(a) Wastewater systems utilizing advanced pretreatment with a DDF less than or equal to 1,500 gpd may only use one of the following modifications to system siting and sizing criteria, unless otherwise identified in this Rule:

• (1) reduction in depth to LC or vertical separation to LC in accordance with Paragraph (b) of this Rule;

• (2) LTAR increase in accordance with Paragraph (c) of this Rule; or

• (3) setback reductions in accordance with Paragraph (d) of this Rule.

(b) The minimum required vertical separation to a LC in natural soil may be reduced with the use of advanced pretreatment in accordance with Table XXVI. Table XXVII provides the minimum depths and vertical separation for new and existing fill. A special site evaluation shall be submitted and approved in accordance with Rule .0510 of this Subchapter when a reduction in vertical separation to a LC is proposed in accordance with this Rule.

(c) The LTAR shall be based on the effluent standard and dispersal field type proposed in accordance with the following:

• (1) The LTAR may be increased by the following factors when compared to the rate assigned by the authorized agent for a new system using DSE:

  • (A) up to 1.33 for NSF/ANSI 40 effluent standards in soils which are Group I or II with suitable structure;

  • (B) up to 2.0 for TS-I or TS-II effluent standards when pressure dispersal is utilized; or

  • (C) up to 2.5 for TS-II effluent standards when all the following conditions are met: minimum of 36 inches of Group I soils from the naturally occurring soil surface; minimum depth to a SWC below the naturally occurring soil surface is 24 inches; space shall be available for an equivalently sized dispersal field repair area; and pressure dispersal shall be utilized.

• (2) A special site evaluation, if required in accordance with Rule .0510 of this Subchapter, shall be submitted and approved.

• (3) The LTAR for an aerobic drip system shall be determined in accordance with Rule .1204 of this Section.

• (4) Trench dispersal products approved for a specific dispersal field reduction in area or trench length when receiving DSE in accordance with this Subchapter or a PIA Approval shall not be reduced by more than 50 percent when any LTAR adjustments are taken in accordance with this Rule.

• (5) When using pressure dispersal systems, the proposed LTAR increases in Subparagraph (c)(1) may be used concurrently with the reduced setbacks for TS-II Systems in Table XXVIII.

• (6) The DDF shall not be increased by the addition of advanced pretreatment to an existing wastewater system by more than 33 and one-third percent on a site without repair area or by more than 50 percent on a site with 100 percent repair area.

(d) Advanced pretreatment systems shall meet the following setback requirements:

• (1) minimum setback requirements of Section .0600 of this Subchapter shall be met, except as shown in Table XXVIII; and

• (2) when any other siting or sizing modifications are applied, such as reduced depth to LC, vertical separation, or increased LTAR, for a TS-I or TS-II system in accordance with Paragraphs (b) and (c) of this Rule, no setback reductions shall be taken except those to artificial drainage systems described in Table XXVII, unless otherwise specified in this Section.

History Note: Authority G.S. 130A-334; 130A-335; 130A-342; 130A-343.