Novel Methodologies to Measure Flows and Collect Automated Samples in Challenging MS4 Systems to meet MS4 Permit Requirements
Traditional flow monitoring and automated sampling equipment implemented for water quality monitoring hails largely from the wastewater industry where the flow measurement and sampling points are located in systems that are designed to produce non-turbulent, laminar flow. The streams and MS4 pipes and conveyances this equipment is now utilized to monitor can often exceed the equipment limitations resulting in poor flow data, nonfunctional automated samplers, and missed monitoring events.
Historically the MS4 permits for the Los Angeles and San Diego regions have required flow monitoring and automated sampling in large receiving water bodies where the monitoring site could be adjusted and the equipment was easily modified to work under these conditions.
Recently issued MS4 permits in the San Diego and Los Angeles regions along with numerous TMDL-related special studies are requiring monitoring of flow and use of automated samplers in increasingly smaller MS4 pipes where flows are either too shallow, or velocity and turbulence may be too intense for flow and automated sampling equipment to function properly.
This presentation presents three case studies of sites that could not be relocated due to permit/study requirements and site constraints. Traditional flow measurement and automated sampling methodologies were not functioning at these sites. Through significant site-specific research and development, modifications were implemented that resulted in successful monitoring points. This presentation will focus on these case studies and engage the audience by guiding them through the process to implement these modifications at similar sites.
For the SCCWRP Epidemiological Study, the monitoring of Tourmaline Creek was restricted to a steep gradient portion of the stream just prior to discharge into the ocean. Velocities exceeded the capabilities of traditional monitoring equipment. A “modified stilling well” approach was developed, trialed, and implemented, resulting in the ability to collect accurate level measurements.
For the City of Los Angeles MS4 Monitoring, monitoring of the Colorado Street drainage system, which discharges into the Reach 3 of the Los Angeles River, was restricted to a steep section at the end of the conveyance due to multiple branching of the MS4 upstream. This system was steeper and smoother than the Tourmaline Creek site. This site provided an upper limit of effectiveness of the modified stilling well approach used for Tourmaline Creek. Additional research and development resulted in an embedded pressure transducer and embedded sample intake approach which ultimately resulted in the ability to collect accurate level measurements and sample aliquots at this site and provided a reliable methodology for use at sites with significant gradient and smoothness.
For the County of San Diego MS4 Permit dry weather flow monitoring requirements at priority outfalls, the County required the ability to monitor low “trickle” flows. These flows were below the capability of existing monitoring equipment to measure. In order to monitor these flows, custom weirs were installed to provide accurate flow measurements. However, certain locations under flood control jurisdiction would not allow for a solid weir. Break-away weirs were developed, tested, trialed, and implemented, which allowed the County to measure trickle flows and also maintain full or near-full pipe capacity during storm events. Following storm events, the weirs are simply snapped back into place to measure the dry weather trickle flows until the next storm event.
This presentation addresses the conference theme since we must we must first know the volume of wet and dry weather discharges we have available as a resource so we can properly plan management measures and potential use of that resource.