May 2, 2019 | GRJH, Inc. Hydrogeologist Jean Patota Email Disputing Location of Aquifer
This message summarizes my findings regarding the location of the unconsolidated aquifer. You requested that I review available information and respond to Save Craryville’s claim that GRJH’s property on the northwest corner of Route 23 and Craryville Road is located within a local aquifer.
Specific comments from two representatives dated April 4, 2019, assert that “The site lies directly over a high-permeability sand and gravel aquifer...” and, “The applicant’s Environmental Assessment Form misled the town... ...the site is squarely above a mapped aquifer. ...which is clearly shown in Figure 6 of the Town of Copake Water Resource Summary.”
I reviewed the referenced “Figure 6” (Mapped Aquifers), and the figure that was prepared by Save Craryville’s consultant. I also reviewed two maps prepared by NYRWA for Columbia County, “Surficial Geologic Materials” and “Unconsolidated Aquifers.” These are the same two NYRWA maps that I enlarged to better show the site vicinity during the April 13 Workshop. I also reviewed the NYSDOT topographic map and the Columbia County Soil Survey.
The map submitted by Save Craryville’s consultant was created with limited data and misrepresents the aquifer boundary near the proposed project. The map was presented as definitive; however, using GIS to selectively apply data while excluding other relevant and publicly available information supports that the map is invalid and misleading. The consultant failed to consider the published soil types or more detailed maps prepared by NYRWA. The consultant falsely incorporated glacial landforms of low-permeability in his delineation to show the site is surrounded by an aquifer. The consultant appears to have simply enlarged Figure 6 without reviewing the reasonableness of the geologic and hydrogeologic representations or correcting the computer-generated boundaries. Accordingly, the conclusions and opinions based on that map are misinformed.
1. The referenced Figure 6 is a generalized geographic map of aquifer locations. That figure from the Water Resource Summary includes a note that cautions in bold “Aquifers were mapped at a very course (sic) scale (1:250,000) and are for general information only; this map should not be used at the site plan scale.” The NYSDEC acknowledges that the large scale of the map is inappropriate for determining specific aquifer boundaries.
2. The NYRWA maps of surface geology and aquifers are not site-specific but were prepared at a scale of 1:24,000, which is more than 10 times smaller in scale (i.e., shows greater detail) than Figure 6. The NYRWA maps show the area northwest of the intersection is underlain by glacial till and that the aquifer boundary is east to south of the project site except at the intersection, where a small area of “alluvium” soil is shown at the northwest corner. The NYRWA interpretations reflect the incorporation of multiple data sources (soils, topography, landforms, drilling logs, field observations, and databases) although specific conditions will vary. The maps are not intended for designing site plans and do not represent precise boundary locations; however, NYRWA’s interpretations appear reasonable and accurate for the represented map scale and intended purposes.
3. The Columbia County Soil Survey indicates the project site is underlain by silt loam (Punsit loam) that was derived from glacial till. Till does not represent a significant water-bearing unit and does not constitute an aquifer or recharge area. Soil to the south (presumed to be hydraulically down gradient) is mapped as “Alden mucky silt loam” between Route 23 and the old railroad bed. The boundary of more permeable soil (Blasdell channery silt loam) is mapped at the highway intersection and immediately to the south and east, within the aquifer. The closest aquifer boundary is under the paved intersection based on the soil survey. The soil type indicates that infiltration (percolation) on site is limited and that ground water migration is not a significant contaminant pathway.
4. The topography and drainage patterns on site indicate glacial landforms (till covered drumlins and till plains) that are consistent with the soil survey, including that the soil has low transmissivity and limited capacity for soil infiltration beyond the top few feet within the till. The engineering plans document that “dense silty sand” was encountered at 48 inches below grade in two test pits near the intersection that were excavated for wastewater design. A representative for the Columbia County DOH also observed the test pits in November 2017, and described the soil as “dense brown silt material” from 2 to 4 feet in depth, where the test pits were terminated.
In consideration of the mapped soil type, I revise my opinion regarding bioremediation of incidental spills. A petroleum spill in till would be most effectively remediated by excavating the impacted soil to physically remove the petroleum. It remains my opinion that runoff and incidental spills onsite are unlikely to be of sufficient volume to flow overland to areas south of Route 23.
Regarding the concern for air quality impacts, Save Craryville’s representative cites findings from outdated references (1993 and 1999) that are irrelevant to project conditions, and misrepresents another 2015 article which is based on the absence of “pollution prevention technology.” It is recommended that the equipment manufacturer and/or Project Engineer be consulted if nuisance odors are reported.
Greater detail of my findings can be provided as requested. You are welcome to contact me at your convenience if there are additional questions. Thank you for the opportunity to be of service.
Jean M. Patota, P.G.
P.O. Box 517
Stillwater, NY 12170