Procedures for the Collection of Representative Water Quality Data from Monitoring Wells

Data collected from six monitoring wells at waste disposal sites in Illinois were used to evaluate procedures for the collection of "representative" water samples from monitoring wells. The effects of four types of pumping mechanisms, the extent of well flushing, the rate and time of pumping, and storage and preservation techniques on chemical composition of water samples were studied. Pump tests and multiple sample experiments provided data on which recommended sampling protocols and sample preservation, preparation, and storage procedures are based. The selection of the type of sampling device; sample preparation, preservation and storage; and sampling procedures all must be tailored to the size and accessibility of the individual well, its hydrologic and chemical character, the chemical constituents of interest, and the purpose for monitoring the site. Generally recommended sampling procedures include: 1) using peristaltic or submersible diaphragm type pumps when possible; 2) conducting pump tests prior to sampling to determine sampling frequency and time and rate of pumping; 3) flushing the well by pumping four to six well volumes; 4) measuring key parameters such as pH, specific conductance, oxidation-reduction potential, and alkalinity at the time of sample collection; and 5) filtering samples immediately on site through a 0.45 μm pore size filter and then preserving the samples immediately after filtration, according to U.S. EPA (1979) recommended procedures. i