NV5 has been performing monitoring and assessment of the water quality and quantity of discharges from the Municipal Separate Storm Sewer System (MS4), pollutant sources and/or stressors and as well as of the water quality improvement strategies implemented as part of the Carlsbad Water Quality Improvement Plan (WQIP). NV5’s scope of services has included dry weather MS4 outfall field screening; non-storm water persistent flow MS4 outfall discharge monitoring; dry weather special study monitoring; Illicit Discharge Detection Elimination investigations; and data formatting, assessment, and reporting of the monitoring programs.
During 2017, NV5 conducted two rounds of MS4 outfall field screening at 37 outfalls for a total of 74 field screenings, including numerous upstream investigations and IDDEs. Since 2015, NV5 has conducted five rounds of non-storm water persistent flow MS4 outfall discharge monitoring at five major MS4 outfall locations. NV5 implemented two rounds of a dry weather special study to characterize temporal flow and fecal indicator bacteria at selected major MS4 outfalls. To accomplish high quality flow data acquisition in low flow conditions, NV5 designed and installed low flow weirs with flowmeters to establish high resolution baseline flow conditions. NV5 is currently implementing a special study to determine whether dry weather discharges from the MS4 originate from groundwater sources, other permitted discharges or originate as anthropogenic non-storm water sources. NV5 utilizes stable isotope analysis to provide the fingerprint of different samples of water. Water samples are collected for hydrogen, oxygen, and strontium isotopes from the MS4 outfall sites and from suspected sources of non-storm water flows that could be entering the MS4. The sources studied include municipal tap water, local groundwater, desalinated water, and recycled water. The distinct isotopic and geochemical signatures provide the isotopic variation among the water samples, allowing the City of Carlsbad to determine if the isotopic composition of one or more potential source(s) match what is measured in the water discharging from the MS4 outfall sites.
