1. (a) GAC filter-adsorber. GAC filter-adsorbers utilized by replacing media in an existing filter, capping an existing filter, or by the installation of a new filter-adsorber are allowed. Some of the sand can be replaced in a single media filter or the coal in dual or mixed media filters with GAC.

   1. (1) When adding GAC to existing filter media, provide a minimum of 15 inches of GAC.
   2. (2) When using GAC as a single media, provide a total depth of 30 to 36 inches.
   3. (3) Filter media must be 12 x 40 mesh (effective size of 1.68 to 0.42 mm) or 8 x 30 mesh (effective size of 2.38 to 0.60 mm) with uniformity coefficient of 1.3 - 1.9.

2. (b) Adsorption with GAC.

   1. (1) A pilot study is required to determine the following design information:

      1. (A) adsorption isotherm of the contaminants to be removed,
      2. (B) type, size, and adsorptive characteristics of the GAC to be utilized in the adsorber,
      3. (C) type, dimensions and configuration of adsorbers, i.e. the number, sequence, and arrangement of the separate GAC contactors,
      4. (D) location of the adsorber(s) in the water treatment process,
      5. (E) superficial (approach) velocity,
      6. (F) minimum empty bed contact time for removal of contaminants to meet regulatory limits,
      7. (G) bed depth of GAC in adsorber(s), and
      8. (H) service time of adsorber(s).
   2. (2) Contactor type and number. Downflow contactors are the only acceptable type for water treatment applications. Where only 2 units are provided, each must be capable of meeting the maximum daily demand. Where more than 2 units are provided, the contactors must be capable of meeting the design capacity with 1 or more units removed from service.
   3. (3) Media. The carbon media must meet current AWWA Standards for GAC. The particle size must be 12 x 40 US Standard mesh (1.68 x 0.42 mm) with uniformity coefficient of 1.9.
   4. (4) Backwashing. Provide provisions for backwashing unless the adsorber does not function as a filter and is designed as a replaceable unit. If the source of water for backwashing is the public water supply, proper cross-connection protection must be provided. Disposal of backwash water must be in a manner approved by DEQ.

Added at 18 Ok Reg 1612, eff 6-1-01