Here are some more.
Modeling Spatial and Temporal Variation In Natural Background Specific Conductivity. https://cfpub.epa.gov/si/si_public_file_download.cfm?p_download_id=540509&Lab=CEMM
Effects Of Land Cover And Geology On Stream Chemistry In Watersheds Of Chesapeake Bay 1https://repository.si.edu/bitstream/handle/10088/135/LiuSpotJAWRA2000.pdf
Factors controlling the major ion chemistry of streams in the Blue Ridge and Valley and Ridge physiographic provinces of Virginia and Maryland. Paywall. https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.3360060108
Characterization of Major-Ion Chemistry and Nutrients in Headwater Streams Along the Appalachian National Scenic Trail and Within Adjacent Watersheds, Maine to Georgia. fig. 16 pg. 52 https://pubs.usgs.gov/sir/2011/5151/pdf/sir2011-5151-508.pdf