mike huffington dan montonye north dakota state university
TRANSCRIPT
Impacts of Subway Tunnels on Goundwater QualityMike Huffington Dan MontonyeNorth Dakota State University
Detrimental effects of subway tunnels on groundwater levels in Seoul
Tunnels may cause significant drop of groundwater levels due to seepage of surrounding groundwater into tunnel Impacts both quantity and quality of the tunnel seepage water Decreased groundwater level from 16.85 to 20.4 meters in
some areas 379 wells near tunnels were abandoned
(Chae et al 2008)
What is happening?BEFORE TUNNEL WATER LEAKS IN
Water Level Well
Tunnel
Pump
Stream
Water Collected and pumped out of tunnel
Detrimental effects on water quality
All samples from collecting stations failed drinking water standards
Tunnel water high in Mn,Fe, and NH4+ compared to previous groundwater data from nearby areas
Some also failed turdity and color standards Most likely result of high Fe and Mn
Most frequent problem is occurrence of pathogenic microbes(Chae et al 2008)
Summary of water quality data
In Comparison to Initial Data
(Chae et al 2008)
What is happening?
Before tunnel After tunnel
Sewer Pipe
Water Level
Construction Materials
Continued….
Sewer Pipe
NH4+ and organic matter
Ground water and soil
Generates reducing conditions
Tunnel Water
Fe and Mn dissolve
Model 1
Initial solution reacted with Fe and Mn Used hematite (Fe2O3), geothite (FeO OH),
and amorphous Fe(OH)3 for Fe minerals Pyrulosite (MnO2), manganite (MnO OH), and
amporphous Mn(OH) for Mn minerals
(Chae et al 2008)
Results of Model 1
Mn and Fe alone had no significant impact on water chemistry
Did not dissolve under oxidizing conditions
(Chae et al 2008)
Model 2
Add sewage water to model 1 to produce reducing conditions
Simplified sewage to CH2O (6.25 mmol added)
(Chae et al 2008)
Model 2 Results
Electrons supplied by oxidation of organic carbon occurs preferentially via Mn reduction
Dissolved Mn and organic carbon controls the redox state of the water
(Chae et al 2008)
Model 3
Effect of Varying amount of Mn solids looked at Addition of .0001 mmol to .1 mmol Hematite used as Fe source/pyrulosite for Mn
and 6.25 mmol CH20 used
(Chae et al 2008)
Model 3 Results Ph had little change Pe decrease – because organic carbon continually provides
e- to oxidize Fe concentration decrease with increase concentration of
Mn Shows redox chemistry of water controlled by amound of
Mn solids in quifer
(Chae et al 2008)
Model 4
Effects of changing amount of organic carbon looked at Vary amount from .625 mmol to 6.25 mmol Pyrulosite kept constant at .1 mmol
(Chae et al 2008)
Results of Model 4 Fe shows progressive increase – due to
reductive dissolution of hematite When organic carbon is supplied in
sufficient quantities the concentration of dissolved Fe increases after the reductive consumption of Mn from all sources
(Chae et al 2008)
Summary of Study• The oxidation of organic carbon releases electrons that are used in the
reduction of iron and maganeese bearing solids• H+ ions are also released causing the solution to become more acidic and
making the reduction of Fe and Mn bearing solids even more favorable Organic carbon CH2O + H2O = CO2 + 4H+ + 4e−
Hematite Fe2O3 + 6H+ = 2Fe3+ + 3H2O
Manganite MnO∙OH + 3H+ + e− = Mn2+ + 2H2O
(Chae et al, 2008)
Summary of Study• One of the controling factors for the solutions redox
condition is the availability of manganese • Dissolved Mn accepts the majority of the electrons
that are released via the oxidation of organic carbon
• Fe only dissolves when there are enough available electrons to satisfy the Mn that is available to the system
(Chae et al, 2008)
Our Analyses• As the contaminated water is dumped into the river system the
concentration of organic carbon is reduced, resulting in a reduction in the number of free electrons available
• The free electrons that are available are accepted by the dissolved Mn, causing Fe to precipitate out of solution and hence causing the water to stain red
1 2 4 70
50
100
150
200
Fe Precipitation vs Organic Carbon Concentration
Organic Carbon (mmol)Perc
ipit
ate
d F
e (
um
ol L-1
)
Cont.
SI Values Before and After Mixing With River Water
Phase SI log IAP log KT
Manganite -15.29 10.05 25.34 MnOOH
Hematite -2.48 -6.49 -4.01 Fe2O3
Manganite -3.20 22.14 25.34 MnOOH
Hematite 10.85 6.84 -4.01 Fe2O3
1:1 ratio
Fe and Mn containing solids in the presence of high organic solid concentration
Same solids after solution mixed with Mississippi River water
Bacteria
• Excess amounts of iron in a system result in fewer free chloride molecules
• This reduction in Cl- makes the environment more suitable for bacteria to grow and survive
• Excess iron also allows bacteria to conserve energy that they would otherwise be used in iron uptake
(Chae et al, 2008)