GRAEF-USA Inc.

LSSES Implementation

GRAEF was selected to provide engineering services for implementing a portion of the recommendations in their 2002 Limited Sanitary Sewer Evaluation Survey Report. Flow monitoring for the LSSES was performed in 32 City sanitary sub-basins of which 11 were determined to be performed poorly in wet weather. GRAEF’s services included preparing plans and specifications for rehabilitation of 483 City sanitary sewer manholes, conducting sanitary sewer flow monitoring in 10 City sub-basins to verify post-rehabilitation performance, and sub-contracting with Visu-Sewer Clean & Seal, Inc. to perform cleaning and televising of 50,400 feet of sanitary sewers within the City’s sub-basins determined to have high infiltration and inflow. GRAEF prepared a report summarizing the sanitary manhole rehabilitation work, sanitary sewer TV inspections, and sanitary basin flow monitoring components of the LSSES recommendations that were implemented by GRAEF and the City of Greenfield.

The intent of the LSSES Implementation project was to aggressively rehabilitate the poorly performing sub-basins identified by the LSSES and verify that significant infiltration/inflow reduction has taken place as a result of the rehabilitations. The City planned to rehabilitate these sub-basins to the point where they would perform at a level that would allow them to be placed into a Capacity, Management, Operation, and Maintenance (CMOM) program, thus no longer requiring aggressive rehabilitation. The City’s goal was to bring their sanitary collection system into complete compliance with current MMSD rules and maintain that level of performance.

The first step that GRAEF took in implementing the recommendations of the LSSES included preparing construction documents for an aggressive manhole rehabilitation project within the poorly performing sub-basins. Manhole rehabilitations included rebuilding manhole chimneys/adding external chimney seals, replacing or adding internal chimney seals, injection grouting precast concrete manhole leaks, lining of brick or block manholes, and rebuilding of manholes. Prior to start of the manhole rehabilitations, GRAEF installed flow meters to monitor flow from the sub-basins containing the scheduled work. Precipitation data was collected from a rain gauge installed on the roof of Greenfield City Hall.

GRAEF then reviewed the TV logs and videos by Visu-Sewer Clean & Seal, Inc. and prepared a summary report with recommendations for rehabilitation. Approximately 14,400 linear feet of sewers were recommended for rehabilitation in the six sub-basins using a cured-in-place lining system. These linings were estimated to reduce the sanitary collection system I/I by an average rate of 240 gpm.

Flow monitoring data was periodically downloaded to spreadsheets and quarterly graphs were created for review and analysis. GRAEF flow metering data identified more than ten significant peak flow events over the entire fifteen month monitoring period. Processing of GRAEF flow data included first identifying the largest peak flow events at each meter location, then calculating the peak hourly flow, average dry-weather infiltration, and average dry-weather flow so that the peak total I/I per unit area could be estimated.

The comparison of peak flow events to MMSD 2020 Facilities Plan values suggested that the City’s aggressive manhole rehabilitation has resulted in a significant overall reduction in peak flow. The combined change in peak flow was a reduction of 2.8 mgd. This is 5.8% of the estimated city-wide total peak I/I of 48.341 mgd as given in the MMSD 2020 Facilities Plan.

The analysis of flow monitoring data allowed Greenfield sewersheds to be separated into those requiring additional investigation/aggressive rehabilitation, and those that can be incorporated into a Capacity, Management, Operation, and Maintenance (CMOM) program. The analysis results gave the City the advantage of knowing where to concentrate their peak flow reduction efforts so that they can efficiently bring their sanitary collection system into complete compliance with current MMSD rules.

The data analysis also indicated that further aggressive rehabilitation for peak I/I reduction within some of the City’s sewersheds was still necessary. Despite the considerable amount of money spent on rehabilitation of public sewers and manholes in those sewersheds, the high peak infiltration and inflow rates remained above the acceptable values established by MMSD. It was determined that extensive rehabilitation on private property is likely required to reduce the peak infiltration and inflow rates in those sewersheds.
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LOCATION Greenfield, WI

FACTS Services Provided: Construction Documents, Manhole Rehabilitation, Sewer Televising, Flow Metering, Supervision, Final Report