Impacts of Subway Tunnels on - PowerPoint Presentation

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Impacts of Subway Tunnels on Goundwater Quality

Mike 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 tunnelImpacts 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 standardsTunnel water high in Mn,Fe, and NH4+ compared to previous groundwater data from nearby areasSome also failed

turdity

and color standards

Most likely result of high Fe and

MnMost 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 tunnelAfter 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 MnUsed 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 chemistryDid not dissolve under oxidizing conditions

(

Chae

et al 2008)

Model 2

Add sewage water to model 1 to produce reducing conditionsSimplified 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 reductionDissolved 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 atAddition 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 changePe decrease – because organic carbon continually provides e- to oxidizeFe 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 atVary amount from .625 mmol to 6.25 mmolPyrulosite kept constant at .1

mmol

(

Chae

et al 2008)

Results of Model 4

Fe shows progressive increase – due to reductive dissolution of hematiteWhen 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 carbonCH2O + H2O = CO2 + 4H+

 + 4e−Hematite

Fe

2

O

3

 + 6H

+

 = 2Fe

3+

 + 3H

2

OManganiteMnO∙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 carbonFe 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

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 Fe2O3Manganite

-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 moleculesThis 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)

Questions??