Design Standards for On-site Treatment Methods

El Paso City Code tit. 18, ch. 18.21, art. V

in effect

El Paso City Code § 18.21.180 Design standards for residential sewerage systems.

18.21.180 - Design standards for residential sewerage systems. A. House Sewer. The sewer from the house plumbing system to the septic tank shall be constructed of structurally sound pipe such as cast iron, ductile iron, or SDR 35 (or equivalent) plastic pipe with metallic locating tape, bedded in sand. Cast iron, ductile iron, Schedule 40 PVC, or high strength pipe should always be used under driveways. The pipe from the house to the septic tank shall have a minimum inside diameter of not less than four inches and be compatible with the house stub out pipe. The slope of the house sewer shall be no less than one-quarter-inch fall per foot of pipe. The stub out location shall be at the highest possible elevation with respect to the house foundation to avoid deep treatment systems. The line must be of watertight construction. A cleanout plug must be provided within three feet of the building and at ninety-degree turns in alignment, both horizontal and vertical, and at every seventy-five feet of straight horizontal piping. Prospective installers and users of low flush commodes should consult with the manufacturers of these devices regarding their grade requirements. Too steep or too shallow slopes on pipes connecting the toilet and the treatment tank may require excessive maintenance. Piping from the treatment tankage to the disposal area must have at least two inches inside diameter, have at least a minimum fall of one-eighth inch per foot and be as sturdy as SDR 35 PVC piping. Metallic locating tape shall be used with the installation of all piping to and within the disposal area. This tape shall be readily detectable with a metal detector. B. Septic Tank Capacity Based on Sewage Loading. A properly designed septic sewage tank shall be watertight. The settleable and suspended solids will undergo partial decomposition under anaerobic conditions. As a result of use, the septic tank will accumulate partially decomposed solids which must be removed periodically. As additional sewage is introduced into the tank, partially clarified effluent is discharged into the subsurface disposal field. The best method for estimating the tank's sewage loading is based upon the number of bedrooms in the house. Table 18.21.180 shall be used to determine the required minimum septic tank liquid capacity. Table 18.21.180 Septic Tank Minimum Liquid Capacities Number of Bedrooms | Septic Tank Capacity (Gallons) Two or less | 1,000 Three | 1,000 Four | 1,250 For each additional | 250 Note: The inside liquid depth of the tank shall not be less than 30 inches. See Table 18.21.230 for calculating the number of bedrooms based on dwelling living area. Consideration shall be given to increasing total tank capacity if extensive use of kitchen sink waste grinder/disposals is anticipated. C. Inlet and Outlet Devices. To assure rapid drainage of house plumbing, the flow line of the inlet pipe shall be at least three inches higher than the operating tank liquid level which is determined by the flow line of the outlet pipe. Liquid penetration of the inlet device shall be at least six inches, but never greater than that of the outlet device. Liquid penetration of the outlet device shall be approximately one-fourth to one-half of the tank's liquid depth. T branches are required for inlet and outlet devices because they provide a means for venting the gases produced by the decomposition process from the tank and absorption system through the house plumbing. Otherwise, gases may escape from around the lid of the tank and cause an odor nuisance in the vicinity of the septic tank. T branches also offer ready access for required maintenance. To prevent the escape of floating solids from the tank to the subsurface disposal field and the possibility of inlet stoppages, the open spaces between the tops of the inlet and outlet devices and the underside of the tank cover shall not be greater than four inches, nor less than two inches (See Figure 18.21.180(A)). In order to provide a good watertight septic tank, the inlet and outlet T branches shall be installed in a permanent manner at the time the septic tank is constructed. Factory built tanks shall have the T branches grouted in place before delivery so that the only connections to the tank at the point of installation will be the influent and effluent lines. Manufacturers of prefabricated tanks shall be allowed to install watertight flanges into the tank walls, into which inlet and outlet stubs can be easily fitted by field installers, causing watertight connections. D. Details of Septic Tank Design. 1. Two single compartment tanks in a series, or a two compartment tank, with approximately one-half to two-thirds of the total volume in the first compartment, will be required for acceptable solids removal. Tanks may be round, rectangular, or of a shape that allows the department's standards to be met. The second tank or compartment shall have inlet and outlet devices designed the same as for a single-com- [image omitted; see the official code] partment tank, except that the elevation, or flow line, of the inlet devices in the second unit shall be the same as the outlet device in the first unit (See Figure 18.21.180(B)). A ten-inch minimum diameter or square port shall be provided to each flow line device for inspection, cleaning, and maintenance. Both the inlet and outlet devices shall be accessible for inspection and maintenance without having to enter the septic tank. For tanks not having more than twelve inches of earthen cover, the use of sectional slab covers will conveniently and safely provide the needed access. For tanks buried more than twelve inches, manholes with risers are required. The septic tank shall be of sturdy, watertight construction. Materials used may be steel-reinforced poured-in-place concrete, steel-reinforced pre-cast concrete, reinforced fiberglass, polyethylene, or other materials approved by the licensing authority. Metal septic tanks are prohibited because they are subject to corrosion. The septic tank shall be structurally designed to resist buckling from external hydraulic loading and exterior loading caused by earth fill, garden tractors, riding lawn mowers, or any expected maximum wheel weights. Tanks exhibiting obvious deflections, leaks, or defects that will impair treatment must not be used. Where concrete tanks are installed, sweating, or condensation at construction joints is acceptable. 2. In the case of poured-in-place concrete tanks, septic tank bottoms shall be at least six inches thick with 6 × 6 × 6 gauge welded steel mesh or number three reinforcing bars on six-inch centers, with such reinforcing materials being extended up into the wall area of the tank so that it will mesh with the reinforcing materials in the walls of the tank. The floor and walls must be constructed monolithically. Walls are to be a minimum of six inches thick. 3. Septic tank tops reinforced with 6 × 6 × 6 gauge welded steel mesh or number three reinforcing bars on six-inch centers must be poured off-site rather than on the tank (not on top of a wooden frame over the tank) and must be moved onto the tank after hardening and then sealed to the tank with a permanent bonding material or rubber gasket having a one-half inch minimum thickness so as to form a seal between tank and top. To facilitate handling, tops may be poured in sections but must be sealed when in place. Tops must be a minimum of three inches thick. 4. Precast concrete, polyethylene, and prefabricated fiberglass tanks are subject to prior approval of the licensing authority, who should consult with the department regarding the uniquely differing materials, manufacturing methods, and designs used. All precast or prefabricated tanks shall be clearly marked, tagged, or stamped with the manufacturer's name, an exclusive serial number, and the capacity of such tanks near the level of the outlet in at least two positions so as to be clearly visible to the inspecting or permitting authority even after they have been placed in the ground. Listing of this information with the address of the installation shall be maintained by the licensing authority. 5. Septic tanks must be installed so as to provide at least twelve inches drop in elevation from the bottom of the outlet pipe to the bottom of the disposal area. A sand pad, sandy loam, or select material with a minimum thickness of four inches must be placed under all prefabricated tanks. All septic tank excavations must be backfilled with sand, pea gravel, select backfill, or loam not containing rocks greater than one inch in size. It is acceptable to mound sandy loam over a septic tank which is set high to maintain fall to the drainfield. 6. When treated sewage must be pumped to the disposal area, an effluent pump shall be placed in a watertight tank. A check valve shall be provided if the disposal area is upgrade and higher than the pump. The tank shall be pro- [image omitted; see the official code] vided with a highwater alarm having a power circuit separate from the pump. The electrical connections shall be hard-wired, external to the pump chamber. Effluent pump tanks shall have a minimum capacity of five hundred gallons after the alarm is activated. (Ord. 9448 (part), 1988)

El Paso City Code § 18.21.190 Design standards for institutional sewerage systems.

18.21.190 - Design standards for institutional sewerage systems. A. General Consideration of Use of Septic Tank Systems. Septic tanks may be used as a means of sewage treatment for nonresidential activities. However, experience indicates that the usefulness of the septic tank systems decreases as the size of the establishment served increases. A registered professional engineer shall be required to design all private sewage facilities serving institutions. B. Sewage Loading. The total quantity of sewage applied per day to the septic tank provides the basis for the determination of its size. Table 18.21.190 will be of assistance in estimating the daily sewage flow per capita for a variety of living and activity situations. Organic loading of sewage from restaurants, hospitals, nursing homes, and other commercial establishments will require an increase in tank size. C. Compartments to be Provided. Two compartments or two or more treatment units connected in series shall be utilized; shall be provided, the first created by a wall with a tee to permit liquid flow from the first compartment to the second one. The flow line of this intermediate fitting shall be at the elevation of the flow line of the outlet fitting of the second compartment. The fitting shall be three inches below the elevation of the flow line of the first compartment's inlet fitting. The capacity of the first compartment shall be one to two times the capacity of the second compartment. All tanks must be vented internally. D. Selection of Septic Tank Capacity. The net volume or effective capacity below the flow line of a septic tank for flows up to two hundred fifty gallons per day shall be at least seven hundred fifty gallons. For flows between two hundred fifty and five thousand gallons per day, the capacity of the tank shall be equal to at least three days sewage flow. For daily flows over five thousand gallons per day, the determination of the necessity for a waste discharge permit must be obtained from the commission. E. Pump Tank Usage. When treated sewage must be pumped to the disposal area, an effluent pump shall be placed in a watertight tank. A check valve shall be provided if the disposal area is upgrade and higher than the pump. The tank shall be provided with a highwater alarm having a power circuit separate from the pump. The electrical connections shall be hard-wired external to the pump chamber. Effluent pump tanks shall have a minimum capacity of one thousand gallons after the alarm is activated. For daily flows over five hundred gallons, a duplex pump configuration must be provided. (Ord. 9448 (part), 1988)

El Paso City Code § 18.21.200 Design standards for aerobic sewerage plants.

18.21.200 - Design standards for aerobic sewerage plants. A. Introduction. A number of small (up to one thousand five hundred gallons per day) aerobic wastewater disposal systems have been designed and marketed for the on-site treatment of sewage. The design standards in this section govern the installation and use of on-site aerobic sewerage plants for private residences, small businesses, and institutions that will not treat more than one thousand five hundred gallons per day. Sewerage plants designed to treat more than one thousand five hundred gallons per day must meet the design criteria for sewerage systems, published by the department and the commission. B. Appropriate Usage. The installation and use of aerobic individual wastewater disposal units, other than septic systems, are acceptable to the licensing authority provided they meet the requirements of this section. Table 18.21.190 Individual Usage Rates in Businesses/Institutions This table may be used for estimating gallons of daily sewage flow per person to determine minimum tank capacity requirements, unless actual water usage data is available and has been carefully checked by the designer of the proposed system. Type of Establishment | Gallons/ Person/ Day Airports (per passenger) ..... | 5 Apartment houses ..... | 50 Boarding schools ..... | 50 Churches (per member) ..... | 5 Country clubs (per resident member) ..... | 100 Country clubs (per nonresident member present) ..... | 25 Day care centers (without kitchen) ..... | 15 Day care centers (with kitchen) ..... | 25 Drive-in theaters (per car space) ..... | 5 Factories (gallons per person per shift, exclusive of industrial wastes) ..... | 20 Hospitals ..... | 200 Hotels ..... | 80 Institutions other than hospitals ..... | 100 Laundries, self-service (gallons per wash, i.e., per customer) ..... | 50 Lounges (bar & tables) ..... | 10 Mobile homes ..... | 75 Motels ..... | 50 Movie theaters (per auditorium seat) ..... | 5 Office buildings* ..... | 15 Parks (without bathhouse) ..... | 5 Parks (with bathhouse) ..... | 15 Restaurants (24-hour full service) ..... | 70/seat/day Restaurants (breakfast/lunch or lunch/dinner) ..... | 35/seat/day Restaurants (fast food—paper plate service) ..... | 15/seat/day Schools without cafeterias, gymnasiums or showers ..... | 15 Schools with cafeterias, but no gymnasiums or showers ..... | 20 Schools with cafeterias, gymnasiums and showers ..... | 25 Service stations (per vehicle served) ..... | 10 Stores (total per day per washroom) ..... | 400 Swimming pools and bathhouses ..... | 10 Townhouses (with clothes washer) ..... | 50 Travel trailer/RV parks ..... | 50 Vet clinics (per animal) ..... | 10 Work or construction camps (semi-permanent) ..... | 50 Youth camps (no showers or meals served) ..... | 15 _____ * Note: Offices without food service or bathing facilities, with restrooms equipped with toilets requiring 1.5 gallon per flush or less, and automatic cutoff faucets: ..... | 6 C. Effluent Disposal Practice. The effluent from an individual small aerobic wastewater disposal unit must be discharged into properly designed and constructed subsurface sewerage system. No discharges to or above the ground surface or into the waters of the state are authorized by the department. No local regulatory program has been established to permit such practices. D. Operation and Maintenance Responsibility. Companies distributing aerobic individual small waste disposal systems shall provide an inspection and repair service. E. Emergency Operation. The principal structure or containing vessel of an individual small wastewater unit is designed to provide treatment to a predetermined amount of daily incoming sewage. In the event of more than one day's failure of mechanical or electrical devices, anaerobic conditions will prevail when aeration equipment is inoperable. The unit's owner shall be prepared for emergencies by contractual arrangement with the plant's seller, by stocking spare parts, by hiring a licensed sewage pumping and hauling company, or by preventing the generation of more sewage until the emergency is eliminated. F. National Sanitation Foundation Criteria. Individual small aerobic wastewater disposal units shall have a National Sanitation Foundation Seal indicating the unit meets the Foundation's standard 40. Units not having a NSF approval rating must be approved through the procedure of Section 18.21.080. G. Treatment Limitations. The prospective user should be aware that small aerobic treatment plants treat sewage differently than septic tanks. Aerobic treatment plants operate by mixing raw sewage together with air and masses of bacteria. Several kinds of bacteria consume the sewage and air, changing it to nitrogen, carbon dioxide and water, all of which are used by plant life. Treated clear effluent still contains microscopic bacteria and viruses that were in the raw sewage so it must be kept out of contact with the general public as much as possible. It is possible to disinfect treated sewage with chlorine, bromine, ultraviolet light, ozone, or other commercially available products. However, nothing will make aerobically treated sewage safe enough to use as fresh water. Disposal systems for aerobic plant effluent shall be the same as for septic tank effluents. H. Siting Considerations. Most aerobic treatment plants sized for single home or small commercial shop use are usually only slightly larger than a septic tank but may not be installed as deeply. The organic loading, of commercial or institutional applications may require individual design considerations. Its inspection access is exposed to the surface, unlike a septic tank which is usually covered over with a layer of gravel or grass sod. The unit is generally one piece construction using concrete or fiberglass. I. Solids Accumulations. Most aerobic treatment plants operate by applying air from an air compressor into the bottom of the tank that first accepts raw sewage. As the air bubbles rise to the surface the sewage mixes with a mass of brownish gray bacteria called activated sludge. Several baffles or compartments are required within the single unit so that several different activities can be done at the same time. These include mixing the air, sewage, and bacteria together, then allowing the bacteria to settle while the treated effluent is drained off the top. Solid materials that the bacteria cannot consume will accumulate in a sludge holding compartment along with grease, oil, and other undigested floating wastes. The sludge and floating wastes will have to be removed occasionally by a sludge hauling company. How often sludge has to be removed depends upon the type and amount of waste the owner applies to the system. (Ord. 9448 (part), 1988)

El Paso City Code § 18.21.210 Design standards for grease traps.

18.21.210 - Design standards for grease traps. A. Installation. Grease traps shall be used on kitchen wastelines from institutions, hotels, restaurants, schools with lunchrooms, and other places that may discharge large amounts of greases and oils to the sewer. However, wastes from garbage grinders must not be allowed to enter a grease trap. The trap shall be installed near the plumbing fixture that discharges greasy wastewater and should be easily accessible for cleaning. When maximum efficiency grease removal is necessary, a dual chambered trap that separates, then stores grease shall be utilized. If the dual chamber trap is installed as close as possible to the source of hot greasy wastes, the separated grease can be conveyed to the secondary chamber, where it accumulates, cools, and solidifies. B. Sizing. Grease trap sizing will depend on the particulars of the application. Building code authorities and trap manufacturers should be consulted prior to sizing the unit. Grease interceptors shall be sized using Chapter 18.20 of this Code. (Ord. 9448 (part), 1988)

Source: City of El Paso, City Code and City Charter (Municode Library, library.municode.com)URL: https://library.municode.com/tx/el_paso/codes/code_of_ordinances?nodeId=TIT18BUCO_CH18.21PRSEFA_ARTVDESTTETRMEFetched: 10/28/2026