  The galactocentric distance of quasar absorption outflows are conventionally
determined using absorption troughs from excited states, a method hindered by
severely saturated or self-blended absorption troughs. We propose a novel
method to estimate the size of a broad absorption line (BAL) region which
partly obscures an emission line region by assuming virialized gas in the
emission region surrounding a supermassive black hole with known mass. When a
spiky Lya1216 line emission is present at the flat bottom of the deep Nv1240
absorption trough, the size of BAL region can be estimated. We have found 3 BAL
quasars in the SDSS database showing such Lya lines. The scale of their BAL
outflows are found to be 3-26 pc, moderately larger than the theoretical scale
(0.01-0.1 pc) of trough forming regions for winds originating from accretion
discs, but significantly smaller than most outflow sizes derived using the
absorption troughs of the excited states of ions. For these three outflows, the
lower limits of ratio of kinetic luminosity to Eddington luminosity are
0.02%-0.07%. These lower limits are substantially smaller than that is required
to have significant feedback effect on their host galaxies.
