The redevelopment of a site may include mass transport of soil for the grading of the building foundation, excavating for a basement or parking garage, or trenching for subsurface utilities. Before contractors are allowed to disturb the soil, it must be tested at an accredited analytical laboratory.
The most important reason is for the safety of the workers and the public. While some chemicals can be detected through visual observation or smell, many chemicals cannot be detected unless they are analyzed in a lab. Certain petroleum hydrocarbons, solvents, metals, and pesticides are carcinogenic (cancer-causing), and may produce acute and/or chronic effects to human health. During soil disturbing activities, these chemicals may be kicked up as dust and inhaled by on-the-ground personnel over the duration of an entire workday. If a strong wind is present, the dust may drift off-site and potentially expose sensitive receptors such as hospitals, schools, or daycare facilities. Regulatory agencies often require dust mitigation measures, dust monitoring, and personal protection equipment at construction sites to protect the health of all individuals involved. Negligence and failure to mitigate these dangers can lead to litigation and damage companies’ reputations.
Another reason to test soil is to determine where the soil can be transported. If the soil is to be disposed of as waste, there are limitations as to which landfill may accept it. Chemical concentrations that exceed federal regulations under the Resource Conservation and Recovery Act (RCRA) are considered the most hazardous and may be subject to additional treatment methodologies (i.e., incineration) and are limited to acceptance at select facilities in the United States. Soil that is hazardous per California Code of Regulations (CCR) Title 22, but does not exceed federal regulations is considered Class I hazardous waste and may be accepted at only two locations in the state of California. Soil that is designated as Class II contains concentrations of contaminants that are below hazardous levels. Class III soil is considered non-hazardous municipal solid waste and may be transported and reused at another job location, which may offset some costs. In order to determine which classification applies to the soil, extensive laboratory testing is required.
The number of representative soil samples to be analyzed depends on the volume of soil that is being removed. A commonly referenced sampling schedule can be found in Information Advisory: Clean Imported Fill Material published by the Department of Toxic Substances Control (DTSC) in 2001; however, it is common that a landfill may request additional samples.
The soil samples are then transported to a state-certified laboratory and analyzed for a minimum of:
1) total petroleum hydrocarbons (TPH)
2) volatile organic compounds (VOC)
3) semi-volatile organic compounds (SVOC)
4) polycyclic aromatic hydrocarbons/polynuclear aromatic hydrocarbons (PAH/PNA)
5) polychlorinated biphenyls (PCB)
6) organochlorine (OC) pesticides
At their discretion, landfills may also request additional analytes and waste extraction tests, which help determine if the waste is hazardous.
Common mistakes that occur during soil characterization include an insufficient number of samples, samples collected at incorrect depths and/or locations, and missing analyte parameters. In a best-case scenario, a mistake such as a missing analyte parameter will require a call to the analytical laboratory to request additional testing be performed. In a worst-case scenario, additional sampling must be performed, which would require remobilization of field personnel and additional lab costs. Misinterpreting the soil classification may also prove to be a costly mistake as well. For example, classifying a soil as Class I is on average hundreds of dollars per cubic yard more expensive than if it were classified as a Class II soil.
Soil disposal is a critical component of almost every development project and is frequently under-budgeted in cost estimates. The revelation of hazardous soil material can add hundreds of thousands of dollars in expenses and severely jeopardize a project’s finances. Performing soil characterization in the early stages of development is key to avoiding costly mistakes and delays in a busy timeline.
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