PERC-RITE DRIP DISPERSAL DESIGN GUIDE FOR SEPTIC TANK OR ADVANCED TREATMENT EFFLUENT MASSACHUSETTS

Transcription

1 PERC-RITE DRIP DISPERSAL DESIGN GUIDE FOR SEPTIC TANK OR ADVANCED TREATMENT EFFLUENT MASSACHUSETTS This Design Guide is to assist you in preparing for the design of a Perc-Rite Drip Dispersal System for General Use or Remedial Use as allowed by Title 5 of the Massachusetts Environmental Code. The Perc-Rite Drip Dispersal System is a unique fluid handling process for ultra-low rate dispersal of wastewater into the soil. Septic tank effluent, secondary effluent (from aerobic treatment units and other treatment systems), or highly treated wastewater from membrane filtration or other methods can be accommodated. The purple tubing is specially designed for our soil conditions to provide a successful solution to your disposal and re-use needs. Most concepts for design will be familiar to the reader with two exceptions. Instead of calculating an exact area needed on the site, you will first determine the linear footage of drip tubing required and then determine the footprint based on the method of construction and site constraints. Additionally, instead of calculations using just the design flow and the soil & percolation test results, you will also vary the amount of tubing needed depending if the project will use septic tank effluent or treated effluent. Offsets to restrictions (i.e. groundwater and bedrock) should be maintained as indicated in the Title 5 and these generally allow a 4 offset from the drip tubing to the seasonal high water table for septic tank effluent, and for upgrades, 2 offset from the drip tubing to the seasonal high water table for pre-treated effluent. Perc-Rite Drip Dispersal is considered equivalent to Pressure Distribution in all instances where this disposal technique is required by Title 5. This Design Guide contains commonly used configurations of smaller wastewater dispersal systems. Engineering design assistance is available for larger flow projects or for projects with unique situations which do not fit within these simple design guidelines.

2 Typical Perc-Rite Drip Dispersal Components 2

3 Perc-Rite Drip Dispersal Design Procedures By following these guidelines and standard design procedures, an Engineer or Sanitarian can specify the appropriate Perc-Rite Drip Dispersal System needed. I. Site Evaluation A. Determine design flow in gallons per day in accordance with Title 5. B. Perform test pits, percolation tests, etc. in accordance with Title 5. Pay closer attention to the upper soil horizons as you might need to consider the suitability of the A soil horizon in the design. II. Perc-Rite Drip Tubing Length Calculation Determine linear footage of Perc-Rite Drip Dispersal tubing required as follows: For septic tank effluent, use the loading rate table for pressure distribution in Title 5 (Section 242) to figure out the square footage area needed for a standard leach field. This number is the minimum linear footage of drip dispersal tubing needed at that job site. For pre-treated effluent, use the loading rate table for pressure distribution in Title 5 (Section 242) to figure out the square footage area needed for a standard leach field. Take this number and divide it by two to determine the minimum linear footage of drip dispersal tubing needed at that job site. (As you see from the calculations above, twice the amount of drip tubing is needed for septic tank effluent as it is for pre-treated effluent). The area on the property to install this tubing varies depending on the method of installation and any site constraints as described below. Note that for standard residential applications, a minimum of 400 linear feet of tubing is recommended. III. Perc-Rite Drip Dispersal System Design A. Determine area on property where drip tubing is to be placed, depict on site plan. For ease of installation, selecting a long and narrow configuration following the contour of the land is recommended. Tubing is typically placed 1-2 feet on-center when laid on an open bed of soil or Title 5 sand fill material; tubing is typically placed 2 feet on-center when plowed into the existing ground in a lawn or lightly vegetated area; and tubing is typically placed >2 feet on-center when plowed or trenched into sites with extensive vegetation. For systems incorporating a reserve area between the tubing, spacing must be at a minimum of 2 feet on-center or a replacement area must be located elsewhere. 3

4 There is no need to depict each drip tubing run on the design plan as long as the appropriate area is available. Note that the only design limitation is the prohibition for Perc-Rite Drip Dispersal to be specified beneath pavement or beneath a gravel or dirt driveway which is driven over regularly. B. Determine longest length of a single run of drip dispersal tubing. This is simply the longest dimension of the drip field measured running parallel to the contour. C. Based on the total linear feet of tubing proposed and the longest single length of drip tubing, refer to the Standard Zone Selection Table in the Appendix and determine the appropriate Zone Detail. This Zone Detail simply depicts the number of zones and the manifold system which will be used to distribute the effluent to the tubing. Breaking the drip field into different zones allows the use of a smaller and more energy efficient pump when compared with trying to feed all the drip tubing at one time. Also, by using one of the pre-established manifold configurations almost any static or friction head loss can be overcome without operational problems. Contact Oakson or visit the Oakson website for an AutoCAD diagram of that detail. 4

5 D. Download from website or contact Oakson to obtain Detail Page to accompany site plan. Typically this is made into the second page of the design plan. Detail Page 5

6 IV. Complete On-Site System Design Plan Site Plan Example 6

7 On the design plan show: A. Location of septic tank and pre-treatment unit (if proposed). B. Location of pump chamber and hydraulic unit. 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. 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 stratum, or water table as indicated in Title 5 (or if used, the Massachusetts DEP approval letter for a pre-treatment technology). E. Indicate the route of the supply and return pipes. F. Depict Standard Detail sheet provided by Oakson. Add specific Zone Detail from table to the Detail Sheet. G. Submit plans to Oakson, Inc. for confirmation of design parameters. H. Submit plans for review to appropriate regulatory agency. 7

8 Design Examples Example 1: Typical Residential Site; Septic Tank Effluent (tree to be preserved) Example 1: Site Plan Acceptable area for drip tubing shown by hatched area on site plan. During actual field installation, on-center spacing will vary to avoid the tree in the dispersal area 8

9 Assume a design flow of 330 gallons per day Assume a percolation rate of <2 minutes per inch, Class I soil From Title 5, determine that Loading Rate to be used to determine the number of linear feet of Perc-Rite Drip Dispersal tubing is gal/day/0.74 = 446 square feet (this is a proxy as if the design was for a leach field) This results in 446 linear ft. of Perc-Rite Drip Dispersal tubing being required From the site plan above, the length parallel to the contour is 75 feet From the Standard Zone Selection Table it can be found that detail Z132 is suited for a run length of 75 feet with 446 linear ft. of drip dispersal tubing Z132 Zone Detail 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 9

10 Example 2: Larger System Design; Treated Effluent (Round up to next largest size in Standard Zone Selection Table) Assume a design flow 4,400 gpd Assume percolation rate of 3 minutes per inch, Class I soil Example 2 Site Plan 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 10

11 From Title 5, determine that Loading Rate to be used to determine the number of linear feet of Perc-Rite Drip Dispersal tubing is ,400 gal/day/0.74 = 5,950 sq ft (this is a proxy as if the design was a leach field) Divide square feet by 2 to determine the required minimum amount of Perc-Rite Drip Dispersal tubing This results in 2,975 linear feet of drip tubing required From the site plan above, the longest length parallel to the contour is 225 From the Standard Zone Selection Table, select the zone detail at the intersection of 225 contour length and 2,975 linear feet. Since no detail exists at this intersection, move to the next largest area and select the zone detail at the intersection of 250 contour length and 3,000 linear feet, which would be Z341 Z341 Zone Detail Note due to the larger flows this calls for a 3 zone system with the control panel automatically rotating between the zones to be fed 11

12 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 tackle a range of projects without significant site disturbance. Our team is committed to making your project using Perc-Rite Drip Dispersal a success. Please feel free to call or us with any projects or other items where we can be of assistance OAKSON1 Or info@oaksoninc.com 12

13 APPENDIX Standard Zone Selection Table Length Parallel to Contour Linear. Ft. of Perc-Rite Drip Tubing Required 400 Z124 Z122 Z Z133 Z123 Z132 Z131 Z Z152 Z151 Z122 Z Z134 Z124 Z132 Z122 Z131 Z Z Z133 Z Z135 Z152 Z132 Z151 Z Z144 Z224 Z136 Z233 Z145 Z252 Z134 Z232 Z142 Z222 Z133 Z251 Z142 Z222 Z132 Z231 Z141 Z221 Z141 Z221 Z141 Z221 Z Z226 Z234 Z224 Z242 Z232 Z222 Z231 Z Z Z233 Z Z272 Z Z235 Z252 Z232 Z251 Z231 13

14 Length Parallel to Contour Linear. Ft. of Perc-Rite Drip Tubing Required 1600 Z244 Z242 Z Z236 Z326 Z234 Z324 Z233 Z323 Z232 Z322 Z331 Z Z Z254 Z252 Z242 Z251 Z Z333 Z Z372 Z Z253 Z Z332 Z351 Z251 Z Z246 Z344 Z244 Z243 Z342 Z Z Z334 Z333 Z Z Z342 Z452 Z352 Z432 Z242 Z422 Z332 Z341 Z431 Z451 Z351 Z341 Z Z442 Z Z353 Z Z344 Z434 Z343 Z433 Z342 Z432 Z441 Z341 Z431 Z231 Z321 Z241 Z331 Z341 Z Z452 Z442 Z451 Z Z443 Z442 Z441 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. 14