Groundwater & Hydrogeology Flashcards
7 cards from real CES practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Groundwater & Hydrogeology flashcards as text
The vadose zone (unsaturated zone) is characterized by pore spaces that contain:
Answer: Both air and water at pressures less than atmospheric
The vadose zone lies above the water table; its pores contain both air and water, with pore-water pressure (matric potential) below atmospheric, which distinguishes it from the fully saturated phreatic zone below.
A slug test is used in field hydrogeology to:
Answer: Estimate hydraulic conductivity of the aquifer immediately surrounding a single monitoring well
A slug test involves rapidly introducing or removing a known volume of water (slug) from a well and measuring the water-level recovery; the recovery curve is analyzed (e.g., Bouwer–Rice or Hvorslev methods) to calculate local hydraulic conductivity.
Natural attenuation as a groundwater remediation strategy relies on which set of processes?
Answer: Biodegradation, dispersion, dilution, sorption, and volatilization occurring without active intervention
Monitored natural attenuation (MNA) relies on naturally occurring physical, chemical, and biological processes—including biodegradation, dispersion, dilution, sorption, and volatilization—to reduce contaminant concentrations without engineered active remediation.
Under RCRA and CERCLA frameworks, the Maximum Contaminant Level (MCL) for a groundwater contaminant typically serves as:
Answer: A health-based cleanup standard representing the maximum permissible concentration in drinking water
MCLs are promulgated by EPA under the Safe Drinking Water Act and represent the legally enforceable maximum concentration allowed in public drinking water supplies; they are widely used as risk-based cleanup targets for groundwater contamination.
Which parameter is measured by a geophysical borehole method to distinguish between clay-rich and sand-rich formations in an aquifer investigation?
Answer: Natural gamma radiation, which is higher in clay/shale due to radioactive potassium and thorium
Natural gamma logs measure naturally occurring gamma radiation; clay minerals and shales contain elevated concentrations of radioactive K-40, uranium, and thorium, giving high gamma counts compared to clean sands and gravels.
A perched aquifer forms when:
Answer: An unsaturated zone lenticular aquitard intercepts infiltrating water, creating a localized saturated body above the regional water table
A perched aquifer is a locally saturated zone that sits above the regional water table, supported by an impermeable or low-permeability lens (e.g., clay layer) that intercepts downward percolating vadose water before it reaches the main aquifer.
During a groundwater sampling event at a monitoring well, the purpose of purging the well before sample collection is to:
Answer: Remove stagnant water stored in the well casing so that the sample represents formation water
Purging removes stagnant casing water that is no longer representative of aquifer conditions; sampling after purging (typically 3–5 casing volumes or until field parameters stabilize) ensures the collected sample reflects actual formation groundwater quality.