v>EPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA832-F-99-015
September 1999
Storm Water
O&M Fact Sheet
Handling and Disposal of Residuals
DESCRIPTION
Polluted urban runoff can be a major source of
water quality problems in receiving waters. Road
deicing activities, automobiles, atmospheric
deposition, chemicals used in homes and offices,
erosion from construction sites, discharges from
industrial plants, wastes from pets, wastes from
processing and salvage facilities, and chemical spills
can all contaminate storm water runoff. These
sources can contribute sediment (organic and
inorganic), nutrients, bacteria, oil and grease, and
heavy metals to receiving waters. Urban storm
water Best Management Practices, or BMPs, are
intended to remove these pollutants from runoff and
to improve water quality in downstream waters.
Yet if storm water BMPs are not properly operated
and maintained, the BMPs themselves can become
sources of storm water pollutants, as the material
removed during previous storms becomes re-
suspended by subsequent storm events. To prevent
this, structural storm water BMPs must be
periodically inspected and cleaned of residual
materials and sediments. As described above, these
residuals may contain a variety of pollutants, and
thus proper handling and disposal of these materials
is essential. This fact sheet describes structural
BMP maintenance programs and discusses methods
for handling and disposing of residual materials from
storm water BMPs.
Properties of Storm Water Residuals
Storm water solids/residuals have properties that are
very site specific, and it is difficult to precisely
estimate "typical" storm water or sediment residual
properties by the BMP employed or even by site
classification. Therefore, this fact sheet presents
information from several site-specific studies of the
properties of storm water solids/residuals presented.
A summary of this data is presented in Table 1.
A 1982 study performed at Marquette University,
Milwaukee, Wisconsin, examined urban runoff
residuals from afield-assembled sedimentation basin
in Racine, Wisconsin, swirl and helical bend solids
separators in Boston, Massachusetts, and an in-line
upsized storm conduit in Lansing, Michigan. The
residual samples from Racine and Boston were
obtained from individual storms, while the Lansing
samples represent a six- month accumulation of
residuals. All of the sample locations were primarily
residential (Marquette University, 1982). Results
from the sampling are shown in Table 1. Table 1
also summarizes the findings presented in two other
technical papers (Schueler and Yousef, 1994, and
Field and O'Shea, 1992).
The 1994 study by Schueler and Yousef reviewed
bottom sediment chemistry data from 37 wet ponds,
11 detention basins, and two wetland systems, as
reported from 14 different researchers. This
research covered a broad geographic range,
although nearly half of the sites were located in
Florida or in the Mid-Atlantic states. These storm
water ponds had been in use from three to 25 years.
Sampling and analysis were restricted to mean dry
weight concentrations of the surface sediments that
comprise the muck layer, which is usually the top
five centimeters (Schueler and Yousef, 1994).
Schueler and Yousef gathered data for nutrients,
trace metals (cadmium, copper, lead, zinc, nickel,
chromium), hydrocarbons, and priority pollutants,
and indicate that the properties of the
solids/residuals from all BMPs are similar except for
those from oil/grit separators. A noted exception
was that grassed swale soils tend to have about
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TABLE 1 PROPERTIES OF URBAN STORM WATER SOLIDS/RESIDUALS
Properties of
Residuals
Solids
Volatile
Suspended
Solids
Total Suspended
Solids
Nutrients
Phosphorus
Total Kjeldahl
Nitrogen
Heavy Metals
Zinc
Lead
Chromium
Nickel
Copper
Cadmium
Iron
Hydrocarbons
Poly Chlorinated
Biphenyls
Wet Ponds1 Sedimentation
Basin 2
6% 104-155mg/l
43% 233-793 mg/l
583 mg/kg < 5 mg/l
2,931 mg/kg <5 mg/l
6-3,171 mg/kg
1 1 - 748 mg/kg
4.8 -120 mg/kg
3 - 52 mg/kg
2 -173 mg/kg
ND- 15 mg/kg
6.1 -2, 970 mg/l
2,087-12,892
mg/kg
0.19- 24.6 Tg/l
Swirl and . Urban Storm
Helical Bend ,, ^™ Water Runoff
Solids Upsjzed Storm Resjdua|s5
Separators3 Conduit
107 310 mg/l 25,800 mg/l 90 mg/l
344-1,140 mg/l 161,000 mg/l 415 mg/l
< 5 mg/l 0.3 - 2,250 mg/l 502 - 1 ,270
mg/kg
< 5 mg/l 0.3 -2,250 mg/l 1,140-3,370
mg/kg
302 - 352 mg/kg
251 - 294 mg/kg
168 -458 mg/kg
69 -143 mg/kg
251 - 294 mg/kg
-
6.1- 2, 970 mg/l 6.1 - 2,970 mg/l
-
0.19 -24.6 Tg/l
(1) Schuelerand Yousef, 1994.
(2) Marquette University, 1982 (Racine, Wisconsin).
(3) Marquette University, 1982 (Boston, Massachusetts).
(4) Marquette University, 1982 (Lansing, Michigan).
(5) Field and O'Shea, 1992.
twice as much phosphorus and lead as detention
ponds. Only one sand filter had been sampled, but
these characteristics in its residuals appeared similar
to those of other BMPs (Schueler and Yousef,
1994). Characteristics of solids/residuals from
BMPs are discussed in the following sections, with
the exception of oil/grit separators, which are
covered in a separate subsection.
Solids-General Composition
Solids from storm water and sediment BMPs can
consist of organic and inorganic material.
According to Schueler and Yousef (1994), the muck
layer of a pond is high in organic matter. An
average of nearly six percent volatile suspended
solids was reported. Pond muck solids have a very
soupy texture, with an average total solids content
of 43 percent, although this parameter was reported
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from only 15 out of the 50 site locations. These
solids have a distinctive grey to black color and a
low density, averaging approximately 1.3 g/cm3.
According to the 1982 EPA study at Marquette
University, total solids concentration of residuals
samples from a sedimentation basin in Racine,
Wisconsin, ranged from 233 to 793 mg/1, with 104
to 155 mg/1 being volatile. Concentrations of total
solids from swirl and helical bend solids separators
inBoston, Massachusetts, ranged from 344 to 1,140
mg/1, with 107 to 310 mg/1 being volatile. The six-
month accumulated samples from the in-line upsized
storm conduit in Lansing, Michigan had a total
solids concentration of 161,000 mg/1 with 25,800
mg/1 being volatile. The 1992 paper by Field and
O'Shea reported estimated annual residual/sludge
volumes for urban storm runoff in the United States
ranging from 27 to 547 million cubic meters (35 to
715 million cubic yards) at an average total solids
content ranging from 0.5 to 12 percent.
Nutrients
The muck layer is enriched with nutrients. In the
1994 paper by Schueler and Yousef, phosphorus
concentrations for 23 studies ranged from 110 to
1,936 mg/kg, with an average concentration of 583
mg/kg. Nearly all of the nitrogen found in pond
muck is organic in nature. Total Kjeldahl nitrogen
(TKN) concentrations were reported for 20 studies
and ranged from 219 to 11,200 mg/kg, with an
average concentration of 2,931 mg/kg. Nitrate was
found to be present in very small quantities,
indicating either that some denitrification is
occurring in the sediments or perhaps that very little
nitrate is initially trapped in the muck layer.
The nitrogen-to-phosphorus ratio in this pond study
averages five to one. In comparison, the nitrogen to
phosphorus ratio for incoming storm water usually
averages about seven to one. Ponds appear to be
more effective in trapping phosphorus-containing
compounds than in trapping nitrogen-containing
compounds. It is also possible that nitrogen-
containing compounds decay faster than
phosphorus-containing compounds in the muck
layer. (Schueler and Yousef, 1994).
The 1982 Marquette University EPA report and the
1992 paper by Field and O'Shea reported urban
sludge nutrient concentrations ranging from 502 to
1,270 mg/kg total phosphorus as P and 1,140 to
3,370 mg/kg TKN. These nutrient concentrations
were reported as being lower than nutrient
concentrations found in combined sewer overflows
(CSOs) and in raw primary sludges (Rexnord, Inc.,
1982 and Field and O'Shea, 1992). The 1982
Marquette University/EPA report presented the
concentration of individual nutrients [total
phosphorus, TKN, ammonia-nitrogen (NH3), nitrite-
nitrogen (NO2), and nitrate-nitrogen (NO3)] in
storm water sediment samples from Boston,
Massachusetts, and Racine, Wisconsin, as never
exceeding 5 mg/1. Urban storm water sediment
samples taken from Lansing, Michigan, were
between 0.3 and 2,250 mg/1 for individual nutrients
(total phosphorus, TKN, NH3, NO2, and NO3)
(Marquette University, 1982).
Heavy Metals
Trace metal levels are typically 5 to 30 times higher
in the muck layer of a pond than in the parent soil
below the muck layer (Schueler and Yousef, 1994).
Trace metal levels were also reported to follow a
consistent pattern and distribution, with zinc having
the highest concentration in the muck layer,
followed by lead. Zinc and lead concentrations
were much greater than chromium, nickel, and
copper concentrations, which were approximately
equal. Cadmium had the lowest concentration in the
muck layer. In the 1994 Schueler and Yousef study,
50 ponds and wetlands were examined and found to
have zinc concentrations ranging from 6 to 3,171
mg/kg (dry weight). Lead and chromium
concentrations ranged from 11 to 748 mg/kg, and
from 4.8 to 120 mg/kg, respectively. Nickel and
copper concentrations ranged from 3 to 52 mg/kg,
and from 2 to 173 mg/kg, respectively. Cadmium
concentrations ranged from being non-detectable to
15 mg/kg (Schueler and Yousef, 1994).
Field and O'Shea reported that median
concentrations of zinc, lead, copper, nickel, and
chromium in urban runoff sludges and residuals
were reported as 316, 268, 263, 131, and 189
mg/kg, respectively (Field and O'Shea, 1992). In
the 1982 study at Marquette University, iron was
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found as the highest concentration of metals in all of
the samples ranging in concentration from 6.1 to
2,970 mg/1. Lead and zinc concentrations ranked
second and third, respectively (Marquette
University, 1982).
As with all pond parameters, trace metal
concentrations are site specific. Ponds that
primarily service roadways and highways are
enriched with trace metals which are presumably
associated with automotive loading sources (e.g.,
cadmium, copper, lead, nickel, and chromium). On
the other hand, storm water ponds that service
primarily residential areas have the lowest trace
metal concentrations (Schueler and Yousef, 1994).
In general, the muck layer is highly enriched with
metals; however, in most cases it should not be
considered an especially toxic or hazardous
material. For example, none of over 400 muck layer
samples from any of the 50 pond sites examined in
the referenced 1994 study exceeded EPA's current
land application criteria for metals (Schueler and
Yousef, 1994).
The Northern Virginia District Planning
Commission (NVPDC) also examined the toxicty of
trace metals from pond sediments (NVPDC, 1995).
One study, entitled "Investigation of Potential
Sediment Toxicity From BMP Ponds," (Dewberry
and Davis, 1990) analyzed sediments from 21 ponds
in Northern Virginia under various land use
conditions. Many of these ponds are owned and
maintained by property owners or homeowners'
associations. Testing was performed for the
presence, concentration, and toxicity of metals
found in the analyzed sediments. The report
indicates that the storm water sediments tested were
not hazardous and could be safely disposed of on-
site or in a landfill. While Dewberry and Davis'
study determined the specific material tested to be
non-hazardous, they recommend that sediments
should be tested further for their use as backfill
material or for topsoil maintenance (Dewberry and
Davis, 1990).
Hydrocarbons
There is limited data on hydrocarbon and poly-
aromatic hydrocarbon (PAH) concentration in the
muck layer of ponds. It was reported that the
concentrations of total PAH and aliphatic
hydrocarbons in the muck layer of a 120 year old
London basin were three and 10 times greater,
respectively, than the base "parent" sediments.
Minor degradation of the hydrocarbons trapped in
the muck layer appeared to have occurred in the
basin in recent years. On the other hand,
hydrocarbons were rarely detected in the muck of
Florida ponds. Hydrocarbon concentrations were
reported for two out of the 50 sites in the 1994
report by Schueler and Yousef. These
concentrations were reported for an industrial and a
residential site as 12,892 and 2,087 mg/kg,
respectively (Schueler and Yousef, 1994).
Bacteria
Urban storm water solids may contain high levels of
bacteria and viruses, including fecal streptococcus
and fecal coliform from animal and human wastes.
These microrganisms have the potential to be spread
from land application of residuals or landfill sites
unless the proper precautions are taken. Measures
that reduce their concentration in the residuals and
minimize any residuals-vector contact include
stabilization of the solids; immediate covering of
landfill trenches after disposal of solids; treatment by
pasteurization, heat treatment, irradiation, etc.; and
public and animal access control away from the site
(Field and O'Shea, 1992).
Oil/Grit
As previously mentioned, the storm water and
sediment solids collected by an oil/grit separator are
often more heavily contaminated than solids from
other storm water BMPs. The metal content of
trapped sediments in an oil/grit separator may be up
to 20 times higher than in other BMPs, especially if
the separator services a gas station. Priority
pollutant and hydrocarbon levels are also much
higher, because most oil/grit separators service
areas that may discharge higher pollutant levels,
such as gas stations and industrial sites, and are
designed to trap lighter fractions of oil than are
usually trapped by other BMPs. Other BMPs, such
as detention basins, usually drain larger watersheds,
which causes dilution of the hydrocarbons and
metals from gas stations or industries. Therefore, it
is doubtful that solids from other BMPs would
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approach metal and hydrocarbon concentrations as
high as those recorded with oil/grit separators
(Schueler and Yousef, 1994).
Other Pollutants
Other potentially toxic pollutants that may be found
in storm water BMP sediments include pesticides
and polychlorinated biphenyls (PCBs). Toxic
wastes in fertilizers, herbicides, and household
substances such as paints and cleaning materials
may find their way into storm water solids/residuals.
In the 1982 report from Marquette University,
PCBs were observed in measurable concentrations
in the Racine, Wisconsin and the Lansing, Michigan
samples. These concentrations ranged from 0.19 to
24.6 //g/1. Of eight pesticides surveyed, only three
(DDT, DDD, and Dieldrin) were observed in
measurable concentrations (Marquette University,
1982).
APPLICABILITY
For any BMP to achieve maximum pollutant
removal, storm water residuals and sediment solids
must be periodically removed from the system.
O&M procedures for removing and for handling
storm water solids/residuals from BMPs should be
planned in the design stages of the BMP. The
removal frequency depends on many factors;
however, some generalized O&M requirements for
each of the structural BMP categories (i.e.,
detention basins, retention/infiltration devices, and
vegetative controls) are provided below.
Detention Basins
Wet ponds will eventually accumulate enough
sediment to significantly reduce the storage capacity
of the permanent pool. This loss of capacity can
affect both the appearance and the pollution removal
efficiency of the pond. The best available estimate
is that approximately one percent of the storage
volume capacity associated with the two-year design
storm can be lost annually (MWCOG, 1987). Even
more storage capacity can be lost if the pond
receives extra sediment input during the
construction phase. A sediment clean-out cycle of
10 to 20 years is frequently recommended in the
Washington, D.C., metropolitan area (MWCOG,
1987). According to the Center for Watershed
Protection, storm water ponds require sediment
clean-out every 15 to 25 years (Schueler and
Yousef, 1994).
Most ponds are now designed with a forebay to
capture the majority of sediments, decreasing the
solids load to the wet pond. A common forebay
sizing criterion is that it should constitute at least 10
percent of the total pool volume (Schueler and
Yousef, 1994). This forebay could lose 25 percent
of its capacity within 5 to 7 years based on a 1.25
cm/year (0.5 inch/year) muck deposition rate and
the assumption that a forebay traps 50 percent of all
muck deposited in the pond (Schueler and Yousef,
1994). However, using a forebay may extend the
sediment removal interval for the main pond to 50
years (Schueler and Yousef, 1994).
To clean out a large wet pond, dragline or hydraulic
dredge methods may be necessary. In ponds not
large enough to warrant a hydraulic dredge method,
mechanical dredge methods, such as dipper,
clamshell, and bucket dredges are sometimes used.
In smaller wet ponds, the pond level may be drawn
down to a point where the residuals can begin to dry
in place. After the material is dried, a front end
loader can be used to remove it from the pond
bottom.
Dry ponds and extended detention dry ponds also
accumulate significant quantities of sediments over
time. This sediment gradually reduces the available
storage capacity within the pond and also reduces
pollutant removal efficiency. In addition, sediment
may tend to accumulate around the control device
of the dry extended detention ponds. This sediment
deposition increases the risk that either the orifice or
the filter medium will become clogged. Sediment
accumulation also gradually reduces storage
capacity reserved for pollutant removal in the lower
stage. Therefore, in an extended detention dry pond
it is recommended that sediment be removed from
the lower stage every five to ten years (MWCOG,
1987). Sediment removal from these systems is
simple if access is available for the equipment.
Therefore, access should be included in the pond
design. Front-end loaders or backhoes can be used
to remove the accumulated sediment.
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Retention/Infiltration Devices
Infiltration basins are usually located in small
residential watersheds that either do not generate
large sediment loads or are equipped with some kind
of sediment trap. Even when the sediment loads are
low, they still impair the basin's performance: the
sediment deposits reduce the storage capacity
reserved for exfiltration and may also clog the
surface soils.
Methods to remove sediment from infiltration
devices are different from those utilized for
detention basins. Removal should not begin until
the basin has thoroughly dried out, preferably to the
point where the top layer begins to crack. The top
layer should then be removed using lightweight
equipment, with care being taken not to unduly
compact the basin surface. The remaining soil can
then be deeply tilled with a rotary tiller or disc
harrow to restore infiltration capacity. Vegetated
areas disturbed during sediment removal should be
replanted immediately to prevent erosion.
In infiltration trenches, the pretreatment inlets of
underground trenches must be checked periodically
and cleaned out when sediment depletes more than
10 percent of the available trench capacity. This can
be done using a vacuum pump or it can be done
manually. Inlet and outlet pipes should also be
checked for clogging and vandalism. Dry wells
should also be checked periodically for clogging.
Performance of sand filter systems may be sustained
through frequent inspections and replacement of the
filter medium every three to five years, depending
on the pollutant load. Accumulated trash and debris
should be removed from the sand filters every 6
months or as necessary. Sand filter systems are
usually cleaned manually (Parsons ES, 1995).
Maintenance of porous pavement involves removing
sediment from the pavement using vacuum
sweeping. It has been recommended that the
porous pavement be vacuum swept and hosed down
by a high-pressure jet four times per year to keep
the pores in the asphalt open (MWCOG, 1987).
Ideally, oil/grit separators should be cleaned out
after every storm to prevent re-entry of any
residuals or pollutants into the storm sewer system
during the next storm. However, because of the
O&M costs and manpower requirements associated
with this schedule, in reality cleaning is less
frequent—it may occur only when an oil/grit
separator is no longer operating effectively. The
Metropolitan Washington Council of Governments
recommends that oil/grit separators be cleaned out
at least twice per year (MWCOG, 1987). As with
all BMPs, the cleaning frequency depends upon the
site-specific pollutant load.
Oil/grit separators can be cleaned out using several
methods. One method is to pump out the contents
of each chamber. The turbulence of the vacuum
pump in the chamber produces a slurry of water and
sediment that can then be transferred to a tanker
truck. Another method involves carefully siphoning
or pumping out the liquid from each chamber
(without creating a slurry). If needed, chemicals can
then be added to help solidify the residuals. The
solidified solids/residuals can then be removed
manually from the separator.
Vegetative Controls
Vegetative controls (basin landscaping, filter strips,
grassed swales, and riparian reforestation) rely on
various forms of vegetation to enhance pollutant
removal, habitat value, or appearance of a
development site. Some natural systems require
periodic sediment removal. For example,
accumulated sediments deposited near the top of a
filter strip will periodically need to be removed
manually to keep the original grade.
ADVANTAGES AND DISADVANTAGES
Proper O&M of storm water BMPs and proper
handling and disposal of storm water residuals will
result in a greater efficiency of BMP pollutants and
will help prevent resuspension of residuals during
subsequent storms. This will protect the water
quality of receiving waters. If BMPs are not
properly maintained, pollutants removed during one
storm may become resuspended during another
storm and may pollute receiving waters. Improper
disposal of storm water residuals may have the same
result. If the residuals are stored too close to an
area that tends to become flooded, they may return
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directly into the storm flow. Finally, there has been
no evidence to show that storm water residuals
should be considered hazardous waste; however,
many states have regulations that residuals be tested
before they are disposed.
KEY PROGRAM COMPONENTS
As described above, the key to ensuring that storm
water BMPs do not become a source of runoff
pollutants is proper operation and maintenance
(O&M), including periodic clean out to remove any
accumulated residual materials. While the pollutant
removal capabilities and efficiencies and the
quantities and types of residuals generated are
specific to each BMP, structural storm water BMPs
can be grouped into categories based on the design
of their pollutant removal mechanisms. The general
categories of structural storm water BMPs,
including detention basins, retention/infiltration
devices, and vegetative controls, each have different
design characteristics and removal mechanisms that
will effect the types and quantities of residuals they
generate. Some of the general characteristics of
these categories of structural BMPs are provided
below.
Detention basins are widely used and are very
effective in reducing suspended solid particles. By
temporarily holding the storm water runoff and
allowing the sediments to settle, detention basins
can reduce suspended solids concentrations by 50 to
90 percent. Examples of detention basins include
dry ponds, wet ponds, and extended detention dry
ponds.
Retention/infiltration devices retain runoff and allow
it to percolate into the ground, thereby reducing the
amount of pollutants released into the receiving
water. Filtration and adsorption occur as the runoff
percolates into the ground, trapping many pollutants
(e.g., suspended solids, bacteria, heavy metals, and
phosphorus) in the upper soil layers and preventing
them from reaching groundwater. These devices,
which can include infiltration basins, infiltration
trenches, dry wells, and porous pavement, can
remove up to 99 percent of some runoff pollutants,
depending on the percolation rate and area, the soil
type, the types of pollutants in the runoff, and the
available storage volume.
Other types of retention devices, such as sand filters
and oil/grit separators, can be used to pre-treat
runoff before it enters the collection system or
infiltrates into the ground. However, relative to the
successes with other infiltration/retention structures,
there has been limited success with some of these
devices. For example, because of low average
detention times, oil/grit separators are limited in
their ability to remove pollutants. Further, these
devices have the added risk that settled material may
be resuspended or released during later storms.
Vegetative BMPs, which can include basin
landscaping, filter strips, grassed swales, and
riparian reforestation, are used to decrease the
velocity of storm water runoff. This promotes
infiltration and settling of suspended solids and also
prevents erosion. Vegetative BMPs also remove
organic material, nutrients, and trace metals. For
maximum effectiveness, vegetative controls should
be used as a first line of defense in removing
pollutants in combination with other BMPs.
As described above, each of these BMP types has
specific removal abilities, and thus each generates
slightly different residual material. In most states,
the responsibility for operating and maintaining
these BMPs falls on the local jurisdiction, which is
responsible for inspecting, maintaining, and ensuring
proper operation of storm water BMPs. However,
in reality, many local jurisdictions do not have the
manpower to inspect all BMPs regularly. For
example, many of the detention basins installed by
local jurisdictions in the 1980s are now requiring, or
soon will require, cleaning and/or dredging for the
first time. This will require these communities to
develop a plan to handle and dispose of residuals
from these O&M activities.
Storm water and sediment solids/residuals must be
handled and disposed of properly. All sediment
solids/residuals should first be tested to determine if
they are hazardous. If the material is determined to
be hazardous, it must be disposed as such. Even if
the solids/residuals are determined not to be
hazardous, they will usually require dewatering prior
to disposal.
Historically, and in most cases, the disposal of
sediments removed through BMPs has posed no
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special regulatory or legal difficulty. Many
municipalities and industries have disposed of such
sediments in the same way that they would have any
uncontaminated soil (Jones, et a/., 1994). In fact,
after drying, storm water sediment has been mixed
with other soil and reused as backfill on
construction projects (Jones, etal., 1994) as well as
cover for landfills (State of Florida, 1995).
However, if the residuals/solids from a BMP are
determined to be hazardous, they must be managed
according to the Resource Conservation and
Recovery Act of 1976 (RCRA) requirements, which
would require either treatment to decrease the
concentration of the hazardous constituent or
disposal in a hazardous waste landfill. RCRA
defines waste as hazardous either because the waste
has certain characteristics (such as ignitability,
corrositivity, explositivity, or toxicity) or because
the waste contains constituents specifically listed in
the RCRA regulations. In nearly all cases involving
storm water BMP solids, the sediments contain
listed chemicals (Jones, et a/., 1994). However, if
no sample contains more than ten percent of the
listed chemical (by volume), or if contact with
precipitation/runoff is unlikely, the sediment would
not be classified as hazardous (Jones, et a/., 1994).
IMPLEMENTATION
The implementation of a storm water residual
handling and disposal program will be site-specific
and will depend on the types of BMPs used and the
residuals that they generate. However, some
generalized information on implementing a handling
and disposal program, as well as some specific
information from case studies, is provided below:
Storm Water/Sludge Handling Alternatives
Centralized Treatment (Bleed/Pump Back to the
Dry Weather Treatment Plant): Centralized
treatment involves temporary storage of storm
water solids followed by their regulated release into
a sanitary sewer during dry weather flow conditions.
Advantages of this residuals handling alternative
include the potential flow equalization through the
timed addition of urban storm runoff to the dry
weather influent, and the use of a central, pre-
existing treatment facility and transportation system
for solids handling. Disadvantages of this system
include: the deposition of large amounts of grit in
the sewer system; the potential for exceeding the
capacity of the dry weather treatment facility;
possible interference with the treatment plant's
operation and efficiency due to differences in the
characteristics of sanitary wastewater and urban
storm runoff residuals; and additional cost for
pumping and treatment (Field and O'Shea, 1992).
The problems associated with bleed or pump back
solids storm water sediment and solids are similar to
those evaluated with regard to CSO solids.
Huibregtse determined that "centralized treatment"
of solids was generally not practical (Huibregtse, et
a/., 1977). In addition to the disadvantages already
listed, some problems that may be associated with
this type of system include: difficulties in effectively
equalizing flow to the dry weather treatment plant
due to the high solids/low volume characteristic of
residual flow, and difficulties maintaining the quality
of treatment plant residuals. Further, significant
increases in heavy solids and toxic substance
loadings will affect a treatment plant's operation and
its effluent's quality. The addition of large amounts
of gritty solids can grossly overload solids handling
facilities at treatment plants and can impair overall
solids quality. Moreover, the addition of these
storm water and sediment residuals to the treatment
system will increase the quantity of residuals that
must be handled (Field and O'Shea, 1992). In a
1982 EPA report, research indicated that the
number of days required for bleed/pump back of the
residuals without overloading the dry weather
treatment facility ranged from 2.8 to 3.9 (Huibregtse
and Geinopolos, 1992). This is considered an
unacceptable bleed/pump back period, considering
the likelihood of overlapping rainfall events
(Huibregtse etal, 1977).
Storm Water Solids Handling at Satellite
Treatment Facilities: Another handling alternative
for urban storm water and sediment solids is
treatment at a satellite facility. As described above,
average characteristics of urban storm runoff differ
substantially from those of sanitary wastewater.
Because of the intermittent and varying quantity and
quality of storm flow, as well as its low organic and
nutrient content, biological processes are generally
not employed for the treatment of storm water
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runoff. The major design concerns for treatment of
storm water flows are the runoff s high grit content,
its low organic content, and the flow's intermittent
nature and short flow duration (Field and O' Shea,
1992).
Evaluation of several CSO solids handling processes
by Huibregtse found the most effective unit
processes to be: conditioning through chemical
treatment; gravity thickening; stabilization through
lime addition; dewatering through vacuum or
pressure filtration; and disposal through land
application or landfill (Huibregtse et al, 1977).
On-Site Handling of Storm Water Solids/Sludge:
The third alternative for handling/disposal of storm
water runoff residuals in on-site handling. On-site
handling of this material is usually very cost
effective as it avoids transportation costs and landfill
tipping fees. This option may be used after the
residuals have been analyzed and determined to be
composed of non-hazardous material. If this
disposal method is intended for implementation, a
dedicated area on the site should be set aside for
land application or land disposal of the residuals
during the design stage of a BMP. The area for
disposal of residual material should be carefully
selected to prevent residuals from flowing back into
the BMP during rainfall events.
To dispose of residuals on- site, residuals must first
be removed from the storm water runoff.
Alternatives for removing solids were discussed
previously. After the solids are removed they will
usually require dewatering. Dewatering is
accomplished by spreading the material out on the
ground and occasionally turning it to help it dry.
This material is then either land applied or land
disposed. Land application involves spreading the
material on dedicated land at approved application
rates. This material cannot be applied to cropland
and would probably be applied to a meadow or
vegetated area. There is very little nutrient value
associated with storm water residuals.
In some cases it may not be feasible to land apply or
land dispose of the material on-site. This may be
due to limited space. In any case, after the residuals
are removed from the storm water runoff, they
should be dewatered on-site if this is feasible. This
will cut down on the volume of material to be
transported. The material can then be loaded using
a front-end loader and transported to either a landfill
or another site for land application or land disposal.
The following sections describe specific case studies
of BMP residual management programs. This
section is not all-inclusive, but is presented to
illustrate how some states, municipalities, and
industries manage the solids/sediments from BMPs.
Waste Reduction, Disposal, and Recycling
Services
A Baltimore, Maryland, firm cleans oil/grit
separators for many commercial industries. They
use a three man crew and two trucks. A liquid
tanker truck is used to pump the oil and water out
of the separator. This mixture is transported to their
facility in Baltimore for treatment (All Waste-Clean
America, 1995).
The solids in the oil/grit separator are further
solidified using chemical addition. Once the
material is solidified, it is shoveled out of the
separator into 55-gallon drums. A composite
sample is taken from each drum. This material is
analyzed for toxicity, ignitability (flash test), and
PCBs. If the material is determined to be non-
hazardous, it is loaded into roll-off dumpsters and
transported to an incinerator, where the company
receives a certificate of destruction for the material
(All Waste-Clean America, 1995).
If the solidified separator residuals are determined
to be hazardous, treatment depends on the
hazardous constituent of the waste. Analytical
results are faxed to the generator. Additional
testing is usually required to determine what
constituent(s) make the sediment hazardous (All
Waste-Clean America, 1995). Hazardous material
is then handled on a case-by-case basis. In most
cases, treatment to lower the hazardous chemical
concentration to a non-hazardous level is preferred
over landfilling in a hazardous waste landfill. For
example, a sediment that contained a high
hydrocarbon content, which may occur at a service
station, would be spread out on an approved site for
a period of time sufficient to allow the concentration
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to decrease in the sediment (All Waste-Clean
America, 1995).
As each cleaning and maintenance job is site
specific, this firm charges by the hour. The cost for
cleaning is $202/hr for the three employees and two
trucks. In addition, the charge for disposal of the
liquid waste is $0.09/liter, the charge for the
chemical that aids in solidification is $9.95/bag,
drum purchase cost is $25/drum, drum disposal cost
is $100/full drum, analytical charge is $145, and
transportation charge is $250. Additional analytical
testing and handling will increase costs.
Prince George's County, Maryland
In Prince George's County, Maryland, ponds are
dredged on an as-needed basis. In some cases, on-
site disposal of the sediment was planned for in the
design of the BMP. However, if on-site disposal is
not possible then a disposal site must be located.
Residual sand and gravel material from the BMP
may be landfilled or transported to construction-
sites for use (Prince Georges County, MD, 1999).
Prince Georges County is also experiencing
problems with oil/grit separators and is phasing
them out. Most of the problems pertain to residuals
management, and include: problems with landfills
accepting residual material from oil/grit separators;
the frequent maintenance and cleaning requirements;
difficulties in dewatering material generated from
the separators; and the expenses assocaited with
dewatering, hauling, and landfilling. In addition, the
county does not have the personnel to routinely
inspect and enforce the cleaning of oil/grit
separators. As an alternative to this BMP, the
county is focusing on pollution prevention and other
structural BMPs (Prince Georges County, 1999).
Fairfax County, Virginia
Most of the wet ponds in Fairfax County are
privately owned, and the owners are required to
maintain the ponds. The regional wet ponds
maintained by the county are designed to be fully
functional even when filled with sediment, and the
county does not have a formal dredging program.
Individual ponds are dredged on an as-needed basis;
the county is planning on dredging one pond in the
fall of 1999 to remove an island that has formed in
the pond. Removed residual material is retained in
a decanting basin for a period oif time until it is
landfilled (Fairfax County, VA, 1999).
Montgomery County, Maryland
Montgomery County has updated its guidance for
the dredging of wet and dry ponds to require
dredging if wet and dry ponds reach greater than 50
percent or greater than 30 percent of storage
capacity, respectively. The State of Maryland has
determined that the sediments from these ponds are
a non-hazardous material; however, inspectors have
the discretion to require testing of the residuals
depending on the suspected content of the runoff.
If the material is determined to be non-hazardous, it
can be disposed of either on-site or in a landfill.
State law requires that these ponds be inspected
once every three years. Since November, 1998, the
county has inspected approximately 1,000 ponds,
and is currently in the process of searching its
records to identify remaining ponds in the county
(Montgomery County, MD, 1999).
Typical oil/grit separators require much maintenance
attention, and Montgomery County is trying to
phase them out. The county has many sand filters
proposed to replace the oil/grit separators, but
information on their maintenance is not available
due to the limited experience with cleaning and
maintaining these filters (Montgomery County, MD,
1995).
State of Florida
Many storm water BMPs in Florida were
implemented in the early 1980s, and are just to the
point where they require dredging (State of Florida,
1995). However, Florida does not have a specific
regulation stating that each jurisdiction must dredge
or remove material from BMPs periodically.
Instead they have issued a "Guidance Manual" as a
supplement to the regulations, which are considered
inadequate for handling storm water sediments for
BMPs.
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The guidance manual recommends testing all BMP
sediments using the Toxicity Characteristics
Leaching Procedure (TCLP), before disposal. The
state has performed numerous analytical studies on
this material, and in no cases was BMP sediment
from any location determined to be hazardous.
However, oil/grit separators were not tested as part
of this study.
Material must have the appropriate laboratory
TCLP paperwork before most landfills in Florida
will accept it. Some cities and counties avoid this
testing by sending BMP residuals to
construction/debris landfills, which are not as
stringent. This practice is not supported by the state
(State of Florida, 1995).
In addition to screening by the TCLP test, Florida
has implemented a clean soil criterion to protect
communities from exposure to elevated
concentrations of materials which might not be
classified hazardous. If a material does not pass the
clean soil criterion, (e.g., if metal concentrations are
high, but not hazardous) then it can be used only in
an area where public access is controlled. Material
such as this can be used as a landfill cover because
public access is limited to most landfills.
Sediments from dry ponds in Florida are removed
using a front-end loader and a dump truck. As
discussed above, it is then recommended that a
TCLP test be conducted on this material before
either disposing on-site, landfilling, or disposing of
in another manner. Wet ponds are dredged;
however, these ponds are sometimes directly
connected to a waterway so caution is needed to
ensure solids are not resuspended in this operation.
This material is usually spread out on the site to
allow drying and is then disposed of on-site. If on-
site disposal is not possible, then the sediments are
usually transported to a landfill (State of Florida,
1995).
State of Delaware
The State of Delaware has followed Florida's lead
in handling and disposal of storm water BMP
residuals. The State of Delaware has conducted its
own tests on storm water BMP sediments, but
considers the material to be non-hazardous based on
Florida's research and other research/reports. The
state also has a storm water management program
in which local jurisdictions are required to inspect
BMPs on an annual basis (State of Delaware, 1995).
The state's storm water management plan includes
BMP construction guidelines for ease of BMP
maintenance and for on-site disposal of the storm
water residuals. Oil/grit separators are not a BMP
alternative in Delaware. In addition to detention
basins, sand filters are commonly used. The
cleaning schedule for a sand filter is site specific, but
three to four times a year is a general estimate.
Typically, a team of three is used to clean a
Delaware filter manually by shoveling out the
material. This process takes approximately 4 hours.
Labor cost to clean the filter is approximately $120.
The material is then transported to a landfill for
disposal (State of Delaware, 1995).
State of Maryland
The State of Maryland conducted a four-year study
on oil/grit separators with the Metropolitan
Washington Council of Governments. This study
evaluated material from oil/grit separators in
Maryland to determine if it was hazardous. The
study also evaluated maintenance of oil/grit
separators, as well as disposal of the residuals/solids
from an oil/grit separator. Results from the study
indicated that the solids from oil/grit separators
were not hazardous; therefore, this material could
be disposed of at a landfill after dewatering.
However, as this material is site specific it was
recommended that it be tested before being sent to
a landfill (State of Maryland, 1995).
All local jurisdictions are required to inspect BMPs.
Every three years, the state reviews storm water
programs and procedures utilized by the local
jurisdiction. The state has noted that many BMPs
are not being properly maintained, and attributes
this to the cost and manpower requirements
associated with regularly inspecting all BMPs.
Further, many homeowner associations have BMP
facilities on their property. Maintenance of these
BMPs is another area of concern for the state
because homeowner associations often do not
implement proper O&M procedures to maintain the
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BMP facility on their property (State of Maryland,
1995).
As long as they are not hazardous, sediments from
wet ponds and dry ponds are usually dewatered and
then disposed of on-site or landfilled. It is a
common practice to spread this material out on a
site for use as a soil amendment (State of Maryland,
1995).
COSTS
In a 1982 report by Huibregtse and Geinopolos, a
cost analysis was performed specifically for the
handling and disposal of urban storm runoff
residuals. This cost analysis compared the following
six alternative residuals handling scenarios for either
swirl or sedimentation concentrated solids:
Gravity thickening, vacuum filtration and
landfill.
Gravity thickening, vacuum filtration and
landspreading.
Gravity thickening, pressure filtration and
landfill.
Gravity thickening, pressure filtration and
landspreading.
Gravity thickening and landspreading.
Landspreading.
These cost estimates are presented in terms of
dollars per hectare for residuals handling in an urban
storm runoff area of 6,000 hectares (15,000 acres).
These estimates were updated to July 1995 dollars
and are presented in Table 2.
As shown on Table 2, the most cost effective solids
handling scenario based on annual costs is lime
stabilization, gravity thickening, pressure filtration,
and landfilling.
The 1982 EPA report from Marquette University
concluded that, of the options evaluated, the most
cost-effective means for handling and disposal of
urban storm water runoff residuals is gravity
thickening followed by lime stabilization and
landspreading or landfilling (Marquette University,
1982). This conclusion was based on urban storm
water studies from Boston, Massachusetts, Racine,
Wisconsin, and Lansing, Michigan involving solids
sampling, characterization, analysis, andtreatability.
The characterization study included analyses for
nine metals, eight pesticides and PCBs, solids,
nutrients, and organics. The treatability study
included bench scale sedimentation tests,
centrifugation tests, lime stabilization tests and
capillary suction time tests (Marquette University,
1982).
REFERENCES
1. All Waste-Clean America, Inc., 1995. S.
Schorr, All Waste-Clean America, Inc.,
personal communication with Parsons
Engineering Science, Inc.
2. Delaware Department of Natural Resources
and Environmental Control, 1995. E.
Shaver, Delaware Department of Natural
Resources and Environmental Control,
personal communication with Parsons
Engineering Science, Inc.
3. Dewberry and Davis, 1990. Investigation of
Potential Sediment Toxicity from BMP
Ponds. Prepared for the Northern Virginia
Planning District Commission, the
Occoquan Policy Board, and the Virginia
State Water Control Board.
4. Field, R. and M.L. O'Shea, 1992. "The
Handling and Disposal of Residuals from the
Treatment of Urban Storm Water Runoff
from Separate Storm Drainage Systems,"
Waste Management & Research (1994) 12,
527-539.
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TABLE 2 COST ESTIMATE ($/HECTARE) FOR RESIDUALS HANDLING IN AN
URBAN STORM WATER RUNOFF AREA OF 6071 HECTARES1
Sludge
Handling
Method
Capital
Sedimentation Annual
O&M
Capital
Swirl
Concentration
O&M
Annual
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Landfill
Lime Stabilization
Gra Thickening
Vacuum Filtration
Landspreading
Lime Stabilization
Gravity Thickening
Pressure Filtration
Landfill
Lime Stabilization
Gravity Thickening
Pressure Filtration
Landfill
Lime Stabilization
Gravity Thickening
Landfill
Lime Stabilization
Landfill
1174
1253
1216
1290
176
188
148
158
331
423
306
385
761
257
460
1252
1312
1359
1406
974
2533
158
166
121
124
215
2115
321
383
289
343
410
2950
(1) Huibregtse et al, 1982. Costs have been updated to July 1995 dollars using the Engineering News Record.
Fairfax County, Virginia, 1999. S.
Aitcheson, Fairfax County, personal
communication with Parsons Engineering
Science, Inc.
State of Florida, 1995. J. Cox, State of
Florida, personal communication with
Parsons Engineering Science, Inc.
Huibregtse, K.R., G.R. Morris, A.
Geinopolos, and MJ. Clark, 1977.
Handling and Disposal of Sludges from
Combined Sewer Overflow Treatment.
Phase II - Impact Assessment. United
States Environmental Protection Agency,
EPA-600/2-77053b.
Huibregtse, K.R. and A. Geinopolos, 1982.
Evaluation of Secondary Environmental
Impacts of Urban Runoff Pollution Control.
United States Environmental Protection
Agency, EPA-600/2-82-045.
9. Jones, J., et. al., 1994. An Enforcement
Trap for the Unwary: Can Sediments that
Accumulate in Storm Water "Best
Management Practice" Facilities Be
Classified as Hazardous Wastes Under
RCRA ? A Practical Review for Engineers,
Lawyers, and Drainage Facility Owners.
Report from Wright Water Engineers, Inc.,
Denver, Colorado.
10. Jones, J., et. al., 1995. "BMPs and
Hazardous Sediment," Public Works, pp.
51-54.
11. Lee, G.F. and A. Jones-Lee, 1995. "Issues
in Managing Urban Storm Water Runoff
Quality," Water/Engineering &
Management, pp. 51-53.
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12. Leersnyder, H., 1993. The Performance of
Wet Detention Ponds for the Removal of
Urban Storm Water Contaminants in the
Auckland (NZ) Region. Master's Thesis,
University of Auckland, New Zealand.
13. Marquette University, 1982.
Characteristics and Treatability of Urban
Runoff Residuals. Prepared for U.S. EPA,
Municipal Environmental Research
Laboratory, Cincinnati, Ohio.
14. Maryland Department of the Environment,
1995. K. Pensyl Maryland Department of
the Environment, personal communication
with Parsons Engineering Science, Inc.
15. Metropolitan Washington Council of
Governments (MWCOG), 1987. Control
Urban Runoff: A Practical Manual for
Planning and Designing Urban BMPs.
16. Mineart, P. and S. Singh, 1994. "The Value
of More Frequent Cleanouts of Storm Drain
Inlets," Watershed Protection Techniques,
Volume 1, Number 3 (Fall 1994).
17. Montgomery County, Maryland, 1999. B.
Church, Division of Environmental Policy &
Compliance, Montgomery County,
Maryland, personal communication with
Parsons Engineering Science, Inc.
18. Northern Virginia Planning District
Commission, 1995. N. Goulet, Northern
Virginia Planning District Commission,
personal communication with Parsons
Engineering Science, Inc.
19. Parsons Engineering Science, Inc. (Parsons
ES), 1995. Navy Pollution Prevention
20. Prince Georges County, Maryland,
Department of Environmental Resources,
1999. L. Coffman, Prince Georges County
Department of Environmental Resources,
personal communication with Parsons
Engineering Science, Inc..
21. Rexnord, Inc., 1982. Evaluation of
Secondary Environmental Impacts of urban
Runoff Pollution Control. Prepared for U. S.
EPA, Municipal Environmental Research
Laboratory, Cincinnati, Ohio.
22. Schueler, T. And Y.L. Yousef, 1994.
"Pollutant Dynamics of Pond Muck,"
Watershed Protection Techniques, Volume
1, Number 2. Summer 1994.
23. Terrene Institute, 1994. Urbanization and
Water Quality: A Guide to Protecting the
Urban Environment.
24. U.S. EPA, 1978. Use of Dredgings for
Landfill; Summary Technical Report.
Municipal Environmental Research
Laboratory, Cincinnati, Ohio, EPA-600/2-
78-088a.
25. U.S. EPA, 1992. Storm Water
Management for Industrial Activities:
Developing Pollution Prevention Plans and
Best Management Practices. Office of
Water, EPA 832-R-92-006.
26. U.S. EPA, 1993. Handbook: UrbanRunoff
Pollution Prevention and Control Planning.
Office of Research and Development,
EPA/625/R-93/004.
ADDITIONAL INFORMATION
Center for Watershed Protection
Tom Schueler
8391 Main St.
Ellicott City, MD21043
State of Delaware
Earl Shaver
Delaware Department of Natural Resources and
Environmental Control
59 King's Highway, P.O. Box 1401
Dover, DE 19903
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Fairfax County, Virginia
Steve Aitcheson
Maintenance and Storm Water Management
Division, Public Works/Environmental Services
10635 West Drive
Fairfax, VA 22030
State of Florida
John Cox
Department of Environmental Protection
2600 Blairstone Road
Tallahassee, FL 32399
Montgomery County, Maryland
Boyd Church
Department of Environmental Protection
Division of Environmental Policy & Compliance
255 Rockville Pike, Suite 120
Rockville, MD 20850
Northern Virginia Planning District Commission
Norm Goulet
7535 Little River Turnpike, Suite 100
Annandale, VA 22003
Prince Georges County, Maryland
Larry Coffman
Department of Environmental Resources
9400 Peppercorn Place
Largo, MD 20774
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for the use by the U.S. Environmental Protection
Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
IMTB
Exceience fh compliance through optftnal technical sotitrons
MUNICIPAL TECHNOLOGY BRANCH
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