Finance Committee

Hic it Discharge Detection and Eimination Plan

12

e Historic combined sewer systems or sewer conversion — Contributing areas that were once
serviced by a combined sewer system but have been separated and contributing areas that were
once serviced by septic systems but have been converted to sewer connections may have a high
illicit discharge potential. Separated systems were assigned a level value of 3, converted systems
were assigned a level value of 2, and areas still on septic were assigned a 1.

e Determined by the permittee as high priority based on the characteristics listed in
Appendix C.

4. Low Priority Outfalls: Outfalls determined by the permittee as low priority based on the
characteristics listed below or other available information.

5 Assessmentand Priority Ranking of Outfalls

The MS4 Permit requires an assessment and priority ranking of outfalls in terms of their potential to
have ilicit discharges related public health significance. The ranking helps determine the priority order
for performing IDDE investigations and meeting permit milestones.

5.1 Outfall Catchment Delineations

4 Sanitary Sewer Overfiows (SSOs)

3 Stormwater System Mapping
A copy of the existing storm system map 1s provided in Appendix B.

2 Authority and Statement of IDDE Responsibilities

2.1 LIegal Authority

As part of the Nashua Revised Ordinances (NROs), the City adopted a Stormwater Management
ordinance in 1998 to address runoff from sites being developed or redeveloped. Since then, the
ordinance has been reviewed and revised to incorporate requirements of the 2003 MS4 Permit and
address other necessary language modifications. Through the City Charter and Nashua Revised
Ordinances, adequate legal authority 1s provided to:

e =Prohibit ilicit discharges

Figure 1-1. IDDE Investigation Procedure Framework

Inventory and Eryn yssarenc Follow-Up

eee a Ole arll

Rank Outfalls (e-| cea ae Screening

i an or an on ae |

System has
been fully

via A ee vialely eed ees Remove lllicits

poll d et =d ay alt Investigations

Investigated

Table 1-1. IDDE Program Implementation Timeline

Completion Date from Effective Date of Permit
IDDE Program Requirement

1 Year 1.5 Years | 2 Years 3 Years 7 Years 10 Years

Written IDDE Program Plan XxX

Some illicit discharges are related to the unsuitability of original infrastructure to the modern regulatory
environment. Examples of illicit discharges in this category include connected floor drains in old
buildings, as well as sanitary sewer overflows that enter the drainage system. Sump pumps legally
connected to the storm drain system may be used inappropriately, such as for the disposal of floor
washwater or old household products, in many cases due to a lack of understanding on the part of the
homeowner.

1 IDDE Program Implementation Tim e line

11 MS Pogrm

This Illicit Discharge Detection and Elimination (DDE) Plan has been developed by the City of
Nashua to address the requirements of the United States Environmental Protection Agency’s (USEPA’s)
2017 National Pollutant Discharge Elimination System (NPDES) General Permit for Stormwater
Discharges from Small Municipal Separate Storm Sewer Systems (MS4) in New Hampshire, hereafter
referred to as the “2017 New Hampshire MS4 Permit” or “MS4 Permit.”