Monitoring dewatering systems

(1) General. Continuous control of seepage into and artesian pressure beneath the excavation is essen­tial for driving the test and foundation piles for the dam, and subsequent construction of the lock and dam. It is therefore imperative that the dewatering systems have adequate capacity to control the ground­water beneath the slopes and the excavation as speci­fied at all times, In order to check the adequacy and performance of the dewatering systems, the Govern­ment will make the following measurements and eval­uate the data:

(a) Measure the groundwater table beneath the bottom of the excavation by means of M, R, S, and T piezometers installed in the deep sand aquifer that underlies the site at specified locations.

(b) Measure the groundwater table at selected locations where the excavation penetrates silts and silty sands in the top stratum overlying the deep sand formation by means of N piezometers installed at the locations.

(c) Measure the flow from individual wells and from the complete dewatering system.

(d) Measure the water level in the dewatering


(e) Measure sand in the flow from dewatering


(/) Measure the head loss through the filter and well screen for selected wells.

(g) Read river stages.

The piezometers for monitoring the groundwater table beneath the slopes and bottom of the excavation shall be installed by the Contractor. The pitometers for measuring the flow from individual wells and from the complete system will be furnished by the Government. Copies of the data obtained by the Government will be promptly furnished to the Contractor. The Contractor will furnish and install the pitometer inserts. Opera­tion and maintenance of the dewatering systems, any supplemental groundwater control facilities if re­quired, and surface water control facilities shall be su­pervised by someone trained and with at least 5 years of actual experience in managing large dewatering sys – terns and operating pumps and engines.