Management of Non-Point Source Pollution CE 296B

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Management of Non-Point Source PollutionCE 296B

• Department of Civil Engineering
• California State University, Sacramento

Lecture 9, March 3, 1998 Sources of Pollutants -
Part V
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Recall that we were looking at the six categories
of pollutants
1. Toxic inorganics - e.g. metals 2. Synthetic
organics - e.g. solvents 3. Biostimulants - BOD,
nutrients 4. Sediment - clay, silt, sand, gravel
? Left off here 5. Pathogenic organisms -
viruses, bacteria, protozoa 6. Trash - use your
imagination
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And the framework for acquiring knowledge about
each category
1. What are the sub-categories in each category
and what are representative members? 2. What are
the origins of pollutants? 3. How pollutants are
introduced to the flow stream? 4. How pollutants
behave in water?? and here
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V. The fourth category of pollutant to examine is
sediment. (cont.)

• D. How do sediments behave in water? Divided
  into three major groups, each one having its own
  effect on water quality objectives and beneficial
  uses
• Transport of particles - Sedimentation effects
  (mass loading).
• Adsorption of other materials - Major determining
  factor for where toxic substances end up and
  effect they have.
• Contribution to turbidity - Concentration effects.

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V. The fourth category of pollutant to examine is
sediment. (cont.) D. How do sediments behave in
water? (cont.)

• 1. Transport of particles
• a. Two modes of transport-
• Suspended in the flow - Wetload
• Being pushed along the bottom - Bedload
• b. Particle size distribution, wetload vs.
  bedload
• Obviously, wetload transport has a smaller
  particle size distribution than bedload.

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Wetload Particle Transport

• I. Questions associated with wetload particle
  transport can be separated into two categories
• A. What is the largest, discrete, particle that
  will remain in suspension?
• Particles that are less than 1 µm in diameter
  are colloidal and will remain in suspension as
  surface forces are greater than body forces. It
  is the size of the particle greater than 1 µm in
  diameter that will remain in suspension.
• B. How much aggregation of particles is taking
  place?
• The idea being that larger, aggregated particles
  are more likely to become part of the bedload.

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Wetload Particle Transport

• II. What controls the size of the largest,
  discrete particle that will remain in suspension?
• For particles greater than 1 µm in diameter, body
  forces are dominant. Unless held in suspension
  physically by turbulence, the particle will
  settle. Thus, as turbulence is proportional to
  the Reynolds Number, the greater Reynolds Number
  associated with the flow, the larger the particle
  that will remain in suspension.

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Wetload Particle Transport

• II. How much aggregation of particles is taking
  place?
• Complex topic, but lessons learned from the
  coagulation process apply here as well.
• Aggregation is dependant on (among other
  things)
• The concentration of multivalent cations (Ca2,
  Mg2) present. Higher concentrations mean
  greater aggregation.
• The concentration of univalent cations (Na, K)
  present. Higher concentrations mean less
  aggregation.

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Wetload Particle Transport

• II. How much aggregation of particles is taking
  place?
• Complex topic, but lessons learned from the
  coagulation process apply here as well.
• Aggregation is dependant on (among other
  things) (cont.)

• An appropriate velocity gradient (G).
• Too large a gradient, and shear forces will tear
  aggregated particles apart.
• Too small a gradient, particles will have
  inadequate opportunity to come into contact.

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Wetload Particle Transport

• III. Thus, the amount of wetload, particulates
  that will be transported rapidly, is dependant
  on
• A. The amount and composition of material
  originally eroded.
• B. The turbulence of the flow stream, either in a
  natural or man-made channel.
• C. The composition of electrolytes in the flow
  stream.
• IV. It is important to note that while fine
  particles are suspended in the wet load,
  partitioning of metals and synthetic organics to
  the solid phase is enhanced.

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Bedload Particle Transport

• I. Particles too heavy to remain in suspension
  may still be transported along the bottom of a
  channel, natural or man-made, by the force of the
  current and the assistance of gravity.
• Of interest in the examination of bedload
  transports is
• The mass flow rate of sediment in the downstream
  direction.
• The fractionation of sediments by size as part of
  the bedload transport process.
• The disposition of sediments when transport
  ceases.

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Bedload Particle Transport

• II. The mass flow rate of sediment in the
  downstream direction is complex (translation, I
  dont know much about it yet). Factors include
• The amount and type of erosion in the watershed.
• The bottom composition (roughness) - a smoother
  surface yields a greater transport rate.
• The flow velocity - higher velocity yields a
  greater transport rate.
• The slope - a steeper slope yields a greater
  transport rate.

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Discussion Break

• Based on what you have seen, and knowledge of
  gravity flow system design, how efficiently will
  sediments, of all sizes, be transported once they
  enter the system?
• Focus of BMPs?

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Bedload Particle Transport

• III. The fractionation of sediments by size.
  Consider the diagram

Thus, along the streambed, natural or man-made,
there will be a sorting out of particles by size
to satisfy first law concerns. So, gravel
deposits, sandbars, mudflats!
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Discussion Break

• All other things being equal, where would you
  expect to find the greatest concentration of
  toxic substances?
• Basis Mass of contaminant per mass of dry soil
  (mg/kg)

Gravel Beds? Sandbars? Mudflats?
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Bedload Particle Transport

• III. The disposition of sediments when transport
  ceases. Two different types of issues are
  addressed
• A. Are the effects of sediment deposits positive
  or negative?
• Positive
• Spawning grounds and beaches (gravel / sand)
• Entombment of toxic substances
• Negative
• Filling of wetland habitat type effects
• Impairment of navigation

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Bedload Particle Transport

• III. The disposition of sediments when transport
  ceases. Two different types of issues are
  addressed (cont.)

• B. Are the deposits permanent or temporary?
• If they are permanent, the same issues discussed
  previously will be valid.
• If temporary
• Will a large flow event, clearing out the deposit
  cause a shock loading problem downstream?
• Will the inevitable large flow event clean out
  a
• positive deposit (beach, spawning ground)?
• negative deposit (clogged wetland)

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V. The fourth category of pollutant to examine is
sediment. (cont.) D. How do sediments behave in
water? (cont.)

• 2. Adsorption of toxic substances to particles.
• Two different aspects to this topic
• How much and how tightly are toxic substances
  bound to particulate material?
• Is this removing toxic substances from liquid
  phase and thus making them less bioavailable or
  is this concentrating toxic substances in one
  place (the bottom sediments)?

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V. The fourth category of pollutant to examine is
sediment. (cont.) D. How do sediments behave in
water? (cont.)

• 3. How much and how tightly are toxic substances
  bound to particulate material?
• In other classes, substaintial effort
  has/is/will be made on behalf of partitioning of
  metals, synthetic organics to the soil matrix (or
  activated carbon). The equilibrium relationships
  developed there only applies to the circumstance
  pore water within a matrix.

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V. The fourth category of pollutant to examine is
sediment. (cont.) D. How do sediments behave in
water? (cont.) 3. How much and how tightly are
toxic substances bound to particulate material?
(cont.)

• Many of the same principles apply to adsorption
  of metals and synthetic organics to soil
  particles suspended in a water matrix, but the
  equilibrium equations do not.

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V. The fourth category of pollutant to examine is
sediment. (cont.) D. How do sediments behave in
water? (cont.) 3. How much and how tightly are
toxic substances bound to particulate material?
(cont.)

• New, yet to be developed relationships may
  describe the equilibrium between liquid phase
  concentrations and adsorbed phase amounts for
  metals and synthetic organics with respect to
  soil particles suspended in a water column.

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V. The fourth category of pollutant to examine is
sediment. (cont.) D. How do sediments behave in
water? (cont.) 3. How much and how tightly are
toxic substances bound to particulate material?
(cont.)

• Factors that would be considered in such a
  relationship
• Concentration of solids
• Clay fraction
• Organic fraction
• Temperature

• Hardness
• Mixing
• Contact time
• pH

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V. The fourth category of pollutant to examine is
sediment. (cont.) D. How do sediments behave in
water? (cont.)

• 4. Finally, wetload sediment transport
  contributes to increased turbidity. In addition
  to being a water quality objective, turbidity
  can
• Have a negative effect on fish. Particulate
  material and gills do not mix.
• Although the correlation is very poor, turbidity
  measurements can be a surrogate measure for
  sediment concentration.

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Recall that we were looking at the six categories
of pollutants
1. Toxic inorganics - e.g. metals 2. Synthetic
organics - e.g. solvents 3. Biostimulants - BOD,
nutrients 4. Sediment - clay, silt, sand,
gravel On to here ? 5. Pathogenic organisms -
viruses, bacteria, protozoa 6. Trash - use your
imagination
25
And the framework for acquiring knowledge about
each category
1. What are the sub-categories in each category
and what are representative members? 2. What are
the origins of pollutants? 3. How pollutants are
introduced to the flow stream? 4. How pollutants
behave in water?
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VI. The fifth category of pollutant to examine is
pathogens.

• A. Define what pathogens are
• A pathogen is a microscopic entity that if a
  sufficient dose is transmitted to a human, a
  disease will ensue. Three broad categories of
  pathogens exist
• 1. Viruses
• 2. Procaryotes
• 3. Eucaryotes

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Viruses

• Viruses (from the Latin virus - poisonous
  substance) are infectious nucleic acid
  encapsulated in a protein coat.
• A virus reproduces by invading a cell, where
  replication takes place. The cell then dies
  releasing many copies of the virus.
• A philosophical debate exists as to whether a
  virus is alive. After all as an entity, it has
  no metabolic functions. All it does is invade
  another cell and let the that cells metabolic
  machinery do all the work for reproduction.

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Viruses

• In most cases a virus has a specific type of cell
  it is capable of invading.
• Viruses are small. The size range is 20 - 350
  ?m. 50 ?m is typical.
• Traditional methods of detecting viruses involve
  tissue cultures, looking to see in the correct
  type of cells grown in culture are infected.
• This makes detection in water samples extremely
  difficult.
• Example water borne pathogen - Polio

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Discussion Break

• Why do you think it is so difficult to detect
  viruses in water samples?
• Policy implications?

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Procaryotes

• Procaryotes, loosely bacteria, are single celled
  organisms capable of metabolic functions that do
  not have a nucleus.
• Structure

• Typical Size

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Procaryotes

• By far, the largest source of biomass on the
  planet.
• As bacterial species are difficult to
  differentiate by morphology, bacteria are usually
  classified by the biochemical processes they do
  best.
• Most schemes to detect bacteria are centered on
  isolating species based on biochemical tests.
  Does the bacteria perform a particular
  biochemical process.
• A major problem with this approach has been that
  many species will perform a given biochemical
  process.

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Procaryotes

• Pathogenic bacteria can be vectored many ways,
  but we are interested in water borne pathogens.
  The most likely source of bacterial pathogens in
  water is fecal matter.
• Examples of water borne pathogens
• Cholera Vibrio cholerae
• Typhus Salmonella typhi
• The pathway for infection is the same for both
  species. After an infected host contaminates a
  water supply, the richest source being fecal
  matter, a victim ingests water that contains a
  large enough number of viable organisms to become
  infected.

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Eucaryotes

• Eucaryotes, loosely protozoa, are organism where
  the cell(s) have a nucleus.
• Size Huge variation, but much larger than
  bacteria.
• Reproduce much slower than bacteria, and thus
  occur in much lower numbers.
• Many fewer viable organisms are required to cause
  an infection.
• Are far tougher than bacteria or viruses. Can
  withstand environmental stress better and are
  more resistant to disinfection.

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Eucaryotes

• Often are parasitic. Treatment is notoriously
  difficult.
• Because of
• Low population densities, and
• Poorly understood biochemistry
• are very difficult to detect.
• Example pathogens
• Giardia lambilia
• Crytposporidium
• Entamoeba histolytica

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Eucaryotes

• The life cycle of these organisms are usually
  poorly understood. It is often assumed, without
  proof, that the major source of contamination is
  fecal matter.
• Other than minimizing fecal matter, a difficult
  chore for wild animals in any case, source
  control measures are hard to come by for
  eucaryotic organisms.

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Discussion Break

• Diarrhea kills more people worldwide than any
  other cause.
• In the U.S., it is not a big problem.
• How real do you think the problem of water borne
  disease is in this country?

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VI. The fifth category of pollutant to examine is
pathogens. (cont.)

• B. Overview of detection of pathogens in surface
  waters
• 1. The number of possible pathogens is huge.
  Each pathogen has a specific test associated with
  it. Many of those tests are difficult and
  expensive to perform.
• 2. A solution to this problem was put forward at
  the turn of the century. That solution is still
  the regulatory standard.

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VI. The fifth category of pollutant to examine is
pathogens. (cont.) B. Overview of detection of
pathogens in surface waters (cont.)

• 3. The idea was to test for an organism that was
  found in fecal material, but that had no other
  source.
• 4. Scientists searched for a biochemical process
  that only took place in the intestinal tract of
  warm-blooded animals. The choice was the
  fermentation of lactose in the presence of bile
  salts.