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Watershed Planning within a Quantitative Scenario Analysis Framework
Published on: July 24, 2016
A comparison of river water quality sampling methodologies under highly variable load conditions.
A Facchi1, C Gandolfi, M J Whelan
1Istituto di Idraulica Agraria, Università degli Studi di Milano, Via Celoria 2, 20133 Milano, Italy. arianna.facchi@unimi.it
Chemosphere
|September 30, 2006
Summary
Grab sampling is inefficient for rivers with variable loads, especially for substances like linear alkylbenzene sulphonate (LAS). 24-hour composite sampling effectively captures average water quality by eliminating diurnal variations.
Area of Science:
- Environmental Science
- Water Quality Monitoring
- Wastewater Treatment
Background:
- River water quality monitoring requires appropriate sampling techniques to accurately characterize average conditions.
- Fluctuating pollutant loads, particularly from sewage treatment works (STW), can significantly impact diurnal water quality cycles.
- Grab sampling may be insufficient when dealing with short-term water quality variations.
Purpose of the Study:
- To compare the effectiveness of grab sampling versus 24-hour composite sampling for monitoring river water quality influenced by a periodically overloaded STW.
- To assess the impact of diurnal pollutant load cycles on water quality variables downstream of an STW.
- To evaluate the spatial and temporal variability of linear alkylbenzene sulphonate (LAS) and boron (B) concentrations.
Main Methods:
- Conducted a water quality monitoring study on the River Lambro, northern Italy.
- Employed both grab sampling and 24-hour composite sampling using automatic samplers.
- Analyzed samples for linear alkylbenzene sulphonate (LAS), boron (B), and routine water quality parameters at the STW overflow and downstream sites.
Main Results:
- Diurnal variability in pollutant concentrations downstream of the STW increased with STW removal efficiency.
- Concentration patterns remained consistent downstream, indicating limited hydrodynamic dispersion.
- In-stream degradation of LAS followed first-order kinetics (k = 0.05-0.06 h⁻¹).
- Grab sampling proved inefficient for variable loads, especially for substances like LAS removed during treatment.
- LAS diurnal variability decreased downstream, improving grab sampling reliability.
- 24-hour composite sampling effectively mitigated diurnal load variations.
Conclusions:
- Grab sampling is inadequate for rivers with significant diurnal load variations, particularly for substances removed by sewage treatment.
- 24-hour composite sampling provides a more accurate representation of average water quality under such conditions.
- Understanding diurnal cycles is crucial for effective river water quality management downstream of STWs.
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