Using GIS to support natural gas leak detection
Data model
Development of in-house software to automate the leak detection process involved
resolving a number of problems related to transferring data between existing systems and
the technicians' field hardware. Before development work could begin, we defined a GIS
data model. The major objects defined for the data model are the Leak Survey Area, the
Survey Type, Survey Stage and the Survey Result.
The model captures the relationships between GIS leak survey areas (LSA), the surveys
associated with those areas, and the routes driven during the leak surveys. LSAs are
digitized and all surveys in a LSA captured in a spreadsheet. Spreadsheet data is loaded
into the GIS model in anticipation of the export process.
Leak Survey Area
LSAs are area objects that represent actual REM survey areas. Due to additions,
replacements and reinforcements to the underground piping or gas main that makes up
the gas distribution system, these drivable areas are very dynamic. Boundaries change,
streets are added as gas main is run, deleted as gas main is abandoned and surveys
modified as gas main piping types are replaced. During any one year, surveys are
modified, deleted or added to the hundreds of REM LSAs. Prior to ALDS project
implementation we maintained these areas by hand and kept all records in books. LSA
maps had to be copied yearly and organized for work scheduling. This manual method of
tracking made it difficult to know how many LSAs needed to be surveyed and when.
Survey Type
State and Federal regulations and company requirements result in different types of gas
mains being surveyed at varying time intervals. Any given LSA could have one to many
surveys to perform and complete. We designed the system to deal with Survey Types.
The Survey Type object is a pictureless object that enables attachment of information
about one or many surveys to a specific LSA. For one survey in LSA E10, one leak
survey object is attached; for ten scheduled surveys in LSA E10, ten different survey
types are attached. This method determines how many and which surveys need to be
done for a particular LSA. The Survey Type contains information such as:
Survey type (19 valid types)
Survey name (for special surveys)
Interval (time between surveys)
Last completed date
Next due date
Surveys are scheduled and rescheduled using field information, interval, and next due
dates. The survey schedule report is on an Excel spreadsheet and can be easily sorted by
the "next due date" field. The spreadsheet is an excellent tool for the leak supervisor in
scheduling survey work. The schedule is automatically kept up to date. No more
calculations using paper and pencil. When a survey is completed, the system takes the
last "next due date" field and increments it by the number of months or years in the
"interval" field.
Survey Stage
Surveys can take anywhere from 10 minutes to 10 days to complete. Additionally,
surveys may need to be stopped and resumed many times before they are completed. The
data model must have the ability to capture portions of survey routes at a time. This is
accomplished with the Survey Stage object. Some of the most important data captured
with this object are:
Leak Survey Area
Survey type
Survey name
Technician
Start data and time
End date and time
Miles surveyed
Leaks found
Survey status
This data is actually captured by the truck application software in a shape file format.
This shape file is eventually uploaded. The shape file format mimics the Survey Stage in
the data model. Multiple Survey Stages can be attached to the Survey Result object. If it
take 3 days to completed a particular survey and the survey needs to be stopped and
resumed 4 times a day there would be 12 stages attached to the result object for this
survey.
Survey Result
The Survey Result object in the data model is basically a totaling bucket. Every time a
new leak survey is begun, a new Survey Stage is imported, a Survey Result created for
that survey, and the Survey Stage attached to the created Survey Result object.
Subsequent Survey Stages for this survey and its data are added to the Survey Result
object. The Survey Result object is itself attached to the Leak Survey Area that this new
Survey Stage is created for. Some of the information totaled for both in-progress and
completed surveys is:
Survey Duration
Survey Miles
Number of Leaks
Status
