SECTION 13222 FILTER UNDERDRAIN SYSTEM

SECTION 13222
FILTER UNDERDRAIN SYSTEM


PART 1 - GENERAL

1.1     WORK INCLUDED

A.   Provide and install as described herein and as shown on the Drawings, filter underdrain systems.
Work shall include all equipment, material and labor required to complete the necessary filter underdrain systems.

1.2     RELATED WORK

A.   Division 3 - Concrete.

B.   Section 13223 - Filter Disinfection. C.   Section 13226 - Filter Media.
1.3     SUBMITTALS

A.   The manufacturer of the filter underdrain system shall submit to the Engineer for review the test records from an independent hydraulic laboratory that demonstrates the equalization of
backwash flow from the underdrains at conditions at least equivalent to the pattern shown on the
Drawings.

B.   The manufacturer shall also submit samples of the following components for review and approval by the Engineer. The Engineer's approval shall be received prior to product shipment.
1.    One (1) lateral block.
2.    One (1) center flume block.
3.    One (1) end flume block.
4.    One (1) "U" anchor rod.
5.    One (1) section of IMS cap material.

C.   The underdrain manufacturer and installation contractor shall have a minimum of five (5) year's experience on similar designs and installations of filter underdrain systems.

1.4     REFERENCES

A. ASTM-C-112. B. ASTM-C-497. C.   ASTM-C-67.

PART 2 -  MATERIALS

2.1     UNDERDRAIN

A.   The underdrain system for the filters shall be a dual parallel lateral type with a media support
cap whereby feeder and compensating chambers are provided within the cross section of a single block. The cross section of the underdrain shall be so arranged that the feeder (or primary) chamber is adjacent and connected to a compensating (or secondary) chambers through a series of orifices.  The orifices shall be located at four different elevations and sized to provide
uniform distribution of water. All internal orifices shall be integrally molded to provide a smooth bore orifice. The primary chamber should provide at least 30 square inches of cross sectional area per block to reduce flow velocity during backwash.
B.   The compensating chambers shall provide the essential uniform pressure and flow distribution from the top of the blocks. The discharge flow from the top of the blocks into the filter bed shall be provided by approximately twenty-three dispersion orifices per square foot of filter area.  The orifices shall not be less than 7/32 inch diameter to prevent clogging and shall be recessed from the surface by approximately 1/8 inch. The top of each orifice shall be encircled by a depression approximately 3/8 inch x 3/4 inch, which shall act to prevent the gravel support media from resting directly on the thereby blocking the dispersion orifice.

C.   The underdrain shall have a horizontal flat top discharge surface, so that the finished filter bottom is essentially flat, with above stated dispersion orifices for uniform energy intensity of water coverage which direct flow vertically for effective penetration and cleaning of the media.

D.   A water recovery channel with return holes shall be incorporated into the top of the underdrain block to ensure uniform and flow from the top deck orifices.

E.   The secondary chambers of the underdrain shall be baffled.

F.   The individual blocks used in the system shall be of impervious high strength, completely corrosion-resistant, high-density polyethylene (HDPE) material.  The blocks shall be resistant to erosion and corrosion and have uniform smooth surfaces.

G.   The block size and weight shall permit ease of handling and installation. The block nominal dimensions shall be 8 inches high by 11 inches wide by 48 inches long. The weight of the block shall be approximately 19 pounds.

H.   When subjected to a flow rate of 20 gpm/sf of filter area the headloss through an underdrain lateral 40 feet long shall not exceed 36 inches water column when the water temperature is approximatlely 60B  F. This does not include head losses for special feed arrangements.

I.    To ensure the underdrain will control distribution (limit maldistribution) and not be over- powered by the media headloss, the minimum headloss through the orifices (primary and secondary) of an individual underdrain block shall not be less than 20 inches water column at a backwash flow rate of 20 gpm/sf of filter area when the water temperature is approximately 60B F.

J.    The blocks shall be arranged end-to-end and mechanically joined to form continuous underdrain laterals approximately equivalent tot he length of the filter cell. The joints shall be gasketed, bell and spigot type with internal alignment tab for proper joint alignment, and be air and water-tight. Joints shall be of snap-lock type so that the blocks are joined with integral interlocking snap lugs and receptors for ease of assembly and installation of the laterals.

K.   A media support cap shall be constructed of HDPE plastic beads sintered together and sealed to the top of the underdrain. The pore size and pore volume shall be sufficient to prevent the media from obstructing or passing through the underdrain.  The Cap shall replace the need for support gravel and shall not increase the underdrain height by more than 1 inch. The cap shall be attached to the underdrain at the factory by type 316 stainless steel self tapping screws and
sealed with caulking.

2.2     REQUIREMENTS

A.   The filter underdrain system shall be designed to operate under the following conditions:


Number of filters 2  
Filter Size, sq. ft. 175  
Filtration Rate, Design, gpm per sq. ft.
(one filter out of service) 5.0  
Water only Backwash Rate, gpm per sq. ft. 20
B.   All material used in contact with the water shall meet National Sanitation Foundation (NSF) Standard 61.


PART 3 -  EXECUTION

3.1     INSTALLATION

A.   The underdrain system shall be a standard product of a filter manufacturer who has been actively providing dual-parallel lateral underdrain equipment for at least 10 years. Upon request, the
filter manufacturer will provide the Engineer with a list of installation of underdrain.

B.   The filer manufacturer shall, at their own facilities, if requested by the Engineer, set up a test lateral run of equal length to that required by the project and provide an opportunity for the Engineer and/or Owner to visit the facility to witness a full scale demonstration of the headloss and flow distribution during backwash.

C.   The Contractor shall provide the services of the manufacturer=s technical representative for not less than 4 working days to inspect and supervise the installation and testing of the filter underdrain system in 2 trips.

D.   The Contractor shall install the filter underdrain system in strict accordance with: (1) the manufacturer=s written instructions and recommendations and the manufacturer=s installation drawings; (2) the oral and written directions provided the manufacturer=s technical representative who is supervising and observing the work; and (3) any additional requirements specified herein.

E.   Care shall be exercised in preparing the filter floor slab and in setting the anchors to assure proper alignment and elevation. Steel anchor rods shall be furnished by the filter manufacturer and set in the floor slab on both sides of the distribution flume in accordance with the drawing provided.  The floor slab shall be screeded into a flat level plane and be free of protrusions and depressions.

F.   The underdrain laterals shall be set in relatively level rows on a bed of grout over the filter floor slab. Plates for closing the ends of each row of blocks shall be furnished by the filter manufacturer and installed by the Contractor. After joining, aligning and setting the blocks, and the bed grout is set-p, as soon as possible, all spaces between the rows of blocks and walls shall be filled with grout so that the entire bed is totally sealed and held firmly in place. Once all grouting is complete, the grout shall be allowed to cure for at least 3 full days before functional testing.

G.   The Contractor shall take all precautions recommended by the underdrain manufacturer or specified herein to ensure that the filter system and any piping communicating therewith is completely clean and free of any debris, dirt, or other foreign materials which could clog the underdrain system or interfere with flow. Backwash water piping shall be thoroughly flushed clean. All loose debris and dirt within the filter cell and flume shall be removed by brooming down and vacuuming. Care shall be taken to keep grout from being deposited anywhere where it could interfere with flow. Any grout so deposited shall be removed. As installation progresses, partially completed portins of the work shall be protected with heavy visqueen or other suitable material to maintain the cleanliness of the underdrain system.  Such protection shall be maintained until the media is installed.