French to English Tech/Engineering Engineering (general) Public water: chlorination systems

From a document about improvements to a public water system by increasing chlorination levels. Most of the document is strtegic/planning etc, but I wanted to check with experts that my understanding of the occasional very technical bit is correct.

• Le travail de fiabilisation de la chloration porte essentiellement sur la définition de cahiers des charges en vue de la reconstruction des postes de chloration (apparemment pas de tentative de fiabiliser l’existant – La régulation sur la base du simple résiduel de chlore n’est pas robuste aux changements hydrauliques : cas des postes de chloration installés en Mai 2004).

My translation of the bit in question is:

(apparently there is to be no attempt to improve the reliability of the existing one - regulation based solely on the residual chlorine level does not stand up to (?)hydraulic changes [changes to the hydraulics?], as in the case of the chlorination stations installed in May 2004.)

Other references in the document to the stations installed in May 2004 are as follows:

• The improvements to chlorination in 2004 possibly made conditions more favourable for the formation of deposits due to stronger oxydation of the iron and possibly of the manganese by the chlorine being present in stronger concentrations. (The deposits causing 'nonconformities' to be detected in the system.)

Although it has improved subsequent to the implementation of additional chlorination (May – September 2004), the stability of these residual chlorine levels remains problematic, as variabilities of more than 50 % are regularly noticed.

I guess it means that if you make changes to the hydraulics (which in this case are apparently extremely complex) it will affect regulation of the chlorination if that regulation is based merely on the residual chlorine levels - does that make technical sense? Thanks.