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HomeMy WebLinkAboutTom Cambareri attachment Dewater Project 090420251 Tom Lee September 8, 2025 Chairman Barnstable Conservation Commission 230 South Street Hyannis, MA 02601 RE: 268 Stevens Street Pump Station and Dewatering Plan – Notice of Intent Dear Mr. Lee, There are two major pieces of information that the Commission should consider in their review and condition of the dewatering system and its impacts. The first is the expected magnitude of drawdown from the pumping and second a potential liability of spreading PFAS . I was made aware of the dewatering project on July 18. It is believed pumping started on July 11th and that the project activity was shut down on Monday July 20th. The duration of pumping then was approximately 9 days. I reviewed the NOI filing and the rate of pumping was specified at approximately 900 gallons per minute which would be 1.3 Million Gallons per Day and over 12 million gallons in total. The identification of nearby wetlands did not include the Hyannis Creek and its associated wetlands that crosses Mitchells Way approximately 260 feet directly west of the dewatering site (Figure 1). The NOI should identify all the adjacent wetland resources on a map. Typical 24-inch gravel packed wells for our water supply rarely pump a volume of 1.3 MGD on a sustained basis. The New Source Approval for public supply wells under 310CMR22 requires a detailed hydrogeologic pump test plan to ensure that fragile surface water dependent ecosystems are not harmed. This includes appropriate monitoring of the drawdown area in relation to the surface waters. While it is clear that the dewatering project is not seeking a permit for long term water supplies, the intent of the requirements to ensure no harm to adjacent wetland systems does fall under the purview of the Commission. Figure 1 Dewater Site and Hyannis Creek 2 The dewatering plan used a surface water gage to target the impact of the discharge on Aunt Bettys Pond. The DPW separately reported that the water levels in the northern wetland recovered about 2 inches several days after the shutdown of the dewatering project. I am intimately familiar with the hydrogeology of this area. I installed monitoring wells in the area to determine the flow path of the WPCF effluent plume from the WPCF in 1983 1. The C5 well located on Mitchells Way at Hyannis Creek had the highest concentrations of signature compounds of effluent in groundwater over a mile from the facility. I took the opportunity to measure water levels in the accessible C5 Well starting July 19th to August 7th. My measurements document the recovery of groundwater levels after the shutdown of pumping 12 Million Gallons after 9 days . The blue line on the graph shows the recovery curve of water level starting with a depth to groundwater of 8.02 feet on July 19th. Twenty days after groundwater recovered to a depth of groundwater of 6.64 feet. This means that the dewatering project lowered the groundwater level by at least 1.42 feet at 260 feet from the dewatering site. Hyannis Creek was dry over the initial measurement days but began to rewet after 9 days with some flow observed as the recovery reached a plateau. Water levels in wetland peat and organic deposits have a lag time response to either drying or wetting. I noted today that the level of water in the creek is higher than early August. The ambient water levels in the region, as measured at the USGS well AIW306 at the High School, is shown as an orange line in the graph. The water levels at the USGS well show a general decline of 0.4 feet due to 1 Thomas Cambareri Hydrogeology and Hydrochemistry of a Sewage Effluent Plume in the Hyannis Outwash, UMASS Master Thesis, 1986 Figure 2 Depth to Water in the C5 Well near Hyannis Creek and the Ambient Groundwater levels from a USGS Well -26 -25.5 -25 -9 -8.5 -8 -7.5 -7 -6.5 -6 USGS AIW306 Well Depth to GroundwaterHyannis Creek Well C5 Depth to Water in FeetGroundwater Level Recovery in Well C5 adjacent to Hyannis Creek and Ambient Groundwater Decline in AIW306 Hyannis Creek Well C5 AIW306 -26 -25.5 -25 -9 -8.5 -8 -7.5 -7 -6.5 -6 USGS AIW306 Well Depth to GroundwaterHyannis Creek Well C5 Depth to Water in FeetGroundwater Level Recovery in Well C5 adjacent to Hyannis Creek and Ambient Groundwater Decline in AIW306 Hyannis Creek Well C5 AIW306 3 the summer conditions exacerbated by a drought at the same time groundwater levels increased 1.42 feet at Well C5 after the pump shut down. A drawdown of 1.42 feet just 260 feet from the dewatering wells is significant, particularly since the discharge of the pumped water into the adjacent pond, reduces the drawdown at that location and results in increased drawdowns to the north as shown in Figure 3. The NOI calculation for the dewatering plan estimated a drawdown rad ius of only 850 ft. Graphics within the NOI calculations indicate 4 feet of drawdown approximately 100 feet from the site which seems to conform to the drawdowns depicted in Figure 3. The NOI should include a more robust estimation of drawdown in the area and its temporary impacts on adjacent surface waters and a robust water level monitoring plan consisting of pre- operation, operation and post operation events with the use of transducers supplemented by manual measurements with a determination of a contingency threshold of drawdown. The NOI indicated a threshold lowering of 4 inches. Since the measurement of surface water above the organic peat deposits will lag behind the changes in water table levels, the threshold should be in groundwater in proximity to the wetlands. The NOI should include a plan that locates wells and gages includ ing the adjacent area of Hyannis Creek. The NOI should also estimate the duration and rate of the dewatering for its various phases. The Notice of Intent (NOI) does not acknowledge the presence of PFAS in the local groundwater. A study examining PFAS occurrence in Barnstable surface waters reported the highest PFAS6 concentrations at Hyannis Creek and Aunt Betty’s Pond, measuring 159 ng/L and 141 ng/L respectively, with total PFAS levels of 252 ng/L and 238 ng/L 2. Poly- and perfluoroalkyl substances are regulated compounds, with the Department of Environmental Protection (DEP) setting a drinking water limit of 20 ng/L for PFAS6. The detection of PFAS is attributed to deeper groundwater migrating through this region, suggesting that groundwater extracted from the site is likely to exhibit similarly high concentrations. Therefore, the Commission should require preliminary PFAS testing of groundwater from the dewatering wells prior to operation, in order to assess concentrations relative to the DEP GW-1 standard of 20 ng/L. 2 Sole Source Consulting, LLC, The Distribution And Composition Of Pfas In Select Water Supply Wells And Surface Waters Of Barnstable, Ma Barnstable Water Supply Division, DPW, 2021 4 Although the pumped water is not for drinking, the pumping of groundwater with a regulated contaminant that is discharged to another location needs to be addressed by a Licensed Site Professional. The NOI, at a minimum , should inc lude an LSP opinion and the monitoring of the discharge for PFAS throughout the pumping event. Advice from DEP should also be sought in this instance. Thank you for your consideration. Please contact me if you have any questions. Sincerely, Thomas C. Cambareri, CGWP, LSP Barnstable Resident Cc: Daniel Santos, DPW Superintendent Mark Ells, Town Manager Felicia, Penn, Town Counciler 5 Figure 3 Preliminary Groundwater Model Output using the2019 USGS 400 ft grid space groundwater flow model showing drawdown caused by pumping and discharging 900 gpm from dewatering over 900 days. The contours are in feet. Approximate Hyannis Creek in Blue. More detail would require finer discretization.