Section 250-RICR-150-10-6.38 - Low Pressure Pipe (LPP)A. LPP design guidelines: LPPs shall also conform to § 6.36(A) of this Part: "General design parameters for all pressurized drainfields." 1. All LPP systems under this guidance shall conform to the design sizing parameters contained in Part 6 of this Subchapter for leachfields. Trench end interconnections are not required when using LPP. If drainfield reduction size is sought due to using advanced treatment technology, it shall conform to the approved letter from the advanced treatment technology immediately before the LPP.2. Wastewater quality: When using LPPs with advanced treated wastewater, the pretreatment must meet the requirements for either Category 1 or Category 2 technologies. When using LPPs with residential septic tank effluent, the quality of the effluent shall conform to BOD5 less than or equal to one hundred seventy (170) mg/L, TSS less than or equal to sixty (60) mg/L and FOG less than or equal to twenty-five (25) mg/L (residential strength septic tank effluent).3. Vertical separation distances: All vertical separation distances defined in §§ 6.33(H), 6.33(I), 6.43(E), and 6.44(C) of this Part must be met when using LPP. The vertical separation distance shall be measured from the base of the LPP (the natural receiving soil surface), to the SHWT or to impervious layer.4. Cover: The cover from the top of the LPP to the proposed grade shall be from six inches (6") to eighteen inches (18") (see § 6.84 and 6.85 of this Part, Figures 26 and 27).5. All LPPs shall be timed-dosed, either by the timed-dosed technology preceding it (i.e. Category 1 technology) or by incorporating a timed-dosed component as specified in § 6.36(B) of this Part.6. Flow differential between first (1st) and last orifice in the laterals: The maximum head differential between the first (1st) and last orifice on each lateral shall be no greater than fifteen percent (15%).7. Pump events per day and maximum dose per LPP orifice: The number of dose events per day shall be between twelve (12) and twenty-four (24). The maximum dose per LPP orifice shall be one half (0.50) gallons.B. Components of the LPP: LPPs shall also conform to other components in § 6.36(B) of this Part: "Common components for all pressurized drainfields." 1. Schedule 40 PVC or equivalent sweep elbows (also called "turnups") shall be attached to the distal end of each lateral to facilitate maintenance and inspection. A standard ninety degree (90°) elbow shall not be used.2. Orifice size and spacing: For advanced treated effluent one eighth of an inch (1/8") diameter (minimum) orifices shall be made in the top of the distribution laterals (12 o'clock position) and spaced according to the dosing requirements of the system. Orifice size for use with septic tank effluent shall be three sixteenths of an inch (3/16") diameter. Every fifth (5th) orifice along the lateral shall be drilled from the bottom of the distribution laterals (at the 6 o'clock position, with no upfacing hole at that location) to allow drainage after a dose and to prevent lateral freezing in cold weather.3. Orifice shields or sleeves for dispersal trenches: Orifice shields shall be used at every orifice. Cold weather orifice shields are required for the down facing orifices (6 o'clock position). In lieu of orifice shields, the pressure lateral may be inserted into a three (3") or four inch (4") diameter high density polyethylene HDPE corrugated slotted or perforated pipe. The sleeve shall extend to the sweep elbow and into the inspection port. Pipe slots or perforations shall point in a downward (6 o'clock) direction (see § 6.84 of this Part, Figure 26). When using plastic chambers, the laterals shall be suspended from the inside top of the plastic chamber with appropriate ties. The ties shall be spaced, at minimum, every three feet (3'). When using concrete chambers, the laterals shall be placed above the crushed stone under the concrete chambers or inside the precast concrete channel. When the lateral is installed above the crushed stone, the knockout at the bottom of each concrete chamber unit shall be open so not to crush the pressure lateral upon installation (see § 6.85 of this Part, Figure 27). When the lateral is placed inside the precast concrete channel inside the concrete chamber, the concrete observation ports shall be removed, only at the required manhole riser interval. For either plastic or concrete chambers, orifice shields shall be placed on the up facing orifices only when the orifice lies within an observation port or manhole. For concrete chambers with laterals installed on top of the crushed stone and for all plastic chambers, orifice shields must be used on all the down facing orifices. Orifice shields are not needed if an HDPE corrugated perforated or slotted pipe sleeve is used or if the lateral is installed inside the precast concrete channel on concrete chambers (other than the up facing orifices within the risers extending to grade).4. Inspection port: The ends of the sweep elbows shall be readily accessible by means of a six (6") to eight inch (8") diameter access box or port brought to the ground surface.C. LPP Installation and maintenance specifications: Other than the components specific to LPP's, the trenches shall be installed and maintained in accordance with the current Department Rules or the Department approved technology equivalent replacement approval letters.250 R.I. Code R. 250-RICR-150-10-6.38
Amended effective 11/25/2018
Amended effective 12/28/2021
Amended effective 7/1/2022