USING GIS TO IMPROVE SEWER LINE MAINTENANCE TO PREVENT SANITARY SEWER OVERFLOWS

Brian Hewes, Department of Earth Sciences, University of South Alabama, Mobile, Al 36688. Email: bjh401@jaguar1.usouthal.edu. Sanitary sewer overflows are extremely detrimental to a surrounding watershed. An overflow occurs when volume exceeds capacity. There are several causes of an overflow; one of these causes is poorly maintained sewer clean out stations, which lead to blockages. Blockages are caused by grease buildup or other foreign objects. These clean out stations need to be serviced regularly to avoid blockages and to provide a more free flowing system. By using GIS, with a network analyst extension, I was able to design routes for a fleet of MAWSS (Mobile Area Water and Sewer System) trucks to cover all of these sewer clean outs in the most timely efficient way. These routes were designed based on where the clean outs are and the number of trucks that will go out cleaning these stations. Historic traffic data was also gathered from the City of Mobile. By being more efficient cleaning the sewer lines, the number of sanitary sewer overflows should be reduced, thus improving the water quality of the surrounding watershed. Keywords: sanitary sewer overflow, network analyst, sewer system

Introduction:

Water quality has and will always be a major area of concern for Dog River Clearwater

Revival. Any event that has a negative impact on the water also has a negative impact on the

entire community. One of these negative events the city is currently trying to combat is sanitary

sewer overflows (SSO). A sanitary sewer overflow is basically a raw sewage spill out of a

manhole into streets or surrounding streams (Fig.1). This untreated sewage can be very

detrimental to the water quality of the surrounding watershed along with the community

associated with the watershed. Because SSO’s contain raw sewage, they can carry bacteria and

viruses. The diseases they may cause range in severity from mild gastroenteritis (causing

stomach cramps and diarrhea) to life-threatening ailments such as cholera, dysentery, infections

hepatitis, and severe gastroenteritis (EPA, 1996). They are caused when the volume of water or

sewage increases to a higher demand than the sewer systems capacity, or when the system fails

to operate at full capacity due to a blockage or a break in the line. Jerrod Frederking showed

that rainfall increases the flow in sewer lines (Frederking, 2010). The United States

Environmental Protection Agency estimates that 27% of all SSO’s are caused by rainwater

infiltration and inflow. They also estimate the leading causes of SSO’s are pipe blockages,

which account for 43% of all SSO’s (EPA, 1996). Pipe blockages can be prevented with

thorough regularly scheduled maintenance. Pipe blockages are caused by a buildup of grease or

other foreign objects as well as root intrusion into the pipes. Mobile Area Water and Sewer

(MAWSS) currently has seven trucks that perform maintenance on sewer line clean outs. A

sewer line clean out is a capped pipe which provides access to the sewer lines that allows

MAWSS to clean out blockages. MAWSS cleans out these blockages at the cleanouts on an as

needed basis, “as needed” meaning these blockages are cleaned out post SSO. By using GIS to

organize and plan routes for each maintenance truck, it is hoped that sewer line cleanout

maintenance will become a preventative measure rather than a post SSO measure.

Figure 1: Sanitary Sewer Overflow. Photo courtesy of The Clean Waterways Program of Frankfort and Franklin County Kentucky

Research Question:

Can GIS be used to better organize and more efficiently perform maintenance on sewer

lines in order to prevent sanitary sewer overflows?

Methods:

Arc GIS with a network analyst extension was used to determine the best route for each

truck to take in order to cover the entire sewer system. Throughout this project, I coordinated

with GIS Supervisor at MAWSS, Matt Sanders. First with the aid of Matt Sanders, a shape file

was made containing the exact coordinates and a history of SSO’s at each cleanout location.

Then it was determined under normal conditions that one truck could perform maintenance on

between 6-8 sewer cleanouts in a normal workday. A network data set was created using traffic

data gathered from the City of Mobile’s GIS data. Then a route was created for each truck that

encompassed between 6-8 cleanouts. Each route started and ended at 4725 Moffett Rd, which is

the MAWSS office for sewer operations.

Results:

Seven routes were designed, one for each truck. These routes cover all of the cleanout

locations. If the cleanouts are close in proximity, the route contains eight cleanouts. If the

cleanouts are widely dispersed, there were only six cleanouts within the route. A large map

containing all of the routes was generated (Fig.2), along with smaller more detailed maps for

each individual route (Fig.3). Driving directions with turn-by-turn images can also be generated

for each individual route. All of these routes have been approved by GIS supervisor Matt

Sanders along with the current sewer line maintenance supervisor of MAWSS.

Figure 2: Map of all seven sewer clean out routes.

Figure 3: Detailed map of Route 1.

Conclusion:

Sanitary sewer overflows are very hazardous to the water quality, and they can carry

diseases to those in the surrounding community. These overflows are caused when flow exceeds

capacity. This occurs when either the flow is increased by rain or the capacity is decreased by

blockages. Treatment companies like MAWSS try to combat these overflows caused by

blockages by performing maintenance on sewer line cleanouts. By utilizing the capabilities of

GIS, specifically the network analyst extension, this project has offered streamlined, productive,

thorough process by which the pipes can be cleaned and maintained. The sewer line cleanouts

will not only be used post SSO but these cleanouts will be utilized as preventative measures. If

SSO’s are reduced then the water quality in Dog River should improve.

There were 17 cleanouts with a documented history of SSO’s within the data I was given

by MAWSS. A majority of those cleanouts fall within the Dog River watershed. It would be

interesting to more closely monitor the number of SSO occurrences over time. That seems to be

the only true way of finding out if SSO’s are actually reduced due to an improved maintenance

schedule.

Bibliography:

Frederking, Jerrod. 2010. Analysis of Rainfall and its Inflow into Mobile, Alabama’s Eslava Sewer Shed. Mobile, Alabama

Mobile Area Water and Sewer System (MAWSS). 2008. Handbook 3 Section 3.16. Handbook.Mobile, Alabama. What causes sewer blockages? [online]. (2007) [Accessed 3 March 2012]. Available from: <http://www.ci.windsor.ca.us/

DocumentView.aspx?DID=967>. Sanitary Sewer Overflows [online]. (1996) [Accessed 29 February 2012]. Available from:

<http://www.epa.gov/npdes/pubs/ssodesc.pdf>. Two Creek’s Overflow (2007). [Print Photo]. Retrieved from

http://cwffc.mcallenweb.net/Portals/50/images/twocreeksov

United States Environmental Protection Agency. 1996. Sanitary sewer overflows what are they and how can we reduce them? Southcat Electronic Format.http://www.epa.gov/npdes/pubs/ssodesc.pdf 16 April 2010