Ill. Admin. Code tit. 35, § 364.404 – Scoring Conventions

a) The priority system established in this Part is applied with the following conventions and general results.
b) For expansion and/or upgrading of an existing sewage treatment plant, a new sewage treatment plant to serve a currently sewered area, or sewer rehabilitation work which will eliminate excessive infiltration/inflow, the MDI value for the plant, together with the F4 value for the treatment processes affected at the plant are used to calculate the GPI value for the need. For sewer rehabilitation projects "treatment processes affected at the plant" are as follows:
1. 1) Where the sewer rehabilitation work will solve an inflow problem, the F4 value shall be determined from the existing need for provision of complying primary treatment and/or disinfection for wet weather flow in excess of maximum dry weather flow, unless additional treatment is required to meet effluent standards.
2. 2) Where the sewer rehabilitation work will solve an infiltration problem, the F4 value shall be determined from the existing need for provision of complying primary and/or secondary and/or tertiary and/or advanced and/or supplemental treatment of dry weather flow.
3. 3) Where the sewer rehabilitation work will solve an infiltration and inflow problem, the F4 value shall be determined from the existing need for provision of complying primary and/or secondary and/or tertiary and/or advanced and/or supplemental treatment of dry weather flow as well as the existing need for provision of primary and/or disinfection of wet weather flow in excess of maximum dry weather flow, unless additional treatment of the excess flow is required to meet effluent standards.
4. 4) Under (b)(1)-(3), existing need is determined using overload/no overload criteria for existing treatment processes and dilution ratio for additional processes required by effluent standards.
c) For construction of a new sewage treatment plant or improvements to existing individual sewage disposal units or a combination of the two for a currently unsewered community, since a quantifiable discharge does not exist, an "equivalent" MDI value must be calculated. For this purpose, the estimated current population equivalent of the area to be served is used in calculating F1; F2 is set equal to 1.0; and the segment to receive the proposed discharge determines F3. A significance factor to reflect the impact of the discharge on the receiving stream and public health hazards is determined as described in Section 364.206 to calculate F6. The MDI is then calculated. The treatment processes required at the proposed sewage treatment plant determine F4. The GPI is then calculated.
d) For construction of a new regional plant or expansion and/or upgrading of an existing sewage treatment plant to phase out one or more existing sewage treatment plants, the highest of the MDI values as sell as the highest of the F4 values among the values for the existing or proposed regional plant and the values for the existing plant(s) to be phased out (exclusive of non-municipally owned treatment works) are used to calculate the GPI for the regional plant.
e) For construction of a new sewage treatment plant or improvements to individual existing sewage disposal units or a combination of the two for a currently unsewered community where a discharge of raw or partially treated sewage does exist. A "discharge of raw or partially treated sewage" exists, for purposes of determining priority, if the applicant establishes that the PE (BOD) of the discharge from the sewer system is at least equal to 65 percent of the total domestic population plus 100 percent of any tributary industrial PE BOD, on the basis of no less than three samples (24 hour composite) of the discharge, collected directly from the "sewer system" outfall to the receiving stream and from comparable flow measurements of the discharge, on different days. Copies of laboratory reports must be submitted as a part of the facilities planning documents to permit a need to qualify under these criteria, and an on-site investigation by Agency representatives may be made, in which case the results of the Agency investigation will be considered conclusive for scoring purposes. Since an MDI value does not exist, an "equivalent" MDI must be calculated. For this purpose, estimated current population equivalent of the area to be served is used in calculating F1; F2 is set equal to 2.0; and the segment to receive the proposed discharge determines F3. A significance factor to reflect the impact of the discharge on the receiving stream and public health hazards is determined as described in Section 365.206 to calculate F6. The MDI is then calculated. The treatment processes required at the proposed treatment plant determine F4. The GPI is then calculated.
f) For relief intercepting sewers, where the existing intercepting sewer is not capable of transporting the flows which are presently tributary to it, proceed in accordance with Section 364.404(b) where the relief intercepting sewer is a sanitary sewer and in accordance with Section 364.404(j) where the relief sewer is a combined sewer.
g) For transport of sewage from end point(s) of existing collection system(s) to an existing or proposed regional sewage treatment plant proceed in accordance with Section 364.404(d).
h) For transport of sewage from end point(s) of proposed collection system(s) to an existing or proposed regional treatment plant or improvements to individual existing sewage disposal units or both, the calculation of the F1, F2 and F6 values proceeds similarly to that in Section 364.404(c) above. The F4 value will be selected from the larger of the values for the degree(s) of treatment which would be required at the local location of the collection system and at the regional plant. The F3 value will also be selected from the larger of the values for the basin segment containing the collection system and the basin segment containing the regional plant.
i) For construction of an intercepting sewer or improvements to existing individual sewage disposal units or both for a currently unsewered community where a discharge of raw or partially treated sewage does exist, an MDI value does not exist, and an "equivalent" MDI must be calculated. For this purpose, estimated current population equivalent of the area to be served is used in calculating F1; F2 is set equal to 1.0; and the segment to receive the proposed discharge determines F3. The MDI is then calculated. The treatment processes required at the proposed sewage treatment plant determine F4. The immediate impact of the discharge on the receiving stream and public health hazard are used as described in Section 364.206 to calculate F6. The GPI is then calculated.
j) For elimination or treatment of on-system wet weather overflow(s) from combined sewers, regardless of the approach to solving this problem or the extensiveness of the problem, the MDI for the plant currently providing service, and an F4 value of 14 (established values for primary treatment and disinfection of maximum wet weather flow) are used in the calculation of a GPI value.
k) For construction of trunk and lateral sewers where rehabilitation work not eliminate excessive infiltration/inflow, the MDI value for the plant, together with F4 and F6 values of 1, are used to determine the GPI value; therefore, GPI = MDI.
l) For construction of a complete new collection system, the GPI value will be equal to that of the proposed plant under Section 364.404(c) or intercepting sewer under Section 364.404(g).
m) For extension of service by an existing collection system, the calculation of the MDI value proceeds similarly to that in Section 364.404(d) except that in this case estimate of the existing population equivalent to be served by the sanitary sewer extension only is used in determining F1. The F4 values for this case are equal to 1, the F6 is calculated in accordance with Section 364.206. The GPI is then calculated.
n) For construction of an intercepting sewer parallel to an existing intercepting sewer, which existing sewer is capable of transporting the flows which are presently tributary to it; flood control projects; and wastewater recycling or wastewater reuse projects, the MDI value for the plant, together with an F4 value of 1 are used to determine the GPI value, therefore, GPI = MDI.