Recovery well pump material in low pH Groundwater

[JimPA]

I'm working on a pump and treat system for a contaminated groundwater site with low pH (3.1-4.5). My consern is with the material compatibility and life span of the well pumps. It is predicted that the system will operate for 15 years. Grundfos claims that the typical application is pH 4.0-7.0 and that the standard 304 stainless steel pumps last 7-10 years. The pumps are available in 316 SS but they have no known experience with water of such low pH. I have no chloride data to share. I'm looking for anyone with experiences with these pH's and/or recommendations for material selection in my situation. Any help is appreciated.

 

[bimr]

Natural groundwater will never go below a pH of 5 because the only thing that causes a low pH in groundwater is CO2. So, the pH that you are anticipating is very unusual. To get below a pH of 5, you need a strong acid (HCl or H2SO4).

I would not be concerned about chlorides unless you are anticipating a chloride concentration over 2000 mg/l. Unless you are close to the ocean and expect saltwater intrusion or something to that effect; you do no have to worry about chlorides.

Most of the groundwater contamination issues have to deal with organic chemicals. Any of the SS's are well suited to handle organic applications.

A SS pump is going to stand up to anything in your groundwater. Even if you have a low pH, that does not mean that the concentration of chemical that is causing the low pH is at a significant concentration. SS's will also handle low concentrations of strong acids. The 304 SS is OK, if the 316 SS is only slightly more, then go with it.

You also should remember that as you are pumping, you should be getting cleaner and more dilute water as well. You should also investigate the complete materials of construction of the pump. You may have a washer, o-ring, or nut made of a less resistant material. That material would then be the weak point.

 

[JimPA]

Thanks for such a quick reply.
Your right that the GW pH is unusual, it is do to past waste acid releases/"disposal". The price difference for the largest of the four pumps (model 150S(N)75-4) is $2,000 vs $3,500. (The formula for cost of 316ss for all Grundfos submersables is 1.5 x 304ss cost) I would assume that labor costs to replace pump would be another $1,500.

If Grundfos claims a 7-10 year life for the 304ss pumps I wouldn't think that the 316ss pumps would last much longer considering failure due to wear. So if we plan to operate for 15 years, all pumps would require replacement once anyway. Sounds like 304 is the way to go.

 

[DMcGrath]

We have had good success with the HammerHead pump from QED Environmental in pumping contaminated groundwater, landfill leachate, etc. It is an FRP pump with SS components and is air driven. Fits down a 4" well casing as well. Of coursse application is head and flow driven as well....Another maker is EPG. They make all SS pumps that are used in landfill leachate pumping and they last for years while submerged in leachate.