Civil and Structural Manual 500 Drainage

Chevron Corporation 500-31 June 1997

537 Component Design ConsiderationsThis section describes some drainage components and tells how they are commonly used. The standard drawings and forms are located in the Standard Drawings and Forms section at the end of this manual.

Engineering Form 611Engineering Form 611 (CIV-EF-611) shows how you can put the components together to make some standard drainage system building blocks. It is intended to give you some good starting arrangements; feel free to make changes or develop other details to suit your needs.

CIV-EF-611 shows bell-and-spigot or plain end-and-hub connections, but similar details can be easily envisioned for materials that require butt or other types of joints. Check the actual dimensions of the fittings to be sure the pieces will fit in the space available and will have adequate cover.

Note that the dimensions of cast iron bell-and-spigot fittings are different from the dimensions of cast iron butt fittings.

Catch Basins and DrainsCatch basins and drains both serve the same purpose: to let liquid wastes enter the underground drainage system quickly and safely.

Catch basins (Figure 500-11) contain a chamber where liquid is briefly retained to aid in settling solids. The chamber is easily accessible for removing the accumu-lated material. Catch basins are normally built with the inlet opening flush with or slightly below grade.

Fig. 500-11 Typical Catch Basin

500 Drainage Civil and Structural Manual

June 1997 500-32 Chevron Corporation

Runoff from unpaved areas will contain suspended sediment that can clog small catch basins, so be sure to use adequately sized basins. Experience is the best guide for size selection.

A drain or drain hub is a simple inlet that has no retention capacity. If it protrudes above grade, it is called a raised drain hub. If it is below grade, it is called a recessed drain hub. Raised hubs can receive waste from vessels or pumps while preventing surface fluids from entering. Details 3 and 4 on CIV-EF-611 show recessed and raised drain hubs.

Sealed Drain Hubs and Catch BasinsCatch basins and drains can also provide a seal, (sometimes called a gas seal or liquid seal) that prevents flammable or toxic gases in the downstream piping from escaping to the atmosphere. Seals also keep heavier-than-air flammable or toxic vapors from flowing into the system, and they prevent fire from traversing the drainage system.

Since sealed drains will accumulate solids and are not easy to clean, do not use them if the liquid will contain solids that might settle out. Instead, use sealed catch basins with sufficient clearance between the bottom of seal and the bottom of basin (Dimension E on Drawing GC-S78325).Detail 8 on CIV-EF-611 shows a sealed drain. Drawing GC-S78325 shows a cast iron, sealed catch basin. Fabricated steel, sealed catch basins are available (see Drawing GD-S-99992). Adapters are available to connect the steel catch basin to non-steel drain lines.

ManholesManholes provide access for inspection and cleaning (hydroblast or roto-rooter) of drain lines, and they act as junction boxes for drains where fittings are not avail-able or are more expensive. Manholes are also a good place to tie in future drain lines.

If the standing water in sealed manholes is a groundwater pollution concern, then a double wall manhole with leak monitoring between the walls might be required.

If the water table is high, ensure that the manhole weight exceeds the buoyant force or anchor the manhole by extending its base beyond its walls.

If your manholes are in traffic areas, design them for wheel loads.

See CIV-EF-411 for typical manhole details.

Manhole CoversManholes in systems carrying volatile flammable or toxic liquid should have vapor-tight covers to prevent the release of gases near ignition sources and people. See Reference [21] for federal regulations governing emissions from manhole covers.If samples will be taken from manholes frequently, consider using covers with sample windows. The sample window shown in Figure 500-12 is not vapor tight.

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Civil and Structural Manual 500 Drainage

Chevron Corporation 500-33 June 1997

Manhole VentsYou should provide vents to relieve pressure and prevent oxygen depletion in manholes with vapor-tight covers.

Vents should end a safe distance (usually a minimum of 25 feet horizontally and downwind if possible) from furnaces or permanent sources of ignition.

Vents should not terminate near walkways, platforms, or air intakes.

Vents within a 10-foot radius of walkways and equipment should end 18 inches above the highest pipe or piece of equipment and 12 feet or more above walk-ways.

Vents in VOC or benzene service must be at least 3 feet in length and less than 4 inches in diameter. In addition, vents in benzene service must be controlled. See Reference [21] for federal regulations on this topic.

Ways to Change Direction, Slope, and SizeAt direction, slope, and size changes, you can use either manholes or fittings. Manholes can be cheaper than large diameter fittings. Find out if local cleaning contractors equipment can negotiate fittings.

If the pipe joint system is flexible enough to allow misalignment without leaking, you can make small changes in slope and direction (a few degrees) by using purposely misaligned joints. Joint manufacturers usually publish limits of flexi-bility. In areas where groundwater protection is very important, you probably should not use this technique except as required for small field adjustments.

Access for Cleaning, Inspection, and RepairManholes provide better access than cleanouts for inspection and repair, but cleanouts are just as good for cleaning. Cleanouts are usually cheaper than manholes unless the cleanouts are built from large diameter fittings. Talk with local

Fig. 500-12 Manhole Cover Sample Window

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Civil and Structural Manual 500 Drainage

Chevron Corporation 500-105 June 1997

20. Akan, A. Osman Kinematic-Wave Method for Peak Runoff Estimates, Amer-ican Society of Civil Engineers, Journal of Transportation Engineering, Vol. 111, No. 4, July, 1985.

Summary: A technical paper that gives several very practical formulas for over-land flow time (for use with the Rational Formula.) The paper gives formulas for plain, flat slopes; flat slopes intercepted by gutters; converging slopes; and others.

21. 40 Code of Federal Regulations Part 60 and 61.Standards of Performance for New Stationary Sources Subpart QQQ, Volatile Organic Compounds Emissions from Petroleum Refinery Wastewater Systems (40 CFR 60.692-2), requires all process drains to have water seals and all junction boxes to be covered. Junction boxes may have a vent pipe, but it must be at least three feet long, and less than four inches in diameter.

The National Emission Standard for Hazardous Air Pollutants Subpart FF, National Emission Standard for Benzene Waste Operations (40 CFR 61.346) applies to facilities at which the total annual benzene quantity from facility waste is more than 10 megagrams per year or aqueous waste streams are treated to a total of 6 megagrams per year of benzene. Process drains subject to this standard must have water seals, and manholes must have covers that allow emissions less than 500 ppm above background levels. Junction boxes must be covered and may have a vent pipe, but it must be at least three feet long, less than four inches in diameter, and emissions from the vent pipe must be controlled.

22. Coatings Manual.

23. Corrosion Prevention Manual.

24. Safety In Designs Manual. (SID)25. Airport Drainage Advisory Circular No. 150/5320-5B. United States Depart-

ment of Transportation Federal Aviation Administration, July 1970.

Summary: This circular provides guidance for the design and maintenance of airport drainage systems. It includes nomographs for flow in open channels and an equation for calculating overland flow time for use with the Rational Formula.

26. NOAA Technical Memorandum NWS Hydro-35, 5 to 60 Minute Precipitation Frequency for the Eastern and Central United States, 1977.

Summary: Gives intensity-duration-frequency information for use with the Rational Formula. Gives rainfall-frequency values for durations of 5, 15, and 60 minutes at return periods of 2 and 100 years for 37 states from North Dakota to Texas and eastward. Equations are given to derive 10- and 30-minute values for return periods between 2 and 100 years.

27. NOAA Atlas 2, Precipitation-Frequency Atlas of the Western United States, Volumes I - XI, 1973.

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