Metal Sorption PropertiesThe binding behavior of Zn, Cu, and Pb relates

to the surface complexation constant, Kint.

Dzombak and Morel, 1990

Assessment of Zinc, Copper, and Lead in the Streams and Streambed Sediments of the Lefthand Creek Watershed, Northwestern Boulder County, Colorado

A.R. Wood, J.N. Ryan, R. Cholas, L. Harrington, L. Isenhart, and N. TurnerDepartment of Civil, Environmental, and Architectural Engineering

University of Colorado at Boulder

Many thanks to all of the individuals who assisted with this research, and to the organizations who provided resources and funding:

– Colorado Department of Public Health and Environment– Environmental Protection Agency– Honeywell, International– University of Colorado Laboratory for Environmental and Geological Sciences– Ohana Scholarship Fund– Research Experience for Undergraduates – Undergraduate Research Opportunity Program – University of Colorado Outreach Program– University Government of Graduate Students

ConclusionsThis study shows that tracer tests and synoptic sampling are effective methods for the identification of metal

sources and the quantification of metal loads in streams impacted by acid mine drainage. The zinc, copper, and lead data presented here reflected the known solubility properties of these metals, indicating

that metal speciation in the Lefthand Creek watershed relates to instream pH.Stream bed sediment metal concentrations exhibited a spatial lag downstream of instream metal spikes.

This suggests that bed sediment metal concentration increases are the result of metal sorption onto sediment particles and/or the settling of colloidal metal species onto the bed.

Zn Cu PbLog Kint 0.99 2.89 4.65

Research Goal and Hypothesis

Goal: Identify and quantify sources of metal loading to Lefthand, James, and Little James Creeks.

Hypothesis: Metal inputs from both surface and subsurface flows can be identified and quantified with metal loading

tracer tests and synoptic sampling. Analysis of stream bed sediment metal concentrations further defines metal

sources.

Study AreaAn active mining past left a legacy of hundreds of

abandoned or inactive hardrock mining and milling sites in the Lefthand Creek watershed. Some of these sites leach acidity and toxic metals to surrounding streams,

threatening aquatic life and downstream water consumers. Local stakeholders and state and federal

agencies desired an understanding of toxic metal sources, transport, and fate to better prioritize

contaminated sites and develop efficient reclamation strategies.

MethodsSampling was conducted on approximately 300 sites along

the three major streams in the watershed, using a conservative LiCl tracer to determine stream flow and

synoptic sampling to collect stream water metal concentrations (Kimball, 1997). Metal loads were

calculated as the products of stream flows and metal concentrations. An HCl-H2O2 partial digestion of the sub-

62 μm size fraction of stream bed sediments was analyzed at 55 sites following the methods of Church

(1993).

0.0 0.5 1.0 1.5 2.0 2.5 3.0

stre

am

flo

w (

L s

-1)

0

100

200

300

400

500

Little James Creektributaries

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Zn

co

nce

ntr

atio

n ( g

L-1

)

0

200

400

600

16800

16900

total Zn, Little James Creekdissolved Zn, Little James Creektotal Zn, tributaries

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Cu

conc

entr

atio

n (

g L

-1)

0

25

50

75

100

250

300

total Cu, Little James Creekdissolved Cu, Little James Creektotal Cu, tributaries

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Pb

con

cent

ratio

n ( g

L-1

)

0

10

20

30

40

50

60

70

total Pb, Little James Creekdissovled Pb, Little James Creektotal Pb, tributaries

0.0 0.5 1.0 1.5 2.0 2.5 3.0

pH

3

4

5

6

7

8

Lefthand Creektributaries

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Cu

loa

d (

kg d

ay-1

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

total Cu, Little James Creekdissolved Cu, Little James Creektotal Cu, tributaries

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Pb

load

(kg

day

-1)

0.0

0.2

0.4

0.6

0.8

1.0

total Pb, Little James Creekdissolved Pb, Little James Creektotal Pb, tributaries

Little James Creek distance (km)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

sedi

me

nt P

b (m

ol/k

g)

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035 Little James Creektributaries

Liittle James Creek distance (km)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

sedim

en

t Zn

(m

ol/k

g)

0.000

0.005

0.010

0.015

0.020

0.025 LIttle James Creektributaries

Liittle James Creek distance (km)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

sedi

men

t Cu

(mol

/kg)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07 Little James Creektributaries

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Zn

load

(kg

day

-1)

0

2

4

6

8

10

12

14

total Zn, Little James Creekdissolved Zn, Little James Creektotal Zn, tributaries

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colloidal metal concentration (ppb)

dis

solv

ed

me

tal c

on

cen

tra

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(p

pb

)

zinc

copper

lead