No. 40] GEOLOGY OF SHEPAUG TUNNEL 1 5 



maintain a certain minimum flow in the stream, some properties 

 being purchased outright, conditional agreements for deferred 

 takings being made with others and in one instance a substantial 

 payment in money representing present value of estimated future 

 damages. 



The main physical problem in this Shepaug development lay in 

 finding the best method of conveying water to the City. In this 

 part of the State, as indeed in most others, the water courses run 

 north and south, separated by ridges of hills. It was found that 

 a gravity pipe line could be built which would carry water all the 

 way to the City without tunnels or excessively deep cuttings, but 

 it must follow such a devious course that its length would exceed 

 21 miles, and much of it would lie in regions not easily reached 

 by vehicles. Other and shorter routes to the City were studied, 

 involving varying lengths of tunnel. It was found that a line 

 almost due east would take water to existing reservoirs in the 

 West Branch Valley, but that its length of about jYa miles would 

 of necessity be substantially all so far below the surface of the 

 ground as to require tunneling. No satisfactory site for a regu- 

 lating reservoir near the City appearing, and direct connection 

 with existing reservoirs by tunnel presenting certain advantages 

 over the long pipe line of necessarily limited capacity, it was 

 finally determined to undertake the driving of the long tunnel. 



After careful surveying of the line, a large number of diamond 

 drill borings were made to determine the elevation of rock and 

 to get some information as to its character and its water-bearing 

 qualities. Particular attention was given to the Bantam Lake 

 Basin, containing the largest natural body of fresh water in the 

 State. Here a serious difiiculty was encountered. It was found 

 that the northern part of the lake consisted of a deep bowl in the 

 rock filled in to a thickness of a hundred feet or more with sand 

 and silt. Here the surface of the rock lies below the grade line 

 of a self-draining tunnel, necessitating an inverted syphon to keep 

 in the rock. Such a drop in the tunnel would form a pocket a 

 mile long, expensive to construct, always full of water after opera- 

 tion of the aqueduct began, and requiring special pumping arrange- 

 ments to make it accessible for inspection. 



Desiring to avoid this condition, and tunnel driving under air 

 pressure at such a depth being quite impracticable, thus barring 

 any location except in rock where work proceeds under atmos- 

 pheric pressure, a reconnaissance with the diamond drill was 

 undertaken and it was found that on a line crossing the lake at 

 the narrows and continuing under Marsh's Point to Sandy Beach 

 the rock was high enough at all points to afford at least a minimum 

 amount of cover for the tunnel. The original location was 

 accordingly changed and the tunnel driven on this line, having two 

 angles in it, instead of being straight as originally proposed. 



Driving of the tunnel was begun in December, 192 1. The 



