Part (a) — Soil Vapor Extraction (SVE). An in-situ physical remediation technology for the unsaturated (vadose) zone: a vacuum applied at extraction wells induces advective airflow through the soil pores, volatilizing sorbed and dissolved volatile organic contaminants directly into the moving air stream. The extracted vapor is collected and treated (granular activated carbon, or thermal/catalytic oxidation) before discharge. It is effective on compounds with a high vapor pressure/Henry's constant and on reasonably permeable soils.
Part (b) — Chemical Stabilization. A chemical (as opposed to purely physical) treatment that immobilizes a contaminant by altering its chemical form — precipitation, complexation, or pH adjustment — to convert it into a less soluble, less mobile, or less toxic species (e.g. reducing hexavalent chromium to trivalent chromium, Question 10, then precipitating it as Cr(OH)3). It is distinct from solidification, which physically encapsulates the waste in a solid matrix without necessarily changing its chemical form; the two are usually applied together as "stabilization/solidification" (S/S, Question 8).
Part (c) — Bioventing. An in-situ biological remediation technology that supplies air to the vadose zone at a deliberately LOW flow rate — just enough to maintain aerobic conditions — to stimulate indigenous microorganisms to biodegrade sorbed contaminants in place, rather than physically stripping them out as SVE does. Because airflow is low, little contaminant mass leaves as vapor, minimizing or eliminating off-gas treatment needs.
Part (d) — Toxicity Characteristic Leaching Procedure (TCLP). A standardized laboratory leaching test (EPA Method 1311) that extracts a representative waste sample with a mildly acidic buffer to simulate co-disposal with municipal solid waste in a landfill. If the leachate concentration of any of the regulated contaminants (heavy metals, specific organics) exceeds its regulatory threshold, the waste is classified as hazardous by the toxicity characteristic (Question 3's framework applies the analogous ignitability/corrosivity tests).
Part (e) — Autotrophic bacteria. Microorganisms that use inorganic carbon (CO2) as their carbon source for cell synthesis, distinct from heterotrophs, which use organic carbon (Question 5 discusses why heterotrophs, not autotrophs, dominate bioremediation). Chemoautotrophs additionally obtain their energy from the oxidation of inorganic compounds (e.g. nitrifying bacteria oxidizing NH4+ or NO2-, or sulfur-oxidizing bacteria); photoautotrophs use light energy instead. Autotrophs are significant in hazardous-waste contexts chiefly as nitrifiers in biological nitrogen removal and as sulfur/iron oxidizers relevant to acid mine drainage chemistry.
Check: the paper prints part (e) as "Autoterotrophic bacteria," read here as a misprint of "Autotrophic bacteria" — the only standard microbiological term the phrase and surrounding list of technical terms is consistent with.
