Introduction
Cotey Chemical Corporation was founded in Lubbock, Texas, in 1949 by Mr. Bradford J. Cotey. Our mission is to provide products which can be safely and easily applied by non-technical personnel for maintenance, development or sterilization of household, industrial and irrigation water wells.
Cotey Chemical has, during almost half a century, developed a well-earned reputation for leadership in the marketing of superior products for the water well industry. Satisfied clients, located throughout the United States and many foreign countries, substantiate the attainment of Mr. Cotey's motto - "BETTER WELLS WITH COTEY CHEMICALS".
This manual is provided for guidance in the use of Cotey Chemical Products. Data is based on the latest information available, but the particular suitability for specific applications should be substantiated by each user's own tests.
Data provided in this manual must be considered as being provided and accepted at each individual's risk. Cotey Chemical Corporation guarantees no specific results and cannot assume obligation or liability in connection with supplied products.
Chemical Treatment of Water Wells
Any water well can be treated with any number of chemicals at any time, but such treatments do not necessarily benefit the well or increase productive capacity. For example, water wells developed in crystalline rock (granite, diorite, monzonite, etc.) can seldom be improved by acid treatments, and no chemical can increase the production of wells which have simply pumped all of the available water. It is therefore important, when considering a chemical stimulation program, to correctly identify the reason(s) for the decreased well yield. COTEY CHEMICAL personnel will gladly help you with such problems.
Decreased water well yields may result from many independent, or several contributory factors. The proper steel may not have been used during well construction and considerable corrosion of the well screen or casing may have occurred. Pumping velocities may have been excessive, or a poor gravel-pack construction may be allowing passage of excessive amounts of silt and clay. Unfortunately, the reasons for such problems cannot be corrected with chemicals, although the results may be correctable on a short-term basis. Commonly, the initial yield of a well may decrease because of movement of the well screen or casing, or because of incrustations of calcium carbonates and iron and manganese hydroxides/hydrated oxides and bacterial slimes, or because of simple silt and clay plugging. Recent developments and uses of various exotic metal alloys and plastics for well casings and screens, many contractors believe, prevent incrustation problems, but studies document that plastic screens and even fiberglass pipes do experience incrustation problems in many areas. The problems can be successfully alleviated by chemical treatments - particularly by using products developed by COTEY CHEMICAL. Thus, let's examine each of the principal clogging mechanisms, the recommended treatment programs needed for correction, and the specific COTEY products.
First though, a word about the time necessary for good chemical treatment of a water well. The speed of almost any chemical reaction is more or less proportional to the temperature, thus, the warmer the well water the faster will be the reaction time to COTEY'S chemicals and the shorter the down time. Unfortunately, in most cases well water will be cool (<60 degrees F), thus the time needed for adequate chemical treatment may seem unusually long and, in many cases, is often cut short by impatient landowners, drillers, or service companies. This is, of course, tantamount to using the wrong chemical or less than required amounts of the right chemical, either one of which is bad business for all concerned. COTEY therefore recommends that if the well cannot be shut down for the needed time period, the chemical treatment should be postponed until the required "down time" can be scheduled.
This manual attempts to outline the various specific uses and applications of COTEY CHEMICAL'S products, and a summation of each product is given in the Product Sheets section. The use of complex chemical equations, technical terminology, and involved reactions is kept to a minimum although a certain familiarity is required for a competent knowledge on the part of representatives, service companies, and local advisory personnel. COTEY CHEMICAL realizes that wells often exhibit what might be termed "individual chemical idiosyncrasies", thus COTEY encourages product users to contact the company for technical assistance. COTEY can also supply professional supervisory personnel for development of a large deep well or the treatment of a large well field.
What Makes a Good Water Well
There are three main ingredients that go into making a good water well: the drilling, the pumping and the development. The first two are indispensable since an opening of some kind has to be made into the water bearing formation and some means has to be supplied for lifting the water to the surface even if it's only a bucket tied to the end of a rope.
Under drilling we can include all the various methods used: direct and reverse circulation rotary, cable tool, scow, driven points and even hand dug wells. Also, we can include running the casing, setting the screen, strainer or liner, cementing, undereaming, gravel packing and all other work done in connection with the construction of the hole.
Under pumping we can include all means of artificial lift, such as deep well turbine, jet, rod, submersible, centrifugal and other pumps. We can also include air-lift and natural artisan flows.
The third ingredient, the development of the well is too often neglected. Many wells are drilled and a pump installed and whatever flow is obtained is accepted even though it may not be as much water as is needed or desired. Many times it is assumed that this is all the water the formation will give up. That probably is not true and the flow could be increased with proper development.
There are many mechanical methods used for developing water wells such as: simply bailing the hole, pumping, back washing or back lashing with the pump, surging with the surge block, explosives, jetting, surging with compressed air, fracturing and other methods used in an effort to open up the perforations and formation by force.
You will note that in all of these mechanical methods the force or pressure being applied is from the well bore out into the formation which is the same direction as the force was applied that put any plugging in place during the drilling operation.
The method being accepted more and more as the most effective way to open up the perforations and the water bearing formation to increase the flow is the use of properly designed chemical treatments.
A great many chemicals have been dumped in wells in an effort to clean up the hole. Various acids have been used, soaps, detergents similar to household cleaners, water softening chemicals, chelating agents, wetting agents, carbide and believe it or not - even Alka-Seltzer has been used.
There are several requirements that any chemical should meet if it is to be used for treating water wells. First, of course, it should be effective in dissolving, disintegrating and dispersing commercial drilling muds, clays and shales so that they can be easily bailed or pumped out. It should be capable of dissolving limestone and water deposited scales, corrosion products and organic growths. It should be relatively non-toxic and should not contaminate the water. It should be safe to use on the mechanical equipment in the well. It should also be safe and easy to handle. From your standpoint, as the contractor or well service company, it should be a service you can perform without any additional equipment. For big jobs there are service companies available in some areas to chemically treat water wells. However, in most cases the cost is too high to justify their use. Consequently many wells are not treated that really should be.
Looking at it again from the contractor's or well service company's point of view, it is now possible, with the chemicals that have been developed specifically for treating water wells, to include chemical treating along with your other services thus adding additional profit to the job and at the same time making a better well for your customer.
Before any chemical treatment is considered it is necessary to admit or establish the fact that some water has been plugged off and that a chemical treatment is the easiest and most effective method of removing any plugging. Some drillers are reluctant to admit the possibility that some water may be plugged off during the drilling operation. They feel it may be a reflection on their ability and some claim that if the water is there they will get it. This is not always true as borne out by the fact that many old wells made more water after treatment that they did when first completed, showing that some water had been plugged off all the time.
When you consider the pressures and methods used in drilling you can see that for all practical purposes it is almost impossible to drill a well without plugging off at least some water.
With this chart we have tried to represent some of the things that happen when a well is drilled with the rotary method. These things will occur whether the drilling is by direct or reverse circulation. In order to drill a fluid must be circulated to remove the cuttings and hold up the hole. In most all cases mud is used. It can be commercial drilling mud or as happens in most wells, there's enough clay in the formation to make a heavy mud as drilling progresses. As the formation is penetrated a mud or filter cake is built up on the walls of the hole. The mud cake must be strong enough to hold the pressure of the column of mud in the hole; otherwise, you will lose circulation and all the mud will go back in the formation. If the mud is too thin the mud cake will build up too far back in the formation and will be more difficult to remove. If the mud is too heavy the mud cake may get too thick and stick the bit.
After the well is drilled it is necessary to remove all the mud cake if the well is to be developed to its maximum capacity. Using this illustration you will note that at the static water level of 200 feet the mud was put in place under 125 PSI pressure and at 300 feet it was 188 PSI. Now, after all the mud has been removed from the hole by bailing or pumping, the only pressure available to push the mud off the wall and out of the formation is the pressure of the water in the formation. At the static water level of 200 feet there is no pressure. At 300 feet the maximum pressure would be only about 43 PSI and this could only be if the formation had uniform vertical permeability which is rarely if ever found. There usually will be several clay or shale breaks which will reduce the total pressure.
So we have the following condition - mud put in place under 125 PSI at the static water level and no water pressure to remove it, and at 300 feet mud put in the formation at 188 PSI and at most, only 43 PSI water pressure to push it out. Naturally, the deeper the hole and the less standing water there is, the greater the differential pressure.
With cable tool or spudder drilling, the same thing occurs but the pressure is applied in a different manner. This drawing represents roughly what happens. As the heavy tool is raised and dropped a tremendous force is developed on the face of the bit. This force acts in a direction at right angles to the face of the bit. As a result as drilling progresses, the formation around the well bore is compacted and the mud and slush in the hole is pounded back into the formation. Here again, the only pressure available to remove any plugging is the water pressure in the formation which will never anywhere near equal the pressure built up by the heavy tool string. Scow drilling, driving casing and reaming also have similar action which tends to plug off some water. The effect of this plugging is naturally a lower
In a sand and gravel well you
wind up with a mud cake on the walls and the formation compacted
around the well bore. Since this is behind the casing or screen
and behind the gravel pack, purely mechanical means will not
be effective in removing it. In order to get maximum capacity
all the mud must be removed and the formation opened up to
allow free flow of water from the formation into the well bore.
Silts and Clay Buildups
Older water wells frequently experience yield declines due to the buildup of silt and clay in the aquifer near the well or in the well's gravel pack, whereas newly drilled wells may not yield expected amounts of water due to "mud-cake" partially sealing the aquifer. In many cases this "mud-cake", consisting of fine silts and clay particles, is partially cemented or consists of minute calcium carbonate fragments, however, standard treatment by many acids will aggravate rather than correct the problem. This results from the acids dissolving cations present in the clay, thereby allowing precipitation of free silicon dioxide (SiO2) as a gel. COTEY CHEMICAL therefore developed Dry Acid® which, not only dissolves the "mud-cake", but acts as a strong sequestering agent which prevents precipitation or flocculation of the silt and clay particles.
Dry Acid is also recommended for new wells, particularly if developed in carbonate aquifers. The Dry Acid will effectively prevent buildup of "mud-cake" if used during the drilling of the well or will quickly remove the "mud-cake" after the well has been drilled. Secondly, Dry Acid is to be recommended over the often used canister of single phosphates thrown down the well to "clean out the muds" because single polyphosphates act as a food source for algae, having no ingredient to kill bacteria and sterilize the well. Dry Acid , other than simply attacking carbonate content in the well, will also completely sterilize the well, certainly a tertiary benefit of major importance at minimal cost.
For wells developed in areas where carbonate is not a problem, "mud-cake", silts and clays, and even oil from oil-lubricated turbine pumps, can be removed by COTEY CHEMICALS Mud-Nox. Essentially, Mud-Nox (a 100 percent active biodegradable octyl phenoxy polyethoxy ethanol) is a superior wetting agent and emulsifier which disperses silts and clays, allowing the particles to be pumped to waste instead of collecting in the well. The emulsification properties insure that any oil in the well will also be mixed with water, and thus also ejectable to waste. Mud-Nox is compatible with all common solvents except the high aliphatics such as kerosene and gasoline.
Carbonate Scales
Probably more water wells experience decreased yields due to incrustations of calcium carbonate (CaCO3) or calcium magnesium carbonate (CaMg(CO3)2) than from any other type of incrustation. Carbonate scales form mainly in water wells producing from hard water aquifers, thus wells located in the hard water areas of the United States may experience such problems.
Carbonate scales are vigorously attacked by acids, the two most commonly used in the water well treatment industry being muriatic or hydrochloric acid (HCL) and sulfamic acid (NH2SO3H). Sulfamic acid is the basis for COTEY CHEMICALS Dry Acid® Special.
Many contractors have used liquid hydrochloric acid (muriatic) in wells plugged by carbonate scales, usually because of local availability and cost. COTEY CHEMICAL, however, strongly discourages use of liquid muriatic acid because of the absence of inhibitors, the possibility of "blowouts", and the prudent safety precautions which should be followed which call for special injection and handling equipment.
The presence of an inhibitor in any water well acid is necessary to prevent destruction of the well screen and pitting of the casing, thus COTEY CHEMICAL uses a very effective inhibitor in its Dry Acid® Special. table 1 illustrates the relative corrosion rates of various metals commonly used in water well construction when treated with (inhibited) COTEY CHEMICALS Dry Acid® Special, commercial muriatic acid, and commercial sulfuric acid. As illustrated, commercial muriatic acid will not only dissolve carbonate scale but, for instance, with 1010 steel pipe, will dissolve the steel pipe over four times as fast as would COTEYS Dry Acid® Special , unless an inhibitor is added (at extra cost): COTEYs Dry Acid® Special , with its inhibited action, is, however, safe for well screens and pumps.
| table 1 - Relative corrostion rates of various metals commonly used in water wells from Dry Acid®Special, muriatic acid and sulfuric acid. | |||
|---|---|---|---|
| Metals | Dry Acid Special | Muriatic Acid | Sulfuric Acid |
| 1010 steel | 1.0 | 4.2 | 2.6 |
| Cast iron | 1.0 | 3.2 | 3.2 |
| Galvanized | 1.0 | rapid | 63.0 |
| Tin Plate | 1.0 | 23.0 | 81.0 |
| 304 Stainless | 1.0 | resistant | 10.0 |
| Copper | 1.0 | 6.7 | 1.5 |
| Brass | 1.0 | 2.8 | 1.5 |
| Bronze | 1.0 | 7.0 | 4.0 |
| Aluminum | 1.0 | 5.3 | 0.6 |
The result of injecting hundreds of gallons of muriatic acid into a water well drilled through or into limestones and/or dolomites is often a "blowout"-the blowback to surface of the acid and water mixture due to the rapid production of tremendous quantities of CO2 gas. Such a "blowback" is dangerous to the people working around the well, contaminates the surrounding field, and is very difficult to clean up. Dry Acid® Special, is an inert powder which is non-toxic, non-explosive and non-fuming, can be safely and slowly added to a water well without special training or special holding tanks and hoses. The slow rate of injection and dissolution eliminates the possibility of a "blowout" and, as a powder, there is no emergency if a spill does occur.
The reaction of almost any acid added to a water well releases free hydrogen, thus if iron sulfide is present in the well the "rotten egg" gas, hydrogen sulfide (H2S), will be formed. Hydrogen sulfide, as well as carbon dioxide(CO2), which may be blowing back, are both heavier than the air, thus the well pit or house, or any adjacent low area, will fill with the heavier gas and the oxygen will be displaced. It is therefore prudent to stay out of well pits during treatment and to conduct chemical treatments only with assistance.
In wells producing from limestone the problem is somewhat different. Limestone is calcium carbonate which is completely soluble in acid. By dissolving part of the formation the channels leading into the well bore are enlarged, thus allowing more water to enter and the flow to increase. Some wells are producing from fissures and cracks in formations that are not soluble in any chemical and wells such as these cannot be helped with any chemical treatment. In these, shooting might be a possibility.
It isn't necessary to get deep penetration into the formation in order to get big increases in yield. The total surface area increases rapidly so that back in the formation there is a big drainage area and the restriction is right at the wall of the hole. This is similar to having a system with a great many one inch pipes all connected to a one inch common header. The capacity of the system is limited to the capacity of the header regardless of how many one inch pipes are connected to it. To increase the capacity of the system all you have to do is increase the size of the header. Essentially this is what is done when the area around the bore hole is opened up.
In old wells the decrease in flow may be due to a build up of water deposited scale on the screen, casing or in the formation. Since most of the pressure and temperature change which is responsible for the deposition of the scale occurs at or near the face of the formation, most of the plugging will be concentrated there. Usually these deposits are acid soluble and can be readily removed with an acid treatment. However, in some cases these deposits may be a silica material and usually it will not be economical or practical to attempt to remove this by chemical treatment.
Some waters are very corrosive and the metal in the well will be corroded and the corrosion products which always occupy more space than the original metal will accumulate and plug the well. These are sometimes difficult to remove but usually a chemical treatment will give the desired results.
Iron and Manganese Scales
Ground water commonly contains iron (Fe) in solution as ferric (Fe+++) or ferrous (Fe++) salts, the ferric iron in solution in amounts greater than 0.01 pm only at a pH less than 5.0. The ferrous ions allow the growth of iron fixing bacteria such as Siderocapsa, Gallionella or Spirophyllum, Crenothrix and Leptothrix which oxidize dissolved iron and manganese, causing precipitation of iron scale and/or iron "slime" and manganese hydroxide. The sulfate-reducing bacteria Dusulfovibrio desulfuricans also produce an iron "slime". Manganese hydroxide or manganese carbonate is apparently produced by bacteria extracting manganese from plant life. Within the well, deposits of ferric oxide scale will be brownish to reddish brown whereas the hydrated ferrous oxide and the manganese oxide will be a black to very dark brown.
When well water containing ferrous (Fe++) iron is pumped to surface the oxygen causes precipitation of ferric hydroxide (Fe(OH)3) by oxidation, thus lowering the pH of the well water by removing the bicarbonate (HCO3-) ion.
Manganese, as iron, also occurs in well water, but in two oxidized states: Mn++ and Mn++++. The typical reaction which occurs when well water containing manganese is pumped to surface is simple oxidation to form manganese hydroxide. Manganese in ground water results from leaching of soils, industrial wastes and bacterial contributions, amounts exceeding 0.30 ppm being deleterious for human water supplies. Most ground water contains less than 0.20 ppm Mn, but in mining areas or areas experiencing leaching by water which has been reduced, Mn may exceed 1.0 ppm.
Iron scale, iron bacteria, sulfate-reducing bacteria, manganese hydroxide and manganese carbonate scales are all soluble in acids, thus COTEY CHEMICALS Dry Acid® Special AND Liquid Acid Descaler are the recommended products. The use of Dry Acid® Special was previously described, thus let's look at COTEY'S Liquid Acid Descaler.
Liquid Acid Descaler is a potent combination of acids with a nonionic surfactant which promotes emulsions. Laboratory and field research by DuPont Chemical shows that light iron and heavy carbonate scale can be removed with a mixture of acids that are used in Liquid Acid Descaler. Any iron bacteria associated with scales treated with Liquid Acid Descaler are naturally destroyed by the acid.
COTEY'S Liquid Acid Descaler also acts as an excellent chelating agent for a number of metals. This simply means that the acid exhibits a complexing ability for iron in its anionic form, thus increasing the iron solubility.
Situations often arise when standard acid treatment periods, and increased concentrations are required, particularly when waste pumpage continues to show incrustation debris being removed from the well.
It should be emphasized that the removal of such scales and the resultant debris from the well will become increasingly effective as the pH of the water is lowered, thus copious quantities of acid are often required and frequent monitoring of discharge is suggested.
Bacteria and Related Incrustations
The accumulation of nuisance organisms such as fungi, algae, molds and various bacteria is a real problem in some areas. Generally speaking, this problem is best solved by preventive treatments rather than waiting until the well is plugged. Usually these organisms can be controlled if every well is sterilized with some accepted method when the well is first completed and then treated periodically. And of prime importance is to construct the well to eliminate any surface contamination. If growths of nuisance organisms are present they can be cleaned up with suitable chemicals and then kept under control with periodic treatments.
All water wells, even if used for cropland irrigation, stock or industrial purposes, should be periodically sterilized. The common test for water pollution is for the presence of coliform bacteria which originates in the intestinal tracts of warm blooded animals. Certainly, the presence of any coliform content in well water shows that other pathogens may also be present which could transmit dysentery, infectious hepatitis, burcellosis or salmonellosis to humans, or scours to swine and livestock. In fact, although caution is seldom exercised in supplying stock water, polluted water will produce a higher than average mortality rate in most animals, being particularly noticeable in slow weight gains and abortions in swine and cattle.
The standard method of treating water supplies for bacterial pollution is by chlorination, unlike chlorine gas, which can be easily and safely added to a well, the complete chemical reaction occurring within the well. Although, admittedly, chlorine gas would produce a quicker result, its use requires special equipment for injection. Chlorine gas is also extremely poisonous, thus few landowners care to have wells treated with such a dangerous chemical, particularly when the wells are near large livestock herds or neighbor's houses: a ruptured hose could result in dead stock and immediate human evacuation!
For many years it has been customary for drillers and household occupants to "disinfect" their water wells with liquid bleach bought at the local supermarket. Such "supermarket bleach" usually contains a 5% solution of calcium hypochlorite and 95% water. While this method is scientifically correct, results are generally 90% worthless due to the low level of chlorine concentration in the bleach and the small amount of bleach commonly used. As a typical example let's take a 400 foot, 12 inch well with 300 feet of water. This well contains approximately 2000 gallons of water (actually 1765), thus, to reach a chlorine concentration of + 500 ppm will require about 20 gallons of bleach. Unfortunately, treatment of this well, by the "supermarket method", would probably consist of dumping one jug of laundry bleach down the hole rather than the 20 jugs actually needed to do the minimum job! When chlorine is added to a well it hydrolyzes, producing hydrogen (H+), chlorine (Cl-) and hypochlorous acid (HOCl). Although weak, the hypochlorous acid smothers the pathogens and dissociates by giving off hydrogen. Unfortunately, many wells treated with chlorine fail to experience an effective "kill" due to changes which occur during treatment. Let's examine these difficulties to insure that your treatments with chlorine is always effective.
The amount of chlorine used in a well treatment is divisible into the demand, the dosage, and the residual. The demand chlorine is the amount necessary to effect the "kill", the dosage chlorine is the amount placed in the well, and the residual is the excess chlorine remaining after the "kill". The majority of chlorination procedures experience trouble when only the demand chlorine is met. For example, if well water is excessively alkaline the hypochlorous acid is dissociated and the efficiency of the chlorine reduced. Secondly, as the water temperature decreases, the effectiveness of the chlorine also decreases (about 50% per 10 degrees F decrease). Thirdly, chlorine efficiency is reduced by well waters having a high nitrogen (N) content which allows formation of inorganic or organic chlorimines. Any organic debris, incidentally, will also preferentially utilize the chlorine, and the presence of incrustations will shield pathogens from the chlorine. Finally, any hydrogen sulfide (H2S) in the system will combine with available chlorine to form hydrochloric acid which, as we've seen, would be detrimental to a silty well.
Fortunately, the solutions to all of these possible problems are provided by COTEY'S chemical products. Basically, any well, regardless of production history, should be cleaned prior to chlorination. Secondly, although some chlorine treatment procedures recommend the use of + 50 ppm chloride concentrations (Texas Highway Department), others 100 to 200 ppm concentrations, and still others at 1000 ppm, COTEY CHEMICAL recommends concentrations of between 400 and 500 ppm for the usual applications, but less than 1000 ppm to hold corrosive effects to a minimum. The reasons for this concentration (500 ppm) are, in addition to those previously stated, to provide that excess of residual chlorine which, as a strong oxidizer, can react with many of the polluting chemicals and incrustations commonly found in wells. As an example, the detrimental effects of nitrates in ground water have been a subject of intense study, primarily because the nitrates (NO3) convert to nitrites (NO2) in the presence of bacteria or zinc. It is the nitrites which cause cyanosis ("blue babies") in infants. This problem can be eliminated by using chlorine. Other cations such as sulphur (which will form hydrogen sulfide gas), iron and magnesium can also be effectively removed from well water by the extra strong chorine concentration recommended by COTEY.
For well systems where iron bacteria have been allowed to flourish, resulting in massive incrustation, (pictured above), COTEY CHEMICAL recommends what is usually termed a "shock chlorination" treatment. Shock chlorination is produced by using a 1000 ppm chlorine concentration (roughly double the amount stipulated above) after a preliminary acid/chelation treatment with Liquid Acid Descaler . Such a treatment usually takes three to four days and requires displacement water and exact timing. This sequence is repeated until the waste returns clean or down-time is exhausted. However, a word of caution, chlorination of water with a high ferrous iron content will cause precipitation of the gelatinous hydrated ferric compounds due to the oxidizing effect of the chlorine unless the pH is kept below 3 to keep the ferric iron in solution. It should be remembered that when iron bacteria are present they are converting the ferrous iron to the ferric state within the well, thus chlorine treatment should be preceded by acidization to kill such bacteria before injection of the chlorine.
Many water wells commonly contain bacterial "slimes" in the form of gelatinous incrustations which plug gravel packs, well screen and/or casing perforations. Such "slimes" are produced by iron and sulfate reducing bacteria, the dissolved oxygen in the water favoring presence of iron bacteria (Crenothrix). Thus, the problem in such wells is not simply to remove the "slime", but to eliminate the bacteria causing the incrustations.
Several of COTEY'S products can be used to remove the incrustations. For example, if the incrustations are mixed with calcium carbonate, use Dry Acid® Special, if the incrustations are an iron/manganese base, use Liquid Acid Descaler , and if the incrustations are mainly silt and clay, use Dry Acid® or Mud-Nox®. Following removal of the incrustations the well is now ready for sterilization.
There are many chemicals available for sterilization of water wells, but the particular chemical used must be carefully selected. The most commonly used chemicals are chlorine, quaternary compounds, copper sulfate and formaldehyde, but unfortunately, chlorine and formaldehyde, though very effective, have only a short-term effect. Copper sulfate, a popular chemical treatment for removal of weeds, algae and protozoa, should not be used on wells which supply domestic water because of the toxicity of copper to living organisms: also copper sulfate is corrosive to aluminum. Use in irrigation wells should also be curtailed because of injurious effects of copper to most crops. COTEY CHEMICAL has therefore developed Welgicide® Cleaner , which is specifically formulated for odor, taste, bacterial and organic "slime" problems.
Welgicide® Cleaner is very effective when used during the months when the wells are not being used in that its bactericidal efficiency remains potent for several weeks. When incrustations contain appreciable amounts of oil (probably from oil-lubricated pumps), organic "slimes", tree roots and vegetative debris from up-hole, and even carcasses of small animals, COTEY'S Welgicide® Cleaner should be used. Welgicide® Cleaner is a mixture of detergency, sequestering, defflocculation, and buffering properties in addition to the strong alkaline properties of all the ingredients. As such, Welgicide® Cleaner is one of the most versatile and effective chemical treatments offered by COTEY.
Maintenance Treatment
Deterioration of a water well's yield is somewhat analogous to the development of periodontal (dental) disease. Once the disease destroys a certain amount of bone structure the teeth become relatively useless, and once incrustations or silting reach a certain point in a water well, well yields are "useless". Fortunately, water wells (like dental structure) can be kept in optimum operating condition by preventative treatments; COTEY CHEMICAL recommends such treatments for a well at least once a year. Needless to say, it is far easier to prevent incrustations and corrosion than it is to remove such deposits.
Iron bacteria have characteristically been difficult to remove from water wells, often reappearing quickly after even the shock chlorination treatments. Chlorination treatments at regular intervals should therefore be implemented to maintain well yield and insure against the buildup of massive incrustations which could completely destroy yield or necessitate several weeks down-time for necessary treatment.
Installation of a drip chlorinator is, in fact, one of the best investments for many water wells. Drip chlorination to either the pump, pressure tanks (if present), or lines, in various concentrations depending on the local well problem, can prevent the infestation of iron bacteria by killing the bacteria and even precipitating the iron from the water. Drip chlorination will also prevent the development of iron and manganese scale, and eliminate any coliform bacteria. Over an extended period the chlorine can be expected to eliminate any iron scale remaining on the well's screen and pump. While doing all of the above, drip chlorination also removes any sulphur, nitrate, manganese and iron in the water.
The continual addition to water wells of polyphosphates, as chlorine, will prevent iron scale formation in the well system or in irrigation channels by keeping the iron in soluble form and causing precipitation of the iron respectively. In-line filters should be used if the water is piped to households.
Concluding Remarks
The loss of flow in many wells is due simply to a lowering of the water table. In this case there is nothing that can be done except drill more wells or use less water.
The problem is not how or why the water is plugged off but how best to remove plugging so that maximum flow can be obtained. Fortunately, much of the plugging will be removed by bailing, swabbing, surging, backwashing or pumping. Dry ice is sometimes used to agitate the water. Compressed air is also used to build up pressure and to air-lift the well in an effort to remove all plugging. As we have pointed out before, you will note that in all these methods the pressure being used is applied in the same direction as that which put the plugging in place. There is nothing that can be done to change the water pressure in the formation. Mechanical agitation in the bore hole will certainly help to loosen the mud but it is still the water from the formation that must wash it out. Since everything in the hole is completely hydrated and water wet, the water can not help in any way other that its mechanical washing action.
Chemicals are available that are effective in removing practically any type of accumulation from water wells. Instead of spending a lot of time trying to completely remove all plugging by mechanical methods, a properly designed chemical treatment will make it possible to do the job better and in less time. Many times one section may be overdeveloped in order to adequately develop another section. By chemically treating along with the usual mechanical methods all sections can be developed uniformly. Cotey Chemical's products were developed with the thought in mind that they would be used by well drilling contractors, pump companies and well service companies. Consequently, they are packaged in small, easy to handle containers, and usually no additional equipment is needed. Many wells equipped with deep well turbine pumps are treated with the pump in the hole. The chemical is simply poured in the well between the casing and pump column and the pump is used to agitate and dissolve the chemical in the water standing in the hole. The pump is used to agitate periodically for about 24 hours and then the well is pumped and developed in the usual manner.
In developing new wells or redeveloping old wells with a rig over the hole, the chemicals are added and a bailer, surge block or other tool is used for agitation. The well is then bailed or the pump set to remove the spent acid solution. The big advantage with chemicals is the fact that they can penetrate through the screen or casing perforations and back into the formation where there is little if any agitation from mechanical methods.
As pointed out earlier, deep penetration is not needed, so usually no additional water is added to the well unless the static water level is considerably above the perforations. In gravel packed wells enough water is usually added to displace the chemical solution back through the gravel wall to the formation where it can act to disintegrate and dissolve the mud and clay.
In some wells the chemical is dissolved in water and the solution added through the drill pipe or tubing. Our experience has been that it is easier and cheaper to use an excess of chemical and dissolve it in the water standing in the hole. In this way none of the chemical is lost in the open porous sections as happens when a solution is added to a well at static.
Most of the chemicals are comparatively non-toxic and are used to treat wells producing potable water. The first water produced after a treatment contains spent chemicals and should be pumped to waste. Most wells will clean up in only a few hours depending on the size and equipment being used.