This report documents LakeVOC, a model to estimate volatile organic compound (VOC) concentrations in lakes and reservoirs. LakeVOC represents the lake or reservoir as a two-layer system and estimates VOC concentrations in both the epilimnion and hypolimnion. The air-water flux of a VOC is characterized in LakeVOC in terms of the two-film model of air-water exchange. LakeVOC solves the system of coupled differential equations for the VOC concentration in the epilimnion, the VOC concentration in the hypolimnion, the total mass of the VOC in the lake, the volume of the epilimnion, and the volume of the hypolimnion.
A series of nine simulations were conducted to verify LakeVOC representation of mixing, dilution, and gas exchange characteristics in a hypothetical lake, and two additional estimates of lake volume and MTBE concentrations were done in an actual reservoir under environmental conditions. These 11 simulations showed that LakeVOC correctly handled mixing, dilution, and gas exchange. The model also adequately estimated VOC concentrations within the epilimnion in an actual reservoir with daily input parameters. As the parameter-input time scale increased (from daily to weekly to monthly, for example), the differences between the measured-averaged concentrations and the model-estimated concentrations generally increased, especially for the hypolimnion. This may be because as the time scale is increased from daily to weekly to monthly, the averaging of model inputs may cause a loss of detail in the model estimates.
Abstract
Introduction
Purpose and Scope
Acknowledgments
Description and Theoretical Basis of LakeVOC Model
General Description
Air-Water Gas Transfer
Theoretical Formulation
Model Operation and Numerical Methods
User Instructions and Information Needs for LakeVOC Model
Using LakeVOC Model
Known Problems or Cautions in Using LakeVOC Model
Verification of LakeVOC Model
Simulations Using a Hypothetical Lake
Lake Mixing and Dilution Tests
Gas-Exchange Tests
Simulations Using an Actual Reservoir
Lake-Stratification and Lake-Volume Simulations
VOC Concentration Simulations
Daily Simulation
Weekly Simulation
Monthly Simulation
Summary
References
Appendices
A. FORTRAN Code for LakeVOC Model
B. LakeVOC Model Input Parameter Files
C. LakeVOC Model Output Files
D. Example Physical/Chemical Properties for Selected Volatile Organic Compounds
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Send questions or comments about this report to the author, D.A. Bender (605) 355-4560 ext. 248.
For more information about USGS activities in South Dakota, visit the USGS South Dakota District home page.
For more information about the USGS National Water-Quality Assessment Program, visit the NAWQA Program home page or more information about the USGS National Water-Quality Assessment Program Volatile Organic Compound National Syntheses, visit the VOC National Systhesis home page.
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