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Counties turn to GIS for NPDES solutions.

THE National Pollutant Discharge Elimination System (NPDES) regulations for stormwater discharges from municipal, separate storm sewer systems have demanded a great deal of attention from water resources managers over the past few years. Complying with the extensive requirements of the Environmental Protection Agency's stormwater permitting program during a period of tight budgets has led America's larger cities and counties to use various innovative approaches.

Geographic Information System (GIS) technology offers an excellent basis for developing cost-effective approaches to meeting the challenges presented by the stormwater permitting requirements. GIS offers a flexible platform for compiling information and developing applications needed to implement a cost-effective NPDES program.

One such GIS application is the Montgomery County, Maryland, Storm Drain Inventory System, which is currently under development for the county's Department of Environmental Protection. The inventory will combine spatial and tabular databases with a menu-driven interface to make data required for the monitoring, modeling, and management of the county's system readily accessible. This accessibility to data and ability to conduct analyses of complex data relationships on demand will prove useful to the county as it complies with NPDES requirements designed to reduce pollutant discharges from its storm sewer system.

GIS technology is not new. Some municipalities have allocated significant resources to develop GIS databases that combine spatial and tabular information. Information such as planimetric, topographic, and cadastral mapping has been combined with property ownership data, utilities information, and other data to form the infrastructure of GIS systems. This foundation provides the basis for developing GIS applications that have the potential to significantly enhance NPDES permitting efforts.

NPDES Background

Deadlines for most regulated jurisdictions to submit their two-part NPDES permit application for the storm sewer system were either November 1992 or May 1993 depending on the population served by the system. NPDES municipal stormwater discharge permits are being issued by the designated permitting agency for each state. The regulated jurisdictions now must undertake steps to comply with the specific conditions of their permits.

The NPDES regulations for stormwater discharges from medium (i.e., population greater than 100,000) and large (i.e., population greater than 250,000) municipalities required submission of various types of information with Part 1 and Part 2 of the applications, such as:

* Data on potential sources of pollution (including the locations of outfalls from the storm sewer system);

* Information to characterize the nature of pollution anticipated;

* Summaries of proposed management plans.

For Montgomery County and numerous other jurisdictions, GIS presented a natural solution to various needs while developing their NPDES permit applications. It provided a means to compile and integrate the required spatial and tabular data. It also provided a foundation to effectively utilize the information compiled to make necessary management decisions for developing plans to control pollutant discharges.

Based on information submitted with the permit applications, the designated NPDES permitting agency within each state is issuing municipal stormwater discharge permits. Although the conditions of these permits will vary widely by state and by individual jurisdiction within each state, the permits are likely to share some common characteristics.

At a minimum, permits will require jurisdictions to implement the management plans developed for the Part 2 application and to carry out additional data collection efforts to support the NPDES permit based on schedules presented in Part 2. Permit conditions could also include requirements to provide information that was not included in the jurisdiction's permit applications due to time or budget constraints.

If early permits are any indication, permit conditions for most jurisdictions are likely to be numerous and cover a wide range of topics. These conditions will set tight deadlines for the submission of studies, plans, and reports. Municipalities will likely need to invest significant time, effort, and expense to stay in compliance with the conditions of their NPDES permit.

GIS Applicability

Municipalities are increasingly turning to GIS to help them implement their NPDES programs. Because much of the data is spatial, GIS is the ideal tool to use for meaningful compilation and analysis, GIS offers the opportunity to:

* Compile disparate information into a coherent database;

* Integrate water quality models with data sources;

* Manage integrated spatial and tabular data;

* Schedule, track, and report NPDES compliance efforts;

* Provide analytical support for management decisions;

* Provide facilities management capabilities.

Numerous jurisdictions, including Montgomery County and Prince George's County, Maryland, have elected to use their GIS for NPDES permitting. These counties, which border Washington, DC on the north and east, respectively, each operate a municipal, separate storm sewer system that serves a population of over 700,000.

Over five years ago the two jurisdictions began a coordinated effort to develop GISs. Many basic components of their systems (i.e., planimetric, topographic, and cadastral mapping) are now coming on line, and the counties are committed to using GIS to help meet the requirements of the NPDES stormwater program.

Both counties are working with Greenhorne & O'Mara, Inc. (G&O), an engineering and GIS consulting firm, to prepare GIS applications in support of their NPDES initiatives. G&O is currently developing Montgomery County's Storm Drain Inventory System. G&O has also undertaken to develop a water quality modeling tool for Prince George's County. Both counties are considering additional NPDES GIS applications such as an illicit discharge investigation module and a public outreach module.

While GIS offers numerous potential benefits for NPDES permitting, exploiting these opportunities requires some initial investment. NPDES applications typically build on a GIS "infrastructure" of planimetric, topographic, property, and utility information. It may be difficult to justify the level of effort required to compile this information for the NPDES program alone if it is not already available.

If a city or county desires to use the GIS approach to NPDES permit compliance, the systems will require some custom programming to meet the specific needs and circumstances of the jurisdiction, It is difficult to find "canned" programs that will effectively meet the varied NPDES requirements of different municipalities. However, in many cases the expense of designing, implementing, and maintaining custom applications is justified by the reduced cost of managing data and the increased capabilities available from the GIS database.

NPDES/GIS Framework

The various components of an NPDES/GIS program must be developed within a coordinated framework to ensure compatibility and effective integration. Under this framework, various GIS applications can be developed as modules that interface with a central database. These applications consist of user interfaces, defined reports, links to other programs, and various analytical tools that together provide support for water quality management decisions.

Potential applications to support the NPDES program are unlimited. Some examples include:

* Storm sewer system inventory;

* Illicit discharge program planning and tracking;

* Water quality modeling;

* Water quality monitoring data storage and analysis;

* Industrial pollutant assessment;

* Public outreach planning and tracking;

* NPDES annual reports.

System Inventory

In many ways, the Montgomery County Storm Drain Inventory System is representative of potential NPDES/GIS applications. The inventory application is designed to build on existing spatial databases to provide a tool that can be used to meet basic NPDES requirements (i.e., locations of outfalls and stormwater management facilities) in a cost-effective manner while at the same time meeting other management objectives (i.e., facilities management). When completed, the application will provide a menu-driven interface to quickly access the storm drain system data required to facilitate NPDES planning.

GIS technology has an obvious application to the problem of maintaining an up-to-date storm sewer system inventory. The combination of spatial and tabular data organized in a relational database allows NPDES planners to not only know where major and minor outfalls are located, but also how these outfalls interrelate within the entire storm sewer system. This information can be combined with other information in the county's database (i.e., land use or property data) to provide support information for a variety of NPDES tasks (e.g., illicit discharge investigations). The storm drain application is being developed using ARC/INFO's Arc Macro Language (AML) and the INFO 4th generation programming language. The system will run on the county's UNIX workstations in a multi-user environment shared by the Department of Environmental Protection, the Department of Transportation, and the Maryland-National Capital Park & Planning Commission.

According to G&O's January 1994 Database Management System Conceptual Design Plan, the objectives for the inventory include: The inventory must enable the county to meet NPDES requirements through an accurate and maintainable storm drain inventory system; The inventory must conform closely to the county's existing work flow for reviewing and approving plans for the county's storm sewer system; The inventory must be compatible with the planimetric, topographic, and cadastral database already under development for the county.

Montgomery County's existing information on its storm sewer system consists of drawings maintained in five separate areas. This information includes sets of construction plans and county-wide storm sewer maps. The construction drawings include the county's own capital improvement projects as well as plans prepared for land development projects.

G&O was responsible for reviewing the various data sources and their respective index systems to compile a comprehensive map covering the county's entire storm sewer system. This spatial data was combined with information compiled from the plans on the characteristics of each component of the system (i.e., manholes, inlets), plus construction information and cross references to permit numbers.

Two basic types of components will be included in the inventory--structures and segments. The structures include: manholes, inlets, outfalls, headwalls, dry ponds, wet ponds, oil-grit separators, dry wells, and other BMPs. Segments to be added to the database include: pipes, culverts, channels, easements, and network connectors.

Most of these components are typical physical features of storm drainage systems. The exception to this, the network connectors, are logical components that, where required, connect the various components of the system to provide a continuous link along drainage paths. The connectors consist of linkages between different parts of the system either along natural stream segments or across stormwater management facilities. The network connectors will enable future development of applications that depend on the connectivity of the system (e.g., illicit discharge tracking, storm drain modeling).

The information from the inventory will be input to the GIS application to seed the database. The county will then maintain the database as new design plans are approved and additions to the system are constructed.

The storm drain inventory can be enhanced to provide a more comprehensive facilities management system in the future. The modular structure of the program provides for expansion to include inspection and maintenance data, permit processing data, field screening scheduling and tracking data, and storm sewer system sampling results.

Illicit Discharges

To illustrate how the various NPDES/GIS modules can build upon each other, consider an application to assist with illicit discharge investigations. The illicit discharge investigation provisions of the NPDES stormwater regulations requires municipalities to develop and implement programs to identify and eliminate illicit discharges to their storm sewer system. An accurate map of the entire storm sewer system provides the foundation required to build a GIS application to perform these illicit discharge investigations.

The storm drain map could be combined with sampling data from the Part 1 application and land use information and property data maintained within the GIS to identify correlations between various activities and the potential for illicit connections. The GIS could then be used for:

* Scheduling and tracking illicit discharge field investigations;

* Recording the results of the field activities;

* Tracking enforcement activities;

* Preparing summary reports.

The NPDES stormwater program provides an opportunity to exploit the full range of capabilities of GIS technology by developing NPDES applications to facilitate cost-effective solutions to regulatory challenges. The storm drain inventory and illicit discharge modules only represent the tip of the iceberg for potential NPDES/GIS applications.

Mr. Timothy C. McCormick is Water Resources Division Manager, Greenborne & O'Mara, Inc., Greenbelt, Maryland.
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Title Annotation:geographic information system; National Pollutant Elimination System regulations
Author:McCormick, Timothy C.
Publication:Public Works
Date:Jun 1, 1994
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