Qualitative and Quantitative Tier 3 Assessment - Santos
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Qualitative and Quantitative
Tier 3 Assessment
Hydrochloric Acid
In accordance with the Chemical Risk Assessment Framework (CRAF), the assessment for this Tier 3
chemical includes the following components: completing the screening; developing a risk
assessment dossier and Predicted No-Effects Concentrations (PNECs) for water and soil; and,
completing a qualitative and quantitative assessment of risk. Each of these components is detailed
within this attachment.
Background
Hydrochloric acid is a component in hydraulic fracturing fluid systems used in stimulation activities.
Hydraulic fracturing fluid systems comprise water and chemical additives (including a proppant)
blended at the surface of the well lease and injected down the cased well to enhance the gas flow
towards the well. The chemical additives are also used to assist well completion by preparing the
well or maintain the gas flow to the well (i.e., prevent the swelling of clays within the target
hydrocarbon formation).
The purpose and maximum quantity for this chemical in the fluid system is summarised in Table 1. A
safety data sheet (SDS) for the stimulation fluid component is included as Attachment 1.
Table 1 Hydraulic Fracturing Chemicals
Chemical Name CAS No. Use Quantity1
Hydrochloric acid 7647-01-0 pH correction 0.0776%
1Volume Percent in Treatment (%)
CAS No = Chemical Abstracts Service Number
The assessment of toxicity of this chemical was used to evaluate human health exposure scenarios
and is presented in Attachment 2. Repeated dose, reproductive and developmental toxicity studies
by the oral route have not been conducted on hydrochloric acid. These toxicity studies would have
questionable usefulness because of the corrosive/irritating nature of hydrochloric acid, which would
limit the amount of absorbed HCl. Hydrochloric acid dissociates to hydrogen (H+) and chloride (Cl-)
ions in bodily fluids, and a significant amount of these ions are already ingested in foods.
Furthermore, both ions are present in the body and are highly regulated by homeostatic
mechanisms. Therefore, an oral reference dose (RfD) and drinking water guideline value were not
derived for hydrochloric acid.
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Australian Drinking Water Guideline (ADWG) value for pH and chloride (see Table 2) may be
applicable.
Table 2 Australian Drinking Water Screening Values
Drinking Water Screening
Constituent (CAS No.) Drinking Water Screening Value
Guideline
Hydrochloric acid pH; chloride 6.5 to 8.5; 250 mg/L (aesthetics)
(7647-01-0)
CAS No = Chemical Abstracts Service Number
mg/L = milligram per litre
For ecological receptors, the assessment utilises the information presented in the dossiers on the
relative toxicity of the aquatic and terrestrial flora and fauna to the chemical. The qualitative
assessment focuses on the aquatic invertebrate and fish species within the surface water resources,
and the soil flora and fauna associated with releases to the soil. The quantitative assessment
includes evaluating the potential risks to these same aquatic and soil ecological receptors, in
addition to higher trophic level organisms such as livestock and terrestrial wildlife.
The determination of toxicity reference values (TRVs) was conducted according to the PNEC
guidance in the Environmental Risk Assessment Guidance Manual for Industrial Chemicals prepared
by the Australian Environmental Agency (AEA, 2009). PNECs for freshwater and sediment are
developed to assess aquatic receptors, and PNECs for soil are developed for terrestrial receptors.
PNEC values were not derived for hydrochloric acid because factors such as the buffer capacity, the
natural pH, and the fluctuation of the pH are very specific for a certain ecosystem. Refer to
Attachment 2 for additional rationale.
A detailed assessment of the risks posed by this Tier 3 chemical is provided in the following sections.
General Overview
Hydrochloric acid can exist in a gaseous phase at room temperature and pressure. Hydrochloric acid
is also very soluble in water and is a strong acid that dissociates completely in water to hydrogen
(H+) and chloride (Cl-) ions. Both ions are ubiquitous in the environment. The molecular structure of
hydrochloric acid is presented in Figure 1.
Figure 1 Molecular Structure of Hydrochloric Acid 1
The addition of hydrochloric acid to an aquatic ecosystem could potentially increase the chloride
concentration and may decrease the pH depending on the buffer capacity of the receiving water. H+
and Cl- ions will not adsorb on particulate matter or surfaces and will not accumulate in living tissues.
1
Source https://chem.nlm.nih.gov/chemidplus/rn/7647-01-0
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The Persistent, Bioaccumulative and Toxic (PBT) assessment for hydrochloric acid is included in the
dossier provided in Attachment 2. Based on physico-chemical properties and screening data detailed
below, the overall conclusion was that hydrochloric acid is not a PBT substance.
Human Health Hazards
Hydrochloric acid is a corrosive liquid. Depending on the concentration, aqueous solutions of
hydrochloric acid are either corrosive, irritating or non-irritating to the skin, eyes and gastrointestinal
tract. Vapours from aqueous solutions of hydrochloric acid can cause respiratory irritation.
Hydrochloric acid is not a skin sensitiser.
No repeated dose toxicity studies have been conducted by the oral route. Subchronic inhalation
studies show localised irritation to the upper respiratory tract of rats and mice, but no systemic
toxicity. Positive findings have been reported in some in vitro genotoxicity studies, which are
considered to be the result of the pH change in the test system. No adequate reproductive or
developmental studies have been conducted on hydrochloric acid. Hydrochloric acid is not a
carcinogen.
TRVs were not derived for hydrochloric acid. The ADWG values for pH (6.5 to 8.5) and chloride (250
mg/L, aesthetics) may be applicable.
Without management controls in place, there is the potential for human receptors to be exposed to
hydrochloric acid in hydraulic fracturing chemicals during stimulation and completion operations and
management of flowback and work-over fluids. Based on an assessment of land use and an
understanding of the project description provided in the Environmental Impact Statement (EIS)
(URS, 2014) and the CRAF conceptual exposure model (CEM), potential human receptors include:
1. Workers at the well lease involved with: blending, injection and recovery of hydraulic
fracturing and work-over fluids; recycling, reuse or disposal of recovered fluids including
beneficial reuse activities such as land applications of drilling materials and dust
suppression; and, mitigating releases from the well lease to an adjacent water body.
2. Agricultural workers/residents at irrigation areas.
In terms of risks associated with transport of chemicals and wastes, this risk is considered to be
managed to a level as low as reasonably practicable. This is because the potential for a release is
controlled through implementation of traffic management principles including use of designated
trucking routes, vehicle signage, vehicle management systems (to manage speed and driving
behaviour/habits) and, in the unlikely event of a vehicular accident, implementation of incident and
spill response procedures. Given the highly regulated nature of transportation of chemicals (at both
a Commonwealth and State level), transport-related scenarios are not evaluated further in this
assessment. However, the outcome of the assessment should be used to inform emergency
response actions.
Unlike drilling there are no large volumes of premixed stimulation fluid systems stored on-site. The
primary fluid stored on-site is water, and chemicals are blended into the fluid stream as it is used.
Exposure of workers to stimulation fluid chemicals is possible via inadvertent spills and leaks, during
the recycling and beneficial reuse of recovered materials (e.g., drilling fluids and cuttings) and during
application of the recovered material to land. However, chemical exposures to workers are
controlled through engineering, management controls and personal protective equipment, which
are focused on elimination and mitigation of the potential for dermal contact and potential for
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incidental ingestion. In addition, Australia SafeWork Place and Santos Occupational Safety Guidance
are used to minimise human health exposure. As a result, petroleum workers, are also excluded
from assessment.
In the unlikely event of a release to ground at the well lease, the potential for exposures (other than
workers) is limited. The well pad sites are fenced and access is controlled, which limits access to the
public. If stimulation fluid chemicals are spilled to ground then investigation, remediation and
rehabilitation activities would be implemented to address soil impacts.
On-lease storage may utilise tanks, pits or turkey nests and there is the possibility that a
containment failure could result in the release of the materials to the well lease and the surrounding
environment. Releases on the well pad would be of limited volumes and, as such, these products
would not be anticipated to migrate a significant distance off lease to the surrounding environment,
including proximal water bodies. Releases from the gathering pipeline would be of higher potential
volumes but the flow back or workover fluid concentrations from an individual well would be diluted
with other waters from other wells also flowing in this gathering network.
Exposure of potential receptors (other than workers) is also possible to residual chemicals in areas
adjacent to a well lease that have been used for the application of materials for beneficial reuse.
However, Environmental Authority (EA) or Beneficial Use Approval conditions regulate project reuse.
A plan for the beneficial reuse of materials has been developed by a Suitably Qualified Person (SQP)
in accordance with the EA conditions which require materials of a certain quality and controls the
maximum volumes that can be applied to land. In addition, the application techniques and location
of application are controlled with specific monitoring required. Irrigation areas are designed to
manage the risk of pooling and run-off with a general deficit irrigation strategy employed; and, are
fitted with monitoring bores to manage the risk of vertical and horizontal migration.
As a result, potential exposures during stimulation activities are considered low due to the
employment of mechanical equipment/processes, engineering controls (including secondary
containment) and other mitigation and management strategies. Similarly, there is a low potential for
human receptors exposed to residual chemicals in areas adjacent to a well lease that have been used
for the application of materials for beneficial reuse and to surface water bodies that may receive
runoff from beneficial reuse applications. Finally, the probability of any surface related discharge
infiltrating subsurface soils and migrating to groundwater is very low.
National Industrial Chemicals Notification and Assessment Scheme (NICNAS) identified hydrochloric
acid as a low concern for workers and the public under the operational scenarios assessed. Best
practice chemical management was recommended to minimise worker and public exposure
(NICNAS, 2017a).
Environmental Hazards
Hydrochloric acid is an inorganic salt that dissociates completely to hydrogen (H+) and chloride (Cl-)
ions in aqueous solutions. The hazard of hydrochloric acid for aquatic organisms is caused by the
hydrogen ion (H+). The toxicity values in terms of mg/L are not relevant because of the varying
buffering capacity of different test systems and different aquatic ecosystems.
Biodegradation is not applicable to these inorganic ions; both hydrogen (H+) and chloride (Cl-) ions
are also ubiquitous and are present in water, soil and sediment. In addition, hydrogen (H+) and
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chloride (Cl-) ions are essential to all living organisms, and their intracellular and extracellular
concentrations are actively regulated. Thus, hydrochloric acid is not expected to bioaccumulate.
In the aquatic environment, the toxicity of hydrochloric acid will be influenced by factors such as the
buffer capacity, the natural pH, and pH fluctuation of the ecosystem. PNEC values for water were
derived as part of NICNAS based on a chronic aquatic toxicity study. However, experimental details
were not available to validate the PNEC. Terrestrial toxicity studies were also not available.
Therefore, PNEC values for water, soil and sediment have not been derived. Based on its properties,
hydrochloric acid is not expected to significantly adsorb to soil or sediment, and if released to the
ground would be neutralised by the slightly alkaline environment of the earth (NICNAS, 2017b).
During the hydraulic fracturing process, there is the potential for environmental receptors to be
exposed to stimulation fluid chemicals such as hydrochloric acid. Pipelines (where treated water is
conveyed) can transect sensitive ecological areas (including Matters of National Environmental
Significance [MNES]). There is the concern of wildlife (terrestrial and aquatic receptors) and livestock
in the vicinity of the well leases to have adverse effects from potential exposures. Potential
environmental receptors include:
1. Wildlife and livestock accessing the well lease and areas adjacent to a well lease, including
surface water features, that have received runoff from an accidental release during
hydraulic fracturing activities or loss of containment.
2. Wildlife and livestock accessing areas of the well lease where materials have been applied,
as well as accessing stored materials in pits and turkey nests.
3. Aquatic flora and fauna within a proximal surface water body that has received runoff from
an accidental release during hydraulic fracturing activities or loss of containment, or from
beneficial reuse applications.
4. Wildlife, including livestock, that have access to the water supply from a bore hydraulically
downgradient of the well lease.
The potential for exposure of sensitive receptors (including MNES) is considered low. The hydraulic
fracturing activities occur over a short duration and are conducted in controlled/operational areas
within a perimeter fence. Further, the activity level, noise, etc. will be a disincentive for wildlife and
livestock to access the lease through gaps in the fencing or unsecured gates.
Based on the engineering and management controls described in the previous section (Human
Health Hazards), there is a low potential for ecological receptors exposed to surface water bodies
that may receive runoff from an accidental release. There is also concern that recovered material
applied to the land surface could migrate to groundwater or surface water, and therefore result in
adverse effects to the environment (e.g., uptake by aquatic receptors). Due to EA conditions
regulating land application techniques, the remote nature of the well leases, vertical separation of
groundwater and distances to watercourses, the ephemeral nature of the watercourses and the
physical and chemical properties of the residual chemicals post treatment or beneficial reuse, these
potential exposures are also low.
Risk Characterisation
The purpose of the risk characterisation portion of the assessment is to provide a conservative
estimate of the potential risk resulting from exposure to hydrochloric acid that may occur during
hydraulic fracturing and work over activities. These exposures may include operational activities
where planned direct releases to the environment may occur (e.g., land application). The risk
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characterisation evaluates the toxicity of this chemical and characterises the risk of the chemical
assessed for specific exposure pathways identified in the previous sections.
A two‐stage process is employed during risk characterization. First, risk ratios are developed for the
chemical for potentially complete exposure pathways associated with applicable release scenarios.
The risk ratio is calculated by dividing the exposure point concentration (EPC) by the applicable risk-
based screening level (drinking water level or PNECs for aquatic and terrestrial receptors). If the ratio
of exceedance of screening levels is less than 1.0, then there are no anticipated adverse effects
associated with the exposure scenario evaluated. No risk / hazard reduction measures are required.
There should be no need for further management controls on the chemical additional to those
already in place (DoEE, 2017).
If the ratio is greater than 1.0, then further quantitative analysis is conducted. Consistent with the
assessment framework, quantitative assessment of risk will consider only Tier 3 chemicals in end use
determination.
Exposure Point Concentration Calculations
A quantitative mass balance calculation was undertaken to estimate the potential concentrations of
stimulation chemicals containing hydrochloric acid within the flowback water that may be accidently
released (e.g., breech of dam or leaking storage tank) to a nearby surface water resource or soils,
and the potential concentrations of the chemicals within the soil phase from the irrigation of
agricultural soils. Two scenarios were evaluated for the incidental release of flowback water to
surface water: a release from the frac tank at the well pad or from the water feed pond at the Water
Management Facility (WMF). Additionally, releases from the permeate pond at the WMF were also
evaluated.
For the mass balance calculation, vendor disclosure forms were used to determine the percentage of
hydrochloric acid in the pre-injection fluid. Additionally, it is assumed that 10% of the COPCs in the
stimulation fluids return to the surface in the flowback water. Table 3 presents the estimated pre-
injection fluid concentration.
Table 3 Mass Balance Estimates for Hydrochloric Acid
Estimated Pre-injection fluid
Chemical Name CAS No.
concentration (mg/L)
Hydrochloric acid 7647-01-0 6.74
CAS No = Chemical Abstracts Service Number
mg/L = milligram per litre
The mass balance of hydrochloric acid was then used to estimate the potential EPC for each of the
release scenarios (see Attachment 3, Table 1). For the first scenario (frac tank release), the EPC was
calculated assuming 20% of the mass returned in the flowback water, which was then diluted with
150% of the injected volume of return water. As an inorganic salt which dissociates completely in
aqueous media, no adjustment for biodegradation was conducted in calculating the theoretical EPCs
for two exposure time periods (0 and 150 days). The estimated EPC for this scenario assumes that
the accidental release of the flowback water to a surface water resources would not be diluted by
surface water within the resource, as many of the surface water features in the area are ephemeral
with high variations in duration and flow volume.
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In the second scenario (water feed pond release), the concentration of stimulation fluid chemicals in
flowback water is assumed to be diluted by an additional 90% in the water feed pond due to the
aggregation of produced water within one pond. Therefore, a factor of 10% was applied to the Day 0
and Day 150 flowback concentrations to assess potential accidental releases from the water feed
pond at the WMF.
For the third scenario (permeate pond release), the concentrations in the water feed pond were
reduced by a factor of 99% to account for efficiencies in the WMF system.
Release Scenario Assessment
There is no potentially complete exposure pathway to sources of drinking water; however, as a
conservative measure, the theoretical concentrations for each of the three release scenarios were
compared to human health toxicity-based screening levels to screen for potential effects as a result
of a release from the well lease that may migrate to surface water used as a drinking water source.
The results of this comparison, including the ratio of exceedance of screening levels, is presented in
Attachment 3, Table 2. As detailed in the table, risk ratios did not exceed the target level of 1 in any
of the scenarios evaluated.
Theoretical concentrations of the three exposure scenarios were also compared to the PNEC for
aquatic receptors. Attachment 3, Table 3 presents the results of this comparison, including the ratio
of exceedance of screening levels. However, a PNEC for water could not be calculated. Therefore, as
presented in Attachment 2, Table 3, a comparison to the theoretical concentrations could not be
made. As noted earlier, in the aquatic environment, the toxicity of hydrochloric acid will be
influenced by factors such as the buffer capacity, the natural pH, and pH fluctuation of the
ecosystem. There is a low potential for ecological receptors exposed to surface water bodies that
may receive runoff from an accidental release.
There is also the potential for exposure of receptors to residual stimulation fluids in irrigated soils
during a release of flowback water to soil or during application of the material to land (irrigation). As
previously described, hydrochloric acid would not be present in soil. Therefore, EPCs were not
developed for these scenarios; and, likewise, further quantitative analysis (i.e., calculation of
hazards) for beneficial reuse via direct contact by agricultural workers or residents and non-MNES
(mammals and avian receptors) was not conducted.
Based on the outcomes of this assessment, no further management controls are considered
necessary.
Cumulative Impacts
The potential for cumulative impacts associated with chemicals proposed for this project is limited
based on the distance between well pad sites where the chemicals are being used. Modelling has
demonstrated that the migration of drilling chemicals is limited in the subsurface with no potential
to interact with those from other wells and hydraulic fracturing chemicals are contained within the
target units. Residual chemicals may be entrained within produced water and subsequently
transported for water treatment at a WMF. However, these chemicals are removed by the
treatment systems; and, therefore, no additional risk is provided during beneficial reuse, including
irrigation. Likewise, the presence of water treatment chemicals at the point of produced water
storage or during beneficial reuse also poses no significant increase in risk.
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Only Tier 3 chemicals which trigger persistence and bioacummulative thresholds are considered to
be chemicals with a potential for cumulative impacts. As noted earlier and discussed in detail in the
dossier (Attachment 2), hydrochloric acid does not meet the criteria for persistence or
bioaccumulation. Thus, there is negligible incremental risk posed by the use of this Tier 3 chemical
and the existing (and proposed) management and monitoring controls are appropriate to ensure
that the risk to MNES (and non MNES) receptors remains low.
Uncertainty Analysis
The procedures and assumptions used to assess potential human health risks in this Tier 3
assessment are subject to a wide variety of uncertainties. However, the presence of uncertainty is
inherent in the risk assessment process, from the sampling and analysis of the chemical in
environmental media to the assessment of exposure and toxicity, and risk characterisation.
Accordingly, it is important to note that the risks presented within this Tier 3 assessment are based
on numerous conservative assumptions in order to be protective of human health and the
environment, and to ensure that the risks presented herein are more likely to be overestimated
rather than underestimated.
The discussion detailed in Table 4 below provides an evaluation of uncertainty for this Tier 3
assessment, including elements previously discussed within this assessment.
Table 4 Evaluation of Uncertainty – Hydrochloric Acid
Risk Magnitude
Characterisation Description of Uncertainty of Effect on Risk Assessment
Component Uncertainty
The concentrations of COPCs in residual
stimulation fluids were estimated based on
previous operations and may not accurately This assumption may
Hazard Assessment estimate the concentrations of COPCs in the overestimate or
– Chemical additive future. Detailed discussions with Santos underestimate the
Low
COPC occurred to identify a conservative estimate calculated risks to receptors,
concentrations of the COPC; however, there is the potential dependent on-site-specific
that the empirical concentrations would conditions.
differ than those presented in the risk
assessment.
The estimated EPC for this scenario assumes
This assumption may
that the accidental release of the flowback
overestimate or
water to a surface water resources would not
Exposure underestimate the
be diluted by surface water within the Low
Assessment – EPC calculated risks to receptors,
resource, as many of the surface water
dependent on-site-specific
features in the area are ephemeral with high
conditions.
variations in duration and flow volume.
Oral toxicological reference doses and
drinking water guidance values were not
derived for hydrochloric acid (which
Low potential to
Toxicity Assessment dissociates completely to hydrogen and Low
underestimate risk
chloride ions). As a result, EPCs were
compared to drinking water guidance values
for chloride.
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Risk Magnitude
Characterisation Description of Uncertainty of Effect on Risk Assessment
Component Uncertainty
PNEC water values were not derived for
hydrochloric acid. The hazard for aquatic
organisms is caused by the hydrogen ion (H⁺). Low to medium potential to
Low to
Toxicity Assessment The toxicity values in terms of mg/L are not underestimate or
Medium
relevant because of the varying buffering overestimate risk
capacity of different test systems and
different aquatic ecosystems.
References
Australian Environmental Agency (AEA). (2009). Environmental Risk Assessment Guidance Manual
for Industrial Chemicals, Commonwealth of Australia.
Department of the Environment and Energy (DoEE). (2017). Exposure draft: Risk Assessment
Guidance Manual: for chemicals associated with coal seam gas extraction. Commonwealth
of Australia, available at http://www.environment.gov.au/water/coal-and-coal-seam-
gas/national-assessment-chemicals/consultation-risk-assessment-guidance-manual
NICNAS. (2017b). National assessment of chemicals associated with coal seam gas extraction in
Australia,Technical report number 14 - Environmental risks associated with surface handling
of chemicals used in coal seam gas extraction in Australia. Project report prepared by the
Chemicals and Biotechnology Assessments Section (CBAS), in the Chemicals and Waste
Branch of the Department of the Environment and Energy as part of the National
Assessment of Chemicals Associated with Coal Seam Gas Extraction in Australia,
Commonwealth of Australia, Canberra.
NICNAS. (2017a) National assessment of chemicals associated with coal seam gas extraction in
Australia, Technical report number 12- Human health hazards of chemicals associated with
coal seam gas extraction in Australia: Attachment 5 – Hazard assessment sheets. Project
report prepared by the Chemicals and Biotechnology Assessments Section (CBAS), in the
Chemicals and Waste Branch of the Department of the Environment and Energy as part of
the National Assessment of Chemicals Associated with Coal Seam Gas Extraction in Australia,
Commonwealth of Australia, Canberra.
URS. (2014). Santos GLNG Project: Gas Field Development Project Environmental Impact Statement.
Available online at: http://www.santosglng.com/environment-and-water/gas-field-
development-project-eis.aspx
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Attachment 1 Safety Data SheetSantos Ltd
Qualitative and Quantitative Tier 3 Assessment – Hydrochloric Acid
October 2020
Attachment 2 Risk Assessment DossierHYDROCHLORIC ACID This dossier on hydrochloric acid presents the most critical studies pertinent to the risk assessment of hydrochloric acid in its use in hydraulic fracturing fluids. This dossier does not represent an exhaustive or critical review of all available data. The majority of information presented in this dossier was obtained from OECD-SIDS documents (OECD, 2002a,b), and the ECHA database that provides information on chemicals that have been registered under the EU REACH (ECHA). Where possible, study quality was evaluated using the Klimisch scoring system (Klimisch et al., 1997). Screening Assessment Conclusion – Hydrochloric acid was not identified in chemical databases used by NICNAS as an indicator that the chemical is of concern and is not a PBT substance. Hydrochloric acid was assessed as a tier 3 chemical for acute toxicity. Data were not available to categorize the substance based on chronic effects. Therefore, hydrochloric acid is classified overall as a tier 3 chemical and requires a quantitative risk assessment for end uses. 1 BACKGROUND Hydrochloric acid (HCl) can exist in a gaseous phase at room temperature and pressure. Due to its high water solubility and low vapour pressure, hydrochloric acid will be found predominantly in the aquatic environment where it dissociates completely to hydrogen (H+) and chloride (Cl-) ions. Both ions are ubiquitous in the environment. H+ and Cl- ions will not adsorb on particulate matter or surfaces and will not accumulate in living tissues. Hydrochloric acid is a corrosive liquid. Depending on the concentration, aqueous solutions of hydrochloric acid (HCl) are either corrosive, irritating, or non-irritating to the skin, eyes and gastrointestinal tract. Vapours from aqueous solutions of HCl can cause respiratory irritation. HCl is not a skin sensitiser. Subchronic inhalation studies show localised irritation to the upper respiratory tract of rats and mice, but no systemic toxicity. No repeated dose toxicity studies have been conducted by the oral route. Positive findings have been reported in some in vitro genotoxicity studies, which are considered to be the result of the pH change in the test system. A lifetime inhalation study showed no carcinogenic effects in rats exposed to HCl. No adequate reproductive or developmental studies have been conducted on HCl. The hazard of hydrochloric acid for aquatic organisms is caused by the hydrogen ion (H+). The toxicity values in terms of mg/L are not relevant because of the varying buffering capacity of different test systems and different aquatic ecosystems. 2 CHEMICAL NAME AND IDENTIFICATION Chemical Name (IUPAC): Chlorane CAS RN: 7647-01-0 Molecular formula: HCl Molecular weight: 36.46 Synonyms: Hydrochloric acid, HCl, chlorane, hydrogen chloride, muriatic acid, chlorohydric acid Revision date: October 2020 1
3 PHYSICO-CHEMICAL PROPERTIES
Key physical and chemical properties for the substance are shown in Table 1.
Table 1 Overview of the Physico-chemical Properties of Hydrochloric Acid
Property Value Klimisch Reference
score
Physical state at 20oC and Colourless to slightly yellow gas of fuming 2 ECHA
101.3 kPa liquid with pungent, irritating odour.
Melting Point -114.22oC 2 ECHA
Boiling Point -85oC 4 ECHA
Density 1.639 g/L @ 0oC (gas) 4 ECHA
1.194 g/mL @ 26 C (liquid)
o
Vapour Pressure 4,104 kPa 4 ECHA
4,723 kPa @ 25 C o
Partition Coefficient (log Kow) Not applicable - -
Water Solubility Very soluble 4 ECHA
Viscosity 1.7 x 10-6 m2s @ 20oC 1 ECHA
Hydrochloric acid can exist in a gaseous phase at room temperature and pressure. Hydrochloric acid
is also very soluble in water and is a strong acid that dissociates completely in water to hydrogen
(H+) and chloride (Cl-) ions.
4 DOMESTIC AND INTERNATIONAL REGULATORY INFORMATION
A review of international and national environmental regulatory information was undertaken (Table
2). This chemical is listed on the Australian Inventory of Chemical Substances – AICS (Inventory). No
conditions for its use were identified. No other specific environmental regulatory controls or
concerns were identified within Australia and internationally for hydrochloric acid.
Table 2 Existing International Controls
Convention, Protocol or other international control Listed Yes or No?
Montreal Protocol No
Synthetic Greenhouse Gases (SGG) No
Rotterdam Convention No
Stockholm Convention No
REACH (Substances of Very High Concern) No
United States Endocrine Disrupter Screening Program No
European Commission Endocrine Disruptors Strategy No
Revision date: October 2020 25 ENVIRONMENTAL FATE SUMMARY
Due to its high water solubility, hydrochloric acid will be found predominantly in the aquatic
environment where it dissociates completely to hydrogen (H+) and chloride (Cl-) ions. Both ions are
ubiquitous in the environment (UNEP, 1995).
The addition of hydrochloric acid to an aquatic ecosystem may decrease the pH depending on the
buffer capacity of the receiving water. In general, the buffer capacity is regulated by the equilibria
between CO2, HCO3- and CO32-:
CO2 + H2O ↔ HCO3- + H+ (pKa1 = 6.35)
HCO3- ↔ CO32- + H+ (pKa2 = 10.33)
A release of hydrochloric acid into the aquatic environment from the use of HCl could potentially
increase the chloride concentration and decrease the pH in the aquatic environment. Table 3 shows
the amount of hydrochloric acid that would need to be added to bicarbonate solutions to obtain pH
values of 6.0 and 4.0. The UNEP (1995) study reported that the 10th percentile, mean and the 90th
percentile of bicarbonate concentrations in 77 rivers in North America, South America, Asia, Africa,
Europe and Oceania were 20, 106 and 195 mg/L, respectively. The data show that the decrease in pH
depends on the buffering capacity (bicarbonate concentration) of the receiving water. The
calculated values in Table 3 were confirmed experimentally.
Table 3 Buffer capacity to maintain the pH based on bicarbonate concentration from UNEP
monitoring data (de Groot and van Dijk, 2002; taken from OECD, 2002b)
Initial concentration of HCO3- Final pH Concentration of HCl required to obtain the
final pH value
Calculated [mg/L]
20 mg/L HCO3- (10th percentile 77 6.0 8.28
rivers)
4.0 11.9
106 mg/L HCO3- (mean value of 77 6.0 43.9
rivers)
4.0 63.2
195 mg/L HCO3- (90th percentile 77 6.0 80.7
rivers)
4.0 116.3
H+ and Cl- ions will not adsorb on the particulate matter or surfaces and will not accumulate in living
tissues (OECD, 2002a,b).
Revision date: October 2020 36 HUMAN HEALTH HAZARD ASSESSMENT A. Summary Hydrochloric acid is a corrosive liquid. Depending on the concentration, aqueous solutions of hydrochloric acid (HCl) are either corrosive, irritating, or non-irritating to the skin, eyes and gastrointestinal tract. Vapours from aqueous solutions of HCl can cause respiratory irritation. HCl is not a skin sensitiser. Subchronic inhalation studies show localised irritation to the upper respiratory tract of rats and mice, but no systemic toxicity. No repeated dose toxicity studies have been conducted by the oral route. Positive findings have been reported in some in vitro genotoxicity studies, which are considered to be the result of the pH change in the test system. A lifetime inhalation study showed no carcinogenicity in rats exposed to HCl. No adequate reproductive or developmental studies have been conducted on HCl. B. Acute Toxicity The oral LD50 values in rats were reported to be 238 to 277 mg/kg and 700 mg/kg (OECD, 2002a,b). [Kl. scores = 2 and 4, respectively] The lethal dose by dermal exposure is >5,010 mg/kg for rabbits (OECD 2002a,b). [Kl. score = 4] The LC50 values in rats for HCl gas are 40,989 and 4,701 ppm for 5 and 30 minutes, respectively (ECHA) [Kl. score = 2]. The LC50 values in rats for HCl aerosol are 31,008 and 5,666 ppm (45.6 and 8.3 mg/L) for 5 and 30 minutes, respectively (ECHA). [Kl. score = 2] C. Irritation Application of a 37% aqueous solution of HCl for 1 or 4 hours was corrosive to the skin of rabbits (OECD, 2002a,b) [Kl. score = 2). Application of 0.5 mL of a 17% solution of aqueous solution of HCl for 4 hours was corrosive to the skin of rabbits (OECD, 2002a,b) [Kl. score = 3]. Moderate skin irritation was observed in rabbits following an application of 0.5 mL of a 3.3% aqueous solution of HCl for five days; no irritation was observed with 0.5 mL of a 1% aqueous solution (OECD, 2002a,b) [Kl. score = 2]. In humans, an aqueous solution of 4% of HCl was slightly irritating, while a 10% solution was sufficiently irritating to be classified as a skin irritant (OECD, 2002a,b). Instillation of 0.1 mL of a 10% aqueous solution of HCl to the eyes of rabbits resulted in severe eye irritation (ECHA) [Kl. score = 2]. Instillation of 0.1 mL of a 5% solution of HCl produced corneal opacity, iridial lesions, conjunctival redness and chemosis in 3/3 animals at 1 hour and at day 1 post- instillation. There was no recovery in any animal and the study was terminated on day 2 (ECHA). [Kl. score = 1] D. Sensitisation Hydrochloric acid was not a skin sensitiser in a guinea pig maximisation test (ECHA). [Kl. score = 2] Revision date: October 2020 4
E. Repeated Dose Toxicity
Oral
No adequate studies were located.
Inhalation
Male and female SD rats and F344 rats were exposed by inhalation to 0, 10, 20 or 50 ppm 6
hours/day, 5 days/week for up to 90 days. Clinical signs were mainly indicative of the
irritant/corrosive nature of HCl. Body weights were significantly decreased in the 50 ppm male F344
rats. There were no treatment-related effects on the haematology or clinical chemistry parameters
or urinalysis. At study termination, heart, kidney and testes weights were increased in the 100
and/or 50 ppm groups; these changes were considered to be mainly related to the treatment-
related effect on body weight. Histopathological examination showed minimal to mild rhinitis in the
>20 ppm dose groups of both strains of rats (both sexes). The NOAELs for systemic toxicity and
localised irritation (site-of-contact) are 20 and 10 ppm, respectively (ECHA). [Kl. score = 1]
Male and female B6C3F1 mice were exposed by inhalation to 0, 10, 20 or 50 ppm HCl, 6 hours/day, 5
days/week for up to 90 days. Clinical signs were mainly indicative of the irritant/corrosive nature of
HCl. Body weights were significantly decreased in the 50 ppm groups. At study termination, absolute
liver weights were decreased in the 50 ppm males. Histopathologic examination showed only
eosinophilic globules in the nasal epithelium in the 50 ppm animals. The NOAEL for this study is 20
ppm (ECHA). [Kl. score = 1]
Male SD rats were exposed by inhalation to 0 or 10 ppm HCl 6 hours/day, 5 days/week for 128
weeks. Survival and body weights were similar between treated and control groups. There was a
higher incidence of hyperplasia of the larynx compared to control, but no serious irritating effects of
the nasal epithelium (ECHA). [Kl. score = 2]
Dermal
No studies were located.
F. Genotoxicity
In Vitro Studies
Table 4 presents the in vitro genotoxicity studies on hydrochloric acid.
Table 4 In Vitro Genotoxicity Studies on Hydrochloric Acid
Test System Results* Klimisch Score Reference
-S9 +S9
Bacterial reverse mutation (S. - - 2 ECHA
typhimurium and E. coli strains)
Mammalian cell gene mutation (mouse - + 2 ECHA
lymphoma L5178Y cells)
Chromosomal aberration (CHO cells) + + 2 ECHA
Revision date: October 2020 5Test System Results* Klimisch Score Reference Saccharomyces cerevisiae (mitotic - - 2 ECHA recombination E. coli W3110 (pol A+) and P3078 (pol A-) - - 2 ECHA repair assay *+, positive; -, negative In the mouse lymphoma assay, the mutant frequency increased as the pH was lowered to 6.5 to 6.0 (from increased HCl) in the presence of metabolic activation. A decrease in pH from the addition of HCl to the medium also resulted in clastogenic effects to CHO cells in the absence or presence of metabolic activation. The positive findings in these two studies are considered to be the result of the pH change in the test media. In Vivo Studies No adequate studies were located. G. Carcinogenicity Oral No studies were located. Inhalation Male SD rats were exposed by inhalation to 0 or 10 ppm HCl 6 hours/day, 5 days/week for 128 weeks. Survival and body weights were similar between treated and control groups. There was a higher incidence of hyperplasia of the larynx compared to control, but no serious irritating effects of the nasal epithelium. There was no increased incidence of tumours in the HCl-treated rats compared to controls (ECHA). [Kl. score = 2] H. Reproductive Toxicity No studies were located. I. Developmental Toxicity No adequate studies were located. J. Derivation of Toxicological Reference and Drinking Water Guidance Values Repeated dose, reproductive, and developmental toxicity studies by the oral route have not been conducted on hydrochloric acid. These toxicity studies would have questionable usefulness because of the corrosive/irritating nature of hydrochloric acid, which would limit the amount of absorbed HCl. Hydrochloric acid dissociates to hydrogen and chloride ions in bodily fluids, and a significant amount of these ions are already ingested in foods. Furthermore, both ions are present in the body and are highly regulated by homeostatic mechanisms. Thus, an oral toxicological reference and drinking water guidance values were not derived from hydrochloric acid. Revision date: October 2020 6
The Australian drinking water guideline values for pH (6.5 to 8.5) and chloride (250 ppm, aesthetics)
may be applicable (ADWG, 2011).
K. Human Health Hazard Assessment of Physico-Chemical Properties
Hydrochloric acid does not exhibit the following physico-chemical properties:
• Explosivity
• Flammability
• Oxidising potential
7 ENVIRONMENTAL EFFECTS SUMMARY
A. Summary
The hazard of hydrochloric acid for aquatic organisms is caused by the hydrogen ion (H+). The toxicity
values in terms of mg/L are not relevant because of the varying buffering capacity of different test
systems and different aquatic ecosystems.
B. Aquatic Toxicity
Acute Studies
The acute aquatic toxicity studies on hydrochloric acid are listed in Table 5.
Table 5 Acute Aquatic Toxicity Studies on Hydrochloric Acid
Test Species Endpoint Results Klimisch Reference
score
Lepomis macrochirus 96-hr LC50 pH 3.25 – 3.5 (20mg/L) 2 ECHA; OECD
2002a,b
Daphnia magna 48-hr EC50 pH 4.92 (0.45 mg/L) 1 ECHA
Chlorella vulgaris 72-hr EC50 pH 4.7 [growth rate](0.73 mg/L) 1 ECHA
72-hr EC10 PH 4.7 (0.364 mg/L)
Chronic Studies
No chronic studies are available.
C. Terrestrial Toxicity
No studies are available.
Revision date: October 2020 7D. Calculation of PNEC PNEC values 1 were not derived for hydrochloric acid because factors such as the buffer capacity, the natural pH, and the fluctuation of the pH are very specific for a certain ecosystem. 8 CATEGORISATION AND OTHER CHARACTERISTICS OF CONCERN A. PBT Categorisation The methodology for the Persistent, Bioaccumulative and Toxic (PBT) substances assessment is based on the Australian and EU REACH Criteria methodology (DEWHA, 2009; ECHA, 2008). Hydrochloric acid is an inorganic salt that dissociates completely to hydrogen and chloride ions in aqueous solutions. Biodegradation is not applicable to these inorganic ions; both hydrogen and chloride ions are also ubiquitous and are present in water, soil and sediment. For the purposes of this PBT assessment, the persistent criteria are not considered applicable to this inorganic salt. Hydrogen and chloride ions are essential to all living organisms, and their intracellular and extracellular concentrations are actively regulated. Thus, hydrochloric acid is not expected to bioaccumulate. No chronic toxicity data exist on hydrochloric acid. The acute EC50 values are >1 mg/L in fish, < 1 mg/L for invertebrates and algae. Thus, hydrochloric acid meets the screening criteria for toxicity. The overall conclusion is that hydrochloric acid is a PBT substance based on toxicity to invertebrates and algae. B. Other Characteristics of Concern Only tier 3 chemicals which trigger persistence and bioacummulative thresholds are considered to be chemicals with a potential for cumulative impacts. As noted in the prior section, hydrochloric acid does not meet the criteria for persistence or bioaccumulation. No other characteristics of concern were identified for hydrochloric acid. 1 An aquatic PNEC (mg/L) has been derived as part of the chemical assessment conducted under National Industrial Chemicals Notification and Assessment Scheme (NICNAS). However, the chronic aquatic toxicity data set used to derive the PNEC value was not available for review. Revision date: October 2020 8
9 SCREENING ASSESSMENT
Chemical Databases of Concern Bioaccumulative
Persistence Assessment Step Toxicity Assessment Step
Assessment Step Assessment Step
Overall PBT Risk Assessment Actions
Chemical Name CAS No. Listed as a COC Identified as
Assessment 1 P criteria Other P T criteria Acute Toxicity Chronic Required3
on relevant Polymer of Low B criteria fulfilled? 2
fulfilled? Concerns fulfilled? Toxicity2
databases? Concern
1 (fish)
3 (algae
Hydrochloric Acid 7647-01-0 Not a PBT No No NA No No No No data 3
& inverts)
(ECHA)
Footnotes:
1 - PBT Assessment based on PBT Framework.
2 - Acute and chronic aquatic toxicity evaluated consistent with assessment criteria (see Framework).
3 - Tier 3 - Quantitative Risk Assessment: Complete PBT, qualitative and quantitative assessment of risk.
Notes:
NA = not applicable
PBT = Persistent, Bioaccumulative and Toxic
B = bioaccumulative
P = persistent
T = toxic
Revision date: October 2020 910 REFERENCES, ABBREVIATIONS AND ACRONYMS
A. References
ADWG. (2011). National Water Quality Management Strategy. Australian Drinking Water Guidelines,
Section 6, Australian Government, National Health and Medical Research Council, Natural
Resource Management Ministerial Council.
de Groot, W.A., and van Dijk, N.R.M. (2002). Addition of hydrochloric acid to a solution with sodium
bicarbonate to a fixed pH. Solvay Pharmaceuticals, Study No. A SOL.S.027; cited in OECD
2002a and 2002b.
Department of the Environment, Water, Heritage and the Arts [DEWHA]. (2009). Environmental risk
assessment guidance manual for industrial chemicals, Department of the Environment,
Water, Heritage and the Arts, Commonwealth of Australia.
ECHA. ECHA REACH database: http://echa.europa.eu/information-on-chemicals/registered-
substances.
European Chemicals Agency [ECHA]. (2008). Guidance on Information Requirements and Chemical
Safety Assessment, Chapter R11: PBT Assessment, European Chemicals Agency, Helsinki,
Finland.
Klimisch, H.J., Andreae, M., and Tillmann, U. (1997). A systematic approach for evaluating the quality
of experimental and toxicological and ecotoxicological data. Regul. Toxicol. Pharmacol. 25:1-
5.
OECD. (2002a). IUCLID Data Set for Hydrogen chloride (CAS No. 7647-01-0), UNEP Publications.
OECD. (2002b). Screening Information Dataset (SIDS) Initial Assessment Report for Hydrogen
chloride (CAS No. 7647-01-0), UNEP Publications.
UNEP. (1995). Water quality of world river basins. UNEP Environment Library No. 14, Nairobi, Kenya;
cited in OECD, 2002a and 2002b.
B. Abbreviations and Acronyms
°C degrees Celsius
ADWG Australian Drinking Water Guidelines
AICS Australian Inventory of Chemical Substances
CHO Chinese hamster ovary
COC constituent of concern
DEWHA Department of the Environment, Water, Heritage and the Arts
EC effective concentration
ECHA European Chemicals Agency
Revision date: October 2020 10EU European Union g/L grams per litre g/mL grams per millilitre IUPAC International Union of Pure and Applied Chemistry Kl Klimisch scoring system kPa kPa LC lethal concentration LD lethal dose m2s square metres per second mg/kg milligrams per kilogram mg/L milligrams per litre mL millilitre NICNAS The National Industrial Chemicals Notification and Assessment Scheme NOAEL no observed adverse effect level OECD Organisation for Economic Co-operation and Development PBT Persistent, Bioaccumulative and Toxic PNEC Predicted No Effect Concentration ppm parts per million REACH Registration, Evaluation, Authorisation and Restriction of Chemicals SD Sprague Dawley SGG Synthetic Greenhouse Gases Revision date: October 2020 11
Santos Ltd
Qualitative and Quantitative Tier 3 Assessment – Hydrochloric Acid
October 2020
Attachment 3 Risk Characterisation TablesAttachment 3, Table 1
Summary of Theoretical Biodegradation of Vendor Chemicals in Stimulation Fluids
(Flowback Fluid in Frac Tank, Water Feed Pond, Permeate Pond)
Flowback Fluid Concentrations
Estimated Initial Frac Tank Concentration in flowback (150% of
Estimated injected fluid volume) per coal seam per 20% of mass returned
Fate and
concentration in pre‐ calculated using equation: Frac Tank Concentration =
Transport
Constituent Name CAS No. injection fluid systems FBconcentration (mg/L)/ FB dilution 150% x percent mass returned
Properties
(mg/L) (mg/L) x Biodegradation (half life)(mg/L)
Temporal Scenario (days)
Fluids Half‐Life (days) 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.898 0.898
Water Feed Pond Concentrations
Estimated
Fate and Estimated Concentration in Combined Balance Water Feed Pond to
concentration in pre‐
Transport WMF
Constituent Name CAS No. injection fluid systems
Properties
(mg/L)
Temporal Scenario (days)
Fluids Half‐Life (days) 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.09 0.0898
Permeate Pond Concentrations
Estimated
Fate and Estimated Concentration in Permeate after 99% treatment efficiency
concentration in pre‐
Transport by RO plant
Constituent Name CAS No. injection fluid systems
Properties
(mg/L) Temporal Scenario (days)
Fluids Half‐Life (days) 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.001 0.000898
Notes:
CAS = Chemical Abstracts Service
FB = Flowback
mg/L = milligrams per liter
NA = not applicable
RO = reverse osmosis
WMF = Water Management Facility
Page 1 of 1Attachment 3, Table 2
Comparison of Theoretical Concentrations of COPCs to Drinking Water Guidelines
Frac Tank
Estimated Initial Frac Tank Ratio of COPC Concentrations and
Fate and
Estimated concentration Concentration in flowback Including Drinking Water Screening Criteria (Ratio greater than
Transport
Constituent Name CAS No. in pre‐injection fluid Biodegredation Half‐Life (mg/L) Screening Level one = unacceptable potential risk)
Properties
systems (mg/L) Temporal Scenario (days) (mg/L) Temporal Scenario (days)
Half‐Life (days) 0 150 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.898 0.898 250 3.6E‐03 3.6E‐03
Water Feed Pond
Estimated Initial Concentration in Ratio of COPC Concentrations and
Fate and
Estimated concentration Water Feed Pond Including Drinking Water Screening Criteria (Ratio greater than
Transport
Constituent Name CAS No. in pre‐injection fluid Biodegredation Half‐Life (mg/L) Screening Level one = unacceptable potential risk)
Properties
systems (mg/L) Temporal Scenario (days) (mg/L) Temporal Scenario (days)
Half‐Life (days) 0 150 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.1 0.0898 250 3.6E‐04 3.6E‐04
Permeate Pond
Estimated Initial Concentration in Ratio of COPC Concentrations and
Fate and
Estimated concentration Permeate Pond Including Drinking Water Screening Criteria (Ratio greater than
Transport
Constituent Name CAS No. in pre‐injection fluid Biodegredation Half‐Life (mg/L) Screening Level one = unacceptable potential risk)
Properties
systems (mg/L) Temporal Scenario (days) (mg/L) Temporal Scenario (days)
Half‐Life (days) 0 150 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.001 0.000898 250 3.6E‐06 3.6E‐06
Notes:
CAS = Chemical Abstracts Service
COPC = constituent of potential concern
FB = Flowback
mg/L = milligrams per liter
NA = not applicable
Page 1 of 1Attachment 3, Table 3
Comparison of Theoretical Concentrations of COPCs to PNECs (Water)
Frac Tank
Estimated Initial Vendor Chemical
Ratio of COPC Concentrations and Screening
Fate and Concentration In Flowback
Estimated concentration Criteria (Ratio greater than one = unacceptable
Transport Including Biodegredation Half‐ PNEC aquatic
Constituent Name CAS No. in pre‐injection fluid potential risk)
Properties Life (mg/L) (mg/L)
systems (mg/L) Temporal Scenario (days) Temporal Scenario (days)
Half‐Life (days) 0 150 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.898 0.898 NA NA NA
Water Feed Pond
Estimated Initial Vendor Chemical
Ratio of COPC Concentrations and Screening
Fate and Concentration In Water Feed
Estimated concentration Criteria (Ratio greater than one = unacceptable
Transport Pond Including Biodegredation PNEC aquatic
Constituent Name CAS No. in pre‐injection fluid potential risk)
Properties Half‐Life (mg/L) (mg/L)
systems (mg/L) Temporal Scenario (days) Temporal Scenario (days)
Half‐Life (days) 0 150 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.1 0.0898 NA NA NA
Permeate Pond
Estimated Initial Vendor Chemical
Ratio of COPC Concentrations and Screening
Fate and Concentration In Permeate Pond
Estimated concentration Criteria (Ratio greater than one = unacceptable
Transport Including Biodegredation Half‐ PNEC aquatic
Constituent Name CAS No. in pre‐injection fluid potential risk)
Properties Life (mg/L) (mg/L)
systems (mg/L) Temporal Scenario (days) Temporal Scenario (days)
Half‐Life (days) 0 150 0 150
Hydrochloric acid 7647‐01‐0 6.74 NA 0.001 0.000898 NA NA NA
Notes:
CAS = Chemical Abstracts Service
COPC = constituent of potential concern
FB = Flowback
mg/l = milligrams per liter
NA = not applicable
PNEC = predicted no effects concentration
RO ‐ reverse osmosis
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