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Letter Stantec - Wellhead Protect Plan Proposal Stantec Consulting Services Inc. 2335 Highway 36 West St. Paul MN 55113 Tel: (651) 636-4600 Fax: (651) 636-1311 January 25, 2013 Harry Taylor Public Works Supervisor City of Cottage Grove 8635 West Point Douglas Road South Cottage Grove, MN 55016 Re: Part 1 Wellhead Protection Plan Proposal, City of Cottage Grove Dear Mr. Taylor: This letter outlines a scope and budget to complete the amendment to your Part 1 Wellhead Protection Plan. The scope of services is based on our previous work completing Cottage Grove’s original Wellhead Protection Plan. Also, our scoping meeting with the MDH on December 13, 2012 is being used to help define the work plan for the Part 1 amendment. Wellhead Protection Planning The City of Cottage Grove is currently in the process of amending its existing Wellhead Protection Plan to bring the plan up to date before it expires in 2015. The wellhead protection plan has a 10-year lifespan, meaning that once it has been approved, it must be updated before the 10-year lifespan is over or whenever the City adds a new water supply well, whichever comes first. The Part 1 Wellhead Protection Plan includes a delineation of the wellhead protection capture zone for the City’s water supply wells, along with a delineation of the drinking water supply management area (DWSMA), which is an expression of the capture zone using overlying land parcels and roadways as boundary lines. The capture zone is determined by using a computer groundwater model to simulate flow within the aquifer(s) and determining the properties of the aquifer itself, such as conductivity, porosity, flow boundaries, and recharge. The Part 1 Wellhead Protection Plan also identifies the vulnerability of the wells and the vulnerability of the aquifer supplying them. The aquifer’s vulnerability to contamination can range across the DWSMA, depending on the amount of geologic protection overlying the aquifer(s). The following tasks will comprise the amendment of Cottage Grove’s Part 1 Wellhead Protection Plan. Task 1: Assembling Required Data Elements Collecting and presenting data elements is an important part of the Part 1 Wellhead Protection Plan. While much of this data is available from different sources, significant effort is usually required to compile, field verify, format, and summarize the data in a usable format. This data is a necessary element that is to be incorporated into the delineation analysis in Task 2. To the extent possible, Stantec will utilize the data already collected for the existing Part 1 Wellhead Protection Plan. However, certain changes in MDH data collection requirements over the past decade will likely necessitate a more extensive collection and analysis of data. Harry Taylor City of Cottage Grove Page 2 of 6 Re: Part 1 Wellhead Protection Plan Proposal Categories of data to be assembled include: Physical Environment Data – This includes data relating to precipitation, geology, soils, and water resources that may be applicable to the Cottage Grove wells and water supply system. Land Use Data – This includes maps that may be used to delineate wellhead capture zones based on real surveyed boundaries, such as parcel maps and political boundary maps. Water Quantity Data – This data is used to determine the volume of water to be modeled in Task 2, both from the City’s own wells and from nearby wells that may impact the size and shape of the capture zone. Water Quality Data – This data includes tests that may indicate the age of the water supplying the City’s wells. Specific age dating testing is typically sought, but any data that shows the presence of recently infiltrated water is useful. In particular, any data that demonstrates interconnection between groundwater and surface water will be needed. Task 2: Delineating Wellhead Protection Areas The delineation of the wellhead protection areas will comprise the largest portion of work to be done for the Part 1 Wellhead Protection Plan. The end result of this task is a scientifically delineated wellhead protection area for each of Cottage Grove’s primary water supply wells. Delineation Criteria Five criteria are used to determine the level of effort and methodology required to delineate the wellhead protection areas. These criteria are used to develop a conceptual model of the groundwater flow system in the aquifer serving the Cottage Grove wells. The five criteria are: Time of travel – The minimum time-of-travel for delineations is 10 years. A one-year time-of- travel must also be computed, which will serve as an emergency response area for wellhead protection management. Other travel times can be modeled and mapped for little extra cost, if desired. Flow boundaries – Hydrogeologic boundaries, such as extents of aquifer formations, rivers, lakes, etc. impact the size and shape of wellhead protection delineations. Daily volume – The amount of water pumped from the aquifer(s) will also impact the size of the delineated area. Accurate, up-to-date data regarding water usage is essential. Planned water usage over the next five years must also be considered. Groundwater flow field – Any relevant information regarding groundwater flow within the aquifer must be considered and incorporated into the delineation process. This data may relate to groundwater elevations, flow direction, flow gradient, recharge, and withdrawals that may affect the delineation. Aquifer transmissivity – The ability of the aquifer to transmit water to a high capacity well must also be considered. Aquifer transmissivity can greatly affect the size and shape of the delineation, when groundwater flow is simulated on a computer groundwater model. Therefore, aquifer pumping test information is used to determine transmissivity. Harry Taylor City of Cottage Grove Page 3 of 6 Re: Part 1 Wellhead Protection Plan Proposal Pre-Delineation Meeting Once the five delineation criteria have been determined and a conceptual model of the groundwater flow system has been developed, a meeting is held with MDH staff to review the conceptual model. This meeting will enable Stantec and the MDH to agree on how best to proceed with the delineation process, to help see that the end result meets with favorable review from MDH staff. WHPA Delineation A computer groundwater model is utilized to create the wellhead protection area capture zones for Cottage Grove’s water supply wells. The criteria determined above are entered into the computer model in order to produce a delineation that meets MDH requirements. The computer model that was used to generate the existing delineations for Cottage Grove’s wells may be utilized for this effort. The model will still require significant updates to reflect current understanding of local geology, current pumping volumes of nearby high capacity wells, current understanding of the recharge and interaction of relevant aquifer units, and current data for model calibration, including groundwater level data from nearby wells. Alternately, Stantec may also decide to utilize the existing Metropolitan Council Metro Model, which is a computer groundwater model that simulates flow in all major aquifer units in the Twin Cities metro area. Using this model may be advantageous, as it reflects a more current understanding of local geology and may require less updates that the model previously used for Cottage Grove’s original Part 1 Wellhead Protection Plan. Stantec will review both models and work with City staff and MDH staff to select the model deemed most appropriate (and most accurate) for the project goals. The wellhead protection delineation generated by the model must, at a minimum, show the one- year and 10-year time-of-travel capture zones for all active primary water supply wells. Wellhead protection areas will be mapped on ArcView GIS using UTM NAD 83 coordinates, as required by MDH rules. Other coordinate projections can be provided to Cottage Grove, if requested. Fractured Flow Delineation Aquifers that contain numerous fractures or solution cavities also required additional analysis to account for the ability of the aquifer to rapidly transmit water over a given distance in a short amount of time. In 2005, the MDH has established guidance for handling fractured bedrock delineations that will need to be applied to the results from the computer groundwater model. In the case of Cottage Grove, the Prairie du Chien aquifer may be highly fractured and can supply water to the underlying Jordan aquifer. As such, the Prairie du Chien aquifer could need additional analysis to ensure the modeled delineation is appropriate for this type of aquifer. The end result is sometimes the expansion of the capture zone to predict additional areas that may supply water to the City’s wells. During the December 2012 scoping meeting with the MDH, Amal Djerrari noted that aquifer data from St. Paul Park suggested that the hydraulic connection between the Prairie du Chien and Harry Taylor City of Cottage Grove Page 4 of 6 Re: Part 1 Wellhead Protection Plan Proposal Jordan aquifer may not be as great as was originally thought for this portion of Washington County. As a result, it is unknown at the present time whether the MDH will require a fracture flow delineation for Cottage Grove. Our budget includes for the delineation (and the time needed to determine if the delineation is needed), in the even the MDH ultimately requires it. DWSMA Delineation The modeled capture zone and fracture flow delineation must then be combined to form integrated management zones. Since the mapped zones cannot be easily identified using surface features, a Drinking Water Supply Management Area (DWSMA) is created to correlate the capture zones with the nearest surface features, such as roads, parcel boundaries, water bodies, and other surveyed features that can readily be identified. The DWSMA will be mapped on ArcView GIS using UTM NAD 83 coordinates, as required by MDH rules. Other coordinate projections can be provided to Cottage Grove, if requested. Task 3: Vulnerability Assessments Once the WHPA and DWSMA delineations have been determined, the next step is to assess the vulnerability of the aquifers underlying these portions of land. We will review geologic data to determine how rapidly contaminants spilled at the surface might be expected to infiltrate to the aquifer of interest. Geologic layers such as clay and shale that might impede vertical infiltration of contaminants are inventoried to determine approximate travel times for contaminants to reach the aquifer(s). The shorter the travel time, the higher the vulnerability level is assigned to the aquifer. Aquifer vulnerability may vary over the area encompassed by the DWSMA. We will provide a map in the project report showing areas of high, moderate, and low vulnerability within the aquifer. The map will also be provided electronically as an ArcView shape file in UTM NAD 83 coordinates. Task 4: Reporting The project report will summarize the efforts undertaken above in Tasks 1-3. The report will serve as the main deliverable for the Part 1 Wellhead Protection Plan, documenting the data and methodology used to develop the WHPA/DWSMA delineations and aquifer vulnerability assessments. The report will also include all maps generated over the course of the project, both as paper printouts and in electronic ArcView formats. Additionally, any computer groundwater model input and output files will be provided electronically, along with supporting data sets that were used in the delineation process. Two paper copies and an electronic CD-ROM copy of the draft report will be submitted to Cottage Grove for review. Upon approval by Cottage Grove, we will submit the draft report to the MDH for their review and approval. Upon MDH approval, the final report will be presented to Cottage Grove as both a Microsoft Word Document and an Adobe PDF document. Six paper copies of the approved report will be supplied, with additional copies available upon request. Harry Taylor City of Cottage Grove Page 5 of 6 Re: Part 1 Wellhead Protection Plan Proposal Task 5: Meetings We anticipate four meetings will occur over the course of the project. These meetings will be used to update Cottage Grove staff on the progress of the project. While most meetings will likely be held at Cottage Grove offices, meetings may also be held via telephone if staff prefers this approach. Additionally, a meeting will be held following MDH approval of the project, when Cottage Grove is required to present the approved Part 1 Wellhead Protection Plan to the general public as part of an official public information meeting. Stantec will attend this meeting to provide a presentation outlining the results of the Part 1 plan and will be available to answer any questions brought forth by the general public. Project Schedule The scheduled due date for completing and submitting the amendment of the Part 2 Wellhead Protection Plan is August 31, 2015. In order to meet this deadline, the amended Part 1 Wellhead Protection Plan should be completed more than a year in advance of the due date to allow sufficient time to complete Part 2. Stantec is proposing to complete the Part 1 plan, including the followup public information meeting by December 2013. The following proposed schedule outlines anticipated completion dates for project tasks. Project Milestone Date Completed Data Collection and Analysis April 2013 Delineation Modeling May 2013 Completion of Draft Part 1 Delineation July 2013 Submittal of Draft Part 1 Report for Approval August 2013 Compensation Stantec proposes to complete the above outlined tasks on an hourly basis, with a not-to-exceed total of $9,375.00 . Should the MDH alter or modify Part 1 delineation requirements during the process of completing the proposed work, Stantec will work with the City of Cottage Grove to modify the work plan, budget, and schedule accordingly. Harry Taylor City of Cottage Grove Page 6 of 6 Re: Part 1 Wellhead Protection Plan Proposal If this proposal is acceptable to you, please provide me with a notice to proceed at your convenience. If you have any questions or comments regarding the above work plan, please contact me at (651) 604-4831 or mark.janovec@stantec.com. Sincerely, Stantec Consulting Services, Inc. Mark Janovec, PG Senior Scientist Cc: Jennifer Levitt, City of Cottage Grove Les Burshten, City of Cottage Grove Rick Alt, City of Cottage Grove David Sanocki, Stantec Mark Rolfs, Stantec