Updated Wellfield Vulnerability Analysis for the Keene Heights Wells

Client: Trent Conservation Coalition Drinking Water Source Protection – Lower Trent Conservation: Ms. Andrea Hicks, 714 Murray Street, R.R. #1, Trenton, ON K8V 5P4

Key Personnel: E.J. Wexler

Earthfx Incorporated delineated wellhead protection areas (WHPA) for all municipal wells within the Trent Conservation Coalition Drinking Water Source Protection Region. Included in this analysis were the municipal wellfields serving the communities of Millbrook, Crystal Springs and Elgeti, and Keene Heights located north of Rice Lake.

A numerical groundwater model, referred to as the “Rice Lake Model”, was developed and calibrated for the area surrounding Millbrook, Crystal Springs, and Keene Heights. The communities were grouped together because of the similarity of their geologic and hydrogeologic setting. Backward particle tracking techniques were applied to delineate 2, 5, and 25 year time-of-travel WHPAs around the municipal wells. Forward particle tracking techniques were applied to assign vulnerability scores to subzones within each WHPA based on advective travel times from land surface to the water table and from the water table to the well screen (SWAT method).

An update to the wellfield vulnerability analysis was conducted to include the new Keene Heights well drilled in 2012. As part of the analysis, the interpretation of the local hydrostratigraphy and aquifer/aquitard properties were revised to include geologic and aquifer test data from the new well and from nearby water wells drilled in the area after 2008. The numerical model code was upgraded from MODFLOW-96 to MODFLOW-NWT V1.07 which resulted in a much more numerically stable model than was used in the previous work. The particle tracking analyses were conducted using the most recent version of MODPATH (Version 6.0). Vulnerability scores were assigned to subzones within the WHPAs based on the updated SWAT analysis. The uncertainty analysis for the WHPA delineation was also revised to reflect the new information that helped remedy the sparsity of data in the wellfield vicinity noted in the previous analysis.