Parameter classifications and rationale

The method for calculating these classifications for any given parameter is not the same as that used in the Statewide River Water Quality Assessment (2004).

Total Nitrogen (TN) - Units in mg/L

Low: < 0.75
Moderate: 0.76 to 1.2
High: 1.3 to 2.0
Very High: > 2

Total Phosphorus (TP) - Units in mg/L

Low: < 0.02
Moderate: 0.03 to 0.08
High: 0.09 to 0.2
Very High: > 0.2

pH - Units in pH

Acidic: < 6.5
Neutral: 6.5 to 8.0
High: > 8.0

Turbidity (TUR) - Units in Nephelometric Turbidity Unit (NTU)

Low: < 5
Moderate: 6 to 10
High: 11 to 25
Very High: > 25

Total Suspended Solids (TSS) - Units in mg/L

Low: < 5
Moderate: 6 to 10
High: 11 to 25
Very High: > 25

Dissolved Organic Carbon (DOC) - Units in mg/L

Low: < 5
Moderate: 6 to 10
High: 11 to 25
Very High: > 25

 

Developed for Swan region water quality monitoring and evaluation reporting

Dissolved Oxygen (DO) - Units in mg/L

Rationale: DO was classified in the 2004 SRWQA using fewer classification bands.  These were increased (from 3 to 5 classification bands) for the purpose of reporting the Swan region data.

Very low: < 4.0
Low: 4.0 to 6.0
Moderately Oxygenated: 6.0 to 8.0
Well Oxygenated: 8.0 to 10
Hyperoxic: > 10

 

Soluble nutrient fractions

Rationale: Using the ANZECC guidelines (as had been done for 2004 SRWQA for TN & TP) the default trigger value for lowland rivers was used as the threshold between the moderate and high classifications. In the case of total oxidised nitrogen this was an eighth (12.5%) of the trigger value for TN so all the TN classifications were divided by 8 to give the total oxidised nitrogen classifications. For N as ammonia the default trigger value was a fifteenth (~6.65%) of that for TN so all the TN classifications were divided by 15 to give the N as ammonia classifications. This method was selected for it’s simplicity and ability to allow comparison to the 2004 SRWQA and the 2008 SLIP update of the SRWQA.

Total oxidised nitrogen (NOX) - Units in mg/L

Low: < 0.09
Moderate: 0.09 to 0.15
High: 0.15 to 0.25
Very High: > 0.25

Nitrogen as ammonia/ammonium - Units in mg/L

Low: <0.05
Moderate: 0.05 to 0.08
High: 0.08 to 0.13
Very High: >0.13

Rationale: The 2004 SRWQA didn’t use the lowland river default trigger value of 0.065 mg/L for the moderate to high classification threshold for TP but rather used 0.08mg/L. The lowland river default trigger value for SRP is 0.04 half of what 2004 SRWQA used for TP so TP classifications were halved and used for SRP classifications; again for reasons of comparability and simplicity.

Soluble reactive phosphorus (orthophosphate) - Units in mg/L

Low: <0.01
Moderate: 0.01 to 0.04
High: 0.04 to 0.1
Very High: >0.1

Replacing salinity with EC - Units in mS/cm)

Based on what has been previously used for the Department’s “River Health Assessment Scheme” classifications.

Fresh: <0.965
Marginal: 0.965 to 1.952
Brackish: 1.953 to 8.835
Saline: >8.835

Heavy metals (Al, As, Cd, Cr, Co, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, Zn)

Generally have three levels “high, low and undetectable” using ANZECC trigger values for 95% (as most metals don’t have trigger values for other protection levels); “high” is above trigger value and “low” is below the trigger value and below the limit of reporting is “undetectable”.

Aluminium (Al) - Units in µg/L

High: > 55.0
Low: < 55.0
Undetectable: < 5.0

Arsenic (As) - Units in µg/L

High: > 13.0
Low: < 13.0
Undetectable: < 1.0

Cadmium (Cd) - Units in µg/L

High: > 0.2
Low: < 0.2
Undetectable: < 0.1

Chromium (Cr) - Units in µg/L

High: > 1.0
Low: < 1.0
Undetectable: < 5.0

Copper (Cu) - Units in µg/L

High: > 1.4
Low: < 1.4
Undetectable: < 1.0

Cobalt (Co) - Units in µg/L

High: > 90.0
Low: < 90.0
Undetectable: < 5.0

Iron (Fe) - Units in µg/L

High: > 300.0
Low: < 300.0
Undetectable: < 5.0

Lead (Pb) - Units in µg/L

High: > 3.4
Low: < 3.4
Undetectable: < 1.0

Mercury (Hg) - Units in µg/L

High: > 0.1
Undetectable: < 0.1

Manganese (Mn) - Units in µg/L

High: > 1900 (1.9 mg/L)
Low: < 1900 (1.9 mg/L)
Undetectable: < 1.0

Molybdenum (Mo) - Units in µg/L

High: > 34.0
Low: < 34.0
Undetectable: < 5.0

Nickel (Ni) - Units in µg/L

High: > 11.0
Low: < 11.0
Undetectable: < 5.0

Selenium (Se) - Units in µg/L

High: > 11.0
Low: < 11.0
Undetectable: < 5.0

Zinc (Zn) - Units in µg/L

High: > 8.0
Low: < 8.0
Undetectable: < 1.0

Total water hardness (as CaCO3) - Units in mg/L (from ANZECC guidelines)

Soft: 0 - 59
Moderate: 60 - 119
Hard: 120 - 179
Very hard: 180 - 240
Extremely hard: > 240

 

Hydrocarbons

Generally have 3 levels ‘high, low and undetectable’ being ANZECC trigger values for 95% (most do not have trigger values for other protection levels) ‘high’ is above the trigger value and ‘low’ is below the trigger value and below the limit of reporting is ‘undetectable’. For those compounds with no ANZECC trigger value then we just have ‘detectable’ and ‘undetectable’ for above and below the limit of reporting, respectively.


Polycyclic aromatic hydrocarbons (PAH)

Naphthalene - Units in µg/L

High: > 16.0
Low: < 16.0
Undetectable: < 0.01

Phenanthrene - Units in µg/L

High: > 2.0
Low: < 2.0
Undetectable: < 0.01

Anthracene - Units in µg/L

High: > 0.4
Low: < 0.4
Undetectable: < 0.01

Flouranthene - Units in µg/L

High: > 1.4
Low: < 1.4
Undetectable: < 0.01

Benzo (a) pyrene - Units in µg/L

High: > 0.2
Low: < 0.2
Undetectable: < 0.01

Benzo (b, k) fluoranthene - Units in µg/L

Detectable: > 0.02
Undetectable: <0.02

All other PAHs

Acenaphthene, Acenaphthylene, Benzo (a) Anthracene, Benzo (b) fluoranthene, Benzo (g, h, i) perylene, Benzo (k) fluoranthene, Chrysene, Dibenz (a, h) Anthracene, Fluorene, Indeno (1, 2, 3-c, d) pyrene, Perylene, Pyrene (Units in µg/L)

Detectable: >0.01
Undetectable: <0.01

 

BTEX

Benzene - Units in µg/L

High: > 950.0
Low: < 950.0
Undetectable: < 1.0

Toluene - Units in µg/L

High: > 80.0
Low: < 80.0
Undetectable: < 1.0

Ethyl Benzene - Units in µg/L

High: > 180.0
Low: < 180.0
Undetectable: < 1.0

Xylene - Units in µg/L

Detectable: > 2.0
Undetectable: < 2.0

 

Hydrocarbons (recoverable)

HC (R) C6 – C9 - Units in µg/L

Detectable: > 25.0
Undetectable: <25.0

HC (R) C10 – C14 - Units in µg/L

Detectable: > 25.0
Undetectable: < 25.0

HC (R) C15 – C28 - Units in µg/L

Detectable: > 100.0
Undetectable: < 100.0

HC (R) C29 – C36 - Units in µg/L

Detectable: > 100.0
Undetectable: < 100.0

Surfactants (as MBAS) - Units in mg/L

Very High: < 0.5
High: 0.3 to 0.5
Moderate: 0.1 to 0.2
Low (undetectable): >0.1

Rules for the data

In order to calculate means and averages, values below the limit of laboratory detection are divided by two and then treated as a numerical value (e.g. > 0.05mg/L becomes 0.025mg/L) even though the laboratory analysis is not sensitive enough to give 0.025mg/L as a result. This is an acceptable and widely used technique to allow analysis of values below laboratory detection limits.

With the data that is left for a project in a given calendar year then if there are fewer than 5 data points then the script must calculate the average (mean) value which it then compares to the classification rankings. If there are 5 or more data points then the script is to calculate the median value which it then compares to the classification rankings. If there are no data points (because all values were below detection limits) then the script is to report that particular chemical parameter as “not detected”.