250 R.I. Code R. 250-RICR-150-10-6.36

Current through December 26, 2024

Section 250-RICR-150-10-6.36 - Pressurized Drainfields

A. General design parameters for all pressurized drainfields

1. All pressurized drainfields shall include timed-dosing, with the use of a control panel containing elapsed time meters and cycle counters for the pump(s) and alarm(s).

2. Setback to foundation and tanks: The minimum setback distance from the pressurized drainfield to any foundation shall be eight feet (8'), provided that the elevation of the basement slab in the dwelling is above the design seasonal high groundwater table (SHWT) depth and that there are no drains associated with the foundation. The minimum setback distance from the pressurized drainfield to any tank equal or larger than one thousand (1,000) gallon capacity shall be four feet (4').

3. Setback to structures impeding groundwater flow: The interior face of any structural or landscape retaining wall that may interfere with ground water flow, down-gradient from the pressurized drainfield, must be located at least twenty five feet (25') from the pressurized drainfield.

4. All setbacks and all other regulatory requirements contained in the Department Rules, that are not mentioned in §§ 6.36, 6.37, and 6.38 of this Part, shall be met.

5. Designs greater than nine hundred (900) gallons per day: Where design flows exceed nine hundred (900) gallons per day, the Department may require additional technical studies to ensure that the soil will accept and transmit effluent at the proposed loading rate without excessive mounding of ground water; seepage outbreak, such as at nearby cut slopes, toe slopes or property boundaries; adverse effects on the operation of the pressurized drainfield; or adverse effects on nearby ground water and surface water resources. The Department shall reserve the right to require additional supporting engineering calculations for the use of pressurized drainfields on design flows greater than two thousand (2,000) gallons per day. The Department may require increased setbacks depending on the site specific conditions. In addition, commercial systems with high strength waste shall incorporate added treatment components to ensure treatment limits herein for BOD5, TSS and FOG are achieved prior to using a pressurized drainfield.

6. Pressurized drainfields must be designed by a Class II or III Licensed OWTS Designer unless the Department determines otherwise. No designer or installer shall undertake the design or installation of a pressurized drainfield pursuant to Regulations unless he/she has received appropriate training by a vendor, professional organization, or institution recognized by the Department for this purpose. Any licensed designer or installer must document to the Department that applicable training has been completed. Class I designers can submit designs to the Department for low pressure pipe (LPP) that follow septic tank effluent only. Class I designers must document to the Department completion of training regarding pressurized dosing (selecting a pump for pressurized systems) that has been conducted by a professional organization, or institution recognized by the Department for this purpose.

7. Residual head: Designs should account for a minimum of two feet (2') of head (pressure) at the distal end of each distribution lateral.

8. Design maintenance notes: Designers should provide adequate notes on their plans to facilitate proper maintenance of all system components.

9. Drainfields at different elevations and zoned drainfields: Site conditions may not facilitate installing drainfield trenches or zones at the same elevation. In these situations, gate valves can be used to provide uniform wastewater distribution. Alternately, orifice plates may be used to help equalize flow to trenches that are not at the same elevation. Ball valves shall not be considered a suitable means for flow control. Access ports must be installed at the locations of all valves, lateral ends and orifice plates. Careful attention should be given to drainback when placing trenches or zones at different elevations since uneven drainback may overload zones or trenches. Types of drainfields that can be placed at different elevations shall conform with the Rules.

10. Sequencing valves: Access ports or manholes shall be required for sequencing valves and shall be sufficiently sized to facilitate maintenance.

B. Common components for all pressurized drainfields

1. General

a. All pressurized drainfields submitted under §§ 6.36, 6.37, and 6.38 of this Part shall use programmable timers.

b. All advanced treatment units to precede pressurized drainfields designed in accordance with §§ 6.36, 6.37, and 6.38 of this Part must fall within one (1) of the following categories:

(1) Category 1 technologies: Advanced treatment units that are timed-dosed and have been classified by the Department as meeting effluent standards less than or equal to twenty (20) mg/L for both BOD5 and TSS; and FOG of less than or equal to five (5) mg/L (see § 6.69 of this Part, Figure 11).

(2) Category 2 technologies: Advanced treatment units that are not timed-dosed and have been classified by the Department to at least meet effluent standards of thirty (30) mg/L for both BOD5 and TSS; and FOG of less than or equal to five (5) mg/L (see § 6.70 of this Part, Figure 12).

2. Dosing Tank Specifications

a. A dosing tank must be provided following the advanced treatment step to provide wastewater storage and to house the pump discharge assembly. All dosing tanks used in a pressurized drainfield system must be watertight. All inlet and outlet pipes to concrete dosing tanks shall have flexible rubber seals secured by stainless steel bands. Watertight rubber grommets must be used at inlet and outlet pipes to plastic or fiberglass dosing tanks as well as on plastic manhole risers attached to concrete tanks.

b. Category 1 technology dosing tanks shall provide storage volume at least equal to the design volume dosed onto the pressurized drainfield during one (1) pump run time. See §§ 6.71 and 6.72 of this Part, Figures 3 and 4.

c. A storage capacity must be provided in pressurized drainfield dosing tanks that follow Category 2 technologies or for septic tank effluent. The surge storage capacity shall be positioned between the elevation of the timer operating control switch and the high water alarm/peak enable control switch. The high water alarm shall be placed a minimum of two inches (2") below the invert of the inlet to the tank.

d. Dosing tanks following treatment units that are not timed-dosed shall be a minimum of four hundred fifty (450) gallons. For single family residential designs the required surge storage shall be seventy five (75) gallons per bedroom; for other designs the surge storage shall be calculated, at minimum, fifty percent (50%) of the daily design flow. See §§ 6.73, 6.74, and 6.75 of this Part, Figures 15, 16, and 17.

e. The pump servicing the pressurized drainfield shall be submerged completely at all times.

f. All manhole risers in the tanks/chambers serving the pressurized drainfield shall be watertight, and installed to finish grade with secure lids, in accordance with § 6.27(H)(2) of this Part.

3. Pump, Discharge Assembly and Transport Line Specifications

a. Pressure requirements: Pumps shall be sized to provide a minimum of two feet (2') and a maximum of seven feet (7') of head (i.e. pressure) at the distal end of each distribution lateral in the pressurized drainfield.

b. Wiring requirements: Pumps dosing pressurized drainfields following a non-timed-dosed system shall be wired on the same electrical circuit as the advanced treatment unit.

c. Discharge assembly: The discharge assembly in the dosing tank shall be provided with a check valve; a mechanical disconnect from the pump to the discharge assembly, reachable within twelve inches (12") of the finish grade; and a valve to hydraulically separate the chamber from the pressurized drainfield. If the transport pipe needs to be drained after each pump event, a weep hole (three sixteenths of an inch (3/16")) shall be placed in a location within the discharge assembly that allows for drainback. Spray from the weep hole shall be directed away from sensors and controls (floats, transducers, etc.).

d. Anti-siphon devices and check valves: If the transport pipe slopes towards a pressurized drainfield having distribution piping at a lower elevation than the maximum water level in the dosing tank, an anti-siphon device shall be used on the pump discharge assembly, or at the highest point in the piping system from the tank to the distribution piping.

e. Shallow transport lines (above frost depth) shall drain after each dose or be insulated. If site conditions do not allow a transport line to drain, then a two foot (2') minimum burial is required and a two inch (2") minimum thick by twenty four inch (24") wide expanded rigid polystyrene plastic insulation must be placed above the pipe.

f. Pump screen: All pumps following Category 2 technologies must have either a screened vault/basket or an in-line effluent filter. All pumps following a septic tank shall have an effluent screen. See §§ 6.73, 6.74, and 6.75 of this Part, Figures 15, 16, and 17.

g. Piping and fittings: All piping from the pump flange to the distal end of the drainfield lateral shall be pressure rated schedule (SCH) 40 polyvinyl chloride (PVC) or equivalent.

h. Excavation: Sagging in the transport line shall be prevented by either:

(1) Placing the transport line in an undisturbed trench bottom excavated to the specified grade; or

(2) Placing a layer of one inch (1") minus gravel, or three quarter inch (3/4") crushed stone, on the undisturbed trench bottom to bring it to specified grade.

i. Velocities within pipes: Liquids shall flow at a minimum velocity of two feet (2') per second and a maximum of eight feet (8') per second. These apply for discharge assemblies, transport pipes, manifolds and laterals.

4. Programmable Timer, Controls and Control Panels

a. Timer settings: The timer shall be programmed to provide several small doses of wastewater to the pressurized drainfield throughout a twenty four (24) hour clock time period.

(1) The system design shall be based on a minimum of one (1) dose per hour and, for typical single residential use, up to two (2) doses per hour.

(2) The designer or the authorized O&M service provider shall ensure that the timer is field-set at the time of system start up.

(3) Two (2) to four (4) weeks after sufficient use of the system, the service provider shall ensure that the timer is reset, as needed, based upon actual flow through the system.

(4) Timer settings shall be checked at every established maintenance and inspection visit and when home occupancy changes and adjusted as needed.

b. Controls

(1) Controls shall be in the form of signal rated floats, pressure transducers or other methods approved by the Department. A high water alarm and pump controls shall be included. A peak enable control shall be included either as part of the timed-dosed pretreatment system (Category 1 technology) or as part of the dosing tank for the pressurized drainfield served by a non-timed-dosed pretreatment system or septic tank.

(2) The peak enable control shall engage the programmable timer into the peak enable mode in the event of timer malfunctions or temporary excessive water use. The peak enable mode in dosing tanks for the pressurized drainfield served by a non-timed-dosed pretreatment system shall cut the "off" time of the pump to half its original setting to catchup with excessive temporary flow. The pump "on" time shall stay the same during the peak enable mode to minimize saturated conditions in the drainfield.

(3) A low water/redundant off control is required for pump tank using timed dosed effluent to a pressurized drainfield (following Category 2 technologies or LPP receiving septic tank effluent).

c. Control panel

(1) The control panel box must be placed outside on a suitable pedestal near the structure that it serves or be mounted on an outside wall of the structure. The panel box must be within view of the system location. The control panel shall be placed at a comfortable height for access.

(2) The control panel and junction boxes must, at minimum, meet the requirements for the NEMA 4X specifications in the National Electrical Manufacturers Association Standard 2502014 "Enclosures for Electrical Equipment (1000 Volts Maximum)" incorporated above at § 6.7(F) of this Part. The electrical conduit to and from the control panel must have NEMA-approved expansion fittings and must also have appropriate seals to prevent gases and moisture from reaching the control panel or junction boxes.

(3) The control panel shall include a pump elapsed time meter ((ETM) to record total pump run time) and cycle event counters ((CC) recording events for each pump, peak enable counter, and alarm event). The ETM and CC shall be nonresettable.

C. Common Final Installation Steps for all Pressurized Drainfields

1. Head requirements: Immediately after any pressurized drainfield has been installed, the head or "squirt height" of the distribution laterals shall be determined, recorded in the maintenance record and left on site. When measuring the distal head, the measurement shall begin at the invert of the lateral.

2. Trees and shrubs: Trees and woody shrubs shall be kept a minimum distance of ten feet (10') from the pressurized drainfield.

D. Operation and Maintenance Requirements for all Pressurized Drainfields

1. General: An O&M agreement is required to be in place for the life of the system. The first O&M agreement of the system shall be recorded in the Land Evidence records of the pertinent City/Town.

2. Site Visits: At each of the operational and maintenance visits, readings from elapsed time meters, event counters, and water meters shall be recorded on the data cards.

3. Routine Periodic Maintenance

a. Laterals: An eight foot (8') long clear graduated PVC pipe shall be temporarily attached at the end of a lateral to measure residual head and compare with the pressurized drainfield start-up measurement. Increased residual head (distal head or squirt height) will signal orifice clogging and lateral cleaning must be performed. Decreased residual head might indicate pump wear, clogging or other problems in pipe(s) or screens needing service/cleaning.

b. All pressurized drainfields shall require lateral flushing/bottle brush treatment at least once a year.

c. Setback to brush/trees: Any brush or trees growing within ten feet (10') of the pressurized drainfield shall be removed.

d. All splice boxes shall be checked for moisture. If moisture is encountered in any splice box, the source shall be identified, corrections made (if needed), and splice box dried and secured before leaving the site.

e. To prevent contamination of the local water supply, the service provider must use his/her own hose with a backflow preventer.

f. Sequencing valves: Sequencing valves shall be tested for proper sequencing through all the outlets (turn pump on/off through all zones).

250 R.I. Code R. 250-RICR-150-10-6.36

Amended effective 11/25/2018
Amended effective 12/28/2021
Amended effective 7/1/2022