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Home My WebLink AboutNC0004979_Allen Pumping Test WP Response to Comments_20180523TECHNICAL MEMORANDUM Page 1 of 3 P:\Duke Energy Carolinas\17.ALLEN\05.EHS CAMA Compliance Support\Assessment\Pumping Tests\Work Plan\Allen Pumping Test Work Plan Response to Comments TM.docx Date: 5/22/2018 File: 1026.17 To: John Toepfer Cc: Tyler Hardin, Courney Murphy, Kathy Webb, Chris Bruce From: Chris Suttell, NC L.G. Subject: Response to NCDEQ MRO Comments to the Allen Steam Station Pumping Test Work Plan This Technical Memorandum summarizes SynTerra’s responses to NCDEQ MRO’s comments to the Pumping Test Work Plan (Work Plan). This memorandum is accompanied by a revised work plan reflecting the changes discussed in SynTerra’s responses below. NCDEQ Comment 1 - Why was there an observation well installed 30 ft. away from the well cluster at AB-35 (AB-35OWAL30) and not at AB-21 well cluster? Why is there not a consistent approach to each well cluster? SynTerra’s Response - At both the AB-35 and AB-21 locations, existing wells will be used for observation points 30 feet away from the pumping wells. Existing wells AB-21S and AB-21SL were proposed to be used as the 30-foot lateral observation well locations (Work Plan, Table 1). At AB-35 existing wells AB-35S (upper ash) and AB-35SS (shallow saprolite) will also be used as observation 30- foot lateral observation wells. The text of the Work Plan has been modified to help clarify this. NCDEQ Comment 2 - In Table 1, it indicates the screen length at AB-35OWAL is 44.5 ft. and that the screen length for AB-35OWAL30 is 45 ft. I assume this is a typo, but please verify and correct if needed. SynTerra’s Response - Table 1 has been modified to reflect the actual screened intervals (yes, this was a typographical error). NCDEQ Comment 3 - Based on review of the work plan, Figure 3 shows the extracted groundwater will be pumped into what looks to be a ponded area west if [sic] the AB-21 well cluster. Please ensure groundwater extracted as part of the proposed pump tests does not provide a source of recharge that could potentially cause interference with the testing. Tech Memo - Response to NCDEQ’s Comments to the Pumping Test Work Plan May 22, 2018 Duke Energy Carolinas, LLC, Allen Steam Station SynTerra Page 2 of 3 P:\Duke Energy Carolinas\17.ALLEN\05.EHS CAMA Compliance Support\Assessment\Pumping Tests\Work Plan\Allen Pumping Test Work Plan Response to Comments TM.docx SynTerra’s Response - Figure 3 of the Work Plan has been modified to show the planned discharge line to extend 400 feet to the south and intercept the discharge channel within the active ash basin. NCDEQ Comment 4 - Figure 4 shows the extracted groundwater will be pumped into a holding tank. While MRO has no issue with the extracted groundwater being pumped to a holding tank, the work plan does not discuss this in any detail specifically how/where the extracted groundwater will be disposed. Please provide information regarding handling/disposal plan for groundwater extracted at AB-35 well cluster. SynTerra’s Response -The Work Plan text has been modified to further explain the proposed discharge of the water at the AB-35 location. It is currently anticipated that the water will be pumped into a holding tank and then discharged through gravity flow or pumping to one of the three primary ponds within the active ash basin (approximately 1,000 feet to the south). NCDEQ Comment 5 - Please ensure any extracted groundwater that is proposed to be discharged to the ash basin is done so in compliance with the existing NPDES permit (please coordinate as appropriate with the NPDES permitting group). SynTerra’s Response – A Duke Energy letter dated May 3, 2018 (Baker to Poupart) notified NCDEQ of the planned pumping tests. NCDEQ responded to the letter on May 4, 2018 with an email from Poupart to Baker, et al., that stated “We concur with your letter of May 3 that water from well tests can be pumped to the ash basins as described as the volumes are minor in comparison to overall system flow and the water is originating from under or groundwater directly adjacent to the ash basin and not expected to cause exceedance of NPDES permit limits or water quality standards in receiving stream.” NCDEQ Comment 6 - It was stated in the work plan that water-quality samples would be collected daily. MRO requests pre-pump test sampling be conducted at each pumping well prior to commencement of the pump testing. SynTerra’s Response – The Work Plan text will be modified to include the collection of a groundwater sample from each of the pumping wells prior to the start of the step test. NCDEQ Comment 7 - Why was it not proposed to monitor the deep and bedrock flow layers within the observation area (AB-21D/BR/BRL and AB-35D/BR)? This could provide valuable information regarding interconnectivity of flow layers, etc. SynTerra’s Response - Based on the planned duration of aquifer test and anticipated conductivity/transmissivity of the ash and flow rates (less than 15 Tech Memo - Response to NCDEQ’s Comments to the Pumping Test Work Plan May 22, 2018 Duke Energy Carolinas, LLC, Allen Steam Station SynTerra Page 3 of 3 P:\Duke Energy Carolinas\17.ALLEN\05.EHS CAMA Compliance Support\Assessment\Pumping Tests\Work Plan\Allen Pumping Test Work Plan Response to Comments TM.docx gpm in the ash and less than 5 gpm in the saprolite as indicated by well development records), it is not anticipated that drawdown will extend vertically to depths monitored by the transition zone or bedrock. However, SynTerra will use this testing opportunity to manually measure water levels three times per day in the transition zone and bedrock at these locations. The Work Plan text and Table 2 have been modified accordingly. NCDEQ Comment 8 - Also, why was it not proposed to monitor other wells in the shallow/deep/bedrock flow layers near the observation area (AB-20S/D, AB-23S/BRU, CCR- 23S/D)? SynTerra’s Response - Similarly as discussed above, based on duration of aquifer test and anticipated conductivity/transmissivity of the ash and flow rates (less than 15 gpm in the ash and less than 5 gpm in the saprolite as indicated by well development records), it is not anticipated that drawdown will extend laterally to the wells mentioned in the comment. However, SynTerra will use this testing opportunity to manually measure water levels three times per day in these wells. The Work Plan text and Table 2 has been modified accordingly. NCDEQ Comment 9 - Please ensure during the pump test that manual readings are collected as indicated in the work plan at 2 hour intervals during active pumping. SynTerra’s Response - Water levels at the pumping test well cluster location will be recorded every 2 hours for the duration of the aquifer test (Work Plan, Table 2). Remote well locations outlined in the previous two comments will not be monitored at night to minimize safety risks associated with decreased visibility (i.e., as driving on unimproved roads), worker fatigue, increased wildlife activity, and unpredictable weather. NCDEQ Comment 10 - What is the estimated amount of groundwater to be extracted during the pump tests? o Per 15A NCAC 02C .0105, any water-well or well system with a design capacity of 100,000 gpd or greater requires issuance of a permit. SynTerra’s Response - Based on well development records, AB-21 PWA and AB- 35 PWA (ash umping wells) are likely to produce sustained yields less than 15 gpm (less than 21,600 gallons per day from each well). Similarly, wells AB-21 PWS and AB-35 PWS (saprolite pumping wells) are likely to produce sustained yields less than 5.0 gpm (less than 7,200 gallons per day from each well). Since the anticipated yields do not encroach upon the capacity threshold triggering a permit requirement, a request for a permit is not planned.