ARCHIVED REPORTS_XR0003267 - Laserfiche WebLink

Home Browse Search

A-3 GROUNDWATER WELL INSTALLATION A-3 1 Monitoring Well Construction Construction details for shallow groundwater monitoring wells are as follows. D The well casing will be 2-inch inside diameter, flush threaded ,joint, schedule 40 PVC pipe U The wells will be constructed in 8-inch diameter borings o Well screen sections will be perforated with 0 010- or 02-inch factory-cut slots o The wells are generally screened from 5 feet above to 15 feet below first groundwater The screen length is reduced if an aquitard with a minimum thickness of 5 feet is encountered. If an apparent aquitard is encountered, the well is usually terminated 1 to 2 feet into the aquitard Effort is made not to screen across two aquifers If confined aquifer conditions or high vadose zone contamination is encountered, the well screen is usually not set above the depth of first encountered groundwater Wells are usually not set in areas of suspected significant soil contamination. o The PVC pipe and end caps are steam cleaned prior to installation o The annular space between the screen and the wall of the boring is backfilled with the appropriate clean Lone Star Industries 0130 or 2112 Monterey sand to approximately 2 feet above the top of the perforated sections. Based on soil logs or a sieve test, modifications may be made regarding the size of sand to be used Installation of the 0130 sand may require that the sand be tremmied, using clean water In this event, a sample of the tremae water is collected, unless the source is thought to be clean � o A 3- to 5-foot bentonite plug is placed above the sand pack to provide a seal against surface water infiltration and to reduce the potential for cement grout to infiltrate into the water o The remaining annular space is filled to the surface with tremmied cement/bentonite grout to the surface. o The wells are secured in an above- or below-ground locking stovepipe The well heads may be enclosed in a water tight cement utility box set flush to the ground surface when located in a traffic area A-3 2 Monitoring Well Development The wells are developed to reduce the effects of drilling on the formation and to increase the effective hydraulic radius of the well Monitoring wells are generally developed 24 to 48 hours after installation to allow the grout to set Each well is first sampled with a clear acrylic bailer to visually inspect for hydrocarbon layer or sheen If no product layer or sheen is observed on the water, the well is developed by surging, pumping or bailing Surging along the screened interval of the well is performed to draw the sediment from the formation into the filter pack and the well, and to set the sand pack The sediment laden water is purged from the well at a rate of between 0 75 to 10 SAPROTQ 1993 { ) Page A-3 24-160241-000 copyright 1993 Kleinfelder, Inc {