Steven speaks use and sizing of effluent disposal field beds presentation

Steven E. SpeaksSteven E. SpeaksP.E./P.L.S.P.E./P.L.S.PresidentPresidentLarry E. Speaks & Associates, Inc.Larry E. Speaks & Associates, Inc.535 Herron Street, Montgomery, AL 36104535 Herron Street, Montgomery, AL 36104

• Bed- an infiltrative surface, square or rectangular in shape, with no internal trench walls

• Limited Site Conditions- ie. setbacks, slope, walls, embankments, limited area, vertical separation/restrictive layer

• Treatment is used

Gravel Field Standard Construction Specifications

(8) As an alternative trench system, a bed may be utilized for conventional systems in Group I, II, and III soils that are not to be modified in accordance with Rule 420-3-1-.94 Controlled Fill System. All sewage subject to this paragraph shall be pretreated to a minimum of the secondary standard.

(a) The total bottom area for all beds shall be computed as follows:

1. The bed length shall be computed by dividing the design flow by the hydraulic linear loading rate in Column 2 of Appendix A, Table 18, and rounded up to the next whole foot.

2. Bed width shall be computed by dividing hydraulic linear loading rate in Column 2 of Appendix A, Table 18 by the application rate in Column 4 of Appendix A, Table 18, and rounded up to the next whole foot.

Gravel Field Standard Construction Specifications (Continued)

3. This shall be the area required for the bed regardless of the configuration.

(b) For Texture Group 4A soils, it is recommended that the bed be configured using the dimensions as calculated from this rule paragraph (8)(a)1 and 2. The bed shall be constructed in accordance with the bed requirements of Converse and Tyler’s Wisconsin Mound Manual with two exceptions:

1. The configuration (not area) may be varied if the lot requires it and is approved by the LHD.

2. Low Pressure Pipe (LPP) and time dosing are required for all beds regardless of the configuration, unless another method of distribution is approved in a Product Permit or a Performance Permit.

For conventional systems on lots in Texture Group 1, 2, 3, and 4A soils and that are not to be modified in accordance with Rule 420-3-1-.85 Gravel Field Standard Construction Specifications paragraph (8)

(Continued)

PERC RATEmin/inch

LINEAR LOADING RATEgal/d/ft

SOIL GROUPU.S.D.A. Textures

BED/PAD LOADING RATE

gpd/sq.ft.

51015

101010

Group ISand, Loamy Sandy

2.272.272.27

202530

987

Group IISandy Loam, Loam

1.801.801.80

354045505560

65.85.65.45.25

Group IIISandy Clay Loam, Silty

Loam, Silty Clay Loam, Clay Loam

1.211.211.210.710.710.71

657075808590

443.53.533

Group IVaSandy Clay, Silty Clay, Clay

0.360.360.360.280.280.28

95100105110115120

NOT SUITABLE

Group IVbHigh Shrink-Swell Clay,

Poorly Structured Soil

0.280.280.280.280.280.28

(Continued)

Length = Width =

Length = Width =

= 90 = 8

EXAMPLE: 3 Bedroom dwelling with a perc rate of 60 min/in.*ROUND UP LENGTH AND WIDTH TO THE NEAREST WHOLE NUMBER.

The area calculated here is required. The configuration is recommended see Rule420-3-1-.85 Gravel Field Standard Construction Specifications.

Daily Design Flow

Linear Loading Rate

Linear Loading Rate

Bed/Pad Loading Rate

450

5

5

.71

Reduced setbacks from 25Reduced setbacks from 25’’ to 15to 15’’ from drainage ways and embankments, from drainage ways and embankments, cuts or retaining walls, per Table 5.cuts or retaining walls, per Table 5.

Maximization of disposal area by utilizing different dimensions Maximization of disposal area by utilizing different dimensions without without trench separation. Eliminates waste of square footage in conventrench separation. Eliminates waste of square footage in conventional 3tional 3’’wide trench designs.wide trench designs.

Reduction in the required REDF. Area required equivalent in squReduction in the required REDF. Area required equivalent in square are footage as required for primary EDF.footage as required for primary EDF.

Gives ability to maximize small areas of good soils.Gives ability to maximize small areas of good soils.

Reduced minimum vertical separation distance from >50% rock Reduced minimum vertical separation distance from >50% rock (weathered rock) from 18(weathered rock) from 18”” to 12to 12””..

(Continued)

Areas with difficult accessibility may design beds with EZAreas with difficult accessibility may design beds with EZ--Flow bundled Flow bundled instead of gravel (reduction for EZinstead of gravel (reduction for EZ--Flow cannot be taken).Flow cannot be taken).

Greater flexibility on bed design with width/length to save treeGreater flexibility on bed design with width/length to save trees and work s and work around other limited areas.around other limited areas.

Given a conventional design for the primary EDF, treatment and bGiven a conventional design for the primary EDF, treatment and bed ed disposal can be specified for REDF.disposal can be specified for REDF.

Given good soil conditions, you can utilize 24Given good soil conditions, you can utilize 24”” of gravel in beds to handle of gravel in beds to handle occasional large volume of effluent (parties, holidays, gatherinoccasional large volume of effluent (parties, holidays, gatherings, etc.).gs, etc.).

Initial cost and periodic maintenance required for treatment Initial cost and periodic maintenance required for treatment atuatu’’ss..

Longer area required for placement of tanks.Longer area required for placement of tanks.