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46 increased frequency of particle collisions. Thus, shear currents and small-scale turbulence enhance coagulation rates, and high dilution impedes them. Because increased salt concentrations favor coagulation, the dilution of a freshwater waste, such as sewage sludge, with saltwater probably favors coagulation. The distribution of particle sizes is important, with heterogeneous suspensions coagulating faster than homodisperse ones. How these factors interact in the ocean is poorly understood. Nevertheless, coagulation is important in determining the fate of particles because it can accelerate particle sedimentaion. The prediction of sedimentation patterns by computer models (e.g., Hendricks, 1982; Koh, 1982) depends on information of three kinds: (1) the pattern of ocean currents and turbulent diffusion as described in the previous sections; (2) the mass emission rate of waste; and (3) the frequency distribution of fall velocities of waste particles in seawater. Fall-velocity distributions can readily be measured in settling columns by the pipette method. Waste material is diluted with seawater by a factor calculated for the prototype discharge (Brooks et al., 1982; Wang and Koh, 1982). This standard laboratory technique does not reproduce the proper flocculation effects, primarily because the turbulent shear of ocean water is not present. However, it is clear that settling velocities are increased by flocculation, which should cause the sedimentation pattern to exhibit higher fluxes near the discharge point Sediment Resuspension and Bioturbation, Turbidity Currents Sediment resuspension and bioturbation also play important roles as determinants of sediment characteristics in the vicinity of a discharge. Bottom currents at a discharge site can periodically reach speeds capable of resuspending surface sediments in the water. Such events will destroy the chronology of sediment deposition (by winnowing away or redepositing lighter material on the top), oxygenate surface sediments, release interstitial water, deplete dissolved oxygen in bottom water, enhance remobilization, and gradually transport sludge materials away from a dis- charge point. If a waste discharge point is on the continental slope or in (or near) a submarine canyon, sediments may be removed by occasional density or turbidity currents or even sediment slumps. Such removal can carry sediment deposits to deeper water (generally .

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47 considered desirable) but may cause sudden release of fine particles and entrapped trace contaminants to the bottom waters. Bioturbation by burrowing animals (except in anoxic sediments) reduces vertical stratification among sediments, moves particles back to the sediment-water interface, and permits sediment oxygenation and other exchanges with the water column by increasing sediment porosity. Together, resuspension and bioturbation may greatly accelerate the release of contaminants from the sediments and the pore water to overlying waters. Most models do not take account of resuspension or bioturbation, but if these factors could be included, the contaminants would be predicted to be generally more widely dispersed in sediments and water. The primary indicator of resuspension is the distribution of grain size in natural sediments at the sediment-water interface. The smallest sizes remaining at a given place are equal to the largest sizes (with their corresponding fall velocities) that are scoured and carried away by strong currents. Light Scattering and Absorption In the case of near- surface discharge of turbid wastes (like sewage sludge), the transmission of light through the water may be significantly reduced by light scattering and absorption. This causes a decrease in the depth of the photic zone. The reduction in light transmissions can be measured in the laboratory with mixtures of waste and seawater at appropriate dilutions. Volatilization Volatilization represents the transfer of volatile chemicals from the water to the atmosphere. To be important in a waste discharge to the coastal sea, particulate and dissolved chemical species must be trans- formed into dissolved, nonassociated chemical species in which the concentration gradient between water and air favors water-to-air transport. Resistance to mass transfer occurs in both the liquid and gas films or on either side of the air-water interface. For most hydrophobic chemical species, resistance to transfer occurs in the liquid phase. Waste disposal that occurs below the thermocline may not allow chemical species to contact the upper mixed zone and to participate in air-water interactions. Waste discharges at depth do not result in losses of volatile components to the atmosphere unless there is significant vertical mixing.

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48 2.2.2.2 Chemical Processes The distribution of chemical constituents in a wastefield is determined by the method of discharge and the initial dilution described above in the section on Initial Dilution under Section 2.2.2.1. The initial ambient concentration (CO) of any substance (after rapid dilution but before chemical changes are considered) is given by C0 = Cb + (CW - Cb)/(S + 1), where Cb = background concentration; Cw = concentration in waste stream; S = initial dilution, as parts of seawater per part of waste. The chemical and biological processes discussed below (as well as the physical processes already discussed) cause concentrations and fluxes to change over space and time. Sorption/Desorption The sorption of inorganic and organic components on particles depends on the properties of sorbent, sorbate, and solution: Sorbent: concentration, surface area, organic carbon content, lipid content, surface properties, particle size, exchange capacity, composition. Sorbate: concentration, polarity, inorganic versus organic, charge, molecular (ionic) size. Solution: pa, temperature, ionic strength, total cation and anion concentrations of specific components. For inorganic components (e.g., metals), sorption depends mostly on particle surface charge and area, on speciation in solution, and on concentrations of competing ions. Ion-exchange processes at the solid-solution interface also determine sorption of many inorganic species. For hydrophobic organic compounds, the surface area and organic carbon content of the particles, and the aqueous solubility of the organic component of interest, are probably the most important properties. Desorption of chemical species depends on the same factors.

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62 Bight suggests that 85 percent of the discharged tPCBs cannot be accounted for by sedimentation in the region of the outfalls. It is likely that the water column is a major reservoir for them. Assuming a water residence time of 100 days and a plume thickness of ~40 m would give an average effluent dilution of 24,000:1. Thus, the initial sludge stream concentration of 50,000 ng/L will be diluted far field to a concentration of -2 ug/L. Assuming sedimentation and other removal processes, far-field tPCB concentrations of several nanograms per liter are possible. Of this amount, -70 to 80 percent will be in the dissolved phase because of the low particle concentrations of less than 0.5 mg/L. 2.3.1.2 Dissolved Oxygen/Biochemical Oxygen Demand If we assume that secondary effluent mixed with the sludge stream has negligible biochemical oxygen demand (BOD), then the BOD in the layer due to the sludge discharge would be 1.7 mg/L--(-l mL/L). Turbulent mixing would further reduce this to 0.5-0.7 mg/L within 12 h. Total oxygen consumption given unlimited time might be 50 percent greater, or 2.1 mg/L (1.5 mL/L). The dissolved oxygen (DO) content at those depths has the same approximate magnitude, indicating that local impacts might be significant. Jackson et al. (1979) estimated sludge degradation rates under these temperature conditions as 1 percent/ day. If the ambient oxygen concentration is 0.5 mL/L, total BOD is 1.5 mL/L, and no mixing occurs subsequent to initial dilution, biological degradation would halve the oxygen concentration of the sludge-seawater mixture in 18 days. Particle removal by settling and mixing processes will decrease this impact on oxygen concentrations. On the basis of these calculations, it seems possible that the naturally low ambient DO concentrations will be slightly depressed locally in the diluted sludge field near the discharge point. However, the sludge discharge system will be specifically designed to prevent signifi- cant oxygen depletion by various methods as more pre- discharge oceanographic information becomes available. Among methods of controlling DO depletion are (1) reducing the BOD mass emission rate by digesting the waste-activated sludge component, (2) reducing outfall depth to get the plume into water with more dissolved oxygen, and (3) employing larger predilutions of sludge with effluent.

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64 inorganic phosphate, and smaller quantities of organic phosphates. Nitrogen will be in the form of NH3 (or N at), NO3, and organic nitrogen. Upon decomposition/ mineralization of the sludge particles, P and N will be released in biologically available forms. In the Southern California Bight, nutrient concentra- tions are lowest in the surface waters owing to biological utilization, peak at -100- to 300-m depth owing to microbially mediated decomposition of settling particles (see table below), and generally decrease downward to the sediments. Surface Water Middepth Water (0 to 60 m) (100 to 300 m) Nutrient uM uM Phosphate 0.2 2-3 Nitrate ~0 30-40 Ammonia 0.3 0.1 Expected concentrations will be Nutrient Discharge Stream 1:1,000 Wastefield TP 4-12 me 4-12 uM TN 17-43 me 17-43 AM TOC 250-300 me 250-300 uM Thus 1:1,000 of the discharge stream will perhaps double or triple the ambient concentrations at depths of 300 m. Far-field dilutions of an additional factor of 10 to 100 lead to additions much below ambient levels. It is possible that >50 percent of the nutrients in the discharge stream will be in soluble form. Assuming that only 10 percent of the P. N. and OC in the initial sludge stream is deposited in the sediments within the ~100 km2 predicted by Koh (1982), then P. N. and OC fluxes are as follows: TP: 0.1-0.4 g/m2 yr TN: 0.2-0.6 g/m2 yr TOC: 2.5-3.0 g/m2 yr These data should be compared to natural nutrient fluxes to the sediments.

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66 seawater. Jackson (1982) calculated the increased metal concentrations in seawater, assuming that the metals are released in proportion to the dissolution of organic matter. Such a calculation has been adapted to the proposed Orange County outfall (Table 2.2). Compared with the uncontaminated levels of cadmium, chromium, copper, lead, nickel, silver, and zinc, sewage disposal will not increase the ambient levels by more than a factor of 3. Further release of metals to seawater could occur from remineralization at the sediment-water interface where organic compounds produced during the degradation of the sedimented organic-rich sludge could complex metals associated with the naturally occurring sedimentary material. These could be either resedimented, diffuse out, or released during sediment resuspension events. Pseudomonas bacteria extracted from Chesapeake Bay sediments have been found to be capable of alkylating tin and may be able to alkylate other metalloids. Such organotins are much more toxic to organisms than is inorganic tin. The extent to which metalloids become alkylated in sludge-rich sediments is not known. Many trace metals have high concentrations in sewage sludge. It is not feasible to monitor all of them through the many possible chemical reactions that can occur after sludge discharge. Judgments must be made as to which metals and metalloids are more likely to affect public health or ecological communities. One possible way to eliminate some metals is to be found by looking at the areas around pre-existing sludge inputs. The Southern California Coastal Water Research Project (1982) has demonstrated that even though concentrations of cadmium, copper, and zinc are elevated in sediments and organisms adjacent to outfalls, the presence of a detoxifying completing agent (metallothionen) in sea urchins and croaker fish enables these species to prevent concen- trations of uncompleted, toxic cadmium, copper, and zinc in their surroundings from entering sensitive cellular sites. In fact, less than 2 percent of the capacity of the metallothionen pool in animals near existing outfalls has been utilized. This has been interpreted as indicating that cadmium, copper, and zinc could be considered nonproblems .

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67 U] o .,, a, o o C Pi o o C) - 1 Sat En Go g a) O A: U] ~5 ~ O ~ W ,1 sat O hi: .,. 3 o m o U] a, Id o 0 a) P U. - 0 o o w Al ~ W J:: 0 t) 0 U] a ~ ~ g 0 0 0 ~ ~ 0 UD o .,, o Cal o U] ~ ~ a, - X ~ 0 a ~ 0 it; O or 1 0 o as anon ~ co ~ Do 1 1 1 1 1 1 1 O O O 0 0 0 0 X X X X ~ x kg 0D u~ a~ ~ c e c c c c kg O O ~1 CO ~1 CO 1 1 1 1 1 1 1 O O O O O O O - 1 ~1 ~1 ~1 ~1 ~1 ~1 X X X X X X U~ ~ L~ C C C C C C C 0o ~ CO ~ U~ O O a, ~ cn _I cc' ~I CO 1 1 1 1 1 1 1 O O O O O O O ~1 ~1 - 1 ~ X X X X X X X U~ ~ O ~ ~ U~ c c c c ~ c c 0h 0 ~ 0D ~ U~ ~ ~C ~ ~mm a) c - 1 1 1 1 1 1 1t- O ~O O O O O O O - a) ~ ~ ~ ~ ~ ~ ~ ~= ~_ 3 ~X X X X X X X O ~ ~C co ~n e C C C C C C C C C .< ~ O C 1 0 \9 ~ ~ - ,' O X 0 ~ ~ .. C =-- .- ~ O a, ~ ~ ~ ~ ~ ~ c 0 a) - ~ .,' 0 C) O ~ Z U] ~U]

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68 2.4 ULTIMATE FATE Present studies of the fate and effects of contaminants rarely extend to-spatial scales larger than several kilometers. Such scales are not always large enough to determine either fate or effects. For example, less than 10 percent of the trace metals that have been discharged from one southern California sewage outfall has been found in nearby sediments (Bering and Abati, 1978; Morel et al., 1975). Discharged substances presumably stay with the water after discharge, either on slowly settling particles or in solution. They will travel with the different plank- tonic organisms in the water. There is little information on their interaction with these plankton. We can infer from the ability of DDT to accumulate in pelicans that there may be interactions. DDT was discharged for several years through a Los Angeles County Sanitation District outfall off Palos Verdes. Pelicans throughout the Southern California Bight accumulated it, and as a consequence were unable to maintain their population levels. Eggshell thinning and subsequent reproductive failures implicated the DDT from the outfall. This accumulation by pelicans implies that the sewage effluent was interacting with planktonic organisms because (1) pelicans must have derived their ODT from the surface fishes (such as anchovy and sardines) that they eat, and (2) surface fish accumulated DDT from the plankton in their diets or directly from the water. Thus, discharged waste can be in contact with plankton long enough to have an impact on these higher-trophic-level organisms. The waste/seawater mixture created by a discharge does not simply drift into oblivion. In coastal areas such as the Southern California Bight, circulation and exchange with the open ocean can be inhibited by subsurface topography. Large-scale circulation rates as well as local advection determine contaminant concentrations over large areas. We expect slower water exchange in deeper waters because topographical constraints also increase with depth. Trace-metal concentration measurements in more than 500 m of water off the southern California coast by Barcelona et al. (1982) suggest that regional near-surface discharge has increased copper concentrations two to five times. This was in areas more than 15 km from the nearest major sewage outfall. Thus, far-field processes are important aspects of waste disposal. The spatial scale over which this occurs implies that releases

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70 2.5.1 Assessment of Capabilities Predictive capabilities exist now to provide first approximations in many cases of the concentrations and fluxes of substances critical to the examination of impacts of ocean disposal systems. Specific combinations of waste, site, and disposal system characteristics result in predictions with greater certainty than do other combinations. For example, predictions of transport and dispersion of wastes in the immediate vicinity of most discharge devices (near-field region) are generally well in hand, while predictions involving larger time and space scales are often less certain. Dissolved oxygen concentrations can be predicted with confidence in some cases, but knowledge of the processes governing the fate of synthetic organics is limited. 2.5.2 Information Needs Resulting from Prediction In addition to the information needed for developing predictions of concentrations and fluxes, including model calibration, information needs are created by the pre- diction process itself. The primary purpose of a prediction is to link or integrate processes affecting concentrations in ways not obvious from independent consideration of each process. Examination of the responses of the linked system to variations in inputs (site, waste, and discharge system), as well as to the representations of the processes themselves, create new information requirements. Response and sensitivity studies provide insight into those data that appear most critical in the determination of concentrations and fluxes. Early evaluation of predictions allows the collection of additional data to reduce uncertainty. Early prediction exercises are important to the design of programs for monitoring and assessing postconstruction performance. REFERENCES Barcelona, M. J., L. C. Cummings, S. H. Lieberman, H. S. Fastenau, and W. J. North. 1982. Marine farming in the coastal zone: chemical and hydrographic considerations. Calif. Cdop. Fish. Invest. Rep. 23:180-187.

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