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Facility Name:
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Bennington
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Gail C. Tiffany, Bennington WWTF Laboratory Director
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Town of Bennington
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Bennington Wastewater Treatment Facility, Final Effluent Discharge, 244 Harringt
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06/11/2019
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06/17/2019
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07:00 am to 02:12 pm
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Discharged partly treated undisinfected effluent
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Other
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Other
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WWTF outfall
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We are not exactly sure what caused the sudden increase in E. coliforms. Some of the factors could be that we have had many heavy rain events; we have locally received over 3.5 inches of rain so far in June. Higher flows will cause scouring of our collection system and washing some material to the plant.
Another possible cause is that we are under construction and we do not have our primary digesters on-line right now. They will be down for 3 months and this causes primary sludge (undigested) to sometime recirculate within the plant. If that sludge contains more bacteria than normal, then our normal dose of chlorine may not be enough.
Another cause may be incomplete nitrification. This may be causing a nitrite lock/nitrogen sponge which will eat up available chlorine and cause partially disinfected water.
The Town of Bennington Wastewater crew has been working to correct this problem since we informed of the problem. We have increased our sampling to at least twice per week instead of the permit requirement of once a week. We have been in contact with state agencies since the beginning and will continue in keep them informed.
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Walloomsac River
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Lawrence J. Gates, Jr., Assistant DPW Director
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nForms
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Y
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On June 5th, the Bennington Wastewater Treatment laboratory analyzed a final effluent sample for E. coliform; the result was 57.62 colonies/100 ml. By permit the WWTF is allowed a limit of 77 colonies per 100/ml.
On June 11th a coliform sample was sent to Endyne Labs in West Lebanon, NH. We were informed the next day – Wednesday, June 12th -- that the result was > 2400 colonies/100 ml.
Thinking that perhaps the sample may have become contaminated during sampling operators resampled – sample and duplicate sample – and drove the samples to Endyne. Endyne called on Thursday, June 13th to inform us that the results were 2400 and 2200 colonies/100 ml respectfully.
Chlorine was increased in the contact chambers and after adequate detention time another final effluent sample was taken. This sample was sent to Hoosac Water Quality District (Williamstown, MA) with whom we have a working relationship and they happened to be running coliforms that day. The result received on Friday, June 14th was 167.9 colonies/100 ml.
Chlorine was again increased, and another sample was sent to Endyne on Friday, June 14th. The result on Saturday, June 15th was 160 colonies/100 ml. Operators increased the dosage of chlorine once the result was received.
On Monday, June 17th the final effluent was again analyzed for E. coliform and the result of analysis was 68.35 colonies/ 100 ml. This brought us back into compliance with our discharge permit. It is possible that compliance was met over the weekend, but we have no documentation to prove that. – E. coliform was again analyzed for in the final effluent on Wednesday, June 19th with a result of 11.225 colonies/100 ml.
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HNQ-NPZJ-89ZS1
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