DETECTING ILLICIT STORMWATER DISCHARGES

Water Protection Program fact sheet
01/2014
Division of Environmental Quality Director: Ed Galbraith
PUB02209

The Water Protection Program has created this fact sheet to help managers of municipal separate storm sewer systems understand basic and technical information about detecting illicit stormwater discharges. This fact sheets covers three topics related to stormwater discharges:

1. Detecting Illicit Stormwater Discharges Overview
2. Water Quality Parameters Useful in Detecting Illicit Stormwater Discharges
3. Water Quality Parameters Useful in Determining Overall Health of Receiving Waters

Detecting illicit stormwater discharges for managers of municipal separate storm sewer systems (MS4s)

Federal and state stormwater regulations require certain communities to develop and administer a comprehensive stormwater management program.  A list of these Missouri communities known as regulated Municipal Separate Storm Sewer Systems (MS4s) can be viewed at www.dnr.mo.gov/env/wpp/stormwater/regulated-ms4.pdf.  One requirement for regulated MS4s is to identify and correct illicit stormwater discharges.  This fact sheet provides communities with a definition of illicit stormwater discharges, potential sources, and how to look for them.

An illicit stormwater discharge is a release of nonstormwater to the stormwater drainage system. Examples of illicit stormwater discharges are untreated sewage, industrial waste, improperly disposed oil, and concentrated pollutants from parking lots or similar contaminants discharged into a MS4 which then drains to a stream, river, or lake.  Resulting contaminants can include heavy metals, oils, greases, solvents, nutrients, detergents, chemicals, and bacteria, which can significantly impact receiving water bodies.

Most MS4s are designed to quickly carry rainwater away from developed areas and solid surfaces such as roadways, rooftops, and parking lots, to natural drainage channels such as rivers and streams.  In general, MS4s provide little-to-no treatment of the water that flows through them. Therefore, untreated domestic sewage, industrial wastewater or other waste streams must not be discharged to the stormwater system.  Those waste streams must be discharged to a municipal wastewater treatment system that is permitted under Missouri’s National Pollutant Discharge Elimination System (NPDES) permit program.

Some communities do not have accurate historical records that show the location of all their stormwater drains, cross-connections between sanitary and storm sewers, and combined sewer overflows (CSOs.)  Therefore, one of the first steps a regulated community must take is to locate, identify, and map the storm drains, municipal sewer lines, and combined sewer overflows, including informal outfall points such as holes in the sides of manholes.  They must then use procedures to detect and eliminate illicit stormwater discharges.  Developing a good mapping system and performing dye and smoke testing of the stormwater pipe system will be necessary. Basic field screening tools and visual screening methods will be useful in detecting potential discharges from outfalls and wet weather drainage areas.

Some useful, yet inexpensive, screening measures to start with are conductivity, pH, and temperature.  A portable meter or water quality test kit can measure these field-screening parameters on-site.  The information obtained should be used as a screening tool to locate problem areas during non-rain events.  If these parameters show readings significantly higher or lower than pre-determined background readings, it is an indication of an illicit stormwater discharge somewhere up stream in the stormwater system.  Visual and odor observations should also be noted to help determine the nature of the discharge (e.g. characteristics such as suds, oil sheens, stains, smudges, and other abnormal or odorous conditions.)

A flow data logger, placed in the drainage area, can collect useful information to determine if discharges take place during non-rainfall events.  For example, if the discharge contains fecal coliform along with an elevated biochemical oxygen demand (BOD), it would be reasonable to search for some type of connection to domestic sewage.  This may be a small subdivision or restaurant.  If the discharge contains heavy metals, an illicit stormwater discharge from an industry might be the suspect. Further investigation will usually require monitoring when the discharge is actually occurring.  Additional field investigations can include asking questions and conducting site surveys.

Monitoring equipment can be expensive, but some items are inexpensive and accurate.  For example, individual conductivity and pH pens cost between $50 and $100 and are available from various laboratory suppliers.

Water Quality Parameters Useful in Detecting Illicit Stormwater Discharges

Visual and odor methods: Color and odor can be good indicators of potential sewage, grey water, and industrial or commercial liquid wastes when searching stormwater systems for illicit stormwater discharge. Odor or distinct coloration of the water may be accompanied by visible sewage, oil sheen, or suds. (Note: suds and surface oil sheen may also occur in natural systems).  Deposits of sediment from nonpoint source runoff may also be visible in the stormwater drainage system.

Chemical and physical methods (*most often determined as field measurements)

Ammonia (NH3): Ammonia is discharged in municipal, industrial, and agricultural wastewaters and is important because of its potential toxic qualities. In aqueous solutions, ammonia assumes two chemical forms: NH4+ – ammonium (less toxic or nontoxic) and NH3 – ammonia (toxic).  The relative concentration of ammonium and ammonia in a given solution are principally a function of pH, temperature, and ionic strength of the aqueous solution.

Ammonia is most useful in differentiating illicit stormwater discharges of sewage, from sources such as potable or natural water.  However, it is possible to detect ammonia in potable water discharges when chloramines are used as a disinfectant in the distribution system.

 Chlorine*: The chlorination of water supplies and polluted waters serves to primarily destroy or deactivate disease-producing microorganisms.  A secondary benefit, particularly in treating drinking water, is the overall improvement in water quality resulting from the reaction of chlorine with ammonia, iron, manganese, sulfide, and some organic substances

Chlorine is most useful in differentiating illicit stormwater discharges of potable water, swimming pool discharge, or industrial wastewater from natural water.  Unless potable water discharge is extreme or located close to the monitoring point, the high chlorine demand in natural waters may limit the utility of this parameter to flows with very high chlorine concentrations from industrial or commercial waste (Brown, 2004).

Conductivity*: Conductivity is a measure of the ability of an aqueous solution to carry an electrical current.  This ability depends on the presence of ions; on their total concentration, mobility, valence, and the temperature of the solution.  Solutions of most inorganic compounds (such as chloride, nitrate, ammonia, sulfate, phosphate, sodium, magnesium, calcium, iron, and aluminum) are relatively good conductors.  Conversely, organic compounds like oil, alcohol, and sugar do not conduct electricity very well and thus do not appreciably change the conductivity of receiving waters.

The presence of an illicit stormwater discharge can increase the conductivity of a body of water over normal background levels. Conductivity is most useful in differentiating sewage, grey water, and industrial or commercial waste from potable water.  Depending upon the geographic region and seasonal conditions, conductivity values in stormwater runoff can be elevated. This is mainly prevalent during the winter months when ice-melting agents are in use (e.g. sodium chloride and calcium chloride).

Detergents and Surfactants: Detergents are commercial or retail products used to wash clothing. Presence of detergents is usually measured as surfactants or fluorescence.  Surfactants are the components of commercial detergents that detach dirt from the clothing. The actual concentration of surfactants is much lower than the concentration of detergent, but analytical methods that measure surfactants are often referred to as “detergents.” To avoid confusion, surfactants can be referred to as “detergents as surfactants.”

Detergents and surfactants are most useful in differentiating sewage, grey water, and industrial waste from potable or natural water.

E. coli and Fecal coliform: Fecal coliform, enterococci, and E. coli bacteria are present in the digestive systems of all warm-blooded animals and are not usually disease-causing organisms themselves.  However, high concentrations suggest the presence of fecal matter, which may contain disease-causing organisms.  Fecal coliform, enterococci, and E. coli bacteria are used as indicator organisms; they indicate the probability of finding pathogenic organisms in a stream. Fecal coliform and E. coli should be measured with caution.

During dry weather conditions, high bacteria levels are most useful as an indicator of sewage in stormwater systems.  However, during stormwater discharges bacteria levels can be high due to runoff that contains fecal waste from pets and other animals.

Florescence: Absorption of ultra-violet light at 253.7 nm has historically been measured to detect some organic compounds in water.  More recently ultra-violet light emission in the 415-445 nm range has been used as an indicator of optical brighteners.  In the United States, 97 percent of laundry detergents contain the optical brightener DSBP (4,4’-bis(2-sulfostyry) biphenyl) and DAS1 (4,4’-diamino-2,2’-stilbene-disulfonic acid). Because household plumbing systems mix effluent from washing machines and toilets together, optical brighteners are associated with human sewage in septic systems and wastewater treatment plants.

Optical brighteners can be useful in differentiating between sewage or grey water and potable or natural water.  Optical Brightener Monitoring (OBM) traps with absorbent pads can be used to capture dry weather flows.  The absorbent pads are then observed under a fluorescent light to help determine if detergents using optical brighteners are present (Brown, 2004). Florescence in combination with fecal bacteria can provide four possible contamination scenarios: 1) high concentrations of optical brighteners and high counts of fecal bacteria, which suggests a malfunctioning septic drain field or leaking sewer pipe, 2) high concentrations of optical brighteners and low counts of fecal bacteria, which suggests gray water in the stormwater system, 3) low concentrations of optical brighteners and high counts of fecal bacteria, which suggests other warm-blooded animals, and 4) low concentrations of optical brighteners and low counts of fecal bacteria, which suggests no source of fecal contamination.

Fluoride: In Missouri, fluoride does not naturally occur in surface water in detectable amounts.  It is generally added to potable water as a public health measure.  Maintenance of an optimal fluoride concentration is essential in maintaining effectiveness and safety of the fluoridation procedure.

When differentiating between sewage and grey water, fluoride is a poor indicator as a lone parameter, but when combined with additional parameters (such as detergents, ammonia, and potassium) fluoride can almost always be used to differentiate between sewage and grey water. Fluoride as a single parameter can almost always differentiate potable water from natural water.

Hardness: The hardness of water is governed by the content of calcium and magnesium salts (temporary hardness) largely combined with bicarbonate and carbonate and with sulfates, chlorides, and other anions of mineral acids (permanent hardness).  Hardness can affect the toxicity of other chemicals present in stormwater runoff.

Hardness can sometimes be used to differentiate discharge from potable and natural water depending on regional characteristics or can be helpful in combination with other parameters.

pH:: Natural surface water generally has pH values ranging between six and nine, depending upon the presence of dissolved substances that come from bedrock, soils, photosynthetic activity, and other materials in the watershed.  If the water in a stream is too acidic or basic, the H+ or OH- ion activity may harm or kill aquatic life by directly disrupting biochemical reactions or it may indirectly affect aquatic life by increasing the toxicity of aqueous compounds.  For example, as pH increases, ammonia becomes more toxic to fish. As pH decreases, the concentration of a metal may increase because higher acidity increases the ability of metals to be dissolved from sediments into the water.

Measurement of pH can sometimes be used to differentiate industrial and commercial discharge from potable and natural water depending on regional characteristics or can be helpful in combination with other parameters.

Potassium: Potassium compounds have a wide variety of municipal and industrial uses.  Major potassium chemicals used in industry are potassium hydroxide, potassium carbonate, potassium sulfate, potassium permanganate, and potassium chloride.  Potassium is also an essential component of fertilizer.

High potassium is most useful in differentiating sewage and industrial waste discharge from potable or natural water.  This may depend on regional soil characteristics and will most likely be helpful in combination with other parameters.

Temperature*: Temperature is an easy and affordable water quality parameter to collect.  Although necessary in determination of ionized ammonia, it may also be useful in detection of illicit stormwater discharges in stormwater systems.  Comparison of ambient and discharge temperatures may help differentiate between industrial or commercial discharge and ground water discharge.

Turbidity: Turbidity is a measure of the cloudiness of water.  Cloudiness in stormwater systems is mostly caused by sediment and organic matter suspended in the water column.  Poorly maintained or non-existent best management practices at land disturbance sites may result in highly turbid runoff.  Suspended soil particles can bury eggs and benthic organisms when they settle in streams and can also carry nutrients, pesticides, and other pollutants throughout a stream system.

During dry weather conditions, turbidity can sometimes differentiate sewage or grey water discharge from potable or natural water discharge depending on regional characteristics or can be helpful in combination with other parameters.

Water Quality Parameters Useful in Determining Overall Health of Receiving Waters

Some regulated Municipal Separate Storm Sewer Systems (MS4s) are required to assist in restoring an impaired water body to its designated uses such as drinking water, whole body contact recreation, aquatic life habitat, fish consumption, or other uses identified in Chapter 7 of Revised Statutes of Missouri.  Municipalities that impact a water body on the impaired waters list and have a site-specific MS4 permit or Small MS4 Master General Permit MO-R040000 (www.dnr.mo.gov/env/wpp/permits/issued/docs/R040000.pdf) will likely be required to develop a plan to assist in restoration of the water body.

An important goal in stream or wetland protection and restoration is the identification and removal of illicit stormwater discharges.  This often requires further study of outfall discharges, quality of receiving waters, potential sources of pollution, and opportunities to restore and protect the existing drainage system.

To assess the health of receiving waters, parameter monitoring data can be compared to specific numeric water quality criteria listed in the Missouri Water Quality Standards (10CSR 20-7).   Parameters in this fact sheet with an asterisk (*) are subject to numeric water quality criteria.  If numeric criteria are not available for certain chemical or physical parameters, monitoring data can be compared to background water quality data of nearby, similar-sized control streams that are relatively unimpacted by pollution sources.

Water quality data are used to characterize waters, identify trends over time, identify emerging problems, determine whether pollution control programs are working, help direct pollution control efforts to where they are most needed, and respond to emergencies such as floods and spills.  Analytical detection limits and methodology are important aspects of monitoring receiving waters protected by specific numeric criteria.  U.S. Environmental Protection Agency approved or accepted analytical methods should be followed when comparing monitoring data to numeric water quality criteria.  

Visual and odor screening methods
Not only can color and odor be good indicators at outfall points, they can also be useful as narrative criteria to assess impacts from sewage, grey water, and industrial or commercial liquid wastes.  Odor or distinct coloration of the water may be accompanied by visible sewage, oil sheen, or suds. (Note: suds and surface oil sheen may also occur in natural systems.)  Visual and/or odor screening can sometimes assist in the decision to collect physical and chemical monitoring parameters.

 Analytical parameters

Biochemical Oxygen Demand (BOD): BOD is the amount of oxygen consumed by bacteria in the decomposition of organic material.  It also includes the oxygen required for the oxidation of various chemicals in the water, such as sulfides, ferrous iron, and ammonia.  While a dissolved oxygen test tells you how much oxygen is available, a BOD test tells you how much oxygen is being consumed and is an indirect measure of the biodegradable organic material content of a sample.  A BOD test can provide valuable information to differentiate the causes of low dissolved oxygen.  Similar tests are used more specifically in wastewater treatment and include carbonaceous biochemical demand (CBOD), which uses nitrogen inhibitors and chemical oxygen demand (COD), which measures the oxygen equivalent of organic matter.

E. coli*: E. coli are present in the digestive systems of all warm-blooded animals and are not usually disease-causing organisms themselves.  However, high concentrations suggest the presence of fecal matter, which may contain disease-causing organisms.  E. coli bacteria are used as indicator organisms; they indicate the probability of finding pathogenic organisms in a stream. The strains of E. coli bacteria present in all warm-blooded animals, including humans, should not be confused with a particular strain of E. coli that is often found in cattle and can contribute to E. coli tainted beef.  E. coli should be measured with caution since stormwater discharges can have elevated bacteria levels from pet and other animal waste that enters the stormwater system during runoff events.

Metals*: The effect of metals in receiving waters ranges from beneficial to troublesome to dangerously toxic.  While some metals are essential, others may adversely affect receiving waters.  Some metals may be either beneficial or toxic, depending on concentration.  In urban runoff, low concentrations of metals in stormwater discharges are often related to vehicle exhaust, worn tires, roofs, or downspouts; however, elevated concentrations may indicate an illicit industrial discharge.

Nitrogen, Total: Total Nitrogen (TN) is the sum of ammonia-nitrogen (NH3-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N), and organically bonded nitrogen.  Because nitrogen in water can be found in these four major forms, each major form is generally analyzed separately; with TN calculated from the sum of the four major forms.  Nitrogen in freshly polluted water is originally present in the form of organic nitrogen and ammonia.  Natural biochemical processes slowly convert the organic nitrogen into ammonia.  Under aerobic conditions ammonia is then biochemically oxidized into nitrite, then into nitrate.  When nitrite and ammonia nitrogen are at or near zero and nitrate is at a maximum value, the water has been fully nitrified.

At present, ammonia is the only direct nitrogen criterion in the Missouri Water Quality Standards.  If an additional nitrogen criterion is added in the future as part of nutrient criteria, it will most likely be expressed as TN.

Nitrogen, Organic: Organic Nitrogen is the byproduct of living organisms.  It includes such natural materials as proteins, peptides, nucleic acids, urea, and numerous synthetic organic materials.  Typical organic nitrogen concentrations vary from a few hundred µg/L in some lakes to more than 20 mg/L in raw sewage.

Nitrogen as Ammonia (NH3)*: Ammonia is one of the most important pollutants in the aquatic environment because of its relatively highly toxic nature and its ubiquity in surface water systems.  It is discharged in large quantities in industrial, municipal, and agricultural wastewaters.  In aqueous solutions, ammonia assumes two chemical forms: NH4+ – ammonium (less toxic or nontoxic) and NH3 – ammonia (toxic).  The relative concentration of ammonium and ammonia in a given solution are principally a function of pH, temperature, and ionic strength of the aqueous solution.

Nitrogen as Nitrate (NO3-): Nitrates are essential plant nutrients, but in excess amounts they can cause significant water quality problems.  Together with phosphorus, nitrates in excess amounts can accelerate eutrophication, causing dramatic increases in aquatic plant growth and changes in the types of plants and animals that live in the stream.  This, in turn, affects dissolved oxygen, temperature, and other indicators.  Excess nitrates can cause hypoxia [low levels of dissolved oxygen) and can become toxic to warm-blooded animals at higher concentrations (10 mg/L or higher) under certain conditions.  The natural level of nitrate in surface water is typically low (less than 1 mg/L); however, in the effluent of wastewater treatment plants it can be up to 30 mg/L (EPA, Water Monitoring and Assessment, Nitrates 5.7).

Sources of nitrates include wastewater treatment plants, runoff from fertilized lawns and cropland, failing septic systems, runoff from animal manure storage areas, and industrial discharges that contain corrosion inhibitors (EPA, Water Monitoring and Assessment, Nitrates 5.7).

Nitrogen as Nitrite (NO2-): Nitrite is extremely toxic to aquatic life.  However, it is usually present only in trace amounts in most natural freshwater systems because it is rapidly oxidized to nitrate.  In sewage treatment plants using a nitrification process to convert ammonia to nitrate, the process may be impeded, causing discharge of nitrite at elevated concentrations into receiving waters.

Phosphorus, Total: Both phosphorus and nitrogen are essential nutrients for plants and animals that make up the aquatic food web.  Since phosphorus is the nutrient in short supply in most fresh waters, even a modest increase in phosphorus can, under the right conditions, set off a whole chain of undesirable events in a stream, including accelerated plant growth, algae blooms, low dissolved oxygen, and the death of certain fish, invertebrates, and other aquatic animals (EPA, Water Monitoring and Assessment, Phosphorus 5.6).

There are many sources of phosphorus, both natural and human.  These include soil and rocks, wastewater treatment plants, runoff from fertilized lawns and cropland, failing septic systems, runoff from animal manure storage areas, disturbed land areas, drained wetlands, water treatments, and commercial cleaning preparations (USEPA, Water Monitoring and Assessment, Phosphorus 5.6).

In nature, phosphorus usually exists as part of a phosphate molecule (PO4).  Total Phosphorus (TP) in aquatic systems occurs as organic phosphate and inorganic phosphate.  Organic phosphate consists of a phosphate molecule associated with a carbon-based molecule, such as plant or animal tissue.  Phosphate that is not associated with organic material is inorganic.  Inorganic phosphorus is the form required by plants.  Animals can use either organic or inorganic phosphate.  Both organic and inorganic phosphate can be dissolved in the water or attached to particles in the water column. (EPA, Water Monitoring and Assessment, Phosphorus 5.6).

At present, there are no direct phosphorus criteria in the Missouri Water Quality Standards.  If a phosphorus criterion is added in the future as part of nutrient criteria, it will most likely be expressed as TP.

Total Solids: Total Solids is a measure of the suspended and dissolved solids in a body of water and is related to both conductivity and turbidity.  Solids are also a vehicle for other pollutants that become attached to them.

Field parameters

Acidity: Acidity of water is waters quantitative capacity to react with a strong base to a designated pH.  Acidity is a measure of an aggregate property of water and can be interpreted in terms of specific substances only when the chemical composition of the sample is known.

Alkalinity: The alkalinity, or the buffering capacity of a stream, refers to how well water can neutralize acidic pollution and resist changes in pH.  Alkalinity measures the amount of alkaline compounds in the water, such as carbonates, bicarbonates, and hydroxides.  These compounds are natural buffers that can remove excess hydrogen (H+) ions.

Conductivity: Conductivity is a measure of the ability of an aqueous solution to carry an electrical current.  It is an indirect measure of the presence of inorganic dissolved solids such as chloride, nitrate, ammonia, sulfate, phosphate, sodium, magnesium, calcium, iron, and aluminum.  The presence of inorganic dissolved solids in illicit stormwater discharges, stormwater runoff, leachate, sewage bypasses, etc. increases the conductivity of a body of water over normal background levels.  Nonpolar organic substances like oil, alcohol, and sugar do not conduct electricity very well and thus do not change the conductivity of receiving water’s appreciably.  Depending upon the geographic region and seasonal conditions, conductivity values in stormwater runoff can be elevated.  This is mainly prevalent during the winter months when ice-melting agents are in use (e.g. sodium chloride and calcium chloride).

Dissolved Oxygen (DO)*: The amount of DO in water is expressed as a concentration.  A concentration is the amount of weight of a particular substance per a given volume of liquid.  The DO concentration in a stream is the mass of the oxygen gas present, in mg/L of water.  Mg/L can also be expressed as parts per million (ppm).  Both excessively high and excessively low levels of dissolved oxygen can be harmful to organisms.  The concentration of DO in a stream is affected by factors such as:

Hardness: Hardness is frequently used as an assessment of the quality of water supplies.  The hardness of water is governed by the content of calcium and magnesium salts (temporary hardness) largely combined with bicarbonate and carbonate and with sulfates, chlorides, and other anions of mineral acids (permanent hardness).  Hardness can affect the toxicity of other chemicals present in stormwater runoff.

pH*: Natural surface water generally has pH values ranging between six and nine, depending upon the presence of dissolved substances that come from bedrock, soils, photosynthetic activity, and other materials in the watershed.  If the water in a stream is too acidic or basic, the H+ or OH- ion activity may harm or kill aquatic life by directly disrupting biochemical reactions or it may indirectly affect aquatic life by increasing the toxicity of aqueous compounds.  For example: as pH increases, ammonia becomes more toxic to fish.  As pH decreases, the concentration of a metal may increase because higher acidity increases the ability of metals to be dissolved from sediments into the water.

Temperature*: Water temperature is a controlling factor for aquatic life.  It controls the rate of metabolic activities and reproductive activities.  If stream temperatures increase, decrease, or fluctuate too widely, metabolic activities may speed up, slow down, malfunction, or stop altogether.  There are many factors that can influence the stream temperature.  Water temperatures can fluctuate seasonally, daily, and even hourly, especially in smaller sized streams.  Spring discharges and overhanging canopies of stream vegetation provide shade and help buffer the effects of temperature changes.  The quantity and velocity of stream flow also influence water temperature.  The sun has much less effect in warming the waters of streams with greater, swifter flows than of streams with smaller, slower flows.

Stormwater discharges that drain a high percentage of impervious surfaces can have a dramatic effect on the temperature of a receiving stream.  During the mid-summer months, impervious surface (such as pavement) temperatures can exceed 100 °F.  During a mid-summer rainfall event, the rainwater becomes heated as it runs off parking lots and roadways and enters the receiving stream, river, or lake system.

Turbidity: Turbidity is a measure of the cloudiness of water.  Cloudiness is caused by suspended solids (mainly soil particles) and plankton (microscopic plants and animals) that are suspended in the water column.  Moderately low levels of turbidity may indicate a healthy, well-functioning ecosystem, with moderate amounts of plankton present to fuel the food chain.  However, higher levels of turbidity pose several problems for stream systems.  Turbidity blocks out the light needed by submerged aquatic vegetation.  Turbidity can also raise surface water temperatures above normal because suspended particles near the surface facilitate the absorption of heat from sunlight.  Suspended soil particles can carry nutrients, pesticides, and other pollutants throughout a stream system, and can also bury eggs and benthic organisms when they settle.  Turbid waters may also be low in DO.  High turbidity may also result from sediment runoff carrying nutrients to the receiving water body, which can lead to plankton blooms.