Park City, Utah Arsenic removal from ground water

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Courtesy of Filtronics, Incorporated

Background

Park City Utah Water, which serves a population of 6,500, has five water sources. Spiro Tunnel and Spiro Portal are two that were in need of Iron and Manganese removal as well as above limits for Arsenic. Filtronics was engaged by the engineering firm of Eckhoff, Watson and Preator (EWP), Salt Lake City, to perform pilot tests for the Park City Municipal Corporation. The purpose of the study was to demonstrate the capability of Electromedia I to remove arsenic and turbidity along with iron and manganese. Electromedia I and the Filtronics designed system is recognized as the “state of the art” iron and manganese removal system.

The results of the tests were presented in the engineers’ report which follows. As a result, the corporation ordered the engineers to design a full-scale treatment facility. At the present time, Filtronics is manufacturing a treatment system with an initial capacity of l,000 gallons per minute for Park City. Incorporated in the first phase are automation, distribution piping and chemical feed capacity for a future expansion, projected for 4,000 gallons per minute.

Scope

This project was conducted to determine the treatability and feasibility of using water flowing from the Spiro Tunnel for municipal supply. The Spiro Tunnel is located to the east of Thaynes Canyon and above Three Kings Drive, adjacent to the Park City Municipal Corporation’s Golf Course Maintenance Facility. Water flowing from the Spiro Tunnel amounts to approximately 7,200 acre-feet per year. Some of this water is currently collected from a low-head bulkhead located approximately three miles inside the Spiro Tunnel mine shaft and is used for municipal supply. The remainder of the water flows through the tunnel and is used primarily for irrigation purposes. To determine the feasibility of using this water as a possible source of municipal supply, Park City Municipal Corporation contracted with Filtronics, Inc. Of Anaheim, California, to deliver a pilot plant and conduct actual field tests to determine the treatability of the water source.

Water Sources

Spiro Tunnel Source

Water collected on the upstream side of the low-head bulkhead, located approximately 13,000 feet inside the mine tunnel, flows through a 12-inch diameter permastran pipeline to the Spiro Tunnel Splitter Vault. This water will be referred to as Tunnel Water hereafter. The characteristics of this water are illustrated in Table 2-1.

Spiro Portal Source

The second source of water considered in this project is water which does not flow into the 12-inch diameter permastran line and includes water that is generated in the first 13,000 feet of the mine tunnel, the Thaynes Drift and the Thaynes Shaft. This water will hereafter be known as Portal Water. This water (see Table 2-1) is considerably higher in iron than the Tunnel Water, with peaks of up to three times the MCL. The arsenic content was comparable to the Tunnel Water concentration. However, this source was considerably more turbid than the Tunnel Source. The source would also be more susceptible to seasonal fluctuations.

Theriot Spring Source

The third source studied was the Theriot Spring, located just to the southwest of the Park City Municipal Corporation’s existing Golf Course Maintenance Facility. The Theriot Spring is a very high-quality water source, very low in iron and arsenic and of very low turbidity (see Table 2-1). It is currently being blended with the Spiro Tunnel Water to reduce the arsenic concentration delivered to municipal customers.

To facilitate the piloting operations, EWP Engineering Developed a Temporary Plumbing Plan to deliver all three water sources to the pilot plant location at the required pressure of 30 psi and at a flow rate of 20 gallons per minute. The EWP Engineering design consisted of a 2-inch diameter PVC Schedule 40 pipe, valves, flow meters and booster pumps to achieve the filter plant requirements.

Column Test

The Filtronics System is based upon their Electromedia I filter media. The media is a specially processed material that is naturally occurring, and was originally developed to filter iron and manganese from municipal water supply sources. The media has an adsorptive surface that attracts ions of iron and manganese. Once attracted to the media, the iron and manganese molecules form a floc which accumulates on the media. To determine the feasibility of using this media and technology on the water flowing from Spiro Tunnel, Filtronics delivered first a 3-inch diameter column testing apparatus and eventually a full-scale pilot plant.

The column testing unit consisted of two 3-inch diameter acrylic columns. The upstream column facilitated chemical mixing while the second column contained the actual filter media. The 3-inch diameter column provided approximately 0.05 square feet of surface area of media which, when loaded at a flow rate of 10 gallons per minute per square foot of surface area, yields 0.5 gallons per minute of finished water. The column was assembled on Thursday, July 12, 1990. On Friday, July 13, the first of the lab testing began on the Tunnel Water. On Wednesday, July 18, the water source was switched to the Portal Water. On Friday, July 20, the column tests were concluded.

Based on the results of laboratory tests, it was determined that the 3-inch column was achieving a 36% reduction in the arsenic concentration in the Tunnel Water and 66% reduction in the arsenic concentration in the Portal Water. It was then decided to continue with further testing, using the full-scale pilot plant.

Pilot Test

On Monday, July 30, the full-scale pilot plant testing began. The full-scale pilot plant is a skid-mounted unit capable of filtering at a rate of 20 gallons per minute. This is achieved using two reaction vessels and one filter vessel. The filter vessel has approximately two square feet of surface area of media which, when loaded at a flow rate of 10 gallons per minute per square foot of surface area, yields 20 gallons per minute. The pilot plant was operated on an automated eight-hour filter run schedule with a four-minute backwash followed by a one-minute purge cycle.

The backwash rate was double the filtration loading rate and was equal to 40 gallons per minute. This is a fairly vigorous flow rate and effectively rubs the particle of the media together and dislodges the floc that has formed on the media. The one-minute purge cycle following backwash serves to settle the filter back from its expanded state and to clear out any possible contaminants.

The pilot plant was operated continuously through Sunday, September 2, when the testing was concluded. The purpose of the pilot plant was to further document the removal efficiencies and to determine the chemical feed rates and required quantities. The evaluation sheet shown as Table 5-1 was completed using information obtained during this pilot plant run.

Finished water shall conform to all other primary and secondary USPHS-MCL standards.

Field tests were conducted on a daily basis by Filtronics personnel to determine changes in operation parameters. The biggest variable in operations is the chlorine feed rate. Chlorine serves the purpose of oxidizing the iron and manganese and prepares these substances for adsorption onto the filter media. Once the field tests indicated favorable removal rates, samples were taken by EWP Engineering personnel to American West Analytical Laboratories (AWAL) and Ford Analytic Laboratories (FAL) for verification. The daily test results are presented in Appendix A (Table 6-1, Specific Laboratory Results) and were targeted at a limited range of parameters.

After nearly continuous operation through the month of August 1990, the daily specific laboratory results were reviewed and it was determined the pilot plant was being operated at optimal conditions. On August 31 the testing to meet the State of Utah Department of Health, Division of Environmental Health, Bureau of Drinking Water/Sanitation requirements began. Appendix A (Table 6-2) illustrates the Complete Laboratory Results compiled from the laboratory testing conducted on samples taken from August 31 through September 2. The following paragraphs explain in further detail some of the more important laboratory results.

The removal rates for arsenic on the Tunnel Water were approximately 36%, while the removal rate for arsenic on the Portal Water was approximately 66%. This, it was felt, could be attributed to the additional iron present in the Portal Water. In order to determine this relationship, the Tunnel Water was inoculated with a solution of ferric chloride, which effectively increased the iron concentration. The results from the Tunnel Water tested with the ferric chloride addition indicated an approximate 70% arsenic removal rate. When the Portal and Tunnel Water sources were combined, the removal rate was approximately 46%. This would further support the hypothesis of enhanced arsenic removal with the presence of iron.

For iron removal, the Filtronics Pilot Plant performed very well. Raw water concentrations of approximately three times the MCL for iron were observed. The resulting iron concentrations in the finished water were below the limits of detection <0.03 mg/l. The MCL for iron is 0.3 mg/l; some raw water iron concentrations were observed as high as 0.8 mg/l.

The Filtronics media also performed very well on manganese removal. Raw water concentrations of 0.06 mg/l were observed. The MCL for manganese is 0.05 mg/l and the resulting finished manganese concentrations again were below detection limits <0.02 mg/l.

In addition to iron and manganese removal, the Filtronics media was very effective in reducing turbidity levels. The MCL for turbidity from surface water sources is 1 NTU and 5 NTU for groundwater. Raw water turbidities were witnessed as high as 8 NTU with resulting finished turbidity levels less than 0.5 NTU.

The Filtronics filter media is also somewhat capable of filtering bacteria and protozoa. This is due to the effective size of the filter media, which is approximately 5-8 microns. The Giardia lamblia has an effective size of 5-25 microns, which would indicate that this filter may be capable of removing the protozoa. Some bacteria removal could be expected, but due to the variation and somewhat smaller size (0.5 to 5 microns), the filter will have a limited effect. However, bacteria is more susceptible to chlorination than the Giardia and can be effectively dealt with using conventional chlorination techniques.

The Electromedia Process

The raw water is oxidized utilizing chlorine as the oxidant and ferric chloride and polymeric aluminum silicate sulfate (PASS) for adsorption. The chlorine and ferric chloride are introduced in front of a one-minute detention and mixing vessel. The PASS sulfur dioxide are introduced at the exit of the first reaction vessel and in front of the second one-minute detention and mixing vessel. The flow from the second reaction vessel is directed to Filtronics Model GWT-1 gravity water treatment system consisting of:

  • Long chain organic polymer addition to aid coagulation and flocculation
  • Rapid mix, 1000 sec -¹ velocity gradient using counter current mixing with a 20-second retention time to maintain consistent mixing and thorough dispersion of the polymer
  • Flocculation, low energy, variable speed turbine, 50 second velocity gradient, 20-minute retention in a baffled chamber to produce a slow, random circulation, maximizing the flocculation process
  • Clarification with Filtronics exclusive SuperSlant parallel plate clarification at very low velocities (600 gallons per day per square foot)

The product of the GWT treatment system is pumped through Filtronics Electromedia I iron and manganese adsorptive media. Recent testing demonstrates that Electromedia I adsorptive characteristics extend to a wide range of heavy metals, including arsenic.

Raw water arsenic levels of 52 to 56 ug/l were consistently reduced to 4 ug/l or less.

Conclusion

The water flowing from the Spiro Tunnel appears to be very well suited for removal of arsenic, iron and manganese and a significant reduction in turbidity using the Filtronics Electromedia I as determined through the extensive pilot plant testing and operations. This treatment process is capable of meeting current USPHS-MCL standards. This water source also appears to be Park City Municipal Corporation’s most economical source for development to meet future demands. As an independent third party observing engineer, we concluded that the use of the Filtronics Electromedia I was effective and feasible. We hereby recommend its use by Park City Municipal Corporation for the treatment of the Spiro Tunnel water source for inclusion with the City’s other potable supply sources

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