Auburn and Lewiston s Hydrant Flushing Considerations

Transcription

1 Auburn and Lewiston s Hydrant Flushing Considerations

2 The Drainage System Drainage is not the sewer we often think of, but it is an underground system of pipes that maintains our quality of life. Drainage systems conveys fallen rainwater, called stormwater, from paved streets, parking lots, our lawns and basements (via sump pump) to prevent pooling and flooding.

3 Lewiston and Auburn s Drainage Infrastructure Auburn 95 Miles of Storm Drain 115 Culverts Lewiston 90 miles of Ditch 5000 Manholes and Catchbasins Logan Brook (Urban Impaired Stream) 127 Miles of Storm Drain 254 Culverts 2 Miles of Open Concrete Storm Channel 17 Miles of Ditch 5900 Manholes and Catchbasins Jepson Brook (Urban Impaired Stream) Hart Brook (Urban Impaired Stream)

4 What is an MS4? A municipal separate storm sewer system is: A conveyance or system of conveyances owned by a state, city, town, or other public entity that discharges to waters of the U.S and is: Designed or used for collecting or conveying stormwater Not a combined sewer Not part of a publicly owned treatment works This term includes systems similar to separate storm sewer systems in municipalities, such as systems at military bases, large hospital or prison complexes, and highways and other thoroughfares.

5 Essence of MS4 Compliance Six Minimum Control Measures Public Education Public Involvement Illicit Discharge Detection and Elimination Construction Site Stormwater Runoff Control Post-Construction Stormwater Management Good Housekeeping and Pollution Prevention

6 Illicit Discharge Detection and Elimination (IDDE) Program Complete drainage system map Assessment of outfalls for illicit discharge potential Systematic procedure for locating and removing illicit connections, includes outfall inventory & monitoring Prevent illicit discharges and SSOs or Sewer Leaks Track program success Annual employee training

7 What are Permitted Non- Stormwater Discharges? Waterline/hydrant flushing Dechlorinated swimming pool water Water from individual vehicle washing Landscape irrigation/lawn watering Groundwater Diverted stream flows Air conditioning/compressor condensate Uncontaminated footer drains Others This permit authorizes the following non-stormwater discharges provided they do not contribute to a violation of water quality standards as determined by the Department.

8 Current Hydrant Flushing Program Auburn Water District delivers 2.8 MGD of water to 6300 customers. Source water from Lake Auburn Maintains over 130 miles of water distribution line. 733 Hydrants Lewiston Water Department delivers 4.2 MGD of water to 9350 customers. Source water from Lake Auburn Maintains over 167 miles of water distribution line. 743 Hydrants

9 Current Hydrant Flushing Program Auburn Water District Conducts spring flushing on all hydrants and fall flushing on approximately 100 hydrants Flushing conducted in April/May and September/October Average flushing flow rate of 673 GPM (~1.5 cfs) Highest flushing flow rate of 2250 GPM (5 cfs) Typical TRC = 1.5 ppm Lewiston Water Department. Conducts spring - fall hydrant flushing on approximately 681 Average flushing flow rate of 500 GPM (~1.5 cfs) Highest flushing flow rate of 2500 GPM (5 cfs)

10 Preliminary Assessment Hydrant Flushing Strategy Key Assumption: Portland Water District evaluation of TRC over distance from hydrant are common in Auburn/Lewiston as well. Flushing rate diffuser ground TRC 50 from hydrant TRC 100 from hydrant TRC 200 from hydrant TRC 300 from hydrant 1,000 gpm 1.24 ppm 0.04 ppm 0.08 ppm 0.07 ppm 0.03 ppm 0.02 ppm From: Portland Water District 2015

11 Preliminary Assessment Hydrant Flushing Strategy Key Assumptions: Acute Toxicity primary concern = ppm chlorine 200 distance from hydrant allows TRC concentration that could be sufficiently diluted by stream at 1.5 cfs (based on average flushing flow rate of 600 gpm) Stream flow data is presumed at this time High likelihood that many small urban waters are at <1 cfs during late summer and fall months. Based on 4 years of flow data from Capisic Brook Portland. Large water bodies >50 cfs not likely a concern due to dilution

12 Preliminary Assessment Hydrant Flushing Strategy Concentration (ppm) at 200' from hydrant Stream Flows (cfs) In-stream concentration (mg/l) for hydrants discharging at 1 cfs (~450 gpm) 0.03 In-stream concentration (mg/l)for hydrants discharging at 2 cfs (~900 gpm) In-stream Values of Concern (> acute toxicity criteria) In-stream concentration (mg/l) for hydrants discharging at 3 cfs (~1350 gpm) From: K. Rabasca, Integrated Environmental

13 Preliminary Assessment Hydrant Flushing Strategy

14 Preliminary Assessment Hydrant Flushing Strategy

15 Preliminary Assessment Hydrant Flushing Strategy Lewiston Program Strategy Mapped Water Distribution System Mapped Drainage Network Used buffers around wetlands and watershed to prioritize higher TRC discharges

16 Preliminary Assessment Hydrant Flushing Strategy

17 Preliminary Assessment Hydrant Flushing Strategy

18 Preliminary Assessment Hydrant Flushing Strategy Lewiston Program Strategy The City of Lewiston intends to use hydrant diffusers and de-chlor Log the following when sampling hydrant flushing Total Chlorine Residual (TCR) Flow Rate Duration of Discharge Date and Time of Discharge Hydrant discharge sampling prior to discharge into receiving water and record distance from hydrant Goal: Keep discharges below acute toxicity in-stream concentration limits

19 Questions?