12. Long term siltation that can bring about premature failure in other leach fields is prevented by the geotextile fabric cover of the In-Drain system. 

13. In-Drains provides greater evapotranspiration than with the conventional stone leach or chamber leach fields. Spaced cluster In-drain layouts allow more oxygen to reach system thus providing more aerobic effluent decomposition. 

14.     Substantially reduced bed sizes require fewer trees to be cut down to prepare a leach field area than for conventional leach fields.  

Standard In-Drains: A non-aggregate biofabric filter module for leach fields produced by the Eljen Corporation. Standard sizes; Type B-36 “wide 48”Iong 7”high & Type HB which is a half-length unit at 36” wide 24”long 7” high. Custom sizes and Type A units are also available on special order.  

Bio-Mat fabric: Special filter fabric within In-Drain modules upon which primary biomat layer forms. Each 3’ x 4’ Type B in-drain has approximately 100 square feet of internal biofabric.  

Geotextile Cover Fabric: Anti-siltation fabric placed over In-Drain assembly to prevent backfill above the units from washing into modules.  

Solid Cuspated Core: Rigid plastic core used to separate Bio-Matt fabric thereby creating multiple infiltrating channels.  

Wire Clamps: Used to laterally secure perforated pipe until back fill is completed. Use is optional with carefully placed back fill.  

In-Drain Cluster Design: Leach field layout which takes advantage of effluent side wall infiltration with parallel rows of modules separated by at least 12” of sand. Cluster designs can be stepped down on sloped sites.  

Serial Distribution: In-Drain layout suited for sloping sites where multiple rows of modules are dosed in series rather than in parallel from a distribution box.  

Combination Systems: Multiple serial distribution layouts generally fed with equally divided effluent flow from a special distribution box or other accurate dosing device.  

Flow Equalizer: Special insert placed in end of distribution pipes at the distribution box to minimize effects of backfilling and settling.  

LTAR: Long Term Acceptance Rate  

STE:  Septic Tank Effluent  

MLF: Most Limiting Factor (Seasonal high water table, and/or bedrock, and/or restrictive horizon).  

Minimum Design Flow per Bedroom: 90 gallon per day. Specific situations may suggest the use of higher values.  

Maine Rules: Subsurface WasteWater Disposal Rules, 144A CMR 241, of latest version.  

1.0 Basic System Design

1.1 Design and Installation: Design and installation of In-Drain systems shall comply with all state and local regulations and the requirements of this manual.

1.2 System sizing: In-Drain systems must be sized on the basis of Table 600.1 of the Maine Subsurface WasteWater Disposal Rules (Maine Rules). Disposal field sizing is based on an approved credit of I sq.ft. of In-Drain bottom area equal to 4 sq.ft. of stone bed. Use In-Drain sizing Table #1 to determine the number of Type B units for a given design flow and disposal field size group. The 4 to 1 credit applied for all systems, commercial and non­commercial. The number of In-Drains required is the same for trench or Eljen’s spaced cluster configurations. Please refer to section 5 for additional design information on commercial systems. Increase septic tank size by 50% and system size by 30% when garbage disposal is used.

1.3 Trench Configurations: Trench configurations shall provide a minimum spacing of 6’ center to center (3 feet between units) with 6” of sand (see section 1.7 for sand specifications) below the In-Drain and 9” of sand around the outer edge of Type B units. Trench configurations utilize the same number of In-Drains as clustered configurations. Most designs utilize cluster configurations unless the site designer feels that the site has some unusual hydraulic capacity characteristics.

1.4  Clustered Configurations: In-Drains may be installed in a clustered configuration with a minimum of 12” of sand (See section 1.7 for sand specification) between rows, 9” of sand around the outer edge of the In-Drains and 6” of sand below the In-Drain rows.

1.5  Experimental Systems: Use of In-Drains at a higher loading rate than the stated in Section 1.2  and or less that 12” of spacing between the rows of In-Drains, are considered experimental systems under Chapter 18 of the Maine Rules. Installations on some sites may result in reduced capacity due to mounding and /or the hydraulic capacity of the site. Special care must be given on sites with Al, All, D or E conditions.

1.6 Depth to seasonal Ground Water Table: Maine rules require 12”,18” or 24” from disposal bed bottom to MLF depending on Design Class and depth to ledge. Eljens conservative leach field design specifies a receiving sand bed layer (level to within 1/2 inch) directly beneath the In-Drain assembly as shown in Figures 3,4, and 5. The bottom of the disposal area is the bottom of the In-Drain unit. The vertical separation from the bottom of the In-Drain unit to the MLF shall not be less than 18”. In-Drain’s low profile results in a system finished grade comparable to or lower than conventional disposal fields.

1.7 Sand and Fill Specifications:

a.   The first 6” directly beneath the In-Drains shall be a medium to coarse sand, with an effective size of 0.25 to 2.0 mm, no greater than 5% passing a #200 sieve, and no particles larger than 3/4 inch; or materials meeting the ASTM C-33 specifications. Washed concrete sand easily meets the above specification and is a reliable choice. Suitability of bank run sand must be verified.

b.   Fill material for raised systems shall meet the requirement of Section 804.0 of the Maine Rules. Fill must be consolidated (stabilized) in lifts to prevent differential settling. Do not use any type compactor.

1.8 Lined Disposal Fields: Disposal fields for very permeable shoreline sites must comply with Chapter 16 of the Maine Rules. Place lining material at required depth followed by a 6" sand bed as described in Section 1.7 of this manual.

1.9    Distribution Pipe Layout: Perforated 4” diameter pipe is placed on top of In-Drain units with holes at 5 and 7 o’clock and secured by Eljen provided wire clamps (hoops). Pipe runs perpendicular to the In-Drains fins and lines up with the stripe painted on the top of the units. Use solid pipe over sand and perforated pipe only over the In-Drains. Refer to Figure 2 for typical pipe layouts. Eljen strongly recommends SDR 35 pipe and fittings as to assure against crushing during backfill. Systems with excessive wheel loading require Schedule 40 depending on design specifics.

1.10  Connection to Distribution Box: Install 4” solid pipe at a minimum 1/8” per foot slope between the end of the In-Drains and the D-Box. Place D-Box on well compacted sand or gravel to prevent settling and effects of frost heaving. Level gravity flow systems may use flow equalizers or other approved equal distribution devices.

1.11   Septic Tank Filters: Eljen strongly recommends the use of septic tank filters and septic tank in series or duel compartment tanks. This is a means to prevent excess solids leaving the septic tank due to lack of owner maintenance.

1.12   System Venting: It is strongly recommended to vent the following systems: Pumped systems, systems over 18” below finished grade, systems beneath paved or any surface condition that would not allow for surface air exchange with the system or areas subject to compaction, such as livestock, patios, and areas with vehicle traffic.

1.13   Geotextile Antisiltation Cover Fabric: Geotextile filter fabric, provided by Eljen, is placed over the top and sides of In-Drain rows to prevent long term siltation and failure. Fabric must drape slightly outward at distribution pipe to prevent blocking holes.

1.14   Backfill and Seeding: Place a minimum of 8” of clean backfill material per section 804.2 of the Maine Rules plus at least 4” of cover material per Maine Rules section 804.2.6 over the In-Drain assembly. Backfill must be free of large rocks that would damage distribution pipe, cover fabric or In-Drain units. All other required fill shall meet the requirements of Section 804.2 of the Maine Rules. Topsoil should be seeded and protected from erosion per the Maine Rules.

1.15  Optimum Leach Field Geometries: The optimum leach field layout for systems is I or 2 rows of Standard In-Drains running along contour lines. Cluster geometries provide the best solution for leach systems requiring fill. Longer narrower proportions are preferred to more square geometries, so as to increase system hydraulic capacity. This can be particularly important for large systems in slow percolation sites and in level areas with high ground water table. Refer to Table 1 and Figure 1 for several design examples.

1.16  System Grading & Erosion Control: Grading in the leach bed area during construction and upon completion must divert surface runoff from buildings, parking areas and nearby sloped terrain. Grade bed area in level systems at a minimum 3% prevent surface ponding.

1.17  Vehicular Traffic: While not generally recommended for subsurface disposal systems, In­Drains can be used under drive and parking areas with proper thickness and quality of fill. Typical design requires 24” of compacted and properly graded material. Distribution pipe with at least SDR35 rating is required. Systems can easily be engineered to handle H20 loading. Please consult with Eljen’s Maine technical representative for design subject to vehicular traffic.

2.0 Systems for Level Sites  

2.1 System Configuration: Level systems layout may employ all leach field configurations. Bottom of systems, In-Drains and distribution pipes are installed level at their design elevations. Flow equalizers are recommended in non-pumped systems using distribution boxes. Non perforated interconnecting pipes between rows of In-Drains at midpoints (in systems over 40’ long) and at ends to form pipe loops to insure long term system capacity. Refer to Figures 2 & 3 for section and plan views of in-ground and raised bed designs.

2.2  In-Ground Systems: The First 6” of material directly under and 9” beside the In-Drains must conform to Section 1 .7a of this manual.

2.3  Raised Systems: Fill material used in raised systems must conform to Section 1 .7a and 1 .7b of this manual.

3.0 Systems for Sloped Sites  

3.1 System Configuration: Sloping sites are best served by serial distribution with In-Drain cluster or trench layouts. Field sizing is the same as for level systems. A securely anchored distribution box is recommend between the septic tank and the leach areas as an access port and for flow velocity reduction.

3.2 Cluster Row Spacing: Minimum spacing between adjacent rows of In-Drains is 12” for sites with 0 to 15% slope. Sites with over 15% slope should have minimum spacing of 24” between rows.

3.3  Distribution piping: The distribution pipe is capped at the end of each row of In-Drains Overflow in achieved by placing an end-capped length of perforated pipe (minimum of 10’ or 50%of the In-Drain row length which ever is longer) at the end of each row next to the distribution pipe and connecting it with solid pipe to the next lower elevation row of In-Drains as shown in the Eljen Installation Instruction sheet. This procedure continues until the end of the last row of In-Drains. Refer to Figure 5 for sloped field design and section detail of over flow pipe.

3.4 Sand and Fill Specifications: Fill material, sand bed bottom and backfill are the same as in level systems. 

4.0 Combination Systems  

4.1 Dosing: Use an appropriate dosing device to assure proper effluent distribution to each field. If standard distribution boxes are used, anchor them adequately on stable compacted fill or place on a concrete pad not subject to frost heaving. The use of flow equalizers are recommended to provide the same effluent volume to each serial leach field. Refer to Figure 5 for combination system detail.    

5.0 Commercial Systems  

5.1 System Sizing: Sizing Table #1 for Standard In-Drains apply for commercial and non­commercial systems. Table 501.2 of the Maine Rules is used to determine design flow for various commercial facilities. Site specific loading conditions as well as expected maintenance levels must be factored into final system size.

5.2 Problem Effluents: Commercial systems for the food service industry shall employ serviceable grease trapping to limit excess grease from the main leach field. Eljen requires installing a grease trap filter in the waste stream. Commercial laundry effluent can contain large quantities of suspended solids, which will quickly clog a leach field. Prefiltering is also required here. Other problems effluent situations include milk product plants, service stations, slaughterhouses and rendering plants. Contact Eljen’s Maine Distributor for additional recommendations on designs for problem effluent and filter type.

5.3 Multiple Tanks: Multiple septic tanks in series or compartmentalized tanks are also recommended as a method of extending leach field life. Frequency of pumping of septic tanks and grease traps should be consistent with maximizing leach field life.

5.4 Ground Water Mounding: Disposal systems can produce ground water mounding in poorly drained sites, particularly those over 1000 GPD. Designers should avoid square leach field geometry. Maximize the leach field perimeter and place the short dimension of the leach field in the direction of the subsurface water gradient. The long dimension should follow the contour lines. Longer more narrow geometries produce the least ground water mounding. Level sites also require longer more narrow goemetries in order to maximize radial dispersion of effluent.

6.0 Pumped Systems  

6.1 Pump to Distribution Box: Please specify an oversized distribution box for pumped systems. Provide velocity reduction in the D-Box with a tee or baffle. Set D-box invert 2” higher than invert of perforated pipe over In-Drain units. Do not use equalizers or other restriction devices in the outlet lines of the D-box.

6.2 Dosing Design Criteria: Use a maximum of 4 gallons per dose per Type B In-Drain in the system. Adjust pump gallons per minute and run time to achieve the above maximum dose. Use a minimum pump run time of one (1) minute. Longevity of currently available effluent pumps is not effected by shorter run times. Choose force main diameter to minimize percentage of dose drain back. Effluent velocity in force main should fall between approximately 3 and 5 ft/sec. Pump flow rate shall be less than 30 G.P.M. in residential systems. Design for 5-6 doses per day. Dosage should be 30-60 gallons per dose on a residential system.

6.3 Pressure Distribution: Dosing with small diameter pressurized laterals is not recommended. No system reduction is allowed.

TABLE 1