The City of Waltham is currently implementing an Illicit Discharge Detection and Elimination (IDDE) Program in order to identify and remove illicit flows entering the City’s storm water collection system. Similar to many communities, the City of Waltham is comprised of a separate sanitary sewer system to convey sanitary waste to a wastewater treatment facility, and a storm drain system to collect and convey rainfall runoff to local waterways. An illicit flow to the storm water system generally consists of a discharge that is not fully comprised of rainfall runoff and contains some amount of additional contamination. Typical illicit flow sources may include improperly connected building sanitary sewer laterals, damaged sanitary mains or laterals leaking into low lying drains, runoff from vehicle washing in the street, or disposal of contaminating materials (such as pet waste) into storm drain catch basins or left on the street.
Under the IDDE Program, the City of Waltham systematically performs identification and elimination of illicit flows following five basic steps:
1. Stormwater Outfall Sampling:
An outfall is the most downstream point of a drainage watershed. Stormwater outfalls usually discharge surface runoff collected by catch basins and conveyed through a gravity pipe network into a waterbody such as a pond, brook, or river.
During this first step of the IDDE Program, all outfalls within the City limits are being inventoried and sampled during both dry and wet weather conditions. Each collected water sample is tested for the following parameters: E.Coli, Surfactants, Ammonia, Total Phosphorus, Dissolved Phosphorus and Total Potassium.
The city-wide outfall sampling program has been divided in three phases. Each phase includes outfalls from different watersheds within the City of Waltham. The list of watersheds to be evaluated in each phase is presented below and depicted in this MAP. Be patient - maps may load slowly.
a. Phase I (2008 and 2009): Charles River and Beaver Brook
b. Phase II (2010): Chester and West Chester Brook
c. Phase III (2011): Masters and Clematis Brook
2. Outfall Prioritization:
Based on the outfall sampling results, outfalls are ranked according to their pollutant contribution to the receiving waterway. The outfall ranking methodology is described in detail in the City of Waltham’s IDDE Plan and summarized here.
3. Investigation of Outfall Areas:
The stormwater systems that contribute flow to the most polluted outfalls are then investigated in order to identify sources of contamination. The investigations consist of visually inspecting and collecting samples from junction manholes during dry weather using a top-down approach, as recommended by the US Environmental Protection Agency (EPA). In other words, investigations start at the most upstream junction manholes within the drainage watershed and progressively move downstream. If the upstream junction manhole shows no signs of contamination, then the investigations proceed to the next downstream manhole. If the junction manhole is polluted, then the isolated upstream pipe sections are investigated in order to identify the source of contamination which will subsequently be removed (see step 4 and step 5). Outfalls and outfall areas within the City of Waltham that have been investigated to date are presented in this map.
4. Illicit Flow Removal:
Construction work is necessary to eliminate the identified sources of contamination. Work may include reconnection of building sanitary laterals to the main sewer pipe, removal of common manholes, replacing damaged pipes, or providing pipe rehabilitation to leaking sewers and/or drains that may be introducing illicit flow into the storm drain system through infiltration.
5. Re-Testing and Investigation of Downstream Manholes:
When the illicit flow removal work has been completed, new samples are then collected in the immediately downstream manhole in order to verify that the contamination has been effectively removed. If samples are compliant, investigations proceed to the next downstream junction manhole. This process is repeated until the outfall is reached and the stormwater discharge is no longer polluted. This map shows IDDE-related construction work performed to date in the City of Waltham since 2008.