vt guide treated may2012

Vermont Design Guide – Version 1.0 – May 2012

Perc-Rite® is a registered trade name of American Manufacturing Company, Inc., Elkwood, VA

PERC-RITE® DRIP DISPERSAL DESIGN GUIDE FOR ADVANCED TREATMENT EFFLUENT

VERMONT This Design Guide is to assist you in preparing a Perc-Rite® Drip Dispersal System plan for new construction, replacement or repairs as allowed by the Vermont Department of Environmental Conservation Wastewater System and Potable Water Supply Rules, specifically section 1-923 which authorizes the use of subsurface drip dispersal. Oakson is the authorized distributor & technical consultant for the “Perc-Rite® Drip

Dispersal System” within New England and New York State. The Perc-Rite® system is a unique fluid handling process for ultra-low rate dispersal of wastewater into the soil. The Perc-Rite system is currently approved for use in Vermont if it follows an aerobic treatment unit or packed media filter. Most concepts for a Perc-Rite® design will be familiar to the reader who has designed other leaching facilities. Vermont also requires drip dispersal systems to be preceded by a filtrate technology system, which then allows the maximum application rate to be doubled. This classification also grants the reduced offsets to the seasonal high groundwater table and bedrock as specified in section 1-916. This Design Guide contains commonly used configurations of smaller wastewater dispersal systems. Engineering design assistance is available for larger flow projects or unique situations which do not fit within these simple design guidelines. The flexibility of the drip tubing, the uniqueness of the pressure-compensating emitter, and the different zone configurations allow for almost any site to be properly fitted with a Perc-Rite® Drip Dispersal System. This design manual has been modified to reflect current state regulations and industry standards. The system designer assumes ultimate responsibility in the use of this technical manual and the incorporation of its contents into a specific design.

Vermont Design Guide - Perc-Rite® Drip Dispersal System (May 2012)

Copyright © 2012 Oakson, Inc., Gloucester, Massachusetts

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Typical Perc-Rite® Drip Dispersal System Components

Adapted from American Manufacturing Company, Inc. 2001-2012 Patent #s 5,200,065; 5,984,574B; 6,261,452B1



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Perc-Rite® Drip Dispersal System Design Procedures By following these guidelines and standard design procedures, a Class 1 Designer can specify the appropriate Perc-Rite® Drip Dispersal System needed.

I. Site Evaluation

A. Determine design flow in gallons per day in accordance with section 1-808.

B. Perform test pits and percolation tests as needed in accordance with standard design procedure. Perform a hydrogeologic study as may be required.

C. Determine whether the site can be built upon, if new construction, according to

the rules in section 1-805. Note that drip dispersal may be used under any of the

design approaches. II. Leaching Area and Perc-Rite® Drip Tubing Length Calculation

A. Determine application rate (AR) using formula AR = 2 x (0.8 x 3/√T); where T is

the percolation rate in minutes per inch. (The AR formula above is based on the

formula for absorption beds and then doubled due to the use of treatment.) If

using a mounded system the AR = 2.0.

B. Determine the minimum area required by dividing the design flow rate by the AR.

C. Determine the linear loading factor (f) from Table 1 in Appendix 7-A of the

Vermont DEC EPR based on soil texture and ground slope. Determine the soil thickness (h) by subtracting 6” from the depth to the seasonal high ground water table.

D. Determine the linear loading rate (LLR). LLR = f x h.

E. Determine the minimum length of the system by dividing the design flow by the LLR.

F. Determine the system width by dividing the minimum area by the system length.

G. Determine the minimum linear footage of Perc-Rite® Drip Dispersal tubing

required by dividing the required area by two. For situations with less than 400’ of

drip tubing proposed, please contact Oakson for assistance.



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III. Perc-Rite® Drip Dispersal System Design

A. Determine the pretreatment unit or packed media filter to be used. Determine the size of pump tank needed. The pretreatment unit or packed media filter must achieve an

effluent quality of less than 30 mg/L BOD and TSS. Pump tank is to be sized depending on

flow rate into it from the treatment system and emergency storage needs for the site.

Typically a minimum of one day’s working capacity is needed to handle peak flows and

distribute them over a 24 hour time period to the drip field.

B. Determine the area on the property where drip tubing is to be placed, depict on site plan. It is recommended that drip dispersal tubing be spaced two feet on center. There is no

need to depict each drip tube run on the design plan as long as the appropriate area is

available. Perc-Rite® Drip Dispersal may not be specified beneath pavement, beneath a gravel

or dirt driveway which is driven over regularly, or beneath a parking or heavy equipment

storage area.

C. Determine longest length of a single drip dispersal run which will be placed parallel

to the site contours. The longest length of a single piece of tubing can be 300’. When the

maximum length of tubing is 150’ or less, the return and supply piping can be on the same

side of the drip field which can often result in easier construction.

D. Refer to the Standard Zone Selection Table in the Appendix of this guide to

determine the appropriate zone detail. Please visit Oakson’s website to download AutoCAD details of the selected zone. The Zone Detail will provide for the proper

manifold system and appropriate number of zones for the project as well as a depiction of how

construction is to occur. Once the zone detail is selected it may be inserted as a separate

detail on the design plan. See the examples starting on page 8.

E. Determine the depth of installation and the installation method. The invert of the

tubing is considered to be the base of the system for all offset distances. Typical installation

depth is between six and eighteen inches. Drip tubing may be trenched or plowed into place

or placed on a bed of sand fill. With a Prescriptive design, offsets to restrictions (i.e.

groundwater and bedrock) will be maintained as a 24” offset from the drip tubing to the

seasonal high water table or bedrock. With an Enhanced Prescriptive design drip dispersal

tubing can be placed closer to the water table with a curtain drain. With a Performance

Based design a mound can be 6” from the ground surface.

F. Design the basal area in accordance with VDEC rules if the drip dispersal system is mounded.



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G. Download from website or contact Oakson to obtain this detail page to accompany

the site plan. Typically this is made into the second page of the design plan, but is not

required.

Detail Page

Adapted from American Manufacturing Company, Inc. 2001-2012



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IV. Complete On-Site System Design Plan

Site Plan Example – residential system, supply and return on opposite ends



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On the design plan show: A. Location of tank and pre-treatment unit.

B. Location of pump chamber, if required, and hydraulic unit. Note the hydraulic

unit must be placed in a location which allows gravity return back to the septic tank

inlet. C. Indicate the area where the tubing is to be installed and depict any limiting

setbacks that may exist such as property lines, wells, etc. Indicate the route of the supply and return pipes.

D. Indicate the depth of tubing for a plowed in installation, or the amount of cover

material to be provided for a raised bed installation. Note that the tubing

installation depth, or the depth of cover material to be imported, is usually influenced by

the separation from drip tubing to bedrock, impermeable layer, or water table as indicated

in the Vermont Wastewater System and Potable Water Supply Rules. E. If desired, depict standard detail sheet provided by Oakson. Enhance the detail

sheet with a zone detail selected from the Zone Detail Table in the Appendix of this guide.

F. Submit plans to Oakson for confirmation of design parameters. G. Submit plans for review to appropriate regulatory agency. H. Discuss with the owner the need for this technology, like any non-traditional

system, to have preventative maintenance performed to assure proper operation. Doing so helps preserve both the investment placed into the property and our shared environmental resources by assuring proper treatment and dispersal of the sewage. A maintenance agreement with a trained and licensed entity should be in place prior to construction for at least the first two years after installation. Annual maintenance is recommended for single-family houses and semi-annual or more frequent for other facilities.



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Design Examples

Example 1: Site Plan – Typical Residential Site

Note layout of the drip field parallel to the existing site contours

Example 1: Residential Site



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• Assume a design flow of 420 gallons per day • Assume a Fine Sandy Loam soil; SHWT=20”; 19% avg Slope • f = 13.5 • h = 20” – 6” = 14” = 1.17’ • LLR = h x f = 1.17 x 13.5 = 15.75 gpd/ LF • Minimum Length = 420 gpd / 15.75 gpd/LF = 27’ (use 35’) • Mounded system uses an application rate of 2.0 g/sf/day • Minimum Area = 420 gpd / 2 gpd/SF = 210 SF • Width = 210 SF / 35’ = 6’ • Minimum length of tubing = 210SF / 2 = 105 LF (use 210 LF) • From the site plan above, the length parallel to the contour is 35 feet, use 50’ and

enter the Zone Detail Table in Appendix to find a Z124 • The bed will be 35’ long by 6’ wide (210 SF), with 210’ of tubing

This image shows the manifold system to be constructed. Note that since this is for a single

family house, the small amount of flow allows use of only one zone so all the drip tubing

will be fed every time the pump is turned on


Vermont Design Guide


Acceptable area for drip tubing shown by hatched area on site plan. Irregular shaped drip fields

are not of concern since the system operates under pressure

to provide even distribution throughout



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Example 2 Site Plan


are not of concern since the system operates under pressure

to provide even distribution throughout

Example 2: Larger System Design


Vermont Design Guide


• Assume a design flow • Assume a Sandy Loam soil; SHWT=36• Percolation Rate = 12.5 minutes/inch• f = 11.2 • h = 36” – 6” = 30” = 2.5• LLR = h x f = 2.5’ x 11.2• Minimum Length = 2,000

= 77.5’) • AR = 2 x 0.8 x 3 / √12.5 mpi = • Minimum Area = 2,000• Width = 1482 SF / 71.5• Minimum length of tubing =

required as the cost differencethe entire drip field)

• Enter the Zone Detail

Due to the flow to be dispersed in this example

Adapted from American Manuf



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n flow 2,000 gpd y Loam soil; SHWT=36”; 2.3% avg Slope

Percolation Rate = 12.5 minutes/inch

2.5’ x 11.2 = 28 gpd/ LF

2,000 gpd / 28 gpd/LF = 71.5’ (site varies, minimum provided

√12.5 mpi = 1.35 gpd/SF 000 gpd / 1.35 gpd/SF = 1482 SF

71.5’ = 20.7’ (more than this provided) Minimum length of tubing = 1482 SF / 2 = 741 LF (use more than minimum

difference is negligible and it affords greater ability to us

etail Table in the Appendix to find a Z242 for 1200’ of tubing

Z242 Zone Detail

Due to the flow to be dispersed in this example, the design will use a 2 zone system

have automatic rotation between the zones


(site varies, minimum provided

(use more than minimum ble and it affords greater ability to use

00’ of tubing

zone system which will



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Thank you for your interest in using Perc-Rite® Drip Dispersal. This document is intended to assist you with design for many common wastewater projects. The flexibility inherent in the Perc-Rite® Drip Dispersal system allows you to successfully dispose of wastewater from sites with a wide range of challenges. Our team is committed to making your project using Perc-Rite® Drip Dispersal a success. Please feel free to call or e-mail us so we can be of assistance. Oakson, Inc. is an authorized user of the Perc-Rite® trade name and related materials for drip dispersal systems.

1-877-OAKSON1

Or

[email protected]



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APPENDIX

Standard Zone Selection Table

Length of Drip Field Parallel to Contour

50’ 75’ 100’ 125’ 150’ 200’ 225’ 250’ 300’

Lin

ear.

Ft.

of

Per

c-R

ite

Dri

p T

ub

ing

400’ Z124 Z122 Z121

450’ Z133 Z123 Z132

Z131 Z121

500’ Z152 Z151 Z122 Z121

600’ Z134 Z124 Z132 Z122 Z131 Z121

625’ Z151

675’ Z133 Z131

750’ Z135 Z152 Z132 Z151 Z131

800’ Z144 Z224

Z142 Z222

Z141 Z221

900’ Z136 Z233

Z134 Z232

Z133 Z132 Z231

Z141 Z221

Z131

1000’ Z145 Z252

Z251 Z142 Z222

Z141 Z221

1200’ Z226 Z234

Z224 Z242

Z232 Z222 Z231 Z221

1250’ Z251

1350’ Z233 Z231

1400’ Z272 Z271

1500’ Z235 Z252 Z232 Z251 Z231

1600’ Z244 Z242 Z241

1800’ Z236 Z326

Z234 Z324

Z233 Z323

Z232 Z322

Z331 Z241 Z231 Z321

1875’ Z351

2000’ Z254 Z252 Z242 Z251 Z241

2025’ Z333 Z331



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Length Parallel to Contour

50’ 75’ 100’ 125’ 150’ 200’ 225’ 250’ 300’

Lin

ear.

Ft.

of

Per

c-R

ite

Dri

p T

ub

ing

Req

uir

ed

2100’ Z372 Z371

2250’ Z335 Z253 2352

Z332 Z351 Z251 Z331

2400’ Z246 Z344

Z244 Z243 Z342 Z423

Z242 Z422

Z341 Z431

Z241

2500’ Z451

2700’ Z334 Z434

Z333 Z332 Z341 Z431

Z331

2800’ Z471

3000’ Z452 Z352 Z342 Z432

Z451 Z351 Z341 Z431

3200’ Z442 Z441 3375’ Z353 Z351

3600’ Z344 Z434

Z343 Z433

Z342 Z432

Z441 Z341 Z431

4000’ Z452 Z442 Z451 Z441 4800’ Z443 Z442 Z441

Adapted from American Manufacturing Company, Inc. 2001-2011 ➔ Note that the three digit Zone Detail number contains first the number of zones, then the

number of laterals per zone, then the number of individual runs of tubing per lateral. For

example Z222 has two zones (each one is alternatively supplied when the pump is activated),

2 laterals within each zone (to better divide up the flow evenly), and 2 individual runs of

purple drip tubing within each lateral. ➔ Even numbers of runs (the last number in the three digit Zone Detail) are frequently

advantageous as they allow the supply and return manifolds to be constructed at the same

end of the dispersal area.

➔ If the appropriate box in the table is blank, choose the next largest detail. This may have the

same or a longer length parallel with the contour.

vt guide treated may2012

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