Smart Planning
Integrating GIS and Mapping to Manage Wastewater Collection Systems
Many New England communities are starting to see more stringent collection system mapping and O&M requirements within their NPDES discharge permits. Between national market drivers such as CMOM, GASB-34 and Asset Management, and regional market drivers through the state regulatory agencies, communities are tasked with compliance with these new requirements with limited resources. A major component of compliance centers is knowing where and what collection system assets exist which need to be maintained in the community. GIS mapping is an excellent tool that many communities and districts use to manage their collection systems and comply with the more demanding regulatory requirements.
Understanding NPDES Requirements
Recent draft and final NPDES discharge permits have very specific collection system mapping and O&M requirements with specific deadlines for adherence. The core of the O&M requirements deal with maintenance staff, preventative maintenance programs, infiltration and inflow control, and developing a collection system O&M plan. Most of the O&M plans need to be finalized within 6 months of permit issuance. Each of these items is directly influenced by the size of the collection system and requires a detailed knowledge of the collection system assets. Because knowledge of the collection system is so closely tied to O&M of the collection system, many NPDES permits have additional mapping requirements.
NPDES Mapping Requirements
Wright-Pierce has noticed a trend in the mapping requirements found in recent NPDES discharge permits. In general, the permits require that mapping show the following:
- All sanitary sewer lines and related manholes
- All combined sewer lines and related manholes
- All combined sewer regulators
- All outfalls
- All pump stations and force mains
- All surface waters
- Other major structures (inverted siphons, air release structures, etc.)
- Numbering system to identify major structures
- Pipe information including diameter, age, type, length, direction of flow,
and invert and rim elevations
Most permits require that mapping be completed within three years of permit issuance.
GIS Mapping for Collection Systems
The first step in creating a GIS is to gather all existing information, such as record drawings and institutional knowledge. Local staff with knowledge of the system can markup preliminary maps or copies of the record drawings. Technicians scan paper drawings and georeference them, or orient them to a base map. This allows users to overlay the drawings on other information, such as aerial photography.
The mapping may require field work, such as locating and opening manholes. However, if a community has detailed orthophotos (aerial photography) and comprehensive record drawings, field work may not be necessary. The next step is to digitize the collection system. In other words, technicians draw pipes, manholes, and other features in the GIS. Each pipe or manhole has information associated with it, such as pipe diameter, material, and year of installation. At the same time, the technicians can create a simple network model in the GIS, which automatically determines flow directions and ensures that there aren’t gaps in the data.
With the resulting GIS, users can print a variety of maps, including wall maps and portable map books. The GIS can also be linked to other data, such as scanned manhole inspection forms, pipeline videos, or a work order database. Beyond satisfying mapping requirements, the GIS will be a helpful tool for maintenance and capital planning.