Electron spectroscopic studies of highly concentrated \ensuremath{\delta} layers of Sb impurity atoms in epitaxially grown Si(001) have revealed the presence of two main Sb environments. An analysis of the kinetic energies of the core-level photoemission and Auger spectra of Sb in terms of the Auger parameter shows that the core holes on each site are less well screened than in the pure element. A simultaneous analysis of shifts in the initial-state and final-state Auger parameters of the two sites and bulk Sb enables one site to be identified with positively charged donors, and the other with neutral Sb, possibly in clusters, defects, or interstitial sites. The donors are found to contribute between 0.12 and 0.20 electrons per Sb atom, in agreement with transport measurements on similarly prepared specimens. The on-site screening of core holes on the two sites, dq/dN, is found to be 0.82 and 0.93 for the ${\mathrm{\ensuremath{\delta}}}_{1}$ and ${\mathrm{\ensuremath{\delta}}}_{2}$ sites, respectively. This result is consistent with the expectation that the donor site will be better screened by access to the electron gas of donated electrons. \textcopyright{} 1996 The American Physical Society.