Transport tracer test at the experimental field of

Transport (tracer) test at the experimental field of the Borden site How will the contaminant behave? Transport retardation due to sorption 1

Note: this presentation requires additional material Because it was not possible to get permission to make available on the internet figures from the two referenced papers, (1) Μackay et al. (1986) and (2) Roberts et al. (1986), please check out these papers (http: //agupubs. onlinelibrary. wiley. com/agu/journal/ 10. 1002/%28 ISSN%291944 -7973/) to find the figures mentioned in this presentation. 2

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Initial contaminant source: unlined landfill operating during 1940 -1976 5

area of test measurements area of landfill 6

Test area, plan view A’ test area a’ dense grid of sampling points in an area with dimensions 120 m x 80 m (within a former sand borrow pit) a landfill A 0 100 m Μackay et al. (1986), Fig. 1 7

a) April 1979 c) October 1979 b) July 1979 d) December 1979 Equipotential lines at the test site The direction of groundwater flow (blue arrows) has seasonal variations at the test site Μackay et al. (1986), Fig. 3 8

Sampling points (every 1 – 4 m): plan view 9 injection wells (over a depth of 2 – 3. 6 m) Μackay et al. (1986), Fig. 5 120 m a’ a 0 m 0 m 80 m 9

Test site, cross section ΑΑ´ A Landfill a A’ a' Site of tracer test Landfill plume Μackay et al. (1986), Fig. 2 10

Sampling points – cross section aa´ (every 0. 2 – 0. 3 m) a a’ 0 m -8 m 0 m 9 injection wells (over a depth of 2 – 3. 6 m) 120 m Μackay et al. (1986), Fig. 5 11

Injected substances: quantities, properties Tracer: a solute that does not sorb and does not degrade 12

Injected substances: tracer spreading chloride boundary of area with chloride detections 60 m 647 days 462 days 85 days 1 day -10 m 30 m Μackay et al. (1986), Fig. 8 13

Injected substances: comparison of spreading chloride carbon tetrachloride 60 m 647 days 462 days 633 days 85 days 380 days 1 day 16 days -10 m Μackay et al. (1986), Fig. 8 30 m -10 m 20 m 14

Injected substances: retardation due to sorption chloride 60 m 647 days carbon tetrachloride, Kow = 500 633 days tetrachloroethene, Kow = 400 -10 m Roberts et al. (1986), Fig. 5 30 m 15

Question for understanding • Q: How can you explain that sorption (Kp) is not analogous to contaminant hydrophobicity (Kow, Koc)? • Α: The main sorption mechanism is not absorption to organic matter • Comment: This is what happens at the Borden site: the organic carbon fraction is low, foc=0. 02%, that’s why the relationship Kp = foc Koc cannot describe measured values 16

Sources of figures Note: the non-original material used in this presentation either it has been uploaded on the internet with a Creative Commons license, or it is publicly available on the internet (e. g. US policy for reports etc. by public agencies) and can be used with suitable attribution, or is used with license from the publisher. Slides 3 -6. Data on Maps: Google © References • • Mackay, D. M. , D. L. Freyberg and P. V. Roberts, 1986, A natural gradient experiment on solute transport in a sand aquifer 1. Approach and overview of plume movement, Water Resources Research, 22: 13: 2017 -2029 Roberts, P. V. , M. N. Goltz and D. M. Mackay, 1986, A natural gradient experiment on solute transport in a sand aquifer 3. Retardation estimates and mass balances of organic solutes, Water Resources Research, 22: 13: 2047 -2058 17