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A plume map marks the property boundary as clean based on wells with 6 m screens that report trichloroethene (TCE) below 1 µg/L. A nearby depth-discrete profile identifies a 0.4 m TCE-bearing interval surrounded by cleaner, more transmissive sand. The consultant uses the boundary-well results to place the plume edge inside the property. What additional work most directly tests that interpretation?
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Correct answer: A - Collect depth-discrete groundwater samples from the corresponding interval at the property boundary.
Question 2
An electron-donor pilot lowers tetrachloroethene (PCE), but cis-1,2-dichloroethene and vinyl chloride persist without ethene production. Field tests confirm donor delivery and suitable pH and reducing conditions. In matched site-water-and-sediment microcosms, extra donor produces no improvement; adding a viable dechlorinating culture produces ethene, while adding the same culture after killing the organisms does not. Which modification has the strongest support for the next field pilot?
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Correct answer: A - Add a culture capable of completing reductive dechlorination.
Question 3
A fuel-terminal groundwater sample is reported as benzene not detected at 1 µg/L; the project decision level is 5 µg/L. Benzene recovery is 99% in the clean-matrix laboratory control sample but 38% in a matrix spike prepared from this groundwater. The specified recovery range is 70-130%, and the other batch controls are acceptable. How should the reviewer handle the proposed conclusion that this well meets the decision level?
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Correct answer: D - Withhold that conclusion until the sample-specific low recovery is resolved.
Question 4
A proposed sentinel well lies 60 m upgradient of a groundwater receptor along the same flow path. Hydraulic conductivity is 8 m/day, head falls 1.2 m over 120 m, effective porosity is 0.20, and total porosity is 0.40. For this planning calculation, assume steady one-dimensional advection without sorption, dispersion, or decay. The response measure requires 180 days after detection. Which assessment correctly combines travel time with sentinel placement?
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Correct answer: D - 150 days; place the sentinel farther upgradient to provide the required warning.
Question 5
A stabilization batch contains 100 metric tonnes of dry soil with 250 mg/kg total lead. Mixing adds 25 tonnes of lead-free dry binder, with no material leaving the batch. The final total-lead result is 200 mg/kg on a dry-mass basis. The receiving facility requires a specified lead-leaching test, which has not yet been performed. Which statement belongs in the waste-characterization record?
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Correct answer: A - The batch retains 25 kg of lead; the lower bulk concentration does not establish leaching-test acceptance.
Question 6
Six months after a chlorinated-solvent source is removed, treatment has lowered dissolved concentrations in a sand aquifer. Concentrations rebound when extraction pauses. Closely spaced samples show much higher dissolved concentrations in an adjacent clay lens than in the sand, and the concentration gradient points out of the clay. Hydraulic testing finds negligible advective flow through that lens, and upgradient concentrations remain low. Which mechanism best fits this combination of findings?
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Correct answer: C - Back diffusion from contaminated porewater in the clay into the treated sand.
Question 7
Before entry into a below-grade collection sump, remote sampling with calibrated instruments repeatedly measures 18.2% oxygen by volume at the work position. Flammable gas and the specified toxic vapors are below their action levels. A worker proposes a full-face air-purifying respirator with cartridges appropriate for those vapors. Why is this respirator unsuitable even if the fit and cartridges are appropriate?
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Correct answer: D - Contaminant filtration does not replace the missing oxygen.
Question 8
A subslab depressurization system serves a warehouse divided by a continuous interior footing. With the fan operating, pressure beneath one bay is 8 Pa below indoor pressure, while the other bay remains 2 Pa above indoor pressure. Increasing fan speed changes readings only in the first bay. A temporary suction point in the second bay establishes negative subslab pressure there. What permanent modification is supported by the commissioning tests?
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Correct answer: B - Add a suction point serving the isolated bay and balance the extraction system.
Question 9
During a monitored natural attenuation program beside a river, benzene concentrations in bank wells fall sharply during a flood and rise again as river stage recedes. Head measurements show flow from the river into the bank during the rise and back toward the river afterward. Specific conductance in the wells temporarily approaches that of the river. The seasonal concentration decline is most reasonably interpreted as:
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Correct answer: B - Dilution by river water entering bank storage, followed by return of the stored water.
Question 10
A field team must obtain trichloroethene and nonvolatile-metal results from the same soil-core interval. The laboratory has supplied separate method-compatible containers. The metals procedure calls for homogenization of the remaining material, whereas the volatile-organic procedure uses a closed, preserved aliquot. The defensible collection sequence is:
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Correct answer: A - Collect and seal the volatile aliquot first, then homogenize the remaining material for metals.
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