Biofouling and Water Wells in the M.D. of Kneehill, Alberta

As part of the Sustainable Water Well Initiative (SWWI), this fact sheet reports on a recent study into the potential role of groundwater bacteria in the reduction of well yields and water quality in the Municipal District (M.D.) Of Kneehill, Alberta, Canada. The work was carried out by PFRA in partnership with the M.D. of Kneehill, Alberta Environmental Protection (AEP) and Droycon of Regina, Saskatchewan.

• To confirm the extent and type of groundwater supply problems,
• To determine the impact of naturally occurring nuisance bacteria in groundwater on water quality, well production rates, and well life expectancy, and
• To make recommendations on how best to treat these problems.

What is biofouling ?

• deteriorating water quality over time. This includes taste and odour as well as other water quality problems
• reduced well yield due to clogging of well screens or the aquifer itself
• red or black slime on pumps, well screens, or in the distribution system (toilet tanks, cisterns etc.). These slimes can lead to increased corrosion of steel well casing, stainless steel well casing, stainless steel well screens, etc.

Nuisance bacteria are naturally present in groundwater. Pumping a well increases the food supply for these bacteria, causing their population to rapidly expand in the vicinity of the well and in the distribution system. The bacteria form a slime or biofilm, that captures mineral scale and other deposits that move to the well during pumping. These deposits can reduce water quality, well yield, and well life expectancy.

How was the study carried out

A sixteen township area (Township 29 to 32, Ranges 21 to 24 W4) was identified for study. Many water users in the targeted area have had to repeatedly replace wells whose yield had deteriorated since original installation. Biofouling was suspected as being the cause of this deterioration.

For the study area, PFRA, Droycon, AEP, and the M.D. of Kneehill:

• carried out detailed survey of 275 well owners to gather basic well information (age, depth, etc.) and information on water supply problems
• collected water samples from 134 wells for microbial testing
• performed intensive diagnostic testing on seven water wells (including more detailed microbiological sampling, visual well inspection using a downhole camera, and pump testing), and
• undertook lab testing to develop a new well treatment process to rehabilitate wells that are severely biofouled.

STUDY FINDINGS:

WELL OWNERS SURVEY

• About 74% of the wells being used were reported to have well yield problems, water quality problems, or both.
• Water quality was a more common concern than well yield. This difference may be due to owners' perceptions, as a slight change in water quality is more noticeable than a gradual reduction in well yield over time.
• The most common water quality concerns were taste and odour
• Pumps pulled for maintenance or inspection were often covered with red slime, black slime, or both.
• Less than one-third of the wells were reported to have undergone some form of well maintenance or treatment.

RESULTS OF MICROBIOLOGICAL TESTING

• About 68% of the wells show evidence of being biofouled with high populations of one or more bacteria types. Bacteria was present at lower populations in most of the other wells tested, suggesting that biofouling may be at an earlier stage in those wells.
• Although biofouling occurs at varying rates in different wells, evidence to date suggests that biofouling is progressive and will eventually occur in most of the wells in the study area.
• Sulfate reducing bacteria is the dominant bacteria type in the study area, although iron related bacteria and total aerobic bacteria are also present. All of these bacteria cause clogging, corrosion, odours, and other problems.
• Well replacement due to performance deterioration becomes increasingly likely after 15 years. Most wells appear to show very few symptoms of biofouling for the first five years.
• A reduction in yield is likely occurring in all of the biofouled wells located within the study area. Owners of low yielding wells are likely the first to notice a reduction in yield. Owners whose usage is much less than the well's capacity would likely not notice a gradual decline in yield, unless they are carefully monitoring the well.

INTENSIVE DIAGNOSTIC TESTING OF SEVEN WELLS

• Biofouling was evident in each of seven wells chosen for detailed diagnostic testing. The down hole videos confirmed that all seven wells showed one or more of the following signs of bacterial growth: biofilms (slime), bacterial threads, bacterial flakes, and cloudy water. The adjacent figure summarizes observations in one well.
• All seven of the wells were biofouled by very aggressive sulfate reducing bacteria.
• Clogging by bacterial growth is very likely causing a reduction of water flow to these wells. This clogging is caused by an accumulation of biofilm, secreted by the bacteria, that fills the well intake openings and the pore space in the aquifer surrounding the well.

LAB STUDIES

Lab tests were used to evaluate a new Ultra Acid-Base (UAB^TM) treatment process developed by Droycon for the rehabilitation of severely biofouled small diameter water wells. The results were very promising and field trails are scheduled for fall 1997 to confirm the effectiveness of the UAB^TM treatment process on typical farm wells.

CURRENT RECOMMENDATIONS

PFRA is continuing to work with Alberta Agriculture, Food, and Rural Development, Alberta Environmental Protection and the water well industry to promote water wells that last for generations. Studies are currently underway to determine the optimum well maintenance and monitoring strategies for this area. IN THE INTERIM, the following is recommended:

1. Preventative maintenance should be carried out in all wells to control biofouling. Shock chlorination once or twice a year is currently the method most often recommended to control biofouling. Well owners can do this themselves or they can hire water well drillers or well service companies. In recent years, newer chemical products have been developed that are reported to have some advantages over shock chlorination (the chemicals are less corrosive and safer to handle; the chemicals penetrate the biofilm more effectively)> Contact your local well driller(s) for ore information.
2. Well owners should monitor their wells on a regular basis. (see r Wells that Last for Generationsication available from Alberta Agriculture, Food, and Rural Development, Alberta Environmental Protection, or PFRA). Monitoring allows a well owner to determine the optimum time between well maintenance. In the study area, monitoring of sulfate reducing bacteria levels will determine the degree of biofouling in about 90 per cent of the wells. A simple monitoring tool for this bacteria (the Presence/Absence SRB-BART^TM test) is available from Droycon Bioconcepts Inc. (306-585-1762 or E-mail: "roy.cullimore@uregina.ca").
3. Alternatives to well replacement should be investigated when biofouling has progressed to the stage where well maintenance will no longer work effectively. Technologies have emerged in recent years that may allow wells to be rehabilitated rather than replaced. As well rehabilitation generally requires the presence of a drill or service rig, the addition of chemicals, and substantial experience with this type of work, qualified members of the water well drilling or well servicing industries should be consulted.

Acknowledgements

Funding for this study was provided under Agriculture and Agri-Food Canada's Rural Water Development Program and under the Canada-Alberta Environmentally Sustainable Agriculture Agreement. Technical assistance provided by Dr. Roy Cullimore and Twyla Legault of Droycon is gratefully acknowledged. Video logging assistance provided by Alberta Environmental Protection is also acknowledged.

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