Water Quality Targets
The IDEM Watershed Management Plan (WMP) Checklist (2009) requires groups to identify targets for water quality parameters of concern. A target is defined as the desired measured level of a water quality or habitat/biological parameter that a group has decided streams in the watershed should meet.
Where an Indiana Water Quality Standard or TMDL exists for a parameter of concern, the watershed group must, at a minimum, set the target to meet the respective standard or the loading limit set in the TMDL. Groups obviously are welcome to set more stringent targets if they wish. Figure 1 shows water quality parameters watershed groups are often concerned with and which have an Indiana Water Quality Standard. A complete list of Indiana’s Water Quality Standards can be found in the Indiana Administrative Code.
Many of the water quality parameters watershed groups are concerned with do not have a standard. In these instances groups are free to set whatever target they deem appropriate, but that freedom can be overwhelming given the myriad of targets being used across the county. This guidance does not attempt to tell watershed groups what targets to choose, but rather, lists in Figure 2 several targets used by other watershed groups in Indiana and the source of those targets. IDEM hopes this information helps watershed groups wisely choose water quality targets for their specific watershed.
| Figure 1 | ||
|---|---|---|
| Parameter | Target | Reference/Other Information |
| Total Ammonia (NH3) | Range between 0.0 and 0.21 mg/L depending upon temperature and pH | Indiana Administrative Code (IAC) |
| Atrazine | Max: 3.0 ppb | U.S. EPA Drinking Water Standard |
| Dissolved Oxygen (DO) | Min: 4.0 mg/L Max: 12.0 mg/L | Indiana Administrative Code (IAC) |
| Min: 6.0 mg/L in coldwater fishery streams | Indiana Administrative Code (IAC) | |
| Min: 7.0 mg/L in spawning areas of coldwater fishery streams | Indiana Administrative Code (IAC) | |
| E. coli | Max: 235 CFU/ 100mL in a single sample | Indiana Administrative Code (IAC) |
| Max: Geometric Mean of 125 CFU/ 100mL from 5 equally spaced samples over a 30-day period | Indiana Administrative Code (IAC) | |
| Nitrate | Max: 10 mg/L in waters designated as a drinking water source | Indiana Administrative Code (IAC) |
| Nitrite | Max: 1 mg/L in waters designated as a drinking water source | Indiana Administrative Code (IAC) |
| Nitrate-N + Nitrate-N | Max: 10 mg/L in waters designated as a drinking water source | Indiana Administrative Code (IAC) |
| Temperature | Dependant on time of year and whether stream is designated as a cold water fisheries | Indiana Administrative Code (IAC) |
| Figure 2 | ||
| Parameter | Target | Reference/Other Information |
| Nitrate-nitrogen (NO3) | Max: 0.633 mg/L | U.S. EPA recommendation * |
| Max: 1.0 mg/L | Ohio EPA recommended criteria for Warm Water Habitat (WWH) headwater streams and Modified Warm Water Habitat (MWH) headwater streams | |
| 1.5 mg/L | Dividing line between mesotrophic and eutrophic streams (Dodd et al. 1998) | |
| 10.0 mg/L | IDEM draft TMDL target | |
| Ortho-Phosphate also known as Soluble reactive phosphorus (SRP) |
Max: 0.005 mg/L | Wawasee Area Conservancy Foundation recommendation for lake systems |
| Suspended Sediment Concentration (SSC) | Max: 25.0 mg/L | U.S. EPA recommendation for excellent fisheries |
| Range: 25.0-80.0 mg/L | U.S. EPA recommendation for good to moderate fisheries | |
| Total Kjeldahl Nitrogen (TKN) | Max: 0.591 mg/L | U.S. EPA recommendation * |
| Total Phosphorus | Max: 0.076 mg/L | U.S. EPA recommendation |
| 0.07 mg/L | Dividing line between mesotrophic and eutrophic streams (Dodd et al. 1998) | |
| Max: 0.08 mg/L | Ohio EPA recommendation to protect aquatic biotic integrity in WWH | |
| Max: 0.3 mg/L | IDEM draft TMDL target | |
| Total Suspended Solids (TSS) | Max: 80.0 mg/L | Wawasee Area Conservancy Foundation recommendation to protect aquatic life in lake systems |
| Max: 30.0 mg/L | IDEM draft TMDL target | |
| Range: 25.0-80.0 mg/L | Concentrations within this range reduce fish concentrations (Waters, 1995) | |
| Max: 40.0 mg/L | New Jersey criteria for warm water streams | |
| Max: 46.0 mg/L | Minnesota TMDL criteria for protection of fish/macroinvertebrate health | |
| Turbidity | Max: 25.0 NTU | Minnesota TMDL criteria for protection of fish/macroinvertebrate health |
| Max: 10.4 NTU | U.S. EPA recommendation | |
* U.S. EPA recommended criteria are different for parts of southwest Indiana within Ecoregion IX. See Ecoregional Nutrient Criteria Documents for Rivers & Streams for more information.
Geometric Mean: The geometric mean, in mathematics, is a type of mean or average, which indicates the central tendency or typical value of a set of numbers. It is similar to the arithmetic mean, which is what most people think of with the word "average," except that instead of adding the set of numbers and then dividing the sum by the count of numbers in the set, n, the numbers are multiplied and then the nth root of the resulting product is taken. A geometric mean, unlike an arithmetic mean, tends to dampen the effect of very high or low values, which might bias the mean if a straight average (arithmetic mean) were calculated. This is helpful when analyzing bacteria concentrations, because levels may vary anywhere from 10 to 10,000 fold over a given period.
Geometric Mean Formula:
Geometric Mean = ((X1)*(X2)*(X3)*.......(XN))1/N
where
X = Individual score
N = Sample size (Number of scores)
Geometric Mean Example:
Use the following set of values - 1, 2, 3, 4, and 5 to find the Geometric Mean.
- Step 1: Find 1/N
- N = 5, the total number of values
- Using the above value, 1/5 = 0.2
- Step 2: Calculate the Geometric Mean
- ((1)*(2)*(3)*(4)*(5))0.2 = (120)0.2
- Geometric Mean = 2.60517
The Indiana Administrative Code uses the Geometric Mean as a calculation for five evenly spaced samples of E. coli over 30-days in order to determine compliance with the water quality standard.
In Microsoft Excel, the equation for geomean is =Geomean(Xx:Yy)
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