Glossary of Water Quality Terms

303(d) list Under Section 303(d) of the federal Clean Water Act, every two years the state is required to develop a list of water bodies that don't meet water quality standards. This list is called the 303(d) list. Pierce County is required to develop a water improvement plan (also known as a Total Maximum Daily Load (TMDL) plan), for water bodies on the 303(d) list.

Benthic Index of Biotic Integrity (BIBI) This is a method for determining the type and number of bugs living in or on the bottom of streambeds. These bugs are called benthic-macroinvertebrates. Macro-invertebrates are animals that can be seen with the naked eye and do not have backbones. Benthic means the bottom area of a stream. Stream bugs are useful indicators of stream health, because they spend their lifecycle in a small area, have a short lifespan and are sensitive to water pollution. Different bugs are more tolerant of water pollution than others. The BIBI score is based on the number of different bugs in a stream.

Dissolved Oxygen (DO) This is oxygen that is dissolved in water. Certain concentrations are necessary for aquatic plants and animals to survive. Low levels of DO are primarily caused by high water temperature and decomposing algae and plants in the water. Excess algae and plant growth is caused by phosphorus and nitrogen pollution.

DO levels often vary by season, and state standards for DO levels vary based on how the stream is used by salmon. In general the state minimum acceptable level of DO ranges from 6.5-9.5 milligrams of DO per liter of water. Higher levels of DO indicate healthier streams.

Fecal Coliform Bacteria This is a bacteria from the intestines of warm blooded animals, including humans, dogs, and livestock. The measure of fecal matter in the water indicates the potential for other disease causing organisms that are carried by feces. It is a health risk for humans to be exposed to water with high concentrations of fecal coliform bacteria. High measurements of the bacteria can also cause shellfish area closures.

EPA defines maximum contaminant level (MCL) based on an average of the samples taken each month. To be in compliance, not more than five percent of the samples can include coliform (fecal or E. coli). pH This is a measure of how acid or alkaline the water is on a scale of 0 to 14. A pH below 7 indicates acidic and a pH above 7 indicates alkaline. Most aquatic organisms are very sensitive to pH. A healthy pH is typically between 6.5 and 8.5. The pH level can be affected by polluted runoff and polluted precipitation, known as acid rain.

Temperature Salmon and trout need water temperatures of 9-12 degrees Celsius (48-64 degrees Fahrenheit) to survive and reproduce. Warm temperature reduces the amount of dissolved oxygen in the water and threatens native fish species. Water temperature can increase from removal of streamside vegetation, eroding stream banks and polluted runoff.

Total Nitrogen and Phosphorus High levels of nitrogen and phosphorus cause excessive algae and plant growth. When these plants die and decompose, they consume large amounts of dissolved oxygen. Common sources of nitrogen and phosphorus are fertilizers and human and animal waste. EPA has determined a healthy level of phosphorous to be less than 1 milligram per liter of water. The acceptable level of nitrogen (EPA MCL) is less than 10 milligrams per liter of water.

Total Suspended Solids (TSS) These are particles, both mineral (clay and sand) and organic (algae and small pieces of decomposed plants and animals) that are suspended in the water. High concentrations can harm aquatic life by blocking sunlight and reducing plant photosynthesis, clogging fish gills and increasing water temperature.

TSS is likely to vary by stream, but in general clear water is 20 milligrams or less of TSS per liter of water.

Turbidity This is a measure of water clarity. Things like algae and suspended solids can increase turbidity, making the water cloudy. Particles suspended in the water absorb heat from sunlight, increasing water temperature and reducing dissolved oxygen. Heavy metals and other toxics can attach to the suspended materials. High turbidity blocks sunlight, decreasing plant and algae photosynthesis which affects the food chain for fish.

Like TSS, turbidity varies by stream. Turbidity is measured in nephlometric turbidity units (NTUs). Every stream has a natural level of turbidity and water quality is determined based on increases to the natural turbidity level. Most streams have a natural level of 50 or less NTUs. An increase of up to 10 NTUs means that turbidity is acceptable. Monitoring data scored indicate the amount increase in NTUs above the natural level of 50 NTUs or less.

Water Quality Index (WQI) - is a number between 1 and 100. A higher number indicates better water quality. Eight parameters - fecal coliform bacteria, dissolved oxygen, pH, temperature, total nitrogen and phosphorus (also known as nutrients), total suspended solids, and turbidity - are measured monthly by Pierce County to determine the WQI.