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The South Texas Sand Sheet (STSS) consists predominantly of medium- to fine-grain eolian sand deposits and sand dunes. STSS covers over six counties with an area of approximately 9.15 × 103km2with thickness ranging between less than a meter and over 10 m. Groundwater contamination is of particular concern as groundwater resources are the principal water source in this area. The preliminary conceptual hydro-geologic model implies that the STSS is a significant hydrologic component for shallow groundwater flow and can be potential storage and/or significant environmental flow input into nearby hypersaline Lower Laguna Madre (LLM). Water (fresh/brackish) held in the STSS should be taken into consideration when accounting for regional water balance/budget, e.g., groundwater recharge and storage, flood control, and discharge to coastal areas. The geospatial analysis was conducted using geographic information systems (GIS) spatial analysis tools with well logs from Texas Water Development Board (TWDB) groundwater database and preliminary drilling in the field. A DRASTIC model developed within a GIS framework was applied to evaluate the groundwater vulnerability of the STSS. DRASTIC modeling suggested that STSS with high risk to pollution is mainly located in the eastern portions of the STSS where factors, i.e., high hydraulic conductivity and high-water table, allow easy access for contaminants to reach the shallow groundwater aquifer. The assessment found that around 94% of the unconfined aquifer in STSS has moderate to high vulnerability to contamination. The sensitivity analysis of DRASTIC model showed that the removal of hydraulic conductivity, topography, and soil media parameters caused an increase in groundwater vulnerability to pollution. Moreover, single-parameter sensitivity analysis results suggested that the net recharge rate, hydraulic conductivity, and soil media parameters were more effective in determining the groundwater vulnerability than the DRASTIC model assumed. Results of this study suggest that the groundwater vulnerability in STSS is high and assessment maps can be used to evaluate possible environmental and economic impacts to ecosystems on the adjacent Lower Laguna Madre.

Sorption tests and pipe‐drum experiments were conducted to study permeation of monoaromatic compounds in gasoline through five polymeric materials used in ductile‐iron (DI) pipe gaskets. Ethylene propylene diene monomer (EPDM) had the highest sorption of premium gasoline, and fluoroelastomer rubber had the lowest. A comparison of gaskets' heel and bulb portions found that the heel sorbed less gasoline, suggesting greater resistance to permeation. Pipe‐drum experiments showed that the order of breakthrough of benzene‐toluene‐ethylbenzene‐xylene compounds for gaskets exposed to premium gasoline was EPDM > chloroprene rubber ≈ styrene butadiene rubber (SBR) > nitrile rubber (NBR). For DI pipes with SBR gaskets exposed to premium gasoline, the benzene concentration after 8 h of stagnation exceeded the maximum contaminant level (MCL). With typical water flow rates in pipes, the estimated benzene concentration did not exceed the MCL. If pipes are to be installed in gasoline‐saturated groundwater, NBR gaskets are preferred over SBR gaskets.

Pipe‐bottle tests were conducted to investigate the permeation of benzene, toluene, ethylbenzene, and xylene (BTEX) compounds through 1‐in.‐diameter high‐density polyethylene (HDPE) pipe exposed to gasoline‐contaminated water and gasolinecontaminated unsaturated soil. Using the time‐lag method, the concentrationdependent diffusion coefficients of BTEX compounds were estimated to be on the order of ~2 to ~9 × 10‐9 cm2/s. Smaller pipes were more vulnerable to permeation than larger pipes, and pipes subject to periodic stagnation were more likely to exceed the maximum contaminant level of benzene than were pipes with continuous water flow. Under otherwise identical conditions, HDPE pipes buried in a soil of high organic matter were permeated to a lesser extent than pipes buried in a soil of low organic matter for exposure times exceeding 30 days.