Jefferson County, Alabama, Environmental Services Department

by Rick A. Hill, GIS Manager; Pete Atwood, GIS Analyst; and Harry Chandler, Assistant Director, Jefferson County Environmental Services

Introduction

In 1998, the Jefferson County, Alabama, Environmental Services Department gained control of the sanitary sewer collection system from 21 municipalities. As a direct result of this acquisition a management system has been implemented to manage this new workload. The new system is called the Sewer Infrastructure Management System (SIMS).

Sewer data is developed in ArcInfo, Bentley MicroStation®, ArcView GIS, and Oracle® and is managed utilizing Pipeworks by Azteca Systems, Inc. Data conversion is automated in ArcInfo to convert .dgn files. This process creates a sewer coverage of arcs and nodes. Sanitary Sewer Evaluation Survey data was used to attribute the sewer network. Data consists of pipe size, pipe type, slope, and reference number. Work orders are created to track sewer rehabilitation work being performed by USInfrastructure, Inc. (USI).

Network Description

The sanitary sewer collection system in Jefferson County consists of over 2,500 miles of pipe, 60,000 manholes, and nine wastewater treatment facilities. The Environmental Services Department manages a maximum capacity of 250 million gallons of sanitary sewer water per day through its treatment facilities.

Case Study

Background
The sewer network is developed from CAD files. The network is converted using paper tax maps as a guide. Due to the inaccuracy of digitizing the CAD files, the Environmental Services Department contracted to have manholes located using a global positioning system (GPS). During this process data is collected on each manhole. Data includes depth, inverts, direction of pipe, and a digital image of the manhole. As data is collected, the CAD located manholes are moved to their correct GPS locations. Moving the manholes in an automated manner, though, created a significant problem.

Problem Identification
The GPS data is viewed in ArcView GIS format as a point shapefile. The manhole number is present in both the sewer coverage and the shapefile; therefore, moving nodes to the GPS location is not a difficult process. However, many manholes have laterals that do not end in a manhole. When these manholes are moved to their GPS location the laterals do not move. This creates significant errors in the sewer coverage. In Jefferson County, Alabama, there are approximately 3,000 laterals that do not end in a manhole. The problem now becomes how to move a manhole to its GPS location while preserving the angles that laterals (with no ending manhole) have that extend out from the manhole.

Problem Resolution
As a manhole node is repositioned to its correct GPS location the x,y coordinates are captured. An ARC Macro Language (AML™) script was written to identify all manholes that move to a GPS location. If a manhole moves, the script checks to determine if any incoming sewer lines connected to that manhole contain the attribute "ENDOFPIPE." The attribute ENDOFPIPE is given to identify sewer lines that end without a manhole. For each manhole that moves, the x,y shift is determined and all associated ENDOFPIPE nodes are moved the same x,y shift. Although not a precise method it does preserve the integrity of the sewer network coverage. The ENDOFPIPE nodes are a temporary solution to lines that do not end with a manhole. As rehabilitation continues in the County, manholes will eventually be placed at the ends of these lines.