Digging is necessary to meet the different requirements for each utility. Furthermore, health department regulations specify a minimum distance between the utilities to prevent cross-contamination if a leak occurs. The sanitary sewer must be deep enough to pick up the sewage coming out of the pipes under the basement floors, while the water main and services need to be a minimum of 7.5 feet deep to keep them from freezing. Storm sewer, however, is kept as shallow as possible so it does not conflict with other utilities. Finally, when utility work is complete, streets are excavated to remove bad soils and install sand and the pavement section.