CHAPTER 44

MARINE STUDIES FOR THE DESIGN AND CONSTRUCTION OF OFFSHORE PIPELINES

David R. Miller Vice Pre side nt; Daniel, Mann, Johnson, &: M e nde nhall Los Angeles, California

ABSTRACT

The design and construction of submarine pipelines involve s special investigations and studies to understand marine environmental conditions which affect the location, installation methods, and design techniques for undersea line s. The paper will discuss application of marine geology, oceanography and marine engineering studie s to sub­ marine pipeline problems. Types of submarine pipelines will be re­ viewed and special application problems of design and installation will also be reviewed.

INTRODUCTION

Submarine pipelines are being used with increasing frequency by civil engineers. Applications are found in marine disposal of wastes, submarine aqueducts, marine gathering lines, fuel loading lines and power plant cooling water intakes. In the past, a principal deterrent t o the use of submarine pipelines has been the cost of installation and a scarcity of available information on marine environmental design. However, with the development of new construction methods and equip­ ment and rapid advances in marine research, submarine pipelines now can be mor e economically used for transportation and/ or disposal of liquids and gases.

Hitherto, the offshore areas have b een the province of the marine scientist and through his efforts a large fund of general knowledge about the sea has been accumulated. However, the civil engineer, in designing a submarine pipeline, is fac e d with the problem of deter­ mining in detail the marine environmental conditions in which the line is to be placed and must translate and apply the fund of general scien­ tific knowledge into specific d esign conditions. The e ngineer must often carry out extensive offshore studies and even engage in special applie d research in order to have sufficient information upon which to base the design of an important project.

991 992 COASTAL ENGINEERING

GENERAL MARThlE ThlVESTIGATIONS

PrograTIls for TIlajor offshore projects, usually involve at least two phases. The first phase of a study prograTIl is concerned with a broad area whi ch encoTIlpasses all possible project alternatives withiJ1 its boundaries. The investigations carried out during this phase are general in nature and have as their objective an unde rstanding of the broad environTIlental conditions so as to identify constraining factor 5 and to provide a basis for the choice of a liTIlited nUTIlber of alternatiVe 5 to be studied in detail in the next prograTIl phase.

The general TIlarine investigations for waste disposal projects " TIlay involve very large areas. The Hyperion Sewerage Marine Inve atl.- gation ProgrciTIl for the City of Los Angeles, for exaTIlple, covered 0- e study area of over 100 square TIliles. The studies for this program p.o-v been reported in detail by Stevenson et al (195 6). The following parO-­ graphs will outline specific activities included in an oceanographic survey of this type. 0 BathYTIletry. An overall bathyTIletric chart of the study area is 3 essential requireTIlent. It will be used aTIlong other studies and will p ee _ the initial TIlap for the definition of study route alternatives. Only r <3.-:r ly will existing hydrographic charts be adequate for this purpose. T p e o 1 TIlap is prepared froTIl fathoTIleter traverses w ith radar position cont:r ~ The fathoTIleter traces should be corrected for tidal variations, and :£ r e quent check points on the fathoTIleter travers es are desirable. The topographic details of the sea floor are contoured with an interval 0:£ one fathoTIl on a chart scale of 1 :40,000.

BottoTIl SediTIlents and SubTIlarine Geology. An investigation 0:£ 1; ~ e type and lateral distribution of bottoTIl sediTIlents will provide TIluch i.~ ­ forTIlation on the general geologic structure of the study area. Apr 0 - ::r " e graTIl of bottoTIl saTIlpling is carried out using orange peel and "snapg saTIlplers. The saTIlples of the bottoTIl sediTIlents are exaTIlined as t o grain size, sorting, percent silt and clay, percent organic TIlatter, -t:; i ­ TIlineral constituents , sphericity and roundness of particles. The v e ~"1::7 1e cal distribution of bottoTIl sediTIlents is deterTIlined to the extent pos G ::J- by coring TIlethods.

~ The results of the bottoTIl sediTIlent study are plotted on the ba £7 __ TIlap and an exaTIlination of this TIlap along with the basic data will pr c::7 in vide an indication" of the direction and average velocity of bottoTIl flo ~ :In the study area and areas of erosion and deposition can be identified. .£?= addition, the aTIlount of organic TIlatter contributed to the sea floor f ~ present discharges can be deterTIlined along with areas of buildup. MARINE STUDIES 993

Tidal Characteristics and Currents. The characteristics of the tides can usually be determined from existing data. However, in cer­ tain instances where tidal forces are the dominant factor in producing water motion, then magnitude and variations of flow must be deter­ mined. Non-tidal currents are studied with particular emphasis placed on the determination of current patterns and the vertical distribution of currents. Wind currents are studied in relationship to general investi­ gations of climatology. Stevenson (1960) has outlined relationships between wind current velocities and surface currents. Techniques of current measurement have been described by Wiegel (1964) and by Sverdrup et al (1942). Because of the variable nature of nearshore currents, a complete description of current patterns cannot be made until currents have been studied through a one-year cycle.

Salinity and Temperature Distribution. Determinations of the vertical and horizontal distribution of salinity and temperature are particularly important for waste disposal projects. The salinity is used to determine water densities which affect direction and magnitude of sewage flow. Water temperature measurements also aid in density determinations and considerations of thermoclines and internal waves.

Sea and Swell. Determinations of significant wave characteris­ tics are particularly important in understanding mixing effect of near­ shore water and water motion in shallow areas. A field investigation should include observations of sea and swell period, wave height, di­ rection and wave length. In many cases, actual information may be lacking or difficult to obtain and hindcasting must be used to obtain sig­ nificant data. Techniques for wave hindcasting have been developed by Burt and Sauer (1948).

Other Parameters. In addition to the factors discussed above, other parameters are frequently studied in marine investigations. Among these are transparency and color and biological investigations which are useful in determining the distribution of water contaminants.

GENERAL MARINE INVESTIGATION PROCEDURES

The procedures for field and laboratory observations in oceano­ graphic studies have been compiled by Gorsline (1958) of the staff of the Allan Hancock Foundation of the University of Southern California. Other general techniques for observations and collections at sea have been described by Sverdrup et al (1942). An important factor in the successful implementation of offshore studies is the use of a vessel properly equipped for field sampling and data collection and preferably for on-board laboratory testing. 994 COAST AL ENGINEERING

DETAILED ENGINEERING STUDIES FOR MARINE PROJECTS

GENERAL

After the cOITlpletion of the general ITlarine investigations, the project engineer ITlust interpret the results and narrow the nUITlber of alternatives to be further studied. The engineer will probably have carried out other preliITLinary engineering studies in parallel with the ITlarine research which assist in the paraITleters for the cOITlparison ITlodel of alternatives. These preliITLinary engineering studies for sub­ ITlarine pipelines projects have been outlined by the author (1958) to include general considerations of alignITlents and terITlinal constraints, structural and hydraulic design factors, and construction considerations.

The culITlination of this effort is a recoITlITlendation for a single route or liITLited nUITlber of alternatives to receive detailed study. In order to ITlake final designs, the engineer ITlust secure additional infor­ ITlation which would include the following:

AlignITlent and profile along the exact route of the pipeline

Soils conditions along the route

Long-terITl stability of the bottoITl and nearshore regions

MaxiITluITl wave forces and currents that would affect the anchorage and stability of the pipeline.

Distribution and character of ITlarine organisITls which ITlay attack the pipe or pipe coating.

Oceanographic conditions affecting construction ITlethods.

Other special studies for ocean outfall as outlined herein­ after.

HYDROGRAPHIC SURVEYS

The first engineering requireITlent for the detailed study of a sub­ ITlarine pipeline is for a carefully controlled, accurate profile of the sea floor a long the alignITlent where the pipe w ill be placed. It is iITlportant to have the survey as close as possible to the actual line of the pipe. For ITlost projects the profile can be traced using a fathoITleter in a launch with control provided froITl two onshore triangulation stations equipped with directional theodolites and radios. The author (1 958) has described techniques for such offshore surveys where observations of up to eight ITliles have been ITlade. In these surveys it is important 995 MARINE STUDIES

to accurately calibrate the fathometer and to correct the trace for tidal variations . Careful attention must be paid to the establishrnent of the tidal datum and its relationship to land datum used. Othe1' sys­ tems for offshore surveys have been reported by Brown (1 960), Cass (1960), and Poirot (1959). General techniques of hydrographic surveys are described in the U. S . Coast and Geodetic Survey Manual, Adams (1942).

While the techniques described above have been successful for surveys extending up to 10 miles offshore, l onger pipelines may re­ quire new methods. Bradbury (1 961) has described the use of elec­ tronic position location equipment for surveys as great as 200 roi1es offshore.

Marine Geologic and Foundation Conditions. While the study o~ bottom sediments and submarine geology may have been carried out ln the general marine investigations phase of a program, once the align­ ment is known, the designer must have more specific information about bottom conditions to be encountered along the line. A program of field investigations would be as follows:

1. Review of fathograms along alignment and sediment data.

2. Investigation of onshore surface geology to deterrn.ipe rela­ tionship to offshore conditions.

3. Investigation of geology and nature of bottom sediITJ-ents along the pipeline alignment. Information concern:iPg the surface sediments and rock outcrops to be obtaine d by direct observation of the bottom by diving geologis t s . In­ formation concerning the nature and thickness of s "L1-bsurface sediments to be obtained by a series of jet probes a.1ong the alignment.

4. Underwater still pictures to be taken of the bottom and other pertinent features.

5. During investigations of the bottom sediments, obs e rva­ tions to be made of marine biologic forms to ascertain the prevalenc e of marine boring organisms.

Geological Traverses. The geology and descriptions of ~he de­ tailed submarine topography are made by geologists using S elf _C c:::> ntained Underwater Breathing Apparatus (SCUBA) as they are being t o~ ed over the sea floor by a survey boat. This technique permits measu- ::r ement of details of the bottom much more accurately than previously p o s sible b e­ caus e the observer is able to make direct observations of the ;::jf: eatures he is describing. 996 COAST AL ENGINEERING

The surveying boat with diving geologists aboard is positioned on a predetermined line by land-based surveyors using transit control. . When the boat is on station, the diving personnel are signaled by rad10 to drop over the side. The position of the boat is then recorded along with the time the divers went over the side.

The divers descend directly to the bottom and at the descent pos­ ition make observations of the bottom micro-topography, sediment diS­ tribution and thickness, take underwater pictures when possible , and sample the bottom sediment or rock. Upon completion of these observa­ tions they would signal the surface by means of a tow line and the boa.t would move ahead towing the geologists slowly along the traverse. The boat is kept on line by radio-given directions from shore-based survey­ ors. The time at the beginning and end of movement along the traverse is recorded underwater by the diving-geologists along with the times of significant changes in bottom conditions. Thes e notations are later correlated with distance along the traverse and used to determine the relative positions of significant features . Upon completion of a tow, which may have a duration of approximately 15 to 30 minutes, the geol­ ogists make another series of detailed observations as they had at the beginning of t h e dive. They then return to the surface and record their findings on data sheets. At the same time as the geologists are mak- ing these detailed observations, the survey boat would move to a posi­ tion directly over the divers (indicated by the bubbles from their divipg equipment) and its position is determined by the surveyors.

This method was used to make continuous underwater geological investigations along the entire l ength of the proposed pipelines betwee:O the mainland and the Islands of Coche and Margarita.

Jet Probes. In addition to the geological traverses, jet probes are made along the propos ed pipeline routes in selected areas which are covered with sedimentary overburden. Jet probing permits the geologists to determine the thickness of bottom sediments, and the gene r al type of sedimentary material found beneath the sea floor in toe area of the probe. The probe itself consists of a four-meter long pip e of 1. 90 cm. diameter whi ch is attached to a hose furnishing high - pressure water from a pump l ocated on the tending boat. A portable, constant-displ acement pump capable of supplying water with a pres su ~ e of 1 O. 6 kg / cm2 (150 psi) has been us ed for these surveys.

With experience, a geologist using the jet probe can tell whethe ~ the pipe is jetting through sand, gravel, shells or clay, or hitting bed - rock by the sound a n d feel of the pipe. The results of the jet probe survey are summarized in large scale profiles of the detailed geology­ along the proposed pipeline alignment and in geological profiles and descriptions. MARINE STUDIES 997

Underwater Photography. Many of the features seen underwater have no surface counterpart and it is, therefore, difficult to convey their exact nature to persons not familiar with the sea floor. Under­ water photographs often help to remedy this lack of direct contact. Pictures of significant features on the bottom are, therefore, taken whenever possible on a survey. Unfortunately, the underwater world is not as favorable for photography as is the land. Visibility during a sur­ vey can be limited by the water turbidity. For this reason large scale features are difficult to photograph; only those features which are small enough to be encompassed at relatively short distance from the camera could be recorded.

Foundation Investigations. In areas where unstable sedimentary soils are traversed and in the near shore regions whe re the pipeline may be deeply buried, more d etailed foundation investigation may be required. For the former conditions, special probes of the sediments are made using piston coring devices. The coring apparatus us ed for these investigations has been described by Brown (1 957) . Samples taken therefrom enabl e the determination of the density of bottom sedi­ ments which affects the selection of pipe weight coatings . For the near­ shore areas, borings should be taken and undisturbed samples obtained. The boring rig is set upon a portable t ower and drilling casing is used. Near the surf zone the portable tower is hazardous to handle and while borings can be taken from shore there generally is a region where it is impos sible to secure borings.

Geophysical techniques are sometimes used to map sub-bottom sediment horizons. Bechmann et al (1960) described a geophysical survey of a Chesapeake Bay crossing and indicated the possibility of using such equipment at depths exceeding 1600 ft. Chambers (1965) outlined the application of a tool used for oil field seismic exploration to submarine pipeline foundation investigations. The method is called a High Resolution Sparker Survey and its use provides an idea of the continuity of layers on the sea floor, with special value obtained from its ability to note conditions between cores .

SPECIAL STUDIES FOR OCEAN OUTFALLS

The disposal of sewage and other wastes into the sea involves ex­ tensive marine studies. These studies seek to understand the effect of the waste on the marine environment, and, conversely, the effect of the marine environment on the waste. The latter objective usually is stated in terms of the ability to achieve certain standards designed to limit marine pollution in receiving wat ers. 998 COASTAL ENGINEERING

Pearson (1955) and (1960) has summarized much of the available information on waste disposal in the marine environment. AIvy, Miller & Lawrance (1957) have described the exhaustive studies carried out for the design of the large Hype rion ocean outfall for the City of Los Angeles. As part of that program, Terry (1956) prepared an annotated bibliography on bacteriology, oceanography and marine geology as they relate to the disposal of waste material into the sea.

DESIGN P ARAME TERS

Marine studies for the design of ocean outfalls must furnish the engineer information on certain design parameters involved in the for­ mulation of dilution requirements. These parameters fall into four main categories:

1. Determination of bacterial survival in sea water.

2. Dilution of the sewage field by jet mixing of the sewage effluent into the sea water.

3. Diffusion and dispersion of the sewage field.

4. Mass transport of the sewage by wind action, waves and local currents.

The evaluation of the bacteriological factors in sewage disposal has been made by Rittenberg (1958) and Gunnerson (1959) reporting on the results of studies for the Hyperion Project. An important finding of these studies was that the bacterial content of sewage discharges var­ ied according to degree of treatment and that the sewage discharge from a particula.r locality had individual characteristics. It was also para­ doxically found that pre-treatment of sewage effluents might adversely affect their viability characteris tics in sea water.

The dilution and diffusion of sewage through jet mixing and the design of special diffusers has been well established by Rawn et al (1960) and others and a further discussion of these factors is not pre­ s ented herein.

Diffusion and Dilution. Despite the many theoretical studies of eddy diffusion, turbulent mixing, a thermal convection and diffusion, the outfall designer will usually decide to conduct field experiments to verify the actions under the actual site conditions. These field experi­ ments involve the determination of sewage field dilution at varying distances from the point of discharge. Dilution can be measured by chemical, physical or bacteriological means. Chemical methods of dilution measurement make use of radioactive substances, arnmonia, MARINE STUDIES 999 salinity, or other chemical constituents of the sea water. Tests of density and the use of dyes are physical means of determining dilution, and bacte riological means involve counting coliform or other type of bacteria present in the sewage.

Radioactive Tracer Studies. Most chemical and physical methods of dilution determination are unable to m easure dilutions in excess of 300. However, radioactive tracers can be used for determinations of up to 10,000 to 1.

The Hyperion Project featured a special r adioactive tracer exper­ iment. This experiment used 20 c uries of radioactive scandium (Sc-46) . This tracer element had been procured from the U. S. Atomic Energy Commission National Laboratories at Oakridge, Tennessee. The Sc-46 was added to ten gallons of water in a mix ing tank at the treatment plant and this mixture was fed at a constant rate into the effluent over a peri­ od of one hour. The activity of the Sc-46 was such that dilutions up to 1 to 10,000 could be d etermined, yet at no time was the maximum per­ missible concentration exceeded. The test was conducted under the inspection of state and local health authorities and was found to be com­ pletely safe.

Radioactivity was detected in the boil over the Hyperion outfall approximately 1 hour after its introduction into the outfall, and measure­ ments were continued in the boil for another hour until the radioactivity started to decrease. Two dye path tags were started, about one hour apart, while the radioactivity was at its peak. A series of patterns, spaced at appropriate intervals were then traversed by the oceanograph­ ic survey vessels, making radioac tive m easurements while underway to d e lineate the extent and position of the radioactivity radioactive field at various time s. Along with this radioactivity trave rs e, an auxiliary survey vessel was making chemical and bac terial tests throughout the field.

The prime purpose of the radioactive tracer study was to determine actual factors of dilution of the sewage field and to provide additional data on the disappearance of coliform organisms. Through the experi­ ment, the survey team was able to compare observed and calculated coliform concentrations resulting from the study. Subsurface radio­ activity m easur e ments were taken at the profile stations and were used to determine the depths of the sewage field.

Current Studies. With the exception of the summer season when strong thermal gradients can keep the sewage fields submerged, the effluent will rise to the surface layer of the ocean and be carried, dis­ p ersed, or both, by the currents in this upper layer. Under ideal con­ ditions for sewage disposal, the currents would be directed away from 1000 COASTAL ENGINEERING

shore all the time and under these conditions, very little treatment of the sewage would be necessary. However, very few sewage disposal sites approach this ideal condition. When the surface currents are directed on shore at least a portion of the time, then some combination of treatment, diffuser and length of outfall is necessary. Of these fac­ tors, the length of outfall is the most easily varied to fit local conditions, and it becomes necessary to determine the rate and frequency of shore­ ward transport.

Two methods are possible for the determination of this shoreward transport. One method relies upon the use of drift cards which are introduced at selected locations in the survey study area and which drift in the direction of the prevailing current. When picked up either on shore or at the end of a selected time period, they provide an indication of the net drift taking place during that period. These cards are best used in areas which are ringed by heavily used beaches and thus the card return can be substantial enough to make the results significant. This type of study as indicated shows the overall net effect of the cur­ rent, but it does not necessarily trace the actual path of the drift cards and thus the actual sewage field. Another method which allows the actual motion of the sewage field to be more closely followed uses short­ term velocities obtained by current meter and float methods, and then statistical analyses are made which take into account variation of cur­ rent direction with time.

Subsurface currents influence the amount of diluting water that can be brought to the diffusers. At certain times of the year, the sewage field will stay submerged; therefore, the dispersal of the field will be subject motion. Theoretically, the flow at depth should be slower and in a different direction from the surface current in accordance with the Ekman spiral relationship. These deep currents can be studied by cur­ rent meter and float measurements to confirm the variations in direc­ tion and velocity with depth. These current studies are statistically analyzed and net averages are compiled to indicate time to shore under IniniInuIn design conditions. Thes e findings are then us ed as the appro­ priate parameter in the design equations. Generally, conservative values are used to insure the soundness of the final results.

SUBMARINE PIPELINE DESIGN AND CONSTRUCTION

When adequate and complete marine studies and investigations are available, the submarine pipeline designer can approach his task in Inuch the saIne way as he would a conventional pipeline, having knowl­ edge of the forces to which the line will be subjected, the conditions under which it will be installed and its functioning under construction and operation. These Inarine studies also can provide needed back- MARINE STUDIES 1001

ground for the contractor to enable him to understand the effect of sea conditions on his work.

It can be dangerous to undertake a large marine pipeline project without having adequate marine studies and investigations. Equipment and methods are now greatly improved and marine specialists are avail­ abl e to serve as consultants to advise on the conduct of required studi es and the interpretation of their results. With current emphasis on more oceanographic research and new equipment, submarine pipelines will be able to reach further and further offshore. Depths even up to 10, 000 feet can be traversed and the economic potential of marine disposal of wastes can be achieved without undue disruptions or degradation of the marine environment.

REFERENCES

Adams, K. T. (1942). Hydrographic Manual; U.S. Department of Com­ merce, Coast and Geodetic Survey, Special Publications No. 143.

Alvy, R. R. , Miller, D. R., and Lawrance, C. H. (1957). Ocean Outfall Design; Hyperion Engineers, October 15, 1957.

Beckmann, W. C., Drake, C. L., and Sutton G. H. (1960) . SDR Sur­ vey for Proposed Chesapeake Bay Crossing: Proceedings of the American Society of Civil Engineers, Journal of the Surveying and Mapping Division, July 1960.

Bradbury, J. T. (1 961 ) . New Miniaturized Raydist Equipment for Off­ shore Oil Exploration: Offsho re, March 1961.

Brown, R. J. (1 957). Soil Mechanics Important in Marine Pipeline Construction: The Oil and Gas Journal, Vol. 5S, No. 23, pp.10S- 115.

Burt, W. U. , and Sauer, J . F. T., Jr. (194S). Hindcasting technique provides statistical wave data: Civil Engineering, Vol. 18, No. 14, pp. 47-49.

Chambers, Pete (1965). The Blue Dolphin Pipeline - An Offshore Texas Milestone: Pipeline Engineer, No. 11, Vol. 37, p.43.

Cass, J. R., Jr. (1 960) . Computer, Radios Speed Survey; Engineering News-Record, February 18, 1960. 1002 COASTAL ENGINEERING

Gorsline, D. S. and staff (1958) . A Field and Laboratory Manual of Oceanographic Procedures: MiIneographed report, Allan Hancock Foundation, University of Southern California.

Gunnerson, C. G. (1959) . Sewage Disposal in Santa Monica Bay: AIner­ ican Society of Civil Engineer, Transaction, Vol. 124, 1959, p.823.

Miller, D. R. (1958). Report on Studies and Investigations for the Sub­ Inarine Aqueduct for Margarita and Coche: Daniel, Mann, Johnson & Mendenhall de Venezuela.

Miller, D. R. (1958 ). Report on Marine Investigations for the SubInarine Aqueduct for Margarita and Coche: Daniel, Mann, Johnson, & Mendenhall d e V enezuela.

Nuclear Science and Engineering Corp. (1956) . Report to Hyperion Engineers, Radioactive Tracer Study of Sewage Field in Santa Monica Bay: Pittsburgh, Pa., June 29, 1956 .

Pearson, E. A. (1960). Waste Disposal in the Marine EnvironInent: Pergamon Press.

P earson, E. A. (1955) . An Investigation of the Efficacy of Submarine Outfall Disposal of Sewage and Sludge: Report to California Water Pollution Control Board, DeceInber, 1955.

Poirot, J. W. (1959). Hydrographic Surveying froIn a Helicopter; Civil Engineering, February 1959.

Rawn, A . M., Bowerman, F. R., and Brooks, N. H . (1959) . Diffusers for Disposal of Sewage in Sea Water; Journal of Sanitary Engineer­ ing Division, American Society of Civil Engineers, Vol. 86, No. SA2, M a rch 1960, pp. 65-105.

Rittenberg, S . J. (1956). Final Bacteriological R eport: R eport to Hyper­ ion Engineers, Allan Hancock Foundation, University of Southern California, SepteInber 1956.

Stevenson, R. E., Tibby, R. B., and Gorsline, D. S. (1956). O ceano­ graphy of Santa Monica Bay: report to Hyperion Engineers.

Stevenson, R. E. (1960). Wind Drift in the Waters of the Southern California She lf: Water & Sewage Works, April, pp.146-150.

Sverdrup, H. 0., Johnson, M. W., and FleIning, R. H. (1942). The Oceans, Their Physics, Chemistry and General Biology: Prentice Hall. MARINE STUDIES 1003

Terry, R. D. (1956). An Annotated Bibliography on Bacteriology, Oceanography and Marine Geology as They Relate to the Disposal of Waste Material into the Sea; Allan Hancock Foundation, Univer­ sity of Southern California, Aug. 3, 1956.

Wiegel, R. L. (1964). Oceanographical Engineering; Prentice Hall, p. 336. 1004 COAST AL ENGINEERING ...... o o Figure 2. Hyperion Ucean Outfall and Sludge Discharge, 7.0 miles, 22" o. D. 01 ...... o o 0)

Figure 3. Near Shore Trestle for laying Hyperion Ocean Outfall for Effluent Discharge, 5 miles 144" diameter