The U.S. Geological Survey (USGS) recommends that alkalinity and acid neutralizing capacity (ANC) be reported in milliequivalents per liter (or microequivalents per liter), if possible. Alternatively, report alkalinity and ANC in milligrams per liter as calcium carbonate.
USGS policy states that reported values of alkalinity and ANC should include all digits known with certainty, plus one digit that is uncertain. That last digit is called the Least Significant Digit (LSD). The same USGS policy also recommends that the analytical results be stored in the USGS database with one additional uncertain digit (LSD+1) because the extra digit may contain useful information when large datasets are evaluated. Published data, however, should be reported only to the LSD.
Using the typical levels of uncertainty associated with alkalinity and ANC titrations, and when following the methods recommended by the USGS National Field Manual (section 6.6.4), the following reporting guidance has been developed. If reporting alkalinity, ANC, carbonate, bicarbonate, and hydroxide in milligrams per liter:
Hydroxide, carbonate, and bicarbonate concentrations cannot be negative. Alkalinity and ANC, however, may be negative because they are a measure of the sample's H+ deficiency relative to a solution of carbon dioxide in water. A negative alkalinity or ANC simply indicates the presence of some amount of mineral acidity. Report negative values of alkalinity and ANC with the same number of significant figures you would use if the values were positive.
Report the average value for duplicate samples or the median when more than two replicate samples are used for quality control and the value falls within the appropriate quality-assurance criterion for variability.
For USGS database users, use the parameter and method codes in the tables below to assign values to alkalinity, ANC, carbonate, bicarbonate, and hydroxide. For more information, consult the USGS parameter and method code dictionaries.
Constituent | Units | Filtered? | Method | Field or Lab |
Parameter Code |
---|---|---|---|---|---|
Alkalinity | mg/L as CaCO3 |
filtered | inflection point | field | 39086 |
lab | 39087 | ||||
Gran | field | 29802 | |||
lab | 29803 | ||||
fixed endpoint | field | 00418 | |||
lab | 00421 | ||||
ANC | mg/L as CaCO3 |
unfiltered | inflection point | field | 00419 |
lab | 00416 | ||||
Gran | field | 29813 | |||
fixed endpoint | field | 00410 | |||
lab | 00417 | ||||
Carbonate | mg/L as CO32- |
filtered | inflection point | field | 00452 |
lab | 29809 | ||||
Gran | field | 63788 | |||
lab | 63789 | ||||
fixed endpoint | field | 29807 | |||
lab | 29808 | ||||
unfiltered | inflection point | field | 00447 | ||
lab | 00446 | ||||
Gran | field | 29798 | |||
fixed endpoint | field | 00445 | |||
lab | 00448 | ||||
Bicarbonate | mg/L as HCO3- |
filtered | inflection point | field | 00453 |
lab | 29806 | ||||
Gran | field | 63786 | |||
lab | 63787 | ||||
fixed endpoint | field | 29804 | |||
lab | 29805 | ||||
unfiltered | inflection point | field | 00450 | ||
lab | 00449 | ||||
Gran | field | 29797 | |||
fixed endpoint | field | 00440 | |||
lab | 00451 | ||||
Hydroxide | mg/L as OH- |
filtered | inflection point | field | 71834 |
lab | 29812 | ||||
Gran | field | 29800 | |||
fixed endpoint | field | 29810 | |||
lab | 29811 | ||||
unfiltered | inflection point | field | 71832 | ||
lab | 71831 | ||||
Gran | field | 29799 | |||
fixed endpoint | field | 71830 | |||
lab | 71833 |
Method codes have been created for field-derived alkalinity and ANC values to record the type of titrator used in the titration. These method codes also record the type of titration method (inflection point, Gran, or fixed endpoint). Use the following method codes for alkalinity and ANC:
Constituent | Units | Filtered? | Method | Field or Lab |
Parameter Code |
Method Code | |
---|---|---|---|---|---|---|---|
Hach Digital Titrator |
Buret Titrator |
||||||
Alkalinity | mg/L as CaCO3 |
filtered | inflection point | field | 39086 | TT061 | TT062 |
Gran | field | 29802 | TT056 | TT057 | |||
fixed endpoint | field | 00418 | TT054 | TT055 | |||
ANC | mg/L as CaCO3 |
unfiltered | inflection point | field | 00419 | TT065 | TT066 |
Gran | field | 29813 | TT058 | TT059 | |||
fixed endpoint | field | 00410 | TT063 | TT064 |
New USGS method codes have been created to make a distinction between the two available speciation methods for calculating carbonate and bicarbonate concentrations. They are:
Choose parameter and method codes from the following tables. Note that each table is for a different titration method. These method codes are new as of early 2008, so your system may or may not yet have access to them. If not, then assign the appropriate "TT" method from the alkalinity/ANC method table above.
Inflection Point Method, Field | ||||||
---|---|---|---|---|---|---|
Constituent | Units | Filtered? | Parameter Code |
Speciation Method |
Method Code | |
Hach Digital Titrator |
Buret Titrator |
|||||
Carbonate | mg/L as CO32- |
filtered | 00452 | advanced | ASM01 | ASM02 |
simple | SSM01 | SSM02 | ||||
unfiltered | 00447 | advanced | ASM09 | ASM10 | ||
simple | SSM09 | SSM10 | ||||
Bicarbonate | mg/L as HCO3- |
filtered | 00453 | advanced | ASM01 | ASM02 |
simple | SSM01 | SSM02 | ||||
unfiltered | 00450 | advanced | ASM09 | ASM10 | ||
simple | SSM09 | SSM10 | ||||
Hydroxide | mg/L as OH- |
filtered | 71834 | advanced | ASM01 | ASM02 |
simple | SSM01 | SSM02 | ||||
unfiltered | 71832 | advanced | ASM09 | ASM10 | ||
simple | SSM09 | SSM10 |
Gran Titration Method, Field | ||||||
---|---|---|---|---|---|---|
Constituent | Units | Filtered? | Parameter Code |
Speciation Method |
Method Code | |
Hach Digital Titrator |
Buret Titrator |
|||||
Carbonate | mg/L as CO32- |
filtered | 63788 | advanced | ASM03 | ASM04 |
simple | SSM03 | SSM04 | ||||
unfiltered | 29798 | advanced | ASM11 | ASM12 | ||
simple | SSM11 | SSM12 | ||||
Bicarbonate | mg/L as HCO3- |
filtered | 63786 | advanced | ASM03 | ASM04 |
simple | SSM03 | SSM04 | ||||
unfiltered | 29797 | advanced | ASM11 | ASM12 | ||
simple | SSM11 | SSM12 | ||||
Hydroxide | mg/L as OH- |
filtered | 29800 | advanced | ASM03 | ASM04 |
simple | SSM03 | SSM04 | ||||
unfiltered | 29799 | advanced | ASM11 | ASM12 | ||
simple | SSM11 | SSM12 |
Fixed Endpoint Titration Method, Field | ||||||
---|---|---|---|---|---|---|
Constituent | Units | Filtered? | Parameter Code |
Speciation Method |
Method Code | |
Hach Digital Titrator |
Buret Titrator |
|||||
Carbonate | mg/L as CO32- |
filtered | 29807 | advanced | ASM05 | ASM06 |
simple | SSM05 | SSM06 | ||||
unfiltered | 00445 | advanced | ASM07 | ASM08 | ||
simple | SSM07 | SSM08 | ||||
Bicarbonate | mg/L as HCO3- |
filtered | 29804 | advanced | ASM05 | ASM06 |
simple | SSM05 | SSM06 | ||||
unfiltered | 00440 | advanced | ASM07 | ASM08 | ||
simple | SSM07 | SSM08 | ||||
Hydroxide | mg/L as OH- |
filtered | 29810 | advanced | ASM05 | ASM06 |
simple | SSM05 | SSM06 | ||||
unfiltered | 71830 | advanced | ASM07 | ASM08 | ||
simple | SSM07 | SSM08 |
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