within this range is typical for silty glacial tills and 

 is generally considered very low. 



o Marine Sand 



As the glacial ice sheet retreated from the area, silt and 

 sand ladened waters melting from the ice flowed into the 

 ocean settling out to form a layer of silty medium to fine 

 sand overlying the glacial till deposits. Where 

 encountered, this stratum ranged in thickness of up to 9.0 

 ft., with the top of stratum varying from approximately 

 El. 109.1 to El. 93.9 (NACA) . 



o Organic Soils 



A stratum of organic soils consisting primarily of sandy 

 organic silt and peat was found to overlie the glacial 

 till or marine sands. This stratum is the original harbor 

 bottom sediments which accumulated prior to site filling. 

 The organic silt and peat are typically soft to hard, with 

 low strength and high compressibility. The strata ranges 

 up to 14.5 ft. in thickness where encountered with the top 

 of strata noted from El. 110.1 to El. 100.1 (NACA). 



o Miscellaneous Fill 



With the development of the harbor area during and 

 following the 17th century, many waterfront structures 

 were built out into Boston Harbor. At this time, a 

 man-made layer of fill was placed across the site to the 

 present grade and primarily consists of an unsorted 

 mixture of coarse to fine sand, silt, clay and fine gravel 

 with varying amounts of wood, cinders, brick, slag and 

 concrete. The thickness of the strata varies from 4.5 to 

 18.5 ft. 



Refer to our report entitled "Report on Oil and Hazardous 

 Materials Site Evaluation - Tudor Wharf, Charlestown, 

 Massachusetts," issued concurrently with this report for 

 further information pertaining to site history and usage. 



3-03. OBSERVED WATER LEVELS 



Water levels measured in boreholes upon completion of a boring 

 may not necessarily represent the true, stabilized groundwater 

 levels. Therefore, to monitor local subsurface water levels 

 over an extended period of time, three observation wells were 

 installed within the upper 15 to 20 ft. of completed borings 

 B102, 3103 .and B104. Observation well installation logs and 



oe 80 



