Abstract Groundwater of the unconfined Chalk aquifer in Champagne-Ardenne (NE France) is contaminated by perchlorate ( ClO 4 − ), a persistent water-soluble anion. The Chalk aquifer is a crucial water resource of the region, with complex hydraulic properties. The presence of ClO 4 − is of concern due to its potential adverse human health effects. In France, three sources of ClO 4 − contamination are suspected: industrial, military and agricultural. Both a comprehensive understanding of hydrogeological characteristics of the aquifer, and a sound knowledge of sources and behaviour of ClO 4 − in groundwater are required to allow the sustainable use of this groundwater resource. From data acquired during hydrogeological, geochemical, isotopic ( ClO 4 − ) and groundwater age (CFCs and SF 6 ) studies, and historical investigations in a study area located east of Reims, a conceptual model of Chalk aquifer function and ClO 4 − transfer has been established. High spatio-temporal heterogeneities in the unconfined Chalk aquifer are discussed. Different correlations between ClO 4 − , major ions and groundwater-level fluctuations are shown and interpreted, highlighting main factors governing the Chalk groundwater geochemistry and ClO 4 − transfer mechanisms, including water-level fluctuation, groundwater residence time, thickness of the unsaturated zone, superficial formations, distribution of fissure networks, aquifer–river relationships, origin and location of ClO 4 − in soil and human activity.

ABSTRACT The Washita Prairie segment of the Edwards (Balcones Fault Zone) Aquifer is a shallow unconfined aquifer that supports several historical springs, perennial streamflow to Lake Waco, and water for rural households and livestock. Secondary porosity in the aquifer is from neotectonic fractures and epikarst in the Georgetown and Edwards Formations. The fractures produce an “effective” porosity of ~1%. Thin soils allow rapid recharge, as indicated by water-level responses in wells within 24 h of rainfall events. Discharge is generally along second-order streams; topography is the dominant influence on groundwater flow direction. The interbedded clays in the Georgetown Formation create a preferred horizontal to vertical anisotropy. The fractured nature of the aquifer produces local heterogeneity, but regionally, the aquifer acts as a diffuse rather than conduit flow system. Weathering results in a layered flow system with greater effective porosity and permeability in an upper zone compared to the deeper zone. Washita Prairie springs are perennial, with discharges generally <0.05 m 3 /s. The groundwater is calcium bicarbonate facies with total dissolved solids (TDS) <500 mg/L in most springs and shallow-zone wells. Water quality in deeper wells is more variable, as these encounter the deeper flow system with slower circulation and higher TDS. The shallow water table and rapid recharge through fractures allow surface activities to impact water quality, and nitrate levels appear to be elevated above average background values in places. The Washita Prairie segment of the Edwards (Balcones Fault Zone) Aquifer may be able to supply over 50,000,000 m 3 of sustainable water on an annual basis with continued study and proper management.

ABSTRACT The northern segment of the Edwards (Balcones Fault Zone) Aquifer is an important source of water for municipalities, industry, and landowners in central Texas. Rapid population growth in this part of Texas has increased interest in the north segment of the aquifer and heightened concerns about groundwater availability. The aquifer consists of Cretaceous limestone stratigraphic units that crop out along its western margin and dip toward the east. Groundwater primarily flows from the aquifer outcrop recharge zones toward discharge zones along perennial rivers and streams in the outcrop area and to a lesser extent toward deeper parts of the aquifer, eventually discharging by cross-formational flow to overlying stratigraphic units, such as the Del Rio Clay, Buda Limestone, and Austin Chalk. Groundwater isotope compositions in the aquifer indicate that groundwater flow is most active in the unconfined parts of the aquifer and that most recharge occurs during late fall and winter months, even though highest monthly precipitation occurs during the spring. Pumping from the northern segment of the Edwards (Balcones Fault Zone) Aquifer is ~6.8 × 10 7 L/d, having peaked at ~1.0 × 10 8 L/d in 2004, but still up from ~3.4 × 10 7 L/d in the 1980s. Most of this pumping (~90%) is for municipal uses. However, in the rural northern and heavily urbanized southern parts of the aquifer, domestic and manufacturing uses, respectively, account for a significant portion of total pumping.