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RECEIVED ■ Smoke testing sanitary sewers ■ Visual and smell indicators MAY 10 2016 ■ Obtaining access to perform test and obtain samples 3.1 Indicator Monitoring IENVIR'NNAENTAL HEALTH D3 :PARTMENT The City's Phase II Small MS4 NPDES General Permit requires indicator monitoring of outfalls that are discovered to have active flows or ponding more than 72 hours after the last rain event. Indicator monitoring is only required to be performed when the source or pollutant associated with the flow is unknown. Indicator monitoring assists in the detection of the likely source(s) based upon analytical characteristics. Indicator parameter monitoring will consist of the parameters identified in the table below (Table 1). Each of the detected parameters is a clue to the potential source(s) of the discharge. By using the indicator parameter results, a more directed source investigation can be performed. Table 1. Indicator Parameters Indicator Parameters Used to Detect Illicit Discharges Parameter Discharge Types It Can Detect Tap Industrial or Sewage Washwater Water Commercial Laboratory/Analytical Challenges Liquid Wastes Ammonia • O O O Can change into other nitrogen forms as the flow travels to the outfall Color O O O O Conductivity O O O O Ineffective in saline waters Detergents— • • O O Reagent is a hazardous waste Surfactants Residual O O • O Chlorine" Hardness O O O O pH O O O O Potassium O O O • May need to use two separate analytical techniques,depending on the concentration Turbidity O O O O • Can almost always(>80%of samples)distinguish this discharge from clean flow types(e.g.,tap water or natural water). For tap water,can distinguish from natural water. O Can sometimes(>50%of samples)distinguish this discharge from clean flow types depending on regional characteristics, or can be helpful in combination with another parameter O Poor indicator. Cannot reliably detect illicit discharges,or cannot detect tap water N/A:Data are not available to assess the utility of this parameter for this purpose. *Residual Chlorine has been selected to replace fluoride as an indicator parameter due to the municipality not fluorinating the municipal water supply. City of Lathrop Spill Response Plan 6 Rev. 10127/15