Monitoring and recovery of free product, spilled gasoline and other organic liquids floating on groundwater, is a big issue at thousands of gas stations in the United States.  Pall Corporation's Schumasoil^® well screen is made by sintering polyethylene beads, hence lacks large openings and is hydrophobic.  The fundamental questions that our research attempts to answer are:  (1) What pore size screen should be used for a given aquifer grain-size distribution? and (2) How does the Schumasoil^® screen compare with the screens commonly used at free product sites?  Laboratory sand-tank experiments were performed to test the screen.  The first experiments focused on two of the main well-screen design variables:  screen pore size (four choices: 200, 80, 40 and 20 microns), and aquifer grain-size distribution [five choices: well-sorted (coarse, medium and fine sands) and poorly-sorted (coarse and fine)].  We performed a factorial series of experiments using all four screen sizes in each of five different matrices.

In most experiments, the 20-micron screen did the best; in a few experiments, the 200-micron screen did slightly better.  The 20-micron screen often excluded water, making the screen act essentially as an oil-water separator.  The small pores of this screen seem to attract kerosene preferentially, becoming highly saturated with kerosene.

We also performed an experiment comparing the 20 and 200-micron Schumasoil^® screens with the best screens available on the market, wire-wrapped stainless steel and PVC.  The 20-micron screen outperformed both of these and the 200-micron Schumasoil^®. 

Further testing of Pall Corporation's Schumasoil^® screens in the field in free product monitoring and recovery wells will measure the effects of aquifer variability, free product biodegradation and screen clogging at a more representative scale, and will determine the need for gravel packs and the best modes of well development.