FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

R&B Trucking �" V Project No.01-37.1.1 March 27,1990 Page 4 thin sand layers. This clay is generally dark brown and shows high plasticity It ranges in hardness from soft to firm and also contains silt. The sand layers contained within the clay unit are fine grained and have a clay matrix. At this depth the sediments are saturated. 3.3 Regional Hydrogeololgy The Tracy area has a shallow water table that ranges from 8 to 16 feet below the surface. This water table is sloping to the north towards the San Joaquin Delta. Factors affecting the local hydrology include agricultural pumping and irrigation. More recently has been the dewatering of the shallow ground water by construction firms installing underground utilities. These dewatering operations can disrupt the normal gradient and bearing of the area's ground water flow. 3.4 Site Hydrogeology The hydrogeology at this site was determined by observing the three monitoring wells located on the site. The well's measuring points(M.P.)were surveyed and tied into an arbitrary plane so that each measurement could be referenced to each other. The survey methods included the use of a Lietz automatic level and a measuring rod subdivided into 1/1000 of a foot. The distance between the wells were measured using an engineer's steel tape graduated to a 1/1000 of a foot also. The angle between each well's measuring point was measured for accurate map placement. — After each monitoring well had been developed and allowed to fully recharge, the standing water in each well was then measured and recorded. The water level was measured with a 9 volt electric water depth probe that was subgraduated to 1/100 of a foot. These measurements were taken in a short period as to get a "snapshot" of the water level surface. The ground water gradient and bearing were measured and calculated for 2 February 1990 and 1 March 1990. On 2 February 1990 the ground water gradient was measured to be 0.00471 (feet/foot of horizontal distance)and was flowing north 74 degrees west. On 1 March 1990 the ground water gradient was measured to be 0.00380 and was flowing north 42 degrees east. The water levels in the wells are shown as follows: Date MW-1 MW-2 MW-3 2-2-90 8.732' 8.726' 8.918' -depth below M.P. 3-1-90 8.790' 8.580' 8.610' -depth below M.P.