www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 15 4.2. CHARACTERISATION OF SURFACE WATER - GROUNDWATER INTERACTIONS In general, warm springs are most likely to have a volcanic origin from deep groundwater with short travel times and it is reflected in the similar ionic characteristics observed between springs and deep groundwater (ref 7). However, similar shifts in water chemistry of surface water towards shallow groundwater have been noted during high flow events. These interactions have been re-assessed using naturally occurring tracer, radon gas. The estimated contributions of deep groundwater to surface water were found to be higher in the headwaters of T stream, Edmonds and Thompson sub-catchments, and Wharekirauponga catchment. Elevated radon levels in the warm spring suggest a deep underground origin. These radon results are more appropriate for applications to further understand possible mixing scenarios and end members based on simple linear mixing calculations than dating water samples as they have very short half-lives. Figure 4-3:Spring Locations, Groundwater Contours and T-Stream and EGV Veins (after GWS)
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