(a) Standards and guidance values shall be used to control taste-, color- and odor-producing, toxic and deleterious substances, as specified in the narrative standards for fresh and saline surface waters and groundwaters and shall be the basis of water quality-based effluent limitations and groundwater effluent limitations for use in SPDES permits issued pursuant to Parts 750-758 of this Title.

1. (1) When deriving a water quality-based effluent limitation from a surface water standard or guidance value, the department may take into account factors, including but not limited to analytical detectability, treatability, natural background levels, intermittent streamflow, wet weather events, and the waste assimilative capacity of the receiving waters.
2. (2) Where these factors indicate that achieving a water quality-based effluent limitation would be clearly unreasonable, the department may substitute a modified effluent limitation. Where the effluent limitation had been derived from an aquatic standard or guidance value, the department shall also require biological monitoring.

3. (3) A surface water effluent limitation for the total of organic substances that have a Health (Water Source) standard for surface water in Table 1 of section 703.5(f) of this Title or a guidance value for surface water derived pursuant to section 702.15(a) of this Part shall be established based on an ambient value of 100 ug/L. Where such standards or guidance values are 100 ug/L or greater, they shall not be included in the total.

   (c) Groundwater effluent limitations.

4. (1) Groundwater effluent limitations are provided in Table 3 of section 703.6(e) of this Title. For those substances not included in Table 3 of section 703.6(e) of this Title and for which a guidance value has been derived as provided in section 702.15(a) or section 702.15(f) of this Part, the groundwater effluent limitation shall be equal to the guidance value.
5. (2) When implementing a groundwater effluent limitation, the department may take into account factors, including but not limited to analytical detectability and treatability.
6. (3) Where these factors indicate that achieving a groundwater effluent limitation as set forth in paragraphs (1) and (2) of this subdivision would be clearly unreasonable, the department may substitute a modified effluent limitation.
7. (4) A groundwater effluent limitation for the total of organic substances that have a groundwater standard in Table 1 of section 703.5(f) of this Title or a groundwater guidance value derived pursuant to section 702.15(a) of this Part shall be established at 100 ug/L. However, substances that have a groundwater standard or guidance value or groundwater effluent limitation of 100 ug/L or greater shall not be included in this total.

(b) Surface water effluent limitations.