Preventing Flooding and Improving Water Quality

Engineering Crews Begin Spring Cleaning

City of Madison Engineering crews have begun a pilot program to clean all catch basins two times per year in conjunction with the Streets Division's spring and fall street sweeping and the Water Utility's main flushing programs. Catch basins are storm structures designed to retain sediment by trapping this material in a sump below the invert of the outlet pipe. Catch basins must be cleaned to maintain their ability to trap sediment, and consequently, their ability to prevent flooding. The benefits of catch basin cleaning also include the removal of pollutant loads from the storm sewer system and the reduction of high pollutant concentrations during the "first flush" of a storm event. Engineering crews began their spring cleaning activities this week. For the next four to six weeks, these crews will be working Sundays through Thursdays from 11:30 PM to 7:30 AM to remove the sand, salt and other debris deposited in catch basins this past winter. The goal is to remove this debris as soon as possible after snow melt and restore maximum storage capacity for sediment and debris before spring rains begin. The fall cleaning will provide for the removal of accumulated debris and leaves that may block the flow of storm water. Combination sewer cleaning machines (also referred to as "Vactors") are used to perform this work. The City Sanitary and Storm utilities share the ownership of five of these machines, each of which costs in excess of $300,000. By running a second shift for these seasonal activities the City is able to maximize equipment usage and save rate payers money. After this phase of work is complete, the Water Utility and Engineering Division will work together to determine if the water being flushed from the distribution system can be used to effectively clean storm mains and/or the smaller particles from the street that street sweepers cannot effectively remove. Samples of catch basin debris will be collected and analyzed to determine if a coordinated approach to cleaning proposed proprietary catchment devices after flushing streets clean will increase the level of small particles collected and aid in the further reduction of total suspended solids in our lakes. Between the spring and fall catch basin cleanings Engineering will inspect catch basins using a Global Positioning System (GPS) data collector. Data collected will include, but not be limited to, depth of sump as well as depth and type of accumulated debris. The objectives of this inspection process are to: • Provide sump depth data for Geographic Information System (GIS) record update. • Identify any structural deficiencies that need to be repaired. • Determine when individual sumps reach 50 percent of their storage capacity so that they can be cleaned to prevent solids from clogging the storm sewer and being washed into receiving waters. • Adjust cleaning frequencies to optimize system functionality and use of City resources. By performing this work at night, the City is able to maximize the use of existing staff and equipment.

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