Development of Ultra Acid-Base (UAB^TM) Water Well Treatment Technology

TABLE OF CONTENTS

• 1.0 INTRODUCTION
• 2.0 UAB^TM TREATMENT PROCESS
  • 2.1 UAB^TM TREATMENT PROCESS DEVELOPMENT
  • 2.2 UAB^TM TREATMENT THEORY
  • 2.3 UAB^TM TREATMENT PROCEDURE
• 3.0 UAB^TMTREATMENT TRAILER AND EQUIPMENT
• 4.0 DISCUSSION
• 5.0 REFERENCES

PHOTOGRAPHS

• Photo 1: Typical UAB^TM Setup Water Truck, Treatment Trailer, and Generator
• Photo 2: UAB Treatment Trailer
• Photo 3: Boiler Used During UAB Treatment
• Photo 4: Pressure Tank, Sand Filter, and Softening System
• Photo 5: Hot Water Accumulation Tank, Mixing Pump, and Re-circulating Pump
• Photo 6: Chemical Dispensing Pumps and Mixing Tank
• Photo 7: UAB Treatment Control Panel
• Photo 8: Computer Setup and Tubing Reels
• Photo 9: Treatment Solution Injection Hose
• Photo 10: Cable Tool Rig Set Up Over Well

INTRODUCTION

The goal of the SWWI is to pursue methods that will sustain the existing water well infrastructure by providing improved advice to rural clients on the diagnosis, prevention, and rehabilitation of well problems. This initiative was created because the water well environment is extremely important to the viability of prairie life. Groundwater is the source for the majority of rural water supplies on the Canadian Prairies; many individuals, small communities, and industries rely on water wells as their principal source of water. Over the past 20 years, PFRA has used programs such as the Rural Water Development Program (RWDP) to help rural clients construct the water well infrastructure used to develop groundwater supplies across the Prairies. However, problems occur with these wells over time, including reduction in yield and deterioration in water quality. Although knowledge of water well construction is quite substantial throughout the water well industry, knowledge regarding maintaining and maximizing the life of wells is still relatively poor. As a result, wells that exhibit deteriorating water yield or water quality are often abandoned and new wells drilled in their place. The costs associated with the replacement of these wells can have a significant economic impact. Therefore, the rural public and the water well industry must be provided with current information about cost-effective preventive maintenance and well rehabilitation methods that will reduce potential water well problems and maximize the investment in water well infrastructure.

The SWWI is currently examining the problem of water well deterioration caused by microbiological activity, commonly referred to as biofouling. It has been recognized that groundwater contains microorganisms and that the activities associated with these microorganisms can have a significant impact on the water well environment. However, bacterially fouled wells are often difficult to recognize since the severity of the symptoms often increase gradually. Symptoms include a gradual deterioration in water quality, a reduction in well yield, and equipment failures due to corrosion and/or encrustations. Over time, these nuisance bacteria can clog the well intake area and aquifer material and can also cause taste, odour, and other general water quality problems. Eventually, biofouling will lead to a dramatic decline in both water quality and/or quantity from a well. In some cases, the biofouling is severe enough to prompt outright well abandonment.

Traditional treatments (e.g. shock chlorination and acidization) to control biofouling tend only to provide temporary relief from the microbiological activity that causes water well deterioration. These treatments stress the bacteria and biofilms and allow increased water flow by shrinkage of the biofilms, which leads to temporary improvement in well yield. However, these methods often do not fully penetrate the protective biofilms, and therefore the majority of the bacteria are not affected. Once the stress is removed, the bacteria create more biofilm for protection and well performance rapidly reverts to pretreatment levels. To counteract this effect and to extend the life of a well, a treatment process is required that effectively penetrates the biofilms and reaches all the areas of biofouling (Cullimore, 1993).

2. UAB^TM TREATMENT PROCESS

In August 1996, PFRA undertook an initiative to find an efficient method for treating biofouled wells on the Prairies. Droycon Bioconcepts Inc., in a joint venture with PFRA, agreed to develop a water well treatment process suitable for use on the Prairies by drawing on their past experience with the microbiological aspects of water well biofouling. DBI was involved in the development of the Blended Chemical Heat Treatment (BCHT ) well treatment process, which has been successfully applied to biofouled water, relief, recovery and injection wells in the United States under the sponsorship of the U.S. Army Corp of Engineers.

2.1 UAB^TM TREATMENT PROCESS DEVELOPMENT

The first step in the development of a water well treatment process suitable for use on the Prairies was to evaluate the potential application of the BCHT process to wells in the rural prairie setting. When this process was considered with respect to the treatment of water wells in the Canadian Prairies, it became apparent that the costs associated with the mobilization of the required equipment would be prohibitive because of the large area that a well treatment firm would have to service.

The UAB^TM treatment process was therefore designed specifically for the rural prairie setting. The design was based on the following stipulations: low treatment cost, easy operation of the treatment equipment, and convenience in mobilization and demobilization.

Laboratory trials were established to develop and test the UAB^TM treatment process, using sixteen one-litre lab-scale model wells. Through a series of experiments, which took place between August, 1996 and March, 1997, the chemical processes of the UAB treatment were developed (Keevill, 1997).

2.2 UAB^TM TREATMENT THEORY

The UAB^TM treatment process involves three phases of chemical application to remove the clogging biofilms. The first phase is intended to shock the bacterial cells and biofilms, the second to disrupt (break up) the biofilms, and the third to disperse the biofilms and other clogging material.

1. Shock Phase
   The purpose of the shock phase is to: (1) kill bacterial cells suspended in the water, (2) stress the biofilms, which causes top layers to shear off and lower layers to compress, (3) increase bacteria metabolic rates at the fringe of the heat zone to increase the rate at which cells absorb the disinfectant, and (4) soften encrustations or hardened bacterial clogs (Smith, 1995).
   
   The shock phase of UAB^TM treatment process begins after pre-heating the well intake area with hot water to increase the down hole temperature to about 65øC. The shock phase itself involves application of a hot water solution, disinfectant, and wetting agent (surfactant). The water in the well and surrounding aquifer is maintained at a temperature of at least 65ºC, since these relatively high temperatures are lethal to some of the bacteria. In addition, high temperatures increase the rate at which chemicals react and reduce the amount of disinfectant needed to kill bacterial cells. The wetting agent helps the hot water and disinfectant to penetrate the biofilms.
2. Disrupt Phase
   The purpose of the disrupt phase is to kill the bacteria by causing a shift from a strongly acidic to a strongly alkaline solution. Although some bacteria thrive in acid conditions and some in alkaline conditions, a shift of 7 pH units over a short period of time is generally lethal to most bacteria found in groundwater. The target pH shift generally involves a pH drop to 3 followed by an increase to 10.
   
   The first stage of this phase is to add a hot water and acid solution to the well until the pH in the well intake area reaches about 3. If possible, the acid solution should be left in the well overnight before the next stage of the process is initiated, since the acid also helps to dissolve iron and manganese oxides which collect in the biofilms and encrustations.
   
   The second stage requires the addition of an alkali and wetting agent solution at a pH of about 10. The wetting agent is added during the alkaline stage to help break up the biofilms and keep other clogging materials in suspension (e.g. silts and clays), so that they can be more easily removed during the disperse phase (Cullimore, 1993 and Smith, 1995).
3. Disperse Phase
   This phase is designed to disperse or remove the biofilms and other clogging material from the aquifer by surging, bailing, and pumping the well. The purpose of surging the well is to further suspend clogging material so it can be removed by bailing and pumping. Heavy debris which falls to the bottom of the well during treatment can plug the intake area of a pump and adversely affect cleaning of the well screen; therefore, this material is removed by bailing the well. Finally, the treated water is pumped out of the well. Pumping should continue until the water is clear and the pH is neutral. Lab studies have shown that each phase of the process is necessary to effectively penetrate and remove the biofilm material. In addition, sufficient volumes of the hot water solutions must be added at each stage to reach areas of biofouling adjacent to the well and extending into the aquifer.

2.3 UAB^TM TREATMENT PROCEDURE

1. Establish Presence of Biofouling
   The UAB^TM treatment procedure begins with an analysis of the reported well problem. This analysis includes testing of water samples for bacterial activity in the well with Biological Activity Reaction Tests (BART ^TMs) to ensure that the well problems are related to biofouling. A down hole video of the well may also be used to examine the well for structural failure and bacterial growth.
2. Obtain Well Record
   Once it is confirmed that the well is biofouled and can benefit from the UAB treatment process, the well drilling record should be examined to determine: (1) original well production rate, (2) location, length and diameter of the well intake, (3) total well depth, and (4) well construction materials. If the well drilling record is not available, this information must be obtained from the well owner or by some other method (e.g. down hole video camera, sounder, gamma logs, etc.)
3. Perform Well Pumping Tests
   Short pump tests are performed before and after rehabilitation of the well to evaluate the effectiveness of the treatment. During each test, water is pumped from the well at a constant rate for a set period of time and the water level is recorded at regular time intervals. Specific capacity results from the pump tests are compared to provide a quantitative measure of the effectiveness of the treatment.
4. UAB^TM Well Treatment Process
   The next step of the procedure includes calculating the volumes of water and chemicals that will be used during the treatment process. The amount of treatment solution required to effectively and economically treat each well will vary with the well's condition. An estimate of the required volume of solution for each treatment application (pre-treat, disinfectant, acid, and alkaline) is determined by calculating the volume of the well intake area, extended about 0.3 metres into the surrounding aquifer. Calculations of the volume of water that will be used to treat the well must also include about 900 litres of water needed to flush the mixing tank after each treatment phase.
   
   The chemical application amounts should be adjusted based on the condition of the well. For example, if the well takes the solution at a very low rate, the total amount of solution added to the well may be decreased to reduce labour costs and to reduce well down-time associated with a long treatment period. Also, if the well intake is heavily encrusted, more acid may be required to achieve the desired pH levels in the well. Therefore, it is extremely important to monitor pH levels during the treatment process to ensure that the treatment objectives are met in an economical manner.
   
   After the chemical applications are completed, the well intake area is surged, bailed, and pumped to remove the clogging material. The follow-up pump test is performed once the water is clear and the water level in the well has reverted to its static water level. Once the treatment process has ended, the well pump is replaced and chlorine is added to the well to eradicate any bacteria that the pump and drop pipe may introduce to the well.

3.0 UAB^TM TREATMENT TRAILER AND EQUIPMENT

Photo 1: Typical UABTM Setup Water truck, trailer, and generator

Photo 2: Trailer

Photo 3: Boiler

The propane fuelled boiler is sited at the front of the trailer and exhaust gases are vented through the chimney stack. The boiler (Photo 3) outputs 700,000 BTU/hr and has a production capacity of 0.5 L/s (5.8 Igpm) of 83 to 85ºC water.

Water from the tank on the truck is pumped into the trailer where it passes through a pressure tank, sand filter, and high capacity water softener (Photo 4). From the softener, the water enters a 380 L (83 Imp. gallon) insulated hot water accumulation tank (Photo 5). This tank provides hot water storage and is part of a circulation loop with the boiler. The accumulation tank is equipped with a small pressure tank to allow thermal expansion of the water without exceeding the pressure rating of the boiler system.

Photo 4: water softener

Photo 5: water tank

Photo 6: mixing tank

The mixing tank is equipped with sensors to monitor pH, temperature and water level. A solenoid valve and ball valve located downstream of the mixing tank control the flow of water to the well head. The flow rate and volume of water/solution leaving the mixing tank is monitored by a downstream flow meter.

Photo 7

Photo 8

Photo 9

A pH probe and a tube containing four thermocouples (on small reels in Photo 8) are also lowered into the well. A total of five thermocouples are used to measure temperatures at the following locations: 1 - mixing tank; 2 - top down hole thermocouple; and 3, 4, and 5, which are subsequent down hole thermocouples located at 9.1 m (30 ft), 18.2 m (60 ft), and 24.4 m (80 ft) below thermocouple 2. Temperature readings are displayed and recorded on a temperature datalogger mounted in the trailer, and are downloaded into the computer at the end of the process. The temperature in the mixing tank is also displayed on the computer screen during the treatment process.

After the well has been treated with hot water and chemicals, a cable tool rig (Photo 10) is used to surge the well intake. This keeps the treated materials in suspension until they can be pumped out. In addition, a bailer is used to remove debris that has accumulated at the bottom of the borehole. Once bailing is complete, water is pumped out of the well until it exhibits no physical or chemical evidence of the treatment.

A software package is also being developed which will control the heating, mixing and application stages of the treatment process. This will allow computer automation of the UAB^TM trailer and all the processes while allowing manual over-ride intervention at any time.

4.0 DISCUSSION

The objective of this phase of the SWWI is to promote the sustainability of water wells by encouraging the development of a water well treatment process suitable for use on the Prairies. As a result, the UAB^TM water well treatment process was established on the basis of successful laboratory trials. The effectiveness of the UAB^TM treatment process is presently being evaluated and refined in field trials.

As part of the SWWI, other important studies that are currently under way will:

• Study the economic impact of biofouling of water wells and the benefits of monitoring, maintenance and treatment.
  This study will illustrate that investments in monitoring, maintenance, and regular well treatments generate an economic benefit through improved water quality and extended well production life.
• Determine the effectiveness of current biofouling treatment processes.
  A definitive study is being set up to determine the effectiveness of the currently available products and strategies being used to control biofouling. As a first step in this process, a literature review will be carried out to identify potential products or strategies that may warrant comparative testing. Product manufacturers and product users (e.g. well drillers) will also be contacted to collect information on costs, recommended uses, and experience in using the products.
• Consider alternative treatment procedures to improve the UAB^TM treatment process.
  Changes to the equipment and procedure will be based on the results of these pilot tests, further laboratory studies, and conclusions from the two studies mentioned above.
• Evaluate biofouling rates and treatment efficiency as they relate to regional aquifer systems.
  The variability in biofouling and effectiveness of treatment techniques from region to region will be determined. Such knowledge will also allow development of the most effective treatment procedure to use for each well environment.

5.0 REFERENCES

This paper was derived from a report prepared by Dr. Roy Cullimore (Droycon Bioconcepts Inc.) and Twyla Legault (U. of Regina engineering student working for PFRA during a co-op work term).

Cullimore, R. (1993). Practical Manual of Groundwater Microbiology. Lewis Publishers, Chelsea, MI.
Cullimore, R. (1997). DBI Interim Report to PFRA. Droycon Bioconcepts Incorporated, Regina, SK.
Keevill, B. (1997). Implementation of the BCHT (Blended Chemical Heat Treatment) Process to Rehabilitate Clogged/Biofouled Groundwater Wells. Fourth Year Engineering Thesis, U. of Regina.
Smith, S. (1995). Monitoring and Remediation Wells. Lewis Publishers, Boca Raton, Florida.