john r. proni^, terry a. - wit press · 2014. 5. 13. · john r. proni^, terry a. ^ no aa/aoml/...

Integrated measurements of sewage effluent

and dredged material discharges

John R. Proni^, Terry A.^ NO AA/AOML/ Ocean Acoustics Division, 4301Rickenbacker Causeway, Miami, Florida 33149, USAEmail proni@aoml . noaa . gov^NOAA/AOML/Ocean Chemistry Division, 4301Rickenbacker Causeway, Miami, Florida 33149, USAEmail nelsen@aoml .noaa.gov

Abstract

Multiple sensor systems, capable of measuring the constituent or subfieldswhich comprise a sewage effluent field arising from discharge in coastal oceanwaters, are shown to improve the credibility of the measurements as a wholewhen properly integrated. The base of proper integration of data is commonalityof time and space data with accuracies on the order of that provided by theGlobal Positioning System (GPS). With accurate integrated data, connectivitybetween field measurement sites distal from the discharge origin, e.g., a diffusersite, and said origin may be established.

1 Introduction

Evaluation of the performance of an operating sewage effluent outfall dischargesystem is complex and requires use of a suite of different state-of-the-arttechnologies. A key part of performance evaluation is the receiving watersmonitoring program. In today's world, the coastal zone is often called upon toabsorb plumes and discharges of many kinds, some occurring naturally, andsome as a consequence of man's activities (anthropogenic discharges). In certainareas of the world, anthropogenic discharge plumes generated in the waters ofone country may drift into the waters of a neighboring country, furtheremphasizing the need for reliable technologies to detect, map, and identifyplume types. Integration of multiple state-of-the-art technologies for

Transactions on the Built Environment vol 40 © 1999 WIT Press, www.witpress.com, ISSN 1743-3509

368 Coastal Engineering and Marina Developments

compliance monitoring purposes is now being done by regulatory authorities inthe USA and in other countries as well. In some circumstances real-time controlover oceanic discharges is being done using the Internet for data transmission.

As a specific example of multiple-sensor-site integrated technologies,the study of a sewage effluent outfall located in coastal waters off the northerncoast of Puerto Rico will be presented. The common basis for linking multiplesensor data is time. The importance of a reliable, accurate and common timebase for all sensor information cannot be over emphasized. Intimately linkedwith time information is position information. For the space and time scales ofimportance in sewage effluent studies, typically tens of meters in the horizontal,and tens of centimeters in the vertical and seconds, respectively, accurate spaceand time information is critical. Fortunately, this necessary accuracy is largelyachievable through the Global Positioning System (GPS), so that linking ofsensors to the GPS time base is critical. As a cautionary note, for certain sewagefield measurements, e.g., precision initial dilution measurements, the time driftassociated with internal computer clocks may be too great to be acceptable forsensor systems linked to separate computers.

2 Background

The Carolina sewage outfall off the northern coast of Puerto Rico (see Figure 1)had been in operation for more than 10 years at the time this study wasundertaken in April, 1998. The outfall was designed as basically a straight-linebottom laying pipe having a total length of approximately 1 mile. The mostseaward last 200 meters of pipe, at a minimal depth of 35 meters, had a series of33 upward pointing ports, spaced approximately 3 meters apart with each porthaving a diameter of approximately 0.2 meters.

A key quantity for environmental as well as regulatory considerationsrelated to sewage effluent outfalls is the dilution which the effluent undergoesupon release into receiving waters. For the Carolina sewage effluent outfallboth "initial" and "subsequent" dilutions were of interest. In this paper, the word"initial" refers to that dilution achieved by the rising effluent plume, either uponreaching an equilibrium depth within the water column, or upon reaching thesurface of the ocean. Also in this paper, the word "subsequent" dilution refers tothat dilution achieved by the sewage effluent plume in extending away from thelocation within the water column where the initial dilution was achieved.

3 Methodology

To evaluate the performance of a sewage outfall, using for example suchquantities as dilution, 4 classes of measurements must be made: 1)measurements prior to entrance of effluent into the oceanic receiving waters,e.g., in-plant flow rates; 2) measurements in the receiving waters for thedischarge effluent; 3) measurements of the effluent plume itself; and 4)measurements of the physical structure of the discharge piping. The effluent


Coastal Engineering and Marina Developments 369

field, Fe (r,0,z,t) is comprised of a set of subfields, [i.e.,Fe (fi(r,6,z,t) ,f (r,0,z,t), fn(r,8,z,t)].

Examples of effluent plume subfields include the total suspendedparticulate (TSP) subfield, the fecal coliform subfield, the enterococcus subfield,the nutrient subfield, the temperature subfield, the salinity (Se) subfield, theacoustic backscatter subfield, the optical backscatter subfield, etc.

It is possible to estimate dilution using many of the eflluent subfields asthe measured quantities. For the Carolina outfall sutdies the parameters selectedfor dilution-related measurements include the salinity, T.S.P. (total suspendedparticuates), <7a (acoustic backscatter coefficient) and c (optical backscattercoefficient). Experience has shown (1),(2) that salinity, T.S.P., 0% and (TO can behighly correlated in space and time so that multiple measurements of thesevarious subfield quantities can confirm and supply consistency amongmeasurements. Of course, addition of tracer quantities such as dye or sulfahexafluoride can be used provided proper insertion periods are utilized.

To use salinity or more correctly salinity deficit for dilution, the salinityof the effluent entering the piping of the discharge system must be measured (aclass (1) type measurement). For many treatment plants the in-plant salinity,Sup, is on the order of 1%, i.e., 1 part per thousand (1 PSU). The effluent flowrate entering the discharge system must also be measured. For the Carolinaplant the effluent flow rate was estimated as 70 million gallons per day.

Multiple sensor systems are required to measure the effluent subfields.For the Carolina study the salinity subfield was measured using both ship-towedconductivity-temperature-depth sensors (TCTD) and on-station vertical castconductivity-temperature-depth sensors (VCTD). Both of these means ofdeployment of a CTD, i.e., either towed or vertical cast, result in line segmentmeasurements of the salinity subfield. Furthermore, it is difficult to establish the"connectivity" of the salinity measurement at a measurement site, i.e., S (r,0,z,t),with the effluent plume arising from the diffuser under study, i.e., the Carolinaoutfall diffuser. The symbols r, 0, z, t, denote a cylindrical coordinate systemcentered at the diffuser.

The issue of connectivity is extremely important not only when theonly discharge plume present in the receiving waters in the vicinity of the outfalldiffuser site is the sewage effluent field, but is also of key importance when"interfering plumes" from other discharges may be present. In the Carolinaoutfall study connectivity of the sewage effluent field was established usingacoustic methods and the c^ subfield. Typical examples of "interfering plumes"include those arising from dredged material disposal operations, river plumes,harbor/inlet plumes, and plumes from other sewage effluent outfalls. Adiscussion of detailed particulate analyses of effluent plume materials ispresented in the paper by Nelsen and Proni (3). The acoustical sensors utilizedincluded a ship-towed acoustical transponder named an acoustic concentrationprofiler (ACP). The acoustic transducer is towed inside a hydrodynamicallyshaped towbody at about 1 meter beneath the ocean surface at a tow speed oftypically 2 meters per second. This device presents a planar view of the watercolumn, from near the ocean surface to near the ocean's bottom.



4. Observations

On April 21, 1998, between 1800-1900 UT, the ship OSV ANDERSONexecuted the track shown in Figure 2. In Figure 2, the coordinate system iscentered on the Carolina diffuser outfall. The diffuser of the outfall extendsalong the north-south axis (the vertical coordinate axis of the figure). Thehorizontal axis of the figure (abscissa) extends in a west-east direction. Twominute marks are placed along the track. The ANDERSON first passes over thediffuser coming from the west and heading toward the east. After passing thediffuser, the ship gradually turns toward the south, then toward the west andthen crosses the diffuser heading in a north-northwest direction. Finally, theship gradually turns to the southeast and then heads west to cross the diffuser afinal time.

The depth history of the TCTD during the track movements shown inFigure 2 is presented in Figure 3. Note that the TCTD remained between 4-5meters in depth from 1807:27-1857. The salinity data obtained during this timeperiod are shown in Figure 4. Note that three distinct salinity minima areobserved. The optical backscatter recorded during this period are shown inFigure 5. The acoustical (ACP) data recorded during this time period are shownin Figure 6 and 7.

5 Analysis

An expanded view of the ship track shown in Figure 2 is shown in Figure 7.The location of all three salinity minima are indicated on this track. Note that allsalinity minima lie nearly exactly on, or very close to, the axis of the diffuser ofthe Carolina outfall. This strongly suggests that the salinity minima shown inFigure 3 are associated with the sewage effluent plume arising from the Carolinaoutfall diffuser. This suggestion is confirmed by the acoustical (ACP) datawhich show the presence of rising effluent plumes and the presence of an oceansurface-adjacent plume. The rising plumes are indicated by arrows and thesurface adjacent plumes are in bright red-range colors. That the plumes containparticulate material is confirmed by the optical backscatter data.

Although the analysis of data from the Puerto Rico study is currentlyongoing, a very preliminary estimate of the dilution may be made. (Thisestimate is subject to change as further analysis is carried out.) The followingequation which employs the salinity deficit is used to make a preliminaryestimate of dilution:



The background or ambient salinity SA (0, 6 ,z) is on the order of 35.4 parts perthousand the in-plant effluent salinity is on the order of 1 part per thousand andminima salinity Sem detected at 4.5 meters depth Sem (0, 6, 4.5) is approximately35.8 parts per thousand. These numbers resulting an initial dilution value ofroughly 60:1 for the salinity subfield. Note that this is an instantaneous dilutiononly and other dilutions such as flux average dilution should be determined forcomparison with models.

6 Summary and Conclusions

A sewage effluent plume field is comprised of a set of subfields. Differentsensors are required to obtain information on the various sub fields. Byintegrating this information, a strong foundation for ascertaining the origin andcharacteristics of a given oceanic plume can be established. A specific exampleof sensor integration was provided for an ocean outfall operating off thenorthern coast of Puerto Rico. Through integration of data from differentsensors, it was possible to "link" or "connect" observations made at locationswithin the water column distant from a diffuser to the plume field emanatingfrom the diffuser.

7 Acknowledgements

The valuable cooperation of Ms Virginia Fox-Norse and Mr. Douglas Pabst ofthe US EPA is recognized. The excellent support of the following NOAApersonnel is recognized: Mr. Jules Craynock, Mr. Ulises Rivero, Mr. JeffBufkin, Mr. Jack Stamates, Ms Alejandra Lorenzo, and Mr. Joseph Bishop.



References

1. Proni, J.R., Huang, H., and Dammann, P. Initial dilution of Southeast FloridaOcean Outfalls, J. Hydr. Engrg, 120, No. 12, 1409-1425, December, 1994.

2. Dammann, W.P., Proni, J.R., Craynock, 1C, and Fergen, R. Oceanicwastewater outfall plume characteristics measured acoustically, Chem andEcology, 5,75-84, 1991.

3. Nelsen, T., and Proni, J.R. Signatures contained in suspended particulatematter with application to coastal-ocean environmental studies. CoastalEngineering 99 Conference. Lenmos, Greece, May 26-28, 1999.

4. Petrenko, A.A., Jones, B.H., and Dickey, T.D. Shape and initial dilution ofSand Island, Hawaii sewage plume. Journal of Hydraulic Engineering, 124, No.6, 565-571, June, 1998.

5. Washburn, L., Jones, B.H., Bratkovich, A., Dickey, T.D., and Chen, M.S.Mixing, dispersion, and resuspension in vicinity of ocean waste-water plume. J.Hydr. Engrg, 118, 38-58, 1992.


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Figure 1. Chart showing locations of Carolina sewage outfall diffuser,North Puerto Rico Coast and Loiza River.


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Figure 4. Salinity data gathered between 1805:27 and 1857:00 UTon April 21, 1998.



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Figure 6. Acoustical backscatter data obtained between 1820 UT and1840 UT on April 21, 1998, and 1840 and 1900 UT.



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Figure 7. Expanded ship's track for April 21, 1998, showing locations of thethree salinity minima and the acoustically detected rising plumes.


john r. proni^, terry a. - wit press · 2014. 5. 13. · john r. proni^, terry a. ^ no aa/aoml/...

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