Section 310.921  Substantial Modifications Defined

Substantial modifications include the following types of modifications:

a)         Modifications that relax POTW legal authorities (as described in Section 310.510(a)), except for modifications that directly reflect a revision to this Part or to 35 Ill. Adm. Code:  Subtitle C, and are reported pursuant to Section 310.923;

b)         Modifications that relax local limits, except for the modifications to local limits for pH and reallocations of the maximum allowable industrial loading of a pollutant that do not increase the total industrial loadings for the pollutant, which are reported pursuant to Section 310.923.  For this Section, "maximum allowable industrial loading" means the total mass of a pollutant that all industrial users of a POTW (or a subgroup of industrial users identified by the POTW) may discharge pursuant to limits developed under Section 310.210;

c)         Changes to the POTW's control mechanism, as the control mechanism is described in Section 310.510(a)(3);

d)         A decrease in the frequency of self-monitoring or reporting required of industrial users;

e)         A decrease in the frequency of industrial user inspections or sampling by the POTW;

f)         Changes to the POTW's confidentiality procedures; and

g)         Other modifications designated as substantial modifications by the Agency on any of the following bases:

1)         The modification could have a significant impact on the operation of the POTW's pretreatment program;

2)         The modification could result in an increase in pollutant loadings at the POTW; or

3)         The modification could result in less stringent requirements being imposed on industrial users of the POTW.

BOARD NOTE: Derived from 40 CFR 403.18(b) (1997), as amended at 62 Fed. Reg. 38414 (July 17, 1997).

(Source:  Amended at 47 Ill. Reg. 5083, effective March 23, 2023)