167 



* 'To predict nutrient concentrations under various environmental conditions and 



wastewater management scenarios in farficld arcas in supfKjn of the biological impact assessment; 



• To predict toxic chetnical concentrations under various environmental conditions and 

 wastewater treatment scenarios in the farfield areas; 



• To update predictions of water quality compliance/non-compliance for specific toxic 

 efQuent constituents (copper, mercury, dieldiin, and PCB) that were predicted to potentially exceed 

 criteria in the Final SEIS and taking into account new loadings presented in Shea, 1992." 



These three needs cannot be fulfilled by the model output as it now exists. First, 

 discussion is lacking regarding the manner in which nutrients are to be transported. There is no 

 simple connection between the hydrodynamical model of USGS and transport of advected/diffused 

 materials: such transport calculations require a more complete water quality model that includes 

 advective and diffusive processes. To my knowledge, the USGS model will not suffice for this 

 purpose, but instead, the ESTM will have to await the HYDROQUAL model results. 



Second, the chemical contaminants commonly become associated rapidly with sediments 

 (organic or inorganic), and are rapidly recycled to the bottom sediments. This process is not part 

 of the USGS model, and thus the model in its present form is not germane for the question of 

 compliance. Though this approximation may provide an estimate of the highest expected 

 concentration of these materials in the water column (a useful calculation) due to direct input from 

 waterbome sources, it ignores the actual processes which accumulate and concentrate toxics in 

 small areas. For instance, geoaccumulation could concentrate toxic chemicals near the bottom; 

 storms could consequently release these materials to the water column, resulting in non-compliance 

 events not estimated by the present analysis. Such calculations require a water quality and 

 sedimentation model, which may not be available until Spring, 1993, or later. 



The Work Plan does propose application of one water quality model: the coupled TEA 

 hydrodynamic model with the companion ELA water quality model. TEA and ELA must be three- 

 dimensional if they are to predict the water quality parameters accurately. Will TEA results be 

 compared with the USGS model? How will the vertical structure of the water column be included 

 in the calculations? What data are to be used to "calibrate" or "verify" the TEA/ELA model as 

 applied to Massachusetts Bay? The Work Plan only states it will use available data for such 

 verification. Are such data adequate to provide the "validation" to within 10 percent, as suggested 

 by the Work Plan? Probably not. This application seems wrought with questions, which cannot 

 be addressed with the abbreviated work plan and sketchy details. 



The Work Plan (or at the least the ESTM) should motivate the application of these different 

 numerical models (TEA/ELA versus USGS/HYDROQUAL) for addressing different issues. It 

 might be better to use the USGS/HYDROQUAL models when they become available, as they are 

 supposed to be superior to the TEA/ELA models. 



GEOLOGICAL PROCESSES: 



Once material enters the water column, whether suspended, dissolved, or otherwise 

 present, it is normally cycled through a variety of chemical, biological, biogeochemical, and 

 geological processes. One common process is the accumulation of toxic material on sediments 

 (through a number of mechanisms) and the subsequent rapid setding of those materials to the 

 bonom of the Bay. This process of "scrubbing" of paniculate or dissolved material from the water 

 column can result in accumulation of toxics in depocenters. These materials may remain for 

 prolonged periods, be covered by sediments and removed from further processing, or may be 

 resuspended and retransported to another location. Physical processes commonly dictate that 



