CCAMP Healthy Watersheds- Healthy Streams Assessment
Threshold Selection Process
(August 12, 2014)
Threshold selection for toxic chemicals in water follows a step-wise process based on the water quality
goal algorithms of Marshack (2011). Threshold sources referenced by Marshack were unavailable for a
number of chemicals, particularly current use pesticides and some PAHs. In order to include these
chemicals in the healthy watersheds assessment, we used thresholds from other well-documented
sources, such as the USEPA Office of Pesticide Programs Aquatic Life Benchmarks. Literature toxicity
values were used for a smaller number of chemicals for which no thresholds have been developed.
Thresholds selection for toxic chemicals in sediment was also a stepwise process prioritizing consensusbased sediment quality guidelines.
For each chemical, thresholds were selected according to the stepwise hierarchy described below. If no
thresholds for a target chemical were available in an earlier step (tier), then thresholds in the
subsequent tier were considered. Some tiers contain multiple thresholds, in which case directions are
given for selecting either the lowest (most protective) among equally applicable thresholds or selecting
thresholds along a hierarchy within the tier.
As with regulatory standards, thresholds are selected for the appropriate beneficial use. For this
assessment, all aquatic life beneficial uses are combined into freshwater (COLD), estuarine (EST), or
saltwater (MAR) based on the salinity of the waterbody. Freshwater thresholds (COLD) apply to waters
with salinity less than 1‰, saltwater thresholds (MAR) apply to waterbodies with salinity greater than
10‰, and the lower of the two thresholds applies to estuaries (EST) where salinities range from 1 to
10‰. Because central coast estuaries are strongly influenced by tidal and riverine flows and have
widely fluctuating salinity, the lower (more protective) of the freshwater or saltwater thresholds was
generally applied to estuarine sites regardless of the actual salinity measured when samples were
collected.
Threshold Selection Process for Aquatic Life - Toxic Chemicals in Water
Step 1: For each chemical, select the lowest value from the following sources:
 Central Coast Water Quality Control Plan (Basin Plan, 2011) water quality objectives
 Water Quality Control Plan Ocean Waters of California (Ocean Plan, 2012) Table 1 six-month
median water quality objectives (for saltwater waterbodies)
 John – what about: Water Quality Control Plan Ocean Waters of California (Ocean Plan, 2012)
Table 1 24-hour, 1-day (for saltwater waterbodies) – where do these fit in?

 California Toxics Rule, Criteria Continuous Concentration (CCC, 4-day average)
 National Toxics Rule, CCC (4-day average)
Step 2: If none of the above thresholds are available, select from the following, if available:
 California Dept of Fish & Wildlife hazard evaluation or water quality criteria (4-day average)
Step 3: If none of the above thresholds are available, select the lowest value from the following
sources:
 US EPA National Recommended Water Quality Criteria, CCC (4-day average)
 US EPA National Recommended Chronic Toxicity info (LOEC)
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks for invertebrate chronic effects
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks for fish chronic effects
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks for vascular plant effects, divided
by 10
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks for non-vascular plant effects,
divided by 10.
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks freshwater CCC.
(Note: The EPA OPP aquatic life benchmarks for vascular and non-vascular plants are usually short-term
EC50 values (usually < 10-d LC50s with duckweed and unicellular algae, respectively). Since these are
both considered acute endpoints, they are divided by 10 to approximate chronic effect levels.)
Step 4: If none of the above thresholds are available, select the lowest value from the following
sources:
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks for fish acute effects, divided by 5
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks for invertebrate acute effects,
divided by 5.
 US EPA Office of Pesticide Programs Aquatic Life Benchmarks freshwater CMC, divided by 5.
 California Department of Pesticide Regulation (Luo et al. 2013) benchmark equivalent, lowest
acute benchmark, divided by 5.
 Luo chronic toxicity where benchmark equivalent not available
 California Toxics Rule (EPA), CMC instantaneous maximum, divided by 5
 California Toxics Rule (EPA), CMC 1-hour average, divided by 5
 EPA 2012 Criterion Maximum Concentration (CMC), divided by 5
 EPA National Recommended WQ Criteria, 1-hour average, divided by 5
 EPA National Recommended WQ Criteria, instantaneous maximum, divided by 5
 EPA National Recommended WQ Criteria, instantaneous maximum, toxicity to algae
(There may be redundancy in the last 5 entries.)
 John do you want to add CTR 24 hour average in here?
 How about Cal Ocean Plan daily max or instant. Max, divided by 5?
(Note: The acute OPP aquatic life benchmarks for fish and invertebrates are calculated from the lowest
acute LC50 divided by 2, thus these are further divided by 5 to approximate chronic effects levels.
Similar calculations are used to derive the other acute, instantaneous, and 1-hour criteria, so these are
also divided by 5. All cases assume an acute-to-chronic ratio of 10 between acute LC50 values and
chronic no observed (adverse) effect values [NOECs or NOAECs]. This is consistent with EPA Region 9
advice and many published studies, though literature acute-to-chronic ratios vary widely.
Step 5: If none of the above thresholds are available, carefully evaluate published toxicity values and
thresholds from other sources, including those below, and select the lowest threshold:
 Ambient Water Quality Guidelines, Canadian Council of Ministers of the Environment (2003)
 CCME Guidelines freshwater and saltwater aquatic life guidelines for long-term exposure
(http://ceqg-rcqe.ccme.ca/ (2013)
 Toxicity values from the EPA Pesticide Ecotoxicity Database (2000), with acute LC50 values divided
by 10
 Toxicity values from the Toxicology Data Network, generally with acute LC50 values divided by 10
 Toxicity values from the scientific literature, generally with acute LC50 values divided by 10.
 Other appropriate standards or criteria evaluated on a source-specific basis.
Threshold Selection Process for Aquatic Life - Toxic Chemicals in Sediment
Step 1: Determine whether to apply freshwater or saltwater guidelines as thresholds.
 For waterbodies with inland surface water beneficial uses (e.g., COLD), select freshwater sediment
quality guidelines by proceeding through steps 2a, 3a, 4a, and 5a.
 For marine waterbodies (MAR) select saltwater sediment quality guidelines by proceeding through
steps 2b, 3b, 4b and 5b.
 For estuaries (EST) select either freshwater or saltwater sediment quality guidelines based on
knowledge of site salinity: freshwater guidelines apply for waters < 1‰, saltwater guideline apply
for waters > 10‰, and the lower of the two for salinity on 1 to 10‰. If site salinity is expected to
vary substantially, select the lower of the two guidelines as the threshold.
A. Freshwater sites (COLD), and in some cases estuarine sites (EST)
Step 2a (Tier 1): Select the appropriate consensus-based threshold effects concentration (TEC) from
MacDonald et al. (2000, 2003).
Step 3a (Tier 2): If no TECs are available, select the lowest value from the following sources:
 TEL (Smith, MacDonald, Keenleyside, Ingersoll, Field. 1996)
 TEC (Persaud et al . 1993) Stortelder et al. (1989)
 EPA Region III BTAG Freshwater Screening Benchmarks. 2004.
 Canadian Interim Sediment Quality Guidelines

Ingersoll et al. (1996) Sediment Effect Concentrations (EPA 905-R96-008 (1996)
(I originally had NOAA SQuiRTS in here – but they are a compendium of different values from different
sources most of which we have already collected here)
Step 4a (Tier 3): If none of the above thresholds are available, select the lowest freshwater LC50 value
from acceptable published results of sediment toxicity tests, and divide the LC50s by 10 to approximate
chronic effects.
Step 5a (Tier 4): If none of the above thresholds or LC50s are available, select the lowest freshwater
value from the following sources:
 EPA National Sediment Inventory Sediment Quality Advisory Level – aquatic life, divided by 10 to
approximate chronic or threshold effects*
 Apparent Effects Thresholds, divided by 10 to approximate chronic or threshold effects
 WA State Department of Ecology Sediment Quality Standards (WDOE, 1995), divided by 10 to
approximate chronic or threshold effects**
 WA State Department of Ecology Minimum cleanup levels (WDOE, 1995), divided by 10 to
approximate chronic or threshold effects**
 Dutch Sediment Targets (from NOAA SWRTs)
B. Saltwater sites (MAR), and in some cases estuarine sites (EST)
Step 2b (Tier 1): Select the appropriate NOAA Effects Range Low (ERL) value (Long et al. 1995, NOAA
1999).
Step 3b (Tier 2):
If no ERLs are available, select the lowest value from the following sources:
 TEL (MacDonald, Carr, Calder, Long, Ingersoll, 1996) (Smith, MacDonald, Keenleyside, Ingersoll,
Field; 1996) (EPA, 1996)
 Canadian Interim Sediment Quality Guidelines (http://ceqg-rcqe.ccme.ca/ (2013)
 MET?
 NOAA Screening Quick Reference Tables include TELs, ERLs, and AETs which we already have from
the original source. So, I removed reference to the SQuiRT tables. There is one thing in there I don’t
think we captured for marine sediment from Field, 2002…think we should track it down?
Step 4a (Tier 3): If none of the above thresholds are available, select the lowest saltwater LC50 value
from acceptable published results of sediment toxicity tests, and divide the acute LC50s (< 10-day) by 10
to approximate chronic effects.
Step 5b (Tier4):
If none of the above thresholds or LC50s is available, select the lowest saltwater value from the
following sources:
 EPA National Sediment Inventory Sediment Quality Advisory Level – aquatic life, divided by 10 to
approximate chronic or threshold effects*
 Apparent Effects Thresholds, divided by 10 to approximate chronic or threshold effects
 WA State Department of Ecology Sediment Quality Standards (WDOE, 1995), divided by 10 to
approximate chronic or threshold effects**
 WA State Department of Ecology Minimum cleanup levels (WDOE, 1995), divided by 10 to
approximate chronic or threshold effects**
What about EPA National Recomm WQ Criteria
Threshold Selection Process for Aquatic Life - Conventional Chemicals in Water
Thresholds for conventional chemicals (such as nutrients, pH, dissolved oxygen, etc.) are generally based
on Basin Plan standards and expert judgment of Region 3 staff. For conventional chemistry, threshold
selection involves special treatment of several analytes with unusual properties. For example, water
temperature, oxygen and pH all have normal distributions, not the typically skewed distributions of
chemical contaminants, for which zero is protective and any increasing concentrations over zero are
steadily more damaging. This resulted in special considerations relative to the scoring approach. We
specify the details of how these analytes are handled here: Conventional Chemistry Thresholds.
Threshold Selection Process for Human Health in Surface Waters
(MUN and COMM beneficial uses)
Selection of human health thresholds for surface waters is based on selecting the appropriate value
from each of the following four categories, and then selecting the lowest of the four category values.
 California Toxics Rule and National Toxics Rule
 Chemical Constituent Objective
 Toxicity Objective
 Taste and Odor-based numeric thresholds
Step 1: CTR, NTR, NRWQC
For each chemical, identify the criteria for human health protection from the California Toxics Rule and
the National Toxics Rule, and select the lower of the two. If neither exists for the target chemical, select
the USEPA National Recommended Water Quality Criterion (NRWQC) for human health protection. If no
NRWQC value exists for the target chemical, eliminate this category from the selection process.
Step 2: Chemical Constituent Objective
For each chemical, select the lowest of:
 California primary Maximum Contaminant Level (MCL), or
 Federal primary MCL.
 Central Coast Basin Plan
Step 3: Toxicity Objective
This step is a composite process wherein each dark bullet point (●) is a sub-category with internal
choices. For each chemical, select the threshold from the first of the following seven hierarchical subcategories that has an available value. (The 7 categories are marked by ●):
 1 - California Public Health Goal

2 - Cal/EPA cancer potency factor at the one-in-a-million risk level

3 - California Drinking Water Notification Level based on toxicity

4 - USEPA IRIS criteria – Select the lowest of the following two:
o One-in-a-million cancer risk estimate
o Reference dose for non-cancer toxicity (as a drinking water threshold)

5 - USEPA Health Advisory — Select the lowest of the following two:
o One-in-a-million cancer risk estimate
o Lifetime non-cancer numeric threshold
o Persons on sodium restricted diets

6 - USEPA MCL Goals — Use non-zero numeric thresholds only

7 - Other health risk-based numeric thresholds - Select the lowest of the following:
o National Academy of Sciences criteria – Select the lowest of:
 One-in-a-million incremental cancer risk
 Drinking water health advisory or SNARL
o Proposition 65 levels (Use only if no other health risk-based numeric thresholds are available.)
Select the lowest of:
 No-Significant-Risk Level
 Maximum Allowable Dose Level
o USGS Health Based Screening Levels (2014)
 Carcinogens
 Non-Carcinogens
 MCLs
8 – Other
o
o
Oregon Human Health WQC
WHO Drinking water guideline values
Step 4: Taste- and Odor-based Numeric Thresholds
For MUN designated waters, select the lowest threshold from the following two:
 California Secondary MCL
 Federal Secondary MCL
If neither is available, select the first available between:
 USEPA NRWQC based on taste & odor
 Taste and odor thresholds published by other agencies or from the peer-reviewed literature
Step 5: Select the Lowest (most protective) Threshold
Compare the thresholds selected in each of the four steps above, and select the lowest (most
protective) threshold as final threshold for human health protection in surface waters.
Threshold Selection Process for Human Health in Surface Waters
(COMM uses)
Step 1: For each chemical, identify the lowest criterion for human health protection from the following:
 California Ocean Plan 30-day averages for human health protection, for carcinogens and noncarcinogens
 California Ocean Plan water quality objective to protect human health
John – I’m not sure what other thresholds are out there that we might want to choose from but think
this is fine for now.
Threshold Selection Process for Human Health in Surface Waters
(REC1 and REC2 beneficial uses)
JH Note: I don’t have this yet but think it is a simple set of E, coli, fecal and total thresholds.
Can we include this in the conventionals?
Notes:
* EPA NSI SQAL values were an average of 15.9 times higher (+ 20) than TEC values for 7 chemicals for
which both values were available (MacDonald et al., 2003 Sediment Quality Assessment Guidelines for
Florida Inland Waters). The 7 chemicals were all OCs and PAHs, for which EPA NSI SQAL values (divided
by 10) might be used as thresholds in CCAMP assessments.
References: USEPA (United States Environmental Protection Agency). 1997. The incidence and severity
of sediment contamination in surface waters of the United States. Volume 1: National sediment quality
survey. EPA 823-R-97-006. Office of Science and Technology (4305). Washington, District of Columbia.
Long ER, MacDonald DD, Smith SL, Calder FD. 1995. Incidence of adverse biological effects within ranges
of chemical concentrations in marine and estuarine sediments. Environ Manag 19: 81–97.
MacDonald, D. D., Ingersoll, C.G., Smorong, D.E., Lindskoog, R.A., Sloane, G., and Biernacki, T. . 2003.
Development and Evaluation of Numerical Sediment Quality Assessment Guidelines for Florida Inland
Waters. p. 116. Florida Department of Environmental Protection, Tallahassee, Florida 32399-2400.
NOAA. 1999. Sediment Quality Guidelines developed for the National Status and Trends Program.
http://archive.orr.noaa.gov/book_shelf/121_sedi_qual_guide.pdf
** Washington State Department of Ecology Sediment Quality Standards and Minimum Cleanup Levels
are based on Apparent Effects Thresholds or were derived similarly to AETs, and are thus also divided by
10 for this assessment.