PURPOSE: This rule describes the minimum standards that must be met in developing a monitoring well.

1. (1) Monitoring well development serves the function of cleaning up the well, setting the filter pack and allowing for the collection of a representative sample from the horizon being monitored. The purpose of development is to remove any fine grained material from the well screen and filter pack that may interfere with analyses and return the monitoring zone to its original hydraulic state, which was disturbed by the drilling of the well. Development will also redistribute the sand grains within the filter pack to allow for coarser sand material to congregate near the slotted screen and finer sand grains may be removed by development.
2. (2) Methods Used to Develop Wells. The method used must not introduce any contaminants into the well. Wells must be developed until water representative of the formation is discharged. The volume of fluid should be a multiplier (three (3) times minimum) of the amount of fluid lost to the formation during drilling or added to the well during development. Mechanical surging in combination with pumping or bailing is a recommended method for well development. Water must be moved both in and out of the filter pack to rearrange the sand grains. If a well is completed in a silt or clay rich material or if the screen straddles the water table, the well discharge may never totally clear up. The purpose of the well development is to remove formation damage caused by the drilling process and produce water that is representative of the formation. The well should be capable of producing clear water samples using appropriate sample methods.
3. (3) The use and installation of sampling, development, maintenance, or testing devices and equipment in monitoring wells, including extraction wells, is not regulated except that pumping system installation in extraction wells used for remediation or clean-up must be performed by a nonrestricted pump installation contractor.

AUTHORITY: sections 256.606, 256.626 and 256.637, RSMo (1994).* Original rule filed Aug. 17, 1993, effective March 10, 1994. Amended: Filed July 13, 1994, effective Jan. 29, 1995. Amended: Filed Nov. 1, 1995, effective June 30, 1996. *Original authority: 256.606, RSMo (1991) and 256.626 and 256.637, RSMo (1985), amended 1991.