Flow Monitoring

G&D has extensive experience in performing flow monitoring in sanitary sewer collection systems. G&D has installed data loggers in sewage lift stations, level sensors in permanent flume installations, and performed numerous temporary flow metering programs. G&D is experienced in most of the commonly used flow metering technologies developed by various manufacturers including Sigma's model 910, Isco's model 2150 and Hach's Flo-Dar.

G&D also has experience constructing permanent flow metering stations typically for billing purposes. G&D will also install rubber-tire fiberglass flumes in temporary metering studies where accuracy at very low flows is required.

Flow Monitoring Specialized Resources

G&D works closely with our clients to determine the study's requirements before proposing an appropriate metering approach and technology. G&D owns and maintains specialized equipment and resources used to perform sanitary sewer flow metering calibrations/inspections. Staff has also completed NASSCO© PACP and MACP certifications and uses these industry standards to categorize system structural defects. All G&D field personnel are equipped with digital cameras, laptop computers with broadband wireless internet access, and Nextel cell phones. This way, if something occurs in the field, such as a meter malfunction, that requires immediate attention from the Engineer or Owner, the information can be sent instantly from the field.

G&D owns backup flow metering equipment that is available, if necessary, including data loggers, area/velocity (A/V) sensors, flumes, rain gages, etc. All crews are fully trained and appropriately equipped to perform the confined space entry (CSE) that is required to install and maintain flow meters (i.e., tripod, winch with backup, harnesses, calibrated gas detector, and air blower) and to calibrate meters (e.g., velocity probe). G&D owns several support vehicles, with four-wheel drive, for accessing easements.

Sanitary Sewer Billing Flow Meter Engineering Review and Assistance

G&D assisted the Town of Gibsonville, NC with monitoring and reviewing of sewer billing with adjacent jurisdictions. G&D installed and maintained five (5) A/V flow monitors and one rain gage for a period of two months.

G&D analyzed the resultant data, and presented a technical memorandum used to support capital asset management decision making. G&D identified capacity problems at one of the Town's sewage lift stations.

Shelby I / I Study

The City of Shelby Public Utilities has experienced elevated peak flows influent to their wastewater treatment plant (WWTP) under wet weather conditions.

The City hired G&D to identify portions of its existing collection system that are subject to higher than normal levels of RDII, develop a plan to eliminate I/I sources therein, and identify and address portions of the collection system that are subject to chronic operation and maintenance (O&M) problems. G&D performed various tasks to meet the project objectives including flow monitoring and data analysis. Five Hach Flo-Dar(TM) temporary flow meters and two rain gages were installed in the collection system in March, 2009. Flow metering data was analyzed and the highest priority areas with respect to I/I were identified.

Two of the meters were subsequently relocated to the highest priority area in late March, 2009 and additional flow data was obtained. Subsequently, G&D oversaw various SSES activities performed by either City staff or a subconsultant including smoke testing and CCTV. G&D was able to identify a downtown industrial area as being I/I prone based on flow metering data, which was subsequently verified through SSES. A rehabilitation plan is now under development.

Harrisburg Master Plan

As a subconsultant to W. K. Dickson, G&D performed a temporary flow monitoring study to support the development of Harrisburg's sanitary sewer master plan. G&D initially installed seven (7) Isco(TM) Model 2150 Area Velocity (A/V) flow meters at all major connections to the Water and Sewer Authority of Cabarrus County's (WSACC) trunk sewer network.

These meters were installed for thirty days and then relocated to the Back Creek basin in Harrisburg for an additional (60) sixty days. G&D performed meter maintenance and generated detailed flow metering data analysis reports that showed that excessive sediment at one location was skewing the data (which was subsequently corrected).

Cold Water Creek Sewer Capacity Study

G&D performed a wet weather engineering study to identify sources of I/I in the City of Kannapolis' Coldwater Creek drainage basin. This project involved the analysis of mapping and flow data, installation and maintenance of temporary, including Flo-Dar©, and permanent flow monitors, hydraulic modeling (using SWMM), and development of a long-term plan to address I/I and capacity issues in the basin.

G&D installed permanent meters at two lift stations in the basin as part of this project. The work has been performed on an ongoing basis for the last three years. A comprehensive two-month duration basin-wide flow monitoring study was performed in the fall of 2008 to support capacity calculations in the Coldwater Creek basin.

G&D subsequently recommended capital improvements to address capacity constraints in the basin, which are now part of the City's capital improvement plan.

Nine of the temporary meters were Hach(TM) Flo-Dar, while the remainder was a Sigma(TM) Model 910 A/V meter. G&D was responsible for all aspects of the temporary metering program including site selection, installation, meter maintenance, data collection, and analysis.

Town of Harrisburg 1/1 Study

The Water and Sewer Authority of Cabarrus County (WSACC) hired G&D to assist the Town of Harrisburg in identifying portions of its system prone to elevated levels of I/I. The scope of work of this Project included the review of CCTV tape of the WSACC-owned trunk sewers, and development and implementation of a temporary flow monitoring plan. The CCTV data and metering equipment, in this case, was generally provided by WSACC, but was supplemented by G&D equipment, when necessary. This project was implemented in multiple phases: (1) Back Creek Phase 1, (2) Back Creek Phase 2, and (3) Rocky River with a total of 30 flow metering locations. The trunk sewers were generally found to be in good condition. The first phase in Back Creek consisted of ten (10) meters and the second phase seven (7). Rocky River consisted of one phase of thirteen (13) meters, three (3) of which were flumes. As part of this work, G&D conducted flow balances in the system to develop and understanding of parallel trunk sewer operation and analyzed pump station run time for evidence of elevated levels of I/I in their tributary areas. A further innovation on this project was the use of temporary fiberglass flumes to measure flow in very low flow (1") applications where the typical A/V type sensor does not provide sufficiently accurate readings.