HYDROLOGIC CYCLE
The cycle which describes how water moves from place to place in the environment and changes from one form to another is the hydrologic cycle. Because this cycle will be discussed in detail in ENV 101, it will not be reviewed here. Nonetheless, it should be noted that less than 1% of the total amount of water on the planet consists of fresh water in rivers, lakes, and groundwater; this is the water that we use for drinking, bathing and other personal activities as well as for irrigation and industrial purposes. While the number 1 use of water is for agriculture in terms of personal use of water, we in the U.S., each use 600 liters per day (usage is higher than this in the summer. Most water is used for toilet flushing and bathing. In the United States, all the water that we use is of a quality fit to drink.
Of the 1% of fresh water resources, only a minuscule is present in rivers, streams and lakes and 96.5% is found beneath the surface of soil as ground water.
Rain water is the ultimate source of all fresh water and depending on patterns of local precipitation, there are some areas of the world where water resources are limited. In fact, there is worldwide concern about the future of water resources. Problems such as excessive pumping of groundwater and pollution of surface waters in some areas have greatly augmented this concern.
SOURCES OF WATER: Groundwater and Surface Water
Approximately half of all Americans and more than 95% of farm families depend on groundwater for their drinking water supplies and 40% of water used for irrigation in the United States is drawn from groundwater resources. (Ref. Nadakavukaren) Although we will discuss this in detail in ENV 101, groundwater exists in aquifers which is the layer right beneath the water table where the spaces between rock particles are completely filled with water. The amount of water that an aquifer can hold depends on its porosity or the ratio of the spaces between the rock particles to the total volume of rock. Aquifers may range from a few feet to several hundreds of feet in thickness and they occur at various depths beneath the soil. Wells are drilled into these aquifers to tap into groundwater supplies.
The advantage of groundwater is that it is generally cleaner and purer than surface water because the rocks and soil through which it runs filters out most of the bacteria, suspended materials, and other contaminants. Although the extent of groundwater pollution is thought to include only .5-2% of total reserves, frequently these cases occur in populated areas where the aquifer is the principle source of local drinking water. (Ref. Nadakavukaren) Nonetheless, potential sources of pollution include private septic systems, dumps, landfills, underground storage tanks (especially gasoline tanks), irrigation practices, mine drainage, field application of pesticides or manure, and others. As noted above, one of the biggest concerns is groundwater depletion.
Nadakavukaren discusses in detail the sources of pollution for surface waters. The Clean Water Act (see below) has greatly improved the quality of the waterways in the United States, although we still have a long way to go before meeting all the goals of this Act. Worldwide, controlling pollution of waterways varies considerably from country to country.
Point sources of waterway pollution (i.e. pollutants that enter waterways at well-defined locations) include sewage treatment plants and industrial discharges. Nonpoint sources (those that run or seep into waterways from broad areas with no one definable source) include urban street runoff, construction site runoff, agriculture (leading source of water pollution), and mine drainage and fallout of a large number and variety of airborne pollutants.
CLEAN WATER ACT (CWA)
The purpose of the CWA is to control pollution at the source. The CWA prohibits the discharge of pollutants from point sources into the navigable waters of the United States.
SAFE DRINKING WATER ACT (SDWA)
SDWA was enacted in 1974 in response to the discovery of organic chemicals and other pollutants in municipal drinking water supplies. It is different from other environmental laws in that it regulates those who provide a product, in this case, drinking water, rather than those who generate pollutants. Numerous amendments were made to the SDWA in 1986 and in 1996.
Provisions of Act (including amendments)
2. MCLs or Maximum Contaminant Levels are established for the 83 pollutants based on economically and technically feasible technologies. The pollutants and MCLs are listed on pages 18 and 19 of "Water On Tap: A Consumers Guide to the Nation’s Drinking Water" (EPA Pub. No. 815-K-97-002, July 1977). The regulated chemicals include inorganic chemicals, organic chemicals, and trihalomethanes. These are discussed below. EPA generally sets MCLs at levels that will limit an individual’s risk of cancer for that contaminant to one case in a million over a life time. For non-cancer effects, the risk assessment estimates an exposure level below which no adverse effects are expected to occur.
3. The SDWA establishes a program to protect underground sources of drinking water from contamination by pollutants and prohibits the use of lead in solder in pipes.
4. Some of the most significant changes in the 1996 amendment required EPA to publish a list of contaminants known to occur in drinking water but had not yet been regulated. Also, EPA must determine whether or not to regulate at least five contaminants every five years beginning in 2001. Especially noteworthy among the 1996 amendments were the requirements to provide consumers with more information about the quality of their drinking water and what is being done to protect them. For example, water systems now have 24 hours to inform their customers via the media of violations of EPA standards that have the potential to have serious adverse effects on health, what these effects are, what is being done to resolve the problem, and the need to use alternative water supplies until otherwise notifed. Further, as of 1998, states are required to compile information about the quality of individual water systems and make this information available to customers.
1. What percentage of the total amount of water on the planet consists of freshwater?
2. What are the sources of freshwater?
3. Define aquifer.
4. What is the advantage of using groundwater as a drinking water supply?
5. List the various sources of pollution of groundwater and surface water. Which of these are point sources and which are non-point sources?
6. List the major provisions of the Safe Drinking Water Act.
OTHER LEGISLATION
The SWTR was originally passed to control the amount of Giardia in water. Cryptosporidium was not included in this rule. Since the SWTR was passed in 1989, numerous outbreaks of disease due to Cryptosporidium have occurred, and thus it was realized that water distribution systems had to also control quantities of this organism. As a result, an interim Enhanced Surface Water Treatment Rule was published in 1994. This rule asked for public comment on the control of Cryptosporidium, Giardia lamblia , and enteric viruses. The final rule has not been published.
Other legislation currently pending for drinking water deals with the amount of disinfectants to add to drinking water. This Disinfectants/Disinfection by Products Rule is aimed at reducing the concentration of trihalomethanes and other substances produced as a result of the disinfection process.
Biological Hazards of Drinking Water
Chemical Hazards of Drinking Water
TREATMENT OF DRINKING WATER
Treatment of Drinking Water
See field trip to Blue Plains for description of wastewater treatment which is qualitively very similar to drinking water treatment (Ref. Nadakavakaren)
Basic Steps (for removal of microorganisms)
1. SEDIMENTATION - Incoming water is heald in a pond or tak for 24 hours to allow the heavy suspended materials to settle out.
2. COAGUALATION - Alum is added to cause smaller suspended solids to form flocs. These then precipitate to the bottom of the tank.
3. FILTRATION- The water is filtered through beds of sand, crushed anthracite coal, or diatomaceous earth. This removes any remaining suspended solids as well as bacteria and protozoa.
4. DISINFECTION - Used to kill pathogens in water. Chlorine is most commonly used.
HOW ARE CHEMICALS REMOVED?
Currently ion exchange resins are used to remove heavy metals and activated charcoal filters are used to remove synthetic organic chemicals. We are constantly searching for new methods.
TESTING PROCEDURES TO ENSURE WATER QUALITY
Although turbidity, biological oxygen demand, (BOD) and coliform testing are used to determine the effectiveness (or in the case of BOD to determine the health of a receiving body of water), treatment only coliform testing will be discused here.
Coliform Counts for Assessing the Quality of Drinking Water
Although E. coli is normal flora in the human intestine, the organism is found in much higher numbers and is easier to grow then the human pathogens. Thus, the detection of this organism adds a built-in safety factor for detecting potentially dangerous fecal contamination. Although positive tests for E. coli do not prove the presence of pathogens, they do establish the possibility.
The test is based on the identification of E. coli in the water sample by observing its growth characteristcs and chemical reaction in various media i.e. E. coli ferments lactose with the production of gas and produces a green metallic sheen on EMB (Eosin methylene blue) agar. (Note: on the Coliscan agar used in the water treatment lab exercise, E.coli colonies appeared as dark pink or purple colonies, indicating the presence of acid byproducts from the fermentation of lactose.)
Drinking water supplies may have no more than one organism/100ml of treated drinking water.
Cryptosporidium belongs to a group of obligate intracellular protozoa named the coccidi. Major reservoirs and routes of transmission of human cryptosporidiois are zoonotic (animal to man), environmental (indirect), and person-to-person. Person-to-person transmission has been responsible for outbreaks in daycare centers, hospital-acquired infections, and traveler’s diarrhea in underdeveloped countries. Water is the most important environmental vehicle of transmission.
Table I summarizes the outbreaks of figure I cryptosporidiosis that have occured and Figure I shows all the factors that play a role in transmission. Only a few key facts will be mentioned here.
As indicated in Figure I, waterborne cryptosporidiosis has been associated with water supplies contaminated with infected livestock effluent or human sewage effluent. The studies of several authors report the relative contribution of animals or human excreta to be unknown. Studies of the New York City Department of Environmental Protection in conjection with Cornell University have shown that when Giardia and Cryptosporidium are detected, they are detected most often in the discharge of wastewater treatment plants, followed by urban watersheds, agricultural watersheds, and least often in undisturbed watersheds. This, of course, still does not answer the question of the relative contribution of these to waterborne outbreaks.
Most of the studies concerning primary source problems of Cryptosporidium have focused on agricultural interventions to limit infected livestock effluent. Most of these studies have been conducted by Cornell University.
A nationwide study has shown that more than 20% of 1-3 week-old dairy and beef calves are positive for Cryptosporidium. (Although there is no documented evidence, young horses, swine, sheep, dogs, cats and rodents probably also serve as sources of oocysts on farms. In order to prevent infection, calves 0-6 months of age, must be spearated from older dairy cows and provided with a clean, dry and well-ventilated environment; the latter may be accomplished by adding ventilation to an existing structure that houses 0-6 month old animals or building double-layer plastic greenhouses for these animals. Studies show daily cleaning of bedding reduces the likelihood of infection as does addition of bedding in some circumstances. Practices in the handling of calf manure are also being investigated such as the separation and treatment of this manure, or if it is mixed with dairy manure, ensuring that it is spread on non-hydrologically sensitive areas. Other strategies for the control of Cryptosporidium parvum infection in calves have focused on the use of oral vaccines or antibiotic treatment.
Drinking Water Treatments to Remove Cryptosporidium
Several studies have focused on the best way to remove Cryptosporidium from drinking water. Although several conventional granular filtration methods when operated correctly and under appropriate coagulation conditions remove Cryptosporidium to a level that probably will be acceptable in the new legislation. They do not remove all the organisms. As a result, many water treatment facilities are using more advanced (and more expensive!) filtration methods known as microfiltration and ultra filtration. Although these methods will not be discussed here, they do remove all organisms.
Environmental Detection Methods It should be noted that there are numerous limitations of the environmental methods for detecting Cryptosporidium.
Because of the limitations of the reference method, "a negative result does not necessarily mean the water is not contaminated with pathogenic protozoa and a positive result does not necessarily indicate a public health threat" (Ref. Rose). Accordingly, the current recommendation for issuing a public health notice concerning the potential contamination of drinking water is for public health officials to examine the protozoa monitoring results within the total context of source water quality and treatment plan efficiency; a single positive immunofluoresence result is not sufficient to trigger the initiation of a public health alert and concomitant precautionary measures.
Susceptible Individuals
Individuals who are most susceptible to Cryptosporidium are immunocompromised patients including patients with AIDS. Cryptosporidium may be fatal in AIDS patients.
EPA and CDC have developed guidelines for severely immunocompromised people who may wish to take extra precautions to avoid the possibility of developing cryptosporidiosis. "Although data are not sufficient for EPA/CDC to recommend that all severely immunocompromised persons take extra caution with regard to their drinking water, individuals who wish to take extra mesures to avoid waterborne cryptosporidiosis can bring their drinking water to a rolling boil for one minute. Boiling water is the most effective way of killing Cryptosporidium. As an alternative to boiling water, people may use a point-of use (personal use, end-of tap, under sink) filter or bottled water.
1. What are the biological hazards of drinking water?
2. What are the chemical hazards of drinking water?
3. List and define the steps in drinking water treatment.
4. How are chemicals removed from drinking water?
5. Discuss the coliform count for testing the quality of drinking water.
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