PASEO Training Tutorial #4  — Elevated Sandmounds

1.0    Introduction:

In this tutorial we will examine:

  • What is an Elevated Sandmound
  • Why is an Elevated Sandmound Used
  • The regulations that apply to Elevated Sandmounds
  • The proper installation of an Elevated Sandmound
  • Ways of doing the job better.

2.0   What is an Elevated Sandmound?

An Elevated Sandmound is essentially a sewage absorption area constructed on a pile of sand.  Effluent injected into the absorption area trickles through the sand filtering the effluent before it reaches the soil surface. 

Prior to 1983, Elevated Sandmounds were generally gravity fed or had a lift pump elevate the sewage into the absorption area.  Elevated Sandmounds permitted after January 1, 1983 are required to be pressure dosed.

  • Why is an Elevated Sandmound Used?

Pennsylvania requires a minimum of 48 inches of usable soil between the absorption area and the limiting zone.  Elevated Sandmounds are used in areas where the limiting zone is less than 48 inches to the surface of the ground.  The sand is used to make up the difference.

4.0   Components of an Elevated Sandmound

5.0 How does an Elevated Sandmound Work?

After the sewage effluent is treated in a septic or aerobic tank, it flows into a dosing tank or a siphon tank. The effluent is stored until a set volume has been achieved.  At that point, the effluent is pumped or siphoned into a pipe referred to as a delivery line.  The delivery line enters the absorption area and conveys the effluent to another pipe referred to as the manifold.  The manifold conveys the effluent to a series of off-set pipes referred to as the laterals.  As more and more effluent is introduced into the laterals, pressure builds up.  The effluent sprays out of holes in the laterals and into the aggregate. 

The effluent splashes around the aggregate where bacteria growing in the aggregate provided a limited amount of renovation.  The effluent flows onto the surface of the sand and spreads out.  Here, bacteria living on the sand surface (the bio-mat) also provide some renovation.  The effluent then enters the sand.  The sand provides 3 functions:

  1. The sand filters out larger particles leaving them on the bio-mat. Functioning correctly, the bacteria in the bio-mat will consume the particles, however, if the amount of particulate matter is excessive, they may contribute to the clogging of the system.
  2. The sand wicks the effluent causing it to spread evenly over the ground surface.
  3. The sand slows the rate in which the effluent enters the soil.

As the effluent leaves the sand, it enters the soil.  It is the soil that provides the greatest renovation of the sewage.  With proper aeration, the soil is home to many organisms that will consume the sewage.  These range from microscopic bacteria, flagellates, fungi, etc. to larger organisms such as earthworms and tree roots.

6.0 Constructing and Elevated Sandmound

There are two methods for constructing an elevated sandmound depending on whether they are dosed by a pump or a gravity-based system such as a siphon.

6.1 Pump Dosed Elevated Sandmounds

An elevated Sandmound dosed with a pump requires that the pump intake be at a lower elevation than the manifold pipe. This is necessary to permit the effluent that is in the pipes after the pump deactivates to flow back into the dosing tank.  The minimum diameter hole size that may be used is 1/4 inch.  Both the dosing tank location and the hole size should be specified on the construction plans.

6.2 Gravity Dosed Elevated Sandmounds

Instead of pumps, some designers opt to dose with siphons or similar gravity dosing devices.  In such cases, the dosing tanks must be higher in elevation than the manifold.  To facilitate draining of the laterals, the minimum diameter of the holes must be 5/16 inch.  Both the location of the dosing tank and the hole size should be specified on the construction plans.

6.3 Pre-construction

Prior to the construction of the elevated Sandmound, the area should be marked and secured to avoid damage to the site.  At minimum, the absorption area location should be staked and flagged.  If conditions warrant, the entire mound area should be roped off or secured with temporary construction fencing.  It is very important that the site be protected from compaction by motor vehicles.

6.4 Clear the mound area.

The first step toward constructing the mound is to clear the area of trees, brush, and other objects that may impair mound construction.  Trees and brush must be cut down.  The stumps must be left in place but cut as close to the ground as possible.  This should be done when the soil is fairly dry to avoid rutting the surface when skidding off logs. In no circumstances should the stumps be pulled or the roots dug out.  The pulling of the stumps or digging of roots is grounds for permit revocation!

Rocks lying entirely on the surface may be removed from the site.  Rocks lying partly in the soil must remain.

In some areas where the surface is covered with low-bush blueberries or similar shrubs, a dense root mass may have formed on the ground surface.  In such cases, the root mass may be peeled from the soil and removed.  Care must be taken not to remove the soil underneath.

Some Sewage Enforcement Officers require an inspection at this point to ensure that the site has been properly prepared.

6.5 Scarification

The next step in constructing the elevated sandmound involves the scarification of the soil (often referred to as chisel plowing).  To scarify the soil, the installer uses a multi-share chisel plow or the teeth of a backhoe bucket to create furrows in the soil.  The furrows may be up to six (6) inches deep with deeper furrows preferred over shallower ones.  Furrows must be run parallel with the ground contour.

Scarifying serves several purposes:

  • It provides better contact between the sand and the soil , lessening the chances of the effluent flowing over the surface and down slope effluent ponding
  • It breaks up any minor compaction of the soil surface
  • It increases the amount of soil surface area for the effluent to enter the soil

The entire area under the mound (toe-of-berm to toe-of-berm) must be scarified.  It is understood that scarification will be less than perfect around stumps and large rocks.

Once scarified, no vehicles may travel over, nor may persons walk over the scarified area except for minor foot travel ancillary to placing the delivery line.

Scarification must be done when the soil is friable to dry.  The scarified area should not be allowed to sit for long periods of time especially when rain is due.

Most Sewage Enforcement Officers require an inspection at this point to ensure that the site has been properly scarified.

A good scarification
The soil was too wet and the installer dug what amounted to trenches. The scarification inspection failed and the permit was revoked.

6.6 Delivery line (pump dosed)

If the system is dosed by a pump, the delivery line is set.  The pipe is laid from the dosing tank to a point somewhat in the center of the mound.  The actual location will vary between systems but should be noted in the construction plans.  It may be necessary to dig into the soil to set the delivery line.  Undoubtedly it will require walking on the scarified soil.  Such walking should be minimized to within two feet of the sides of the delivery line.

Gravity dosed systems (siphons, etc.) have the delivery lines set at a later point in the construction process.  (See section 6.9.1)

6.7 Placing the sand

Sand should be placed on the area that will be under the absorption area.  It is preferable that the sand be placed on the site one bucket-at-a-time by an excavator bucket. However, the installer may opt to dump the sand at the edge of the system and work it into place with a machine.  In either case, the machine should work from the upslope side of the mound.  No equipment or walking on the site should be allowed until there is at least one foot of sand in place.  When the appropriate amount of sand has been deposited, the sand pile should be raked into place.  The top of the sand should be level across the entire area that will be under the absorption area.  The side of the sand pile must be raked out so that the sand falls at a 2 to 1 slope.  That is, for every foot that the pile is high, the sand will extend two feet out from the top of the pile.

The sand must meet the requirements of § 73.55 (c) and certification will be required to document this.

Most Sewage Enforcement Officers require an inspection at this point to ensure that the sand has been properly placed.

6.8 Placing the aggregate

Aggregate is then placed on the sand pile.  In order to keep the aggregate from falling over the sides, many installers place some of the berm around the sand. 

The aggregate must met the requirements of § 73.51 (a).  Typically the first 6 inches of aggregate is placed on the mound and raked level although some installers will place the entire amount and trench in the pipes.

Here the installer placed the aggregate directly on the sand. The aggregate has rolled down the outside of the sand. This would allow the effluent to flow around the sand.
Note the berm has been partially installed to keep the aggregate in place.

6.9 Installing the piping

The manifold and laterals are then installed in the size and configuration specified in the construction plans.  The holes are pointed downward.

An inspection is normally done this point to ensure that the piping has been properly installed and the holes are properly placed. Most Sewage Enforcement Officers require pressurization of the laterals as part of the inspection.

6.9.1 Installing the Piping (Gravity-Dosed)

Unlike pump dosed systems, systems dosed by a siphon or other gravity powered device do not drain back into the dosing tank.  Larger holes in the piping (minimum 5/16”) allow for drainage of the pipes.

To prevent low spots that do not drain, the delivery line enters from the uphill side and goes directly into the aggregate. 

The delivery line is installed with the mound piping.

End view schematic of an elevated sandmound employing gravity dosing.
Top view schematic of an elevated sandmound employing gravity dosing.

6.10 Covering the Piping

After the Sewage Enforcement Officer approves the covering of the piping, the installer adds the remaining aggregate, or pushes aggregate over the trenched in piping.  The aggregate is raked level.

Piping covered by 2 inches of aggregate.

A soil barrier in the form of geo-textile fabric, untreated building paper, or 2 inches of hay or straw is placed over the aggregate to prevent the cover soil from falling into aggregate.

Aggregate covered with geo-textile fabric

The entire mound is covered with 12 inches of soil and the remaining berm is put into place.  The berm is to be flared at the slope indicated in the plans.  Usually this would be a 2 to 1 slope, but 3 to 1 and 4 to 1 are sometimes called for.

The mound is then seeded with grass.  Most installers will cover the mound with mulch to protect the seed and deter erosion.

Most Sewage Enforcement Officers require an inspection at this point to ensure that the berm and top cover has been properly installed, and that the mound is ready for operation.

A completed elevated sandmound.

7.0 Inspecting the construction of an elevated sandmound

The sewage regulations do not have a specified list of inspections that may be performed.  Instead, the regulations state …

§ 72.30. Inspection.

 (a)  No part of an individual or community onlot sewage system may be covered until a final inspection is conducted and final written approval is given by the local agency.

 (e)  The local agency may inspect and make tests before, during or after construction and may by order require a sewage system to be uncovered at the expense of the applicant, if the sewage system has been covered contrary to this chapter.

Most Sewage Enforcement Officers do not have the luxury to sit and observe the entire construction from start to finish.  As such, the most common way to inspect an elevated sandmound is to spot check it at various points during the construction process. The local agency’s sewage ordinances may specify when these inspections shall occur.  If the ordinance is silent on the issue or the Sewage Enforcement Officer believes more inspections are needed, the local agency should adopt an inspection schedule either by ordinance or written policy.  A copy of the inspection schedule should accompany the sewage permit when sent to the applicant.

It should be recognized that there will be times when extra inspections may be warranted.  Such cases might include instances when an installer will be constructing a sandmound for the first time, there are site specific conditions that warrant extra caution, or if the installer requests extra inspections.  Otherwise, Sewage Enforcement Officers should avoid randomly determining the inspections required in order to avoid accusations or favoritism or improperly burdening particular installers.

With the above so noted, the authors of this tutorial offer the following list of recommended points of inspection.

7.1 Pre-construction

Although not necessary for every permit, an on-site pre-construction meeting should be considered when the construction involves a large system, a contractor who is not familiar with constructing elevated sand mounds, or there are permit specific or site specific circumstances that warrant extra consideration.

A preconstruction inspection is also beneficial in the wet season so that the SEO may determine if the soil is dry enough for scarification.

This soil is clearly too wet for scarification. Doing so may result in the SEO having to revoke the permit. A preconstruction meeting could avoid such a problem.

7.2   Scarification

An improper scarification can greatly reduce the life of the system.  Therefore, it is highly recommended that the SEO inspect and approve the scarified soil prior to the placement of the sand.

§ 73.55. Elevated sand mounds.

(b) Construction.

   (1)  Vegetation shall be cut close to the ground throughout the area to be utilized for the absorption area and berm. Bushes and trees shall be cut flush with the ground surface; roots shall be left in place. Cut vegetation or organic litter shall be raked and removed from the absorption and berm areas.

   (2)  The proposed absorption area not obstructed by stumps or other obstacles shall be roughed or plowed parallel with the contour to a maximum depth of 6 inches, using a multiple share chisel plow or similar implement attached to light-weight equipment. Rotary tilling is prohibited.

   (3)  Under no circumstances may equipment travel on the plowed soil surface until the sand is in place.

The SEO should look to determine if the scarified area is large enough to site the entire mound (edge of berm to edge of berm) to a depth of up to 6 inches. The furrows of the scarification should be parallel to the slope of the ground.  All stumps should have been cut as close to the ground as possible.  Look to see if there is any evidence of stumps having been pulled. 

7.3  Sand Placement

Typically, Sewage Enforcement Officers schedule an inspection to check the sand placement.

§ 73.55. Elevated sand mounds.

(b) Construction.

   (4)  Immediately after plowing, sand shall be placed over the exposed plowed surface. Sand shall be placed from the upslope side of the bed using only lightweight equipment.

   (5)  The slope of the sand not directly beneath the aggregate area shall be approximately 50%.

  • The top of the sand directly beneath the aggregate shall be level to a tolerance of ±2 inches per 100 feet.

 (c)  Sand. Sand suppliers shall provide certification in writing to the sewage enforcement officer and permittee, with the first delivery to the job site from every sand source listing the amount of sand delivered, and that all sand supplied meets the requirements posted in the Department of Transportation specifications Publication #408, section 703. The size and grading shall meet bituminous concrete sand Type B #1 or #3 requirements from a Department of Transportation certified stockpile. The sieve analysis shall be conducted in accordance with PTM #616 and #100.

The regulations require that the sand meet the requirements of § 73.55 (c) and that the installer must provide the SEO with written certification attesting to its status.

The SEO should inspect the sand installation for the proper depth at the most uphill point in the system.  This depth will vary from permit to permit and may be found on the system design. 

The SEO should check that the top of the sand is level and that the sides flare out 2 feet for every one foot of drop.  (2 to 1 slope.)

The sand should also be level on top.

The SEO should also look for any evidence that the installer has taken “liberties” during the sand placement such as burying extraneous material, backing sand trucks over the scarified area, or otherwise violated the regulations or the permit.

7.4 Piping (Pressure Inspection)

After the sand has been inspected, it is recommended that the berm be placed to support the aggregate when it is placed.  An inspection of the piping is required and although the regulations do not require it for mounds with an aggregate area of less than 2501 square feet, most SEOs require the piping to be pressurized.

At the pressure inspection, the SEO should verify that …

  • There is 6 inches of aggregate under the pipes [§ 73.52 (b)(8)]
  • The manifold and laterals are of the proper diameter piping [§ 73.44 (a) (4)]
  • The laterals are of the proper length  [§ 73.53 (6)]
  • The laterals are the proper distance apart [§ 73.53 (4)]
  • The pipes are joined by pressure fittings 
  • There is no leakage from the joints or end caps  [§ 73.44 (a) (1)]
  • The holes are spaced as required in the system plans
  • The holes are drilled to the size specified in the plans (usually ¼ inch diameter).
  • Lateral cleanout are installed – if required in the plans
  • There is a minimum of 3 feet of terminal head at the end of the laterals.  [§ 73.44 (b) (11)]
  • The laterals and manifold are level  [§ 73.52 (b) (10)]
  • The effluent left in the laterals after the pump has deactivated drains back to the dosing tank.  [§ 73.44 (a) (3)]  Note:  This does not apply to gravity dosed systems.

During the inspection, the SEO should always consult the system design as plans will vary for each permit.

The above represents three possible variations in sandmound piping. The first is a typical situation where the laterals are equally spaced on both sides of the manifold (in red). The second represents a system where the laterals are longer on one side of the manifold than the other. The third shows a system with two different lateral lengths on each side of the manifold. Just one reason that the SEO should consult the permit plans before inspecting the system.

8.0 Tips for Doing the Job Better

As a sewage enforcement officer your job is to inspect the construction of the mound to ensure that it meets the requirements of the regulations. 

8.1 Review the Site Before Issuing the Permit

Although site review is a topic for another tutorial, a proper review of the site during testing and before permit issuance may help avoid problems during construction.  Placement of the mound in an area with less trees can avoid issues with stumps.  Are there boulders peaking out of the soil?  As SEO you can not dictate where the mound must go.  The decision is that of the property owner. You can, however, provide input to allow the property owner make an informed decision.

8.2 Avoid Trees

Trees need food and water to survive.  Sewage effluent supplies both.  Siting a mound near trees can result in the tree roots penetrating the mound and clogging the system.  In addition, shade provided by the tree will reduce evaporation of the effluent and will retard the growth of grass resulting in erosion of the berm.  The SEO should encourage the property owner to avoid placing an elevated sandmound near trees.

8.3 More Inspections

§ 72.30. Inspection.

 (a)  No part of an individual or community onlot sewage system may be covered until a final inspection is conducted and final written approval is given by the local agency.

 (e)  The local agency may inspect and make tests before, during or after construction and may by order require a sewage system to be uncovered at the expense of the applicant, if the sewage system has been covered contrary to this chapter.

Without Superman-like x-ray vision, you can not look at a mound and determine if it was built correctly.  Yet, Chapter 73 does not reference any inspection except the final inspection.  When the mound is almost fully constructed and the piping is exposed, it will be impossible to determine if the site was properly scarified, the proper amount of sand was used, or if the stumps were cut close to the ground.  Because of this, PASEO recommends that, at minimum, the following inspections should be considered:

  • Scarification inspection – After the ground is scarified and before placement of the sand
  • Sand inspection – To check the depth and side slope of the sand
  • Final (pressure) inspection – Bottom layer of aggregate is in place and piping exposed. The pipes are dosed to verify the pressure and ensure that the holes are not clogged.
  • Completed system inspection – To review the completed system before use

Of course, these inspections may be performed concurrently with the inspection of the other system components.  For example, the dosing tank might be inspected at the same time as the pressure inspection.

There is some debate whether SEOs may require these additional inspections by fiat or if they must be specified in the local agency ordinance or inspection schedule.  If not in the local agency’s ordinance, the SEO is advised to contact the local agency’s solicitor (lawyer) to determine the legality of requiring the additional inspections.  If the solicitor determines that an ordinance change is in order, the SEO should discuss the matter with the governing body and inform them of the need for additional inspections.

Regardless of whether the Ordinance requires the inspections or the SEO determines the inspection schedule, the SEO MUST schedule the same number of inspections for ALL permitees.  Doing otherwise would bring about accusations of favoritism or prejudice and could result in the loss of one’s job or certification.

8.4 Require a Pressure Inspection

Contrary to the belief of many SEOs, the regulations have no requirement for a pressure inspection of the piping of elevated sandmounds under 2501 square feet in aggregate area.  The pressure inspection requirement found in § 73.55 (c) (10) only applies to systems over 2500 square feet in size.  But requiring a pressure inspection is a good thing to do. 

Pressurizing the system can reveal faulty joints and clogged holes before they piping is covered.  It can also allow the SEO to verify that there is adequate pressure in the event that the model of pump has been changed or the dosing tank has been relocated.

8.5 Require Sand Certification After the Sand is in Place

§ 73.55 (c) states, in part “Sand. Sand suppliers shall provide certification in writing to the sewage enforcement officer and permittee, with the first delivery to the job site from every sand source listing the amount of sand delivered …” 

This may have made sense in the early days of the regulations when certified sources were few and far between.  However, logically, it does not fit today.  When an installer gives the SEO a sand certification BEFORE the last load of sand is delivered, it acts as a promissory note.  Essentially it is saying, “Trust me.  I will get all my sand from this source and it will meet these requirements.”  Unfortunately, unscrupulous installers have been known to purchase an initial load of sand from an approved source then purchase the remainder of the sand from non-certified quarries.

By requiring the certification at the end, the SEO can look at the tonnage to ensure that all the sand was supplied by the same quarry.

8.6 Require Aggregate Certificates

§ 73.51 (a) Requires that the aggregate in a sandmound meet “Department of Transportation specifications, Publication #408 (1994) section 703 available from the Department of Transportation. The size and grading of the aggregate shall meet AASHTO No. 57 requirements from a PADOT certified stockpile and shall be of Type B quality requirements.  It is unlikely that the average SEO can visually tell if the aggregate used will meet these requirements.  Therefore, knowledgeable SEOs require the installer to supply aggregate certificates attesting to the aggregate meeting the 73.51 requirements.

8.7 Educate Your Installers

Whether you hold formal meetings, informal get-togethers, or just talk to them in the field, educate your installers in how to do a better job.  While some may reel at being told how to do things, most will appreciate tips that prevent them from getting call-backs. 

The following are some suggestions, unless required by ordinance, the SEO may not require the installers to take these actions.

8.7.1 Flush the Lines

Drilling holes leaves burrs inside the pipe.  Glue can often gum up the holes.  Mice and chipmunks often place seeds and nuts in open laterals.  Sometimes these problems can be avoided if the laterals are flushed before installing the end caps.

Flushing the laterals can remove materials that might otherwise clog the holes.

8.7.2 Use Clean Aggregate

Even certified aggregate can cause problems.  Freshly created aggregate will always contain some fines.  Gravity, especially when assisted by rain, will allow the fines to work their way through to the bottom of the pile.  Therefore, the aggregate at the bottom of the stockpile often contains more fines then the rest of the pile.  When the loader scoops up the aggregate, it may have more fines than the rest of the pile.  While this may not be a problem when constructing a driveway, the additional fines can wreck havoc on a sewage system.  Installers should request that the quarryman scoop the aggregate from a foot or two off the bottom of the pile.

Fine material in the aggregate will wash off during dosing and could clog the surface of the sand.

Though taken from a certified stockpile, this aggregate has almost as much fine material (by volume) than stone. This picture was taken while the system was being constructed.

8.7.3 Use Geo-Textile Soil Barriers

The soil barrier is a barrier that prevents the cover soil from dropping into the aggregate.  If the soil migrates into the aggregate, it can clog the surface of the sand.  In more extreme cases, the soil will drop completely into the aggregate turning it into stony mud. 

Straw, hay, and untreated building paper are commonly used as soil barriers.  Unfortunately, these materials decompose over time.  If the grass on the cover soil has not developed a good root system, the cover soil will start to drop.

Breathable to allow the passage of air and water, geo-textile fabric will not decompose in the mound.

Geo-textile materials are woven to allow water and gasses to flow through while holding back soil.  It does not decompose and should prevent the cover soil from migrating into the aggregate.

This 10 year old system malfunctioned when the soil barrier decomposed allowing the cover soil to migrate into the aggregate.

8.7.4 Do Not Mix Sand from Different Sources

It is lawful to purchase the sand from two or more sources provided that both sources are PennDOT certified stockpiles and sand certificates have been submitted.  However, should the system malfunction and the sand was found to be a contributing factor, whose sand would it be?  It’s best to only use one quarry’s sand in a system.

8.7.5 Mulch the Mound

§ 73.55 (b) (8) requires that the berm and top cover “seeded to assure stability”.  Presumably the seed the regulation is referring to is grass seed.  However, placing seed on the mound does not ensure stability of the berm.  Seed placed in the baking sun of summer may germinate and die.  See that germinates just before winter also does poorly.  Ideally, the installer would lime, fertilize, and water the seed as one would do a lawn.  However, that rarely happens.  In most cases, the seed is scattered and the installer moves on to other work.

This mound, nicely mulched with straw, will resist erosion until the grass takes hold.

8.7.6 Use the proper Seed

Many installers seed the mound with grass seed known as “contractor’s mix”.  Contractor’s mix has a high percentage of annual ryegrass seed, often up to 100%.  It is used for several reasons.  Annual ryegrass germinates and spreads quickly which can greatly reduce erosion.  Annual ryegrass is also very inexpensive.  The problem with annual ryegrass is that it often doesn’t reproduce well in Pennsylvania and that a well grassed mound this year quickly becomes more sparse as the years go on. 

Property owners should be alerted to this and told to seed their mound with a good grass seed mix of fescue, perennial ryegrass, bluegrass and other types developed to perform well in your area.  The mound might need to be reseeded annually for the first few years.

9.0  Job Aids