6 Regulatory Limits
We calculated regulatory limits based on freshwater quality standards listed from state and federal regulatory agencies. Some regulatory threshold values are static and do not depend on additional environmental parameters, while some threshold values depend on local conditions like hardness, temperature, or pH.
6.1 Metals
6.1.1 Metals with Static Regulatory Threshold Values
The metals parameters in the downloadable table below have static thresholds assigned.
Static regulatory values are represented as solid horizontal lines in the parameter-specific chapters that follow.
# read in static reg values in wide format
static_metals_reg_vals <- read_xlsx("other/input/regulatory_limits/master_reg_limits.xlsx", sheet = "static_regulatory_values") %>%
filter(!is.na(agency),
standard_type %in% c("drinking_water","irrigation_water","stock_water")) %>%
remove_empty() %>%
select(parameter_baseline_name,standard_type,reg_value,reg_unit) %>%
pivot_wider(names_from = standard_type, values_from = reg_value) %>%
rename(characteristic_name = parameter_baseline_name)
# source formatted data
dat <- read.csv("other/output/analysis_format/baseline_analysis_format.csv")
# join static regulatory values to parameter results, and identify when/where exceedences occur
static_metals_thresholds <- left_join(dat,static_metals_reg_vals) %>%
mutate(drinking_water_exceed = case_when(
drinking_water >= result_measure_value ~ "Y")) |>
mutate(stock_water_exceed = case_when(
stock_water >= result_measure_value ~ "Y")) |>
mutate(irrigation_water_exceed = case_when(
irrigation_water >= result_measure_value ~ "Y")) Static-value metals thresholds: download sheet of all static threshold values and their exceedences here
6.1.2 Metals with Hardness-Dependent Regulatory Values
Some regulatory values for metals are not simple static values, and are instead hardness-dependent (i.e. toxicity depends on calcium and magnesium concentrations). Hardness varies by site, by season, and with hydrologic conditions. We calculated hardness according to the following formula:
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.
The metals parameters in the downloadable table below have hardness-dependent thresholds assigned.
# hardness-dependent criteria
# see page 29 of "Alaska Water Quality Criteria Manual for Toxic and other Deleterious Organic and Inorganic Substances" for parameters and formulas
# read in parameters which have hardness dependent criteria
diss_metals_hard_param <- read_excel("other/input/regulatory_limits/master_reg_limits.xlsx", skip = 1, sheet = "diss_metals_hard_parameters") %>%
remove_empty() %>%
select(-parameter_agency_name) %>%
filter(!is.na(characteristic_name),
!is.na(m_a))
# make downloadable list metals which have calculated parameters
dir <- "other/input/regulatory_limits/formatted_reg_vals/calculated_metals_list.csv"
write.csv(diss_metals_hard_param,dir, row.names = F)
embed_file(dir, text = "Download List of Metals with Hardness-Dependent Regulatory Threshold Values")6.1.2.1 Acute and Chronic Hardness-Dependent Regulatory Threshold Values
We calculated hardness-dependent regulatory criteria based on formulas published on the Alaska Department of Environmental Conservation’s Water Quality Standards Section website (https://dec.alaska.gov/water/water-quality/standards/). 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.
Hardness-dependent criteria is calculated from the following formula for metals in freshwater:
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; specific that sampling event’s hardness conditions. See figure X for an example
(to do: show graphic example of values above threshold here)
Hardness-dependent metals thresholds: download sheet of all calculated threshold values and their exceedences here
# general approach: export sheets of static and hardness-dependent results; use this to intake for all figures6.2 Hydrocarbons
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.
6.3 Nutrients (Nitrogen and Phosphorus)
6.4 Bacteria
6.5 Total Suspended Solids
6.6 Other Parameters
# end of script task: combine dataframes from all parameters evaluated against regulatory thresholds. export into "other/output/analysis_format", then source this table for the boxplot and table download functions
# Metals with Static Regulatory Threshold Values
## static_metals_thresholds
# Metals with Hardness-Dependent Regulatory Threshold Values
## hardness_dependent_metals_thresholds
# Hydrocarbons
##
# Nutrients
# Bacteria
# Total suspended solids
# Field parameters