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Remediation Technologies Screening Matrix, Version 4.0  
Chapter 7 Soil Washing/Solvent Extraction
Table of Contents


7-2 Hazard Analysis

Principal unique hazards associated with soil washing/solvent extraction include:

Physical Hazards Chemical Hazards Radiological Hazards Biological Hazards

a. Physical Hazards

(1) Description: During soil excavation, workers may be seriously injured or killed by heavy equipment such as front-end loaders and scrapers. Excavation activities include the operation of heavy equipment, which may present a noise hazard.

Control: Heavy equipment should be equipped with a backup alarm that alerts workers. When approaching operating equipment, the approach should be made from the front and within view of the operator, preferably making eye contact. Hearing protection should be worn when working around operating equipment. CONTROL POINT: Construction, Operations

(2) Description: During excavation into soils saturated with flammable or combustible materials, fire or explosion hazards may exist. The bucket of a backhoe or the blade of a crawler may cause a spark during contact with rocks, buried metal, or other objects and ignite a flammable vapor that may be generated.

Control: Controls to help prevent the ignition of vapors during excavation include equipping the backhoe with a non-sparking blade and periodically wetting the active work area with water. CONTROL POINT: Design, Operations

(3) Description: The movement of soil from the excavation area to the treatment unit by use of a conveyor may constitute pinch-point hazards from unguarded rollers. Workers' clothing may become entangled with the rollers, causing injury or death.

Control: Controls for minimizing exposure to moving equipment include guards for conveyors belts and rollers, and associated equipment to prevent accidental contact. CONTROL POINT: Design

(4) Description: Fire and explosion hazards may exist as soils containing flammable materials are crushed and sized or screened for treatment. As aggregate soils are crushed, heat that may be generated may be sufficient to ignite vapors which have volatilized from the soil. Noise and vibration may also be present during equipment operation. Workers may also be exposed to flying projectiles as a result of the crushing/grinding operation.

Control: Periodic application of water may help to reduce the potential for a fire or explosion during soil sizing or screening. Vibration (and noise) hazards should be reduced by installing equipment on vibration dampening bushings. Noise may be controlled by the use of baffles, or sound deflecting/absorbing walls between the source and the operator or by the use of hearing protection. Safety glasses with side shields should also be used to help prevent eye injuries from projectiles during operation of soil sizing and screening equipment. CONTROL POINT: Construction, Operations

(5) Description: Fire and explosion hazards may exist during distillation of solvents used in the extraction process. Over-pressurization may result in rupture of the vessel. The resulting release of flammable solvent may pose a fire or explosion hazard.

Control: Controls to prevent over-pressurization of distillation and solvent delivery systems should include the use of pressure relief valves and hazard warning alarms. CONTROL POINT: Design

(6) Description: Steam pressure washing of equipment may expose workers to thermal or burn hazards, eye hazards due to flying projectiles dislodged during pressure washing, slip hazards from wet surfaces, and noise hazards.

Control: Thermal burns from the operation of steam pressure washing equipment may be prevented by using insulated gloves (e.g. silica fabric gloves). Eye injuries and hearing loss may be prevented by wearing safety goggles and hearing protection during pressure washing activities. Slip hazards may be controlled by workers wearing slip-resistant boots and draining water away from the decontamination operation into a tank or pit. Walking surfaces should be drained and free of standing liquids or mud. CONTROL POINT: Construction, Operations, Maintenance

(7) Description: Depending on soil types, exposure to respirable quartz may be a hazard. Consult geology staff to confirm the presence of a respirable quartz hazard (e.g. to determine if soil types are likely to be rich in respirable quartz). As an aid in determining respirable quartz exposure potential, sample and analyze site soils for fines content by ASTM D422, followed by analysis of the fines by X-Ray Diffraction to determine fine material quartz content.

Control: Worker exposure to dust rich in respirable quartz may be minimized by periodically wetting the soil with water or amended water or by the use of respiratory protection, such as a air-purifying respirator equipped with a HEPA(N100, R100, P100) filter/cartridge. CONTROL POINT: Design, Construction, Operations

(8) Description: During site activities, workers may be exposed to direct and indirect sunlight and corresponding ultraviolet (UV) radiation. Even short-term exposure to sunlight can cause burns and dermal damage. Exposure to hot and humid conditions may also result in heat stress, which can manifest itself as heat exhaustion and heat stroke.

Control: Exposure to direct and indirect sunlight should be minimized where possible in the summer months. Workers can minimize direct sun exposure by wearing long-sleeve shirts and full-length pants, and by applying UV barrier sunscreen. If possible, the work and break areas should be shaded. Exposure to heat stress conditions can be minimized by taking frequent breaks, drinking adequate fluids, and performing work during the early morning and late afternoon hours. CONTROL POINT: Construction, Operations

(9) Description: Workers may be exposed to confined-space hazards during entry into mixing/reaction vessels for maintenance. Confined space may expose workers to toxic atmospheric hazards or to hazards associated with oxygen depravation.

Control: Prior to entry into tanks, vessels, or other confined space, testing of the atmosphere within the confined space is required. Appropriate health and safety steps also include ventilation of the space, entry using supplied air and confined space techniques for eliminating the hazards (see 29 CFR 1910, 146). Air handling systems should be designed to minimize or eliminate oxygen-deficient locations in the treatment train. CONTROL POINT: Design, Operations, Maintenance

(10) Description: Operation of temporary and permanent electrical equipment, such as lights, generators, and soil washing/solvent extraction system components may cause electrical hazards.

Control: Verify that the hazardous area classifications, as defined in NFPA 70-500-1 through 500-10, are indicated on the drawings. All controls, wiring, and equipment should be in conformance with the requirements of EM 385-1-1, Section 11.G and NFPA for the identified hazard areas. Equipment should be grounded and/or provided with ground fault interrupter circuit (GFIC) protection if required by EM 385-1-1, Section 11 or NFPA 70 requirements. CONTROL POINT: Design, Construction, Operations, Maintenance

(11) Description: Emergency shower/eye wash equipment required by 29 CFR 1910.151 are not always equipped with adequate floor drains, thereby creating potential electrical hazards or walking surface hazards during required testing/use.

Control: Showers/eye wash equipment should be equipped with accompanying functional drains to isolate and collect the shower/eye wash water from unprotected electrical equipment and walking surfaces that, when wet, create electrical or slipping hazards. CONTROL POINT: Design

b. Chemical Hazards

(1) Description: Workers may be exposed to VOC emissions from either extracting agents (surfactants and concentrated acids), and/or solvents used in the solvent extraction process, or to wastes in the extraction/washing process. Examples of solvents include methyl ethyl ketone, pentane, and citric acid derivatives.

Control: The exposure to the extracting agents and to the wastewater treatment chemicals may be controlled if the chemicals are added to the system under closed or properly ventilated conditions. Respiratory protection (e.g. an air-purifying respirator with organic vapor cartridges) may also be used to control inhalation exposures. An assessment of the exposure (with exposure monitoring) is needed to determine the type of respirator for the particular application. CONTROL POINT: Design, Construction, Operations, Maintenance

(2) Description: During system failure, workers may be exposed to either solvents or extraction agents should the system experience a release from over-pressurization or other malfunction.

Control: The system design should include redundant safety features including automatic warning systems to prevent a release of chemicals from over-pressurization or other malfunction. CONTROL POINT: Design

(3) Description: During the process of treating water from the operation, workers may be exposed to chemical hazards from acidic or caustic precipitation chemicals or to the sludge generated from the process via the inhalation/dermal/ingestion routes. The sludge may contain heavy metals, including lead, or organic compounds such as fuels.

Control: Worker exposure may be controlled by designing a closed-feed system for the addition of precipitation chemicals as well as for sludge handling and removal. Other controls include using less toxic precipitation agents and the use of personal protective equipment (PPE) (e.g. nitrile gloves for dermal protection from fuels, and an air-purifying respirator with combination HEPA/organic cartridges for control of inhalation hazards). CONTROL POINT: Design, Operations, Maintenance

c. Radiological Hazards

Description: Radiological materials may be segregated in the soil washing process, and naturally occurring radioactive material (NORM) may be present in soils, sludge, and groundwater. Some radioactive materials may present an external hazard. All radioactive materials may present an internal exposure hazard through inhalation or ingestion.

Control: Radioactive materials may be known to be present at the site. Soil, sludge or groundwater may be tested to determine if radioactive materials are present. If any radioactive material above background levels is found, a qualified health physicist should be consulted to determine the exposure potential and any necessary engineered controls or PPE to put in place or use. CONTROL POINT: Design, Construction, Operations

d. Biological Hazards

Description: At those sites involving medical wastes or sewage sludge, microorganisms in the soil may pose exposure hazards during the soil mixing and waste stabilization activities. Workers may be exposed to inhalation/ingestion/dermal contact with pathogens such as Coccidioides sp., Histoplasma sp., and Mycobacterium sp. if contaminated dusts become airborne.

Control: The generation of airborne microbe-contaminated dust may be reduced by the periodic application of water, amended water, or emission-suppressing foams to the active excavation and mixing areas. The addition of foam to control vapors may also create a slip and fall hazard. Workers should not walk on areas to which foam has been applied. Other controls may include minimizing the amount of soil agitation during mixing operations, the erection of wind screens and portable surface covers, the use of the proper types of PPE (e.g. an air-purifying respirator with HEPA(N100, R100, P100) cartridges), frequent health and safety awareness meetings, use of experienced workers, decontamination stations, and other standard procedures. CONTROL POINT: Design, Operations


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