By Hans Peterson, SRC, Saskatoon SK, Rob May, PFRA, Watrous SK and Bob Buchanan, Alberta Agriculture, Food and Rural Development, Barrhead AB
Most dugouts were designed purely from a water supply perspective with little consideration for water quality. Their main function was to trap water and to then store it.
The major problem with this is that the dugout water originated mainly from runoff across agricultural land, bringing with it nutrients and organics. When this type of water is put into a stagnant hole in the ground, it provides all the requirements for extensive biological growth by both weeds and phytoplankton, often resulting in terrible water quality. Such water bodies are difficult to manage because, in addition to being full of nutrients, dugouts are shallow and are constantly being mixed. As a result, sediments (also full of nutrients) are dragged from the bottom up into the water making the water quality problem even worse.
Some band-aid solutions have been advocated in the management of these water reservoirs, including the use of various pesticides (e.g. copper sulphate and diquat), inorganic chemicals (e.g. lime, aluminum sulphate, and ferric chloride), as well as various other products of doubtful utility, including hydrogen peroxide and chlorine. Some of these treatments are potentially quite effective in reservoir management, especially if they make the nutrients unavailable.
However, following dugout treatments with such chemicals, there is the potential for more runoff entering the dugout, re-introducing nutrients, dissolved organics, and parasites. To avoid this problem, a small elevated sedimentation pond is recommended. During pond construction, the excavated clay material can be used to construct a berm which will prevent runoff water from entering the pond. The berm can also be compacted and thereby provide additional water storage.
The pond should have steep slopes and weed growth can be discouraged by either a plastic liner or a floating plastic cover. In areas with low clay content, this pond can be lined and an extra precaution can be taken by rototilling in bentonite into the soil at the bottom of the pond and 30 cm up the side-slopes.
The simplest intake system consists of putting the poly-pipe through a small hole that is cut in the poly-liner and tying the liner around the pipe to make a water-tight seal. Should it leak around the intake pipe, the bentonite would effectively seal it and quickly stop any leak. One such pond was constructed in 1995 (200,000 L capacity) and several similar ponds (300,000 L capacity) are now under construction. Water is pumped into the pond, and drainage water from surrounding areas cannot enter it because of the raised berm. The water in the pond can be effectively and inexpensively treated because of the plastic liner and low volume of the pond.
We suggest that dugouts be retrofitted with a treatment pond that will hold a six-month supply of water. This water should be treated with a heavy dose of a coagulant (alum or ferric chloride), which can effectively remove parasites and dramatically lower the content of organics in the water (including colour). During the summer, a floating plastic cover can be put on the pond; this cover is small enough to be removed in the fall and stored until the following spring. The water would then be able to be treated with conventional equipment or with alternative treatment methods, such as biological filtration, nanofiltration, or reverse osmosis.
Elevated sedimentation ponds are ideal for people who are battling water quality problems with their existing dugouts. They are less expensive to construct than trying to re-excavate (clean out) an existing dugout. They will also provide a much longer-term and more reliable solution to dugout water quality problems. We often refer to these as two dugout systems.
One such sedimentation pond was constructed in the Outlook area. In October 1995, this sedimentation pond was coagulated by the addition of alum until the pH level reached 5.9 (starting pH was 8.6). Sixty litres of liquid alum was added in less than 30 min. The pH had recovered to 6.3 the following day. Phosphorus immediately decreased to below the chemical detection limit (90% reduction). The day after treatment, the dissolved organic carbon level had dropped from 4.7 mg/L to 1.9 mg/L (a 60% reduction). Chlorination of water with a dissolved organic carbon level of 2 mg/L would likely produce trihalomethane (possibly carcinogenic compounds) four times lower than that recommended in the Guidelines for Canadian Drinking Water Quality. This water after coagulation had a dissolved organic carbon content that is on average less than 50% of Regina and Saskatoon. Maybe the time will come when people from the cities will haul water from their friends in rural Saskatchewan instead of the other way around!
To contact the authors, write to the Saskatchewan Research Council, 15 Innovation Blvd., Saskatoon, SK S7N 2X8.
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