Loading...
HomeMy WebLinkAboutWQ0004972_Hydrogeologic Review_20230711DWR Division of Water Resources State of North Carolina Department of Environmental Quality Division of Water Resources Non -Discharge Branch Hvdrogeological Investigation Report Review Form WQ0004972 MHC TT, L.P. Forest Lake Preserve WWTP 192 Thousand Trails Drive Advance, NC 27006 Primary Permit Reviewer: Zachary Mega Date submitted for Review: April 28, 2023 Hydrogeological Investigation Report Reviewer: Leah Parente Date of review completion: July 11, 2023. 1. Are the following elements included in the hydrogeological investigation report? a. Report signed and sealed by a PE, LG, or LSS yes b. Cursory examination of nearby properties and wells within 500 feet no c. Field observations no* d. Maps (topographic, overview, and site detail) no* e. Published reports no f. Sufficient number of bore holes with drilling/sampling logs in the area of system operation no* g. Sufficient number of wells with drilling/sampling logs in the area of system operation no* h. Shallow aquifer tests with detailed supporting data and appropriate analyses yes i. Groundwater modeling results with supporting test data and reasonable assumptions yes WQ0004972 Forest Lake Preserve WWTP Page 2 of 6 *List any missing elements, including others not mentioned above: • In the "Approach" section of the Hydro Report (page 5), it is stated that 3 borings were installed in areas identified for new spray fields. However, there is no mention of these borings later in the report. • Well construction data for the existing monitoring wells was insufficient to assess the site. On page 10 of the report, it was stated that data collected from MW-1 was not used to determine the Geomean value for hydraulic conductivity because it was not known if the well was at least partially screened into the fractured bedrock. The media in which these wells are located should be known and verified to determine if the calculated hydraulic conductivity value is appropriate for this site. • The topographic map of the site that was provided is an overview of the site and the surrounding area. Because of the scale of the map, it is not possible to determine the topography of the site. • No physical description of the subject site was provided. Review of records for the site shows that there is a large lake on the property with a stream that appears to flow from Forest Lake into the Yadkin River. This stream appears to go through or near one of the proposed spray fields. 2. Was a field visit conducted? A site visit was conducted by the Regional Office Staff a. Was the physical information contained in the hydrogeological investigation report verified by the field observations? See the "Site Visit Summary" conducted by Caitlin Caudle. 3. Aquifer parameters were determined by falling head slug tests. 4. Was a mounding analysis submitted? Yes 5. Was the methodology used for analysis adequate? Yes 6. Approximate depth to groundwater mound at steady state: Not provided 7. Site conditions to be maintained as assumed in the analysis (e.g. drainage features): This site will be undergoing construction of new spray irrigation fields and therefore will be changing. WQ0004972 Forest Lake Preserve WWTP Page 3 of 6 8. Was a contaminate transport analysis submitted? No Please provide commentary on the necessity of a contaminate transport analysis: A contaminant transport analysis was not provided as a part of the report. Due to the historic use of the site as a spray irrigation fields, a contaminant transport analysis should be provided. 9. Effluent quality used in analysis demonstrating protection of 2L standards: Not provided 10. Are there concerns with protection of 2L standards at the Compliance Boundary? N/a List the areas of concern: 11. Are monitoring wells needed at this facility? Yes a. The number and locations of the monitoring wells should consider such factors as the size of the application area, the locations of the Compliance and Review Boundaries, and the existence of nearby water supply wells. Do the number and locations of the monitoring wells proposed in the hydrogeological report concur with the recommendations of the APS? No MW-4 is currently located in the middle of the proposed new spray field. This well must be permanently abandoned prior to the operation of the new spray field. There was no mention in the Hydro Report of plans to abandon this well. Please comment on the future of this well. There is no discussion in the hydro report of where the new downgradient monitoring well will be located that will be replacing MW-4. Additionally, it is recommended that a second new monitoring well be located on the western edge of the proposed spray irrigation area. Please provide a map showing the proposed location of all new monitoring wells. b. The recommended substances to be monitored are as follows: same as previous permit issuance. WQ0004972 Forest Lake Preserve WWTP Page 4 of 6 12. The hydrogeologic report should meet the following standards described in the Aquifer Protection Section's Hydrogeologic and Reporting Policy and Groundwater Modeling Policy of May 31, 2007. Does the hydrogeologic report: a. Focus on the waste application area? Yes b. Include borings advanced to a depth of 20 feet or more? Yes c. Include enough borings in appropriate locations to create a reasonable hydrogeologic conceptualization of the waste application area? No d. Include a sufficient number of slug tests or pumping tests that were properly performed and analyzed for basic hydrogeologic parameters? No e. Utilize appropriate calculations or computer software to assess the potential for mounding beneath the application area and/or contaminant transport beyond the Compliance Boundary? Yes f. Use recognized assessment methods that are consistent with standard scientific practices and interpretations? Yes g. Have analyses and/or conclusions which include "safety factors" such as conservative assumptions to compensate for gaps in the field data or questionable test results? No 13. List in detail any additional information or items that are needed to evaluate the site: • The topographic map of the site that was provided is an overview of the site and the surrounding area. Because of the scale of the map, it is not possible to determine the topography of the site. Please provide a legible topographic map of the subject site. • There is no discussion of the 100-year floodplain in the report. A review of publicly available data from the Federal Emergency Management Agency shows that a portion of the proposed spray irrigation area may be located in the 100-year floodplain. Please provide comment on this and how it will affect site conditions. • Page 10 of the report states that boring logs were used to determine subsurface conditions. These boring logs are not included anywhere in the report. Please provide a copy of all boring logs from the subject site. WQ0004972 Forest Lake Preserve WWTP Page 5 of 6 • Well construction data for the existing monitoring wells was insufficient to assess the site. On page 10 of the report, it was stated that data collected from MW-1 was not used to determine the Geomean value for hydraulic conductivity because it was not known if the well was at least partially screened into the fractured bedrock. The media in which these wells are located should be known and verified to determine if the calculated hydraulic conductivity value is appropriate for this site. Please provide well construction data for all existing monitoring wells. In the "Approach" section of the Hydro Report (page 5), it is stated that 3 borings were installed in areas identified for new spray fields. However, there is no mention of these borings later in the report. Were these borings completed? If so, please provide a map showing the locations of these borings, construction records, and all other relevant data regarding these borings. Page 10 of the report states that the calculated geomean value for hydraulic conductivity of the surficial unit is 2.63 ft/day. However, on page 12 of the report, it is stated that a value of 3 ft/day was used for hydraulic conductivity in the model. Please provide justification for the use of 3 ft/day instead of the calculated value of 2.63 ft/day. In several places in the report, it is stated that the site is located within the Carolina Slate Belt. This is not corrected. The subject site is located in the Charlotte and Milton Belts. The hydraulic conductivity of Unit 2 was assigned an initial value of 0.01 ft/day in the model based on literature values for fractured granite and rocks of the Carolina Slate Belt. Please comment on how the model will be affected when correct values for the Charlotte and Milton Belts are used. • Please provide a justification for the use of a variable drainage coefficient for the existing spray fields in the mounding analysis on page 20 of the report and explain why a variable drainage coefficient was not used for the proposed spray fields. In Table 5 on page 20, the mounding analysis shows that there is no irrigation capacity for existing spray fields during the month of April. This is not explained anywhere in the report. Please provide an explanation for the lack of irrigation capacity during that time of year. On page 20 of the report, it states that the areas shown in red in Figures 11 through 22 indicate where modeled depth to groundwater is one foot for less. However, the captions for those figures state that the figures show areas where modeled groundwater is less than two feet in depth. Please clarify the depth to groundwater being depicted in the model results for Figures 11 through 22. WQ0004972 Forest Lake Preserve WWTP Page 6 of 6 Several errors were noted in the water balance shown on page 33 (Table 6). The area listed for the new spray fields is not correct. Additionally, the water balance was calculated assuming there is no water in the storage pond. This is an incorrect assumption as the storage pond will contain effluent when the new package plant is installed. The storage pond cannot be completely drained because a minimum liquid level will always be maintained to protect the irrigation pumps. Please resubmit the water balance calculations taking these two factors into consideration. • In the Conclusion on page 33 of the report, it is stated that groundwater flow patterns are consistent with the conceptual model. Groundwater flow paths are not discussed in the report. Please provide clarification on this matter. • A contaminant transport analysis was not provided as a part of the report. Due to the historic use of the site as a spray irrigation fields, a contaminant transport analysis is necessary to assess conditions at this site. Please conduct this analysis and provide a report summarizing the results. • MW-4 is currently located in the middle of the proposed new spray field. This well must be permanently abandoned prior to the operation of the new spray field. There was no mention in the Hydro Report of plans to abandon this well. Please comment on the future of this well. • There is no discussion in the hydro report of where the new downgradient monitoring well will be located that will be replacing MW-4. Additionally, it is recommended that a second new monitoring well be located on the western edge of the proposed spray irrigation area. Please provide a map showing the proposed location of all new monitoring wells. 14. List in detail any special conditions related to groundwater monitoring or hydrogeological issues that should be included in the permit: not applicable at this time 15. Other areas of concern or importance: mounding is a potential limiting factor in the water balance 16. Recommendation on permit issuance based on hydrogeological investigation report: Request additional information based on above comments.