Discussion of “Ocean Outfall Dilution: Effects of Currents”

It is generally agreed that both the landfill option, or the civil techniques option for the final disposal of contaminated harbour sludge involves the isolation of the sludge from the environment. For short time scales, engineered barriers such as a bentonite screen, plastic sheets, pumping strategies etc. can be used. However for long time scales the effectiveness of such measures cannot be counted upon. It is thus necessary to be able to predict the long term environmenttal spread of contaminants from a mature landfill. A model is presented that considers diffusion and adsorption in the landfill site and convection and adsorption in the underlaying aquifer. From a parameter analysis starting form practical values it is shown that the adsorption behaviour and the molecular diffusion coefficient of the sludge, are the key parameters involved in the near field. The dilution effects of the far field migration patterns are also illustrated.

Download Full-text

Far field modeling of the Mamala Bay outfalls

Water Science & Technology ◽

10.2166/wst.1998.0418 ◽

1998 ◽

Vol 38 (10) ◽

pp. 323-330

Author(s):

Philip J. W. Roberts

Keyword(s):

Field Model ◽

Near Field ◽

Far Field ◽

Field Modeling ◽

Visitation Frequency ◽

Statistical Variation ◽

Long Time ◽

Harmonic Average ◽

Ocean Outfall ◽

Acoustic Doppler Current Profilers

The results of far field modeling of the wastefield formed by the Sand Island, Honolulu, ocean outfall are presented. A far field model, FRFIELD, was coupled to a near field model, NRFIELD. The input data for the models were long time series of oceanographic observations over the whole water column including currents measured by Acoustic Doppler Current Profilers and density stratification measured by thermistor strings. Thousands of simulations were made to predict the statistical variation of wastefield properties around the diffuser. It was shown that the visitation frequency of the wastefield decreases rapidly with distance from the diffuser. The spatial variation of minimum and harmonic average dilutions was also predicted. Average dilution increases rapidly with distance. It is concluded that any impact of the discharge will be confined to a relatively small area around the diffuser and beach impacts are not likely to be significant.

Download Full-text

Wastewater treatment and risk assessment in ocean outfall evaluations

Water Science & Technology ◽

10.2166/wst.1998.0416 ◽

1998 ◽

Vol 38 (10) ◽

pp. 309-316

Author(s):

William F. Garber

Keyword(s):

Wastewater Treatment ◽

Los Angeles ◽

Energy Use ◽

Epidemiological Studies ◽

Environmental Risks ◽

Advanced Treatment ◽

Negative Effect ◽

Ocean Outfall ◽

Treatment And Disposal ◽

The City

Past evaluations of the success of wastewater treatment and submarine outfall placement and operation have considered only a limited number of parameters affecting the marine and onshore environments. Important questions regarding the best allocation of available funds have not been adequately addressed. The relative contamination of the sea from airborne and landwash contaminants has not been considered. Neither has the increased air pollution deriving from the energy required for advanced treatment. Similarly, regular epidemiological studies to evaluate actual changes in morbidity arising from drastic changes in treatment and disposal have not been made prior to very large committments of funds. Most importantly, little attention has been given to the relative ranking of all environmental risks within a catchment area. The net result is that, when all factors are considered, the very large expenditures and increased energy use for sanitary wastewater treatment and outfall disposal will have a net negative effect on the physical and societal environment. The City of Los Angeles and the Los Angeles Metropolitan area can be used to illustrate this probability.

Download Full-text