The predevelopment condition of the parcel to be developed,
as determined by the Township Engineer, shall be considered the state
of the land surface on the date that the developer entered into an
agreement to purchase the property. If the property has been partially
or completely developed at the time of purchase, the Board of Supervisors
may, at its option, require the new owner, if he proposes to redevelop
or further develop the property, to take remedial action for compliance
with the requirements of this subsection. If remedial action is required,
regardless of the condition of the surface, the design runoff shall
not exceed curve number 75 applied to class C "good meadow" soils
(see Tables 2-1 and 2-2 of T.R. 55). The developer may pass through
stormwater originating upstream of his property, but if he elects
to control it, bypass devices he installs shall be capable of handling
the 100-year, twenty-four-hour peak flow, and he may trade off, as
compensation for such installations, control measures that would normally
be required on his property, provided that the total control system
results in equal or better protection for downstream properties. If
a property is to be laid out in lots, no reduction in lot size shall
be permitted to accommodate storm drainage detention structures.