Resolving aquifer behavior near a focused recharge feature based upon synoptic wellfield hydrogeochemical tracer results

Stream Loss Contributions to a Municipal Water Supply Aquifer in Memphis, Tennessee

“…Ivey et al (2008) used an inverse age-distribution model along with estimated mixing ratios of shallow and Memphis aquifer water and measured 3 H/ 3 He data to simulate vertical recharge fluxes to the Memphis aquifer and derive a probable recharge window location. The recharge window location of Ivey et al (2008) is partially coincident with the window location estimated by Parks (1990) and is consistent with a paucity of clay layers in the upper Claiborne confining unit within the central part of the well field (Larsen et al, 2002;Gentry et al, 2005). Although the above studies established the probable location for leakage into the aquifer near the Sheahan well field, no detailed hydrologic studies have been conducted of the probable recharge source, Nonconnah Creek.…”

“…The water table surface in the shallow aquifer is generally within 1 m above the base of the shallow aquifer (e.g., well 96s). However, well 99s was screened in the sandy upper part of the upper Claiborne confining unit at this site because no water was present in the shallow aquifer (Gentry et al, 2005); thus, in this well the water table is substantially below the base of the shallow aquifer. Given that the shallow aquifer has as much as 8 m of saturation at the NC cluster, a pronounced lateral gradient exists from the Nonconnah Creek to the Sheahan well field area in the shallow aquifer.…”

“…The chemical evolution and mixing of both Nonconnah Creek and shallow aquifer waters with water in the Memphis aquifer was modeled in a manner similar to that used by Larsen et al (2003a) and Ivey et al (2008). Water chemistry for Memphis aquifer waters affected by leakage is represented by production well 99 (Ivey et al, 2008), which is in an area in which a hydrologic window is present within the upper Claiborne confining unit (Gentry et al, 2005;Ivey et al, 2008). Unaffected water in the Memphis aquifer is represented by production well 78A (in the northeastern part of the well field), which consistently shows little or no 3 H and 3 He (Gentry et al, 2005;Ivey et al, 2008).…”

“…Water chemistry for Memphis aquifer waters affected by leakage is represented by production well 99 (Ivey et al, 2008), which is in an area in which a hydrologic window is present within the upper Claiborne confining unit (Gentry et al, 2005;Ivey et al, 2008). Unaffected water in the Memphis aquifer is represented by production well 78A (in the northeastern part of the well field), which consistently shows little or no 3 H and 3 He (Gentry et al, 2005;Ivey et al, 2008). The Memphis aquifer water chemistry is from 2002; however, comparison of data from Larsen et al (2003a), Gentry et al (2005), and Ivey et al (2008) indicates little interannual variability in water chemistry.…”

“…Previous studies (Larsen et al, 2003a;Ivey et al, 2008) have shown as much as 30 percent modern water contributing to groundwater pumped in the Sheahan well field from the semi-confined Memphis aquifer, the municipal water source in much of western Tennessee. Studies (Larsen et al, 2003a;Gentry et al, 2005) of multiple tracers show that several geochemical reactions, especially oxidation-reduction reactions, take place during the recharge process. Although Ivey et al (2008) demonstrate a leakage location into the Memphis aquifer proximal to the Sheahan well field, the overlying shallow aquifer receives little direct recharge and is almost completely unsaturated, Parks (1990).…”