> > > >

1950-51 Theatre Catalog, 9th Edition, Page 190 (170)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 190
Page 190

1950-51 Theatre Catalog, 9th Edition, Page 190

FIGURE 2 Plan drawing of a recommended septic tank.

Metal tanks should be at least 12 gauge and should be coated or treated to prevent excessive corrosion. Where the coatings of metal tanks have been damaged, the tanks should not be used unless the coating is restored.

All tanks should be designed to allow the sewage to enter at one end, have a slow uniform horizontal How through the tank, and discharge the liquified sewage at the other end with the least possible disturbance of the contents. Tanks should be designed with a length not less than two, or more than three, times the width and with a minimum depth of four feet.

As seen in Fig. 1, there is little need for a multiplicity of partitions, baffle walls, or connecting pipes from various chambers. Such construction adds to cost and often reduces the efiiciency of the tank by decreasing sludge storage capacity and increasing the velocity of flow through the tank, thus interfering with sedimentation.

Baffles should extend a reasonable distance below the liquid level, project at least 6" above the fiow line, and be spaced far enough away from the ends of the tank. The invert of the inlet should be somewhat elevated above the invert of the outlet.

In the lower left-hand corner of Fig. 1, an item indicated as 6" Sludge Drain will be noted. This drain is connected to a 6" gate valve which is frequently located in a small well deeper than the drain. At such infrequent preiods as the septic tank may require cleaning, a pail is lowered into position under the outlet from the gate valve; the valve is then opened by a key attached to a long iron rod, and the sludge is removed.

With further reference to Fig. 1, the reader will note a small hooded vent

protruding through the top of the concrete slab. Since the efiicient operation of a septic tank depends on the gas bacilli that attack the solid matter until

it disintegrates and decomposes, there

is a wide belief that fresh air is fatal to the bacilli and should not, therefore, be admitted to the tank while it is in operation. ,

On the other hand, the gas caused by the decomposition of the solid matter must be allowed to escape, or an explosion may occur. Therefore, in order to permit the escape of the gas, without allowing fresh air to enter the decomposition chamber, the aforementioned vent is installed. Many tanks are designed without this vent on the theory that the gas will escape through the discharge outlet with the efiiuent. If the filter bed is properly vented, the foregoing theory is workable, but if vents have not been provided, the acoumulated gas may often cause a blow-up.

The septic tank cover or slab (see Fig. 2) should be designed for a dead load of not less than 150 pounds per square foot. When constructed of concrete, the slab should be reinforced and at least 4" thick. As stated previously, it should be covered with an earth cushion at least one foot thick to protect it from trafiic overhead. The tank slab should provide a watertight cover for the tank, and, when constructed in one piece or monolithically with the tank, it should have at least one manhole. Sectional slab covers may also be used, but in doing so great pains must be taken to make sure that no surface drainage or ground water can seep into the system.

Fig. 3 shows how waste from the concession stand is made to bypass the septic tank. As stated previously, no

FIGURE 8 Recommended method for lay-passing the tank.

surface, soapy, or greasy water should be permitted to enter the septic tank. This problem, as seen in the drawing, may easily be surmounted by running a separate connection from the refreshment stand to the filter bed.

Size Requirements

In spite of the fact that in the majority of states all sewage disposal systems must be approved by the state or local health authorities, comparatively few states have an effective code covering this Vital part of drive-in construction. As a result, either the authorities require a system that is far in excess of actual requirements, or plans are approved that are utterly inadequate for the purpose intended. Due to this variance in state and local regulations, it is difficult to establish design criteria for size that will be applicable in every situation without exception, but it is possible to outline broad provisions for the construction of septic tank systems in capacities which will fit both legal and other conditions generally applicable throughout the United States.

While there is some disagreement as to realistic size requirements for septic tanks to be used in drive-in theatres, it is a recognized fact that the capacities of the tanks do not increase in direct ratio to the number of cars parked. The larger the number of patrons, the smaller the percentage of persons who use the toilet facilities will be. Neither is there any factual comparison between the use of the toilet facilities in a conventional theatre and those in a drive-in. The probable reason for this situation is that patrons of conventional houses often attend the theatre after being absent from their homes for several hours, whereas drive-in patrons are seldom away from home more than three hours. This condition naturally effects the use of the toilet facilities.

At the time drive-in theatre operations were still an innovation in the entertainment field, there was considerable discussion as to the capacities of the septic tanks that should be installed, and many sanitary engineers demanded that provisions be made on the basis that every admission would make use of the toilet facilities. The falsity of this assumption was definitely proven after a few drive-ins were erected in locations available to city water supply. By checking the reading on the water meter at the start of the operating season and again at the close of the season, it was a simple matter to estimate the actual amount of water used for toilets, sprinkling, and other uses. However, as it was impossible to determine exactly the amount of water used nfor other purposesfi it was assumed for practical purposes that all of the water was used in the rest rooms.

The total seasonis consumption of water in gallons at several theatres of varying sizesrwas then divided by five, the normal quantity of water required to flush a water-closet. By using these figures it was then possible to obtain the approximate number of times that the toilets were used per day.

Results of this analysis, which has been used as a yardstick in the construction of many drive-in theatres, are noted in Table I.

1950-51 Theatre Catalog, 9th Edition, Page 190