Field Diagnosis Of Well And System Problems

Transcript

rehabilitation/ Field Diagnosis of Well and System Problems Solving issues in the well is more important than ever before. By David Hanson T he day is coming all too soon when drilling new wells will become less of an option. It’s critical to your survival to understand different directions that complement your business now. Customers today are demanding more and better answers, and it’s our job to understand and provide solutions. Customers want more water and better water. And when having problems, they want good, solid answers. This requires some education on our part. Part of the problem is water chemistry; part may be biological (slime or odors), and part may be physical issues with the well casing or piping. It will require some work and it’s a little different than pulling levers behind a rig, but this is an emerging market and you need to be aware of it. Some of the customers’ issues include coliform bacteria, discolored water, odors, iron bacteria, corrosion. All are problems that can be understood and solved. My intention here is to give you tips to use in the field to understand what to look for and where to look, and therefore give you a better chance to solve your customers’ problems. Odors in a New Well Odors in potable water are most often caused by bacteria, assuming there is no contamination present. The most common complaint is the “rotten egg” odor, normally caused by sulfate-reducing bacteria. SRB are anaerobic only, which means they thrive in low-oxygen or no-oxygen environments and require some sulfate or gypsum as a nutrient. They are naturally occurring soil organisms most likely found in clay or shale lenses. These formations provide the low-oxygen environment and necessary nutrient. If screens are placed through clay lenses or if an open hole is completed exposing open shale lenses, this odor may be noticed immediately. In the initial design, use shorter lengths of screen in only clean sand/gravel areas. This will minimize or eliminate the problem. If drilling in sandstone or limestone formations, set and grout casing through the deepest shale lenses and drill the clean part of the formation, open hole. If this problem already exists in a new well, do not shock chlorinate as it will not solve the problem more than short term. Plus, large amounts of chlorine causes corrosion to any metal in the well and may even cause nonmetal parts like PVC to become brittle. When field testing a customer complaint: ● Check if odor is present in the hot water only in the system. If in the hot water only, take the anode rod out of the hot water heater. ● If odor is present in the cold water, pour a glass of water. Let it set for 10 seconds. If the odor goes away, it’s a gas probably caused by SRB. If a bladder pressure tank was installed, the bladDavid T. Hanson, the 2003 NGWA McEllhiney Lecturer, is the owner of Design Water Technologies, a company dedicated to understanding and treating wells for iron bacteria and coliform. You can contact him at [email protected]. 24/ April 2007 Water Well Journal der contains this gas, so the first atmospheric condition is at the faucet. Install a bladderless tank, an open tank, or an air injection to an iron filter. All allow oxygen contact to the water and dissipates the odor. Over time there may be a minor amount of sulfate powder that will accumulate in the bottom of the tank. Odors Suddenly Appearing in an Older Well If this happens within a couple of weeks to years of operation, you have to suspect that there may be changes of environment in the well. A “rotten egg” odor may be caused by SRB. Musty, oily, fishy, or metallic odors can be caused by other slime formers or iron bacteria. Odors that suddenly appear when there is: ● Slime formation in the well can harbor anaerobic, odor bacteria beneath the polysaccharide debris. Odors can vary in severity with time. Check inside any piping for the presence of soft, sludgy debris. For domestic systems, check at the “union joint” by the pressure tank. For larger systems, check a gasketed water meter or check valve. You can also do “timed tests” to determine the presence of hydrogen sulfide gas in the casing and aquifer. ● A sump in a well. A sump is a pipe below the screen that allows sediment to collect, but is a nonproductive zone that can harbor anaerobic bacteria. This same condition can happen in the bottom of a rock well in a nonproductive zone. Look at the original drillers log for either condition. Either provides a low-oxygen environment for anaerobic (odor). In some cases, you can install an airline or water flushing tube into this zone to automatically flush this area during pumping. ● A simple change from a bladderless pressure tank to a bladder tank in an older system. A standard bladderless tank allows direct water to air contact which releases the gas, and the odor is dissipated within the tank. When a new bladder tank is installed, the first atmospheric condition occurs and the odor “suddenly” appears when it was not present with the old tank. ● Potential for corrosion in the casing allowing debris to fall into the well, creating potential odors and discolored water on a continuous basis. Recommendations for Diagnosis or Questions for Customers Consider asking the following questions as well as performing the following actions: ● Was a new bladder tank recently installed on a domestic system? ● Look inside piping for the presence of slime debris. Check union joints by the pressure tank on domestic wells as well as gasketed water meters, check valves, etc. on large diameter wells. ● ● Check the well log for the possibility of dead or sump areas in the bottom of the well. Test at the wellhead for presence and severity of the odor in a timed test. Measure for hydrogen sulfide gas on a timed test. For domestic wells, test for hydrogen sulfide for one to two minutes of pumping and at three hours of continuous pumping. If hydrogen sulfide gas levels remain the same or rise, the problem is in the aquifer. If odor declines drastically, there may be a slime growth in the well. General Corrosion Most ground water is not corrosive to a point of major problems, but the majority of problems will be caused by certain conditions. Some of these can be caused by improper grounding. Most water chemistry tests can be done by a local lab or with a test kit. Check for: ● Total dissolved solids greater than 600 ppm ● Chloride greater than 500 ppm ● pH lower than 6.0 ● Carbon dioxide greater than 50 ppm, but test has to be done on-site ● Dissolved oxygen greater than 2 ppm, but test has to be done on-site ● Hydrogen sulfide odor (rotten egg) caused by sulfate-reducing bacteria ● Massive presence of any of the iron oxidizing bacteria (iron bacteria). Total dissolved solids greater than 600 ppm can cause electrolysis between two different metals in water that is highly conductive to energy. When any dissimilar metals are placed in this type of water, the lesser metal will show corrosion, and the nobler metal may show deposits. The higher the TDS, the greater the potential for issues. Some examples of lesser metals are cast iron and mild steel. Examples of more noble metals are stainless steel and hardened metals. You may even see problems within the same material, as simple differences can occur in the metal itself. The rolling of metals, forming/shaping, or the cutting of threads change the structure of the metal. You will often find debris on the inside of piping. For domestic systems, look inside the union joint at the pressure tank. In large diameter systems, look under a gasketed water meter or check valve for debris. Scrape some debris and dry. Crush debris into small particles and put on a piece of paper. Run a magnet under the paper to understand the percentage of particles that are magnetic. Magnetic debris is most often a corrosion byproduct. Most mineral deposits (iron, manganese) are not magnetic. A small percentage of dried bacterial deposits can be magnetic. Recommendations for Normal Corrosion Conditions This is a condition that cannot be changed by treatment. Simply move the corrosion issue to a field diagnosis/continues on page 26 NGWA.org field diagnosis/from page 24 replaceable metal at the well. This will require a lesser noble metal, say magnesium. This can simply be done by: 1. Strapping a magnesium wire to the pump column pipe. 2. Burying a magnesium rod as a sacrificial anode by the metal well casing. Dig a 3 to 4-foot-deep trench near the well and place this rod horizontally. Attach one end of this rod with a cable attached to the casing. You might be able to increase conductivity by adding 3 to 4 inches of bentonite chips below and above this rod. Then simply check every three to four years and replace when necessary. Call an oil pipeline or a buried tank company to buy these magnesium anodes. Massive or Early Corrosion Severe corrosion within a short period of time (less than three years) may be resulting in more than simple chemistry. Just one millivolt of stray DC voltage can dissolve 12 pounds of steel per year. If you have reviewed the water chemistry and don’t find any issues, try looking at stray DC voltage. This may take the form of replacement pumps or drop pipe in a very short period of time. If you see severe or early signs of corrosion in a well or piping, check any hard wiring in the area for stray DC voltage. This is done with a “C” clamp-type DC voltmeter. Sources of DC voltage may be phone lines, some low voltage lighting systems, electric fences, and corrosion protection of buried tanks or pipelines. Stray DC voltage can even happen through ground surfaces. Voltage will follow water that is highly conductive. Clay lenses or shallow ground water containing high TDS water may allow conductance from miles away. You can use ground stakes in a circle around the well and measure resistance between the stakes. If the source is within a household or building through wiring, the ground must be changed. See an electrician for this. Coliform There are potential problems with samples that show multiple samples with “present” for coliform. Some of the issues include: Where the sample was taken. If you are taking a sample at a house or somewhere in the system, you must assume the problem can be from that point backward to the well. Do not assume the well is always the problem unless you are testing at the wellhead. If problems persist, test at the wellhead. Install a sample tap in the basement of a new house to separate the well system from the house piping. Shelf life of liquid chlorine. Liquid chlorine (common bleach or industrial sodium hypochloride) will lose up to 20% effectiveness every month. Natural pH of water. If standard chlorine is used, pH will rise as all liquid and granular chlorine is an alkaline which causes a rise of pH. The more chlorine you use, the higher the pH, and therefore the less effective it becomes. If natural pH is 7.0 or greater, consider using ChloraPal or similar chemistry to control pH with chlorine at between 5.5 and 6.0 to make the chlorine 200 times more effective. Placement of chlorine. Chlorine will not automatically mix evenly to the bottom of the well if you pour it into the well from the surface. What really happens is chlorine hits the static level, causing a tremendously high pH (ineffective but 26/ April 2007 Water Well Journal minutes. Minor MPN is less than 10 colonies/ 100 mL. Major MPN is greater than 20 colonies/ 100 mL. ● IF MPN is high in the “casing” sample and low or zero in the “aquifer” sample, the problem is probably contained in the well and should be treatable. ● IF MPN is high in the “casing” sample and high in the “aquifer” sample, consider a continuing source of organisms, such as failed grout allowing a continuous source outside the casing from an upper level source, a failure in the casing allowing a continuing source inside the casing, a source in the aquifer itself. You cannot get a safe sample in this case until the physical problem is fixed. If you are testing in the system and continue to get “presence” of coliform even with the timed test, install a pressure gauge on the well side of the pressure tank. Allow the pump to build to shutoff pressure (50 psi) and monitor pressure. If there is a leak, the pressure will drop drastically within a few seconds. Then you must lift the pump discharge to make sure the check valve in the submersible pump is holding. If the check valve is holding, the leak is in the buried line and needs to be replaced. Just one millivolt of stray DC voltage can dissolve 12 pounds of steel per year. If you have reviewed the water chemistry and don’t find any issues, try looking at stray DC voltage. This may take the form of replacement pumps or drop pipe in a very short period of time. If you see severe or early signs of corrosion in a well or piping, check any hard wiring in the area for stray DC voltage. highly corrosive), and very slowly sinks to lower levels, but will not seek out bacteria. Pellets placed in the well will sink to the bottom, but will lie there undissolved for years. Consider using two volumes of the well in a tank at the well. Mix the desired chlorine into this tank and pour or pump into the well. You will first displace the volume of water in the well, and the second volume will flow into the formation. Surge the well with either pressure from the surface or movement of the pump up and down to create some movement for additional contact. Presence of bentonite hiding coliform. If no or little development was done in the well and bentonite was used in the drilling process, the blockage must be removed. To break bentonite: (1) calculate the volume of the screen in gallons; (2) multiply that volume by five; (3) have a tank at the surface with that volume of water; and (4) mix 0.03 gallon of common bleach per gallon of water in that tank. This will create a pH of 10 and the oxidation process will break the polymer chain of the bentonite. Place this equally throughout the screen with a tremie pipe. Surge the well screen with a surge block. Let it set overnight. Airlift the well from the bottom of the well for removal. Dechlorination may be required. Severity of problem, not just present/absent. If you have had more than two “present” samples, then ask your lab to do a “counts as MPN (most probable number) of coliform.” Understanding the location of coliform. If you want to separate a well problem from a potential aquifer problem, do timed testing. Here is the procedure: Let the well set overnight with no pumping. Sample at the wellhead for a “casing” sample if possible. Let the pump run for 50 times the volume of the well for an “aquifer” sample. In domestic wells, take a “casing” sample at one minute to two minutes of pumping and the “aquifer” sample in three hours. In large diameter wells, take the “casing” sample at two minutes after water vacates the pump and calculate the volume of the well and divide by gallons per minute for sample time in E. coli or Fecal Coliform If E. coli or fecal coliform bacteria are present in the sample, it means there is probably a physical source causing the problem, which can be dead animals, fecal material, or sewage contamination. Do not chlorinate the well, as chlorine will not remove the physical source or fix problems with failed grout or physical problems with the well. If E. coli was present in a system, test at the wellhead first. If present at the well, set an airline to the bottom of the well. Airlift all debris out of the well until the water is clear. Chlorinate and retest. If you are still getting “present” for E. coli, consider doing a timed test, following the procedure that was explained earlier. If there is a “present” in both the “casing” and “aquifer” samples, consider the potential for a physical problem with the well casing (failed grout, improper seating of the casing to rock, failed fittings in casing). Understand the source before treating the well. If negative at the well but positive somewhere in the system, there is a problem in the system. Plugging in line filters or pipelines, sudden discoloration, sudden odors, or debris present on pumps during routine maintenance. First, any plugging or sudden discoloration, especially on startup of the pump, may be caused by a mineral buildup, slime created by bacterial activity, or silts/fine sand. First, inspect piping. For domestic systems, look into piping at the union joint by the pressure tank for debris. For large diameter wells, take off the covers on gasketed water meters or check valves and inspect any residue on the inside. This diagnosis is critical, as successful treatment is based upon the problem. Mineral Deposits ● ● Debris inside piping is hard and will be scrapable in chunks or plates. Coloration may be red/brown (iron), black and brittle (manganese), light tan/brown (calcium), or green (sulfate). field diagnosis/continues on page 28 NGWA.org field diagnosis/from page 26 ● ● Video of well will show flakes that will float but sink to the bottom with camera movement. Debris will be more noticeable in the screen area or open hole only. Check water chemistry, pH > 7.0, iron > 1.0 ppm, manganese > .02 ppm, sulfates > 40 ppm, hardness > 200 ppm. Water chemistry should be consistent over long periods of time. Compare iron and manganese with past samples. If there are major increases, see as follows. Iron Bacteria, Slime Bacteria ● ● ● ● ● ● ● ● Debris may be slimy, soft, granular sludgy. Dried debris may be dusty or break apart easily because of high oxygen content. Color of debris may be brown, red, black, green, or in some cases, clear. Odors may be noticeable within debris. Sudden odors may appear in the system and may be rotten egg, fishy, oily, metallic, or musty. Notice increasing or fluctuating levels of iron or manganese. Change in chlorine or phosphate injection rates in a system. Video may show stringy debris, fluffy debris, or gelatinous masses. Puffiness may occur with camera movement. Debris loosened will most often float during camera movement. Debris will be very noticeable from static to pumping level and throughout the screen. 28/ April 2007 Water Well Journal Low or Changing Yields Finale Customers may complain of air in the system when plugging occurs in wells. A plugging of the screen or fractures in an open rock well will not allow normal flow of water to the well. This will require more drawdown to attempt to pump water. It is critical to understand the specific capacity (SC) of the present well condition and compare to the original SC. If the original SC was 8 gpm/ft of drawdown and it’s now 3 gpm/ft of drawdown, the yield has declined 62% and needs some attention. In some cases, the SC is never calculated originally when the well was drilled. You have to pump the well, so why not record the static level, pumping level at a given time (say, 30 or 60 minutes in domestic wells and three hours in a large diameter well). You don’t even have to make the calculation when the well is drilled; it can be done at any time. It doesn’t take any more time but does require a drawdown gauge. A reduction of yield will be caused by either: ● Mineral deposits ● Slime or iron bacterial deposits ● Fine sand filling in a screen or caving formation into an open borehole ● Changes in the static level in a water table aquifer drastically reducing the pumping capability of the aquifer ● Changes in flow conditions within an aquifer due to other wells in the area conflicting with flow or even seismic changes restricting flows to a well. That’s it. If you are stumped, seek out a lab service. It is critical to be correct on the diagnosis to be successful. When it comes to well rehabilitation, you have to be a doctor of sorts to diagnose and solve the problem. The problem may be due to water chemistry, microbiology, or physical issues with either the well or the system. These physical issues can include failed grouts allowing a continuing issue outside the casing into the intake area of the well, failed well casing allowing a continuing issue inside the casing into the intake of the pump, or failed buried piping where the problem occurs in the system but not the well. If you are looking for something more exciting in your career, look at water treatment and well rehabilitation. The problem? Misdiagnosis will result in failure. For example, if your customer has a slimy growth in their system and you shock chlorinate the well, you know it’s only a short-term fix. The problem will come back, but in a shorter frequency. Do you treat again or solve the problem? Mistreatment will result in continued problems. But you can make more money if you solve problems. There isn’t much competition for someone who solves the problem. Why is this an emerging market? Regulations will make it difficult to continue to drill wells. Customers demand more water and better water quality. Will you look at new directions? Are you up to the challenge? Will you stand apart from the crowd? I hope so. WWJ NGWA.org