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New names:6 Regulatory Limits
We calculated regulatory limits based on freshwater quality standards listed from state and federal regulatory agencies…
6.1 Metals
6.1.1 Static Regulatory Threshold Values for Metals
Some regulatory threshold values for metals are static and do not depend on additional environmental parameters. The metals parameters in the downloadable table below have static thresholds assigned.
6.1.2 Metals with Hardness-Dependent Regulatory Values
Some regulatory values for metals are not simple static values, and are instead hardness-dependent. Hardness varies by site, by season, and with hydrologic conditions. We calculated hardness according to the following formula:
:::{.callout-note appearance = “simple}
Hardness = 2.497(Total Calcium in mg/L) + 4.119(Total Magnesium in mg/L)
:::
For sampling events with duplicate samples, we calculated average hardness.
`summarise()` has grouped output by 'activity_identifier',
'activity_start_date'. You can override using the `.groups` argument.
Joining with `by = join_by(activity_identifier, activity_start_date)`We calculated hardness-dependent regulatory criteria based on formulas published on the Alaska Department of Environmental Conservation’s Water Quality Standards Section website. The “Alaska Water Quality Criteria Manual for Toxic and other Deleterious Organic and Inorganic Substances” (2022) document, along with the “Inorganic Toxics Criteria Worksheet” provide parameter-specific formulas for many substances.
https://dec.alaska.gov/water/water-quality/standards/
Hardness-dependent criteria may be calculated from the following for freshwater metals:
Acute (dissolved) = exp{mA[ln(hardness)]+ bA} (CF) Chronic (dissolved) = exp{mC [ln(hardness)] + bC} (CF)
where mA, bA, mC, and bC are numerical parameters specific to each substance, and CF is the conversion factor for acute vs. chronic criteria.
These values are graphically displayed in the following chapters not juxtaposed against static horizontal lines, but instead they are highlighted by shape or color when the calculated threshold is exceeded.
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6.2.1 Total BTEX
Total aromatic hydrocarbons (TAH) means the sum of the following volatile monoaromatic hydrocarbon compounds: benzene, toluene, ethylbenzene, and the xylene isomers, commonly called BTEX.
For each sampling event with available data, we calculated the sum of the parameters that compose BTEX and compared them to a static threshold value.