High pH in Concrete Lake

We own a seaside resort in Chile with a 16 acres man made lake (it can be seen in www.uva.cl/snalfmar )  The water is obtained from wells beside the sea . It has HDPE liner on the bottom and concrete walls. The water of the lake is having a severe increase in pH . This is causing turbidity, chemical and biological problems. Please let us know if these problems could be caused by the concrete.

We also have high sulfate levels. Could this aggravate the problems. We keep waiting your valuable reply.
Thank you for your mail. It was nice to see that we reach around the world as well.  I was unable to see your lake - Web site could not be found - but I will try again later.

I seriously doubt that the concrete is causing the high alkalinity of the water. It would require a very large surface of concrete and very small volume of water to cause any such effect, if at all. I suspect that it has to do with the wells (and soil). Did you have the well water tested?

Besides, alkalinity in concrete comes from Ca(OH)2. In contact with sulfates it reacts to create Gypsum - removing both from the system.

- The high sulfate level in the water (I assume it is in the water...) is not good. Sulfates will cause deterioration of concrete that was not designed to withstand that attack. It takes concrete made with Type V Cement and very low water/cement ratio to achieve protection. This attack will be evident above water level, especially in the area close to that level where the concrete goes through cycles of wetting and drying.

The early signs of attack will be surface scaling, pitting, and spalling of the concrete. If sever enough, the dusty material removed from concrete surface into the water could cause some cloudiness of the water (but not increase the pH).

I suggest sending samples of water from the well and from the lake for complete analysis. This will give you a better understanding of the mechanism involved.

Let me know if this helps, and if you have additional information. Good luck
Many thanks for you reply.

We have done complete analysis of water from the wells and the lake.  The pH from wells is at an average 7.6 , but when we drain the lake and fill it again , after a couple of weeks the pH starts increasing (over 8.8) and the water gets turbid.