FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

BALBI&CHANG ASSOCIATES Groundwater Monitoring Well Installation Groundwater monitoring wells are installed into the soil borings after logging and soil sampling are completed. The borings are drilled to at least 15 feet into the saturated layer or below the elevation of encountered groundwater. If a clay or impervious layer is encountered in the saturated zone, and if it is greater than 5 feet in thickness, drilling would stop and the boring would be backfilled with grout to the top of the clay or impervious layer. The monitoring well is then constructed above the backfilled layer. Our monitoring wells are constructed with 2-inch I.D. schedule 40 PVC pipes having 0.02-inch slot-perforated sections. The well screen is placed such that the screen length will accommodate seasonal groundwater fluctuations and extended at least 5 feet above the saturated zone. The annular space between the pipe and the wall of the boring is backfilled with #3 clean Monterey sand to about one foot above the top of the perforated section. A two to three feet of bentonite plug is then placed over the sand pack to provide a seal against surface water infiltration. The remaining space is then backfilled with concrete. Screw-on or friction cap is used to seal the bottom of the well casing. All well casing heads are secured with water-tight locking caps and protected by either concrete Christy box or metal vault. All wells are recorded with the Department of Water Resources by means of "Water Well Drillers Report". The report states the name of current owner, location of well including a well location sketch, well construction, well tests, and subsurface soil descriptions. A copy of the report is filed in our office and field files, and with the drilling company. All monitoring wells are thoroughly developed to stabilize the sand pack surrounding the screen section of the well and to free the well of silt, sand, and turbidity. The development of the wells are accomplished by using a teflon hand pump. Approximately four to ten well-volume of water is removed and/or the turbidity has subsided prior to sampling. A TSP solution is used to wash the hand pump and later rinsed with water prior to developing each monitoring well. Sample Storage and Handling All samples are stored refrigerated in our "clean lab" after arrived from the field. They are labeled with the date of sampling, project name, project number, boring or well number, and depth of sample. 2of3