Engineer Soil Environment flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cation exchange capacity

The total quantity of exchangeable cations a soil can hold, expressed in cmol(+)/kg or meq/100 g; it rises with clay content and organic matter and governs nutrient retention and metal binding.

Base saturation

The percentage of cation exchange capacity occupied by exchangeable bases such as calcium, magnesium, potassium, and sodium, calculated as exchangeable bases divided by CEC times 100.

Bulk density

The dry mass of soil per unit bulk volume, including pore space; it is used with particle density to compute porosity and to convert concentration to mass per unit area.

Darcy's law

The relation stating that specific discharge equals negative hydraulic conductivity times the hydraulic gradient; it describes saturated flow through porous media and underpins groundwater velocity estimates.

Redox sequence

The order in which terminal electron acceptors are consumed as oxygen is depleted: oxygen, nitrate, manganese and iron oxides, sulfate, then carbon dioxide producing methane.

Mycorrhizae

Symbiotic associations between plant roots and fungi that extend the absorbing surface and trade soil phosphorus for plant carbon; tillage and high soil phosphorus reduce their benefit.

Nitrification

The microbial oxidation of ammonium to nitrite and then nitrate by ammonia-oxidizing and nitrite-oxidizing organisms; it acidifies soil and produces the mobile nitrate anion.

Denitrification

The microbial reduction of nitrate to nitrous oxide and nitrogen gas under low-oxygen conditions; it is a major nitrogen loss pathway and a source of greenhouse gas.

Soil respiration

Carbon dioxide efflux from soil, used as a proxy for microbial and root activity; it increases with temperature and moderate moisture but falls under saturation from oxygen limitation.

Conceptual site model

A representation linking contaminant sources, release mechanisms, transport pathways, and receptors; a complete exposure pathway requires all elements to be present.

Soil-water partition coefficient

The ratio Kd of contaminant concentration sorbed to soil divided by concentration in water; it is estimated as Koc times the fraction of organic carbon.

DNAPL

A dense non-aqueous phase liquid that is denser than water and sinks below the water table, pooling on low-permeability layers and acting as a long-term dissolved-phase source.

LNAPL

A light non-aqueous phase liquid that is less dense than water and floats on the water table, spreading laterally and dissolving into groundwater over time.

Background concentration

The concentration of a constituent in soil or groundwater at reference locations unaffected by the site, used to distinguish contamination from natural conditions.

Soil vapor extraction

An in situ treatment that applies vacuum to the unsaturated zone to volatilize and remove volatile organic compounds; design depends on air permeability and vapor pressure.

In situ chemical oxidation

A remediation approach that injects oxidants such as persulfate or permanganate to destroy contaminants; soil organic matter and reduced minerals consume oxidant and reduce efficiency.

Thermal desorption

A treatment that heats excavated soil to volatilize contaminants; low-temperature units operate near 90 to 320 degrees Celsius and high-temperature units above that range.

Solidification and stabilization

Remediation methods that reduce contaminant mobility by physical encapsulation or chemical fixation; effectiveness is evaluated with leaching tests such as the TCLP.

Permeable reactive barrier

An in situ permeable wall containing reactive material such as zero-valent iron that treats contaminated groundwater flowing through it by reduction or sorption.

Field duplicate

A second sample split from the same material and submitted as an independent sample; comparison with the original quantifies sampling and analytical precision.

Trip blank

A sample of clean water or sorbent carried through the sampling trip without exposure; it detects contamination introduced during transport and storage.

Low-flow purging

A groundwater sampling technique that withdraws water slowly to minimize drawdown and turbidity, preserving representative conditions and reducing colloid mobilization.

Chain of custody

A documented record tracking sample possession from collection through laboratory analysis, including dates, times, samplers, and analyses requested.

Holding time

The maximum period allowed between sample collection and analysis or extraction, set by the analytical method to preserve sample integrity; volatile compounds have short holding times.

Reference dose

An estimate of the daily exposure likely to be without appreciable risk over a lifetime; the hazard quotient equals exposure divided by the reference dose.

Hazard quotient

The ratio of estimated exposure to the reference dose; a value greater than one indicates that exposure exceeds the level considered without appreciable risk.

Slope factor

A cancer potency value expressing the increased cancer risk per unit of daily dose; carcinogenic risk equals exposure multiplied by the slope factor.

Toxicity characteristic leaching procedure

A regulatory extraction test used to determine whether a waste leaches hazardous concentrations of toxic constituents under conditions simulating landfill disposal.

Universal Soil Loss Equation

A model estimating average annual soil loss as rainfall erosivity times soil erodibility times slope length and steepness times cover management times support practice factors.

Sediment delivery ratio

The fraction of eroded soil that is transported to a downstream point; it generally decreases as drainage area increases because of deposition and storage.

Riparian buffer

A vegetated strip along a watercourse that traps sediment and nutrients; effectiveness depends on width, slope, vegetation density, and uniform flow.

Data quality objectives

A planning process that defines the type, quantity, and quality of data needed for a decision, guiding sampling design and analytical method selection.