Chlorofluorocarbons as Tracers of Groundwater Transport Processes in a Shallow, Silty Sand Aquifer

P. G. Cook; D. K. Solomon; L. N. Plummer; E. Busenberg; S. L. Schiff

doi:10.1029/94WR02528

Chlorofluorocarbons as Tracers of Groundwater Transport Processes in a Shallow, Silty Sand Aquifer

P. G. Cook, D. K. Solomon, L. N. Plummer, E. Busenberg, S. L. Schiff

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Abstract

Detailed depth profiles of Chlorofluorocarbons CFC‐11(CFCl₃(, CFC‐12 (CF₂Cl₂) and CFC‐113 (C₂F₃Cl₃) have been obtained from a well‐characterized field site in central Ontario. Aquifer materials comprise predominantly silty sands, with a mean organic carbon content of 0.03%. Nearly one‐dimensional flow exists at this site, and the vertical migration of a well‐defined ³H peak has been tracked through time. Detailed vertical sampling has allowed CFC tracer velocities to be estimated to within 10%. Comparison with ³H profiles enables estimation of chlorofluorocarbon transport parameters. CFC‐12 appears to be the most conservative of the CFCs measured. Sorption at this site is low (K_d < 0.03), and degradation does not appear to be important. CFC‐ 113 is retarded both with respect to CFC‐12 and with respect to ³H (K_d = 0.09−0.14). CFC‐11 appears to be degraded both in the highly organic unsaturated zone and below 3.5 m depth in the aquifer, where dissolved oxygen concentrations decrease to below 0.5 mg L⁻¹. The half‐life for CFC‐11 degradation below 3.5 m depth is less than 2 years. While apparent CFC‐12 ages match hydraulic ages to within 20% (up to 30 years), apparent CFC‐11 and CFC‐113 ages significantly overestimate hydraulic ages at our field site.

Original language	English
Pages (from-to)	425-434
Number of pages	10
Journal	Water Resources Research
Volume	31
Issue number	3
DOIs	https://doi.org/10.1029/94WR02528
Publication status	Published - Mar 1995
Externally published	Yes

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@article{e03e389df9c24e36ac453354d8623338,

title = "Chlorofluorocarbons as Tracers of Groundwater Transport Processes in a Shallow, Silty Sand Aquifer",

abstract = "Detailed depth profiles of Chlorofluorocarbons CFC‐11(CFCl3(, CFC‐12 (CF2Cl2) and CFC‐113 (C2F3Cl3) have been obtained from a well‐characterized field site in central Ontario. Aquifer materials comprise predominantly silty sands, with a mean organic carbon content of 0.03%. Nearly one‐dimensional flow exists at this site, and the vertical migration of a well‐defined 3H peak has been tracked through time. Detailed vertical sampling has allowed CFC tracer velocities to be estimated to within 10%. Comparison with 3H profiles enables estimation of chlorofluorocarbon transport parameters. CFC‐12 appears to be the most conservative of the CFCs measured. Sorption at this site is low (Kd < 0.03), and degradation does not appear to be important. CFC‐ 113 is retarded both with respect to CFC‐12 and with respect to 3H (Kd = 0.09−0.14). CFC‐11 appears to be degraded both in the highly organic unsaturated zone and below 3.5 m depth in the aquifer, where dissolved oxygen concentrations decrease to below 0.5 mg L−1. The half‐life for CFC‐11 degradation below 3.5 m depth is less than 2 years. While apparent CFC‐12 ages match hydraulic ages to within 20% (up to 30 years), apparent CFC‐11 and CFC‐113 ages significantly overestimate hydraulic ages at our field site.",

author = "Cook, {P. G.} and Solomon, {D. K.} and Plummer, {L. N.} and E. Busenberg and Schiff, {S. L.}",

year = "1995",

month = mar,

doi = "10.1029/94WR02528",

language = "English",

volume = "31",

pages = "425--434",

journal = "Water Resources Research",

issn = "0043-1397",

publisher = "Wiley-Blackwell",

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T1 - Chlorofluorocarbons as Tracers of Groundwater Transport Processes in a Shallow, Silty Sand Aquifer

AU - Cook, P. G.

AU - Solomon, D. K.

AU - Plummer, L. N.

AU - Busenberg, E.

AU - Schiff, S. L.

PY - 1995/3

Y1 - 1995/3

N2 - Detailed depth profiles of Chlorofluorocarbons CFC‐11(CFCl3(, CFC‐12 (CF2Cl2) and CFC‐113 (C2F3Cl3) have been obtained from a well‐characterized field site in central Ontario. Aquifer materials comprise predominantly silty sands, with a mean organic carbon content of 0.03%. Nearly one‐dimensional flow exists at this site, and the vertical migration of a well‐defined 3H peak has been tracked through time. Detailed vertical sampling has allowed CFC tracer velocities to be estimated to within 10%. Comparison with 3H profiles enables estimation of chlorofluorocarbon transport parameters. CFC‐12 appears to be the most conservative of the CFCs measured. Sorption at this site is low (Kd < 0.03), and degradation does not appear to be important. CFC‐ 113 is retarded both with respect to CFC‐12 and with respect to 3H (Kd = 0.09−0.14). CFC‐11 appears to be degraded both in the highly organic unsaturated zone and below 3.5 m depth in the aquifer, where dissolved oxygen concentrations decrease to below 0.5 mg L−1. The half‐life for CFC‐11 degradation below 3.5 m depth is less than 2 years. While apparent CFC‐12 ages match hydraulic ages to within 20% (up to 30 years), apparent CFC‐11 and CFC‐113 ages significantly overestimate hydraulic ages at our field site.

AB - Detailed depth profiles of Chlorofluorocarbons CFC‐11(CFCl3(, CFC‐12 (CF2Cl2) and CFC‐113 (C2F3Cl3) have been obtained from a well‐characterized field site in central Ontario. Aquifer materials comprise predominantly silty sands, with a mean organic carbon content of 0.03%. Nearly one‐dimensional flow exists at this site, and the vertical migration of a well‐defined 3H peak has been tracked through time. Detailed vertical sampling has allowed CFC tracer velocities to be estimated to within 10%. Comparison with 3H profiles enables estimation of chlorofluorocarbon transport parameters. CFC‐12 appears to be the most conservative of the CFCs measured. Sorption at this site is low (Kd < 0.03), and degradation does not appear to be important. CFC‐ 113 is retarded both with respect to CFC‐12 and with respect to 3H (Kd = 0.09−0.14). CFC‐11 appears to be degraded both in the highly organic unsaturated zone and below 3.5 m depth in the aquifer, where dissolved oxygen concentrations decrease to below 0.5 mg L−1. The half‐life for CFC‐11 degradation below 3.5 m depth is less than 2 years. While apparent CFC‐12 ages match hydraulic ages to within 20% (up to 30 years), apparent CFC‐11 and CFC‐113 ages significantly overestimate hydraulic ages at our field site.

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ER -

Chlorofluorocarbons as Tracers of Groundwater Transport Processes in a Shallow, Silty Sand Aquifer

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