Changes in Pumping-Induced Groundwater Quality Used to Supply a Large-Capacity Brackish-Water Desalination Facility, Collier County, Florida: A New Aquifer Conceptual Model

Thomas M Missimer,Zoie R Kassis,W Scott Manahan,Robert G Maliva,Quillan L Arico,Weixing Guo

doi:10.3390/w13141951

Thomas M Missimer, Zoie R Kassis + Show 4 more

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https://doi.org/10.3390/w13141951

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Abstract

Brackish-water reverse osmosis (BWRO) desalination facilities are designed to treat feedwater within a fixed range in salinity. If the salinity and ion concentrations of the feedwater rises above the maximum design concentrations, then the plant may ultimately fail. BWRO plants typically use groundwater as a feedwater source. Prior to the process design, a detailed groundwater assessment is made to characterize the source aquifer system and to develop a solute-transport model that is used to project the changes in water quality over the expected useful life of the facility. Solute transport-modeling performed for the Collier County (Florida) South BWRO facility, which was designed to produce 30,303 m3/d with an expansion to 75,758 m3/d, used an aquifer system conceptual model that assumed upwards migration over time of brackish waters with higher salinities into the production zones. This conceptual model is typical of how most BWRO systems developed in the United States operate. The original solute transport model predicted a range of increases in dissolved chloride concentrations over a 20-year period from a low of 5 mg/L/yr, a mid-range of 35 mg/L/yr, and a high range of 85 mg/L/yr. Actual data collected over a 11- to 13.5-year period showed that the dissolved chloride concentration average of the feed water decreased by 16 mg/L/yr. The original conceptual model was found to be inaccurate in that it suggested an upwards recharging system, whereas downward leakage (or perhaps lateral migration) of fresher water appears to be occurring in the system. This is an example of a long-term solute-transport model audit, which is rarely performed, in which a new conceptual model was found to be applicable to an aquifer system used to feed a BWRO facility.

Highlights

Freshwater shortages plague many regions of the world, in high-population growth areas and arid regions [1]
Brackish water is defined by the U.S Geological Survey to have a total dissolved solids (TDS) concentration lying between 1000 and 10,000 mg/L [2]
Cannot be used directly as drinking water based on the drinking water quality standards [5]

Summary

Introduction

Freshwater shortages plague many regions of the world, in high-population growth areas and arid regions [1]. Brackish water is defined by the U.S Geological Survey to have a total dissolved solids (TDS) concentration lying between 1000 and 10,000 mg/L [2]. The lower range of brackish-water, between TDS concentrations of 1000 and 3000 mg/L, can replace some uses of freshwater, for irrigation of salt-tolerate plants and some industrial applications [3,4]. The U.S Environmental Protection Agency defines underground sources of drinking water to have a TDS of less than 10,000 mg/L [5]. The Collier County South BWRO facility was originally designed to contain 14 pro2.1. The Collier County South BWRO facility was originally designed to c Additional production wells, 24 completed in Hawthorn Aquifer Zone I and three wells in duction wells with individual well capacities m3/d (700 gpm).

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