April 17, 2014
By Terry Arko
Before draining a pool for closing, cleaning, or renovation, consider the effect the water will have on the environment. Unfortunately, swimming pools can contribute to the pollution and degradation of our waterways and oceans. As responsible owners, it’s important to realize how pools affect the environment and make every effort possible to minimize their environmental impact. More than 1000 fish died last October when water from a heavily chlorinated swimming pool in Vancouver was drained directly into the Musqueam Creek.
Another contamination problem arising from pool water can be excessive levels of nutrients, such as phosphates and nitrates. When lakes, rivers, and streams become overwhelmed with the by-products of increased agriculture and industry, the result is an influx of algae-enriching nutrients that decrease dissolved oxygen levels and kill fish. Nutrient-rich water in streams and rivers that flow to oceans cause persistent red tides comprising toxic algae that kill marine mammals and fish. Additionally, people who come in contact with algae may also develop respiratory illnesses. Environmental experts agree the only way to solve increasing algae problems is to limit the amount of nutrient pollutants entering our lakes, rivers, and streams.
When preparing to drain a pool, the first step is to evaluate the water’s condition. Has the pool been properly sanitized throughout the season or is it a swamp? Is the chlorine level high? Does the water contain high levels of metals or salts? Is it properly balanced? Has it been tested and treated for phosphates?
If the water hasn’t been sanitized recently or is in a swamp condition, super chlorinate it to kill bacteria, algae, and organic matter. If draining to the sewer is permitted, you may not need to super chlorinate the water, as it will be treated at the municipal plant. If you do super chlorinate before draining, decrease the chlorine to 30 ppm and hold it for 12 hours. This will inactivate most bacteria and protozoa that can be present.
Before draining your pool, ensure the water is dechlorinated. The best way to achieve this is to stop chlorinating the water so levels decrease naturally. Be sure to allow several days before draining. If it is not possible to allow the chlorine level to come down naturally, the pool can be quickly dechlorinated using sodium thiosulfate. It takes about 25 g (0.9 oz.) of sodium thiosulfate to remove 1 ppm of chlorine in 10,000 l (2642 gal) of pool water.
Once the pool has been dechlorinated, test for phosphates and, if needed, treat the water to decrease levels to at least 125 ppb before discharging. Treating for phosphates is a simple eco-friendly practice that can help minimize a pool’s environmental impact before draining.
After treating for phosphates, add a natural-based clarifier and filter for at least 24 hours. Look for products that are oil-free and non-synthetic.
Before draining, check for the potential of hydrostatic pressure, which can occur when your pool is located in an area with a high water table from heavy rains, or near a lake, river, or an underground spring.
Check with your builder to ensure your pool is equipped with a hydrostatic relief valve. (These are usually located at the deepest point of the pool, likely in the floor’s main drain.) When draining the water, the valve opens automatically to allow ground water underneath the pool to enter and equalize the pressure within and without the structure.
At a minimum, you should always know what the water table level is for the area in which your pool is located. Failure to check this could lead to literally popping the pool out of the ground when draining, which can cause major damage and expense. If you are unable to drain to the sewer, consider a grassy area such as a field, as this will provide natural filtration to remove many chemicals and nutrients that may still be present in the water. When draining anywhere, it is recommended all chemical levels be as low as possible. Never drain high chlorine water onto lawns, as this will kill and bleach the lawn.
Many pools now use salt chlorine generator systems to sanitize. Some jurisdictions have strict regulations for draining salt chlorinator pool water. For example, Winnipeg’s city service water and wastewater department prohibits pool water from being drained into catch basins (i.e. storm drains). Instead, it advises disposing salt water in one of the following ways:
Using eco-friendly water treatment products combined with the techniques discussed here can result in swimming pool water that is clean, clear, and safe. From opening your pool this spring, treating the water during the swimming season, and closing it for the winter, a simple regimen of care can ensure an enjoyable and safe swimming experience for you and your family.
Terry Arko has more than 30 years’ experience in the swimming pool and spa industry, working in service, repair, retail sales, chemical manufacturing, customer service, sales, and product development. He is also a certified pool operator (CPO) and CPO Instructor through the National Swimming Pool Foundation (NSPF). Arko is currently product specialist for SeaKlear Pool and Spa Products a subsidiary of Halosource Inc., a clean water technology company based in Bothell, Wash. He can be reached via e-mail at firstname.lastname@example.org.
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