guidelines for alberta at-grade systems for onsite

Guidelines for Alberta At-Grade Systems for

Onsite Wastewater Treatment

Prepared by Alberta Onsite Wastewater Management Association

Introduction The objectives of the Alberta At-Grade Systems for Onsite Wastewater Treatment Guidelines are:

1) to obtain acceptance for At-Grade Systems as a province-wide variance to the Alberta Private Sewage Standard of Practice (SOP) as authorized by Alberta Municipal Affairs and Housing or local Safety Codes Officer (SCO);

2) to supplement current efforts toward ensuring At-Grade Systems become recognized

within the SOP as there are no guarantees that variances will be permitted over the long-term; and

3) to provide designers and installers with specific At-Grade System installation procedures.

These guidelines and the industry-driven process that has been undertaken to develop them represent an important step toward the goal of ensuring At-Grade Systems become an approved final treatment solution within future editions of the Alberta SOP. Continuous industry input will be among the largest contributors in the development of the final version of these guidelines. In addition, a variety of other sources have been referenced to support this grassroots effort:

1) Alberta Private Sewage Systems Standard of Practice 1999 Handbook 2) 2002 OWTS Training Modules 100 through 117

3) 2007 Proposed SOP Draft

4) Research and data collected from the Universities of Alberta and Calgary

5) Technical and field experience of current and previous members of the At-Grade

Technical Advisory Group (AGTAG) and other members of the Alberta Onsite Wastewater Management Association (AOWMA).

At-Grade Guidelines03/10/2008

1.0 Permits and Variances At-Grade Systems, like all onsite wastewater treatment systems, require approval from a local SCO. The approval application should include a request for variance and sufficient evidence of a suitable site evaluation. The application must include a description of the soil profile and demonstrate that the profile’s characteristics have been considered and addressed within the At-Grade System’s design. Approved At-Grade Systems are granted as a variance to the Alberta SOP. This variance is issued at the discretion of the SCO only after the design proves to provide acceptable levels of safety and effluent treatment. Although a variance may be issued, the designer, installer and homeowner must be fully aware of the conditions and liabilities associated with a variance. The variances must be submitted with the PSDS permit application along with any other supporting documentation.

NOTE: While this guideline assists the designer/installer and the SCO in developing or considering an At-Grade System for a particular application, it does not create a standard.

2.0 Description The Alberta At-Grade effluent treatment system is a method of accomplishing the final treatment and pressure distribution of effluent from an advanced wastewater treatment component. The At-Grade treatment system is an arrangement of pressurized distribution piping placed above the surface of in situ (original) soil. The distribution system must be designed so that soil hydraulic over-loading does not occur. The distribution piping is covered by an open bottom chamber, which provides a shielded housing to protect the distribution system. Woodchips (or approved cover material) are placed to a depth of not less than 12 inches from the top of the housing and to a width of not less than the infiltration area derived from the linear loading rate. Table 8.1.1.10.A Effluent Soil Loading Rate and Linear loading Rate (see Appendix B). The cover material reduces the risk of human and/or animal contact with the wastewater effluent. In sites that have excessive wind velocity or little forest undergrowth, additional erosion measures may be required. Some examples of erosion protection are:

1) a mixture of sandy loam or loamy sand topsoil mixed 50/50 with woodchips; and 2) covering woodchips with a coconut leaf matting or similar erosion control products.

3.0 Concept of Design

See detail Drawing 1 of Appendix A.


4.0 Design Considerations An At-Grade System is a desirable option for areas where other final wastewater treatment systems are not the most suitable solution, and in cases where forested areas of the property are to be preserved.

4.1 Site Suitability

At-Grade System requirements are taken from and align with the requirements of the documents acknowledged in this guideline’s introductory section. 4.1.1 System Geometry and Linear Loading Rate Design

1) The design and geometry of the soil-based treatment area shall result in a linear effluent loading rate that does not exceed the soil profile’s capability. This will permit the horizontal movement of the effluent away from the treatment system. It shall consider the values set out in the Effluent Soils Loading Rates and Linear Loading Rates Tables (Appendix B, Tables 1 and 2). The tables illustrate horizontal movement of effluent through the soil to the characteristics of a soil profile and the slope of the landscape.

2) Sites suitable for At-Grade Systems must also meet all of the

objectives and requirements in the documents acknowledged in this guideline’s introductory section.

4.1.2 LFH Layers

Suitable At-Grade System conditions have been within forested areas with an established LFH on not less than 50 mm (2 inches). LFH soil layer means: L – The structures of the organic material are easily recognized. F – The accumulated organic material is partly decomposed. H – The original structures of the organic material are unrecognizable. The “litter layers” found on forest floors comprise the L, F and H horizons. Degrees of decomposition in the litter material distinguish the three layers from one another. The three layers are found together in sequence as L, F and H from top to bottom. NOTE: LFH is NOT the A horizon of the soil. The A horizon lies below

the LFH layer.

If possible, the At-Grade System should be positioned on a sloped area (see Section 4.3.1).


4.2 Soil Conditions

4.2.1 Infiltration into Original Soil

Intent: To ensure that an adequate area of soil is available for the effluent to infiltrate the in-situ soil, and that the permeability of the cover material may temporarily store the effluent and provide increased opportunity to readily distribute over the infiltration area and prevent mounding and/or ponding of the effluent in the LFH.

Intent: Having a natural slope to the site is beneficial to At-Grade Systems especially if installed with a shallow restrictive layer.

1) The area of contact with the original soil that is within the At-Grade forming the down-slope and treatment area, excluding the end slopes, shall provide an infiltration area into the original soil and must meet the following conditions:

a. The effluent loading and linear loading rates suitable for

the soil profile identified at the site, as characterized by the texture and structure of the soil, shall be determined by using Effluent Soils Loading Rates and Linear Loading Rates Table and Soil Classification Triangle (Appendix B).

b. When on a slope exceeding one per cent, includes only

the area down-slope of the up-slope side of the LFH area receiving the effluent.

c. The cover material forming the At-Grade mound must

meet the minimum required infiltration area as calculated. If the cover material slope is 3:1 or steeper, a suitable erosion control material must be applied over the cover material. Slopes 3:1 or wider do not require erosion control material. Note: 3 = Horizontal along ground 1 = Vertical is height of woodchips.

4.2.2. Loading Rate Under Chambers (effluent application rate)

1) At-Grade Systems, in most cases, will be designed on fine texture soils ranging within the classification from loam to clay. Therefore, based on supporting documents of the most recent soil science studies, the loading rate of the LFH layer shall not exceed 0.83 imperial gallons per square foot per day.

2) Actual open area with in the inside walls of a chamber must be verified

by manufacturer specifications.

NOTE: To achieve sufficient infiltration surface area, one or more laterals may be installed side-by-side within the same At-Grade System (See Detail Drawing 1 in Appendix A.


4.3 Effluent Conditions

All At-Grade Systems must have effluent applied to each lateral through pressure distribution with advanced secondary treated effluent. Targeted values of treated effluent quality must meet NSF 40 Class 1 Packaged Treatment Plant specifications.

4.3.1 Controlling the Rate of Effluent Relative to Slope

Determining loading rates at gallons per linear foot per day shall be conducted by performing a site evaluation. The geometry of the At-Grade System shall conform to the surface slope contour of the site on which it is placed such that:

1) the long axis of the At-Grade System (its longest dimension) is orientated 90 degrees to the slope direction;

2) the long axis of each lateral where it makes contact with the in-situ

soil surface is level within two per cent as measured from end-to-end or in any 3 m (10 feet) segment of the lateral; and

3) it is level within 100 mm (four inches) as measured within any 600

mm ( 2 foot) segment.

4.3.2 Effluent: Considerations and Cautions

The degree of slope and the type of underlying soil will determine the rate by which the effluent will move down-slope. Therefore, the design should maintain substantial distance down-slope before installing another At-Grade lateral. (Handbook Appendix C). CAUTION: The installation of an additional lateral should be avoided if possible. However, if unavoidable, care should be taken to ensure the total linear loading rate is not exceeded in combined laterals.

The slope assists in moving the effluent through the upper highly permeable soils away from the lateral and down the slope. The slope causes the effluent to move downhill, spreading over a larger area to be eventually absorbed into the soils.

CAUTION: Sufficient down-slope material cover must be available to protect the At-Grade System from effluent break-out as determined by using the At-Grade Worksheet (Appendix D).

Installed on level ground, the At-Grade System’s design and layout require different considerations.


4.4 Selecting Orifice Sizing and Spacing The appropriate At-Grade System design must show adequate distribution through proper orifice spacing and must meet all specifications noted in Pressure Distribution , Prescriptive Requirements and Installation Standards.

4.4.1 Pressure Distribution At-Grade Systems must meet all specifications laid out in Pressure Distribution – Prescriptive Requirements and Installation Standards. In addition to the current standard, At-Grade Systems shall be installed to the following specifications:

1) Maximum orifice spacing in an At-Grade System is 2 feet. 2) Squirt height shall be a minimum of 5 feet.

3) Design loading rate shall be calculated for design squirt height.

4) 24 hour, electronically controlled timed dosing must be applied to At-

Grade Systems.

5) All At-Grade Systems must include the capacity to record the volume of effluent dosed. Recording devices can include an hour meter or cycle counter.

6) No single lateral shall exceed 65 feet.

7) Orifice(s) must be orientated within the distribution lateral(s) piping

so that treated effluent being dispersed is not applied directly onto the soil interface.

8) Orifice orientation must be such that the distribution piping will drain.

9) The distribution piping in each lateral(s) must not lie on the soil or be

submerged in effluent.

4.4.2 Effluent (Delivery) Line

Ensure all delivery lines are protected from freezing. Example; Delivery line drains after dose volume has been delivered.

5.0 Design Considerations Effective At-Grade System design must account for human, animal and environmental risk factors in advance of system design and installation.


5.1 Preventing Direct Contact with Effluent

Preventing the risk of humans or animals coming into direct contact with the effluent is a key purpose of any onsite wastewater system. Effluent contains pathogens, regardless of whether it has been treated through a secondary system component or not. Since At-Grade Systems are installed directly on top of the ground, the physical separation provided by conventional sub-surface field beds does not exist. Thus, to minimize risks, ensure that the layer of cover material extends far enough to the side slopes to allow the effluent to enter the soil before coming to the edge of the toe of the slope (Appendix A, Detail Drawing 1). NOTE: The above paragraph reinstates the importance of timed dosing which prevents instantaneous high flows in subsequent doses, and extends the dose volumes over a number of lapsed hours.

5.1.1 Inspection Access Port(s) The At-Grade System design shall include inspection access ports to enable monitoring of the At-Grade’s interior area. As a minimum, the design must include two access ports per lateral. One is to be located at each end of the length of the At-Grade lateral, positioned between the last two orifices. The other port shall be positioned between the first two orifices. Note: If system design has one lateral to the right and one to the left of a header, only one port is required on either side of the intersection. (See Appendix A, Drawing 4). The access ports must be:

1) extended to finished grade, 2) positioned midpoint between orifice spacing,

3) fitted with a manufactured access cover,

4) positioned top-centre of chamber,

5) attached securely to the top of the chamber, and

6) located only within the vertical section of the At-Grade System lateral

so as to monitor the depth of ponded effluent (See Appendix A, Drawing 2).

When more than one chamber is used in one single At-Grade System lateral, monitoring ports shall be provided for each continuous row of chambers.

5.2 Protection from Wind and Freezing

5.2.1 Cover Material At-Grade Systems are allowed only in forested areas because the shelter of trees provides a degree of wind protection. Snow cover provides a degree of frost protection.


The cover material over the protected housing is normally woodchips. Woodchip material has a substantially higher R rating than soil, thereby providing better frost protection. 5.2.2 Stabilization Methods

1) Use erosion matting or equivalent to cover the woodchip mound to protect from wind erosion.

2) In forested areas with minimal tree cover or little undergrowth, place a minimum of 6 inches of loamy sand or sandy loam seeded topsoil over the woodchip mound.

3) Use erosion matting or equivalent to cover woodchip/topsoil mound

also to encourage rapid vegetation growth.

5.2.3 At-Grades Outside Forested Areas

At-Grades outside forested areas are currently not covered by this guideline. Such systems must include additional frost protection if they are to be considered, as there is no LFH and less frost protection for underlying horizons. Both the SCO and designer/installer must be cautious when considering such designs. The application for a variance must include specific and reasonable design changes to allow for an installation in these circumstances.

5.3 Protection from Traffic The location of the At-Grade System must be protected from human and animal traffic, and motorized vehicles. Locating the system in a forested area will generally provide adequate protection. Regardless, footpaths and animal trails must be considered and measures must be taken to reroute traffic where necessary. Surround the system with fencing or other means to deter traffic. Example: large fallen trees can be placed around the At-Grade. 5.4 Protection of LFH and A Horizon

At-Grade Systems are designed and constructed so as to take advantage of the LFH and upper horizons. Therefore, it is extremely important not to damage the surface horizons during construction of the At-Grade System. If mechanical equipment is required to accomplish construction of the At-Grade System, operate equipment up-slope of the system if possible.


6.0 Separation Distances 6.1 At-Grade Systems

1) An At-Grade positioned on level land shall not be located within:

a. 7.6m (25 ft.) of property line b. 15m (50 ft.) of a water source

c. 15m (50 ft.) of a water course

d. 3m (10 ft.) of a packaged sewage treatment plant

e. 9m (30 ft.) of all buildings

f. 7.6m (25 ft.) of property line from end of lateral run

2) An At-Grade positioned on a sloped area, 1% or greater, shall not be

located within:

a. 3m (10 ft.) if area is sloping away from property line into owners property

b. 7.6m (25 ft.) if area is sloping off of owner’s property c. 15m (50 ft.) of a water source

d. 15m (50 ft.) of a water course

e. 3m ( 10 ft.) of a packaged sewage treatment plant, if sloping away

from plant

f. 7.6m (25 ft.) of a packaged sewage treatment plant, if sloping toward plant

g. 9m (30 ft.) of all buildings, if slope is away from house.

h. 15m (50 ft.) of all buildings, if slope is toward house.

For the purposes of definition of the above sections, all measurements are to be taken from the point where the side slope of the At-Grade System intersects with the natural soil contour.

7.0 Diverting Run-off Water Some At-Grade systems may be positioned on a slope that may experience excessive rain or spring run-off from above landscape. If the installer chooses, and is able to do so without increased damage to the landscape, consideration may be given to construct a diversion berm or swale up-slope of the At-Grade System.


Wood Chip Cover

Cap or Turf Box

PVC Pipe Minimum 4 Inch DiameterRestraining Collar, Secured to Top of Chamber

Minimum 12 Inchesof Cover

Chamber

LFH Layer

Pressure Distribution Lateral

Pipe Support Device4 InchesAbove LFH

Note:Position Monitiring PortOn CenterBetween Orifice Spacing

Typical Inspection Port

Appendix "A" Drawing #2

3 1

January, 2008 by L.S.

Insulation Plug

2 1or

Possible Point Loading

At-Grade System

Concave Hill Side

Appendix "A" Drawing 3

January, 2008 by L.S.

At-Grade System

Sub-Surface Flow

Sub-Surface Flow

Typical Point Loading


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Appendix B


APPENDIX C HANDBOOK

The following handbook will be using a fictitious site, for example purposes, and evaluated using the following soil profile.

1) 3-4 inches LFH 2) Silty Clay Loam Texture 3) Grade 2, Blocky Structure, down to 24 inches 4) Massive, Clay texture below 24 inches. 5) 35 feet from down-slope property line. 6) Positioned on a 2% slope away from building envelope

The following discussion will walk through the work sheet process and assist in

understanding the information required to design an at- grade system.

Step 1) Determine the expected volume of sewage per day: As in all onsite wastewater treatment systems, you first need to determine the volume of daily sewage flow you are dealing with for the specific project. By using Table 3.1.1.14.A Page 24 in the SOP 1999, we can determine the expected flow by calculating 75 gallons per person, times the number of people in the residence. The SOP uses 1.5 people per bedroom, therefore if we, for example determined 4 bedrooms, equates to 6 people would normally live in the residence. 75 gallons per person per day X 6 people = 450 gallons for the daily flow. Keep in mind any additional water using devises such as a large hot tube. Step 2) Determine the slope criteria of the installation site: From the information compiled during your site evaluation, you will have surveyed and recorded the slope, if any. From the above scenario we determined the slope at 2%. This will be needed when you are determining the linear loading rate. You also need to know if there is a slope and what direction to position the at-grade properly for the set-backs. Step 3) Determine native soil infiltration Loading Rate: We have found from the lab analysis’s that the soil texture is Silty Clay Loam. We also know we have a grade 2 Blocky structure. From this if we look at the Loading rate table on page 12 of the At-Grade Guideline, we can determine that the loading rate is 0.45 gal/sq.ft. for secondary treated effluent which is less than 30 mg/L of BOD. Step 4) Determine the Linear Loading Rate: Basically this is the same thing from Step 3, other than we need to look for the slope of 0-4% column and the Infiltration distance. We recorded in the above scenario that the depth of Silty Clay Loam was 24 inches, below that was a massive soil. Therefore our infiltration distance is in the 12-24 inch column. Follow this down to the Grade 2 Silty Clay Loam and we find our linear loading rate is 2.9 gal/linear foot. Step 5) Determine Length of At-Grade: In Step 1 we determined our daily flow to be 450 gallons, in Step 4 we found we can apply 2.9 gallons of effluent for every foot of at-grade, therefore if we divide 450 by 2.9 we find we need 155 feet of At-Grade to satisfy our daily flow demand. On some sites you may find that one at-grade run of 155 feet is not practical or just don’t have that kind of area to run the 155 feet. You could look at splitting into two 77.5 foot runs, however keep in mind the runs will need to be separated as far apart as you can allow. The suggested


minimum separation is 25 feet toe-to-toe. Best is to find another area sloping away or another direction from the first lateral run. Step 6) Calculate "Total" Effluent Application surface area required: (the area under the chambers the effluent is applied to) We want to insure surface are under the woodchips have a sufficient area that we know the effluent will not bust out the toe-of-slope. In section 4.2.1.2 Page 3 of the Guideline, it states we can not apply any more than 0.83 gallons per square foot of effluent to the LFH surface. Therefore we know our daily flow is 450 gallons, divide that by 0.83 gal/sq.ft. equates to 542 sq. ft. for effluent application surface area. Step 7) Determine actual open area required under chambers for effluent application area: All At-Grade design’s must use chambers to cover the pressure distribution systems, and we need to determine the surface area required for effluent application under the chambers. The SOP allows 20% of the surface area to be out side of the chamber, either between chambers or the outer sides of the chamber. Therefore we need to calculate what 80% of the “Total” effluent application surface area is, (from step 6) Effluent Application Surface Area from Step 6 = 542 sq.ft. X .80 equates to 434 sq.ft. that needs to equate the surface area under the chambers. Step 8) Determine the minimum width of effluent application area: Now that we know the surface area (434 sq.ft.) that is required under the chambers, we can divide it by the length of the At-Grade lateral, determined from step 5, which was 155 feet. Therefore, 434 sq.ft. divided by 155 foot length = 2.80 width required under chamber or number of rows of chambers. Step 9) Select the chambers to be used and the number of rows of chambers required: This step may be repetitive until you find the right width of one chamber or a combination of chambers to satisfy the full coverage width of 2.80 feet. For example: If the inside width of a particular chamber was 20 inches wide, or 1.66 feet wide, times 2 rows of chambers = 3.32 feet of total width under the combined two rows of chambers. 3.32 feet is greater than 2.80 feet required width. This is fine, the combined chamber area width is greater than the effluent application area, however, you may want to choose a different chamber model to narrow it down to a closer width. Step 10) Calculate minimum Native Infiltration Surface Area: We have now insured we have sufficient surface area under the chambers, and the effluent will pass through the LFH layer properly. Know we need to insure we have the proper loading rate to travel into and down through the below soil horizons. From the scenario site evaluation, we said we found a Silty Clay Loam, Grade 2 Blocky structure. From Appendix B, Table 8.1.1.10.A we find in the “Effluent Quality” column, <30 mg/L of BOD and down to SICL, Grade 2-3, Blocky structure, our loading rate is 0.45 gal/sq.ft. Our daily flow is 450 gal/day, divided by 0.45 gal/sq.ft. = 1000 sq.ft. of “Native Soil Infiltration Area” This is the area to be covered by the woodchip cover and includes the area under the chambers. Step 11) Determine Minimum Width of Native Soil Infiltration Area: We have determined we require a minimum of 1000 sq. ft. of area under our at-grade system to properly distribute the effluent into the soils below the chambers. We also know we are making the at-grade 155 feet long. By dividing the 1000 sq.ft. by 155 feet length we find our width to be 6.45 feet.


Step 12) Determine Slope criteria for Toe of Slopes: Step 12 is just to refer back to Step 2. We need to know if we are designing on a level site or is there a slope. This particular example we have been using 2% slope on the site. Step 13) Calculations for Side slopes of At-Grade 1% or Less. If the site was on level ground, we would use Step 13. If we look at Table 1, attached to back of the worksheet, and look at 0% grade, we can see for 3:1 slope = 6 feet and 2:1 slope = 4 feet. This measurement would be from the edge of the chamber to the right and to the left. So for example, if we decided to design 3:1 slopes we would use the left box in Step 13. Under the box it states: “A8 + (0% slopes X 2)”, this equates to 2.8 feet + (6 feet X 2) = 2.8 + 12 = 14.8 feet width of at-grade toe to toe. As you can see you have to choose 3:1 slope, 2:1 slope or insure your toe to toe slope exceeds A11. In this example, A11 equates to 6.45 feet. The example equated to 14.8 feet toe to toe, which exceeds A11 of 6.45 feet. Step 14) Determine width of Effluent Application Area & Downslope Berm Step 14 is used if the site is on a sloped area 1% or greater. This is important as we know the effluent will have a tendency to run down hill, therefore we need to insure we have sufficient down-slope woodchip coverage and frost protection over the infiltration area. As you can see on worksheet, you have a choice of 3:1 or 2:1 side slopes. For this example we will design 3:1 slopes. From Table 1 we can determine the downslope length is between 6 ft and 6.6 ft. 2% is closer to 6.6 ft. therefore we will use 6.6ft for our calculation. We then add the calculation derived from box A8 equating to 2.8 ft. 6.6 ft. + 2.8 ft. = 9.4 ft. We need once more to insure we exceed the Native Soil Infiltration area found in box A11, which equated to 6.45 ft. Our width under the chambers and the down slope woodchips equals to 9.4 ft. Step 15) Determine of Upslope Berm Know we still need to finish off the upslope width of the at-grade berm. Looking at Table 1, we can see we need approximately 5.5 ft of width for a 3:1 slope. We need not to check our Native Soil Infiltration area, as we know the effluent will be running down hill from the chamber area. If you are confident there will be no chance of effluent weeping up hill, or the site slope is fairly steep (example 3% or greater) you may choose to design the up slope berm 2:1 and reduce the amount of wood chips required. Step 16) Determine toe to toe width of At-Grade. All that’s left to do is to determine the toe to toe width of the at-grade. If we add A14 and A15a or A15b we will get the total width. In our example Step 14 = 9.4 ft. + Step 15 = 5.5 ft. Therefore the total toe to toe on this 2% sloped site equates to 14.9 ft.


Descriptive Cross Section Of Typical At-Grade

THE TERMS USED IN THIS DRAWING DESCRIBE SPECIFIC AREAS OF THE AT-GRADE AND ARE USED IN THE FOLLOWING WORKSHEET AND THE GUIDELINE.

PSDS Design- Worksheet "A" v.1At-Grade Area Sizing

The complete system is to comply with the Alberta Private Sewage Systems Standard of Practice with exception as set out in the Guideline and this worksheet.

This Worksheet is for use in Alberta to: Size the effluent application area under the chamber(s) area, To size the area that must be covered by the woodchip material.

It can be used for: Design of At-Grade

Use only Imperial units of measurement throughout in this work sheet (feet, inches, Imperial gallons, etc.)

Use the following worksheet to determine the minimum required dimensions for an At-Grade and fill in the blanks on the appropriate diagram below for a level site or a sloping site of over 1%

Woodchip LayerNo Erosion Protection @ 3:1 SlopeErosion Protection @ 2:1 Slope

Native Soil Infiltration Area

Effluent Application Area LFH LayerLFH Layer

Edge of Chamber to Left Edge of Chamber to Right

If Required, One Or More Rows of Chambers

Length of At-Grade = Design Flow Linear Loading Rate

Each Chamber RowMust be of Eqivalent Width

Surface Area Under Chambers Must Be A Minimum Of80% Of Effluent Application Area


Level Site

Sloping Site

Effluent Application AreaLFH Layer

LFH Layer

Upslope

Downslope

A17

From A8

From A14

Treatment Area Length: Feet

Overall Length of At-Grade: Feet

Note:Downslope Toe must be greater than Box A11

From A15a or A15b

Native Soil Infiltration Area

Effluent Application Area LFH LayerLFH Layer

Centre to Left Centre to Right

Between Centre toCentre of Chambers

A13A or A13B

From A8

From A11

A12A or A12B A12A or A12B

Treatment Area Length: Feet Overall Length of At-Grade: Feet


Expected Volume of Sewage per Day

A1

Slope of Installation Site

A2

Effluent Loading Rate on Native Soil

See: Appendix B, Effluent Quality, <30 mg/L BOD Colunm, At-Grade Guideline 2007, Page 12 A3Gal./Sq. Ft. / day

Linear Loading Rate

A4Gal./per Linear Ft. per day

Expected Volume of Sewage Per Day Linear Loading Rate

Length of At-Grade chamber lateral or laterals

Divided By: EqualsA5

From A1 Feet

Expected Volume of Sewage Per Day Effluent Application Area


From A1 Sq. Ft.

Effluent Application Area

Reduction factor allowed for chamber width irregularities and

assumed spreading of effluent beyond edge of

chambersActual open area required

under chambers

Multiply by: 0.8 EqualsA7

From A6 Sq. Ft.

From site evaluation information the following needs to be determined: 1) Soil Texture, 2) Soil Structure, 3) Grade & 4) Depth of infiltration distance. From above data, determine the effluent loading rate from Effluent Soil Loading Rates and Linear Loading Rates Table, Appendix B At-Grade Guideline 2007, Page 12

Insure that sewage strength does not exceed the requirements laid out in Section 3.1.9 SOP Handbook 1999

Step 2) Determine the slope criteria of the installation site:Note: If the slope of the installation site exceeds 1% use the drawing "sloped site". If there is no slope,

use the drawing "level site" 1% or less.

Step 1) Determine the expected volume of sewage per day:Note: Use Table 3.1.1.14.A page 24 SOP Handbook 1999 as a guide to determine expected volume of

sewage per day. Provide allowance for additional load factors as detailed in 3.1.1.14

Step 4) Determine the Linear Loading Rate:

From site evaluation information the following needs to be determined: 1) Soil Texture, 2) Soil Structure, 3) Grade & 4) Depth of infiltration distance. From above data, determine Linear loading rate from Effluent Soil Loading Rates and Linear Loading Rates Table, Appendix B At-Grade Guideline 2007, Page 12

0.83 gal per sq. ft.From At-Grade Guideline

Section 4.2.1.2, Page 3

Step 7) Determine actual open area required under chambers for effluent application area:

Step 5) Determine Length of At-Grade:

From A3

Step 6) Calculate "Total" Effluent Application surface area required: (the area under the chambers the effluent is applied to)

Step 3) Determine native soil infiltration loading rate:


(the width covered by a chamber or # of chambers)

Area Under Chambers Length of At-GradeMinimum Effluent

Application area Width

Divided By EqualsA8

From A7 From A5 Feet

Width of selected chamber in feet -enter

actual internal effective width, not manufacturers

nominal widthNumber of chamber rows

selected

Actual open area provided by chambers for effluent

application area

Multiply By EqualsA9

Eg. 22 inches divided by 12 inches = 1.8 feet

FeetThis amount must exceed the amount

in box A8

Expected Volume of Sewage Per Day

Native Soil Infiltration Loading Rate

Required Native Soil Infiltration Area


From A1 From A3 Sq. Ft.

Native Soil Infiltration Area Length of At-Grade

Width of Native Soil Infiltration Area

Divided By EqualsA11

From A10 From A5 Feet

On a sloped site this area includes only the area downslope of the upslope side of the chambers

Slope of Installation Site

From A2

Step 8) Determine the minimum width of effluent application area:

Step 10) Calculate minimum Native Soil Infiltration Surface Area: (this is the area to be covered by the woodchip cover and includes the area under the chambers)

Step 9) Select the chambers to be used and the number of rows of chambers required:

Step 11) Determine Minimum Width of Native Soil Infiltration Area:

Step 12) Determine slope criteria for toe of slopes:

Note: For slopes 1% or less use Steps 13, Greater than 1% proceed to Step 14.


toe-to-toe based on 3:1 toe-to-toe based on 2:1Width of required infiltration area

or OR A11A8 + (0% slopes) X 2 A8 + (0% slopes) X 2

A13

The greater of (3:1 or 2:1 Box) or A11 Box

3:1 Downslope Berm 2:1 Downslope Berm

From Table 1 From Table 1

+ +Effluent Application Width Effluent Application Width

A8 A8

= =

Or Or A11

The Greater

A14

3:1 Dimension 2:1 Dimension

A15a Or A15b

Step 16) Determine toe-to-toe width of At-Grade.

+ = A16A14 A15a or A15b

+ = A17

A17 Centre-to-Centre of Chambers Total Width of At-Grade

Step 13) Calculations for side slopes of At-Grade 1% or less.

Step 17) If designed 2 or more rows of chambers, add centre-to centre width:

Step 15) Determine Area of Upslope Berm

Step 14) Determine width of Effluent Application Area & Downslope Berm


"At-Grade Dimensions on Slopes" Table 1

0%

6 ft.

12%

0%

3%

6%

9% 3%

6%

9%

12%

6 ft.

6.6 ft.

5.5 ft.

5 ft. 7.3 ft.

8.3 ft.

4.6 ft.

4.2 ft.

9.4 ft.

3:1 Slopes

0%

3%

6%

9%

12%

3 ft.

1 ft.

0%

4 ft.

12%

0%

3%

6%

9% 3%

6%

9%

12%

4 ft.

4.2 ft.

3.7 ft.

3.5 ft. 4.5 ft.

4.8 ft.

3.3 ft.

3.1 ft.

5.2 ft.

2:1 Slopes

0%

3%

6%

9%

12%

2 ft.

1 ft.


18303 – 60th Avenue, Edmonton, Alberta, T6M 1T7 Phone: 1-877-489-7471 Fax: 1-780-486-7414

VARIANCE APPLICATION FOR AT-GRADE SEWAGE TREATMENT SYSTEM

Date of Application

Month Day Year

Applicant Information Property Owner Information

Owner’s Authorized Representative Information (when variance application is applied for by someone other than owner). Name Application Date _________________ Signature Telephone Number ______________ Mail Address Postal Code ___________ PSDS # ____________________ Owner Information (owner of premises). This information must always be filled out. Name Application Date _____________________ Signature Telephone Number ________________ Mail Address Postal Code _____________

Legal Land Description LSD _____ 1/4 ______ Sec. ______ Twp. _____ Rge. W of _____

Lot _____ Block _____ Plan ___________

County/MD __________________ OR

House and St./Ave. #_______________________

City/Village/Town __________________________


Issuance Approval This variance is issued under the authority of AT-GRADE Guideline # approved by Alberta Municipal Affairs and Housing, June 2007. All construction and design procedures must also fully comply with all standards and regulations set out in the 1999 Alberta Private Sewage Systems Standard of Practice and all future SOPs.

Explaination of Request for an AT-GRADE Variance

(what article in the SOP needs to be addressed in order to request for an AT-GRADE variance. ie. vertical separation from a restrictive layer, cover material, LFH thickness, etc.)

_________________________________________ _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ _________________________________________ ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

At-Grade Design Details

Site evaluation date (dd/mm/yy): ________________________________ Soil Texture Classification is: Horizon_________Texture____________________Thikness__________ Horizon_________Texture____________________Thikness__________ Horizon_________Texture____________________Thikness__________


Horizon_________Texture____________________Thikness__________ Soil samples have been analyzed by: ________________Certified Lab. (Please attach lab report) Pertinent Soil Structure for Site: Horizon _____Grade# _____Structure ____________Thickness_______ Horizon _____Grade# _____Structure ____________Thickness_______ Horizon _____Grade# _____Structure ____________Thickness_______ Horizon _____Grade# _____Structure ____________Thickness_______ The Infiltration Loading Rate determined to be: ________ gal/sq.ft./day The Linear Loading Rate determined to be: ____________ gal/l.ft./day The LFH layer thickness is: _____________ inches Make and Model of Chamber System_____________________________ The material used to cover chamber and it’s thickness is: ____________________________________________________________ The type and level of Secondary Treatment Plant is: _______________ ____________________________________________________________

Design Layouts

Must include drawings of : 1. Plot Plan of the property indicating where the proposed system is will be with all pertinent details and dimensions. 2. Distribution Lateral Layout for the proposed At-Grade System including all pertinent details and dimensions.

Identification of Safety Codes Officer (SCO to fill out)

Designation #: __________________ SCO #:___________________ Safety Codes Officer _______________________________________ Agency: __________________________________________ Signature: _____________________________

Issued on behalf of (SCO to fill out)

Accredited Municipality, or ___________________________________

Accredited Corporation, or ___________________________________


Municipal Affairs (non-accredited areas) _______________________

Request approved Request rejected Request conditionally approved

Comments. Info can be attached (Filled out by SCO)

Advisement of Offense Non-compliance with the instructions contained in this Variance is an offense under the Safety Codes Act. Variances will only be granted if it is determined that the equipment or method of installation involved does not present a hazard to persons or property and that strict compliance with the Act or applicable regulations was not practicable.


guidelines for alberta at-grade systems for onsite

Documents