Once-through cooling water systems for thermal power plants offer an economical means of dissipating the differential energy of modern-day turbines. Before the decision to proceed with the design of a oncethrough cooling water system is made, a considerable study effort must be undertaken in order to determine that no harmful effects will accrue to the environment from the plant's operation. These studies must include: 1. A comprehensive literature search 2. Field investigations of the air and water 3. Analytical evaluation of the field data The Pacific Gas and Electric Company has been conducting environmental studies at its operating thermal power plants and at proposed sites since 1958. This paper describes the approach used by the Company in conducting environmental studies. Meteorological data were obtained from on-site sensors, stored on magnetic tape, and subsequently computer-processed. Oceanographic data in the form of water temperatures, salinity, and dissolved oxygen profiles, as well as current speed and direction, were obtained from surface vessels. Remote sensing systems were used to obtain dispersion and dilution information, sea-surface temperature data, and aerial photographs of flora indigenous to the study area. All remote-sensed data, except for the aerial photographs, were stored on magnetic tape, in flight, and later processed in the computer with graphic off-line printout.

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