Problems With Free-Product Recovery
During my 33 years in the environmental field, I have been involved in a lot of sites with free product. In the 1980’s light non-aqueous phase liquids (LNAPL) such as gasoline were removed by the following methods:
- Bailing by hand with a disposable bailer from a well
- Pumping with a 2 pump system (depression pump and product pump)
- Pumping with a total fluids pump and separating above ground with an oil\water separator
- Skimming with a belt skimmer in to a drum above ground
- Pumping with a peristaltic pump (shallow applications)
- Using the in-well product skimmer developed in the late 80’s
The product skimming pump is still used a great deal today, in addition to removal methods such as dual phase extraction. The pumps have evolved from a pump that recovers product and water and expels the water back into the well before pumping the product to the surface, to a pump that only recovers product. Is there such a thing as a pump that will only recover and pump product? From a design point of view, yes, but from an application point of view, not really.
Why would a pump designed to recover and pump only LNAPL still pump water or not recover product? We will assume we are using a recent model pneumatic pump with a floating intake (span of 18 inches) and a reservoir that is above the floating intake. I have compiled a list of the items that can and will cause the pump not to work as designed:
- No product in the well to recover
- So little product in the well it could take months to fill the hose to ground surface(assuming the empty cycle is set just to move the recovered product out of the pump and above the check valve using a minimum amount of air)
- The intake on the pump is installed below water or become submerged soon after installation
- The pump intake is installed above the product
- The intake on the pump is blocked by biomass due to lack of maintenance
- The compressor pressure is set too low for the pump to operate or set too high and damaged the pump soon after installation
- The compressor is on but the air valve is off, or the compressor is not on
- The lines in the well were kinked during installation of the pump
- The pneumatic timer in the pump is not operating due to slime and/or water in the air supply. The air dryer recommended by the pump manufacturer was not used due to cost
- Pump check valves blocked by debris not allowing the pump to expel the product
- The product in the well is a DNAPL and a LNAPL pump was installed to recover it
At first glance you may think some of the scenarios above are too stupid to occur. Considering the lack of course work available at universities for this area and the lack of training given to those who are sent to install these pumps, this stuff happens all the time. Are the manufacturers blameless in this scenario? Not really. Most don’t spend any more time producing procedures for installation than the consultants spend training the installers. It is mostly common sense, right? Or is common sense a lot less common these days?
When is a good time to use a product pump?
When you have isolated pockets of product and actual thickness in the formation of 2 inches or less.