I have a well casing with no pump attached in my front yard, it appears to be an abandonded artesian well from the previous owner. When I removed the pipe cap (2 inch pipe), water came up the casing and flowed into the yard, not a tremendous flow rate but enough, and also there were gas bubbles present in the water. I installed an above ground shallow well pump with a foot valve approximately 50 feet down into the well for irrigation purposes. It initially worked fairly well but as the gasses built up inside the well casing while pumping, this pressure pushed the water level down inside the well and this caused cavitation in the pump. When I initially installed the pump and foot valve, I sealed the well casing at the top where pipe runs down into the well. This traps the gasses that build up which in turn causes the water level to fall inside the well. I found that I had to vent the casing (drilled small hole in well head) to get rid of the gas/pressure and this allowed the water level to rise and the pump works fine with no cavitation, but when the pump turns off, water comes from this new vent hole and floods the yard. What can I to do about this gas problem?