recorded from 1700 hours, 21 August to 1400 

 hours, 22 August. Dye injection began at 1500 

 hours on 23 August 1987, at a rate of 5 Ib/h (1.85 

 kg/h). This was increased to 7 Ib/h (2.6 kg/h) 26 

 hours later so that a dye concentration of 2.2 ppb 

 by weight was achieved at the quarry cut. Dye 

 concentrations at the cut were first observed about 

 3 hours after dye injection began and stabilized 

 there about 10 hours after changes occurred at 

 the injection point. Dye injection was suspended 

 at 1750 hours on 26 August at the conclusion of 

 the intensive mapping period (0657 to 1605 hours, 



26 August 1987); flourescence at the quarry cut 

 continued to be monitored until 1200 hours on 



27 August 1987. 



Survey vessels 



Two NUSCO vessels, 'Northeast I' and 'North- 

 east ir, were equipped with instrumentation ap- 

 propriate for use during the intensive mapping 

 phase of the study. Both vessels had Turner 

 Model 10 flourometers equipped with thermistors. 

 'Northeast I' was rigged to allow surficial dye 

 concentration and temperature measurements to 

 be taken along 41 predetermined transects during 

 the four tidal mapping sessions. The transects 

 were oriented nominally perpendicular to the axis 

 of the thermal plume and along well defined 

 plume boundaries. 'Northeast If was rigged to 

 collect depth profiles of temperature and dye con- 

 centration at 27 specific locations to characterize 

 the vertical mixing of the thermal plume. 



Survey vessels were positioned using either a 

 computerized system, developed by OSI, that per- 

 mits an accuracy of ± 50 ft ( 1 5 m) or a manual 

 system employing a hand-held VHF range finder. 

 WTiere the computerized system could be used, 

 the person at the helm could locate the vessels' 

 position with respect to the intended survey 

 trackline on a video monitor. The desired trackline 

 could be followed by making course corrections 

 indicated on the display. Where site conditions 

 did not permit the use of the computerized system, 

 the survey vessel was controlled along a bore sight 

 representing the intended survey transect by the 

 transit operator using the VHF range finder. In 



all cases, actual position data were automatically 

 recorded; tracklines are presented in the Appendix 

 to this section. 



In situ current, temperature and 

 salinity monitoring 



Continuous measurements of current speed and 

 direction, and water temperature and salinity, 

 were obtained from an Endeco Type 174 in situ 

 recording device positioned at stations east and 

 southeast of Millstone Point (Attachment Fig. 1). 

 Stations JCE and JCW were occupied on 24 and 

 25 August and TTIC and MP were occupied on 

 the day of mapping, 26 August. 



Between 8 and 29 October 1987, NUSCO staff 

 deployed two solid-state temperature recorders 

 (TempMentors), which continuously logged water 

 temperatures at two depths, at seven stations (Fig. 

 1). These data loggers provided additional infor- 

 mation on the variability of the position and ex- 

 tent of the thermal plume between tidal stages 

 and under a variety of meterological and opera- 

 tional conditions. The date and duration of each 

 deployment are listed in Table 4. The loggers 

 were returned to the lab and data was processed 

 using an IBM PC. 



TABLE 4. Deployments of the TempMentor continu- 

 ously recording thermistors during 1987. At each lo- 

 cation a thermistor was set 1 m below the surface and 

 1 m above the bottom. 



* see rig. 1 



Presentation of isothermal data 



Because both dye concentration and water tem- 

 perature are considered conservative, the percent 

 drop in the temperature of the plume with respect 

 to the total temperature difference between the 

 discharge water and the receiving body of water 



Hydrothemial Studies 329 



