Stormwater discharges from city storm drains are covered under Maryland’s Phase II NPDES permit for state and federal small Municipal Separate Storm Sewer Systems. As part of compliance efforts, KCI was tasked with updating the city’s database of stormwater Best Management Practices (BMP) and then reconciling drainage areas and the amount of treatment at each facility. For most locations, necessary data was taken from existing as-built or design plans. When dimensions were missing, the team used assumptions based on their experience with typical designs. Sites without plan data required engineers to use Google Earth’s time-lapse feature to identify the approximate date of construction, which was critical in estimating the type of BMP and the amount of treatment that would have been expected during that design era. Field measurements of surface area and spot measurements of depth along with assumptions based on the date of construction allowed treatment volumes to be estimated.