REHS Domain 6: Solid and Hazardous Waste - Complete Study Guide 2027

Domain 6 Overview & Exam Weight

Domain 6: Solid and Hazardous Waste represents a critical component of the REHS examination, testing your comprehensive understanding of waste management systems, regulatory frameworks, and environmental protection protocols. This domain challenges candidates to demonstrate expertise in both municipal solid waste operations and complex hazardous materials management.

Understanding Domain 6 is essential for success on the REHS exam, as waste management intersects with virtually every other environmental health discipline. Whether you're following Track A, B, or C eligibility requirements, mastering this domain's concepts will significantly impact your overall performance on the 225-question examination.

The content closely aligns with real-world environmental health specialist responsibilities, making it particularly relevant for professionals working in state and local health departments. Many of the 16+ states using REHS as their licensing exam emphasize Domain 6 concepts in their regulatory frameworks.

Solid Waste Management Systems

Solid waste management forms the foundation of Domain 6, encompassing collection, transportation, processing, and disposal of non-hazardous wastes. Understanding integrated waste management systems is crucial for REHS candidates, as these systems directly impact public health and environmental quality.

Municipal Solid Waste Characteristics

Municipal solid waste (MSW) composition varies significantly based on geographic location, economic factors, and seasonal patterns. Typical MSW contains organic materials (food waste, yard trimmings), paper and cardboard, plastics, metals, glass, wood, textiles, and other miscellaneous materials. Understanding these composition patterns helps environmental health specialists design effective management strategies.

Waste Component	Typical Percentage	Management Priority
Food Waste	21-22%	Composting/Anaerobic Digestion
Paper/Cardboard	27-28%	Recycling
Yard Trimmings	13-14%	Composting
Plastics	12-13%	Recycling/Energy Recovery
Wood	6-7%	Reuse/Energy Recovery

Generation rates typically range from 3-8 pounds per person per day in developed areas, with significant variations based on income levels, urban versus rural settings, and local waste diversion programs. Environmental health specialists must understand these patterns when evaluating system capacity and effectiveness.

Collection and Transportation Systems

Effective collection systems balance service quality, cost efficiency, and environmental impact. Key considerations include collection frequency, vehicle routing optimization, transfer station operations, and worker safety protocols. The complete guide to all 7 REHS exam domains emphasizes how waste collection intersects with other environmental health areas.

Transfer stations serve as intermediate facilities where waste is consolidated from collection vehicles into larger transport units. These facilities require careful design to minimize odors, vector attraction, and environmental contamination while maximizing operational efficiency.

Hazardous Waste Regulations & Classification

The Resource Conservation and Recovery Act (RCRA) provides the regulatory framework for hazardous waste management in the United States. Understanding RCRA's requirements is essential for REHS success, as these regulations govern identification, generation, transportation, treatment, storage, and disposal of hazardous wastes.

Hazardous Waste Identification

RCRA defines hazardous waste through two primary mechanisms: characteristic wastes and listed wastes. Characteristic wastes exhibit ignitability, corrosivity, reactivity, or toxicity properties. Listed wastes appear on specific EPA lists (F, K, P, and U lists) based on their source and composition.

The four hazardous waste characteristics each have specific testing protocols and regulatory thresholds:

• Ignitability (D001): Liquids with flash points below 60°C, non-liquids causing fire through friction, ignitable compressed gases, and oxidizers
• Corrosivity (D002): Aqueous wastes with pH ≤ 2 or ≥ 12.5, or liquids that corrode steel at rates exceeding 6.35mm per year
• Reactivity (D003): Wastes that are unstable, react violently with water, generate toxic gases, or are capable of detonation
• Toxicity (D004-D043): Wastes that exhibit toxicity characteristics based on Toxicity Characteristic Leaching Procedure (TCLP) results

Generator Requirements

RCRA classifies hazardous waste generators into three categories based on monthly generation quantities. Each category has distinct regulatory requirements for manifesting, storage, treatment, and disposal activities.

Generator Category	Monthly Generation	Storage Time Limit	Key Requirements
Small Quantity Generator	100-1,000 kg	180/270 days	Basic manifesting, limited storage
Large Quantity Generator	>1,000 kg	90 days	Full manifesting, permits, contingency plans
Very Small Quantity Generator	<100 kg	Indefinite	Minimal federal requirements

Understanding these classification systems is crucial for environmental health specialists conducting facility inspections and compliance assessments. The regulatory complexity requires thorough preparation, which is why many candidates benefit from comprehensive study resources and practice testing platforms that cover these detailed requirements.

Waste Treatment & Disposal Methods

Effective waste management relies on appropriate treatment technologies and disposal methods that protect human health and environmental quality. REHS candidates must understand both conventional and emerging treatment approaches, their applications, limitations, and regulatory requirements.

Solid Waste Treatment Technologies

Modern solid waste management employs a hierarchy of treatment options designed to maximize resource recovery while minimizing environmental impact. The waste management hierarchy prioritizes source reduction, reuse, recycling, composting, energy recovery, and disposal.

Composting represents a critical biological treatment process that converts organic waste into stable humus-like material. Successful composting requires proper carbon-to-nitrogen ratios (typically 25-30:1), adequate moisture content (50-60%), appropriate particle size, and sufficient oxygen availability. Temperature monitoring ensures pathogen destruction while preventing excessive heat buildup.

Anaerobic digestion offers an alternative biological treatment approach that generates renewable energy while processing organic wastes. This process occurs in oxygen-free environments and produces biogas (methane and carbon dioxide) along with digestate that can serve as soil amendment.

Hazardous Waste Treatment Technologies

Hazardous waste treatment technologies are specifically designed to reduce toxicity, mobility, or volume of dangerous materials. Treatment methods fall into three primary categories: physical, chemical, and biological processes.

Physical treatment methods include stabilization/solidification, which immobilizes contaminants in a solid matrix, and thermal treatment processes like incineration and pyrolysis. These technologies can significantly reduce waste volume and destroy organic contaminants, but require careful monitoring to prevent air emissions.

Chemical treatment approaches include neutralization for corrosive wastes, oxidation/reduction for certain organic and inorganic compounds, and precipitation for metal-containing wastes. Each method requires specific process controls and often generates secondary wastes requiring additional management.

Disposal Methods and Requirements

Despite emphasis on treatment and recovery, disposal remains necessary for many waste materials. Modern disposal methods must meet strict regulatory requirements designed to prevent groundwater contamination, air emissions, and other environmental impacts.

Subtitle D landfills accept non-hazardous solid wastes and must incorporate liner systems, leachate collection, groundwater monitoring, and gas management systems. These engineered systems provide multiple barriers against environmental contamination while accommodating large waste volumes.

Subtitle C landfills handle hazardous wastes and require more stringent design standards, including double liner systems, enhanced monitoring requirements, and stricter operational controls. These facilities serve as the final disposal option for hazardous wastes that cannot be effectively treated or recycled.

Environmental Monitoring & Assessment

Environmental monitoring programs provide essential data for evaluating waste management system performance and identifying potential health risks. REHS candidates must understand monitoring design principles, sampling protocols, analytical methods, and data interpretation techniques.

Groundwater Monitoring Systems

Groundwater monitoring represents a critical component of waste facility oversight, providing early warning of potential contamination and demonstrating compliance with regulatory standards. Effective monitoring systems require strategic well placement, appropriate sampling protocols, and comprehensive analytical programs.

Monitoring well networks typically include upgradient (background) wells and downgradient (compliance) wells positioned to detect potential contaminant migration. Well construction must prevent cross-contamination between aquifers while allowing representative sampling of groundwater quality.

Sampling protocols must address quality assurance/quality control requirements, chain-of-custody procedures, and proper preservation techniques. Understanding these protocols is essential for REHS candidates, as monitoring data often drives regulatory decisions and enforcement actions.

Air Monitoring and Emissions Assessment

Air monitoring at waste management facilities focuses on criteria pollutants, hazardous air pollutants, and odor compounds that may impact surrounding communities. Monitoring approaches vary based on facility type, waste characteristics, and regulatory requirements.

Stack testing protocols evaluate emissions from thermal treatment units, requiring isokinetic sampling techniques and specialized analytical methods. Understanding these procedures helps environmental health specialists assess facility compliance and potential health impacts.

Ambient air monitoring may be required near waste management facilities to demonstrate compliance with air quality standards and assess community exposure levels. This monitoring often focuses on particulate matter, volatile organic compounds, and facility-specific contaminants of concern.

Remediation & Cleanup Strategies

Environmental remediation addresses contamination from past waste management practices and accidental releases. The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) provides the regulatory framework for cleanup activities at contaminated sites.

Site Investigation and Risk Assessment

Effective remediation begins with thorough site characterization to define contaminant distribution, migration pathways, and potential exposure scenarios. Site investigation activities typically progress through multiple phases, from preliminary assessments to detailed remedial investigations.

Risk assessment methodologies evaluate potential human health and ecological impacts from site contamination. These assessments consider exposure pathways, receptor populations, toxicity data, and site-specific conditions to determine cleanup requirements and remedial objectives.

The risk assessment process typically includes hazard identification, dose-response assessment, exposure assessment, and risk characterization steps. Understanding this framework helps environmental health specialists evaluate contaminated sites and prioritize remedial actions.

Remedial Technologies

Remedial technologies range from simple containment approaches to complex treatment systems designed to destroy or remove contaminants. Technology selection depends on contaminant properties, site conditions, regulatory requirements, and cost considerations.

Technology Type	Application	Advantages	Limitations
Pump and Treat	Groundwater contamination	Proven technology, containment	Long timeframes, limited mass removal
Soil Vapor Extraction	Volatile contaminants in soil	Cost-effective, minimal disruption	Limited to volatile compounds
Bioremediation	Biodegradable organics	Destroys contaminants, cost-effective	Time requirements, site conditions
Thermal Treatment	High-concentration organics	Rapid treatment, volume reduction	High cost, air emissions

In-situ treatment technologies treat contamination without excavation, potentially reducing costs and minimizing site disruption. These approaches include chemical oxidation, enhanced bioremediation, and thermal treatment methods applied directly in the subsurface.

Inspection & Enforcement Procedures

Environmental health specialists regularly conduct inspections of waste management facilities to ensure regulatory compliance and protect public health. Understanding inspection procedures, documentation requirements, and enforcement options is essential for REHS success.

Inspection Planning and Preparation

Effective inspections require thorough preparation, including review of facility records, permits, previous inspection reports, and applicable regulations. Pre-inspection planning helps ensure comprehensive coverage of regulatory requirements and efficient use of inspection time.

Inspection checklists provide systematic approaches to facility evaluation while ensuring consistent application of regulatory standards. These checklists typically address operational procedures, maintenance activities, record-keeping requirements, and environmental monitoring programs.

Understanding facility operations helps inspectors identify potential compliance issues and assess environmental health risks. This knowledge enables more effective questioning during inspections and better evaluation of facility management practices.

Documentation and Report Writing

Proper documentation during inspections provides the foundation for enforcement actions and regulatory decisions. Inspection reports must accurately describe observed conditions, identify regulatory violations, and provide sufficient detail to support enforcement activities.

Photographic documentation can provide valuable evidence of facility conditions and regulatory violations. However, photographs must be properly labeled with date, time, location, and description information to serve as effective enforcement tools.

Chain-of-custody procedures may be necessary when collecting samples during inspections. Understanding these procedures ensures sample integrity and admissibility in enforcement proceedings.

For candidates preparing for the challenging REHS examination, mastering these inspection and enforcement concepts is crucial. Many find that understanding the exam's difficulty level helps them allocate appropriate study time to complex domains like waste management.

Study Strategies for Domain 6

Success in Domain 6 requires a systematic approach to learning complex regulatory frameworks, technical processes, and practical applications. The breadth of waste management topics demands strategic study planning and multiple learning approaches.

Regulatory Framework Mastery

Understanding the interconnected web of federal, state, and local waste management regulations represents one of the most challenging aspects of Domain 6 preparation. Start with foundational statutes like RCRA and CERCLA, then build understanding of implementing regulations and guidance documents.

Create regulatory flowcharts and decision trees to visualize complex processes like hazardous waste determination and generator requirements. These visual aids help clarify regulatory pathways and decision points that commonly appear on REHS examinations.

Regular practice with online practice exams helps identify knowledge gaps and builds familiarity with question formats commonly used in Domain 6. The 1000+ question bank provides extensive coverage of waste management topics with detailed explanations.

Technical Concept Integration

Waste management involves complex technical processes that require understanding of chemistry, engineering, and environmental science principles. Focus on understanding process mechanisms rather than memorizing isolated facts.

Develop conceptual models for key processes like composting, anaerobic digestion, and various treatment technologies. Understanding how these processes work helps answer application-based questions that require analysis and problem-solving skills.

Practice calculating key parameters like waste generation rates, treatment system sizing, and monitoring frequencies. Mathematical applications frequently appear in Domain 6 questions and require comfortable manipulation of formulas and unit conversions.

Practice Questions & Key Concepts

Domain 6 questions often present complex scenarios requiring integration of regulatory knowledge, technical understanding, and practical judgment. Success requires ability to analyze situations and select best answers among plausible alternatives.

Common Question Types

Hazardous waste classification questions test understanding of characteristic and listed waste categories. These questions may present waste descriptions and require proper classification or management determination.

Treatment technology questions evaluate knowledge of appropriate technologies for specific waste types and contamination scenarios. Understanding technology limitations and applications helps select correct answers.

Regulatory compliance questions assess understanding of generator requirements, manifesting procedures, and storage limitations. These questions often involve calculating time limits or determining applicable requirements.

Inspection and enforcement questions test practical knowledge of facility evaluation procedures and regulatory response options. Understanding escalating enforcement approaches and appropriate documentation requirements helps answer these questions correctly.

Key Study Areas

Concentrate study efforts on high-yield topics that frequently appear on examinations. RCRA hazardous waste management represents the largest single topic area within Domain 6 and receives extensive examination coverage.

Solid waste management systems, including collection, treatment, and disposal methods, appear regularly on examinations. Understanding integrated waste management approaches and technology applications provides strong examination preparation.

Environmental monitoring and remediation topics require understanding of technical processes and regulatory frameworks. Focus on monitoring system design, sampling procedures, and remedial technology selection criteria.

Many successful candidates report that combining structured study approaches with comprehensive study resources significantly improved their Domain 6 performance. The key is consistent preparation over time rather than cramming before the examination.