Groundwater recharge by treated STP effluent & ground water extraction within 15-30 ft : Implications on health & safety

I am staying in a Residential complex having 136 dwelling units in 96,000 sq.ft plot size generating  100,000 liters of sewage per day. The treated effluent (90%) from MBR based STP is recharged into ground water in the same premises after partly re-using it for toilet flushing. As per builder's design, recharge well as well as extraction are within the radius of 15-30 ft. And also Ground water and re-charging depth are more or less in the same depth of 20-30 ft.

I apprehend that ground water may get contaminated by chemical/biological impurities of treated effluents from STP whenever it malfunctions. I kindly request you to help me with information on
a) safe distances  between recharge & ground water extraction
b) depth considerations for deep recharge & ground water extraction should be calculated.

Relevant standards or regulations may be mentioned.

A.Authimoolam
authi123@rediffmail.com

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