Environmental Monitoring & Assessment Flashcards

Which statistical test is commonly used to check for a monotonic concentration trend in a monitoring well's time series without assuming the data are normal?

Answer: Mann-Kendall test

Mann-Kendall is a nonparametric rank-based test that is widely used for groundwater trend analysis and tolerates non-normal data and nondetects.

Under current EPA ProUCL guidance, which method is preferred for handling nondetects when computing summary statistics?

Answer: Kaplan-Meier estimation

ProUCL recommends Kaplan-Meier or similar methods over arbitrary substitution, which can bias the mean and variance.

Two wells 250 m apart along a flow line have hydraulic heads of 102.5 m and 100.0 m. What is the hydraulic gradient?

Answer: 0.01

i = Δh/L = 2.5 m ÷ 250 m = 0.01.

An aquifer has K = 10 m/day, a hydraulic gradient of 0.01, and an effective porosity of 0.25. What is the average linear (seepage) velocity?

Answer: 0.4 m/day

v = Ki/ne = (10 × 0.01) ÷ 0.25 = 0.4 m/day.

A solute has Kd = 0.5 mL/g in an aquifer with a bulk density of 1.6 g/cm³ and a porosity of 0.4. What is the retardation factor?

Answer: 3.0

R = 1 + (ρb·Kd/n) = 1 + (1.6 × 0.5 ÷ 0.4) = 3.0.

Which graphical tool is most commonly used to classify groundwater by major-ion chemistry and compare water types across monitoring wells?

Answer: Piper trilinear diagram

A Piper diagram plots major cations and anions as percentages of milliequivalents, which shows hydrochemical facies and mixing.

Which observation in a TCE plume most strongly suggests active biological reductive dechlorination?

Answer: cis-1,2-DCE far exceeding trans-1,2-DCE, along with vinyl chloride and ethene

Biological reductive dechlorination preferentially produces cis-1,2-DCE, then vinyl chloride and ethene, under anaerobic conditions.