Minimizing enviromental damage from drainage

[aussiboy]

I own 16 acres on Beaver Lake, Arkansas which will have 40 houses. I want to install a pool for use by residents, indicatively 75 feet by 30 feet. It is not connected to the city sewer so it will have an on site community septic waste water system.
Filter backwash and pool drainage can not be discharged into the above septic system. It can be drained onto the property as long as it does create a public health nuisance.

To the extent the pool needs to be drained e.g. for repairs, or water splashes over the side and needs to be drained, I can drain the water to the heavily forested dirt on the site. However, I want to ensure the least possible environmental damage to the site from drainage as retaining the forest is very important. Plus water discharged could find its way into Beaver Lake which is a water source for local residents and is used for swimming and I would not want to interfere with the ecology of the Lake.

What sanitation system/s for the pool would you recommend to minimize any environmental damage from drained water? For example Wikipedia says salt chlorinated pools have been found to generate unacceptably high levels of carcinogenic disinfection byproducts, the predominant form being bromoform.

Many thanks

 

[teapot]

Hi Aussieboy,

I would be careful of most wikipedia postings as it is a free donation encyclopedia and many articles are steered by people with vested interests, i.e. Ecosmarte, not eco or smart IMO.

This forum is used by people who mostly only subscribe to chlorinated pools be they salt chlorinated or direct chlorination. That said if you have the space for a holding tank then splash out and maintenance water could be stored until the chlorine has reduced or could be filtered with activated charcoal to remove the chlorine and by-products.

There are other alternatives using very low levels of chlorine but chlorine is pretty much the best at what it does.

PM me if you want further information.

 

[chem geek]

First of all, welcome to TFP!

As for the environmental impact of what is in your pool, it partly depends on what you will put into your pool over time. For example, if you use copper-based algaecides or Borates or other persistent algaecides, then these will tend to disturb plant life generally if too concentrated. The key is sufficient dilution of the water so if this is a one time dump event, then spreading the water around a large area and watering with additional water (if possible) will minimize the concentration. This is also helpful to reduce the salt content of the pool which can also be harsh to more delicate plants.

The chlorine itself is the easiest to take care of since you can either let it drop on its own or use a chlorine reducer (such as sodium thiosulfate). You don't need to get below 1 ppm FC since even tap water (in many areas) has that level of chlorine and is not (that) harmful in watering. The EPA allows up to 4 ppm FC in drinking water so unless you are at rather high FC levels, I wouldn't worry so much about the chlorine. If it is a concern, then the chlorine reducer or activated carbon filter (as teapot mentioned) can be used such as on the outlet for backwashing (most likely requiring a temporary holding tank since most water filters don't handle very high GPM rates).

The Cyanuric Acid (CYA) in the water will get broken down by soil bacteria into ammonia so essentially acts like a form of fertilizer (a source of nitrogen).

The other major components in pool water are calcium and bicarbonate which are relatively innocuous compared to the above.

75 x 30 x 4.5 feet (I'm assuming an average depth) would be around 76,000 gallons. Backwashing varies, but generally water replacement in a commercial/public pool is around 7 gallons per person (possibly person-hour). Let's just figure on 250 gallons per week which may be on the high side. If I assume typical pool values of 3 ppm Free Chlorine (FC), 80 ppm Total Alkalinity (TA), 50 ppm Cyanuric Acid (CYA), 300 ppm Calcium Hardness (CH) and around 1000 ppm Total Dissolved Solids (TDS), then the following are the weight of substances for a complete drain and for a weekly backwash.

............. Drain ......... Backwash ..... Comments
FC ..... 1.9 pounds .. 0.1 ounce ..... 1.8 gallons of 12.5% chlorinating liquid for drain (1-1/2 tablespoons for backwash)
TA ..... 90 pounds ...... 5 ounces .... sodium bicarbonate (aka baking soda)
CYA ... 32 pounds ... 1.7 ounces .... cyanuric acid (aka stabilizer or conditioner)
CH ... 211 pounds .... 11 ounces .... calcium chloride (anhydrous) plus some magnesium that is part of total hardness
TDS .. 317 pounds ..... 1 pound ..... about 500 ppm TDS is from the above so 500 ppm additional listed here is salt (sodium chloride)

Richard