Chapter 17

General Principles The fresh groundwater and surface water on

the continents constitutes less than 1% of the water in the hydrosphere

Any natural water contains dissolved chemicals – some are unhealthy and some are produced by a variety of human activity (agriculture, industry, and as people live)

General Principles:Geochemical CyclesResidence TimeResidence Time and PollutionPoint and Non-point Pollution Sources

Geochemical Cycles All of the chemicals in the environment

participate in geochemical cycles of some kind, similar to the rock cycle

Simplified cyclea. Precipitationb. Weatheringc. Ions transported as dissolved load in stream or ground

waterd. Minerals precipitate out and cycle continues

Many systems become more complex because of subcycles

Simplified calcium cycle

Residence Time Residence Time = Capacity/Rate of Influx

Residence Time – how quickly a substance cycles through each of reservoirs

Capacity – maximum concentration of a substance a reservoir can reach before saturation occurs

Rate of Influx – how much of a substance a stream or ground water system brings into the reservoir

Oceanic residence times for different elements vary widely

Humans can alter the rate of influx or other parts of this equation by our activity

Residence Time and Pollution

Residence times for many natural compounds are known and understood

Residence times for more complex chemicals and compounds, including synthetic ones, are not well known

Chemical behavior of complex and synthetic compounds often need time to be studied and understood – that time isn’t always available before these compounds are introduced into the market place

Point and Nonpoint Pollution Sources

Sources of pollution may be subdivided into two categories

1.Point source – pollution enters a system from one, identifiable spot. The point sources are often easier to identify as potential pollution problems

2. Nonpoint source – pollution enters a system from multiple and more diffuse sources. We can still identify them by using natural geochemical tracers

Point sources of water pollution

Organic Matter Nature and Impacts

In general organic matter is the substances of living or dead organisms and their by products○ Algae in a pond○ Human or animal waste○ Run off from an animal feedlot○ Discharge from food processing plants○ Run off from municipal streets or highways

In time organic matter is broken down by microscopic organisms (bacteria)○ If ample oxygen is available then aerobic

decomposition occurs○ If oxygen is depleted then anaerobic decomposition

occurs

Uncontrolled runoff from a livestock yard

Organic Matter Biochemical Oxygen Demand (BOD)

Measure of organic-matter load in a body of waterBOD of a system is the measure of the amount of

oxygen required to breakdown the organic matter aerobically○ The more the organic matter, the higher the BOD

BOD may exceed the amount of dissolved oxygen in the system

An oxygen sag curve is a graph of dissolved oxygen content as a function of distance from a waste source

Organic Matter Eutrophication – complex breakdown of excess

organic matter that enriches water with plant nutrients (nitrates, phosphates, and sulfates)plants such as algae thrive on these nutrients and can

produce algal bloomsAlgal growth proceeds in the photic zone and chokes

out other plantsThese dead plants drop to the bottom of the pond

where they become part of the organic-matter load and increase the BOD

This process consumes oxygen and re-releases abundant nutrients into the water and the cycle is repeated

Layers of water become depleted in oxygen and will kill oxygen dependent animals

Industrial Pollution

Hundreds of new chemicals are created by industrial scientists each year

Out of 66000 drugs, pesticides, and other industrial chemicals, no toxicity data at all were available for 70% of them; a complete health hazard evaluation was possible for only 2%

In 1990, more than ten million new chemicals have been created or identified since 1957

It is not possible to have a complete toxicity assessment for many substances

Industrial Pollution Con’t. Inorganic Pollutants – Metals

Manufacturing, mining, and mineral processing activities can increase the influx of metals to a system

These increases can range from natural levels to toxic levels

Some metals, such as heavy metals which include cadmium, lead, mercury, plutonium, and others, will accumulate in the bodies of simple organisms

These simple organisms are food for more complex organisms and concentrations of heavy metals increase up the food chain

In humans, heavy metals can cause central nervous system problems and brain damage; usually these are irreversible

Heavy metal poisoning can cause death or cancer

Industrial Pollution Other Inorganic Pollutants

Nonmetallic elements can reach toxic levels in aquatic systems○ Chlorine, used to kill bacteria in municipal

waste water systems, can kill algae and harm fish populations

○ Acids, from industrial plants or mine drainage, may act to leach out toxic metals from rocks or mine tailings

○ The toxic effects of certain asbestos minerals were not manifested or well defined until long after initial release into the environment by human activities

Industrial Pollution Organic Compounds (carbon containing compounds)

New herbicides, pesticides, and insecticides are created each year○ Some are toxic or carcinogenic to humans○ Examples include DDT and dioxin

Oil spills occur each year from intentional dumping and accidental spillage

Other compounds such as PCBs and MTBE are found in natural systems

Problems of ControlAs efficiency of removal of pollution substances increase,

the costs tend to sky rocketFew systems to treat this waste are 100 % cleanThe benefits of these compounds sometimes out way the

risk or the cost

Industrial Pollution Con’t. Thermal Pollution – release of excess or waste

heat into the environmentExcess heat is given off as a by product of

generating powerWaste heat is given off from automobiles or heating

systemsImpact may not be apparent to humans but to fish

and migratory animals it can be devastating○ Streams kept unseasonably warm may trap warm-

water dependent animals near power plants○ Local food supply may be stripped of the food these

animals need

Agricultural Pollution Pollution associated with agricultural activity

1. Fertilizers and Organic Waste○ Nitrates, phosphates, and potash are common

constituents of fertilizer○ Fertilizers, when not applied to the land correctly,

buildup toxic levels in run off water○ These fertilizers contribute to eutrophication problems○ Proper application of fertilizers, plus crop rotation

strategies, may help reduce these problems○ Animal feedlots create problems because of the

concentration of many animals in a small area○ Rain runoff will dissolve nutrients and carries them into

the environment

Agricultural Pollution Con’t.

2.Sediment PollutionFarmland is exposed to wind and rain that can

carry away soil into local waterwaysThis loss is typically fine-grained sediments that

choke waterways and reduce sun light penetration

Fish, animal, and plant success is reduce by murky water

Solutions require planning such as contour plowing, terracing, and installing wind breaks and settling ponds

Surface runoff and settling pond

Agricultural Pollution Con’t.

3.Herbicides and PesticidesFarmers are using these chemical additives at all

time high ratesInappropriate use can expose animals and

humans to toxic levels of pollutionOften application of more chemical than is needed

occurs and too much is wasted and runs off into streams (for example: DDT)

New technology and education may help reduce this hazard in the future

Reversing the DamageSurface Water

1.Dredging:of a pond, or lake, may permanently remove

the fine sediments that are laden with toxic compounds that are attached to the sediments

We must be sure these dredged sediments are removed from the environment also

An expensive but often necessary operation in many places in the future

Reversing the DamageSurface Water

2.Physical Isolation or Chemical Treatment of SedimentsBarriers can be constructed to isolate polluted

sediments in a pod or portion of a streamPlastic (impermeable) liners can also isolated

toxic water in a systemCareful addition of salts of aluminum, calcium, or

iron to phosphorous laden sediments may reduce the risk of eutrophication

Reversing the DamageSurface Water

3.DecontaminationToxic spills often require treatment to

decontaminate water, animals, and sediments

4.AerationOxygen levels in a lake that is oxygen-

depleted can be restored by aerationA simple fountain may be required to keep a

decorative pond from eutrophication in an area where fertilizers are used

Groundwater Pollution Pollution is difficult to detect and remediate since

groundwater is not visible Requires testing and monitoring A matter of routine for municipalities, but a

burden for a single private well homeowner A significant time lapse between the introduction

of a pollutant into the system in one spot and its appearance in ground or surface water elsewhere

But, groundwater pollution in karst areas may spread unexpectedly swiftly

Groundwater Pollution Recharge zones must be protected from improper use

of herbicides, pesticides, and insecticides Polluted recharge water will pass into the subsurface

where they may remain dissolved and can result in pollution of ground water

Residence times are important because recharge water may be discharged from a well before the residence time has elapsed

Migration of polluted ground water by a pollution plume can result from a point source

Monitoring wells and knowledge of ground water flow direction and flow rates are required to remediate a pollution plume

Often they are found near landfills, waste sites, or abandoned tanks

Reversing the DamageGround Water1. Often the most effective and economical way to

treat polluted ground water is allow natural processes to remove or destroy pollutants

2. Commonly, polluted groundwater is only treated after it is extracted for use

3. Decontamination after extraction, also called pump-and-treat, is useful if ground water is needed before residence times elapse

4. Air stripping, where air is pumped into the extracted water laden with volatile organic pollution, transfers the pollution into air rather than leaving it in the water

5.Activated charcoal filters and absorbs many organic compounds from water