(1) Preventive measures shall be performed to ensure against contamination from equipment used to install or sample monitoring wells. Particular care must be exercised when equipment used to install or sample monitoring wells in contaminated environments is subsequently used to install production wells for domestic use.

(2) When practicable or feasible, monitoring well installation should proceed from areas with no or low levels of contamination to areas with higher levels of contamination.

(3) If contamination is detected during installation of a monitoring well, down-hole equipment should be decontaminated before use on another well or at another site. Appropriate methods of cleaning or decontamination will depend upon the level and type of contaminants, but may include steam cleaning, rinsing with uncontaminated water, or thorough cleaning with surfactants and deionized water.

(4) Contamination of down-hole equipment on the drill rig itself by hazardous materials requires thorough cleaning to prevent transport of hazardous contaminants to other locations. On-site decontamination may be necessary under particularly hazardous conditions.