This module summarizes four major reasons for employing monitoring during design and operation of a land application site: documentation of existing water quality and system performance, confirmation of design parameters, provision of data for future designs and for management decisions. Monitoring requirements are examined for different land treatment options--overland flow sites and others employing collection of surface runoff, underdrained sites, rapid infiltration sites with recovery wells, and downslope emergence of treated effluent from irrigation sites. Methods of taking water samples and soil moisture measurements are discussed. Wells, lysimeters, tensiometers, and piezometers are described in conjunction with this sampling. Monitoring of parameters other than water is discussed briefly. A very brief summary of governmental regulations pertaining to monitoring is included. (Author/BB)