POTENTIAL USES OF RELATIVELY LOW-PERMEABILITY LINER SYSTEMS IN
PIT LAKE ENVIRONMENTS
Joe Jersak, Ph.D., CPSS 1; John Hull, P.E., D.E.E.1; and Phil Hutton, P.G.2
Introduction
Liners, also referred to as caps or barriers, are used in naturally occurring lakes, rivers,
streams, and estuaries where contaminated sediments occur to fulfill one or more functions:

Physically isolate contaminated sediments from the aquatic community (sedimentdwelling invertebrates, fish, etc.);

Stabilize and provide erosion protection for contaminated sediments, preventing their
resuspension and transport to other downstream sites; and/or

Chemically isolate and reduce movement of dissolved and sediment-bound
contaminants by advective and/or diffusive transport processes.
To date, granular materials (e.g. sand and gravel) have often been used to cap sediments.
While sands and gravels can be effective at many sites, such materials are relatively
permeable, chemically non-reactive, and can be eroded in energetic sediment
environments.
Finer-grained materials (clays) are generally recognized as lowerpermeability, more reactive, and more cohesive (erosion-resistant), and thus appropriate
candidates for capping materials. However, difficulties in effective placement of such finergrained materials have, until relatively recently, precluded their use in capping contaminated
sediments.
AquaBlok™ is a patented, composite-aggregate technology resembling small stones and
comprised of a central core (often stone aggregate), clay or clay sized materials (the
sealant layer), and polymers. This particular clay based material, largely because of its
implementability and unique performance attributes, is gaining increased attention within the
“contaminated sediment community” (e.g. US EPA 2000; US EPA 2004a; US Navy 2000).
For typical freshwater formulations, the clay component usually consists largely of sodium
bentonite clay. Other types of clay materials, including attapulgite (palygorskite), can
instead be incorporated into the product for saline applications. A large variety of other
reactive minerals or materials can also be used to amend basic product formulations for
specific purposes. Such amendments may include, but are not limited to: organoclays,
gypsum, carbonates, zeolites, elemental sulfur, oxides, zero-valent iron, organic substrates,
plant seeds, nutrients, and microbes. Other technology parameters, such as relative clay
content or core density, for example, can also be modified as needed.
Typical AquaBlok use generally involves placing dry masses of product through water and
across the target surface. In several days, the material hydrates and expands, with the
layer of initially discrete particles coalescing into a homogeneous and relatively cohesive,
low-permeability cap, or barrier, between the impacted material and the overlying water
column.
1
2
AquaBlok, Ltd., 3401 Glendale Ave., Ste. 300, Toledo, Ohio 43614; phone (800) 688-2649; email services@aquablokinfo.com
Hull & Associates, Inc., 707 Skokie Blvd., Ste. 600, Northbrook, Ill 60062; phone (847) 291-4321; email phutton@hullinc.com
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To address one or more cap functions in sediment environments, AquaBlok barrier designs
have ranged from relatively simple monolayers to more involved composite designs. Some
composite barrier designs may include geotextile, topsoil, organic media, and/or armor
components. The nature and complexity of cap design will depend on project goals and site
conditions.
Potential Uses for Liners in Pit Lake Environments
Full-scale use of AquaBlok as a liner material in impacted sediment environments has been
successfully demonstrated (www.aquablokinfo.com). Thus, this clay based liner material
could also potentially be applicable in pit lake environments as well. However, it is clearly
recognized that environmental problems related to typical impacted sediment environments
– not to mention the physical, hydraulic/hydrologic, chemical, biological, and other
environmental characteristics related to such environments – are not the same as those
problems and characteristics unique to pit lake environments. It is with this recognition,
then, that several questions must first be posed:
1) Does the concept of liner use, in general, have potential relevance to pit lake
environments?
2) If “yes”, would clay based liner materials, like AquaBlok, have particular advantages
over granular liner materials in such environments?
3) And, if “yes” still, are their physical or other characteristics inherent to pit lakes
(including unique limnological characteristics) that could limit or restrict the
implementability or effective use of liner materials?
To begin answering these questions, it is instructive to first identify some of the
environmental problems associated with many pit lake environments, and then evaluate
whether or not liner use may – at least conceptually speaking - help solve the problem(s).
Table 1 (below) provides a listing of such typical problems and conceptual liner based
solutions (or functions). For clarification, the nature and extent of environmental problems
at a given pit lake site and the potential applicability of liner-based solution(s) will obviously
depend on project goals and site-specific conditions, including whether a particular lake is
characterized as “terminal” or “flow-through”.
General Performance Attributes of AquaBlok
The intention of this paper is not to tell the “pit lakes community” that a clay based liner
solution can and will solve all of their problems, especially considering perceived or real
challenges posed by the uniqueness of their systems (e.g. steep side walls, great lateral
expanses, extensive water depths, etc.). No one should know better than the community
itself whether or not remedial solutions involving liners are, or could be, applicable to pit
lake systems.
Instead, the goal here is to introduce one particular clay based liner technology to the pit
lakes community, and outline some of the material’s recognized attributes. In so doing,
researchers, site managers, and regulators working with pit lake systems can decide if such
liner materials may be appropriate.
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ENVIRONMENTAL PROBLEM
ASSOCIATED WITH PIT LAKES
CONCEPTUAL SOLUTION (OR FUNCTION)
PROVIDED BY CLAY BASED LINER
Place liner across sulfide-bearing wall-rock areas to minimize
exposure to atmospheric oxygen. If significant geologic
heterogeneity, selective placement of liner only over sulfidic areas
allows for: (1) continued hydraulic communication/equilibrium
between surface and groundwaters; and possibly (2) continued
buffering of surface waters from continued exposure of non-sulfidic
(e.g. carbonate-bearing) areas.
A
Exposure of sulfide-bearing geology in
wall rock to atmospheric oxygen.
B
Subsequent oxidation of sulfide materials
and generation of sulfuric acid, dissolved
metals, and sulfate.
Once exposed to oxygen, little can be done to minimize oxidation
and generation of sulfuric acid and dissolved metals. However,
impact could be lessened overall by other positive long-term
effects of liner placement.
C
Translocation of acidic, metal-rich
solutions from sulfidic wall-rock areas into
pit lake surface waters.
Low-permeability liner should significantly limit advective/
diffusive flux.
D
Negative impacts of acidic, metal-rich
solutions translocating from wall-rock
areas into pit lake surface waters.
Liner material, either in non-amended or amended form, could: (1)
neutralize acid influxes; (2) promote precipitation of some dissolved
metals in higher-pH liner environment; (3) promote formation and
precipitation of metal-sulfide complexes by amending liner material
with sulfides, nutrients, a carbon source, and even microbes; and/or
(4) fix dissolved metals to clay surfaces within liner material.
E
Infiltration of acidic, metal-rich surface
waters into underlying groundwater
resources.
Liner across lake bottom could significantly reduce flux of degraded
surface waters into adjacent groundwaters (and surface waters)
while maintaining hydraulic communication/equilibrium between
surface waters and adjacent (unlined) wall-rock areas.
F
Resuspension of acidic, sulfidic, and/or
metal-rich sediments from lake bottom into
water column as result of turnover and
wind-driven mixing of water column.
Liner across lake bottom could stabilize sediments, minimizing
their resuspension into - and thus potential impacts to - overlying
water column.
G
Surface water runoff of degraded surface
and/or groundwaters into adjacent creeks,
streams, lakes, etc.
Liner will do little to address this issue directly. However, effect
may be lessened overall by other positive long-term effects of
liner placement.
H
Lack of adequate faunal & floral habitat
in littoral areas due to degraded water
quality, sediment quality and/or sediment
abundance.
Improvement of surface-water quality could occur overall as result
of other positive long-term effects of liner placement, as described
herein. Liner material could also serve as substrate/habitat in
littoral areas. SubmerSeedTM (i.e. seed-amended AquaBlok
product) could also enhance or create beneficial vegetative habitat.
I
Ecological impacts of degraded water
and/or sediment quality on existing fauna
and flora.
Ecological impacts could be lessened by liner material serving as
surrogate substrate/habitat in littoral areas, and by other positive
long-term effects of liner placement.
J
Evaporative concentration of acids,
metals, and salts in pit lake surface waters.
Liner will do little to address this issue directly. However, effect of
this process may be lessened overall by other positive long-term
effects of liner placement. Saline-compatible liner material may be
most appropriate in some cases.
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Summarized below are selected attributes of the AquaBlok technology – attributes that
could be applicable to a variety of subsurface and subaqueous environments – including pit
lakes.
Flexibility in Product Formulation and Liner Design
AquaBlok formulations can be designed or amended for specific application to pit lakes (e.g.
Table 1, item D). Non-amended or amended product can then be incorporated into a
variety of liner designs to fulfill particular functions, as appropriate.
Flexibility in Product Manufacture, Handling, and Placement
AquaBlok can either be manufactured on site, or manufactured elsewhere and shipped to
the site in various ways (in packaged or bulk form). The most appropriate manufacture
scenario will depend on various factors including: site location, availability of on-site facilities
and other support infrastructure, availability of local rail lines and spurs, location of raw
materials, relative costs, etc.
Once manufactured and ready for use at a site, AquaBlok can be placed using a variety of
commonly available equipment and technologies. The most appropriate placement method
for a given project and site will depend of various factors including: water or shoreline
access, surface water characteristics, size of the project area, relative costs, etc.
With respect to liner placement on steep side-wall areas: AquaBlok has been placed on
relatively steep (2:1) slopes at sediment sites, using geosynthetic materials (e.g. GeoWeb)
to help stabilize the product in place (www.aquablokinfo.com). It is recognized that many
wall-rock areas may be steeper still, and may present additional placement challenges. The
appropriateness and practicality of, and need for, liner placement in such portions of a pit
lake site should be evaluated on a site-by-site basis.
Low Permeability
As expected, freshwater (bentonite-based) product formulations of various gradations and
clay contents display very low permeabilities to freshwater circum-neutral permeants in the
laboratory, on the order of 10-9 cm/s. Permeability of bentonite-based formulations to
brackish waters is also low, at or below 10-7 cm/s, although increases are observed with
increasing salinity, due in large part to increased effective porosity resulting from increased
clay flocculation; the use of clay blends or attapulgite may be more appropriate for many
saline environments. As a note, laboratory derived permeability values vary somewhat as a
function of cell pressures and hydraulic gradient at testing, independent of formulation and
salinity levels.
Some published literature indicates that bentonite- and attapulgite-bearing environmental
barriers can also display low permeability values, on the order of 10-7 to 10-8 cm/s, upon
infiltration of highly acidic permeants (pH 2.4 to 3.0) (e.g. Ahtchi-Ali and Casper 1997;
Kashir and Yanful 2000, 2001). However, still other researchers (Shackelford 1994) note
that low-pH solutions may instead promote clay flocculation and increases in hydraulic
conductivity. Regardless, most workers agree that the ultimate effect of acid permeants on
barrier permeability (or hydraulic conductivity) is the collective function of many factors,
including: clay content, confining stress, substrate buffering capacity (including the potential
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for formation of secondary mineral precipitates and pore-space infilling), changes to
physical fabric, etc.
It is also worth noting that bentonite-bearing materials can still display low permeabilities –
on the order of 10-8 cm/s - even while their ability to neutralize the acidic permeants is highly
limited (e.g. Kashir and Yanful, 2000). This has particular relevance to the use of bentonitebased liners in pit lake environments.
Ability to Neutralize Acids and Fix Some Dissolved Metals
As indicated above, an ability to buffer (or neutralize) strong acids is not requisite for lowpermeability environmental barriers to be effective. Nevertheless, even non-amended
AquaBlok material can neutralize strong acids to some degree, probably because of trace
carbonates in the sodium bentonite. For example, non-amended material can increase the
pH of a sulfuric acid solution (initially pH 3.0) to circum-neutral values (up to 7.2) over a
relatively short (five-day) period. The material’s ability to neutralize strong acids appears to
depend in large part on the acid : AquaBlok ratio (by weight), with the rate and degree of pH
increase – as measured in the overlying water column and not within the saturated liner
material per se - inversely proportional to the acid : AquaBlok ratio.
The potential for long-term, “passive” neutralization of acidic lake waters due to placement
of a clay based liner needs to be investigated, and we are currently conducting such
research. Regardless of the outcome of this work, however, liner placement across the
bottom of a pit lake and/or across selected sulfidic wall-rock areas may significantly reduce
periodic/seasonal resuspension of acidic (or acid producing) bottom sediments, or reduce
acid fluxes from wall-rock areas, thereby potentially resulting in long-term improvements to
surface water quality, including pH neutralization.
In addition to reduced metal solubility and mobility through liner materials because of
increased pH, the high surface-area characteristics of montmorillonitic clay (dominant clay
component of sodium bentonite) also provides for significant adsorption of many dissolved
metal species, thus also actively attenuating their movement through liner material.
Ability to Serve as a Vector for Delivery of Treatment Materials (Amendments)
As indicated above, one or more treatment materials can be added to AquaBlok’s sealant
layer to serve a variety of functions, over and above the low permeability demonstrated by
non-amended product. Such treatment materials could include:

Carbonate or other basic minerals – to help neutralize acidic solutions;

Elemental sulfur, nutrients (N, P), a labile carbon source, and even microbes – to
collectively provide for microbially mediated precipitation of metal sulfides within the
liner material; and

Wetland plant seeds, organic substrates – to provide high-quality habitat for fauna
and flora in littoral zones.
The concept of incorporating one or more treatment agents or materials into liner materials
for the purpose of creating “active caps” - designed to actively treat mobilized and
contaminated pore waters migrating into and through barrier material - is currently being
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demonstrated at one particular impacted sediment site located on the Anacostia River in
Washington, D.C. (US EPA 2004; HSRC/S&SW 2004). AquaBlok is included in this field
demonstration, and is also the exclusive focus of a US EPA SITE program project currently
being conducted at the same site.
Summary
The AquaBlok liner technology - by virtue of its many attributes and as successfully
demonstrated at a number of contaminated sediment sites – could have applicability in
solving one or more of the environmental problems unique to pit lake environments. To this
end, we welcome at least conceptual-level consideration of the technology and its potential
uses by pit lake researchers, site managers, and regulatory agencies.
References
Ahtchi-Ali, F. and Casper. 1997. Effect of Acidic Leachate on Material Degradation of Slurry
Trench Cutoff Walls, In: International Containment Technology Conference Proceedings,
February 9-12, 1997, St. Petersburg, FL, pp 78-84.
Hazardous Substance Research Center/South & Southwest (HSRC/S&SW). 2004.
Research Brief #28, Site Characterization and Cap Placement Activities in Anacostia River
Active Capping Demonstration, July 2004.
Kashir, M. and E. Yanful, 2000. Compatibility of Slurry Wall Backfill Soils With Acid Min
Drainage, Advances in Environ. Research, Vol. 4: pp. 251-268.
Kashir, M. and E. Yanful, 2001. Hydraulic Conductivity of Bentonite permeated with Acid
Mine Drainage, Can. J. Geotech./Rev. Can. Geotech. Vol. 38, No. 5. pp. 1034-1048.
Shackelford, C. 1994. Waste-Soil Interactions that Alter Hydraulic Conductivity, In:
Hydraulic Conductivity and Waste Contaminant Transport in Soil, ASTM STP 1142, D.
Daniel and S Trautwein (editors), pp 111-168.
US EPA, 2002. Contaminated Sediment Remediation Guidance for Hazardous Waste Sites,
OSWER 9355.0-85 DRAFT, November 2002.
US EPA, 2004a. Engineering Performance Standards, Technical Basis and Implementation
of the Residuals Standard (for the Hudson River Site), Vol. 3 of 5, prepared for USACE by
Malcolm Pernie, Inc. and TAMS Consultants, April 2004.
US EPA, 2004b. Active Capping Demonstration on Anacostia River, Technology News and
Trends, Issue 12, May 2004.
US Navy, 2002. Contaminated Sediments at Navy Facilities: Cleanup Alternatives,
NAVFAC TechData Sheet, Naval Facilities Engineering Command, TDS-2092-ENV,
December 2002.’’
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