During the Summer of 1999 the vacuum in LER was studied in order to answer a few questions: (1) how fast is the vacuum system cleaning; (2) when will the required operating pressure 10 nTorr be reached; (3) how fast do the TSP's saturate; and (4) what is the present average pressure in LER and what is the corresponding beam lifetime? Once {Delta}P/I, the coefficient relating the pressure to beam current and the base pressure is calculated, it is easy to find the time constants associated with the cleaning of the vacuum system and the saturation of the TSP's. In addition, these calculations showed that vertical steering of the LER orbit affects the vacuum and that leaks cause the TSP's to saturate. It is difficult to calculate the average pressure in the ring because most of the ion pumps in the straight sections do not read pressure accurately. Secondly, how do you calculate the conductance between the chamber and the anti-chamber? Thirdly, the gas load is unevenly distributed along the ring because of photon stops and leaks. However, the average vacuum pressure seen by the beam in the arcs is roughly three times higher than the pressure measured at themore » ion pumps, according to Artem Kulikov. Instead of calculating the average pressure in the ring, the author has calculated the coefficient relating the inverse beam lifetime to the beam current to see the long term improvement of the LER beam lifetime as the vacuum system is scrubbed. These calculations showed that the lifetime, including the low intensity lifetime, is limited by the vacuum pressure. The results reported here are obtained from numerical calculations.« less