United States

Environmental Protection

Agency

Office of Water

Washington, D.C.

EPA 832-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 resuspended 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 a field-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
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

Properties of

Residuals Wet Ponds1 SedimentationBasin 2

Swirl and

Helical Bend

Solids

Separators3

In-Line

Upsized Storm

Conduit4

Urban Storm

Water Runoff

Residuals5

Solids

Volatile

Suspended

Solids

6% 104 - 155 mg/l 107 310 mg/l 25,800 mg/l 90 mg/l

Total Suspended

Solids

43% 233-793 mg/l 344 - 1,140 mg/l 161,000 mg/l 415 mg/l

Nutrients

Phosphorus 583 mg/kg < 5 mg/l < 5 mg/l 0.3 - 2,250 mg/l 502 - 1,270

mg/kg

Total Kjeldahl

Nitrogen

2,931 mg/kg <5 mg/l < 5 mg/l 0.3 - 2,250 mg/l 1,140 - 3,370

mg/kg

Heavy Metals

Zinc 6 - 3,171 mg/kg - - - 302 - 352 mg/kg

Lead 11 - 748 mg/kg - - - 251 - 294 mg/kg

Chromium 4.8 - 120 mg/kg - - - 168 - 458 mg/kg

Nickel 3 - 52 mg/kg - - - 69 - 143 mg/kg

Copper 2 - 173 mg/kg - - - 251 - 294 mg/kg

Cadmium ND - 15 mg/kg - - - -

Iron - 6.1 - 2,970 mg/l 6.1- 2,970 mg/l 6.1 - 2,970 mg/l -

Hydrocarbons 2,087 - 12,892

mg/kg

- - - -

Poly Chlorinated

Biphenyls

- 0.19 - 24.6 mg/l - 0.19 - 24.6 mg/l -

(1) Schueler and 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.

TABLE 1 PROPERTIES OF URBAN STORM WATER SOLIDS/RESIDUALS
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/l, with 104

to 155 mg/l being volatile. Concentrations of total

solids from swirl and helical bend solids separators

in Boston, Massachusetts, ranged from 344 to 1,140

mg/l, with 107 to 310 mg/l being volatile. The sixmonth accumulated samples from the in-line upsized

storm conduit in Lansing, Michigan had a total

solids concentration of 161,000 mg/l with 25,800

mg/l 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 nitrogencontaining 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), nitritenitrogen (NO2

), and nitrate-nitrogen (NO3)] in

storm water sediment samples from Boston,

Massachusetts, and Racine, Wisconsin, as never

exceeding 5 mg/l. Urban storm water sediment

samples taken from Lansing, Michigan, were

between 0.3 and 2,250 mg/l 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
found as the highest concentration of metals in all of

the samples ranging in concentration from 6.1 to

2,970 mg/l. 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 onsite 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 polyaromatic 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
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 Fg/l. 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.
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
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 l980s 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
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 al., 1994). In fact,

after drying, storm water sediment has been mixed

with other soil and reused as backfill on

construction projects (Jones, et al., 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 al., 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 al., 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, preexisting 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

al., 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 et al., 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
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 nonhazardous, 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
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, onsite 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 constructionsites 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.
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 onsite 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
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: 

C 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, and treatability.

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.
Sludge

Handling

Method

Capital Sedimentation

O&M

Annual Capital Swirl

Concentration

O&M

Annual

Lime Stabilization

Gravity Thickening

Vacuum Filtration 

Landfill

1174 176 331 1252 158 321

Lime Stabilization

Gra Thickening

Vacuum Filtration 

Landspreading

1253 188 423 1312 166 383

Lime Stabilization

Gravity Thickening

Pressure Filtration 

Landfill

1216 148 306 1359 121 289

Lime Stabilization

Gravity Thickening

Pressure Filtration 

Landfill

1290 158 385 1406 124 343

Lime Stabilization

Gravity Thickening 

Landfill

 - - - 974 215 410

Lime Stabilization 

Landfill 761 257 460 2533 2115 2950

(1) Huibregtse et al, 1982. Costs have been updated to July 1995 dollars using the Engineering News Record.

 TABLE 2 COST ESTIMATE ($/HECTARE) FOR RESIDUALS HANDLING IN AN 

 URBAN STORM WATER RUNOFF AREA OF 6071 HECTARES1

5. Fairfax County, Virginia, 1999. S.

Aitcheson, Fairfax County, personal

communication with Parsons Engineering

Science, Inc. 

6. State of Florida, 1995. J. Cox, State of

Florida, personal communication with

Parsons Engineering Science, Inc.

7. Huibregtse, K.R., G.R. Morris, A.

Geinopolos, and M.J. 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.

8. 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.
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: Urban Runoff

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, MD 21043

State of Delaware

Earl Shaver

Delaware Department of Natural Resources and

Environmental Control

59 King’s Highway, P.O. Box 1401

Dover, DE 19903
For more information contact:

Municipal Technology Branch

U.S. EPA

Mail Code 4204

401 M St., S.W.

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.