Feb 7, 2019 | Save Craryville Environmental Engineer's Cursory Review - Bart Clark, P.E.
February 7, 2019
Oakwood Environmental Associates
Bart Clark, P.E.
27 Reverie Road Warren, Connecticut 06754 (860)868-1367
Jamie Carano, SaveCraryville@gmail.com
Re: Save Craryville, Plan and Submittal Review GRJH Convenience Store and Fuel Station,
Dear Ms. Carano,
As requested, I have reviewed the materials on the SaveCraryville website concerning the application submitted for the GRH Convenience Store and Fuel Station. A Site Plan application has been made to the Town of Copake Planning Board. The review has been a cursory review meant to identify areas of concern associated with Stormwater Management and Onsite Wastewater Disposal. We have not prepared a full compliance review where the design plans and materials submitted have been closely compared to the governing regulations and permit requirements.
With that understanding, there are several issues of concern that this review has identified. The specifics of the issues are more completely described on the memo attached to this letter. As a brief summary, the issues are:
The existing conditions at the site have not be fully characterized with respect to soil conditions and watersheds.
The Stormwater Pollution prevention plan is out of date and should be revised to reflect current conditions.
The drainage design should include provisions for preventing clean water from flowing onto the site and becoming contaminated by the fueling activities.
Inlet capacities for various stormwater structures should be investigated and designs revised to allow for adequate capacity.
The wastewater adsorption fields location needs to be reconsidered giving the flooded conditions that exists and the proximity to stormwater drainage at the location currently being proposed.
Soil testing for the absorption fields needs to be performed in the location of the fields and the location and results documented on the plans.
Again, this is a brief summary. Please refer to the memo for the details of each issue. If you have any questions, please contact me.
Oakwood Environmental Associates
Bart Clark, P.E.
NYS PE No. 070346
Oakwood Environmental Associates
From: Bart Clark, P.E.
Re: Save Craryville, Plan and Submittal Review
GRJH Convenience Store and Fuel Station
Save Craryville has requested that I perform a cursory review of the application materials and project site and offer opinions concerning proposed stormwater management and wastewater disposal.
The documents that I have reviewed are listed below:
- Stormwater Pollution Prevention Plan, titled “GRJH Convenience Store & Fuel Station”, prepared by Steven E. Smith Civil & Architectural Engineering, dated August 28, 2017, last revised September 20, 2018;
- Drawings prepared by Steven E. Smith Civil & Architectural Engineering, for “GRJH Convenience Store & Fuel Station”, various titles, sheets C101, C102, C501, C502, C503, C504 with various revision dates from 11/26/18 and 12/21/18.
The Soils mapping. A soils report prepared from the NRCS website is included as appendix C in the report. The are a few important issues to highlight with regards to this report. First is the Warning at the bottom of page 6, “Soil Map may not be valid at this scale.” This is not uncommon to see on the reports, but, what it suggests is that the soil map is not the definitive source for information concerning soils on the site. The soils report indicates that approximately 2/3rds of the site consists of Punsit silt loam, PuB, which has a depth to ground water of 6” to 18”. This suggests that there are significant areas on the site that have a shallow depth to groundwater. The Soils report also indicates that Punsit Silt loam can have inclusions of Alden Silt Loam which is a hydric (wetland) soil type. On site testing is crucial to understanding the soils and this understanding is important to the design of both the stormwater system and wastewater disposal system.
Based on a brief visit to the site, there is clearly an area where the soil is frequently flooded and may be hydric. The photo in figure A shows an area near the Post Office property line that was flooded.
This ponded area is providing some benefits such as improvement of water quality, reduction of total volume and some minor mitigation of the peak flows during small storm events.
The presence of this ponded area also suggests that the watershed shown in the existing conditions map SWM-1are not correctly modelling the existing conditions on-site. The plans indicate a 15” diameter pipe between the Catch Basin on Rte 23 and the intermittent water course. The inlet to this pipe was not found by the surveyor hired by the applicant. This suggests that the opening to the pipe has been blocked possibly due to accumulation of sediment and other organic debris which has changed drainage paths. The aerial photos from the NYSGIS Clearing house, figure B, and the presence of a large area that has not been mowed suggest a large area where the groundwater is at or near the surface which appears partially due to the water that no longer flows into the culvert.
[A. Photo showing ponded water near Post Office Boundary]
[B. 2017 Aerial Photos of Proposed site]
The SWPPP identifies the proposed use as a stormwater hotspot. It correctly eliminates infiltration features for those areas where stormwater may come into contact with spillage from fueling activities. However, the proposed plan does not acknowledge that water draining on to the site should be prevented from flowing onto those surfaces where fueling takes place. The idea is to keep clean water clean.
The SWPPP prepared in 9/2018 is no longer representative of the conditions at the site due
to changes in the Site Plan and not accurately reflecting existing conditions at the site and,
so, needs to be revised.
The proposed plan should seek to replace the water quality and volume reduction currently
provided by existing areas where water ponds on the site. While infiltrative water quality basins are not advisable for the refueling area, these benefits could be provided using Green Infrastructure for the clean water areas.
An CDS Separator is shown on the plans. The manufacturer’s (Contech) design data appears to have a primary focus on nutrient and sediment removal and not on the design pollutant, hydrocarbons. The CDS separator has fixed capacity for the removal of hydrocarbons likely to be seen in the stormwater at this site. The capacity of the selected unit would require frequent maintenance to allow it to trap and hold hydrocarbons. The hydrocarbon removal efficiency should be verified and possibly a unit with higher capacity should be selected to allow for a less frequent maintenance. The maintenance schedule on p. 16 of the SWPPP may need to be more aggressive depending on the capacity of the unit selected.
The proposed plan should provide for facilities that help insure clean water does not flow onto the fueling areas. Diversions should be provided at the property line where possible similar to what was shown on earlier versions of the Site Plan.
The design of the intake for the culvert which intercepts the intermittent water course should be revised to prevent clogging. The flat top basin is unlikely to have the capacity to pass the 10 year design storm flow of approximately 50 cfs and is unlikely remain open because of accumulation of debris. When the capacity is exceeded due to heavy rainfall or a clogged grate, the water will run across the parking area causing trouble year-round.
The entire site is drained by a single catch basin. It is unlikely that this basin top will have the capacity to pass the 10-yr design storm which would lead to frequent ponding. Additional inlet capacity should be provided to allow water to enter the treatment system with enough additional capacity to make allowances for a grate partially clogged with debris.
The Water Supply and Wastewater Systems
The water supply is proposed to be a newly drilled well. It would seem prudent that any approval should require the well to be drilled and tested prior to beginning construction on the site. There is no guarantee that a well drilled in the proposed location would have the yield and water quality needed. The location of the well and its 200 ft protective radius is critical to the location of the wastewater system components on this tight site. If the well needs to be moved, the site plan would likely require revision.
The wastewater system is designed to provide for enhanced treatment as compared to a standard septic tank and leaching system. However, the system design needs additional justification to overcome several potential issues. These issues include:
The soil testing data includes no results from percolation testing and specifies no location for any testing that may have been done. The current location of the absorption system is in an area that is frequently flooded (See figure A). The ability of this location to accept the discharge from the absorption system is suspect. The application rate of 1.2 gpd/sf might apply to the proposed fill used for the mound, but, it does not appear to reflect the conditions of the existing soils in the absorption field location.
The soil testing data includes a summary of the observations from test pits and does not specify the location of this testing. The existing condition of and vegetation on the absorption field area (See figures A and B) does not appear to be representative of the reported soil profiles. The plans call for replacement of 12” of the existing soil in this area with bank run gravel and, then, building a mound on top. Replacing a limited amount of soil is unlikely to overcome any deficiency of the existing soil.
The absorption fields layout does not appear to be optimal to allow a soil with a high seasonal water table to accept the additional water. The fields are generally perpendicular to the contours rather than “Parallel with the contours of the site” as indicated in the Mound Construction notes on Sheet C-504. It would appear that other locations should be considered for the adsorption fields.
On Sheet C-504, Detail F8 suggests that an infiltration barrier is to be installed. However, the plan does not appear to show the location of this barrier. My assumption would be that it is to protect the drainage in Rte 23 from infiltration of contaminated water being discharged by the absorption fields. The absorption fields are approximately 33 ft away to the drainage pipe in Rte 23. It would seem to be a fair assumption to consider this drainage pipe to be an open or groundwater intercepting drain which would require a 50 ft separation distance rather than 35 ft to a tight pipe. The barrier appears to be an attempt to reduce this distance. Other locations for the absorption fields appear to be available.
The low pressure distribution design suggests 15 ft of head on the pump in the design data on sheet C-103. Based on a quick review, the head appears to be closer to the 50 ft. The calculations should be double checked. If a pump that supplies the flow at less than the head required is used, then the absorption fields will not function as intended.
There are other details needed for the low pressure distribution system to allow it to be set up, operate and be maintained properly. These include balancing valves on the laterals, orifice shields, lateral terminal clean-outs/pressure monitoring assemblies, pump lift out mechanisms in the pump chamber to eliminate entry into the vault, confined space warning signs, proper start-up instructions, etc.