Fluoride Reduction in Community Water Supplies
A 92-page report prepared for the state of South Carolina, Department of Health & Environmental Control, Water Supply Division. Volume One – 1980.
Forty-three community water supplies located along the east coast of South Carolina contain fluoride concentrations which exceed the limit established by law. During the course of this study, each high fluoride supply was evaluated in an effort to identify one or more viable alternatives that might be implemented to achieve compliance.
The primary option proposed for the majority of systems was blending. By constructing shallow wells that tap a low-fluoride aquifer and mixing their yie1d with that of the existing deep wel1s, fluoride concentrations can be attenuated to acceptable levels in the combined supplies. For blending to be successful? twenty-five communities would be required to drill 204 new wells. The total estimated capital cost of blending is $15,305,000.
The remaining communities can achieve compliance by imp1ernenting one of four other alternatives. Those alternatives and their attendant capital costs are as follows: seven would replace existing wells with new ones at a cast of $385,000, eight would abandon existing supplies and purchase water from an adjacent utility at a cost of $200,000, two would employ activated alumina treatment to reduce fluoride at a cost of $10,472,000, and the remaining one would construct a separate distribution system to serve exempt users exclusively at a cost of $230 1 000.
Implementation of the primary alternative by all forty-three communities would require a state-wide capital expenditure of $26,592,000.
As of the 24th of June, 1977, water supplies throughout the United States were required to comply with the Environmental Protection Agency (EPA) National Interim Primary Drinking Water Standards. Those standards established a maximum contaminant level (MCL) for fluoride and nine other inorganic chemicals. Enforcement responsibility for the standards was requested by, and subsequently granted to, the South Carolina Department of Health and Environmental Control (SC DHEC). As an initial step toward bringing South Carolina water supplies into compliance with the law, the State authorized this study of fluoride reduction alternatives. During the course of the study, which was funded by EPA and conducted under the auspices of SC DHEC, forty-three community water supplies were evaluated and conceptual solutions for reducing fluoride concentrations were formulated for each of the affected systems. For systems where treatment of an existing or alternate water source was indicated, desk-top system designs were developed; where fluoride attenuation by blending the existing supply with the yield from proposed shallow wells was indicated, designs were based upon estimates of water quality and quantity obtained from well drillers, the South Carolina Department of Water Resources and United States Geological Survey personnel. Planning-level cost estimates were prepared in 1980 dollars for all alternatives and served as a Individual reports documenting the results of the study, as applicable to a specific system, were prepared and transmitted to the respective purveyor responsible for each supply determined to be in non-compliance. Copies of those reports are contained in Volume Two of this document.
PROPOSED FLUORIDE REDUCTION METHODS
All high fluoride water utilized as a community source of supply in South Carolina is drawn from wells. Reduction of the fluoride concentration in the yield from those wells can be achieved in one of three ways. The water can be treated to remove a portion of the fluoride, it can be blended with a low fluoride source, or the source can be abandoned in favor of a more acceptable supply. Depending upon a host of site-specific conditions, variations of all three basic fluoride reduction methods can be implemented by the various purveyors to bring their respective systems into compliance.
Blending low fluoride water with existing supplies to achieve an acceptable mix was determined to be a viable option for twenty-seven systems. Of those, blending ranks ?s the least expensive solution for twenty-five. Implementation of the primary alternative in all systems would require the construction of 204 new shallow blending wells having a combined capacity of 11,573 gallon per minute (GPM).
The cost of designing and constructing the blending facilities was estimated at $15,305,000. The blended supply would be distributed to 29,465 consumers (approximately 100,000 people).
The scope of this study did not include the construction of test wells; consequently, availability and capacity were estimated from existing information obtained from private contractors and governmental agencies. Some capacity variation will occur in all wells constructed in response to the information provided in this report. However, the projected yield should be attainable in most instances.
Blending shallow well water with existing supplies will create iron-related aesthetic problems in most communities. The severity of those problems will vary with the actual iron concentrations that are encountered and with the blending ratios required to reduce the fluoride content of the combined supply to acceptable levels.
Lacking accurate quality data, the assumption was made that sequestering would provide a relatively inexpensive means of controlling red water in most systems. Iron removal was included in the blending scenario for three communities where the success of sequestering is doubtful. Those communities are the City of Conway, Bulls Bay Rural Community Water District, and North Myrtle Beach.
Shallow wells are generally more susceptible to bacterial contamination than are deep wells. Consequently, gas chlorination equipment and contact tanks were included in the estimated cost of several specific blending alternatives.
Abandonment of existing wells in favor of another source of supply was determined to be a viable option for twenty-five communities. Purchasing water from another utility and constructing new wells were the two variations of abandonment found to be feasible.
Buying water from an adjacent utility was presented as a primary option for eight systems. Of those, five would be able to obtain a low-fluoride supply, the remaining three would tie to a larger system that is in noncompliance. The rationale behind connecting to a larger non-complying utility lies in the economy-of-scale that would be realized by the large purveyors in reducing fluoride as opposed to the small system operator. For example, Crystal Lakes Mobile Home Park would incur an annual per consumer cost increase of $540.00 by installing an activated alumina treatment system on its existing supply. However, by purchasing water from the City of Myrtle Beach, which would also employ activated alumina treatment, Crystal Lakes could reduce its annual per consumer cost increase to $133.11. Comparison of the two treatment alternatives in terms of cost per unit of installed capacity verifies the economy-of-scale to which the significant decrease in consumer cost is attributed. That comparison is as follows …
DEMINERALIZATION BY REVERSE OSMOSIS
The reverse osmosis process was reported to be employed in more than five hundred plants having capacities greater than 25,000 gpd in 1977.31 The principle underlying desalination by reverse osmosis (RO) is that fresh water will diffuse out of a brine solution across a membrane when the pressure applied to the brine side is greater than the osmotic pressure.32, 33, 34, 35 The applied pressure, the ambient water temperature, and the permeability of the membrane are the major factors determining the quality and quantity of the product water. As an indication of fresh water flux across the membrane, approximately 1,000 mg/1 of total dissolved solids (TDS) is equivalent to 10 psig osmotic pressure; the volume of desalinated effluent will be directly proportional to the difference between the externally applied pressure and this osmotic head.31
… “Forty-three community water supplies located along the East coast of South Carolina contain fluoride concentrations which exceed the limit established by law. During the course of this study, each high fluoride supply was evaluated in an effort to identify one or more viable alternatives that might be implemented to achieve compliance.”
The communities are:
Bulls Bay Water District – Central MHP – Conway – Crystal Lakes MHP – Edisto Beach – Forest Acres MHP – Garden City Beach – GCW&SA Pawley’s/Murrell’s – GSW&SA Garden City Area – GSW&SA Socastee – Hemmingway – Inlet Oaks MHP – Isle of Palms Water Company – Jamestown – Kingstree – Lane – Little River – Loris – Mike Williamson MHP – Mt. Pleasant – Myrtle Beach – Myrtle Beach Air Force – North Myrtle Beach – North Tranquil Acres – Oakey Swamp MHP – Pine Ridge MHP – Plantersville Water System – Platt Water Company – Red Hill Water System – Rock Bluff S/D – Rose Hill Water System – Sangaree S/D – South Tranquil Acres S/D – Town of Stuckey – Sullivans Island – Surfside Beach – Sycamore Acres S/D – Wagon Wheel Farms.
*The 92-page report is online at http://fluoridealert.org/wp-content/uploads/south-carolina.fluoride-reduction-alternatives-report.1980.pdf