New Mexico Administrative Code
Title 20 - ENVIRONMENTAL PROTECTION
Chapter 7 - WASTEWATER AND WATER SUPPLY FACILITIES
Part 3 - LIQUID WASTE DISPOSAL AND TREATMENT
Section 20.7.3.807 - LOW PRESSURE DISPOSAL SYSTEMS
Universal Citation: 20 NM Admin Code 20.7.3.807
Current through Register Vol. 35, No. 18, September 24, 2024
A. Low pressure dosed (LPD) disposal systems are used to achieve uniform distribution of wastewater throughout the entire disposal system. Effluent is pumped under low pressure through solid pipe into perforated lateral lines installed within a disposal system.
(1) Low pressure dosed disposal systems may
be used with any on-site liquid waste system including conventional treatment
systems, gray water systems and advanced treatment systems.
(2) Low pressure dosed disposal systems may
be used with any disposal system including trenches, beds, mounds, gravelless
systems and evapotranspiration systems.
(3) Lift stations are not classified as low
pressure dosed disposal systems.
(4) Low pressure dosed disposal systems may
use a timer to equalize the flow over a 24-hour period. LPD disposal systems
may also be designed to rotate between separate disposal areas by using rotator
valves.
(5) All pumps shall be
rated by the manufacturer for pumping sewage or effluent.
(6) A single pump may be used for design
flows equal to or less than 1,000 gpd. Dual alternating pumps are required for
design flows over 1,000 gpd.
(7)
Design of the system shall include:
(a) design
flow;
(b) except for mound systems,
soil absorption area sized according to the effluent loading rates found in
20.7.3.703 NMAC;
(c) total length
of header and lateral pipes;
(d)
diameter of perforated lateral lines used;
(e) size and spacing of holes or emitters;
and
(f) pump performance sizing
with allowances for head and friction losses at rated flows in gallons per
minute.
(8) A ball valve
shall be located vertically at the end of each lateral line for inspection and
flushing except for proprietary drip irrigation systems.
B. A low pressure pipe (LPP) disposal system is a pressurized distribution system placed in shallow, narrow trenches. The effluent discharged to a LPP system must meet, at a minimum, primary treatment standards.
(1) The low pressure pipe system
shall be sized as follows.
(a) The required
absorption area shall be sized in accordance with Subsection H of 20.7.3.703
NMAC.
(b) A sizing credit of five
square feet per linear foot of lateral pipe shall be applied to the total
required absorption area.
(c) Each
individual lateral shall not exceed 75 feet in length from the feed point
unless the design is such that the discharge rate between any two points in the
system does not exceed 10%.
(2) Design for LPP systems shall conform to
the following.
(a) Trenches shall be 12 inches
to 18 inches wide and 12 inches deep.
(b) When aggregate is used, the lateral pipe
shall be embedded at or above the center of the column of aggregate.
(c) The aggregate shall be covered with
geotextile material to prevent soil intrusion.
(d) If a proprietary drainfield product other
than aggregate is used, the distribution pipe shall be placed so as to prevent
soil intrusion into the pipe.
(e) A
minimum of four inches and a maximum of 18 inches of soil cover over the trench
is required.
(f) Lateral lines
shall be placed parallel to the natural contours of the site.
(g) Provisions shall be made for the
prevention of siphoning back to the pump tank on upgrade systems and the
prevention of draining of the tank on downgrade or flat systems.
(h) All requirements for conventional
disposal systems shall be met, including but not limited to, setback and
clearance requirements, lot size, design flow calculations, septic tank sizing,
prohibitions, wastewater characteristics and advanced treatment
requirements.
(i) Runoff shall be
diverted away from the system to avoid oversaturation, where
possible.
(j) A vegetative cover
shall be maintained over the disposal area.
(3) Materials and equipment for LPP systems
shall conform to the following.
(a) All
treatment units and pump tanks shall meet the structural requirements of
20.7.3.501 NMAC.
(b) The pump tank
shall be a single compartment with a 500 gallon minimum useful volume and
allowance to be made for tank volume between the pump intake and tank floor.
For septic tank effluent, a separate pump tank, in addition to the septic tank,
is required.
(c) Effluent type
pumps are required on all systems.
(d) A system design shall demonstrate that
the system comes to the design pressure during every pumping cycle.
(e) An alternating valve or solenoid valve
system is required to feed separate laterals with elevation differences
resulting in 23 feet (10 psi) or greater head differentials. Manual or
automatic flushing valves with turn-ups are required on distal ends of all
laterals.
(f) In areas of freezing
conditions, provisions for the draining of the headers must be made, such as
vacuum breakers or vent holes at the system high points.
(g) Pipe shall be rated at 160 psi minimum,
ASTM compression drainpipe, schedule 40 or better.
(h) The manifold pipe shall be sized
appropriately for system size and configuration. The lateral pipe shall be one
inch to two inches in diameter.
(i)
The orifice size shall be 5/32 inch to 1/4 inch for septic effluent and 1/8
inch to 1/4 inch for secondary and tertiary treated effluent.
(j) The lateral pipe shall be installed with
orifices facing upward.
(4) A maintenance contract shall be required
on all LPP systems. Maintenance is to include pump inspection and cleaning,
float operation (if applicable), lateral flushing annually at a minimum and
septic tank and pump tank pumping as needed.
C. Designs that do not conform to the design parameters specified in Subsections A and B above must be accompanied by documentation justifying the design submitted, including proprietary software input and output reports, and will be considered on a case-by-case basis.
Disclaimer: These regulations may not be the most recent version. New Mexico may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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