Constituent (Lead) Mass Balance - Lakes-Rivers System: Consider for the scenario described below the potential contamination by lead of a raw drinking water drawn from one of the rivers in the lake system presented schematically in Figure 1 (Lakes-Rivers System without Evaporation as Sink)

Constituent (Lead) Mass Balance - Lakes-Rivers System: Consider for the scenario described below the potential contamination by lead of a raw drinking water drawn from one of the rivers in the lake system presented schematically in Figure 1 (Lakes-Rivers System without Evaporation as Sink).A large underground clay-lined waste pit at a former industrial site is located alongside River A, near itsconfluence with LAKE I. The existence of this pit has been known for sometimes, but no seepage has ever been found. After a recent Richter-scale three earth tremor, however, a waste plume from the pit has been discovered,the major contaminant in the stream being lead (Pb+2). Following the onset of the relatively steady new seepage from the pit, dissolved Pb2+ concentration averaging 100 μmol/L are found in River A immediately above its discharge to LAKE I. A community located along River F just downstream from LAKE II draws its public water supply from that river. The community has a relatively simple water treatment plant that has no provision for removal of dissolved Pb+2. The drinking water standard for lead is 0.05 mg/L. Determine whether the water supply to the community will exceed this standard if there is no remediation of the pit seepage.The Pb2+ undergoes a precipitation reaction of the form:

Pb2+ + 2OH- ↔ Pb(OH)2(s) ↓

At a rate given by r = k [Pb2+] [OH-] 2, where k = 5.0 × 107 (L/mol) 2 (min-1). The lakes are well buffered at pH

= 8.3.