The Safe Drinking Water Act (SDWA) requires that all public water systems sample and test their water supplies for all contaminants with MCLs. The exact type and frequency of testing depends on the seriousness of any potential adverse health effects and on state and local regulations. Those concerned about their drinking water quality
TABLE 14.1. Recommended Water Tests Test Name
Bacteria (total coliform)a Nitratea
Lead
Volatile organic chemical scana Hardness (total)
Iron Manganese Sodium pH
Corrosivity
Radioactivity (gross alpha)a Mercury
Source: Adapted from Shelton, 1989.
MCLor SMCL None detected
10 mg L-i NO) 0.05 mg L-i
If positive, retest for specific chemicals 150 mg L-i
0.3 mg L-i 0.05 mg L-i 50 mg L-i 6.5-8.5
Langelier index ±l.0 5 L-i pCi
0.002 mg L-i
aDenotes an MCL based on health standard. Additional pollutants, depending on concerns, include arsenic, barium, chromium, lead, selenium, silver, and fluoride.
508 SOIL AND WATER DECONTAMINATION TECHNOLOGIES
could obtain the complete water test results required under the SDWA directly from the local water utility. The recommended tests for such water systems are given in Tables 14.1 and 14.2.
Table 14.2. Additional Water-Testing Recommendations for Common Problems or Special Situations
Problem Common Signs/Situations
"Hard" water Large amount of soap required to form suds.
Insoluble soap curd on dishes and fabrics. Hard scaly deposit in pipes and water heaters Rusty colored Rust stains on clothing and
water porcelain plumbing.
"Rotten egg"
odor
Metallic taste to water.
Rust coating in toilet tank. Faucet water turns rust-colored after exposure to air
Iron, steel, or copper parts of pumps, pipes, and fixtures corroded. Fine black particles in water (commonly called black water). Silverware turns black
"Acid" water Metal parts on pump, piping, tank, and fixtures corroded. Red stains from corrosion of galvanized pipe; blue- green stains from corrosion of copper or brass
Cloudy turbid Dirty or muddy appearance water
Chemical odor of fuel oil Unusual
chemical odor
Well near abandoned fuel oil tank; gas station
Well near dump, junkyard, landfill, industry or dry cleaner
Causes Calcium, magnesium,
manganese, and iron (may be in the form of bicarbonates, carbonates, or chlorides)
Iron, manganese, or iron bacteria
Hydrogen sulfide gas, sulfate-reducing bacteria, or sulfur bacteria
Carbon dioxide. In rare instances mineral acid- sulfuric, nitric, or hydrochloric
Silt, sediment, micoorganisms Leaking underground
storage tank
Groundwater contamination,
underground injection, or leaching waste site
Test Recommended Hardness test
Iron test Manganese test
Hydrogen sulfide test
pH Langelier index
Check well con- struction with local well driller Volatile organic
chemical scan or specific fuel component Check with Health
Dept., Organic chemical scan, heavy metals
(continued)
14.3 IN SITU TECHNOLOGIES Table 14.2. Continued
Problem No obvious
problem Recurrent
gastro-in- testinal ill- ness Sodium re-
stricted diet; salty, brackish, or bitter taste
Common Signs/Situations Well located in area of
intensive agricultural use Recurrent gastro-intestinal
illness in guests drinking the water
Well near seawater, road salt storage site, or heavily salted roadway
Source: From Shelton, 1989.
Causes
Long-term use of pesticides and fertilizers
Cracked well casing, cross connection with septic system
Saltwater intrusion, groundwater contamination
509
Test Recommended Test for pesticides
used in area, nitrate test.
Bacteria (coliform test) nitrate test
Chloride, sodium, total dissolved solids (TDS)
Throughout this book, emphasis is placed on the reactions between soil and water and how such reactions control the composition and/or quality of soil and water. In this section, the focus is on water quality with respect to household uses, including drinking. A goal of the modern environmental soil chemistry discipline is to ensure that the degradation of natural water is kept to a minimum when land (soil) is used for producing food or for any other purpose (e.g., industrial development). However, even with the best intentions, water quality is affected to some degree by humans or by nature in general, and not all water on the earth's surface is suitable for household uses, including drinking. For this reason, prior to using much of the surface- or groundwater, testing and further treatments are necessary to make such water suitable for human consumption.
14.5.1 Some General Information on Water Testing
A problem that has often been reported with drinking water is the presence of lead, a heavy metal. Shelton (1989) outlined the following steps to minimize human exposure to lead:
1. Flush the plumbing to counteract the effects of "contact time." Flushing involves allowing the cold faucet to run until a change in temperature occurs (minimum of 1 min).
2. Hot water tends to aggravate lead leaching when brought in contact with lead plumbing materials.
3. Water-treatment devices for individual households include calcite filters and other devices to lessen acidity which increases lead release.
4. Use lead-free materials for repairs and installation of new plumbing.
510 SOIL AND WATER DECONTAMINATION TECHNOLOGIES
5. Lead can be removed from tap water by installing ion-exchange filters, reverse- osmosis devices, and distillation units.
14.5.2 Microbiological Maximum Contaminant Levels
The standard bacteriological method for judging the suitability of water for domestic use is the coliform test. It detects the presence of coliform bacteria, which are found in the natural environment (soils and plants) and in the intestines of humans and other warm-blooded animals. Any food or water sample in which this group of bacteria is found is to be suspected of having come into contact with domestic sewage or animal manure. Such a water supply may contain pathogenic bacteria and viruses responsible for typhoid fever, dysentery, and hepatitis (Shelton, 1989).
The two standard methods for determining the numbers of coliform bacteria in a water sample are the multiple-tube fermentation technique and the membrane filter technique. In the multiple-tube fermentation technique, a series of fermentation tubes containing special nutrients is inoculated with appropriate quantities of water to be tested and incubated. After 24 hr, the presence or absence of gas formation in the tubes is noted. In the membrane filter technique, a quantity of water is filtered through a specially designed membrane filter which traps bacteria. The filter, with certain specified nutrients, is incubated for 24 hr. The results are usually expressed as number of coliform colonies per 100 mL of water sample. Currently, emerging waterborne pathogenic organisms of parasitic OO/cysts of Giardia and Cryptosporidium are a major concern. They are distributed ubiquitously in pristine and human impacted water. The concern about pathothegic organisms has arisen because methods of analysis are inefficient and expensive (Shelton, 1989).
When water destined for drinking does not meet federal and/or state standards, appropriate treatments are introduced. Some of the current technologies used to meet federal water drinking standards are briefly discussed below.
14.5.3 Activated Carbon Filtration
This technology is effective for certain chemicals, including pesticides, radon gas, chlorine, and trihalomethanes, as well as for odor. The carbonaceous material made from bituminous coal, lignite, peat, or wood is activated (pore formation) under high heat by steam, but in the absence of oxygen. Organic contaminants present in water are sorbed by the pore surfaces formed during activation. They are specifically effective in removing organic contaminants with low solubility (e.g., pesticides, benezene, and chlorinated hydrocarbons).
14.5.4 Air Stripping
The technology involves air-stripping columns where water flows downward by gravity while air is pumped upward. As the water flows down and passes over a packing
14.3 IN SITU TECHNOLOGIES 511 material possessing a large air-liquid interphase, the volatile organic compounds (VOC) are transferred from the water to the air. It is effective in removing organic as well as inorganic contaminants including hydrogen sulfide. The efficiency of VOC removal by air-stripping columns depends on the type of VOCs present in the water, air:water ratio, type of packing material, height of packing material, temperature of the water and air, and concentration of VOc.
14.5.5 Disinfection
Disinfection destroys microorganisms capable of causing disease in humans. Some methods of disinfection are chlorination, chloramines, ozone, ultraviolet light, as well as chlorine dioxide, potassium permanganate, and nanofiltration. Disinfection kills disease-causing organisms and inactivates Giardia Lamblia cysts and enteric viruses.
There are two kinds of disinfection: primary, which kills or inactivates microorgan- isms, and secondary, which protects the finished water from regrowth of microorgan- isms.
The EPA Surface Water Treatment Ruse (SWTR) requires public water supplies, under the direct influence of surface water, to be disinfected. Some disinfectants produce chemical by-products; SWTR requires that their concentration remain within the MCL. Currently, one such by-product is trihalomethanes. Water disinfection is effective when combined with conventional treatment, such as coagulation, floccula- tion, sedimentation, and filtration. The latter is accomplished by sand or diatomaceous earth. The effectiveness of disinfection is evaluated by determining total coliform bacteria which are not pathogenic, but their presence suggests that certain pathogens may have survived. The various chemicals commonly used as disinfectants are presented below and some of their advantages and disadvantages are listed.
Chlorine. It is a toxic, yellow-green gas under normal pressures but becomes a liquid under high pressures. It is very effective as both a primary and secondary disinfectant.
It is lethal, however, at concentrations as low as 0.1 % by volume.
Sodium Hypochlorite Solution. It is available as a solution in concentrations of 5-15% chlorine and for this reason is easier to handle than chlorine gas. However, sodium hypochlorite is very corrosive and easily decomposes.
Solid Calcium Hypochlorite. It is a white solid in granular, powdered, or tablet form that contains 65% available chlorine, easily dissolves in water, and is very stable in the absence of moisture. However, calcium hypochlorite is corrosive with a strong odor and readily adsorbs moisture-forming chlorine gas. Reactions between calcium hypo- chlorite and organic material can cause a fire or explosion.
Chloramines. It is formed when water containing ammonia is chlorinated or when ammonia is added to water containing chlorine (hypochlorite or hypochlorous acid).
It is an effective bactericide and produces fewer disinfection by-products. However, chloramine is a weak disinfectant (less effective against viruses or protozoa than
512 SOIL AND WATER DECONTAMINATION TECHNOLOGIES
chlorine) and is more appropriate as a secondary disinfectant to prevent bacterial regrowth. When water pH is below 5, nitrogen trichloride appears to form. It may be harmful to humans and produces undesirable taste and odor. Using the proper amount of the chemical avoids such problems.
Ozone. It is a gas composed of 3 oxygen atoms. It is a powerful oxidizing and disinfecting agent formed by passing dry air through a system of high-voltage electrodes. Ozone is widely used as a primary disinfectant in many parts of the world, partly because it does not produce halogenated organic substances unless bromide is present. However, it is very unstable and must be generated on site. Because of this instability, it does not maintain an adequate residual in water and chlorine is required as a secondary disinfectant.
Ultraviolet Light (UV). It is generated by a special lamp and disrupts cell division processes. It is highly effective against bacteria and viruses, has no residual effects, and thus does not produce any known toxic by-products. However, UV does not inactivate Giardia Lamblia or Cryptosporidium cysts and it is not suitable for water with high levels of suspended solids, turbidity, color, or soluble organics. These materials absorb the UV radiation, reducing disinfection performance.
14.5.6 Distillation
In this technology, water is heated until it turns to steam, which is then condensed as distilled pure water, free of most dissolved or any solid contaminants including bacteria and viruses. Because distilled water is free of all minerals, it may not be ideal for drinking. Furthermore, certain organic contaminants with a lower boiling point than water (e.g., pesticides) evaporate with the water and end up with the processed water.
Advanced distillation units could eliminate this problem.
14.5.7 Ion Exchange
This is a process by which ions that are dissolved in water are transferred to, and held by, a solid material or exchange resin. It is a process commonly used for softening water. When water containing dissolved cations associated with hardness (e.g., Ca2
+, Mg2+, Fe2+, and Mn2+), as well as heavy metal or radioactive cations, contacts the resin, the cations are exchanged for the loosely held sodium ions on the resin. The process makes the water "soft."
Eventually, the resin loses all of its sodium ions; thus, no more cations associated with hardness can be removed from the incoming water. The resin at this point is
"recharged" or "regenerated." This involves replacement of the cations associated with hardness by Na, having as its source NaC!. The water used during this process is discarded. Anion exchange may also contain relatively high levels of anions (e.g., nitrates and sulfates) (Shelton, 1989).
14.6 BOTILEDWATER 513 14.5.8 Mechanical Filtration
This process removes dirt, sediment, and loose scale from the incoming water by employing sand, filter paper, or compressed glass wool or other straining material.
These filters will not remove any dissolved substances.
14.5.9 Reverse Osmosis
This technology successfully treats water with high salt content, cloudiness, and dissolved minerals (e.g., metal sulfate, metal chloride, metal nitrate, metal fluoride, salts, boron, and orthophosphate). It is effective with some detergents, some taste-, salt-, color-, and odor-producing chemicals, certain organic contaminants, and specific pesticides. It works by passing water under pressure through cellulosic or noncellulosic (polyamide) membranes. It removes 90-95% of most dissolved contaminants and, when membrane density is in the submicron range, may remove many types of bacteria. However, reverse osmosis is a slow and wasteful process. In some systems, for every gallon of portable water obtained, approximately 4-6 gal of water will be discarded (Shelton, 1989).