Metheny - The Moldering Privy Green Mountain Club Exit Strategies Conference, 2010, Sustainable Summits Initiative

1. The Moldering Privy
Green Mountain Club
Exit Strategies - 2010

2. 2
Double Crib
Privy at Spruce
Ledge Camp

3. 3
History in Vermont
• Concept introduced to Long
Trail/Appalachian Trail System in 1997 by
Green Mountain Club Volunteer Dick
Andrews. 1st
site was Little Rock Pond
Shelter in 1997.
• Concept based on Andrew’s Clivus
Multrum composting toilet in his home –
same composting techniques used.

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Moldering Defined
• Moldering method of composting employs
mesophilic temperature range (68° to
112°F). AKA “Slow Composting.”
• Not hot enough to kill disease-causing
pathogens.
• Moldering toilets substitute long retention
time of waste to ensure pathogen
destruction – minimum of 2 years. The
longer the better.

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Moldering – Where to use?
• At low to medium use sites.
• Defined as a site where it will take a minimum of 2+
years for one crib to fill up. If it fills faster than this a
batch-bin or commercial system is called for. Alternately
you can build more cribs – you as a manager need to
determine how many cribs you can accept
environmentally and aesthetically. GMC limit is two cribs.
• GMC recommends you choose a site where you believe
you have low use and where you can measure the use.
See how long it takes to fill a crib – use this data to
define your “use threshold.”

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Original Crib design circa
1999 – Single Crib, 6x6
construction

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Drilling Pilot Holes for
rebar

8. 8
Cribs are held together with rebar
that link together each corner and
are embedded in the ground.

9. 9
Note 2x4 corner
bracing

10. 10
Raising
Outhouse onto
Crib System

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Existing
Outhouse is
placed on crib
system

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Finished Single Crib
unit. Privy attached to
crib with angle
brackets

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The finished unit is
tall. Stairs or an
Accessible
ramp/stair system is
required.

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Design Principles
• Basic Crib Capacity is 4’x4’x3’ (w/l/d).
• Shallow depression is made in the ground
below the crib to focus blackwater into
biologically active soil.
• Air Slots are covered on both sides with
hardware cloth and externally with dark
insect screening to prevent waste escape
and vector access.

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Design Styles
• Original design utilized 6x6 timbers (treated and
untreated).
• Easy to design and build but very heavy to pack to
remote backcountry campsites. A second or third crib
would need to be packed in when the first one was full.
• Current design is a two-chambered unit built with 4x4
uprights held together with 1x6 horizontal members. The
composting crib is covered with a removable roof
system. This unit is much lighter, easier to pre-build in
the frontcountry, and is more readily adaptable to double
and triple-chambered units.

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The new design is a double-
chambered unit. The basic
frame is composed of six
4x4’s each 3 feet tall.

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Puffer Shelter
System under
construction – new
privy and cribs.

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Note strapping used to
reinforce hardware cloth to
crib.

19. 19
Installing
hardware cloth.
Note divider
separating two
cribs.

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Corner Bracing provides
extra strength.

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22. 22
Securing 1x6
horizontal
members

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24. 24
Finished crib system
contains 21 main
structural pieces.

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Top sills are attached
with metal plates.

27. 27
Attaching stair treads.

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Finished 2 chambered system
showing installed hardware
cloth, insect screening, and
composting bin cover.

29. 29
Finished 2-
Chambered
Moldering
Toilet

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Modified Moldering System w/
Liquid Separator
• Installed at AMC’s Upper Goose Pond
Cabin.
• A caretaker periodically homogenizes the
waste and adds bulking agent as needed.
• Crib is shallower and thus requires regular
tending to prevent overflow.
• Liquid separator requires a separate seat
and drains to a modified French Drain.

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Upper Goose Pond
Moldering Toilet –
Note shallow cribs.

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Access Door
and urinal
drain hose

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Access Hatch –
provides access for
knocking down the
cone.

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Accelerated Moldering
Process – Bulking agent
is leaves and forest duff.

35. 35
Removing finished
compost for spreading
on the forest floor

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Side by Side: Urinal on
left and solid waste hole
on right.

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Unisex Urinal

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French Drain for Urine

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Clivus-Style Moldering Privy
• Constructed on the Appalachian Trail in
Maryland and Pennsylvania.
• Utilizes large sloping chamber.
• Dual Chambered Units create long retention
time for waste.
• No contact with soil – needs large base of
bulking agent added to create composting “bed.”
• System improvement needed: liquid drainage
system to French Drain or Beyond the Bin
Barrel.

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Single
Chamber
Clivus Style
“Pennsylvania
Composter.”

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42. 42
Double Chambered
Unit under construction.

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Current Design – Lessons Learned
• Bulking agent (carbon source) must be brought in.
Reliance on area leaves and duff proved hard on the
resource. GMC has had the most success with dry
softwood planer shavings – most absorbent.
• A base of 4 to 6 inches of bulking agent should be added to
bottom of the crib to create a composting bed. This assists
in aeration and increases percolation of liquids by providing
separation.
• An access lid must be incorporated into the design so the
cone can be knocked over periodically and the waste pile
homogenized. Access through the seat is unsanitary.
• Pile can and will dry out if the manager does not monitor
pile moisture and add water as needed. A dry pile will not
compost – pathogens go dormant and persist.

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Current Design – Lessons Learned
Continued
• GMC has begun to perforate the roof cover that goes
over the composting crib so that rain water can percolate
in and keep pile moist. For the active pile we ask users
to urinate on the pile – unless use levels create an
objectionable odors.
• GMC has added a sloping metal roof cover to
the composting chamber to prevent excessive
moisture and reduce the chance of cave-in from
heavy snow load.

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Resources
Appalachian Trail Conservancy and Green
Mountain Club’s Backcountry Sanitation
Manual (1st
edition 2001)
http://atfiles.org/files/pdf/atcsanitation.pdf

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Thank You
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