OAR 690-240-0460: Monitoring Well Screen, Filter Pack, and Filter Pack Seal

(1) The screen and filter pack, when properly designed and installed, allows a water quality sample to be collected that is representative of water in the formation. (2) The well screen shall: (a) Be commercially fabricated and constructed of material that is not knowingly readily reactive with the subsurface environment; (b) Have a collapse strength great enough to withstand the pressures exerted during construction and development of the monitoring well; (c) Be in new or like new condition, being free of pits or breaks; (d) Be cleaned using methods outlined in OAR 690-240-0450(3); and (e) Be centered in the borehole. (3) The use of lead packers with the screen sections is prohibited. (4) A bottom cap or end plug shall be attached to each well casing. (5) The filter pack shall: (a) Consist of clean, chemically inert, well rounded material; (b) Not extend more than three feet above the top or one foot below the bottom of the well screen; and (c) Be placed in such a manner as to ensure placement opposite the well screen without bridging or size segregation. (6) The filter pack seal shall consist of: (a) A two foot thick layer of fine grained sand above the filter pack if a grout or grout slurry is used; and/or (b) A minimum of a three foot thick layer of dry bentonite. If a grout slurry is to be used as the annular seal, the bentonite shall be adequately hydrated prior to placement of the annular seal to prevent grout infiltration into the filter pack.