Background Trace Element Concentrations in the Franciscan Complex, San Francisco, CA MS Thesis...
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Background Trace Element Concentrations in the Franciscan Complex,
San Francisco, CA
Background Trace Element Concentrations in the Franciscan Complex,
San Francisco, CA
MS Thesis Defense
Megan Simpson
March 16, 2004
MS Thesis Defense
Megan Simpson
March 16, 2004
The ProblemThe Problem
•Superfund clean-up sites are overwhelming problem in US
-Hunter’s Point Shipyard
-Presidio
•To assess a site for contamination, background trace element levels need to be determined
•Superfund clean-up sites are overwhelming problem in US
-Hunter’s Point Shipyard
-Presidio
•To assess a site for contamination, background trace element levels need to be determined
IntroductionIntroduction
• This study examines background trace element levels in the Franciscan Complex
(chert, sandstone, greenstone, serpentinite)
• Samples analyzed for trace element levels (chromium, cobalt, nickel, lead, strontium)
• Performed statistical analyses and created trace element distribution maps
• This study examines background trace element levels in the Franciscan Complex
(chert, sandstone, greenstone, serpentinite)
• Samples analyzed for trace element levels (chromium, cobalt, nickel, lead, strontium)
• Performed statistical analyses and created trace element distribution maps
PurposePurpose• Will aid in understanding of the distribution of
background trace elements– data reflects naturally occurring levels found in
native bedrock
• Assist environmental clean-up projects by providing source of baseline data for measuring soil quality
• Expand current trace element level database
• Will aid in understanding of the distribution of background trace elements– data reflects naturally occurring levels found in
native bedrock
• Assist environmental clean-up projects by providing source of baseline data for measuring soil quality
• Expand current trace element level database
Previous ResearchPrevious Research• Work by Kearney Foundation in 1996
– looked at trace elements in soil– often referenced in remediation projects, land use planning– only two samples close to San Francisco Area
• Work by Schlocker in 1974– looked at potassium feldspar in sandstone– fewer samples (5-7) for each rock type
• My work enhances the range of sample locales and quantities
• Work by Kearney Foundation in 1996– looked at trace elements in soil– often referenced in remediation projects, land use planning– only two samples close to San Francisco Area
• Work by Schlocker in 1974– looked at potassium feldspar in sandstone– fewer samples (5-7) for each rock type
• My work enhances the range of sample locales and quantities
What elements are we looking for?
What elements are we looking for?
• Previous work shows Cr, Co, Ni, Pb and Sr to be prominent in soil and rock within SF
• Presidio and Hunter’s Point have high levels– much time and energy dedicated to clean-
up of these sites
• Previous work shows Cr, Co, Ni, Pb and Sr to be prominent in soil and rock within SF
• Presidio and Hunter’s Point have high levels– much time and energy dedicated to clean-
up of these sites
Geologic BackgroundGeologic Background
San Francisco is part of the Mesozoic Franciscan Complex, which formed in accretionary wedge
San Francisco is part of the Mesozoic Franciscan Complex, which formed in accretionary wedge
Subduction zone ~200-80 myaSource: U.S. Geological SurveySource: U.S. Geological Survey
Franciscan ComplexFranciscan Complex
Franciscan Complex
Serpentinite
Greenstone
Sandstone
Melange up to 10,000 ft thick
Also chert, shale, limestone, conglomerate
Depositional EnvironmentDepositional Environment• Most likely a low latitude marine environment:
– marine fossils in some clastic rocks, Radiolaria in chert
– highly fractured, interbedded greenstones (rapid cooling of hot lava)
• Conglomerate and massive graywacke beds created by turbidity currents– further evidence:
• shale layers between graded beds, small scale current bedding, ripple marks
• Most likely a low latitude marine environment:– marine fossils in some clastic rocks, Radiolaria in
chert– highly fractured, interbedded greenstones (rapid
cooling of hot lava)
• Conglomerate and massive graywacke beds created by turbidity currents– further evidence:
• shale layers between graded beds, small scale current bedding, ripple marks
Methods and MaterialsMethods and Materials
• Prior to sampling– aerial photographs
• Sampling– Samples were collected from 45 accessible
outcrops around SF– Clean hands/dirty hands technique (minimizes
cross contamination)– At least 5 fresh rock chips collected from
outcrop and pooled– Latitude/longitude of location noted with GPS
unit
• Prior to sampling– aerial photographs
• Sampling– Samples were collected from 45 accessible
outcrops around SF– Clean hands/dirty hands technique (minimizes
cross contamination)– At least 5 fresh rock chips collected from
outcrop and pooled– Latitude/longitude of location noted with GPS
unit
Aerial PhotographyAerial Photography
• USGS collection from 1940s-1970s
• Provided insight into previous industrial activity
• Showed sampling areas free from major contaminating factors
• No evidence of alteration of background levels
• USGS collection from 1940s-1970s
• Provided insight into previous industrial activity
• Showed sampling areas free from major contaminating factors
• No evidence of alteration of background levels
Presidio Area
45 sample locations45 sample locations
Presidio
Twin Peaks/
Glen Park
Potrero Hill
McLaren Park
Chert Sample LocationsChert Sample Locations
• 15 samples• Glen Canyon Park,
Twin Peaks• light tan to red• distinct bedded
layers with folding
• 15 samples• Glen Canyon Park,
Twin Peaks• light tan to red• distinct bedded
layers with folding
Greenstone Sample LocationsGreenstone Sample Locations
• 8 samples• McLaren Park, Corona
Heights, Twin Peaks• highly fractured• extensively weathered• dark gray to dark
reddish-brown
• 8 samples• McLaren Park, Corona
Heights, Twin Peaks• highly fractured• extensively weathered• dark gray to dark
reddish-brown
Sandstone Sample LocationsSandstone Sample Locations
• 10 samples• McLaren park, Castro• large, thick bedded
outcrops• randomly fractured• highly weathered• brown to gray
• 10 samples• McLaren park, Castro• large, thick bedded
outcrops• randomly fractured• highly weathered• brown to gray
Serpentinite Sample LocationsSerpentinite Sample Locations
• 12 samples• Potrero Hill, Presidio,
Baker Beach• greenish-gray to blue• highly weathered,
sheared• soft, friable
• 12 samples• Potrero Hill, Presidio,
Baker Beach• greenish-gray to blue• highly weathered,
sheared• soft, friable
Geochemical AnalysisGeochemical Analysis• 48 samples submitted to SGS Mineral Services in
Toronto (45 plus 2 blind duplicates and 1 reference sample)
• Tested for 40 trace elements using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry)
– Samples decomposed using mixture of HCl, Nitric, Perchloric, HF
– Digestion is aspirated and elemental emission signal is measured for elements
• 48 samples submitted to SGS Mineral Services in Toronto (45 plus 2 blind duplicates and 1 reference sample)
• Tested for 40 trace elements using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry)
– Samples decomposed using mixture of HCl, Nitric, Perchloric, HF
– Digestion is aspirated and elemental emission signal is measured for elements
•Identification of outcrop samples
•Geochemical results
•Statistical analysis
•Mann-Whitney and ANOVA
•Developed trace element distribution maps
•Identification of outcrop samples
•Geochemical results
•Statistical analysis
•Mann-Whitney and ANOVA
•Developed trace element distribution maps
Results and DiscussionResults and Discussion
Identification of Outcrop SamplesIdentification of Outcrop Samples
• Field Identification
• Thin sections from each rock type (Univ of Utah)
• X-ray Diffraction (XRD) evaluation
• Field Identification
• Thin sections from each rock type (Univ of Utah)
• X-ray Diffraction (XRD) evaluation
Thin Sections (USGS Petrographic Microscope)
Thin Sections (USGS Petrographic Microscope)
X-ray DiffractionX-ray Diffraction
• Scattering of x-rays from a crystal where resulting interference pattern determines structure of crystal
• Performed by Mineral Services Lab at USGS• Showed minerals consistent with each rock type
– Serpentinite (lizardite, chrysotile)– Chert (quartz)– Sandstone (quartz)– Greenstone (albite, diopside)
• Scattering of x-rays from a crystal where resulting interference pattern determines structure of crystal
• Performed by Mineral Services Lab at USGS• Showed minerals consistent with each rock type
– Serpentinite (lizardite, chrysotile)– Chert (quartz)– Sandstone (quartz)– Greenstone (albite, diopside)
XRD of Chert
Quartz
0
7000
40 2 theta
Count/s
Geochemical ResultsGeochemical Results• Results for Cr, Co, Pb, Ni, Sr compared to
data from Schlocker show:• Results for Cr, Co, Pb, Ni, Sr compared to
data from Schlocker show:
Chromium
Lead
Cobalt
Nickel
Strontium
Statistical analysis comparing my data to
Schlocker’s data
Statistical analysis comparing my data to
Schlocker’s data
• Assists in description and analysis of data– generated descriptive statistics (mean, std
dev, ranges, etc.)– histograms (show distribution and
observations of sample)– tests for normality (data fits bell shaped curve)
• Komolgorov-Smirnov, Shapiro-Wilk
– Q plots (compare data to linear ideal)
• Assists in description and analysis of data– generated descriptive statistics (mean, std
dev, ranges, etc.)– histograms (show distribution and
observations of sample)– tests for normality (data fits bell shaped curve)
• Komolgorov-Smirnov, Shapiro-Wilk
– Q plots (compare data to linear ideal)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5Fr
eq
ue
ncy
Statistical TestingStatistical Testing
• If data is ‘normally distributed’, randomly collected, Student ‘t’ test can be used
• If data is not ‘normally distributed’, Mann-Whitney U test is appropriate
• Tests on Schlocker data showed data not not normally distributed, therefore Mann-Whitney U analyses most appropriate to demonstrate significant differences between datasets
• If data is ‘normally distributed’, randomly collected, Student ‘t’ test can be used
• If data is not ‘normally distributed’, Mann-Whitney U test is appropriate
• Tests on Schlocker data showed data not not normally distributed, therefore Mann-Whitney U analyses most appropriate to demonstrate significant differences between datasets
Mann-Whitney U TestMann-Whitney U Test
• Data obtained from two random samples (n1 and n2)
• Samples are combined, each value assigned a rank (smallest is rank 1, largest is rank n1+ n2)
• U statistic based on totals of ranks (Ta, Tb)
• The smaller value of either Ta or Tb, the greater the
evidence that samples from different populations
• Tests were performed using 95% confidence level (95% of all samples give interval that includes the mean, 5% would give interval that does not)
• Data obtained from two random samples (n1 and n2)
• Samples are combined, each value assigned a rank (smallest is rank 1, largest is rank n1+ n2)
• U statistic based on totals of ranks (Ta, Tb)
• The smaller value of either Ta or Tb, the greater the
evidence that samples from different populations
• Tests were performed using 95% confidence level (95% of all samples give interval that includes the mean, 5% would give interval that does not)
HypothesisHypothesis
• Null hypothesis states:– ‘the difference between the mean ranks of
the datasets is not statistically significant’– OR
– average level of specific trace element found in given rock type in Schlocker’s data is not statistically different from average level of same element, same rock type found in my data
• Null hypothesis states:– ‘the difference between the mean ranks of
the datasets is not statistically significant’– OR
– average level of specific trace element found in given rock type in Schlocker’s data is not statistically different from average level of same element, same rock type found in my data
Comparison of Trace Element Levels between Schlocker and Simpson Datasets using Mann Whitney TestComparison of Trace Element Levels between Schlocker and Simpson Datasets using Mann Whitney Test
ChromiumChromium
•significant differences seen in serpentinite (means of 564 vs. 1384 mg/kg) and chert (means of 3 vs. 22 mg/kg) data
•no significant differences seen in greenstone and sandstone
ChromiumChromium
•significant differences seen in serpentinite (means of 564 vs. 1384 mg/kg) and chert (means of 3 vs. 22 mg/kg) data
•no significant differences seen in greenstone and sandstone
CobaltCobalt
•significant differences seen in sandstone (means of 25 vs. 7 mg/kg) and serpentinite (means of 59 vs. 81 mg/kg)
•no significant differences seen in chert and greenstone
NickelNickel
•significant differences seen in all rock types: chert (means of 43 vs. 22 mg/kg), greenstone (means of 180 vs. 46 mg/kg), sandstone (means of 57 vs. 27 mg/kg), serpentinite (means of 3000 vs. 1773 mg/kg)
LeadLead
•significant differences seen in chert (means of 0.25 vs. 40 mg/kg) and sandstone (means of 2.6 vs. 14 mg/kg)
•no test on greenstone and serpentinite
StrontiumStrontium
•significant difference seen only in chert (means of 5 vs. 38 mg/kg)
ANOVAANOVA
• Determines significant differences in the means of two or more datasets
• Performed on my data comparing means of same trace element between four rock types– Data is normally distributed, equal
variances, from randomly collected samples
• Null hypothesis: means of sample populations are statistically equal
• Determines significant differences in the means of two or more datasets
• Performed on my data comparing means of same trace element between four rock types– Data is normally distributed, equal
variances, from randomly collected samples
• Null hypothesis: means of sample populations are statistically equal
Mean (mg/kg) and Standard Deviation for each rock type in conjunction with ANOVA resultsMean (mg/kg) and Standard Deviation for each rock type in conjunction with ANOVA results
a Identical letters indicate no significant difference at the 95% confidence level.b,c Non-identical letters indicate a significant difference at the 95% confidence level
• Chromium and nickel concentrations are ~15-35 times higher in serpentinite
Trace Element Distribution MapsTrace Element Distribution Maps
• Created to illustrate levels of trace elements throughout San Francisco
• Within sampled areas, data is accurate
• Outside of sampled areas (west, upper northeast, southeast corners) data is interpolated
• ArcInfo/ArcMap 8.3 Inverse Distance Weighted (IDW) interpolation method– assumes each sample point has a local influence that
decreases with distance
• Created to illustrate levels of trace elements throughout San Francisco
• Within sampled areas, data is accurate
• Outside of sampled areas (west, upper northeast, southeast corners) data is interpolated
• ArcInfo/ArcMap 8.3 Inverse Distance Weighted (IDW) interpolation method– assumes each sample point has a local influence that
decreases with distance
N
Chromium Distribution Map
Cobalt Distribution Map
Strontium Distribution Map
Lead Distribution Map
Nickel Distribution Map
ConclusionConclusion• This study:
– enhances understanding of background trace element distribution in Franciscan Complex
– will assist in development of future environmental clean-up studies
– expands trace element database
• Improvements to this dataset:– increasing sample size/location– examining other trace elements– sampling soil
• This study: – enhances understanding of background trace element
distribution in Franciscan Complex– will assist in development of future environmental
clean-up studies– expands trace element database
• Improvements to this dataset:– increasing sample size/location– examining other trace elements– sampling soil