This letter summary report discusses the background, methodology, results, conclusions, and follow-up recommendation of an iron and manganese removal system pilot study performed July 9, 2002, on City of McCleary Well Nos. 2 and 3. The pilot test was conducted to evaluate performance and establish design criteria for an ATEC™ Iron and Manganese Removal System. Equipment was provided and testing was performed by Bill Ketchum of ATEC™ Systems Associates, Inc. Parametrix, Inc. witnessed the pilot study and independently sampled treated well water for iron and manganese. Independent samples were analyzed by STL Seattle Laboratories.
BACKGROUND
Well No. 2, constructed in 1952 to a depth of 82 feet, currently pumps 300 gallons per minute (gpm) and is the primary source of the City's water system. Well No. 3 was constructed in 1962 to a depth of 93 feet. Well No. 3 is used in periods of high demand and has a pumping rate of 540 gpm. Both wells have concentrations of manganese exceeding the state secondary MCL. Well No. 3 also exceeds the state secondary MCL for iron. Water from Well No. 2 is currently treated with sodium hypochlorite and a sequestering agent (Aqua-Mag). Water from Well No. 3 is hypochlorinated, but no sequestering agent is added.
Permitted water rights for both wells and the combined water system are shown in Table 1. Current pumping rates at Well No. 3 are greater than the maximum instantaneous flow rate and should be reduced to 500 gpm. The City of McCleary Water System Plan projects a planning horizon peak day water consumption rate of 486 gpm. The Water System Plan indicates that the "City would like to alternate use of Well Nos. 2 and 3." Iron and manganese removal treatment designed to treat the maximum water right flow rate of 500 gpm at Well No. 3 is recommended to meet current and future peak demand conditions and allow well alternation.
| Table 1. Well Nos. 2 and 3 Water Rights | |||
| Water Right | Well No. 2 |
Well No. 3 |
Combined Water System |
| Instantaneous Flow Rate (gpm) | 400 | 500 | 900 |
| Total Annual Flow (ac-ft/yr) | 640 | 673 | 673 |
PILOT TEST PROCEDURE
The ATEC™ trailer-mounted pilot test system was brought on site to perform water testing on July 9, 2002, (see Attachment A for pilot test system specifications). The pilot test equipment was first set-up next to the City's Well No. 2 pump house. Water from Well No. 2 was tested for approximately 4 hours before moving the equipment several hundred feet to the Well No. 3 pump house. Water from Well No. 3 was tested for approximately 5 hours.
Test equipment such as flow meters, metering pump, and the pilot filters were already pre-connected and ready to use inside the trailer. The pilot test filter system consisted of the following equipment:
Start-up of the pilot system was accomplished by connecting the pilot system to each well's discharge main with a rubber hose. The connection to the water line was made prior to hypochlorite and Aqua-Mag injection. The chlorine metering pump of the pilot injected hypochlorite solution into the pilot unit feed line slightly upstream of the filter to achieve the recommended 10 to 30 seconds contact time.
The pilot system set up at Well No. 2 was put into operation at approximately 8 a.m. The system was first backwashed to ensure clean filter media and then operated for a few minutes before taking the initial samples. Sample data analysis and recording at Well No. 2 started at 8:30 a.m. Both influent and effluent iron and manganese concentration were analyzed and recorded approximately every half-hour during the test. Instantaneous flow, totalized flow, effluent temperature, and effluent pH were measured continually by data recorders. Chlorine dose was calculated from the measured chlorine pumping rate and a known hypochlorite solution feed concentration.
Testing at Well No. 3 followed the same procedures as for Well No. 2, with the first samples analyzed and recorded at 12:40 p.m. To confirm anticipated low concentrations of H2S in the water source, one influent sample was analyzed for H2S during testing at each well.
RESULTS OF TESTING
ATEC™ Field Test Results Influent manganese concentrations were significantly higher than the allowable Maximum Contaminant Level (MCL) for both wells. Influent iron concentration at Well No. 3 also exceeded the MCL. MCL for iron and manganese are 0.3 mg/L and 0.05 mg/L, respectively. Test results at both wells indicate that iron and manganese concentrations were reduced to significantly below the MCL over the duration of pilot testing. The trend in iron and manganese removal efficiency did not vary significantly due to changes in flow rates and chlorine dosages. However, a filter vessel valve was inadvertently left in the backwash position during the first two sample events at Well No. 3, which lowered both iron and manganese removal efficiency for those samples. A summary of the field test data is shown in Table 2. Complete field test data for Well Nos. 2 and 3 are provided in Attachments B and C, respectively.
Field testing (with the Hach DR/2010 Spectrophotometer) of effluent chlorine, iron, manganese and H2S was performed immediately after the samples were taken. In addition, flow, chlorine solution pump rate, temperature, and pH measurements were recorded continually while the pilot test system was in operation.
| Table 2. ATEC™ Field Test Pilot Data Summary | ||
| Parameter | Well No. 2 |
Well No. 3 |
| Average Flow (gpm) | 7.89 | 8.70 |
| Average Loading Rate (gpm/ft2 media) | 10.05 | 11.08 |
| Calculated Average Chlorine Dose (mg/L) | 1.91 | 1.73 |
| Iron MCL (mg/L) | 0.3 | 0.3 |
| Average Influent Iron (mg/L) | 0.089 | 0.321 |
| Percent of MCL | 29.7% | 107% |
| Average Effluent Iron (mg/L) | 0.009 | 0.055 |
| Percent of MCL | 3.0% | 18.3% |
| Average Iron Removal Efficiency | 86.9% | 83.1% |
| Manganese MCL (mg/L) | 0.05 | 0.05 |
| Average Influent Manganese (mg/L) | 0.092 | 0.135 |
| Percent of MCL | 180% | 270% |
| Average Effluent Manganese (mg/L) | 0.002 | 0.006 |
| Percent of MCL | 4.0% | 12.0% |
| Average Manganese Removal Efficiency | 97.4 % | 95.4 % |
Independent Test Results
In addition to the field testing, duplicate samples were taken to an independent laboratory (STL Seattle) for verification of field results. One influent alkalinity and three effluent metals samples (for analysis of both iron and manganese) were collected during pilot testing at each well. The independent laboratory sample data is summarized in Table 3. The complete laboratory data record is included in Attachment D.
| Table 3. Laboratory Data Summary | ||||
Sample Time |
Iron Concentration (mg/L) |
Manganese Concentration (mg/L) |
Alkalinity (mg/L) |
|
| Well No. 2 | 09:00 | ND | 0.0060 | |
| 09:30 | 76 | |||
| 10:00 | ND | 0.0055 | ||
| 12:00 | ND | 0.0055 | ||
| Average % of MCL | < 33.3% | 11.3% | ||
| Well No. 3 | ||||
| 13:00 | ND | 0.0146 | ||
| 14:00 | ND | 0.0102 | ||
| 15:00 | 72 | |||
| 16:00 | ND | 0.0077 | ||
| Average % of MCL | < 33.3% | 21.7% | ||
| Note: ND = Not detectable at the sensitivity level of the laboratory testing method (0.10 mg/L). | ||||
BASIS OF DESIGN
Design criteria for the installation of a full-size ATEC™ filter system are based on pilot test results, ATEC™ specifications (see Attachment A), and the City's future needs as stated in the City of McCleary Water System Plan. Although iron and manganese removal efficiencies were very good over the range of loading rates tested, a maximum design loading rate of 10 gpm/ft2 was conservatively selected. This value is within the range of ATEC™ specifications (5 to 15 gpm/ft2). The full-scale system would be designed to contain at least 50 square feet of filter area to effectively remove iron and manganese from a maximum design flow of 500 gpm.
A system of four 4-foot-diameter ATEC™ filters is proposed (see System Drawing in Attachment E). An ATEC™ model number 48-48-04 filter with a maximum pressure rating of 150 psig would be used to meet the design flow of 500 gpm. This filter system would provide 50.3 ft2 of surface area and 151 ft3 of media. The four filter units would be arranged in a row and connected by a manifold system at the inlet and outlet to provide flow for backwash without the need for an external backwash supply.
Iron and manganese are removed from the water by adsorption to the filter media. To maintain efficient adsorptive removal of iron and manganese over extended periods of time, a continuous application of chlorine adequate to yield a free chlorine residual in the range of 0.5 mg/L to 1.0 mg/L in the filtered water is required. ATEC™ specifications indicate that optimal iron and manganese removal results are achieved when chlorine contact time with the influent water is between 10 and 30 seconds prior to entering the filter system. Existing chlorine injection equipment at each well pumphouse is adequate for the required chlorine dose; however, it is anticipated that the filter building would be located near the Well No. 3 pump house to achieve the optimal chlorine contact time for the larger source (of Wells No. 2 and 3) with the highest iron and manganese concentrations. An approximately 20-foot-by-30-foot filter building would be constructed to house the filter system and supporting equipment. The filter building size could be increased in order to provide space for chlorine injection equipment and chemical storage if the City desires to relocate and consolidate equipment.
Control valves would be provided to allow either Well No. 2 or Well No. 3 water supplies to be filtered. In the event that both wells are in operation concurrently (i.e. during reservoir cleaning), only the Well No. 3 water supply will have iron and manganese removal. The blended flow of Well No. 3 (filtered) and Well No. 2 (unfiltered) would meet the iron and manganese MCL.
OPERATION AND MAINTENANCE
The operation and maintenance costs for this system are estimated to be $3,000 per year based on monthly metals testing; periodic inspection of system operation; and routine filter, valve, and pipeline maintenance. This system eliminates Aqua-Mag injection, but may slightly increase chemical supply costs due to increased chlorine consumption.
CONCLUSIONS AND RECOMMENDATIONS
Iron and manganese removal by adsorptive processes is a feasible and established technology. Numerous successful pilot tests of the ATEC™ system have been completed in Washington and approximately ten systems have been installed. All of the operating filter systems have shown excellent removal results. An identically sized system (500 gpm) was recently installed in Orting, Washington, and has proven to reliably meet WSDOH standards for iron and manganese concentrations.
Alternative iron and manganese removal equipment, evaluated for the Orting project include a sand-pressurized filter marketed by General Filter. The system uses potassium permanganate to oxidize and precipitate the metals so the metals can be collected on a filter. Polymer is also added to assist in the process. The filters require backwash with treated water. Costs for design and construction for this system were approximately double those for the ATEC™ filter system.
PRELIMINARY PROJECT COST ESTIMATES
A preliminary project cost summary for an ATEC™ 500-gpm filter is shown in Attachment F. Project cost estimates were based on ATEC™ price quotes and recent design and construction of an identically sized ATEC™ filtration system in Orting, Washington. Construction cost components are broken down in Attachment F. Equipment cost for the ATEC™ filter is $58,475. Included in the preliminary construction cost estimate is the filter equipment cost, filter installation, approximately 400 feet of water main, 1,200 feet of backwash discharge piping to the sanitary sewer at Summit Road, construction of necessary support facilities, a 15 percent contingency, and sales tax. The total Planning Level Construction Cost is approximately $384,000. The project total is approximately $495,000 and includes a project report for DOH approval, design engineering, construction engineering services, and operation and maintenance manual.
PROJECT SCHEDULE
The project sequence and proposed project schedule are shown in Table 4. The schedule assumes that sufficient funding is available prior to the start of design and construction. Duration estimates are approximate and are based on previous filtration system design and construction experience. Total project duration is anticipated to be 18 months.
| Table 4. Proposed Project Schedule | |
| Activity | Duration |
| Project Report | 2 months |
| DOH Review and Approval | 1 month |
| 50% Design | 2 months |
| City Review | 2 weeks |
| 100% Design | 2 months |
| City Review | 2 weeks |
| DOH Review and Approval of Plans and Specifications | 1 month |
| Project Bid and Award | 2 months |
| Project Construction | 6 months |
| Start-Up / Commissioning | 1 month |
We thank you for the opportunity to work on resolving taste and odor problems in the City's water system. Please let us know if you would like to proceed with a project report meeting DOH requirements contained in WAC 246-290. Following DOH approval of the project report, plans and specifications for the water system improvements may then be completed. As always, please call us at (253) 863-5128 if there are any questions we can answer regarding the project.
PARAMETRIX, INC.
August 20, 2002 PMX# 216-1669-025 (03/04)
David J. McBride, P.E., Project Manager
Matthew DeBoer, Project Engineer
Attachments: