HomeMy WebLinkAboutApplication Files_82693_pg0458 Date. February 8,2010 2 '
Project No.: 72189.00
Soils and Surficial Geology ,
According to the Connecticut Environmental Conditions Online(CTECO)the surficial geology of the Site
is classified as glacial outwash deposits(glacioflucial)consisting of sand overlying fines. Refer to
enclosed CTECO map in Appendix B. According to the Natural Resources Conservation Service Web '
Soil Survey soils at the Site are mapped primarily as Windsor loamy sand(Map Unit 36),Ningret and
Tisbury soils(21)and Udorthents-Urban land complex (306). Windsor soils are excessively drained
soils formed in sandy glacial outwash with a minimum depth of at least six(6)feet to a seasonal water ,
table. Ninigret and Tisbury soils are moderately weII drained soils formed in loamy over sand and
gravel outwash;the minimum depth to a seasonal water table,when present,is 24 inches. A copy of
the soil survey map and report are also enclosed in Appendix B.
Bedrock Refusal and Fill '
Test pit depths excavated by the excavator were between 120 and 144 inches deep before stopping '
excavation due to instability of the non-cohesive sands causing collapse of the sidewalls from
infiltrating groundwater. No confining layers or restrictive features (bedrock,silt/clay layers,dense
till,etc.)were encountered in any of the excavated test pits. Hand augered test pits were advanced
between 84 and 165 inches deep. Depth of investigation was limited either to instability of the non- '
cohesive sands causing collapse of the boring sidewalls or the maximum length of the auger.
equipment(approximately 165 inches). No confining layers or restrictive features were encountered in
any of the hand augered test pits. Shallow fill or regraded native soil materials(generally referred to '
as Human Transported Materials or HTM)was encountered in test pits TP-8,TP-9,TP-23,TP-27,TP-
28,TP-30,and TP-31.
Groundwater{observations and Estimated Average Seasonal High Water Table '
Groundwater/free water was observed in the majority of test pits and ranged in depth from 44 to 142
inches. Refer to groundwater depth and estimated SHWT summary table in Appendix C. VHB '
conducted two groundwater monitoring events to confirm the depths to the SHWT(December 23,
2009 and January 15,2010). Wells installed were installed at test pits TP-27,TP-28,TP-30 and TP-31 on
February 12,2010 and read later that same day. Although these measurements were not collected
during the height of the wet season(e.g.,March-May)they are thought to be within approximately one ,
half foot of the SHWT.The depth to Average Seasonal High Water Table(ASHWT)may be estimated
by interpreting redoximorphic features present in the soil profile. Redoximorphic features were
observed at various heights in several,but not all,test pits. The shallowest observed distinct or ,
prominent,common to many redoximozphic concentrations,primarily consisting of iron and
manganese soft masses and nodules,were interpreted to represent the ASHWT. In general and where
present,these redoximorphic features were observed between 0.5 to 0.7 feet above groundwater ,
depths measured during monitoring.
Saturated Permeability
A constant head well perrneameter test is a widely used and accepted procedure for measuring the
saturated permeability(Ksat)of a soil.In this technique,the steady state flow rate of water under a
constant pressure(or height of head)at the bottom of a cylindrical auger hole of known radius is
measured. The rate of flow of water into the soil is typically determined by measuring the change in .
the height of water in a reservoir over time. In this method,a constant head of water is established
and water is allowed to infiltrate the soil until steady state is achieved. These data are then used in an
appropriate equation to calculate Ksat. ,
On this site,data from these tests were used to calculate Ksat using the Glover solution which ignores
unsaturated flow in its analysis.This solution has been recommended for calculating Ksat when the
distance between-the bottom of-the hole used for the test and any impermeable layer below the hole-is
substantially greater than the applied head used for the field test. The Ksat determined using this
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