102 



Critical Scientific Issues and Recommendations: 



Many imponant scientific issues were raised by the NMFS Biological Opinion. Several of 

 these issues were also ones I had raised in my review of the EPA Biological Assessment The 

 Conservation Recommendations of NMFS largely address these issues. I summarize and amplify 

 below the issues/recommendation 1 feel are most imponant. 



Literature review: 



I agree with the NMFS that a thorough comparative review of existing ocean outfall sites 

 should be required (NMFS recommendation A-8). I believe, however, that this should be done 

 prior to issuance of the NPDES permit The focus of the review should be on examlnadon of 

 impacts of nutrient loading on plankton and benthic community structure, species distribudon and 

 abundance, productivity patterns, plume transport, toxic loadings and their spatial and temporal 

 incorporation into the food webs, and other components of habitat degradation. New insights are 

 likely to be gained by examining sites with similar physical or biological propcnies to the Bays 

 region. This analysis should include examination of historical satellite imagery (CZCS and IR) to 

 determine patterns and extent of cutrophicarion in relation to wind forcing. The literature review 

 alone, however, is insufficient, and further modeling and monitoring studies are needed. 



Modeling: 



If effluent dilutions predicted by the modeling studies of Roberts and Signell are correct, 

 nutrient and toxic increases in habitat areas will be indistinguishable ftom background levels. This 

 presupposes that the modeling results are accurate. Although the NMFS asserts (p 36) that the 

 model has a "high degree of reliability relative to verification with field data", they also note (p 28) 

 that the model is not accurate for summer conditions. It would be worth comparing the modeled 

 dilution contours shown in Rgure 4 with field data. 



Potential prtiblems that remain to be addressed with the modeling studies are related to initial 

 dilution, sub-grid scale mixing, stratification, wind-forcing, and Gulf of Maine boundary 

 conditions. Specific problems to be addressed include: 



• The accuracy of tiic initial dilution model is critical, since, on a volume basis, the daily discharge 

 volume is approximately the same as the volume of tiie initial dilution zone. This means tiiat the 

 latter volume must nimovcr 50 times per day for a 50:1 dilution. The EPA mixing zone (1.2 km2) 

 contains a volume tiiat is only 3-7 times that of tiie daily discharge. In order to meet EPA dilution 

 requirements at the edge of the mixing zone, the turnover of the volume of this zone must be very 

 high. The model of Roberts indicates that the proper dilution will be achieved and EPA asserts that 

 the model predictions are even conservative, but, to my knowledge, the effects of wind and tidally 

 induced advecdon have not been examined. 



*iA°"c""^ stratified conditions, the tiicrmocline in Massachusetts Bay is at depths of 10-25 m (p 

 10). Since tiic bonom depth at the proposed site is about 30 m, tiiis means the distance between 

 Uiennocline and the diffusers (which will be on the bottom) will be only 5-20 m. It is not clear 

 whether tins distance is enough for tiic discharged effluent to mix sufficiently so that it will not 

 penetrate the thcrmocline and enter the surface mixed layer. 



• If sub-grid scale mixing processes are substantially different from those modeled, plume patches 

 including filaments and streamers could remain intact in the surface layer or at tiie pycnocline over 

 longer periods tiian predicted by tiie current models. 



