How To Install Drip Micromounds

Peter Installation

Micromounds are on-contour at-grade bed with sand (8″-12″), netafim tubing, more sand (2″), and soil (12″). They are primarily used when slopes are between 0 and 15 percent, soils are greater than or equal to 10″ to SHWT and 16″ to rock, and there is sufficient length on contour. In the American Perc-Rite Alternate Listing, the PA DEP specifies the design, permitting, and installation requirements. This article will guide you through the steps of micromound installation, and is a resource to be used on it’s own or with our PA Micromound Installation Class.

Micromound Layouts

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Site Preparation Steps

Step 1: Stakeout

  • The micromound must be on contour.

Step 2: Prepare the absorption area.

  • This includes the downsloping berm.
  • Cut grass, trees, and shrubs close to the ground surface.
  • If the micromound is being installed on a wooded site, make sure to rake leaf litter off of the site.
  • Do not pull stumps out, remove top soil, sod, or boulders.

Step 3: Soil Moisture Inspection / SEO Inspection

  • Area may not be scarified until a soil moisture test has been completed.
  • Soil must crumble at the 6″ to 8″ plow depth.
  • Must prevent soil “smearing.”

Scarification

The purpose of scarification is to:

  • Roughen the surface to allow for better infiltration into the top soil.
  • Provide a more transitional contact between the sand and soil.

What to scarify: Make sure to scarify the entire basal area (where it says “Sand Area” below).

micromound-layout

How to scarify for micromounds:

  • Most preferred: chisel teeth mounted to backhoe (great around stumps).
  • Next, chisel plow behind a tractor (open sites).
  • Last, backhoe bucket with sharp teeth (time consuming).
  • Important: Rototillers are prohibited.
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Sand Type

The sand specification is found on page 5 of the Alternate Technology Listing, under the Micromound Absorption Area (g). The quote is below:

“Sand used must meet the requirements specified by Section 73.55(c). Material passing through #200 sieve should be <5%. Cement Concrete Sand TYPE “A” or ASTM C-33 concrete sand preferred.”

Below are different types of sand that can be used:

  • Sand Type A
  • Sand Type B
  • Sand Type C

Sand Placement

Once the site is tilled, the sand must be placed before it rains. Make sure to not mix the sand, but apply so that it naturally fills the voids. The sand should be placed with a backhoe, and leveled.This is not to be a flat sand bed; it is to be even, along the contour, and sloping with the grade.

Stake the sand boundaries and elevations:

  • Sand Boundaries A
  • Sand Boundaries B

Begin to place and spread the sand:

  • Placing Sand
  • Spreading Sand

Continue to spread the sand until complete:

  • Continue Spreading Sand
  • Complete Spreading Sand

Stakeout with sand elevations, which helps with sand placement:

  • Sand Elevations A
  • Sand Elevations B
  • Sand Elevations C

Tubing Placement

The micromound design must specify:

  • Number of tubing Runs
  • Length of tubing Runs
  • Spacing between tubing Runs

Run = Length of Tubing Across Contour:

  • Tubing Runs A
  • Tubing Runs B

Tubing spacing should be between 1/2 foot and 3/4 foot apart (6″ to 9″):

  • Tubing Spacing A
  • Tubing Spacing B

A lateral is one or more runs looped together: make sure to elevate the loop ends.

  • Laterals A
  • Laterals B

Manifold Construction

—Manifolds are used to deliver the effluent to a Zone from the Tanks Via the Supply Lines.

manifold-construction

Construct Manifolds: Top Feed.

  • Manifold Top Feed A
  • Manifold Top Feed B

Construct Manifolds: Side Feed.

  • Manifold Side Feed A
  • Manifold Side Feed B

After Micromound Installation, Before Startup

  • —Install Septic Tank.
  • —Install Pump Tank and components.
  • —Install Hydraulic Unit (central unit).
  • —Install Supply and Return Lines to the Mound.
  • —Install and Wire Control Panel.

Septic Tank Installation

Chapter 73 Regulations require 8″ of sand for aerobic treatment and 12″ of sand for septic tank effluent.

  • Septic Tank Installation
  • Septic Tank Effluent Filter

Install Pump Tank and Components

The pump tank can handle 1,000 to 2,000 gallons of effluent for residential purposes. The working volume is greater than or equal to 60% of design flow.

  • Pump Tank
  • Pump Tank

Pump tank innards:

  • Pump Tank
  • Pump Tank
  • Pump Tank

Hydraulic Unit

Hydraulic Unit

Backfilled Hydraulic Unit (left) and Hydraulic Unit Grounding Rod (right):

  • Backfilled Hydraulic Unit
  • Hydraulic Unit Grounding Rod

Final Grading

Before Final Grading:

  • Before Final Grading

After Final Grading:

  • After Final Grading
  • After Final Grading

Supply & Return Lines

1. All lines exit the Hydraulic Unit and drop to 3’ below grade. Typically 1” in diameter (bottom left).

2. The supply and return lines are conveyance lines that run at a 3’ depth all the way to the micromound location (bottom right).

  • Supply Return Lines
  • Supply Return Lines

3. Conveyance lines feed the top feed or side feed manifolds.

  • Supply Return Lines
  • Supply Return Lines

Control Panel

Installed on home (bottom left) or installed in field (bottom right).

  • Control Panel On Home
  • Control Panel In Field

Wiring Performed By Electrician

Ground the control panel locally via a grounding rod or an approved grounding method.

  • Control Panel Wiring
  • Control Panel On Wall

Time for System Startup

  1. Performed by the manufacturer’s representative.
  2. The system is pressure tested for leaks, clogs and proper amount of tubing.
  3. Upon a successful start-up, the system can be covered.

Pressure test reveals 2’ spacing for emitters.

  • System Startup

Cover With Sand

The tubing is covered with an additional 2” of sand.

  • Sand Cover
  • Sand Cover

Cover With Geotextile Layer

Then the system is covered with a layer of geotextile synthetic fabric.

  • Geotextile Layer Cover
  • Geotextile Layer Cover

Covering The Mound

  • 12” of suitable cover the top of the Micromound.
  • 8” of suitable cover over the sides and shoulder of the Micromound.
  • Cover the downsloping berm and extend the toe (the toe must support vegetation).
  • 14 inches over the Manifolds
  • 12 inches suitable cover over the mound

Final Grade

Surface water must move away from the Micromound and may not accumulate on top, or up slope, of the mound.

final-grade

Vegetation

  1. Seed and straw the area immediately to avoid erosion.
  2. Sod is recommended.
  3. Establish and maintain aggressive turf.
  4. Erosion control may be necessary on some sites with steep slopes.
  • Vegetation

Winter Cover

Thick winter cover of straw or mulch is necessary for late fall installations.

  • Winter Cover
  • Winter Cover

Don’t Forget Tank Protection

Tank Protection

Good fall protection will protect against harsh winter weather

  • Fall Protection
  • Harsh Winter Weather

Six Months After Installation

6 Months After Installation