3 Stormwater System Mapping
A copy of the existing storm system map 1s provided in Appendix B.
The City of Nashua has managed a GIS system since 2000, which has been continuously updated to
reflect up to date stormwater system information. Nashua’s GIS Specialist within the Division of Public
Works 1s responsible for updating the stormwater system mapping pursuant to the 2017 MS4 Permit.
The City of Nashua will report on the progress towards completion of the storm system map in each
annual report. The most up-to-date map can be found at the following link:
https://newegis.nashuanh.gov/NashuaNH/default.aspx.
The MS4 Permit requires the storm system map to be updated in two phases as outlined below.
3.1 Phase IMapping
The City has completed all Phase I Mapping requirements, as listed below:
e Outfalls and receiving waters (previously required by the MS4-2003 permit)
e Open channel conveyances (swales, ditches, etc.)
e Municipally owned stormwater treatment structures
e Water bodies identified by name and indication of all use impairments as identified on the most
recent EPA approved Massachusetts Integrated List of Waters report
e Initial catchment delineations. Topographic contours and drainage system information may be
used to produce initial catchment delineations.
3.2 Phase II Mapping
The City has completed the following Phase I] Mapping requirements:
e¢ Outfall spatial location (latitude and longitude with a minimum accuracy of +/-30 feet)
e Pipes
e Manholes
© Catch basins
e Municipal Sanitary Sewer system (if available)
e Municipal combined sewer system (if applicable).
Phase II mapping must be completed within ten (10) years of the effective date of the permit July 1,
2028) and include the information per Part 2.3.4.5.b of the MS4 Permit. Still outstanding as part of the
Phase II Mapping requirements 1s the following:
e Refined catchment delineations. Catchment delineations must be updated to reflect information
collected during catchment investigations.
Hic it Discharge Detection and Himination Plan 7
