WorldWide Drilling Resource

23 WorldWide Drilling Resource ® AUGUST 2013 Environmental Monitoring by Thomas Kwader, Ph.D., P.G. Preventing Well Biofouling - The Key is in the Well Construction Biofouling, the growth of unwanted algal slimes and encrustation, can occur in screened and open hole well con- structions. There is, however, one fac- tor common in both types of wells that experience reduced well yield due to the growth of bacteria (biofouling) in these wells. The factor is air, and proper well construction can prevent air from im- pacting the well. Generally, the deeper the well cas- ing, the less air (oxygen) is present in the groundwater. Ideally, a properly de- signed well should have plenty of well casing below the water level to ensure the water level does not draw down below the top of the screen or open hole. Why? If the water level drops to below the top of the screen or bottom of the casing, any water falling or cas- cading into the well will pick up air, which tends to promote bacterial growth in and near the well. The bacteria will grow and potentially plug pores in the formation, well screen, and impellers of the pump. Once plugging begins, it actually pro- motes more plugging by causing more drawdown, which causes more plugging. The plugging of the screen and bore- hole can be difficult to eliminate because the chemicals used to kill the bacteria must reach out to all areas to contact and kill the bacteria. Any bacteria not killed will quickly multiply and grow to all areas where there is food (dissolved metals, sul f ides, etc.) and oxygen present. Unfortunately, once a well is con- structed, it is very difficult to modify the construction to eliminate the cascading of water in the well. The best solution may be to reduce the amount of draw- down in the well by reducing the flow (using a smaller pump or valve at the surface) to keep the water level higher in the well casing. Also, during the design of the well, the use of a shorter screen length and lower pump setting to maintain submer- gence of the open hole or screened portions of the well will minimize the chance of biofouling to occur. Tom Tom Kwader may be contacted via e-mail at admin@ worldwidedrillingresource.com )0&"%1 "6)&4 ,, ,, 2)&0 -%3120*"+ )0&"%1 "-% 312., )0&"%1 "-3'"$230&0 .' -&02*" !&+%&% 0*++ */& 3"+ !"++ 0*++ */& !*0&+*-& 0*++ .% "1*-( .,/.1*2& !*0&+*-& 0*++ .%1 .-*$ 0*++ */& "1*-( *21 &0$311*.- "1*-( *21 0*++ .++"01 *1)*-( ..+1 3#1 2"02&0 .%1 "-% 2"#*+*7&01 0*++ */& -$ )*0% 2 8 !*-12&% ).-& 8 8 "5 2., %0*++/*/&*-$ $., The October issue deadlines are: Space Reservation - August 23 rd . Ad Copy - Display & Classified - August 30 th .