35 Ill. Adm. Code 604.1420
Valves
Section 604.1420 Valves
a) A
sufficient number of valves must be provided to isolate portions of the
distribution system during repairs and maintenance and to facilitate
unidirectional flushing.
b) Location.
Unless otherwise approved by the Agency under Section 604.145(b), valves must
be located:
1) at not
more than 500-foot intervals in commercial districts;
2) at
not more than two blocks or 1200-foot intervals in other districts.