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Monitoring soil geochemistry in the urban environment: A comparison of studies in p 1972 and 2005 in Denver, Colorado David B. Smith, Karl J. Ellefsen, U.S. Geological Survey Robert G. Garrett, Geological Survey of Canada L. Graham Closs,

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Monitoring soil geochemistry in the urban environment: A comparison of studies in p 1972 and 2005 in Denver, Colorado

David B. Smith, Karl J. Ellefsen, U.S. Geological Survey Robert G. Garrett, Geological Survey of Canada

L. Graham Closs, Colorado School of Mines

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Outline

Two soil geochemical surveys of the

Denver metro area

1972

200

2005
Abundance and distribution of selected

elements from each survey elements from each survey

Observed changes in soil composition

between 1972 and 2005 between 1972 and 2005

SLIDE 3

1972 Geochemical Survey

Skyline Laboratories, Wheat Ridge, CO
Roadside soils (top 15 cm)
433 sites at 1-mile centers (section

( corners, as defined by the Public Lands Survey System) y y )

Sieved to less than 250 µm
Analyzed for Cu Pb Zn Cd Hg
Analyzed for Cu, Pb, Zn, Cd, Hg

SLIDE 4

Power Power Plants Smelters Downtown

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View from Globe Smelter toward Denver Denver

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2005 Geochemical Survey 2005 Geochemical Survey

USGS Colorado School of Mines
USGS, Colorado School of Mines
Collected same sites as 1972 survey
Sieved to less than 250 µm
Analyzed both 2005 samples and

y p 1972 samples for more than 40 elements

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Change between 1972 and 2005 Change between 1972 and 2005

El t h i t h * Pb A H Elements showing most change: Pb, As, Hg, Cd, Mo, Al Based on Wilcoxon rank sum test and confirmed by Kolmogorov-Smirnov test at 95% confidence level

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61 83 19 61

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N t A

Nat. Avg.

19 mg/kg

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Nat. Avg.

19 mg/kg

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SLIDE 14

Concentration in 2005 minus concentration in 1972

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0.6 0.7 0.2

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Summary

Pb, As, Hg, Cd, Cu, Mo, Sb, Sn, and Zn elevated in

“central Denver” in both surveys—Anthropogenic sources

Greatest change generally for these elements
Clean Air Act (1970)
Remediation activities
Urban geochemical “footprint” ~20 – 30 km in

diameter

Mg, K, Fe, Al, V, Ce, La have clear geogenic sources

Mg, K, Fe, Al, V, Ce, La have clear geogenic sources

Quantifying change not straightforward
Site duplication uncertain
Roadside soils “dynamic” sample medium

Roadside soils dynamic sample medium

Possible dilution from roadside dust and debris over 33 yrs

SLIDE 23

Denver study: Chapter 30, Chapter 30,

p. 521 - 546,