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Management of Non-Point Source Pollution

CE 296BDepartment of Civil Engineering

California State University, Sacramento

Lecture #19, April 26, 1998

Management Strategies - Part II

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A. Location with respect to where the pollution is coming from and where it is going:

• Front of the pipe

• In the middle of the pipe

• End of the pipe

• BMP’s that don’t seem to be associated with the pipe at all.

I. Categories of BMP’s (cont.)

Recall where we left off:

Here

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B. At the front of the pipe, categories could include:

• BMP’s that seek to minimize the use of a substance that could be a pollutant.

• BMP’s that seek to adjust peoples behavior.

• BMP’s that seek to keep pollutants in their place.

• BMP’s that seek to prevent pollutants that have been mobilized from entering the pipe.

I. Categories of BMP’s (cont.)

Recall where we left off:

And Here

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2. Existing Facilities. Many sub-categories exist here. Some are:a.Cleaning up of spilled material b.Cleaning surfaces

c.Maintaining vegetative cover

d.Storing materials properly.

II. Front-of-Pipe BMP’s (cont.)D. Keeping pollutants immobilized. Two

principle categories come to mind here, BMP’s associated with construction and BMP’s associated with existing facilities. (cont.)

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Cleaning-up Spilled Material-I

• In the course of human activities, materials are sometimes spilled onto the ground.

• When those materials could be a pollutant, clean-up procedures need to be implemented.

• There are several factors associated with quality clean-up procedures:

– The people cleaning up a spill have to know that it occurred. The means of assuring each spill gets reported to the appropriate people in a timely fashion is difficult. This is probably the weakest link in most spilled material clean-up procedures.

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Cleaning-up Spilled Material-II

• Factors associated with quality clean-up procedures:

– The people cleaning up a spill must:

• Be able to actually find the reported spill in a timely manner given the varied quality of reporting information.

• Have at their disposal the appropriate equipment to clean-up the spilled material.

• Have adequate knowledge of the material spilled

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Cleaning-up Spilled Material-III

• Factors associated with quality clean-up procedures:

– The drainage path to the receiving water from any patch of ground that is likely to be spilled upon picked at random must be known. In a large metropolitan area, having this kind of knowledge of the storm-drain system is very difficult.

– If the spill has entered the drainage system, the ability to intercept it should exist.

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2. Existing Facilities. Many sub-categories exist here. Some are:a.Cleaning up of spilled material

b.Cleaning surfacesc.Maintaining vegetative cover

d.Storing materials properly.

II. Front-of-Pipe BMP’s (cont.)D. Keeping pollutants immobilized. Two

principle categories come to mind here, BMP’s associated with construction and BMP’s associated with existing facilities. (cont.)

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Cleaning Surfaces - I

• One idea for preventing pollutants that are on the surface from becoming mobilized is to clean those pollutants off of that surface.

• On impervious surfaces, this has typically meant sweeping.

• Two types of materials are typically cleaned from a surface:

– Trash

– Particulates

• With trash, this typically works fairly well.

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Cleaning Surfaces - II

• Cleaning large particulate material, coarse sand and above, works fairly well also.

• The ability to pay for surface cleaning activities varies from one kind of public entity to another.

• Cleaning particulate material off of impervious surfaces has a problematical pollution control benefit. There is an equilibrium thickness of fine particulates that is difficult to change. Consider the animation on the following slide:

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Equilibrium Thickness of Fine Particulate Layer - I

Time

Fin

e pa

rtic

ulat

e la

yer

thic

knes

s• Start with a “perfectly” clean surface.• Assume that no wind is blowing.• Watch the dust accumulate.

Fine particulate accumulation rate

• Turn on normal wind conditions

No windWind

Wind blowing away particulates faster than they accumulate

Wind blowing away particulates at the same rate they are accumulating

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Equilibrium Thickness of Fine Particulate Layer - II

Time

Fin

e pa

rtic

ulat

e la

yer

thic

knes

s

• Start with a completely clean surface• Normal wind conditions exist• Note the accumulation of particulates with time

Wind free accumulation rate

Equilibrium layer thickness

Layer thickness moving towards equilibrium

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Equilibrium Thickness of Fine Particulate Layer - III

Time

Fin

e pa

rtic

ulat

e la

yer

thic

knes

s• Start with system at equilibrium• Sweep the surface partially clean

Equilibrium conditions

Wind free accumulation rate

Sweeping OperationSweeping Operation

Sweeping Operation

• Repeat

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Discussion BreakWhat are the kinds of “wind” we have been talking about?

Are there locations in an urban area that might collect a substantial amount of material through “wind” action?

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Discussion BreakWhy is there a concern about cleaning up the fine particulate material off of impervious surfaces?

With respect to non-point source pollution, what kinds of surfaces benefit more from sweeping operations? What kind less? Why?

How much of a difference does a highly effective cleaning device make over a moderately effective device? Why?

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Discussion BreakThere has been a suggestion in some quarters that to help meet TMDL’s, an urban discharger might measure and count the pounds of pollutant in street sweepings.

Does this mean that those pollutants have really been removed from the non-point source stream?

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2. Existing Facilities. Many sub-categories exist here. Some are:a.Cleaning up of spilled material

b.Cleaning surfaces

c.Maintaining vegetative cover d.Storing materials properly.

II. Front-of-Pipe BMP’s (cont.)D. Keeping pollutants immobilized. Two

principle categories come to mind here, BMP’s associated with construction and BMP’s associated with existing facilities. (cont.)

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Maintaining Vegetative Cover

• Many surfaces in urban locations, both public and private, are covered with vegetation that holds sediment in place.

• Establishing vegetative cover where it does not exist and maintaining existing cover is the focus of much non-point source pollution effort in urban areas.

• In California, maintaining vegetative cover usually requires irrigation. This potentially produces a flow stream during dry weather that could be considered non-point source pollution.

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Discussion BreakA chic idea is to use California native plants for vegetative cover. One of many positive attributes to this idea is that California native plants are by nature drought resistant and require less irrigation. Several problems do exist though:

Is it worth the expense of keeping out exotic plants?

During drought conditions, many native plants provide less cover, making it possible that erosion would take place. How does this fit with the context of the CWA?

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2. Existing Facilities. Many sub-categories exist here. Some are:a.Cleaning up of spilled material

b.Cleaning surfaces

c.Maintaining vegetative cover

d.Storing materials properly.

II. Front-of-Pipe BMP’s (cont.)D. Keeping pollutants immobilized. Two

principle categories come to mind here, BMP’s associated with construction and BMP’s associated with existing facilities. (cont.)

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Proper Material Storage - I

• Many items that are pollutants are pollutants if they find their way into a receiving water have legitimate uses. As these items are stored for use the idea is to prevent them from becoming mobilized in a flow stream. Examples include:

– Aggregate piles

– Sacks of fertilizer

– Containers of herbicides, pesticides, or fungicides

– Petroleum products

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Proper Material Storage - II

• BMP’s associated with proper material storage direct that techniques specific to the:

– Material in question

– Particular use of that material

– Location of that material

Be devised.

• The list of such techniques is endless, but includes:

– Placing a tarp over aggregate piles

– Storing materials on a pallet

– Construction a berm around a storage area.

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A. Recall our drawing defining what the pipe is:III.Middle-of-Pipe BMP’s

Overland Flow

Receiving Water

Watershed

Polluting Activities

“Pipes”

Storm or C

ombined Sewer

Small Watercourse

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B. The idea of middle-of-the pipe BMP’s is to arrest the movement of pollutants that have found their way into the non-point source pollutant stream on it’s way to a receiving water. These can be BMP’s that:

1. Hold the pollutant in place until it can be retrieved.

2. Make the pollutant part of the “pipe”

III.Middle-of-Pipe BMP’s (cont.)

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C. Storm drain type pipes. Basic engineering principles used in the design of storm drains insure an efficient transport of pollutants. After all, the point of most storm drains is to get the water away as efficiently as possible.

Thus, devices in storm drains to intercept pollutants have an uphill battle to fight.

The most often discussed item here is a catch basin and variations on that theme.

III.Middle-of-Pipe BMP’s (cont.)

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Catch Basin Usage - I

• Picture to be inserted by tonight.

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Catch Basin Usage - II

• The basic problem with this idea is the extremely short detention time. It is often less than one second meaning that only very large and dense items will be trapped.

Rocks are typically not thought of as pollutants.

• Cleaning costs can be extremely high as well.

• A variation on the theme of a catch basin is the use of filtering inserts placed in the basin. These inserts made up of adsorbent material are designed to trap fine particulates and dissolved constituents.

The maintenance on these is appalling.

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Discussion BreakPeriodically, the use of catch basins are studied as a means of reducing non-point source pollution (going back decades). The conclusions are usually the same.

Despite this, they still keep coming back as a suggested BMP.

Why do you think this is?

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Discussion BreakHow could these type devices serve to enhance the propagation of disease vectoring?

If they did improve water quality, how would you compare those benefits with the detriments of increase disease due to insect vectors? What is the equation?

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D. Small water course type pipes. These can be flood control type channels (the classic concrete trapezoidal channel) or small, often ephemeral, streams.

A popular, but expensive idea is to reestablish or enhance existing riparian habitat. Wetlands restoration is particularly popular.

III.Middle-of-Pipe BMP’s (cont.)

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Discussion BreakAs mentioned in the previous slide, this is an expensive process. If multiple benefits could be established for such a process the probability of securing adequate funding improves.

What are other benefits of constructing BMP’s that enhance small water courses?

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E. Overland flow type pipes. When water flows over a grassy slope in a thin sheet, substantial pollution control benefits may accrue. Among them:

1. Removal of sediment

2. Removal of conventional organics

3. Removal of nutrients (if the grass is mowed and removed to a landfill)

4. Removal of metals (somewhat temporary though)

III.Middle-of-Pipe BMP’s (cont.)

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Problems include:

1. Irrigation requirements, in an arid region this may mean several feet of water.

2. Maintenance requirements.

3. Possible disposal problems associated with the clippings if they contain metals.

4. These systems only work well if the grass is of a particular height. What if the grass is too long when it rains?

III.Middle-of-Pipe BMP’s (cont.)E. Overland flow type pipes. (cont.)