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Chemical Monitoring

Watershed Management and Monitoring
Phone: 410-887-5683
Fax: 410-887-4804

Monitoring the Health of our Local Waterways

EPS monitors 40 sites monthly for chemical conditions. Results of Environmental Protection and Sustainability (EPS) monitoring are published annually in its National Pollutant Discharge Elimination System (NPDES) report. Water samples are collected from selected stream sites using small sterile containers. Just as your doctor doesn’t test you for every known disease, EPS conducts 19 tests for pollutants that are prevalent in streams or are listed by the United States Environmental Protection Agency. 

Monitoring the water on a regular basis is important, because any individual sample is just a snapshot of stream conditions at that moment. Water quality conditions change constantly due to weather and other factors. For example, a sudden rain shower might flush nutrients and bacteria from nearby agriculture into the stream. Roads act as conduits for pollution, with stormwater washing sediment, litter and roadway contaminants into storm drains that flow directly into streams with no filtration. Other pollution sources can occur intermittently, such as a failing septic tank, wildlife scat and pet waste.  

Go underground with Baltimore County natural resource specialists and utilities crew members to locate the source of waterway contaminants by watching our short video, "Watershed Moments—Water Pollution Detectives," featuring County Executive Johnny Olszewski.

Categories of Pollutants 


Nutrients like nitrogen and phosphorus are chemicals that are vital to growth in plants, but an overabundance results in the growth of large quantities of algae. Algae can cause algal blooms in the bay and create problems with oxygen levels and water clarity and contribute to dead zones. EPS tests for several different forms of nitrogen and phosphorus to get a complete understanding of how much of these chemicals are in our waterways. Sources of nutrients include fertilizers, sewage, wildlife, agriculture and atmospheric pollutants.

Depleted Oxygen Levels

In addition to testing for the levels of nutrients themselves, we also measure for problems they can create, like poor water clarity and depleted oxygen levels. Total suspended solids and total solids are measured to gauge the clarity of the water. Biological Oxygen Demand (BOD) indicates the amount of oxygen required by aerobic microorganisms to decompose the organic matter in a sample of water. Chemical Oxygen Demand (COD) indicates the amount of oxygen that is needed to oxidize reactive chemicals in water. 

Heavy Metals

EPS also tests for heavy metals, particularly cadmium, copper, zinc and lead. Heavy metals are generally toxic to both wildlife and humans and can cause a variety of problems. The metals often sink into the sediments in the bottom of streams and lakes and are particularly problematic for the aquatic life there. These metals can accumulate in some species of fish that people like to eat and can adversely affect human health.

How We Use the Data

Baltimore County combines the data from chemical monitoring with information gathered from observing the physical conditions of the stream and from biological surveys to help provide a more complete picture of the condition of our waterways. All the data together can help identify the streams that are at risk and contribute to creating an informed plan to reduce pollutants and improve water quality.

To help further understand the health of waterways, EPS measures temperature, pH and the volume of water flowing in the streams. All of these test results are examined along with results of biological monitoring and studies of the physical conditions of the streams. 

Pollution Misconceptions

Foam Can Be Natural or a Sign of Pollution

Foam can occur naturally in streams when dissolved organic compounds act as surfactants. They reduce the surface tension of the surface film of water. This allows fine bubbles and froth to form, accumulate on the surface, and be moved into calm areas by wind and water currents. A good way to tell if it’s natural or manmade is the smell. Naturally occurring foam usually has an earthy or fishy smell, where as the manmade detergent foam has more of a perfume smell. Don't hesitate to contact us if you notice something suspicious.

About Surface Oils and Slime

Iron bacteria, also called iron flocculent, can be found in slow moving or stagnant areas of a stream. It can appear as a rusty, orange slime and may create an oily sheen on the water surface. This is a naturally-occurring bacteria. You can tell the difference between an iron bacteria oily sheen and real oil by poking the surface of the water with a stick. If the globules move back together again, this is a true oil sheen.

Report Concerns

If you have concerns about your stream or see something suspicious, report it on the EPS Report Pollution page. We will investigate any problems that may negatively affect the environment, such as trash dumping or wash water discharging to a stream.

Revised May 4, 2021         


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