16 February 2016 Via Electronic Mail Mr. Ken Wangerud Remedial Project Manager Superfund Remedial Program USEPA Region 8 – EPR-SR 1595 Wynkoop Street Denver, CO 80202-1129 Subject: ERM Comments on OU1 Preliminary Remedial Action

Objectives for Feasibility Study Screening for US Magnesium NPL Site

Dear Mr. Wangerud:

This letter provides ERM-West, Inc.’s (ERM’s) comments on the Preliminary Remedial Action Objectives (PRAOs) for OU-1 received from the United States Environmental Protection Agency (USEPA) as Attachment 1 to a letter dated October 7, 2015 (Ref:8EPR-SR). ERM’s comments and suggested edits to the PRAOs are provided as Attachment A. The comments are in green font inserted beneath the original USEPA text in black font.

As agreed to during the salt cap treatability study scoping meeting in November 2014, ERM has prepared draft provisionary applicable or relevant and appropriate requirements (ARARs) for OU-1, which are provided as Attachment B to this letter. The lists of provisionary Federal and State ARARs provided in Attachment B were developed in accordance with the requirements under Section 121(d) of CERCLA and NCP §300.430(f)(1)(ii)(B) and incorporating guidance from the following documents:

USEPA. 1988. CERCLA Compliance with Other Laws Manual: Interim Final. EPA/540/G-89/006. August.

USEPA. 1988. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA. Interim Final. EPA/540/G-89/0004. October.

Environmental Resources Management 7272 E. Indian School Rd. Suite 108 Scottsdale, AZ 85251 (480) 998-2401 (480) 998-2106 (fax)

ERM

Mr. Ken Wangerud

16 February 2016 Page 2

Environmental Resources Management

Naval Facilities Engineering Command. 2014. Toolkit for Identifying Applicable or Relevant and Appropriate Requirements (ARARs). Final. August.

For documentation and transparency purposes, the lists provided in Attachment B include requirements that were not identified as ARARs in addition to requirements that were identified as applicable, relevant and appropriate, or to be considered, i.e., identified as ARARs. By doing so, these lists document the basis for not identifying certain requirements as ARARs. As the RI/FS progresses, the ARARs will be refined based on an improved understanding of site conditions, site contaminants, and remedial action alternatives.

ERM has also initiated preparation of the draft technology screening technical memorandum required by Section 6.2 of the AOC and referenced in your October 7, 2015 letter, however the draft of this document cannot be completed until the PRAOs and ARARs are finalized.

If you have any questions, please contact me at (480) 998-2401.

Sincerely,

David J. Abranovic, P.E. Project Coordinator (ERM) DJA/sxg/0132320 Attachments cc: David Gibby (US Mag) Mark Ransom (ERM)

Attachment A ERM Comments on the Preliminary Remedial Action Objectives for US Magnesium NPL Site

U.S. EPA Region 8 Superfund Program and Utah Department of Environmental Quality OU1 – Sitewide Soils, Sediments,

Solid-Waste and Waters

In support of a Screening Feasibility Study The remedial action objective for the US Magnesium NPL Site is to reduce or eliminate exposures of humans and ecological receptors to contaminated media in locations that exceed risk-based concentrations, including:

- exposures to solid media (soils, sediments and solid wastes) through ingestion, inhalation, dermal contact, and the food chain;

- exposures to acids and other site-related contaminants in surface waters through ingestion and dermal contact pathways.

ERM Comment: The elimination of exposures to acid in surface water is not an appropriate PRAO for the Feasibility Study. Low pH surface waters are currently and will continue to be generated as part of ongoing US Magnesium operations and will be managed as appropriate according to all applicable State and Federal waste management regulations. Based on the human health survey conducted in 2014, there isn’t any ingestion exposure pathway of surface waters for human receptors (i.e. dermal contact exposures only). Given that US Magnesium is an operating facility and will continue to operate in the future, ERM suggests adding the following general PRAO:

Ensure ongoing use of the PRI Areas for US Magnesium operations as necessary.

More specifically, the EPA and UDEQ have developed the following preliminary remedial action objectives (PRAOs) for OU1:

• Eliminate acid waters that pose risk to human health and the

environment. ERM Comment: As stated above, low pH surface waters will continue to be produced as part of ongoing US Magnesium operations and will be managed

as appropriate according to all applicable State and Federal waste management regulations. ERM suggests adding the following general PRAO:

Eliminate unacceptable risk to human health and the environment that could result from contact with acid waters.

• Eliminate releases of toxic wastes that pose risk to human health and

the environment. ERM Comment: Suggest rewording this PRAO as follows:

Eliminate the migration of contaminants from site media that pose unacceptable levels of risk to human health and the environment.

• Eliminate risks from contaminated foods to wildlife species that utilize

the Great Salt Lake and surrounding habitats. ERM Comment: Suggest rewording this PRAO as follows:

• Prevent impacts to biota from ingestion/direct contact with contaminants causing toxicity or impacts from bioaccumulation through the food chain to human and ecological receptors.

• Eliminate by treatment, removal/consolidation, or effective in-place

containment and isolation, unacceptable risk posed to human- and eco-receptors in contact with contaminated solid-waste, soils, sediment, and water.

ERM Comment: Suggest rewording this PRAO as follows:

• Eliminate by treatment, removal/consolidation, or effective in-place containment and isolation, unacceptable risk to human- and eco-receptors that could contact contaminated solid waste, soils, sediment, and water.

• Provide, by treatment, removal, or effective in-place isolation-

containment, remediation of waste-lagoon materials present within the historic lakebed and mudflats for permanent protection of the Great Salt Lake ecosystem.

ERM Comment: The “Great Salt Lake ecosystem” is too broad of a term,

would be difficult to define and monitor, and is not related to ARARs that can be used to establish when the objective has been achieved. Furthermore this PRAO is not significantly different than the PRAO preventing impacts to biota. ERM suggests eliminating this PRAO.

• Protect groundwater resources from adverse degradation and

limitations on future use. Comment: Site groundwater is designated as Class IV under Utah Administrative Code (UAC) R317-6. The protection level required for Class IV groundwater is discretionary and must protect human health and the environment. Class IV groundwater by definition is not a suitable drinking water source and therefore ingestion is an incomplete exposure pathway. The only potential complete exposure pathway to site groundwater is direct contact with surface expressions (i.e. springs and seeps). ERM therefore suggests that this PRAO be reworded as follows to ensure the protection level required by R317-6 is achieved:

• Prevent groundwater degradation that would result in surface waters exceeding risk-based concentrations for human and ecological receptors.

Attachment B Applicable or Relevant and Appropriate Requirements

Summary of Potential Federal ARARsOU-1US Magnesium LLCTooele County, Utah

Potential Standard, Requirement, Criterion or Limitation Citation Description Comment

Safe Drinking Water Act 42 USC 300 (f) Federal Maximum Contaminant Levels (MCLs) 40 CFR 141 MCLs have been promulgated for a number of common organic and inorganic

contaminants, which regulate the concentrations of contaminants in public drinking water supply systems.

Not an ARAR. Groundwater and surface water are not current drinking water sources. Future use as drinking water also unlikely due to poor water quality in the area (e.g., high salinity levels and TDS, etc).

Maximum Contaminant Level Goals (MCLGs) 40 CFR 141 MCLGs are non-enforceable health goals, which establish the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur.

Not an ARAR. Groundwater and surface water are not a current drinking water sources. Future use as drinking water also unlikely due to poor water quality in the area (e.g., high salinity levels and TDS, etc).

National Secondary Drinking Water Regulations (NSDWRs) 40 CFR 143 NSDWRs set non-mandatory water quality standards for 15 contaminants. They are established only as guidelines to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color and odor

Not an ARAR. Groundwater and surface water are not a current drinking water sources. Future use as drinking water source is unlikely due to poor water quality in the area (e.g., high salinity levels and TDS, etc).

Clean Water Act 33 USC 1251

Effluent Discharge Standards 40 CFR 122 and State Regulations Approved under 40 CFR 131; 40 CFR 125; and 40 CFR 136

Establishes requirements for discharge of treated wastewater surface water bodies under NPDES permit.

Is potential ARAR for remedial alternatives involving the discharge of treated wastewater or other discharges to a surface water body - see State ARARs

Surface Water Quality Standards 40 CFR 131 Establishes regulatory criteria used by the states to set surface water quality standards Is potential ARAR for remedial alternatives involving discharge of treated wastewater or other discharges to the Great Salt Lake and other surface water bodies. Limits are established by individual states based on the location and water usage by humans and wildlife - see State ARARs.

Resource Conservation and Recovery Act (RCRA) 42 USC 6901

RCRA Groundwater Protection Standards 40 CFR 264.94 Establishes groundwater protection standards which apply to RCRA regulated units. Would not be an ARAR if impacted materials are managed on-site through consolidation and/or capping in place, but may be relevant. Potential ARAR if material is excavated and disposed on-site, outside of existing location or if material is treated and then disposed on-site.

Solid Waste Disposal Act Amendments of 1980 (Public Law 96-482) 43 FR 58946 (§3001(b)(3)(A)(i-iii)) Bevill Amendment is pertinent to special wastes and exempts from the definition of hazardous waste waste from the extraction, beneficiation, and processing of ores and minerals

Would be an ARAR for discharges of beneficiation waste streams, e.g. acid and gypsum, and of "process wastewater from primary magnesium processing by the anhydrous process."

Land Disposal Restrictions 40 CFR 268 Establishes concentration levels that must be met prior to land disposal of hazardous wastes

Would not be an ARAR if impacted materials are managed on-site through consolidation and/or capping in place. Potential ARAR if material is excavated and disposed on-site, outside of existing location, or if material is treated and then disposed on-site.

Other USEPA Regions 3, 6, and 9 Regional Screening Levels (RSLs) for Chemical Contaminants at Superfund Sites

Risk-based guidelines establishing concentrations of compounds in soil, air and water considered to be protective of human health.

Potential ARARs to guide initial decision making, i.e. the selection of potential contaminants of concern in the Screening Level Risk Assesement, but are not appropropriate to be used as clean up levels.

Migratory Bird Treaty Act 16 USC 703 This Act makes it unlawful to “take, capture, kill,” or otherwise impact a migratory bird or any nest or egg of a migratory bird.

Would be an ARAR if remedial actions have the potential to impact or harm migratory birds.

National Historic Preservation Act 16 USC 470 Requires protection of historical and cultural resources to the maximum extent practical

Would be an ARAR if there are identified historical or cultural resources that may be impacted or disturbed by a remedial actions.

National Archaeological and Historical Preservation Act 16 USC 469 Establishes requirements for the protection of archaeological resources and human remains

Would be an ARAR if there are identified archeological or human remains that may be impacted or disturbed by a remedial action.

Clean Water Act 33 USC 1251 Requires protection of wetlands Would be an ARAR if remedial actions have potential to impact or impair wetland areas.

Endangered Species Act 16 USC 1531 Requires protection of threatened and endangered species and habitat Would be an ARAR if remedial actions have the potential to impact or harm any indentified endangered species.

Fish and Wildlife Coordination Act 16 USC 661 Requires notification to USFWS, Department of Interior or any other department exercising administration of wildlife resources in a given state, if any stream or other water body is diverted or impounded or otherwise controlled.

Would be an ARAR if remedial actions divert, impound or otherwise control surface water bodies.

Other

Chemical Specific

Location Specific

ERM Page 1 of 4

Summary of Potential Federal ARARsOU-1US Magnesium LLCTooele County, Utah

Potential Standard, Requirement, Criterion or Limitation Citation Description Comment

Executive Order No. 11593 Enhancement of the cultural environment. These measures include assuring that steps are taken to make records, drawings, and/or maps and have such items deposited in the Library of Congress when, as the result of a Federal action, a property listed on the National Register of Historic Places is to be substantially altered.

Potential to be considered material if there are identified historical or cultural resources that may be impacted or disturbed by a remedial action.

Executive Order No. 12898 Federal agencies shall conduct “activities that substantially affect human health or the environment, in a manner that ensures that such programs, policies, and activities do not have the effect of excluding persons (including populations) from participation in, denying persons (including populations) the benefits of, or subjecting persons (including populations) to discrimination under such programs, policies, and activities, because of their race, color, or national origin.”

Potential to be considered material.

Executive Order No. 13352 The Department of Interior shall, to the extent permitted by law, “implement laws relating to the environment and natural resources in a manner that promotes cooperative conservation."

Potential to be considered material.

Preservation Brief 36 Guidelines for planning, treating, and managing historic landscapes. Potential to be considered material if there are identified historical or cultural resources that may be impacted or disturbed by a remedial action.

National Register Bulletin 38 Guidelines for evaluating and documenting traditional cultural properties. Potential to be considered material if there are identified historical or cultural resources that may be impacted or disturbed by a remedial action.

Floodplain Management and Wetlands Protection 40 CFR 6.302(a) & (b), 40 CFR 6 Appendix A

Before undertaking an action, agencies are required to perform certain measures in order to avoid the long- and short-term impacts associated with the destruction of wetlands and the occupancy and modification of floodplains and wetlands. The regulation sets forth requirements as means of carrying out the provisions of Executive Orders 11988 and 11990.

Potential to be considered material for any remedial action that has the potential to affect wetland areas.

Executive Order 11988 – FloodplainManagement

Executive Order 11988 requires evaluation of the potential effects of actions that take place in a floodplain to avoid, to the extent possible, adverse impacts.

Potential to be considered material for any remedial action that has the potential to affect floodplain areas.

Executive Order 11990 ‐‐ Responsibilities of Federal Agencies to Protect Wetlands

Executive Order 11990 requires that potential impacts to wetlands be considered, and as practical, destruction, loss, or degradation of wetlands be avoided.

Potential to be considered material for any remedial action that has the potential to affect wetland areas

Resource Conservation and Recovery Act (RCRA) 42 USC 6901Standards for the Design, Siting, Operation and Closure of Hazardous Waste Management Units

40 CFR 264, 256 Establishes the standards for the design, operation and management of hazardous waste management units

Would not be an ARAR if impacted materials are managed on-site through consolidation and/or capping in place, but may be relevant and appropriate. Potentially applicable ARAR if material is hazardous waste and is excavated and disposed on-site, outside of existing location or if material is treated and then disposed on-site.

Land Disposal Restrictions 40 CFR 268 Establishes concentration levels that must be met prior to land disposal of hazardous wastes

Would not be an ARAR if impacted materials are hazardous wastes and are managed on-site through consolidation and/or capping in place, but may be relevant and appropriate. Potentially applicable ARAR if material is hazardous waste and is excavated and disposed on-site, outside of existing location or if material is treated and then disposed on-site.

Standards Applicable to a Generator of Hazardous Waste 40 CFR 262 Establishes general requirements for the identification and management requirements for hazardous waste.

Would be an ARAR if impacted media are hazardous wastes and are shipped off-site for disposal. Would also be ARAR for any ancillary generation of hazardous waste arising from remedial actions (e.g., potential wastes by-products from treatment process).

Clean Water Act 33 USC 1251Discharge of Treatment System Effluent 40 CFR 122 and 125 National Pollutant Discharge Elimination System requirements that regulate

discharges of pollutants from any point source into waters of the United States. Would be an ARAR for any remedial activitiy involving the operation of a water treatment system that discharges to surface water body.

Storm water discharges from construction 40 CFR 122 and 125 National Pollutant Discharge Elimination System requirements that regulate discharges of pollutants from any point source into waters of the United States.

Would be an ARAR related to storm water associated with any construction activity involving the disturbance of 5 acres (e.g., clearing, grading or excavation)

Discharge of Dredge or Fill to Waters of the United States 33 CFR 320-330, 40 CFR 230 Establishes prohibitions on the discharge of dredge and fill materials to the waters of the United States.

Would be an ARAR if remedial activities have potential to discharge dredge or fill materials to waters of the United States.

Safe Drinking Water Act 42 USC 300 (f) Underground Injection Control 40 CFR 144 Establishes conditions under which wastes or fluids can be injected underground Would be an ARAR if remedial activities involve underground injection (e.g., in-situ

chemical treatment of groundwater or injection of wastewater).Clean Air Act 40 CFR 1-99 Establishes regulations and limits on the amounts of pollutants that can be discharged

to the air. Would be an ARAR for remedial actions that emit criteria or hazardous air pollutants to the atmosphere (e.g., establishment of treatment facility or construction activities).

Occupational Safety and Health Act 29 USC 651General Industry Health and Safety Hazards 29 CFR 1910 OSHA regulations and standards for general worker safety. Is an ARAR relative to general worker safety during remediation activities OSHA Hazardous Waste Operation and Emergency Response Standards

29 CFR 1910.120 and 1926.65 Specific OSHA requirements for workers engaged in response or hazardous waste operations.

Would be an ARAR for workers engaged in hazardous waste clean-up operations.

Action Specific

ERM Page 2 of 4

Summary of Potential State ARARsOU-1US Magnesium LLCTooele County, Utah

Potential Standard, Requirement, Criterion or Limitation Citation Description Comment

Utah Water Quality Act Regulations Standards of Quality for Waters of the State R317-2-7 and R317-2-14 Establishes surface water quality standards based on the use designations for surface

waters of the stateWould be an ARAR for remedial alternatives involving the discharge of treated wastewater or other discharges to a surface water body

Utah Groundwater Quality Standards R317-6-2 and R317-6-3 Establishes groundwater quality standards and groundwater classes. Standards are equivalent to MCL levels in most instances.

Is a potential ARAR, but since site groundwater is designated as Class IV it is not a current drinking water source and future use as drinking water is unlikely due to naturally occurring high salinity levels and TDS, etc. Therefore MCLs are not applicable or appropriate standards for site groundwater. Additionally, the regulation states under R317-6-6.15A.3 that the procedural provisions of R317-6-6.15 are not applicable to a site where a corrective or remedial action is implemented under a program that the Director determines meets the substantive standards of the rule, including specifically the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA).

Utah Safe Drinking Water Act Regulations Primary and Secondary Drinking Water Standards R309-200-5 and R309-200-5 Establishes drinking water standards for public water systems Would not be an ARAR. Groundwater and surface water are not current drinking

water sources. Future use also unlikely due to quality of naturally occurring groundwater and surface water.

Utah Hazardous Substances Act Regulations Corrective Action Clean-Up Standards Policy R311-211 Establishes cleanup requirements at CERCLA and UST sites. The rule lists general

considerations for establishing cleanup standards Potential ARAR for considering and developing cleanup standards.

Cleanup Action and Risk Based Closure Standards R315-101 Establishes requirements to support risk-based cleanup and closure standards at sites for which remediation or removal of hazardous constituents to background levels will not be achieved

Potential ARAR for considering and developing cleanup standards.

Historical Preservation R455-4, UCA 9-8-301-308 and UCA 9-8-304

State and federal agencies that undertake projects must “take into account” how their project activities will affect historic and archaeological resources. They must also provide the State Historic Preservation Officer (SHPO) with a written evaluation of the project and an opportunity to comment

Potential ARAR if there are identified historical, cultural or archeological resources that may be impacted or disturbed by a remedial actions.

Utah Water Quality Act Regulations Standards of Quality for Waters of the State R317-2-7 and R317-2-14 Establishes surface water quality standards based on the use designations for surface

waters of the state; use designations vary by water body. Presumptive classificatons apply for water bodies not specifically classified (e.g., all drainage ditches and canals and ditches not otherwise described).

Would be an ARAR for remedial alternatives involving the discharge treated wastewater or other discharges to a surface water body.

Utah Air Conservation Act Regulations R307General Requirements for Control of Air Pollution Sources R307-101-1 and R307-401 Regulates new installations which have the potential to emit criteria or hazardous air

pollutants to the atmosphere.Would be an ARAR for remedial actions that emit criteria or hazardous air pollutants to the atmosphere (e.g., establishment of treatment facility or construction activities).

General Fugitive Dust Control Requirements for Construction and Demolition Activities

R307-205-5 Any person engaging in clearing or leveling of land greater than one-quarter acre in size, earthmoving, excavation, or movement of trucks or construction equipment over cleared land greater than one-quarter acre in size or access haul roads shall take steps to minimize fugitive dust from such activities. Such control may include watering and chemical stabilization of potential fugitive dust sources or other equivalent methods or techniques approved by the director

Would be an ARAR for any construction activities that generate dust.

Utah Water Quality Act Regulations Standards for Quality for Waters of the State R317-2 Establishes discharge requirements for facilities that discharge potential pollutants to

surface water. Requires compliance with surface water numeric criteria for various water classes.

Would be an ARAR for any remedial alternative that discharges directly or indirectly any pollutant to surface water. Note - Great Salt Lake does not currently have established numeric water quality standards.

Groundwater Quality Protection R317-6 Establishes discharge requirements for facilities that discharge potential pollutants to groundwater

Would be an ARAR for any remedial alternative that discharges directly or indirectly any pollutant to groundwater.

Underground Injection Control Program R317-7 Establishes permit requirement and conditions for the injection of fluids into the subsurface.

Would be an ARAR for any remedial alternative that involves the injection of fluids into the subsurface (e.g., chemicals injected for in-situ treatment).

Utah Pollutant Discharge Elimination System R317-8 Requires permits for the discharge of pollutants from any point source into waters of the State, including management of storm water during construction activities.

Would be an ARAR for remedial alternatives involving the operation of a water treatment system that discharges to surface water body. Would also be applicable to storm water discharges during construction.

Chemical Specific

Location Specific

Action Specific

ERM Page 3 of 4

Summary of Potential State ARARsOU-1US Magnesium LLCTooele County, Utah

Potential Standard, Requirement, Criterion or Limitation Citation Description Comment

Utah Solid and Hazardous Waste Hazardous Substances Act Standards for the Design, Siting, Operation and Closure of Hazardous Waste Management Units

R315-8, R315-302 R315-303 and R315-310

Establishes the standards for the design, operation and management of hazardous waste management units.

Not anticipated to be an ARAR. Potential ARAR if impacted materials are hazardous wastes and are managed on-site through consolidation and/or capping in place, but may be relevant and appropriate. Potential ARAR if material is a hazardous waste and is excavated and disposed on-site, outside of existing location or if material is treated and then disposed on-site.

Land Disposal Restrictions R315-13 Establishes concentration levels that must be met prior to land disposal of hazardous wastes

Not anticipated to be an ARAR. Potential ARAR if impacted materials are hazardous wastes and are managed on-site through consolidation and/or capping in place, but may be relevant and appropriate. Potential ARAR if material is a hazardous waste and is excavated and disposed on-site, outside of existing location or if material is treated and then disposed on-site.

Standards Applicable to a Generator of Hazardous Waste R315-1, R315-2 and R315-5 Establishes general requirements for the identification and management requirements for hazardous waste.

Would be an ARAR if impacted materials are hazardous wastes and are shipped off-site for disposal. Would also be an ARAR for any ancillary generation of hazardous waste arising from remedial actions (e.g., potential waste by-products from treatment process).

Land Treatment Disposal Standards R315-307 Establishes general requirements for land treatment, landfarming, or landspreading operations.

Would be an ARAR for any remedial activity involving landfarming.

State Engineer, Department of Natural Resources Drilling Standards R655-4 Establishes the requirements and standards for the well construction and

abandoment of wells 30 feet or greater in depth. Wells less than 30 feet in depth are exepmt

Would be an ARAR for the construction and abandoment of all wells greater than 30 feet in depth.

Appropriation of Groundwater or Surface Water UCA 73 Establishes requirments for the appropriation and diversion of waters of the state. Would be an ARAR for any remedial action involving the extraction or diversion of groundwater or surface water (e.g., groundwater extraction system).

State OSHA Rules R574 Adopts federal OSHA standards for worker safety. Is an ARAR relative to general worker safety during remediation activities.

ERM Page 4 of 4

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8

Ref: 8EPR-SR

Mr. David J. Abranovic, P.E. Project Coordinator ERM West, Inc.

1595 Wynkoop Street Denver, Colorado 80202-1129

Phone 800-227-8917 www.epa.gov/region8

May 2, 2016

7272 East Indian School Rd., Suite 108 Scottsdale, AZS 85251

Re: EPA Response to ERM Comments on OU 1 Preliminary Remedial Action Objectives for Feasibility Study Screening for US Magnesium NPL Site

Dear Mr. Abranovic:

The U.S. Environmental Protection Agency (EPA), in consultation with the Utah Department of Environmental Quality (UDEQ), has reviewed your letter of February 16, 2016, that provides comments on the draft PRAOs prepared by the EPA. Except as noted below, the Agencies accept your suggested revisions. In keeping with the format of ERM's letter, the original text by the EPA is in black, ERM's comments and suggested changes are in green, and the EPA' s newly-modified and current PRAOs are shown in blue. For convenience, the current PRAOs are listed in Attachment 1.

1. RELEASE OF ACID WATER

Original EPA text:

The remedial action objective for the US Magnesium NPL Site is to reduce or eliminate exposures of humans and ecological receptors to contaminated media in locations that exceed risk-based concentrations, including:

- exposures to solid media (soils, sediments and solid wastes) through ingestion, inhalation, dermal contact, and the food chain;

- exposures to acids and other site-related contaminants in surface waters through ingestion and dermal contact pathways.

More specifically, the EPA and UDEQ have developed the following preliminary remedial action objectives (PRAOs) for OUl:

• Eliminate acid waters that pose risk to human health and the environment.

ERM commented:

The elimination of exposures to acid in surface water is not an appropriate PRAO for the Feasibility Study. Low pH surface waters are currently and will continue to be generated as part of ongoing US Magnesium operations and will be managed as appropriate according to all applicable State and Federal waste management regulations. Based on

the human health survey conducted in 2014, there isn 't any ingestion exposure pathway of surface waters for human receptors (i.e. dermal contact exposures only). Given that US Magnesium is an operating facility and will continue to operate in the future, ERM suggests adding the following general PRAOs:

• Ensure ongoing use of the PRJ Areas for US Magnesium operations as necessary. • Eliminate unacceptable risk to human health and the environment that could

result from contact with acid waters.

Agency response:

The Agencies agree that the PRAO is not to eliminate the release of acid water, but to minimize the risks that may be associated with human or ecological exposure to acid waters. In that regard, ERM's first general PRAO, above, is not necessary, while the second bullet is an appropriate correction to the EPA' s specific PRAO. In the future, if acid waters generated by plant operations are neutralized before release into the environment, the PRAO would largely be addressed. If acid water releases continue, then other strategies for minimizing potential human and ecological risks would need consideration.

2. RELEASE OF TOXIC WASTES

Original EPA text:

Eliminate releases of toxic wastes that pose risk to human health and the environment.

ERM commented:

Suggest rewording this P RAO as follows:

• Eliminate the migration of contaminants from site media that pose unacceptable levels of risk to human health and the environment.

Agency response:

The Agencies agree that the PRAO is not to eliminate the release of toxic wastes, but to ensure that toxic wastes that are generated by plant operations do not result in unacceptable exposures of humans or ecological receptors. ERM's suggested revision is useful, but only addresses exposures associated with migration from the site of waste disposal. The PRAO needs to address exposures both at the site of disposal, as well as exposure points that might result from migration.

Accordingly, EPA has made the following revision of this PRAO:

• Eliminate or minimize exposures to site-related toxic wastes that are of potential health concern to humans or ecological receptors. This includes exposures both at the site of waste disposal as well as exposures that might result from the migration of toxic wastes in the environment.

Original EPA text:

• Eliminate risks from contaminated foods to wildlife species that utilize the Great Salt Lake and surrounding habitats.

ERM commented: Suggest rewording this P RAO as follows:

• Prevent impacts to biota from ingestion/direct contact with contaminants causing toxicity or impacts from bioaccumulation through the food chain to human and ecological receptors.

Agency response: Revision is accepted.

Original EPA text:

• Eliminate by treatment, removal/consolidation, or effective in-place containment and isolation, unacceptable risk posed to human- and eco- receptors in contact with contaminated solid-waste, soils, sediment, and water.

ERM commented: Suggest rewording this PRAO as follows:

• Eliminate by treatment, removal/consolidation, or effective in-place containment and isolation, unacceptable risk to human- and eco-receptors that could contact contaminated solid waste, soils, sediment, and water.

Agency response: Revision is accepted.

Original EPA text:

• Protect groundwater resources from adverse degradation and limitations on future use.

ERM commented:

Site groundwater is designated as Class JV under Utah Administrative Code (UAC) R31 7-6. The protection level required for Class IV groundwater is discretionary and must protect human health and the environment. Class JV groundwater by definition is not a suitable drinking water source and therefore ingestion is an incomplete exposure pathway. The only potential complete exposure pathway to site groundwater is direct contact with surface expressions (i.e. springs and seeps). ERM therefore suggests that this P RAO be reworded as follows to ensure the protection level required by R3 l 7-6 is achieved:

• Prevent groundwater degradation and releases that would result in surface waters exceeding risk-based concentrations for human and ecological receptors.

Agency response:

The Agencies understand and accept that Class IV groundwater is an improbable source of human drinking water, and that, under current site conditions, the primary reason for concern over groundwater contamination is exposure of ecological receptors to groundwater that is, or may become, expressed at the surface. However, the current status (nature and extent) and the potential rate of changes (fate and transport) for the groundwater system must be understood as it pertains to a future potential source of drinking water. Therefore, prevention of groundwater degradation is an important PRAO that must be maintained.

Lastly, the EPA appreciates your submittal of Preliminary Provisional ARARs. The agencies are continuing review of that material, but in the meantime, as discussed, are providing you with the updated PRAOs for your use in preparing the draft Screening FS.

Ken Wangerud Remedial Project Manager Superfund Remedial Program

Enclosure: Preliminary RAOs for RIFS (April 2016) cc: Michael Storck, UDEQ-DERR

Preliminary Remedial Action Objectives for the Remedial Investigation/Feasibility Study

US Magnesium NPL Site

EPA-UDEQ, April 2016

1. Release of Acid Water

A. Eliminate unacceptable risk to human health and the environment that could result from contact with acid waters.

2. Release of Toxic Wastes

A. Eliminate or minimize exposures to site-related toxic wastes that are of potential health concern to humans or ecological receptors. This includes exposures both at the site of waste disposal as well as exposures that might result from the migration of toxic wastes in the environment.

B. Prevent impacts to biota from ingestion/direct contact with contaminants causing toxicity or impacts from bioaccumulation through the food chain to human and ecological receptors.

C. Eliminate by treatment, removal/consolidation, or effective in-place containment and isolation, unacceptable risk to human- and eco-receptors that could contact contaminated solid waste, soils, sediment, and water.

D. Prevent groundwater degradation and releases that would result in surface waters exceeding risk-based concentrations for human and ecological receptors.