7  Regulatory Limits

We calculated regulatory limits based on freshwater quality standards listed from state and/or 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.

We discuss how various parameters are assessed against standards below.

7.1 Metals

7.1.1 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 chapters that follow. (to do: show graphic example of values above horizontal line here)

Download Regulatory Limits for Metals with Static Regulatory Threshold Values

# 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(static_category == "static_metals",
         standard_type %in% c("drinking_water","irrigation_water","stock_water")) %>%
  remove_empty() %>%
  select(parameter_baseline_name,standard_type,reg_value,reg_unit,agency,source) %>%
  pivot_wider(names_from = standard_type, values_from = reg_value) %>%
  rename(characteristic_name = parameter_baseline_name,
         reg_agency = agency,
         reg_agency_source = source) 

# source formatted data
dat <- read.csv("other/output/analysis_format/baseline_export_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")) 

7.1.2 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 (Ca) and magnesium (Mg) concentrations). 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")

Download List of Metals with Hardness-Dependent Regulatory Threshold Values

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. Note that some sampling events do not have calculated hardness values because total Ca and/or total Mg values were not available.

Download Kenai River Baseline Hardness Data

7.1.2.1 Acute and Chronic Hardness-Dependent Regulatory Threshold Values

Separate hardness-dependent standards often apply for acute vs. chronic metals toxicity.

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. Rather than juxtaposed against static horizontal lines, instead they are highlighted by shape or color when the calculated threshold is exceeded; specific to that sampling event’s hardness conditions. See figure X for an example

(to do: show graphic example of values above threshold as colored asterisks here)

Hardness Dependent Regulatory Thresholds for Metals - Kenai River Baseline Water Quality

# possible general approach for graphic plots: export sheets of static and hardness-dependent results; use this to intake for all figures

7.2 Hydrocarbons

Note: the 2016 baseline report presents hydrocarbon data chapters structured as follows:

• Diesel Range Organics

• Gasoline Range Organics

• Residual Range Organics

However, as of 2025-07-17 it is unclear which specific hydrocarbon parameters, or grouped sums of hydrocarbon parameters, have equivalent names in our data set downloaded from the EPA WQX. As a result, in this report we will structure data to simply assess BTEX values against the ADEC regulatory standard. There may be federal standards that also apply to hydrocarbons, to be addressed later.

Download Regulatory Limits for Hydrocarbons with Static Regulatory Threshold Values

7.2.1 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. The Alaska Dept of Environmental Conversation describes a maximum static regulatory value of 10 ug/l BTEX.

For each sampling event with available hydrocarbons data, we calculated the sum of the parameters that compose BTEX and compared them to a static threshold value.

To prepare our existing data to be assessed against this standard, we addressed the following issues:

• In some cases, BTEX data is quantified as a total mixture (sum of all benzene, toluene, ethylbenzene, and the xylene isomers). In other cases, the individual substances are instead quantified separately.

• In yet other cases, both the values of individual components of BTEX and the total mixture values are reported separately.

• To create a consistent parameter, we summed the total quantities of benzene, toluene, ethylbenzene, and xylene by unique sampling event (unique location/time) when it had not already been reported as such.

• In some cases, multiple isomers of the same hydrocarbon are quantified (e.g. o-xylene vs m,p-xylene). In these cases, we summed the total quantity of the substance for all isomers.

7.3 Nutrients (Nitrogen and Phosphorus)

The following nurtient parameters names are present in the dataset:

• “Phosphorus”
• “Inorganic nitrogen (nitrate and nitrite)”
• “Nitrate”

The previous reports on these data (Guerron Orejuela 2016 and McCard 2007) use only the terms “Nitrate” and “Phosphorus” to describe nutrients.

In our dataset, we have 24 observations of “Nitrate” and 592 observations of “Inorganic nitrogen (nitrate and nitrite).” Both of these parameters are reported to use the identical lab analytical method (4500-NO3(E)). For this report, will treat the two parameter names as indistinguishable, and data appears in the figure as such.

7.4 Fecal Coliform Bacteria

A variety of fecal coliform standards are described in ADEC standards (18 AAC 70). Fecal coliform bacteria may be assessed against criteria in two ways:

• Instantaneous point values, where criteria are exceeded if 10% of samples are above threshold within a 30 day period
• Geometic mean within a 30-day period

In this project, we collect only single samples on single days for each site. Thus, data are not structured to be assessed against existing state standards. In this report, we display two fixed threshold values for a) harvesting aquatic life and b) secondary recreation (contact with water), but it should be notes that single values above these lines do not represent regulatory exceedences.

• helpful data to understand where/when more monitoring is needed
• important to help understand spatial trends

Additional sampling beyond this project is needed to reasonably characterize bacteria conditions in the Kenai River, and several major efforts between 2010 - 2020 contributed to this effort. For more information and detailed reports on Kenai River bacteria monitoring, visit https://www.kenaiwatershed.org/other-water-research/ and click on “Bacteria Monitoring.”

7.5 Total Suspended Solids

Alaska Department of Environmental Conservation (ADEC) standards require that fine sediment in the range of 0.1 mm to 4.0 mm cannot increase over 5% by weight higher than natural conditions in gravel beds used by anadromous or resident fish for spawning, and the sediment can never exceed a maximum of 30% by weight in freshwater for the growth and propagation of fish, shellfish, other aquatic life, and wildlife (ADEC 2025). More generally, the ADEC standard also states that the amount of deposited or suspended sediment cannot cause adverse effects on aquatic life, including their habitat and reproduction.

As such, there is no fixed standard for total suspended solids. Data from this project is best interpreted by either examining long term trends and/or evaluating results in the context of data that provide evidence for “natural conditions.”

7.6 Other Parameters

Download List of pH Regulatory Threshold Values

The following parameters are also monitored for each sampling event:

• pH - The ADEC standard for pH maintains that freshwater may not have a pH less than 6.5 or greater than 8.5 for the growth and propagation of fish, shellfish, other aquatic life and wildlife.

• Water Temperature - See https://aktemp.uaa.alaska.edu/

• Turbidity - see chapter on turbidity for details

• Dissolved Oxygen - monitored, but not reported in 2016 study

ADEC. 2025. “18 AAC 70 Water Quality Standards.” https://dec.alaska.gov/media/1046/18-aac-70.pdf.