United States

Environmental Protection

Agency

Office of Water

Washington, D.C.

EPA 832-F-99-022

September 1999

Storm Water

Management Fact Sheet

Non-Storm Water Discharges to Storm Sewers

DESCRIPTION

Identifying and eliminating non-storm water

discharges to storm sewers is an important and very

cost-effective Best Management Practice (BMP) for

improving runoff water quality. Non-storm water

discharges can include discharges of process water,

air conditioner condensate, non-contact cooling

water, vehicle wash water, or sanitary wastes, and

are typically the result of unauthorized connections

of sanitary or process wastewater drains to storm

sewers. These connections are common, yet often

go undetected. Typically these discharges are

significant sources of pollutants, and, unless

regulated by an NPDES permit, they are also illegal.

Environmental impact evaluations have shown that

the elimination of non-storm water discharges is an

effective BMP, because such discharges may

contain a significant loading of pollutants.

Several studies exist on the contents of non-storm

water discharges. Pitt and Shawley (1982) reported

that non-storm water discharges were found to

contribute substantial quantities of a variety of

pollutants, even though the individual

concentrations of each pollutant were not high.

During extended periods of base flow conditions,

the lower concentration was offset, leading to a

substantial loading of pollutants. Gartner, Lee and

Associates, Ltd. (1983) conducted an extensive

survey of non-storm water discharges in the Humber

River watershed (Toronto). Out of 625 outfalls,

about 10 percent were considered significant

pollutant sources. Further investigations identified

many industrial and sanitary non-storm water

discharges into the storm drainage system. 

Sources found in industrial areas included liquid

dripping from animal hides stored in tannery yards,

and washdowns of storage yards at meat packing

facilities. Therefore, it is anticipated that elimination

of non-storm water discharges will be a highly

effective BMP.

Identifying and eliminating non-storm water

discharges has rarely been done at industrial

facilities. Part of the problem is education: many

facility operators are unaware of what constitutes a

non-storm water discharge and what the potential

environmental impacts of these discharges are.

Compliance with NPDES permit requirements for

the presence of non-storm water discharges will

greatly improve the implementation of this BMP.

APPLICABILITY

Almost every industrial facility that has not been

tested or evaluated for the presence of potential

non-storm water discharges should be so evaluated.

Typically NPDES permit certification includes:

• Identification of potential non-storm water

discharges.

• Results of a site evaluation for the presence

of non-storm water discharges.

• The evaluation criteria or test method used.

• The date of testing and/or evaluation.

• The on-site drainage points that were

directly observed during the test and/or

evaluation.

This certification must be signed in accordance for

the facility's NPDES storm water permit. A sample

certification form is shown in Figure 1.
NON-STORM WATER DISCHARGE

ASSESSMENT AND CERTIFICATION

Worksheet Completed By: _______________________

Title: ________________________________________

Date: ________________________________________

Signature: ____________________________________

Date of Test or

Evaluation

Outfall Directly

Observed During

the Test (Identify as

indicated on the site

map)

Method Used to

Test or Evaluate

Discharge

Describe Results

from Test for the

Presence of NonStorm Water

Discharge

Identify Potential

Significant Sources

Name of Person

Who Conducted

the Test or

Evaluation

 Source: U. S. EPA, 1992.

FIGURE 1 SAMPLE WORKSHEET FOR RECORDING NON-STORM WATER DISCHARGES

ADVANTAGES AND DISADVANTAGES

Identifying and eliminating non-storm water

discharges can be an easy and cost-effective method

for preventing runoff contamination and pollution of

receiving water bodies. However, identifying these

discharges may be problematic. Possible problems

in identifying non-storm water discharges include:

• A non-storm water discharge may not occur

on the date of the test or evaluation.

• The method used to test or evaluate the

discharge may not be applicable to the

situation.

• A lack of available data on the location of

storm drains and sanitary sewers, especially

in older industrial facilities, may make

identifying an illicit connection difficult.

KEY PROGRAM COMPONENTS

Key program criteria include identifying and

locating non-storm water entries into storm drainage

and investigating their sources.

For any effective investigation of pollution within a

storm water system, all pollutant sources must be

included. For many pollutants, storm water may

contribute the smaller portion of the total pollutant

mass discharge from a storm drainage system. In

addition to conventional storm water runoff

associated with rainfall, pollutant sources may

include dry-weather entries occurring during both

warm and cold months and snowmelt runoff.

Consequently, much less pollution reduction benefit

will occur if only storm water is considered in a

control plan for controlling storm drainage

discharges.

The investigations may also identify illicit point

source outfalls that do not carry storm water.

Obviously, these outfalls also need to be controlled

and permitted. Figure 1 can be used as a sample

worksheet to report non-storm water discharges.

There are four primary methods for investigating

non-storm water discharges.

Visual Inspection 

The simplest method for detecting non-storm water

connections in the storm water collection system is

to observe all discharge points during periods of dry

weather. Key parameters to look for are the

presence of stains, smudges, odors, and other

abnormal conditions. 

Sanitary and Storm Sewer Map Review 

A review of a plant schematic is another simple way

to determine if there are any unauthorized

connections to the storm water collection system.

A sanitary or storm sewer map, or plant schematic,

is a map of pipes and drainage systems used to carry
process wastewater, non-contact cooling water, and

sanitary wastes. These maps (especially as-built

plans) should be reviewed to verify that there are no

unauthorized connections. However, a common

problem at many sites is that they often do not have

accurate or current schematics. 

Dye Testing 

Another method for detecting improper connections

to the storm water collection system is dye testing.

A dye test can be performed by simply releasing a

dye (either pellet or powder) into either the sanitary

or process wastewater system. Discharge points

from the storm water collection system are then

examined for color change. 

Sampling and Chemical Analysis 

Sewer mapping and visual inspection are also

helpful in identifying locations for sampling.

Chemical tests are needed to supplement the visual

or physical inspections. Chemical tests can help

quantify the approximate components of the

discharge mixture at the outfall or discharge point.

Samples should be collected, stored, and analyzed in

accordance with standard quality assurance and

quality control (QA/QC) procedures. Statistical

analysis of the chemical test results can be used to

estimate the relative magnitudes of the various flow

sources. In most cases, non-storm water discharges

are made up of many separate sources of flow, such

as leaking domestic water systems, sanitary

discharges, ground water infiltration, automobile

washwater, etc. Key parameters that can be helpful

in identifying the source of the non-storm water

flows include biochemical oxygen demand (BOD),

chemical oxygen demand (COD), total organic

carbon (TOC), specific conductivity, temperature,

fluoride, hardness, ammonia, ammonium, potassium,

surfactant fluorescence, pH, total available chlorine,

and toxicity screening. It may be possible to

identify the source of the non-storm water discharge

by examining the flow for specific chemicals.

Just as high levels of pathogenic bacteria are usually

associated with a discharge from a sanitary waste

water source, the presence of certain chemicals is

generally associated with specific industries. Table

1, includes a listing of various chemicals that may

be associated with a variety of activities.

IMPLEMENTATION

Identification of non-storm water discharges should

be part of every facility’s maintenance program.

Facilities should conduct annual inspections for

non-storm water discharges, even if previous tests

have found no such discharges. New processes,

building additions, or other plant changes may have

brought about unauthorized connections to the

storm water conveyance system.

COSTS

The above methods are mostly time-intensive;

therefore, the cost is dependent on the level of effort

employed, and on the level of expertise. Visual

inspections are the least expensive of the three. Dye

testing may be more cost effective for buildings that

do not have current schematics of their sanitary and

storm sewer systems. The cost of disconnecting

illicit discharges from the storm water system will

vary depending on the type and location of the

connection.

The full use of all of the applicable procedures is

most likely necessary to identify all pollutant

sources. For example, attempting to reduce costs

by examining only a certain class of outfalls, or

using inappropriate testing procedures, will

significantly reduce the utility of the testing

program and result in inaccurate conclusions.

REFERENCES

1. California Environmental Protection

Agency, Draft, 1992. Staff Proposal for

Modification to Water Quality Order No.

91-13 DWQ Waste Discharge Requirements

for Discharges of Storm Water Associated

with Industrial Activities. 

2. Gartner, Lee and Associates, Ltd., 1983.

Toronto Area Watershed Management

Strategy Study, Technical Report No. 1,

Humber River and Tributary Dry Weather

Outfall Study. Ontario Ministry of the

Environment, Toronto, Ontario.
TABLE 1 CHEMICALS COMMONLY FOUND IN INDUSTRIAL DISCHARGES

Chemical Industries

Acetic Acid Acetate rayon, pickle and beetroot manufacture

Alkalis Cotton and straw kiering, cotton manufacture

Ammonia Gas and coke manufacture, chemical manufacture

Arsenic Sheep-dipping, felt mongering

Chlorine Laundries, paper mills, textile bleaching

Chromium Plating, chrome tanning, aluminum anodizing

Cadmium Plating

Citric Acid Soft drinks and citrus fruit processing

Copper Plating, pickling, rayon manufacture

Cyanides Plating, metal cleaning, case-hardening, gas manufacture

Fats, Oils Wool scouring, laundries, textiles, old refineries

Fluorides Gas and coke manufacture, chemical manufacture, fertilizer plants, 

Formalin Manufacture of synthetic resins and penicillin

Hydrocarbons Petrochemical and rubber factories

Hydrogen Peroxide Textile bleaching, rocket motor testing

Lead Battery manufacture, lead mining, paint manufacture, gasoline

Metcaptins Oil refining, pulp mills

Mineral Acids Chemical manufacture, mines, iron and copper pickling, brewing, textiles

Nickel Plating

Nitro Compounds Explosives and chemical works

Organic Acids Distilleries and fermentation plants

Phenols Gas and coke manufacture, synthetic resin manufacture, textiles,

Silver Plating and photography

Starch Food, textile, wallpaper manufacture

Sugars Dairies, foods, sugar refining, preserves, wood process

Sulfides Textiles, tanneries, gas manufacture, rayon manufacture

Sulfites Wood process, vicose manufacture, bleaching

Tannic Acid Tanning, sawmills

Tartaric Acid Dyeing, wine, leather, and chemical manufacture

Zinc Galvanizing, plating, viscose manufacture, rubber process

Source: Pitt et al., 1992.
For more information contact:

Municipal Technology Branch

U.S. EPA

Mail Code 4204

401 M St., S.W.

Washington, DC, 20460

3. Pitt, R. and G. Shawley, 1982. A

Demonstration of Non-Point Pollution

Management on Castro Valley Creek,

Alameda County Flood Control District

(Hayward, California) and U.S. EPA,

Washington, DC.

4. Pitt, R., D. Barbe, D. Adrian, and R. Field,

1992. Investigation of Inappropriate

Pollution Entries Into Storm Drainage

Systems -- A Users Guide, U.S. EPA,

Edison, New Jersey.

5. Pitt, R., and R. Field, 1992. Non-Storm

Water Discharges into Storm Drainage

Systems. NTIS Report No. PB92-158559.

6. U.S. EPA, 1992. Storm Water

Management For Industrial Activities:

Developing Pollution Prevention Plans and

Best Management Practice. EPA 833-R92-006.

7. Washington State Department of Ecology,

February, 1992. Storm Water Management

Manual for the Puget Sound Basin.

ADDITIONAL INFORMATION

Center for Watershed Protection

Tom Schueler

8391 Main Street

Ellicott City, MD 21043

King County, Washington

Dave Hancock

Department of Natural Resources, Water and Land

Resources Division, Drainage Services Section

700 5th Avenue, Suite 2200

Seattle, WA 98104

State of Minnesota

Lou Flynn

Minnesota Pollution Control Agency

520 Lafayette Road North

St. Paul, MN 55155

Northern Virginia Planning District Commission

David Bulova

7535 Little River Turnpike, Suite 100

Annandale, VA 22003

Southeastern Wisconsin Regional Planning

Commission

Bob Biebel

916 N. East Avenue, P.O. Box 1607

Waukesha, WI 53187

The mention of trade names or commercial products

does not constitute endorsement or recommendation

for the use by the U.S. Environmental Protection

Agency.