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Home My WebLink About5.a. Well 16 Update ROSEMOLINTEXECUTIVE SUMMARY UTILITY COMMISSION Utility Commission Meeting: August 11, 2014 AGENDA ITEM: Well 16 Update AGENDA SECTION: New Business PREPARED BY: Andrew J. Brotzler, PE, Director of Public AGENDA NO. Works/City Engineer ATTACHMENTS: Technical Memorandum APPROVED BY: RECOMMENDED ACTION: Motion to recommend that the City Council Direct staff to proceed with the design of production well and well house for Well 16. BACKGROUND The test well for Well 16 was completed earlier this year. With the completion of the test well,it was determined through the collection and testing of two separate water samples that the radium level in the test well of 7.1 pCi/L is in excess of the Minnesota Department of Health maximum level of 5. The attached technical memorandum provides a summary of the radium levels in the test well, existing city wells, and neighboring Inver Grove Heights. The memorandum also outlines a number of progressive strategies to reduce the radium level from proposed Well 16 to below MDH standards for the finished water. These options include the following: 1. Utilize in-place raw water lines to blend water from Well 15 and Well 16 to reduce radium levels to below 5. • 2. Develop 2.5 MG of new storage at the future water treatment plant site near Well 14 to blend water from Wells 14, 15 and 16 to reduce radium levels to below 5. Additional storage will be necessary in the near future to support additional growth such that consideration to add storage now would serve multiple purposes. 3. Develop a water treatment plant near Well 14. This would be similar to Inver Grove Height's process to address radium levels in the source water. Staff and Jamie Wallerstedt with WSB &Associates, Inc. will review the technical memorandum with the Commission at the meeting. SUMMARY Staff is requesting Utility Commission consideration to recommend the City Council to authorize the continuation of the Well 16 project as proposed. G:\ENGPROJ\416\20140811 UC Well 16 Update.docx WSB engineering-planning• environmental- construction 701 Xenia Avenue South Suite 300 Minneapolis,MN 55416 Tel: 763-541-4800 Fax: 763-541-1700 Technical Memorandum To: Utility Commission City of Rosemount Dwight Johnson, City Administrator City of Rosemount Copy: Andy Brotzler,PE,Public Works Director/City Engineer City of Rosemount From: Joe Ward,PE WSB&Associates,Inc. Date: August 11,2014 Re: Well 16 and Water Supply System Issues City of Rosemount,MN WSB Project No. 1582-18 INTRODUCTION Currently,several water system supply improvements and issues are being evaluated for the continued expansion of the City's municipal water supply system to support the City's continued growth. These issues generally include the following: • Addition of Well No. 16 • Addition of observation wells in accordance with Minnesota Department of Natural Resources (MnDNR)ground water appropriation permit • Addition of water storage EVALUATION Proposed Well No. 16 The City has planned for a well field of seven wells(including Wells No. 14 and 15) in the north central area of the City as part of the City's Comprehensive Water System Plan(CWP). This well field would utilize the Prairie du Chien-Jordan geologic formation(Jordan). Other geologic formations are available; however each has their challenges. The Mt. Simon-Hinckley-Fon du Lac geologic formation(Mt. Simon) is protected by state statute in the metro area. The Franconia-Ironton-Galesville geologic formation(FIG) can be used;however, it typically yields '/2 the volume of water of the Jordan formation thereby doubling the cost of the well system to meet demands. Lastly,groundwater is available in the glacial drift areas; however,these wells may prove to be less reliable because they are susceptible to contamination. In the metro area,the Jordan formation typically provides the best value for groundwater wells. Equal Opportunity Employer wsbeng.com A:01582-180:1lroln Docs TECH 11L110-.111ro¢!er-II'ell 16 urxl mien,Imp.Aoc Utility Commission Dwight Johnson,City Administrator City of Rosemount August 11,2014 Page 2 In order to meet increasing water demands as discussed previously, Well No. 16 is currently under design. A test well was completed for the project for which test results indicated the radium concentrations exceeded the maximum contaminant level(MCL)under the Safe Drinking Water Act(SDWA). Since no other well in Rosemount exhibited this characteristic,the water quality was tested twice. Combined radium(Ra 226 and Ra 228)must be less than 5 picocuries per liter(pCi/L)to meet the MCL. Combined radium in the first test was 6.6 pCi/L and 7.1 pCi/L in the second test. In addition, iron and manganese exceeded Secondary Standards. The Secondary Standards for iron and manganese are 0.3 mg/1 and 0.05 mg/1,respectively,and water quality testing indicated the levels were 0.408 mg/L and 0.154 mg/L. Exceeding the Secondary Standards will not impact a consumer's health, therefore treatment is not required. However,the water quality will be undesirable for aesthetic reasons. Excessive iron and manganese concentrations can cause red,black, brown, and yellow colored water. Water with concentrations above the Secondary Standards will typically cause customer complaints if some form of water treatment is not used. These complaints can be controlled either by sequestering or by removing the iron and manganese. Well No. 16—Iron and Manganese The City of Rosemount currently uses polyphosphates to sequester iron and manganese. Sequestering does not remove the iron and manganese. The polyphosphates form a weak chemical bond with the iron and manganese to reduce the formation of precipitates, which cause, red, black,brown, and yellow water. However,the chemical bond deteriorates with time. American Water Works Association(AWWA)guidance is that sequestering will not be successful for water with manganese levels greater than 0.10 mg/1 or water with combined iron and manganese levels greater than 1.00 mg/1. At iron and manganese concentrations greater than the recommended levels, sequestering becomes less effective. In accordance with these guidelines only Well No. 12 as shown in Table No. 1 is a candidate for successful sequestering, however, Wells No. 14 and 15 both use polyphosphate. Table No. 1 Iron and Manganese Data Iron+ Well No. Iron (mg/L) Manganese <0.10 (mg/L) Manganese <1.00(mg/L) (mg/L) (mg/L) Secondary Standard 0.3 0.05 n/a n/a n/a 12 0.453 0.072 Yes 0.525 Yes 14 0.159 0.119 No 0.278 Yes 15 0.147 0.154 No 0.301 Yes TW 16 0.408 0.116 No 0.524 Yes K.01562-160 Adoon Does 166 11.11E11O-.1lirotzler-Hell 16 mnl srstror imp.doe Utility Commission Dwight Johnson,City Administrator City of Rosemount August 11,2014 Page 3 Although iron and manganese levels exceed secondary standards and recommended levels below which sequestration is effective, City staff have had minimal complaints about water quality concerns. The City has constructed a raw water main system for the wells that would bring untreated water back to a common treatment site. Therefore,treatment has been planned for and can be added with minimal impact to the water distribution system. Therefore, it is recommended not to treat well water based on iron and manganese alone. Similar to other wells within the City, iron and manganese sequestration can be provided. If proved to be ineffective, treatment can be added in the future. Well No. 16—Radium The City of Rosemount currently does not treat for radium removal since radium concentrations in other wells are less than the 5 pCi/L MCL. There are four alternatives to resolve the radium issue: 1. Mothball well and relocate to a new site. Complete a test well at the new site,and construct the production well there if radium levels are less than the 5 pCi/L MCL. 2. Blend water from Well No. 16 in raw water lines with Wells No. 14 and 15 to reduce the total concentration below the 5 pCi/L MCL. 3. If blending water from Wells No. 15 and 16 in raw water main is not a feasible option,evaluate development of a 2.0 MG GSR at the future water treatment facility(WTF) site for blending water to reduce the total concentration below the 5 pCi/L MCL. 4. Expansion of well field may continue to have radium issues(reference Inver Grove Heights radium levels in Table No. 2). The ultimate solution may be a WTF for radium removal to less than the 5 pCi/L MCL. There are substantial risks and costs to each one of these alternatives. Well No. 16—Alternative 1 This alternative would include abandoning the currently planned well site near the intersection of Bacardi Avenue and 128th Street West. A new site would then be selected and a test well drilled at another location in order to determine if radium is potentially less than the current site. To determine the feasibility of this option WSB reviewed radium concentrations in general for the state and locally at Inver Grove Heights. The MDH has studied radium concentrations and has generally found a band of wells in the Jordan formation exceeding the MCL as shown on the attached map from the December 21, 2010, Distribution of Radium in Minnesota Drinking Water Aquifers study (MDH Radium Study). Inver Grove Heights provided WSB with information regarding their wells which indicates that each of their seven wells exceeds the 5 pCi/L radium MCL. Radium concentrations for the Inver Grove Heights wells ranged from 5.8 pCi/L to 9.0 pCi/L and are shown in Table No. 2. A':01532-ISO--Wrni,Docs 71C'111/F_1/O-:IBro¢ler-II'ell 16 and.rrx enr inrp.Jac Utility Commission Dwight Johnson,City Administrator City of Rosemount August 11,2014 Page 4 Table No. 2 Radium Data for Inver Grove Heights and Rosemount Wells MDH Maximum Contaminant Wells Well 12 Well 14 Well 15 Test Well 16 Level (MCL) Combined Radium 5 5.8-9 1.4 3.7 2.3 7.1 pCi/L Well Aquifer Jordan, Jordan Jordan Jordan Jordan 1-Mt. Simon There is substantial cost in constructing additional test well and there appears to be a significant risk of finding radium concentrations in excess of MCL in other locations based on the MDH Radium Study. Therefore, it is not recommended to proceed with Alternative 1. Well No. 16—Alternative 2 Pending MDH approval, it should be possible to blend water from Well No. 16 with water from another well in order to distribute drinking water to the system with a radium concentration less than the 5 pCi/L MCL. WSB has discussed the issue with the MDH who indicated that blending is generally guaranteed if the water is mixed within a reservoir. Also, blending can be achieved by pumping Well No. 16 concurrently with Well No. 15 as long as it can be proven the MDH that nearby residents do not receive drinking water with a radium level greater than the 5 pCi/L MCL. Using the City's raw water piping system,water from Well No. 16 could be blended with water from Well No. 15 or pumped directly to a new reservoir near the Bacardi tower,where it would be blended to achieve a radium level less than the 5 pCi/L MCL. As part of the City's CWP, it was planned that a 2.0 MG GSR be constructed near the future WTF site, see Alternative 3. It is recommended to pursue this alternative. As part of this alternative, it is recommended to further discuss and evaluate with MDH the potential for blending water from Wells No. 15 and 16 to achieve a radium concentration less than the 5 pCi/L MCL. The raw water mains necessary for blending are in place,so the cost is substantially less than constructing a new reservoir(discussed in following sections). Well No. 16—Alternative 3 Should blending Wells No. 15 and 16 prove to be infeasible to achieve a radium concentration less than the 5 pCi/L MCL,construction of a new reservoir should be evaluated. The MDH has indicated that storage would provide a more guaranteed method for blending water from Well No. 16 with water from other wells in the system to provide residents with water meeting the 5 pCi/L radium MCL. Construction of a new reservoir will likely be recommended in the future based on Rosemount's continued growth, so the reservoir would likely be constructed in the near future even if it is not necessary for blending. 015 82-180.fi lm,noc..Ieen11F1O-=imor_i•.-u.d 16WO,1Yn•,,,;,r'',dot Utility Commission Dwight Johnson,City Administrator City of Rosemount August 11,2014 Page 5 A detailed evaluation of supply and storage planning was completed in the October 28,2013,Rosemount Water Storage/Supply Capacity Design Memorandum(Storage/Supply Capacity Memo). Based on Rosemount's increasing water demands,the Storage/Supply Capacity Memo recommended that planning for construction of additional water storage begin in 2017 in order to bring the facility on line by 2020. As discussed previously, water demands fluctuate based on many factors so it is recommended to reevaluate storage/supply capacity annually. The City's CWP indicates the next planned storage facility for the City should be a 2.0 MG GSR at a new WTF. Regardless of the need for a new WTF, a new GSR could be constructed at the future WTF site. However, a preliminary WTF layout and feasibility study would be necessary to confirm the site would be adequate for the WTF and 2.0 MG GSR. In 2011, WSB designed and managed the construction of a 2.0 MG GSR in the City of Rogers. The final total project cost of the GSR was approximately $2,100,000. Due to construction cost inflation,a 2.0 MG GSR will cost more in 2019-2020. Additionally,site constraints and City preferences related to the GSR would need to be evaluated before an accurate engineer's opinion of probable cost could be provided. For example,the Rogers GSR was not completely buried. If the tank were completely buried it would have increased construction cost approximately 10%to 20%. Well No. 16—Alternative 4 Under this alternative,the production well (Well No. 16)would be drilled at the location originally planned. In some instances,the radium concentration in a production well has been found to be less than that of a test well. For example,the test well for Well No. 12 had a radium concentration of 5 pCi/L,but the production well had a concentration of only 1.4 pCi/L. Following the drilling of the production well, water quality would be tested to confirm the radium concentration. If radium levels were to be found in excess of the 5 pCi/L MCL a treatment system would be designed to remove radium. The treatment process required for radium removal has been implemented in many communities in Minnesota. It generally includes oxidation of manganese to form solid particles(radium then adsorbs to the manganese particles), which are then filtered from the water. This is the treatment process Inver Grove Heights uses. There are several different methods available for oxidation of manganese and several different methods available for filtration. A site for treatment has been designated near Well No. 14 and the Bacardi Tower. Water from Well No. 16 would be pumped directly to the water treatment facility through raw water mains that have already been constructed. Following treatment at the water treatment facility,treated water would be pumped into the system. K:0 1581-180:IAmin Docs TE('H 1 16_11O-.-IBrotrIc r-Ifrll 16 mx(.srstrm mop Utility Commission Dwight Johnson,City Administrator City of Rosemount August 11,2014 Page 6 Observation Wells The MnDNR permits the volume of water that can be withdrawn from the groundwater below the City of Rosemount through an appropriation permit. The City's appropriation permit has been amended several times as wells have been added to the water system and the volume of permitted withdrawals increased. As part of the most recent appropriation permit amendment to add Well No. 15 and increase the volume of water that can be withdrawn,the MnDNR required the City to construct three observation wells in order to monitor the groundwater level. Also, MnDNR's approval of Test Well No. 16 indicated that the test well should be retained as a potential future monitoring well. Associated with the monitoring wells, the City is required to install level monitoring equipment to record the water level data and submit the data periodically to the MnDNR. The three observation wells required by the appropriation permit for Well No. 15 are listed below. 1. One located near the center of all the City's wells(around the downtown area). 2. One located in the northwest well field (northwest of the Bacardi water tower). 3. One located outside the drawdown area of the City's wells(e.g. UMore area or south of the City boundary). The existing monitoring well at Well No. 14 meets requirement no. 2. A monitoring well has been constructed in UMore which satisfies requirement no. 3. The City recently completed an investigation of Wells 4 and 5, funded by a grant from the MDH. The status of these wells was unknown and represented a potential conduit for contaminants to reach the groundwater if not properly sealed. Recommendations resulting from the investigation were: • Well No.4—Contract with a licensed well driller for the well to be partially drilled out,casing perforated, and grouted in accordance with Minnesota Well Code. • Well No. 5—Contract with a licensed well driller to clean out the well. Following well cleaning, a decision can be made to either seal the well in accordance with Minnesota Well Code or use it as an observation well as required by the City's DNR Appropriation Permit. As discussed previously,the City is required to construct an observation well near the center of the City in accordance with the MnDNR appropriation permit amendment approval. Depending upon the condition of Well 5, it may be possible to use this well as an observation well. If it is not possible to use Well 5 as an observation well,a new one would likely have to be drilled. 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