ATGRADE SYSTEMS

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AT-GRADE SYSTEMS

• by
• Albert R. Jarrett,
• Professor of Biological Engineering

2
The Pennsylvania Protocol

• In Chapter 73 (Conventional).
• In-Ground Systems (Limiting Zone gt60 in).
• Beds.
• Trenches.
• Subsurface Sand Filters.
• Elevated Sand Mounds (Limiting Zone gt20 in).
• Individual Residential Spray Irrigation System
• Bedrock Limiting Zone gt 16 in.
• Water Table Limiting Zone gt10 in.

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The Pennsylvania Protocol

• There are two additional categories
• Alternate Systems.
• Started as an Experimental System.
• Was tested and approved for use.
• Listed in the Alternate Systems Guidance.
• Experimental Systems.
• Proposed systems.
• Being tested.

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The Pennsylvania Protocol

• You either have
• A Conventional system its in Chapter 73.
• An Alternate system its on the alternate
  guidance.
• An Experimental system being tested.

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The Alternate Systems

• As of February, 2007 Alternate Systems
• Alternate Systems may be substituted for
  Conventional Systems.
• Alternate Systems are generally more costly than
  Conventional Systems.
• Alternate Systems require more maintenance than
  Conventional Systems.

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At-Grade Systems

• At-Grade On-Lot Disposal Systems are Alternate
  Systems.
• There are two types of At-Grade Systems.
• At-Grade Absorption Area
• Shallow Limiting Zone At-Grade Absorption Area.
• The following series of slides will present the
  details required to understand and design these
  At-Grade Systems.

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At-Grade Absorption Area

• Minimum Depth to Limiting Zone 20 inches
• Primary Characteristics
• Aggregate placed on the soil surface.
• Must be pressure dosed.

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If Slope 12

• Perc Rate must be 3 to 180 min/in.
• Sized according to a Elevated Sand Mound
  requirements.
• Seepage bed must have a minimum 41 length to
  width ratio.

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If Slope gt 12 and 15

• Perc Rate must be 3 to 90 min/in.
• Sized according to a Elevated Sand Mound
  requirements.
• Seepage bed must have a minimum 61 length to
  width ratio.

Slope
Width Length 6Width
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Treatment Requirements

• Treatment requirements as a function of the Depth
  to the Limiting Zone
• Limiting Zone ? 48 inches
• Primary Treatment Only (Septic Tank)
• Limiting Zone ? 20 inches ? 48 inches.
• Secondary Treatment
• Aerobic Treatment Tank
• OR Primary Treatment (Septic Tank)
• Free Access Sand Filter _at_ 5 gal/d/ft2 (Max)
• Buried Media Filter _at_ 0.8 gal/d/ft2 (Max)

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Limiting Zone ? 48 inches.
SepticTank
At-Grade Absorption
Soil Water
House
13
Limiting Zone ? 20 inches but
? 48 inches
Secondary Treatment
Primary Treatment
SepticTank
Soil Water
At-Grade Absorption
Sand Filter
House
Aerobic Tank
At-Grade Absorption
Soil Water
House
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Shallow Limiting Zone At-Grade Absorption Area

• Minimum Depth to Limiting Zone
• 10 inches to seasonal high watertable.
• 16 inches to rock.
• Primary Characteristics
• May not be placed on concave topography.
• Aggregate placed on the soil surface.
• Must be pressure dosed.
• Only trenches maybe used (no beds).

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Slope must be 15

• The absorption area is sized based on
• Horizontal Linear Loading Rate, and
• Hydraulic Linear Loading Rate
• Requires a Soil Scientist do the evaluation.

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Treatment Requirements

• With the Shallow Limiting Zone
• Water Limiting Zone ? 10 inches
• Rock Limiting Zone ? 16 inches.
• Primary Treatment (Septic Tank) Plus
• Advanced Treatment Unit
• Recirculating Sand Filter _at_ 1.3 gal/d/ft2 (Max)
• Free Access Media Filter _at_ 1.25 gal/d/ft2 (Max)
• Buried Media Filter _at_ 0.67 gal/d/ft2 (Max)
• Peat Filter
• UV Disinfection

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Shallow Limiting Zone
Advanced Treatment
Trenches
Recirculating Sand Filter Sand Filter Peat Filter
Septic Tank
At-Grade Absorption
Soil Water
House
UV
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At-Grade System Components

• Primary Treatment (Septic Tank)
• Secondary Treatment (Filtration)
• Advanced Filtration
• At-Grade Soil Absorption Area.

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Primary TreatmentTwo-Chamber Septic Tank
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Secondary Treatment LZ 20 in

• A Secondary treatment unit (usually filtration
  and biological treatment).
• These are filtration systems.
• Placed after the treatment tank.
• Placed before the At-Grade Absorption area.

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Secondary Treatment LZ 20 in.

• Secondary Treatment Systems
• Free Access Gravity Sand Filter.
• Buried Media Filter.

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Free Access Gravity Sand Filter
3 Min 12 Max Depth
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Advanced Treatment LZ 20 in

• Advanced treatment unit (slow filtration and
  biological treatment).
• These are slower filtration systems.
• Placed after the treatment tank.
• Placed before the At-Grade Absorption area.

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Advanced Treatment LZ 20 in.

• Advanced Treatment Units
• Recirculating Sand Filter
• Free Access Media Filter
• Buried Media Filter
• Peat Filter

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Free Access Recirculating Subsurface Sand Filter
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Free Access Gravity Sand Filter(Lower Loading
Rate)
3 Min 12 Max Depth
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Peat Filter
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Peat Filter
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Absorption Area LZ 20 in.

• Option A
• Aggregate is placed at an 10-inch uniform depth
  over chisel-plowed soil surface.
• Aggregate footprint must have at least a
  4(L)1(W) ratio across the slope.
• 3-foot wide subsoil berm must be placed on both
  ends and bottom of aggregate.
• Cover aggregate with separation layer.
• 8 to 10-inch depth of topsoil is placed over the
  aggregate and berm and planted with suitable
  plants.

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At-Grade Bed System
10 in aggregate 6 in below pipes, 2 in above
pipes.
8 min. topsoil cover
1
6
6
3
Subsoil Berm
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Option A
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At-Grade Bed System
41 LW Ratio
2 to 5
Option A
3 wide subsoil berm
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Absorption Area LZ 20 in.

• Option B
• Aggregate is placed at a minimum 10-inch depth
  over chisel-plowed soil surface. Top of aggregate
  must be level.
• Aggregate footprint must have at least a
  4(L)1(W) ratio across the slope.
• Cover aggregate with separation layer.
• 8 to 10-inch depth of topsoil is placed over the
  aggregate and planted with suitable plants.

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At-Grade Bed System
10 in min aggregate 6 in min below pipes, 2 in
min above pipes.
8 min. topsoil cover
2 to 5
6
31
21
Option B
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At-Grade Bed System
41 LW Ratio
2 to 5
Option B
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Shallow LZ 20 in.

• But when the depth to the Limiting Zone is 20
  inches or less, the system is assumed to dispose
  of the effluent differently.

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Shallow LZ 20 in.
Must use a trench (one pipe)
10 in aggregate Min
10 inch backfill

• 10 inches Water
• 16 inches Rock

Plan for at least 25 feet down slope.
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QUESTIONS???