association of County Engineers, and
the Water Quality Association.
Jim Wolf is the
Manager of Environment for IMC Salt - a division of IMC Global. IMC Salt produces sodium chloride from natural
mineral deposits through underground, solar, and injection mining/evaporation processes. Mr. Wolf provides multi-media environmental
oversight for IMC Salt's 11 North American manufacturing plants and 55 distribution
facilities. He has 15 years of environmental
experience and is a chemical engineering graduate of Kansas State University. Prior to IMC, Mr. Wolf was employed within the
hazardous waste remediation and disposal industry where he worked in engineering and
technical management capacities at a Part-B permitted TSD facility in Atlanta, GA and
coordinated CERCLA-cleanup, RCRA-closure, and related remediation projects in the
Southeast U.S.
ABSTRACT
The use of roadway deicing salt is
necessary to maintain high levels of winter safety and mobility on streets and highways
throughout the North American snowbelt. Because
its use is restricted to the winter months, large salt storage piles must be maintained by
salt producers at distribution sites. Such
distribution piles vary in size and may contain more than 100,000 tons of salt. The distribution piles provide public and private
winter maintenance agencies with the salt inventory necessary to supplement their limited
storage capabilities. Public and private
winter maintenance agency piles vary in size from 100 tons up to 15,000 tons.
Strategically
located salt storage facilities with adequate capacity ensure prompt and reliable delivery
of salt for roadway application during periods of high demand created by unpredictable and
severe winter weather conditions. Salt
storage pile size and location raise environmental concerns, particularly for storm water
runoff that may impact ground water and local surface waters. This presentation/paper provides a comprehensive
review of structural and non-structural measures for effective management of salt storage
piles.
Structural
measures are engineered systems and controls that include fixed and permanent enclosures,
impermeable storage pads, waterproof covers, berms or curbing for containment and
drainage, discharge systems, etc. Non-structural
measures are best management practices or procedural controls for pile construction, pile
configuration, pile shaping, pile covering, cover maintenance, housekeeping, salt
reclamation, storm water runoff management, etc.
For the Forum
presentation, the authors shall provide a comprehensive review of acceptable controls
observed during a collective 43 years of experience in the salt industry. The presentation will be in a PowerPoint format
and include pictorial examples of controls from various salt storage sites. In addition, a brief review of applicable federal
and state regulatory requirements will be provided along with a substantial amount of
resource materials for effective management of salt storage piles. This paper is the text that will be used as the
basis for the presentation.
* * * * * * * * * * * * * * *
Introduction
The use of roadway deicing salt is
necessary to maintain high levels of winter safety and mobility on streets and highways
throughout the North American snowbelt. Deicing
salt is produced from underground halite deposits through conventional underground mining
techniques, and by solar evaporation of seawater or natural brine.
A significant percentage of the deicing
salt produced in North America is shipped from the production sites to distribution
locations using water transportation - lake vessels and river barges. Shipment activity occurs in the spring, summer,
and autumn. Water access becomes severely
restricted in the winter months due to freezing conditions.
Consequently, large distribution stockpiles of salt are placed at port and
terminal facilities along the Great Lakes and navigable inland river waterways. These stockpiles range in size from 2000 tons up
to 350,000 tons. The average size for a
typical distribution pile is 40,000 tons.
Smaller local stockpiles are
constructed with salt shipped from the distribution stockpiles by truck or from the
production sites by truck or rail. These
smaller stockpiles are located "inland" and closer to the points of use. They range in size from 20 tons up to 20,000 tons. The average size for a typical pile of this type
is 2000-3000 tons.
Potential for Adverse Environmental Impact
In the absence
of appropriate controls, the handling and storage of deicing salt present the potential
for adverse environmental impact. The larger
distribution stockpiles have the potential to adversely impact adjacent surface water
bodies. The smaller inland stockpiles have
the potential to adversely impact local ground water.
The primary means for such impact is through fugitive particulate matter
releases and storm water runoff.
Use of an
empirical relationship for material drop operations1 allows one to estimate the
fugitive particulate matter emissions associated with stockpile construction. For example, for roadway deicing salt conforming
to established standards,2 fugitive particulate matter generated from vessel
unloading activities when constructing a 40,000-ton distribution stockpile is
approximately 320 pounds. Salt particulate
matter tends to be on the upper end of the particle size range and consequently has a
parabolic fallout pattern with minimal drift. In
addition to localized air quality impact, such salt dustfall impacts surface and ground
water through storm water runoff and percolation.
To demonstrate
the potential impact to surface and ground water, consider a 40,000-ton distribution
stockpile having no control measures. A
typical 40,000-ton stockpile located along a navigable river and constructed by barge
shipments will have a footprint of approximately 80,000 sq.ft. A 1" rainfall event on this area will
generate about 49,900 gallons of water. In
utilizing assumptions based on worst case conditions,3 the 1" rainfall
event may dissolve up to 46 tons of salt and generate runoff having a chloride (Cl)
concentration of up to 134,000 mg/l. In
addition to chloride, other pollutants associated with salt dissolution and runoff include
sodium (Na) and total dissolved solids (TDS).
Controls
The selection
and implementation of appropriate controls are critical for the effective management of
salt storage piles. Such controls eliminate,
reduce, and/or limit the potential for adverse environmental impact.
Salt stockpiles
contained within fully enclosed, permanent structural cover provide a best case scenario. Specialty structures such as domes provide optimal
protection from precipitation and eliminate runoff issues.
These structures are costly. For
example, a typical structural cover with a 10,000-ton capacity has a capital cost of
$450,000, and a similar structure with a 100,000-ton capacity has a capital cost of $1
million to $2 million.4 Consequently,
large capacity structures are not feasible for large distribution stockpiles and are often
not feasible for smaller stockpiles owned and operated by public and private entities on
limited budgets.
Public and
private agencies often employ alternate methods of "creative" storage in lieu of
constructed enclosures. Such alternate
methods are subject to local resources and often have restrictions that present
disadvantages. For example, limestone caves
that once served as borrow areas for construction materials and aggregate are sometimes
used for salt storage.6 These
spaces also provide optimal protection from precipitation and eliminate runoff issues. However, logistics, vehicular access and
mobility, and other physical restrictions present disadvantages that compromise the
non-existent or limited capital cost.
An economic
alternative to structural cover and specially-built sheds or buildings is an impermeable
salt storage pad with a non-permanent, flexible stockpile cover consisting of a waterproof
tarp. These limited but adequate structural
controls require implementation and maintenance of complementary non-structural controls,
or best management practices (BMPs). For
example and as a comparison to estimates provided earlier, a 10,000-ton capacity storage
pad would require an initial capital cost of $25,000 to $35,000 and an annual cost of
$2500 for cover installation and disposal.7
Table I below
provides a summary of the comparative costs for salt stockpile storage facilities.
Salt Stockpile Storage Facility
Comparison
(Basis: 10,000-ton capacity, excl. cost
of land)
STRUCTURE TYPE |
CAPITAL COST |
ANNUAL OPERATING COST |
Permanent Structural Cover |
$450,000 |
$0 |
Open End Shed or Building |
$50,000 - $100,000 |
$0 |
Pad with Temporary Cover |
$25,000 - $35,000 |
$2500 |
Best Management Practices (BMPs)
Best management
practices, or BMPs, are standard operating procedures, schedules of activities, and
prohibitions of unfavorable practices that are implemented and maintained. Salt handling and storage BMPs are designed to
minimize potential adverse impact to the environment by the elimination, reduction or
control of: dust, contaminated runoff, leaks, spillage, and drainage from material
handling and storage areas. These BMPs
include product transfer, pile construction, pile configuration, pile shaping, pile
covering, cover maintenance, housekeeping, salt reclamation, and storm water runoff
management.
Various
published and unpublished documents relative to BMPs for deicing salt handling and storage
have been generated by industry and regulatory agencies.
A partial and non-exhaustive list is provided below:
§
"The Salt Storage Handbook,"
Salt Institute - Alexandria, VA, rev. 1997.
§
"Salt Institute Voluntary Salt
Storage Guidelines for Distribution Stockpiles," Salt Institute - Alexandria, VA,
rev. 1998.
§
"Proper Bulk Salt Storage Training
Manual (Based on the Salt Institute Voluntary Salt Storage Guidelines for Distribution
Stockpiles)," Salt Institute - Alexandria, VA, rev. 2000.
§
"Guidelines for Environmental
Management of Depot Stockpiles," IMC Salt - Overland Park, KS, rev. 1999.
§
"Storage Pile Best Management
Practices," Wisconsin Department of Natural Resources - Bureau of Watershed
Management, Publication # WT-468-96, November 1996.
§
"Stockpiling Safety," U.S.
Department of Labor, Mine Safety & Health Administration, National Mine Health &
Safety Academy - Manual No. 30, 1994.
§
"Storm Water Management for
Industrial Activities," U.S. EPA - Office of Water, EPA 832-R-92-006, September 1992.
Salt Storage Pad
Recommended
structural criteria for a salt storage pad should incorporate design, construction,
impermeability, site drainage, pad elevation, and slope.
Evaluation of a proposed salt storage pad location must include an
examination of conditions such as topography, hydrology, and soils to determine potential
environmental impact on ground and surface waters.
Design and construction of an asphalt
storage area require an adequate pad sub-grade thickness to ensure pad integrity and
stability. The pad base and sub-base must be
constructed to achieve the highest durability consistent with asphalt construction
techniques. This is achieved using a base
and/or sub-base composition having an appropriate mixture of coarse aggregate, fine
aggregate, and bitumen. Design and
construction of an asphalt storage area also require an adequate surface or wear layer
thickness to ensure pad impermeability and proper drainage.
The pad surface must be constructed to achieve the lowest permeability
consistent with asphalt construction techniques. This
is achieved using a wear layer composition having an appropriate mixture of fine aggregate
and bitumen.
The pad elevation should be sufficient
so that storm water runoff from the adjacent terrain will not run onto the pad. This is typically accomplished by topographic
elevation differences, curbs or berms along the edge of the pad, or drainage ditches
around the pad perimeter.
The salt storage pad should have a
minimum slope of 0.5% to allow proper drainage of precipitation. This slope may be from end-to-end of the pad. Or, the slope may be along the longitudinal axis
of the pad so as to create a "crown," i.e., sloping away from the centerline in
opposite directions. The pad slope must be
consistent with site-specific salt storage and handling BMPs.
Recommended non-structural criteria or
BMPs for a salt storage pad should incorporate provisions for capacity, working face, and
prevailing wind direction. The structural
criteria for the salt storage pad require consideration of these BMPs.
The storage pad size must be adequate
to contain the quantity of salt that will be placed at the site. The pad size must also be sufficient to provide
for the maneuvering of trucks, loaders, and other equipment.
The storage pad should be configured so
that the working face of the salt stockpile is downwind of the prevailing wind direction. For example, if the prevailing wind direction is
from the northwest, the pad should be configured so that the working face is at the
southeast end of the stockpile. In addition,
and equally important, the working face must be consistent with the pad slope and
prevailing wind direction. For the example
just cited, the up-gradient pad end would be to the northwest; the down-gradient end would
be to the southeast.
Other BMPs relative to the salt storage
area include periodic inspection, maintenance, and repair of the asphalt pad. These activities may include asphalt patching,
crack sealing, etc.
Salt Unloading and Stockpile Construction
Recommended structural criteria for
salt unloading and stockpile construction should incorporate systems for the control of
fugitive particulate matter emissions. Salt
stockpiles may be constructed by self-unloading vessels, crane/clam-shell transfer into a
hopper/conveyor system, truck transfer, or similar type methods. Dust suppression controls should be employed for
such methods. Suggested dust controls include
telescopic chutes or elongated trunks for salt discharge/unloading, enclosure of transfer
points, and controlled water spray/mist systems for rapid transfer activities.
Recommended non-structural criteria or
BMPs for salt unloading and stockpile construction should incorporate procedural
activities and stockpile configuration. A
minimum feasible vertical distance between the salt drop point (e.g., end of conveyor) and
the ground or stockpile should be maintained to reduce the potential for generation of
excessive salt dust. Pile construction should
begin at the up-gradient end of the pad and proceed to the down-gradient end of the pad. There should be established parameters for
suspension of unloading activities. Such
parameters should include excessive wind, excessive precipitation, spillage of salt beyond
the storage pad area, etc. Operators
constructing salt stockpiles from multiple vessels, barges, rail cars, and/or trucks
should minimize the delivery time between transport vehicles. The stockpile configuration should be in
conformance with the pad configuration while preserving salt's natural angle of repose (32
deg.) and maintaining a constant pile width. The
crown, or the top of the stockpile, should be graded so that the slope of the planar
surface is consistent with the slope of the pad, i.e., sloping toward the working face of
the stockpile and toward the down-gradient end of the pad.
Stockpile Cover
The recommended
structural criterion for a salt stockpile within an unenclosed area is the installation of
a waterproof tarp or cover to protect the salt from contact with precipitation. The tarp should have sufficient thickness and
composition for durability purposes - it should be capable of withstanding elevated wind
speed, abrasion, ultraviolet light degradation, etc.
The cover should be secured to the pile using an appropriate tie-down
system. The cover should extend beyond the
edge of the stockpile and this cover "apron" should be secured to the ground
using a suitable anchor system.
Recommended
non-structural criteria or BMPs for stockpile covers should incorporate federal and local
requirements. For instance, EPA has
identified the following covering requirement for salt stockpiles:8
"Storage piles of salt used for deicing or other commercial or industrial purposes
and which generate a storm water discharge associated with industrial activity which is
discharged to waters of the United States shall be enclosed or covered to prevent exposure
to precipitation, except for exposure resulting from adding or removing materials from the
pile." Because of this, large salt
stockpiles should be constructed in stages and likewise covered in stages. Other BMPs relative to stockpile covering
activities include periodic inspection, maintenance, and repair of the cover system. The covers are sometimes damaged by abatement of
tie-down or anchor systems, excessive winds, wear and tear, vandalism, etc. Prompt corrective action ensures the integrity of
the stockpile cover.
Outbound Salt Shipping From the Pile
Controls
relative to reclamation of salt from the stockpile are largely non-structural as opposed
to structural. These are essentially
procedural "do's" and "don'ts" for equipment operators conducting
outbound salt shipment activities. Initiation
of salt reclamation from the stockpile should occur at the down-gradient end of the
pile/pad. The removal of the stockpile cover
at the working face should be limited to accommodate the anticipated daily shipment
tonnage. The working face should be
maintained perpendicular to the long axis of the pile by loading alternately left to right
and right to left. The distance between the
working face and the outbound vehicles during loading activities should be minimized. Housekeeping exercises should be conducted on a
frequent basis and should include crushing and blending of any salt chunks back into the
pile, sweeping of tailings back toward the working face, etc.
Permit(s) and Pollution Prevention Plan
An operator of a
salt storage site should review federal and local environmental regulations to determine
potential permit applicability and comply accordingly with any such requirements. Regardless of permit applicability, the operator
should implement and maintain a written pollution prevention plan for the salt storage and
handling activities. This plan should be
based on the protection of ground water, surface water, and air quality. The plan should include structural controls and
BMPs.
Environmental Regulation
The U.S.
Environmental Protection Agency and some State agencies have developed regulations or
requirements for salt handling and storage. As
noted above, an operator of a salt storage site should review federal and local
environmental regulations to determine potential permit applicability and comply
accordingly with any such requirements.
The EPA
requirements for salt storage have been promulgated under the Clean Water Act (CWA).9 The CWA regulations contain programs for storm
water management.10 Within these
programs, EPA has identified storm water provisions for salt storage piles in the General Permit Program for Storm Water Discharges
Associated with Industrial Activity11 and in the Storm Water Multi-Sector General Permit Program.12 Both of these permit programs require
implementation of select BMPs and development and maintenance of a Storm Water Pollution
Prevention Plan.
Among the State
agencies that have developed requirements relative to salt handling and storage are, for
example, Michigan13 and Wisconsin.14
These two States have promulgated regulations that are more extensive than
EPA's minimum requirements under the CWA storm water program. In the absence of specific regulatory
requirements, salt industry voluntary guidelines provide the basis for environmentally
sound salt storage and handling with minimum potential for environmental impact. Operators of salt handling and storage sites are
encouraged to implement and maintain site-specific structural controls and BMPs that
provide protection for ground water, surface water, and air quality.
Salt Institute Resources
The Salt
Institute (Alexandria, VA) is the association of the major North American and
international salt producers. IMC Salt is one
such member of the Salt Institute. Many
member companies produce rock salt and solar salt for deicing roadways during the winter
months. The Salt Institute has developed a
number of programs for salt producers and end users to ensure environmentally responsible
management of salt handling, storage and use. The
Salt Institute has also amassed numerous resources developed by other public and private
groups. All information is available on the
Salt Institute's web page at www.saltinstitute.org.
Conclusions
There are a
variety of structural controls for effective management of salt storage piles. Costs associated with such structural controls are
highly variable. Salt producers and public
and private salt storage operators often construct and maintain salt storage areas with
limited but adequate structural controls in conjunction with complementary non-structural
controls, or BMPs. Storage facilities of this
type present an economic alternative to permanent structural cover and open-end storage
sheds and buildings while still affording protection for ground water and source water.
BMPs include procedures, activities,
and practices for the elimination, reduction or control of: dust, contaminated runoff,
leaks, spillage, and drainage from material handling and storage areas. Operators of salt handling and storage sites are
encouraged to implement and maintain site-specific structural controls and BMPs that
provide protection for ground water, surface water, and air quality. Ineffective implementation and maintenance of
controls by the industry and deicing salt end users may result in increased regulatory
requirements for salt handling and storage. There
is an abundance of literature, training publications, and audio/visual materials, etc.
relative to salt storage structural controls and BMPs.
A good starting point for a comprehensive review of such resources is the
Salt Institute - Alexandria, VA.
Footnotes
1 Compilation
of Air Pollutant Emission Factors - Volume 1: Stationary Point & Area Sources (AP-42),
U.S. Environmental Protection Agency, EPA-454/C-95-001, 5th ed., Section
13.2.4.3 - Predictive Emission Factor Equations.
2
ASTM (American Society for Testing and Materials) D-632-00 or AASHTO (American Association
of State Highway and Transportation Officials) M-143-86.
3 The
stockpile was not enclosed or covered. Rainfall
on the stockpile was assumed to become saturated with salt.
All rainfall was reported as runoff.
4
Salt Institute (2001).
5
Ibid.
6
Example: EcoSpace Business Park, Louisville Underground, Inc. - Louisville, Kentucky.
7 IMC
Salt (2001).
8 57
FR 41311 (9/9/92): EPA General Permit for Storm Water Discharges Associated with
Industrial Activity - Guidance for Developing Pollution Prevention Plans and Best
Management Practices.
9 PL 92-500, 33 USC 1251 et
seq.
10 40
CFR Part 122.26.
11 57
FR 41236 (9/9/92).
12 60
FR 50804 (9/9/95).
13
Michigan Surface Water Quality Division, Water Resources Protection - General Rules, Part
5: R323.1157 through R323.1169.
14
Wisconsin Department of Transportation - Chapter Trans 277.