3-02. SUBSURFACE SOIL AND ROCK CONDITIONS 



The subsurface explorations indicate the following general soil 

 and rock sequence in order of increasing depth from ground 

 surface: 



o Miscellaneous Fill 



o Organic Silt and Peat 



o Marine Sands 



o Glacial Till 



o Bedrock (Assumed) 



Due to the complex geologic environments responsible for 

 deposition of the materials, all the units may not be present 

 at specific site locations. The units are discussed below in 

 order of deposition and are indicated graphically on Subsurface 

 Profiles A-A and B-B, Figures 3 and 4, respectively. 



o Bedrock 



Bedrock was not encountered in any of the test borings. 

 However, according to available geologic maps and our 

 previous experience, bedrock in the project area is 

 believed to consist of Cambridge Argillite, a grey 

 slate-like mudstone of extremely variable quality. 



o Glacial Till 



During an advance of the glacial ice sheet over the Boston 

 area during the Pleistocene time period, a very dense, 

 nonstratif ied, unsorted material known as glacial till was 

 deposited over the bedrock surface in the project area. 

 The glacial till encountered at the site typically 

 consists of a very dense, silty fine sand to sandy silt 

 with trace to some gravel and contains occasional cobbles 

 and boulders. 



The top of this strata was encountered between El. 102.1 

 and El. 86.3 (NACA) . The thickness of the glacial till 

 strata was not determined since none of the test borings 

 conducted were advanced into the underlying bedrock. 



The results of the two in-situ falling head peirmeability 

 tests conducted in the glacial till indicate that the 

 strata has an average permeability ranging between 

 4.7 x.10'5 and 9.2 x 10' "^ cm/sec. Soil permeability 



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