NOTE: this is based on Panama's laws

A company, which uses cadmium in its process, discharges Cd into the San Quintin stream at $0\mathrm{.}01$ g$/$L$.$

The DGNTI$-$COPANIT$-35-2019$ regulation establishes a Cd value at $0\mathrm{.}01$ mg$/$L$.$

Solve the following problem:

In recent years, applications of cadmium and its compounds have come under increasing pressure due to the danger they pose to the environment. In surface waters, cadmium occurs as a free ion and its solubility influences the hardness, pH$,$ soluble complexes and colloidal sulfides of these, in this medium it binds to particulate matter.

When fresh water reaches the sea, the cadmium $2+$ ion, like other heavy metal ions, tends to be deposited in sediments and is thus limited to the waters of the coasts and estuaries. This immobilization is potentially dangerous, since they can dissolve again if the pH decreases.

Generally, the concentrations of this element in drinking water are less than $5$ g$/$L while in seawater, they range between $0\mathrm{.}04$ and $0\mathrm{.}03$ g$/$L $($Albert$,2002).$

According to Executive Decree $75-2008,$ the concentration of cadmium in a body of continental water for recreational use, with and without direct contact, must be less than $0\mathrm{.}03$ mg$/$L$.$

A city of one million inhabitants is located on the banks of a ravine. The cadmium industry continues to operate with a utilization of $1$x$10$ L$/$h$.$ On the other hand, the Chemical Oxygen Demand concentration is $7$ g$/$L$,$ the BOD$5/$COD ratio is $0\mathrm{.}2.$ The city's daily per capita wastewater production is $90$ gallons and BOD is $0\mathrm{.}03.$

kg; The BOD$/$COD ratio is $0\mathrm{.}5$ while the Cd concentration of the discharge is $4$ g$/$L$.$

Determine the COD concentration associated with domestic wastewater.

If the river has a flow rate of $60$ m$/$min and a basal concentration of $0$ mg$/$L of COD and Cd$.$ Estimate the concentration of BODs and Cd in the river downstream of these discharges.

Do these waters meet the quality required for recreational use with direct contact, Executive Decree, $2008,$ in terms of BOD$5(3$ mg$/$L$)$ and Cd $(0\mathrm{.}03$ mg$/$L$).$ Knowing that there is a community of squatters downstream of these discharges who use the water to

human consumption. According to Albert $(2002)$ Would it exceed its value?

Determine the BOD concentration of the city and the industry to comply with Executive Decree $75,2008.$ How much should the Cd discharge be to comply with said Decree?