Abstract
The San Antonio Water System (SAWS) serves more than two million people and is among the largest water utilities in the United States. Much of SAWS’s supply is sourced from the Edwards (Balcones Fault Zone) Aquifer (Edwards BFZA), a major sole‑source karst aquifer in south‑central Texas. The aquifer exhibits pronounced spatial heterogeneity in well performance due to its karstic nature, structurally complex setting, and variable depositional facies. Recent severe drought and pumping restrictions have emphasized the need to understand where within the aquifer to drill and how inter‑station performance differs under stress. This study evaluates production variability across SAWS pump‑station wells completed in the artesian zone and intersecting distinct members of the Edwards Group. We relate well-scale performance, characterized primarily by specific capacity and drawdown data, to member-scale heterogeneity and structural setting using station records, aquifer‑test data, and published interpretations of fracture‑dominated flow at the well scale and conduit influence at regional scales. Inter‑station variability reflects how wells with similar construction and operating conditions can differ markedly in production, an effect that becomes increasingly important as climate related stressors intensify pressure on groundwater supplies. Observations indicate that production differences among stations reflect both local hydrogeologic variability and broader geologic controls, including depositional changes and structural boundaries. These differences highlight how documented hydrogeologic heterogeneity within the Edwards BFZA is expressed through variability in well performance across SAWS production system. Engineering implications include improved well-site selection and completion strategies, and integration of aquifer-test data with geologic interpretation to better characterize well and station performance. SAWS operates an extensive, hydraulically interconnected pressure‑zone system, and production variability at the wellfield scale translates directly to system‑wide considerations, including pressure management, zone balancing, and drought-stage operations. These findings inform utility‑scale decisions related to drilling, testing, and operational planning.
DOI
https://doi.org/10.5038/9781967518012.1014
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Production Variability in the Edwards Aquifer, South-Central Texas, USA
The San Antonio Water System (SAWS) serves more than two million people and is among the largest water utilities in the United States. Much of SAWS’s supply is sourced from the Edwards (Balcones Fault Zone) Aquifer (Edwards BFZA), a major sole‑source karst aquifer in south‑central Texas. The aquifer exhibits pronounced spatial heterogeneity in well performance due to its karstic nature, structurally complex setting, and variable depositional facies. Recent severe drought and pumping restrictions have emphasized the need to understand where within the aquifer to drill and how inter‑station performance differs under stress. This study evaluates production variability across SAWS pump‑station wells completed in the artesian zone and intersecting distinct members of the Edwards Group. We relate well-scale performance, characterized primarily by specific capacity and drawdown data, to member-scale heterogeneity and structural setting using station records, aquifer‑test data, and published interpretations of fracture‑dominated flow at the well scale and conduit influence at regional scales. Inter‑station variability reflects how wells with similar construction and operating conditions can differ markedly in production, an effect that becomes increasingly important as climate related stressors intensify pressure on groundwater supplies. Observations indicate that production differences among stations reflect both local hydrogeologic variability and broader geologic controls, including depositional changes and structural boundaries. These differences highlight how documented hydrogeologic heterogeneity within the Edwards BFZA is expressed through variability in well performance across SAWS production system. Engineering implications include improved well-site selection and completion strategies, and integration of aquifer-test data with geologic interpretation to better characterize well and station performance. SAWS operates an extensive, hydraulically interconnected pressure‑zone system, and production variability at the wellfield scale translates directly to system‑wide considerations, including pressure management, zone balancing, and drought-stage operations. These findings inform utility‑scale decisions related to drilling, testing, and operational planning.