AWWA WQTC50352 ✓ Most Recent

The Champlain Water District (CWD) intake is positioned 2480 feet offshore at a depth of approximately 75 feet in the northern channel of Lake Champlain's Shelburne Bay in Northwestern Vermont. Current and temperature profiles were gathered from July 1997 to June 1998 at one mooring in close proximity to the intake. Weekly microbial samples were analyzed for E. coli beginning in 1996. This sampling led to raw water microbial source tracking (MST) samples being collected during fall 1997 and spring 1998. Raw water turbidity data were also routinely obtained. Current and temperature data obtained 30 meters to the southwest of the intake pipe documented the presence of an interanl standing wave (seiche) with a period of approximately one day. This was in strong contrast to the dominant unimodal internal seiche of the central main lake with a period of approximately 4.3 days. Temperature data indicated that the CWD intake was occasionally impacted by warmer surface waters during May-October and that the metalimnion (thermocline) gradually dropped below the intake level in mid-October. Year-long observations created an understanding of the dynamics and quality of source water entering the intake pipe to ensure proactive treatment during unusual raw water quality fluctuations. Ater source dynamics training, CWD Treatment Specialists use weather forecasts and raw water temperature to predict sanitary and turbidity impacts at the intake. Future practices should include: online monitoring of the thermocline level and runoff density; and reducing the impact of sanitary and turbidity sources. Due to the discovery of the smaller seiche that affects Shelburne Bay, source protection area delineation has been narrowed from the entire lake to local Shelburn Bay and, possibly, Burlington Bay impacts. Includes 22 references, tables, figures. See more