Various methods might be used. Basically you would want an Wastewater indicator that is so different from the lake water quality and storm water runoff that may be included at times and complicate deciding what is polluting. If the Wastewater treatment is effective, the water quality difference may not be enough, especially if the contamination is leaked and is diluted in the lake before it is measured. If you know where the Wastewater contamination might occur, perhaps a small catchment basin could be excavated to capture. It is somewhat difficult to visualize your problem area, perhaps a schematic would help, but you mentioned pressurized pipes on seabed (is that the lakebed), and where does the pollution go from the pipes under the lakebed to some other upland treatment pond or disposal area? The volume of lake would probably influence approach. If the Wastewater is high in sewage, coliform may be a good indicator (see our report in Researchgate concerning Stekoa Creek). If the leak occurs in the lakebed, the volume of the lake may be enough that small or even moderate leaks could go undetected. I have used fluorescent dyes as an indicator in pesticide aerial sprays to help detect overspray into streams. If you added sufficient Rhodamine B or WT to the wastewater during a test period, you could use a fluorometer to detect extremely low levels of dye, perhaps even to the part per billion or maybe parts per trillion range if I remember right. One of my projects dealing with treatment of Spruce Budworm pesticide spray program in Oregon has some information perhaps useful, and you could add the dye and then take repeated samples or flow through design with fluorometer to se if dye showed up. I would not use fluorescein as sunlight may degrade its concentration.

Whether the ammonia electrode might be a good indicator, I don’t know, but if the dilution factor is very high before you capture readings, it may be difficult to use, and ammonia can dissipate with time. Periods of rain events and stormwater may also have somewhat higher dissolved ammonia.

Another idea might be to attach a wastewater flow meter on the discharge pipe before the lake and another flow meter in the pipe after it leaves the lake. Some accuracy calibrations May be needed, before comparing the two metered volumes. Be sure the pressured line is empty before and after the test by blowing out with compressed air, or perhaps you could test with line full before and after test, but under some circumstances, air voids can sometimes be present.

It's an interesting subject, but can be kept truly methodical.

All influents and outfluent streams getting in or flowing out need to be audited ie both qlty and qnty are kept note off.

There are simple methods of NbSs ie Dewats wwt process Etc. Thses can be applied and cleaner water in same capacity is evolved.

If the above methodology is followed, sufficient relief is got and ideal condition would prevail.

Well wishes

Prof Ajit Seshadri

Vels University Chennai India

PMMoV (as an RNA target) or crAssphage, among other targets, could be used. With the rapid development of wastewater-based epidemiology in recent years, one of the biomarker/bionormalizers for wastewater could be used.