ON-LOT SEWAGE DISPOSAL PROGRAM DESIGN OF PRESSURE-DOSED ELEVATED SAND MOUND BED

Transcription

1 ON-LOT SEWAGE DISPOSAL PROGRAM DESIGN OF PRESSURE-DOSED ELEVATED SAND MOUND BED INSTRUCTIONS In order to design an elevated sand mound bed using pressure dosing which meets Pennsylvania Department of Environmental Protection (DEP) standards as set forth in Chapter 73 of the Sewage Facilities Act, the following information must be determined and incorporated into detailed plans for the system. In addition to the attached information, a complete design must also include the following: 1. Plot plan showing the elevated sand mound in relation to your property and associated features such as the approved test site, house, driveway, wells, property lines, easements or rights-ofway, streams, ponds, etc. 2. Detail of sand mound indicating manifold and lateral placement, and hole spacing. 3. Cross-section of the sand mound, including depths of sand, aggregate, and soil cover. 4. Septic tank specifications. 5. Dosing tank detail. 6. Pump performance curve. PLEASE SUBMIT TWO (2) COPIES OF THE COMPLETE DESIGN. ONE COPY OF THE APPROVED DESIGN WILL BE RETURNED TO YOU AND THE OTHER WILL BE RETAINED IN OUR FILES. Contact your ACHD Sewage Enforcement Officer for help should you need it. 336-CS-0498

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3 Page 1 APPLICANT NAME PERMIT APPLICATION NO. SITE ADDRESS MUNICIPALITY 1. BED DESIGN Based on your percolation rate of minutes per inch and the minimum daily flow set for a proposed bedroom house of gallons per day, the minimum size absorption area required for the elevated sand mound bed would be square feet. Any bed dimensions that give this square footage are acceptable, although a longer, narrower design is easier for the installer to construct, the finished system is more readily landscaped out of view, and generally less sand is required than with a more square shape. Square feet of absorption area Feet wide x Feet long Laterals, each ft. long, 1.5 inch in diameter Holes per lateral, 1/4 inch in diameter with spacing as shown. The first hole of a lateral is 3 feet from the manifold. Additional holes are placed 6 feet on center with the last hole placed directly in the end cap. Laterals are on center from each other Manifold pipe is feet long, inches in diameter. 2. MINIMUM CAPACITY OR FLOW RATE OF THE PUMP Pump capacity equals the total number of holes in the laterals x 0.75 gallons per minute (gpm). Laterals x holes per lateral = total number of holes Holes x 1.28 = gallons per minute 3. TOTAL HEAD REQUIRED FROM THE PUMP Total head is a combination of 3 factors: 1. Head level to be maintained at the end of the laterals (always 3 feet for standard distribution systems) 2. Friction loss within the system

4 Page 2 3. Elevation change between the pump and the distribution manifold. A. HEAD LEVEL Head level to be maintained = 3 feet. B. FRICTION LOSS Friction loss depends on the rate of flow and the diameter of the pipe. Table IX-2 lists various diameters of plastic pipe and the head loss / 100 feet of pipe occurring at flow rates from 1 to 400 gpm. Table IX-2 shows a head loss of feet per 100 feet of inch diameter pipe at your pump flow rate of gallons per minute. Next, the length of pipe from the pump to and including the manifold must be calculated. Most important, before you arrive at a figure for the length of pipe from the pump to the manifold, you must determine exactly where on your lot the dosing tank for the pump will placed: Mark this spot with the stake for future reference: Next, stake off the site of the proposed absorption area. NOTE: Placing the dosing tank as close to the site of the absorption area as possible will minimize friction loss, thus allowing for the use of a less expensive pump. However, to avoid disturbing the soil downslope of the absorption area when installing the delivery pipe, do not place the dosing tank directly downslope from the mound. Also, do not place the dosing tank within the berm area of the sand mound. Length of pipe from pump to and including manifold = feet. If the delivery line connects to the manifold in the center, count only half the length of pipe used to make the manifold. For purposes of calculating friction loss, the total length of pipe includes not only the lineal lengths of pipe, but the equivalent lengths for the various fittings used in the delivery pipe. Consult table IX-3 for equivalent lengths of plastic pipe for fittings.

5 Page 3 List all fittings used in the delivery pipe and next to each fitting list the equivalent length of plastic pipe indicated in Table IX-3. Do not include couplings used to form the laterals, or fittings used to connect the laterals to the manifold. A check valve is prohibited on the delivery pipe. Add up all the equivalent lengths for the fittings: 90E elbow(s)... feet 45E elbow(s)... feet Standard Tee... feet Coupling(s)... feet Quick Disconnect... feet TOTAL EQUIVALENT LENGTH OF FITTINGS = FEET Now add the length of pipe and the total equivalent length of fittings. Total length of pipe and equivalent lengths of fittings = feet. Last, total friction loss = Total pipe length x Friction loss / 100 ft. pipe 100 feet x 100 / 100 ft. pipe Friction loss = feet

6 Page 4 C. ELEVATION CHANGE In order to determine elevation change, consult the attached diagram 1. Depth to bottom of dosing tank * = feet 2. Elevation change from A to B ** = feet 3. Subtotal (1 and 2) = feet 4. Required depth of sand = feet 5. Aggregate beneath manifold = feet 6. Subtotal ( ) = feet 7. Elevation of pump above tank bottom = feet 8. Total elevation change (6 minus 7) = feet * If the depth of the tank commonly used in the area is known, use that depth; otherwise use 7 feet. ** If the slope from A to B is uphill, add steps 1 and 2; if the slope from A to B is downhill, subtract step 2 from step 1; where both A and B are the same elevation, insert 0" in step 2.

7 Page 5 TOTAL HEAD REQUIRED FROM PUMP Add up the following to determine the total head the pump must overcome when delivering liquid to the system. A. Head level to be maintained feet B. Friction loss feet C. Elevation change feet Total head to be maintained = feet Submit along with your detailed plans for a pressure dosed elevated sand mound bed, a performance curve for the specific pump you plan to use in the system. The curve for your pump must show that it will provide a minimum gallons per minute when operating at feet of head. Refer to next page to determine the Minimum Dose Volume, the Minimum Dose Tank Capacity, and the Float Spacing needed to provide the minimum dose volume. MINIMUM DOSE VOLUME Minimum dose volume equals five times the internal liquid capacity of the delivery pipe, manifold, and laterals, or 100 gallons, whichever is greater. The dose volume is the amount of liquid discharged to the absorption area each time the pump operates. Liquid Capacity of Piping Length of: (in feet) A x B = C Diameter Delivery Pipe Manifold Laterals Total Gal / Ft Gallons 1.5 inch inch inch 0.37 Total Gallons *Delivery pipe length includes all piping from the pump outlet to the manifold connection. Total Gallons x 5 = Minimum Dose Volume (gallons) (if less than 100 gallons, use 100 gallons as a minimum dose volume)

8 Page 6 DOSE TANK CAPACITY Minimum Dose Tank Capacity equals two times the designed dose volume plus sufficient space for electrical connections and proper pump control operation. Minimum Dose Volume x 2 = + (space for wiring) Minimum Dose Tank Capacity (gallons) PUMP CONTROL SETTINGS The pump control floats must be spaced to provide the required minimum dose volume. Always use the inside dimensions of the dosing tank when calculating the following: Gallons per Vertical Inch of Tank Depth If using a circular tank: [diameter (inches) ] = Gallons per Vertical Inch of Tank Depth [ inches ] 2 = Gallons per Inch If using a rectangular tank: width (inches) x length (inches) = Gallons per Vertical Inch of Tank Depth 231 (inches) x (inches) = Gallons per Inch 231 Distance Between Pump On / Off Settings Minimum Dose Volume Gallons per Vertical Inch of Tank Depth = Inches per Dose Min. Dose Gallons per Vertical Inch = Inches per Dose