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HomeMy WebLinkAbout2020.11.18_CCOA.p1_ChemoursResponseToDEQCommentsGeosyntec Consultants NC P.C. RESPONSES TO NCDEQ COMMENTS Chemours Fayetteville Works TR0795 Page 1 November 2020 On October 5, 2020, Chemours received comments from the North Carolina Department of Environmental Quality (NCDEQ) on the following two mass loading protocol documents submitted by Chemours on August 31, 2020 as required under Paragraph 1(a), (b), and (c)(ii) of the Addendum to Consent Order Paragraph 12: Geosyntec Consultants, 2020a. Site Conveyance Network and Outfall 002 PFAS Mass Loading Calculation Protocol (Version 1). Chemours Fayetteville Works. August 31, 2020. Geosyntec Consultants, 2020b. Cape Fear River PFAS Mass Loading Calculation Protocol (Version 1). Chemours Fayetteville Works. August 31, 2020. The table below summarizes the comments received by NCDEQ, Chemours’ responses to those comments, and the subsequent changes made in second versions of these protocol documents submitted to NCDEQ on November 18, 2020. Comment # Protocol Document Comment Description Response Section Edit 1 Outfall 002 For the Site Conveyance Network, the facility suggests the use of 3.5 days composite samples and 24-hour composite sampling. The 3.5 days sampling is inconsistent with our regulations and underestimates the load, only 24-hour composite data should be used in the calculations. The protocol will specify using 24-hour composite samples collected from Outfall 002. The protocol calculation will still retain the ability to consider 3.5-day composite samples in calculations for historical data sets where in the past only 3.5-day composite samples were collected. Section 3.4 2 Outfall 002 The document mentions the phrase “estimated PFAS concentration” several times. Please clarify the use of that term and note that measured PFAS concentrations are expected to be used in the calculations. For example, k = is the measured or estimated total PFAS concentration. All mass loading quantities will be determined based on measured concentration values. The word document has been edited accordingly to provide clarity. Across Document 3 Outfall 002 The protocol states how PFAS concentrations from the site-conveyance network may be estimated if there are data gaps, and for the intake, estimated concentrations will be determined from Transport pathways 1 (upstream at mile 76), 2 (Willis Creek estimated modeled load), and 3 (aerial deposition). Actual concentrations will also be measured monthly with a 24hr composite sample at the intake. It would be better to take weekly 24hr composite samples at the intake to determine loading from the site-conveyance network. This would also provide more data comparison to refine the loading as estimated from Pathways 1-3 since two of those inputs are modeled loading and not actual measurements. The last sentence of 2.4 says; For the purposes of these calculations, flows at the river intake are assumed to be equal to dry weather Outfall 002 flows. This seems to indicate there is no consumptive loss from the variety of processes used at the industrial site. Shouldn't the water balance include water lost from hauling process wastewater and evaporative loss from various processes? 1. Intake sampling described in the original protocol text outlined usage of existing sampling programs as Site NPDES permit has not yet been renewed. Chemours agrees as part of this protocol to specify weekly 24-hour composite samples be collected at the Intake in assessing loading from the site-conveyance network at Outfall 002. To avoid duplicative sampling, Chemours will modify this protocol to incorporate and be consistent with intake sampling frequency requirements at such time as the NPDES permit for Outfall 002 is renewed. 2. Determinations of PFAS mass loading from the river water intake will be calculated using measured intake flows from the transfer pipe between the river water pumps and the facility. This will more accurately reflect PFAS loads entering the Site via the intake. The document previously had assumed that intake flows were equal to measured Outfall 002 flows. Sections 2.2 and 2.4 4 Outfall 002 The document suggests the use of a 60-day rolling average. This is inconsistent with our standard procedures, a 30-day rolling average should be used. The protocol has been modified to specify a 30-day rolling average. Sections 3.4 and 3.5 5 Outfall 002 The list of PFAS parameters that will be analyzed should match the list contained in the recently issued NPDES permit – NC0089915 and as comprised during CO negotiations. The sampling described in this protocol document is being implemented pursuant to paragraph 1(c) of the Consent Order Addendum entered into court on August 13, 2020. The Consent Order Addendum requires analysis for PFAS compounds listed in Attachment C of the Consent Order (CO) (February 25, 2019). -- 6 Outfall 002 The CO states that for Outfall 002, Chemours shall also conduct 24-hour composite sampling within 24 hours of any rain event predicted two days before with at least a 70% likelihood to be of 1 inch or greater over a 24-hour period. The weather service used for the precipitation prediction should be stated and approved by the department. National Oceanic and Atmospheric Administration (NOAA) National Weather Service hourly forecasts (for the Fayetteville Regional Airport) will be used to track rainfall predictions at the site. A link to this weather station is included in the document. Section 2.3 11 Outfall 002 Section 3.1. The variables “j” and “k” are not defined in Section 3.1. The document has been revised to include definitions for “j” and “k”. Section 3.1 12 Outfall 002 Section 3.2 provides Equation #2 and has a variable “F” that needs further explanation. Is the factor a constant or will it change each time? The factor is constant; the text has been revised. Section 3.2 Geosyntec Consultants NC P.C. RESPONSES TO NCDEQ COMMENTS Chemours Fayetteville Works TR0795 Page 2 November 2020 Comment # Protocol Document Comment Description Response Section Edit 7 Cape Fear River Mass Loading OLDOF-1, this sampling location is approximately 500' upstream from the confluence with the CFR. Sampling should take place closer to the mouth unless it can be demonstrated that the CFR is interfering with sampling between the designated location and the 'mouth' of the old outfall 002 channel. Chemours does not recommend moving the old outfall sample location closer to the Cape Fear River based on the following: • The current sample location represents the overwhelming majority flows from the Old Outfall channel that will reach the river. The stretch of channel downstream of the current sampling location and the river was investigated on November 6, 2020, and Chemours’ contractors identified only one area with seepage. The seepage was estimated to be less than 100 milliliters per minute (“drips”) which would be equivalent to ~0.004% of total flow in the Old Outfall. • Chemours does not own this property. Closer to the river the ground is less stable and safe access would require improvements. The area near the river has poison ivy present. Chemours cannot unilaterally alter the land to address these issues; • The area closer to the river is low lying and is prone to inundation; • Portions of the channel closer to the river mouth become similar to a braided stream where flows are not all in the same channel. Sampling from this environment will not be representative of the entire channel flow; • Placing the sampling infrastructure (an autosampler) closer to the mouth of the Old Outfall increases the likelihood of the sampler being vandalized as it brings the sampler closer to a more publicly accessible area. -- 8 Cape Fear River Mass Loading The FRO discovered two seeps at the boat ramp below L&D#3 draining into the river. They sampled the seeps and the results are attached. The loading from these seeps should somehow be captured in the sampling plan. • Chemours contractors identified and sampled an offsite seep near the Lock and Dam in March 2020, which is likely the ‘West Seep 31’ identified by FRO. Chemours’ contractors have gone out multiple times (most recently in October 2020) and have not observed a seep on the east side (East Seep 32). It is postulated that surface water runoff from a recent rainfall occurred in the days preceding DEQ sampling (July 2020) and this residual flow was identified as East Seep 32. Chemours will include sampling and estimation of flow measurements of the west side seep (West Seep 31) when water flow is present. • Previously Chemours had requested one time access to the Lock and Dam Seep from the United States Army Corps of Engineers (USACE). Chemours is presently arranging a longer- term access agreement with the USACE to facilitate collecting samples from West Seep 31 (i.e. the Lock and Dam Seep) as part of this protocol. The mass discharge from this seep will be included in the Mass Loading Model. • In the six month period after protocol approval, Chemours will observe the east side of the boat launch area monthly and take photographs and, if possible, measure flow, collect a grab samples, and estimate loading of the East Seep 32. At the end of the six month period, Chemours will discuss the need for continued sampling of East Seep 32 with DEQ. Sections 2.4 and 4.4.4.1 9 Cape Fear River Mass Loading Section 4.2: Equation 6 is used to estimate the mass of PFAS at the intakes for the two water treatment plants downstream of Chemours (Bladen Bluffs and Kings Bluff). We understand the equation, except Chemours does not explain why the flow recorded at the W.O. Huske Dam needs to be adjusted for travel time for the Bladen Bluffs plant using Equation 7. The text has been clarified to note that a time offset is applied to the flow data to account for travel time for the flow passing the W.O. Huske Dam to reach the Bladen Bluffs. River flow passing the W.O. Huske Dam is estimated to have a travel time between 2 and 12 hours to reach Bladen Bluffs depending on river flow (e.g., the flow rate passing W.O. Huske Dam at 8 am will arrive at Bladen Bluffs at 11 am for a 3 hour travel time). Section 4.2 10 Cape Fear River Mass Loading Chemours should provide an example dataset for the equations presented in the protocol, along with the spreadsheets planned for calculating the mass loads and mass discharges (the spreadsheets could be populated with the example dataset). This would further aid in understanding the formulas and also provide a mechanism to check for errors. An excel work product was submitted on August 31,2020 with the protocol documents, as required by the Consent Order Addendum. Files were re-sent to NCDEQ on October 7, 2020. -- Geosyntec Consultants NC P.C. RESPONSES TO NCDEQ COMMENTS Chemours Fayetteville Works TR0795 Page 3 November 2020 Comment # Protocol Document Comment Description Response Section Edit 13 Cape Fear River Mass Loading Section 4.4 does not include loading from the floodplain deposits adjacent to the Cape Fear River: The PFAS mass loading model does not account for PFAS loading of the river from groundwater contamination or contaminants in soil of the vadose zone. Loading of PFAS from the floodplain deposits to the river will occur until the extraction well system and/or barrier wall are constructed. Chemours should clarify why PFAS loading from the floodplain deposits are not included. 1. The Floodplain Deposits are not always in hydraulic connection with the Cape Fear River as this layer is above the water line and the Floodplain Deposits have an order of magnitude lower hydraulic conductivity.  The mass discharge from the Floodplain Deposits was estimated using the same method that was used to estimate the mass discharge from the Black Creek Aquifer.  Using data from the Q2 2020 sampling event, the mass discharge from the Floodplain Deposits and the Black Creek Aquifer were estimated to be 0.06 mg/sec and 3.9 mg/sec, respectively. Therefore, the loading from Floodplain Deposits is 1.5% of the Black Creek Aquifer loading value, and 0.3% of the total modeled mass discharge, which does not meaningfully impact the results of the model.  As part of the groundwater remedy pre-design investigation, data from passive flux meters is being used to better understand this differential.  Chemours will include an estimate of mass discharge from the Floodplain Deposits into an annual sensitivity analysis. 2. The vadose zone is where water infiltrates primarily vertically under gravitational forces to the water table. Therefore, we expect limited contributions from the vadose zone directly to the Cape Fear River and do not recommend including in the model. Section 4.4.4.2 and Appendix D 14 Cape Fear River Mass Loading Section 4.4.1: The equation labelled “[1]” should perhaps be labelled the 9th equation presented in the body of the text. Chemours also does not have an equation #8 in the protocol. The text has been clarified. Sections 4.2, 4.3, and 4.4.1 15 Cape Fear River Mass Loading Section 4.4.4: Pathway TP-5 is the upwelling of PFAS from the Black Creek Aquifer into the River at 8 segments of the river bank. Mass discharge for each segment will be determined using the cross-sectional area, the hydraulic gradient for the groundwater surface near the river and the hydraulic conductivity (K) estimated from slug tests performed on individual wells screened in the Black Creek Aquifer. In general, K values estimated from multiple well aquifer pumping tests are preferred over those estimated from slug tests. Kruseman and de Ridder (1994) note that “…slug tests cannot be regarded as a substitute for conventional pumping tests” and that a slug test “…determines the characteristics of a small volume of aquifer material surrounding the well, and this volume may have been disturbed during the drilling and construction.” Chemours has indicated that pumping tests are planned during the design phase for building of the groundwater extraction system and barrier wall. Chemours is presently conducting pumping tests (also known as aquifer yield tests) to better establish hydraulic properties near the Cape Fear River. As noted in Section 4.5, these enhanced hydrogeological data will be incorporated into the mass loading model as they become available. -- 16/17 Cape Fear River Mass Loading [#16] Section 4.4.6 references Appendix D, which has an equation for the total PFAS discharged from groundwater adjacent to Chemours (east side of river) and downstream of Chemours within a 1-mile distance of the river. Wells with contaminated groundwater were detected within the 1-mile width on either side of the river. The equation includes a unitless “scaling factor” which is a ratio of the length of the river adjacent to the site + downstream [#17] Based upon our review, it appears more appropriate to input “land areas” into the ratio instead of “river length” units. Chemours includes a figure that shows the off-site land areas underlain by impacted groundwater and the river lengths. The figure shows a width that extends greater than 1 mile on either side of the river, based on comparing the mapped widths to the bar scale. Length was used as the method for scaling downstream offsite loadings since the river is in direct contact with the land it is passing through. Using land area adds unnecessary complexity as it is unclear how the distance of land from the river should be considered in the land area calculation; i.e., land further away from the river will not have the same contribution effect. An assessment comparing both approaches showed that the two approaches yielded roughly similar scaling outcomes of 0.38 and 0.55 for the length and area methods, respectively. Chemours will include an estimate of loading from adjacent and downstream groundwater using the land area scaling method into an annual sensitivity analysis. Regarding Figure D1, the widths on either side of the river are indeed one mile. There was an issue with the scale bar on this figure, which has now been corrected. Section 4.4.6 and Appendix E 18 Cape Fear River Mass Loading The Draft Mass Loading Assessment Summary dated Dec. 6, 2019 determined hypothetical mass loading scenarios of HFPO-DA as reductions occurred at the facility. To continue this modeling and confirm these predictions PFAS samples should be taken below Outfall 002 The protocol document specifies that downstream samples are being collected at CFR- TARHEEL, which is sufficiently downstream of the Facility such that PFAS inputs into the river from the Facility are well mixed throughout the water column. Sampling requirements -- Geosyntec Consultants NC P.C. RESPONSES TO NCDEQ COMMENTS Chemours Fayetteville Works TR0795 Page 4 November 2020 Comment # Protocol Document Comment Description Response Section Edit (outside the mixing zone as determined by the dilution model) and below Outfall 003 when samples are taken upstream. pertaining to Outfall 003 and Outfall 002 permits are being arranged by Chemours and NCDEQ separate from this Cape Fear River PFAS Loading Protocol. Additional Comment A Cape Fear River Mass Loading What will be the timeframe for establishing the Cape Fear River PFAS Baseline? This protocol document describes development of the Cape Fear River PFAS Mass load Baseline in Section 4.1. The baseline period began on March 28, 2020 and will conclude on March 28, 2021. The date of March 28, 2020 is when the autosampler at CFR-TARHEEL was put into service and Chemours began regular collection of samples at this location. Pursuant to the Consent Order and the Consent Order Addendum, three PFAS transport pathways require compliance demonstrations relative to a defined baseline: 1. Air Emissions reductions addressed under Paragraphs 8 and 9 of the Consent Order; 2. Long-Term Seep Remediation Objective addressed under Consent Order Addendum Paragraph 2(c) and described in the Onsite Seeps Long-Term Loading Calculation Plan submitted by Chemours on October 30, 2020 (Geosyntec, 2020a); and 3. The Cape Fear River PFAS Mass Load Baseline required pursuant to Paragraph 16 of the Consent Order and specified in this Cape Fear River PFAS Mass Loading Calculation Protocol (Geosyntec, 2020b). Section 4.1.1 Additional Comment B Cape Fear River Mass Loading Please provide an example of how the load of PFAS reduced by the remedies will be calculated in the estimation of the PFAS baseline load calculation? The protocol document has been updated. Section 4.1.3 and Appendix B