August Update on Mill River Dredging

The following is a monthly project update for the cleanup of lead impacted sediment by hydraulic dredging in the Mill River.

The CT Department of Energy and Environmental Protection together with TRC, the firm conducting the cleanup work for Exide are currently in the process of dredging, dewatering the sediment, treating the filtrate water from the dewatering process, and discharging treated water back to the Mill River.

All of the sediment dewatering and water treatment work is occurring at the facility on Exide’s property at 2190 Post Road in Fairfield.

During July the following activities happened: 

  • Dredging in Area II – the portion of the Mill River adjacent to Exide’s property, between the Metro North railroad bridge and the Post Road bridge;
  • The turbidity meters (yellow buoys with solar panels), turbidity curtains (floating yellow items), and the large orange pipeline (that conveys sediment to Exide’s property) were moved periodically, as dredging progressed in Area II;
  • Dewatering of sediment and treatment of filtrate at Exide’s property is ongoing. The filtrate (i.e., water) treatment process has been very effective. For example, since the filtrate treatment plant (WTP) began operation in October 2014, the average concentration of lead in water discharged through July 29th is very low, 18.76 ug/L (i.e., parts per billion). This is approximately 13% of the CT DEEP permitted discharge limit of 150 ug/L;
  • Monitoring and sampling, as required by CT DEEP is being conducted, and permit limits are being met with the exception of a minor WTP effluent result of lead over the permitted limit. The engineers notified CT DEEP at once and immediately discontinued dredging and discharge of treated water to the River. Working closely with DEEP, the engineers and on‐site staff adjusted the water treatment plant operations. Don Gonyea of CT DEEP authorized re‐start of discharge to empty the basin and evaluate treatment changes and requested the evaluation to continue upon re‐start the dredging operations a few days later. Under DEEP’s supervision, the WTP operations were re‐started and the follow‐up effluent samples have all been non‐detect for lead.
  • The dredge that was working in Area III – the portion of the Mill River between the Post Road bridge and Tide Mill Dam, is temporarily positioned in an alcove near the Post Road bridge. This dredge remains in Area III as it is not possible to move it under the Post Road bridge due to water levels. The dredge will be needed again in two months to facilitate dredging in Area IV. It is also possible that after final sediment verification sampling occurs in Area III, that additional “polishing” dredging may be required. Exide received approval from CT DEEP for the Certificate of Permission to temporarily position this dredge. The Harbor Management Commission’s review did not object to the temporary positioning of dredging equipment;
  • During the last week of July, some additional equipment was working on Exide’s property and in the vicinity of Post Road. The equipment was to remove some sediment along the sheet pile wall area and the southwest corner of Area II that is not accessible to the dredge. This material was placed away from the wall so that the dredge could remove it more readily.

In August, the following activities will be conducted:

  • Dredging will continue in Area II and the planning for Area IV dredging. Dredging in Area IV will commence on October 1st, after the end of the shellfish spawning restriction period. The turbidity meters (yellow buoys with solar panels), turbidity curtains (floating yellow items), and the large orange pipeline that conveys sediment to the Exide property will be moved as dredging progresses in Area II;
  • Dewatering of sediment and treatment of filtrate will continue at Exide’s property;
  • Monitoring and sampling will continue, as required by CT DEEP.

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