United States
                 Environmental Protection
                 Agency
                                          Solid Waste and
                                          Emergency Response
                                          (OS-305)
EPA530-F-93-020
August 1993
                 Office of Solid Waste/Office of Waste Programs Enforcement
x°/EPA
                 Environmental
                 Fact  Sheet
                CONTROLLING THE IMPACTS
                OF REMEDIATION ACTIVITIES
                IN OR AROUND WETLANDS
  Remediation of hazardous waste sites
 is accomplished under both the Re-
 source Conservation and Recovery Act
 (RCRA) and the Comprehensive Envi-
 ronmental Response, Compensation,
 and Liability Act (CERCLA or Super-
 fund). The remediation process at RCRA
 and Superfund sites uses a variety of
 technologies on hazardous constituents
 in the air, surface and ground water,
 soils, and sediments. Some of these
 technologies, involve either removal or
 containment, and can be performed in
 situ. Others are implemented through
 excavation, extraction, and in some
 cases, on-site treatment and replace-
 ment. During clean-up operations that
 involve a surface or subsurface recon-
 figuration of a site, pre-existing condi-
                                        tions can be disturbed, and the distur-
                                        bance may result in physical and
                                        chemical changes to the site and to the
                                        adjacent areas. In some cases, the site
                                        or the adjacent areas may contain
                                        wetlands. Special considerations are
                                        warranted when remediation sites are
                                        in or adjacent to wetlands because
                                        clean-up efforts have the potential to
                                        negatively impact a wetland's ecosystem
                                        and its functions.
                                         This fact sheet provides technical
                                        information that can be used to protect
                                        wetlands from the potential negative
                                        impacts caused by the more common
                                        technologies used to remediate
                                        hazardous waste sites.
Waste Excavation and Surface Reconfiguration
  At many sites, contaminated
sediment and debris are excavated,
treated on site (through incineration or
soil washing) and returned to trie
excavated area (e.g., back into a
landfill). In other scenarios, all wastes
removed from the site are disposed of
somewhere else on- or off-site.
                                         Various surface reconfigurations can
                                       result from site activities. Elevations
                                       can be lowered and slopes may be
                                       regraded following excavation. To mini-
                                       mize water contact with exposed con-
                                       taminants and to contain spills, water
                                       may be rechanneled or diverted from
                                       existing drainage patterns and dikes,
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and embankments may be built. Waste
piles may be created to temporarily
store contaminated media for treat-
ment or to store treated media to be
deposited on-site. Stabilization methods
to minimize migration of hazardous
contaminants by reducing surface
infiltration to ground water can include
clay caps or other ground cover sys-
tems. All of these changes can affect
shallow ground water and the flow rates
and chemical makeup of precipitation
runoff.

Impacts from Surface Reconfiguration
and Excavation
  Remedial technologies that require
surface reconfiguration will usually
result in some degree of environmental
change to surrounding areas if proper
precautions are not taken. Impacts to
nearby wetlands from remediation
activities at hazardous waste sites can
result from sedimentation due to in-
creased erosion rates, contamination
from fugitive dust emissions, and dis-
ruption of the water table due to the
creation of earthen structures.

Erosion
  When construction activities bare or
create slopes, surface erosion from
rainfall and flowing water can result.
Even on well-designed slopes, some soil
loss will result from certain mechanical
and chemical processes that transport
sediment and contaminants downslope
into nearby low-lying areas, including
wetlands. Mechanical processes include
sheet, rill, and gully erosion. Colloidal
erosion and erosion rates of some soils
are influenced by chemical processes.
  The velocity of a raindrop has been
measured to be about 20 miles per
hour, and impact energy increases with
drop size. Mechanical processes of soil
erosion begin when falling rain impacts
the soil at high velocities and detaches
soil particles from the ground. The
loosened soil particles can then be
transported by shallow overland (or
sheet) flow of rainwater across the land
surface causing sheet erosion.
  Progression of sheet erosion can
eventually lead to the development of
small shallow channels in the soil,
called rills. Rill erosion occurs as a
portion of the overland flow becomes
concentrated into rills. As the channel-
ized flow increases in velocity, soil par-
ticles are detached by the shearing
energy of the runoff, and by slumping
due to channel undercutting (e.g.,
headward erosion). If slopes are steep
and long, and runoff velocity increases,
larger and deeper channels  or gullies
can develop. Erosion in gullies can have
a correspondingly higher rate of erosion,
but rill and sheet erosion (over bare
slopes) can cause the loss of more soil.
While larger particles may be trans-
ported only short distances, small
particles such  as clay and silt may
t>ecome suspended in water and trans-
ported for large distances until they
settle out of the water column in a
quiescent setting.
  The potential for erosion also de-
pends on the type of material exposed
at the surface. Soils high in silt or very
fine sand generally have the highest
potential for erosion relative to other soil
textures. At hazardous waste remedia-
tion sites, clay materials are often used
to form low-permeability barriers sepa-
rating waste and moisture. Clays can be
eroded through mechanical processes
such as those described above, but the
rate at which some clays erode is highly
dependent on their pore water chemis-
try. Erosion rates in unsaturated mont-
morillonite clays used in embankments
and landfill caps can  vary by a factor of
200 due to pore water chemistry at the

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 surface. Uniformly maintaining the
 optimum moisture content during
 construction of embankments and caps
 can control the erosion caused by pore
 moisture chemistry.
   Erosion of fine soil materials can also
 occur from slaking, which occurs when
 soil aggregates break down from immer-
 sion in water (e.g., due to cation ex-
 change), and are transported by run-
 ning water. Slaking is common in clay
 soils.

   Another form of erosion occurs
 through dispersivity or colloidal erosion.
 As water runs over the surface of fine
 soils, the texture of the soil contributes
 to uneven flow and mixing. Colloidal
 particles, or clay and organic particles
 that are so small that they tend to
 remain  suspended in water, are washed
 out of the surface soil. Since colloidal
 particles are probably the primary
 carriers of chemical compounds in the
 soil (i.e., contaminants), the chemistry
 of the runoff can change. For example,
 the runoff may become more alkaline or
 acidic.

  Wetlands can be disrupted as a result
 of increased deposition from changes in
 rates  of soil erosion, and due to
 chemical changes in runoff. Although
 natural  rates of deposition in wetlands
 are generally beneficial, increased
 depositional rates in wetlands due to
 human  activities can accelerate
 changes of such a magnitude that some
 organisms cannot adapt. Rapid changes
 may raise the bottom of the wetland,
 and alter water depth, circulation, light,
 and temperature. The disappearance of
 some  species and the potential entrance
 of other species may cause a chain
 reaction that completely alters the
 original  ecologic association. In
 addition, flood storage capacity of a
wetland may be reduced or lost.
Chemical changes in runoff that enters
wetlands can similarly affect sensitive
plant and animal species, and result in
ecologic upset. Chemical changes also
create the potential for significant
reductions in contaminant or nutrient
removal efficiencies from the water, and
the accumulation of toxic materials.
Erosion Control
  There are many sources of informa-
tion concerning the control of erosion.
Engineering handbooks on this topic
have been developed by government
entities such as the Soil Conservation
Service, the U.S. Army Corps of Engi-
neers, and the Federal Highway Admin-
istration. Topical areas such as runon
and runoff control, dam construction,
and open channel hydraulics may
provide additional design information.
  Preventative measures for erosion
control are listed below
• As a precursor to erosion control
  measures, estimate the average soil
  loss annually from sheet and rill
  erosion for the disturbed area. The
  Universal Soil Loss Equation (USLE)
  from the U.S. Department of Agri-
  culture can be used for such pur-
  poses, and to determine whether
  there is an appropriate vegetative
  cover to protect exposed areas. The
  USLE is composed of factors that
  estimate the inherent erosion
  potential at the site, and potential
  reductions of soil losses through
  compensation factors such as
  erosion control.

• EPA recommends that landfill covers,
  for example, be designed such that
  the rate of soil erosion is no more
  than 2 tons per acre per year as
  calculated by using the USLE. This
  number should be adjusted according
  to the potential effects of the runoff on
  wetlands.

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 • Implement contoured grading to
   break up long, steep slopes and to
   reduce the velocity of runoff before
   the flows have a chance to form
   gullies. For example, performance
   standards to protect wetlands in
   Florida require that slopes are no
   steeper than a three to one (horizontal
   to vertical) ratio.

 • Construct crown ditches at the tops
   of slopes or interceptor ditches
   perpendicular to slopes to capture
   and convey water to the ends of the
   slope or into reinforced (rip rap)
   channels leading downslope and
   away from the wetland.

 • Construct retaining walls of resistant
   material, such as sand bags or grout
   bags.

 • Seed or plant vegetative cover that is
   suited to the site's soil and climatic
   conditions so that it can protect soil
   from raindrop impacts and provide
   soil stability.
 •  Apply porous geotextile fabrics or
   erosion control mats to slopes to
   reduce erosional impacts while still
   allowing surface drainage and infil-
   tration. Nonporous geomembranes
   and liners to be used in water
   retainment systems, such as ditches
   and ponds, and as siltation devices.

 •  Increase slope stability and temp-
   orarily reduce erosion potential by
   adjusting soil moisture for optimal
   compaction during fill emplacement.
 • Coordinate activities during
  construction to prevent unnecessary
  erosion. For example, compacting soil
  immediately after grading it will
  reduce soil erosion.
• Alter the soil water chemistry of
  surface clays to reduce their erosion
  potential. Calcium montmorillonite
  clays, for example, can be treated
   with sodium salts such as
 • Design a storm-water catch basin to
   equalize and neutralize runoff.

 Fugitive Dust Emissions
   Fugitive dust can become a signifi-
 cant factor during remediation of haz-
 ardous waste sites where surface con-
 struction activities are involved.
 Wind-induced erosion of unprotected
 soil and such activities as earth-moving
 or stockpiling, excavation, and moving
 vehicles, can suspend fine particles into
 the atmosphere. These particles may be
 widely dispersed, and may settle over
 nearby areas depending upon precipita-
 tion and wind-speed.
   In a dry spell, fugitive dust emissions
 may cover the leaves of wetland vegeta-
 tion, disabling or reducing their photo-
 synthesis efficiency. Loss of some wet-
 land vegetation may occur due to
 excessive  dust emission in a dry season.
 Fugitive Dust Emission Control
   Impacts from fugitive dust emissions
 on wetlands can be prevented by spray-
 ing water  or special dust-control formu-
 lations over the construction area(s).
 Basic control strategies can be adopted
 to minimize fugitive dust emissions. For
 remediation activities at hazardous
waste sites, these strategies can involve
engineering and operational controls
that are similar to soil erosion controls,
but limit the amount of dust that may
become suspended. To reduce fugitive
dust emissions the following techniques
may be considered.
• Road Maintenance. Paved roads
  withinthe hazardous waste sites can
  be cleaned by water flushing to dis
  lodge road dust. Cracked or abraded
  roads can be resurfaced with non-
  erodible materials to minimize dust
  accumulation. Wet unpaved roads to
  suppress dust.

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   Traffic controls. To minimize dust
   emission, site coordinators could
   apply a practical limit to the use of
   unpaved roads to low-weight vehicles,
   require lower travel speed, and
   require washing of excavation/moving
   equipment prior to leaving the site.
   Stabilization. Disturbed surfaces and/
   or storage piles could be stabilized by:
   (1) wet suppression (similar to wetting
   unpaved roads) to agglomerate small
  particles into larger particles; (2)
  vegetative cover to reduce wind veloc-
  ity and bind soil particles; and (3)
  covering the disturbed surface with
  hay mulch.
 • Dust barriers. Create windscreens of
  fabric, wood, or other light-weight
  materials to reduce surface winds or
  to trap particles downwind of dis-
  turbed areas, waste storage piles, and
  construction activities.
 Pumping and Treating Ground Water
  Pumping contaminated ground water
to the surface for treatment is a com-
mon clean-up technology at many
hazardous waste sites and RCRA facili-
ties. Pump-and-treat technology ex-
tracts contaminated ground water and
treats it on the land surface. The treated
water is then discharged either on- or
off-site, or reinjected into the soil.

  Generally, surface activities at haz-
ardous waste sites or shallow burials of
waste are more likely to contaminate
ground water in the uppermost aqui-
fers. Contaminated ground water from
the upper aquifers also recharges into
surface streams, creeks, rivers, and
wetlands. Aquifers from which the
ground water is withdrawn can be
composed of consolidated bedrock or
soft, unconsolidated sediments. These
characteristics influence the rate and
likelihood of contamination, as well as
the extent to which the subsurface
responds to disturbances by various
remedial technologies.

  Depending upon the site-specific
circumstances, ground water that has
been pumped to the surface and treated
may either be discharged on the surface
(e.g., to a stream or publicly owned
treatment work), or it can be reinjected
into the subsurface. Frequently, the
ground water will be reinjected into the
same aquifer from which it was with-
drawn to enhance further ground-water
recovery.

Impacts from Pumping
  Overpumping for the removal of
contaminated ground water without
adequate recharge  can result in two
potentially deleterious effects on wet-
lands: dewatering  and land subsid-
ence. The two effects are not indepen-
dent from one another. In the first case,
removal of ground water at a greater
rate than it can be  replenished can
cause a significant  drop in the water
table, which is called drawdown. Since
the water table in wetlands is usually at
or near the surface, drawdown of the
local water table can severely dewater
wetlands that depend on a shallow
water table for moisture. Even in situa-
tions in which wetlands are fed by
surface water sources, dewatering as a
result of drawdown can occur as sur-
face water is lost to the subsurface.
  In the second case, excessive draw-
down of the water table or lowering of
piezometric levels as a result of fluid

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 extraction can trigger land subsidence.
 Subsidence typically occurs very slowly
 over a wide area, particularly in areas
 that contain thick layers of soils with
 high concentrations of clay, which is
 typical of some wetland environments.
 Consequently, subsidence introduces
 potential long-term impacts to wet-
 lands.

   Subsidence as a result of ground
 water pumping is widely documented.
 As underground pore fluids separating
 individual soil particles are removed,
 underground stresses are redistributed,
 and the effective pressure from the
 overburden increases. In response to
 these new stresses, soil particles adjust
 and consolidate into a smaller volume.
 As the effects from this phenomena
 move through the subsurface, the
 surface expression may result in sub-
 sidence over a large area. The potential
 for subsurface strata to compress in-
 creases as the piezometric head is
 lowered.  Subsidence from ground water
 withdrawal is generally lenticular
 shaped at the surface, with decreases in
 elevation that can range from a few
 millimeters in stiffer underground for-
 mations to several meters in soft uncori-
 solidated soils. Organic and peat soils
 commonly found in wetland environ-
 ments are especially prone to large
 amounts of settlement.
  The long-term effects of subsidence in
 wetlands can result in changes to wet-
 land hydrology. As elevations and
 slopes are altered, stream courses,
 stream gradients, and the amount of
 surface flow into the wetland can be
 increased, decreased, or reversed to
 upset the delicate water balance of the
wetland. An increase in the volume or
velocity of flow into the wetland can lead
to increased flooding and sediment
deposition, potentially smothering
benthic organisms. Conversely, a de-
 crease in flow to the wetland may result
 in desiccation and loss of function.
 Similarly, wetlands along large water
 bodies that experience subsidence may
 become susceptible to permanent flood-
 ing, and develop into deepwater habi-
 tats. The extent of flooding depends
 upon the differences in elevation be-
 tween the water body and the wetland,
 including tidal influences. In cases
 where wetlands become deepwater
 habitats, wetland functions and species
 that use air as the principle medium
 would be replaced by functions and
 species that primarily use water.

 Control of Water Loss
  The surest way to prevent water loss
 and subsequent subsidence of wetlands
 is to prevent over-extraction of ground
 water. The water table will not drop and
 subsidence will not occur if the
 recharge rate equals the rate of fluid
 withdrawal.
  When implementing a pump-and-
 treat operation, the following factors
 should be considered to avoid unneces-
 sary impacts to wetlands:
 • Optimize pumping rates and quanti-
  ties based on a water-balance rela-
  tionship between the natural (or
  artificial) recharge rate and the maxi-
  mum rate of withdrawal.
 • Estimate tolerance limits for drops in
  the water table or piezometric level
  thatwill not cause adverse impacts to
  the wetland.

• Estimate tolerance limits for the
  magnitude of subsidence that can
  occur without significant adverse
  impacts on the wetland for various
  drops in the water table.
• Estimate the maximum amount of
  subsidence  that could occur based
  on planned pumping rates, and aqui-
  fer and soil characteristics for given

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  drops in water levels and surface
  elevations.
• Place an impervious barrier, such as
  a slurry wall, between the pumping or
  dewatering system and the wetland.
• Monitor ground-water levels and
  surface elevations.
Landfill Capping and Runoff Diversions
  Installation of impermeable cover
systems on top of RCRA or CERCLA
landfills may cause additional surface
runoff from the landfill area. The associ-
ated diversion berms/ditches also are
sometimes routed differently than pre-
existing conditions. A general decline in
the water table for an adjacent area
may occur from preventing direct seep-
age or by recharging a shallow water
table. If the adjacent area happens to be
a wetland, a decline in the wetland's
water table may result from caps and
runoffs.

Impacts from Routing Runoff Control
Ditches In a Landfill Cover System and
Control
  Major activities involved in the con-
struction of landfill  cover systems in-
clude earth-moving and surface recon
figuration. Impacts  on wetlands from
such activities at landfills are addressed
under "Waste Excavation and Surface
Reconfiguration."

  Construction of landfill cover systems
also may include construction of runoff
control/diversion ditches. These sys-
tems usually cause some degree of
change in the shallow water table. For
example, if the runoff control ditches
are diverted away from the adjacent
wetland where the water enters a
stream at a distant location, quite a bit
of water from the diversion ditches will
be lost to evaporation. Obviously, more
water loss to adjacent wetlands will
occur from a large landfill, and less will
occur from a small one.
  Measures to minimize adverse im-
pacts involve routing stormwater runoff
from the ditches through an emergent
pool for sedimentation, and erosion
control prior to discharge into the low-
lying marsh or wetland areas.
                           More Information
 RCRA Hotline: Accepts calls Monday-Friday, 8:30 a.m. to 7:30 p.m. EST. The
 national, toll-free number is: (800) 424-9346; TDD (800) 553-7672. In
 Washington, D.C.. the number is: (703) 412-9810; TDD (703) 412-3323.
 Wetlands Protection Hotline: Accepts calls Monday-Friday, 9:00 a.m. to 5:30
 p.m. EST. The national, toll-free number is: (800) 832-7828
 RCRA Docket: For copies of other documents on solid waste issues, or to receive
 a catalogue of solid waste documents, write: RCRA Information Center (RIC),
 U.S. Environmental Protection Agency, Office of Solid Waste (OS-305), 401 M
 Street SW, Washingtoa D.C. 20460.

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U.S. Environmental Protection Agency
401 M Street SW (OS-305)
Washington, DC 20460

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