SITE HISTORY - Laserfiche WebLink

Home Browse Search

ter M (YVATC 1117 Lone Palm Avenue, Suite BModesto, CA 95351www.atcassociates.com 209-579-2221 ASSOCIATES I N C . Fax 209-579-2225 Environmental, Geotechnical and Materials Engineers approximately 20 feet of slotted (0.020-inch slots) 2-inch diameter Schedule 40 PVC well screen. The annulus of the screened portions of MW16 and MW17 was backfilled with a #2/12 sand filter pack extending from the bottom of the screen to at least two feet above the top of the screen in each borehole. At least two feet of bentonite chips were placed on top of the upper filter pack and hydrated to form an annular seal. I . Monitoring wells MW18 and MW19 were installed to a depth of 90 feet bgs and were each constructed with approximately 85 feet of blank 24neh diameter Schedule 40 PVC casing and approximately 5 feet of slotted (0.010-inch slots) 24nch diameter Schedule 40 PVC well screen. The annulus of the screened portions of MW18 and MW19 was backfilled with a #2/12 sand I' filter pack extending from the bottom of the screen to at least 2. 5 feet above the top of the screen in each borehole. At least 2. 5 feet of bentonite chips were placed on top of the upper filter pack and hydrated to form an annular seal . Cement grout was placed on top of the bentonite and the wells were each completed at grade with a watertight, flush-mounted, traffic-rated vault. Well construction details are depicted on the well logs contained in Appendix A. The locations of the monitoring wells are shown on Figure 3 . 2_3 Monitoring Well Development and Surveying �'. Groundwater monitoring wells MW16, MW18, and MW19 were developed on February 28, 2008, by pumping at least nine well volumes of groundwater from each well. MW17 was purged ii dry after removing one gallon of water. The odor of grout in the purged groundwater coupled C with high pH measurements (9.5 — 11 .6) indicated the potential presence of grout inside the well. The total depth of the well was measured to be approximately 50.6 feet. Purged groundwater was temporarily stored on site in 55-gallon drums prior to disposal . Development logs for MW16 through MW19 are included in Appendix B . jOn February 28, 2008, monitoring wells MW16 through MW19 were surveyed relative to NAD 83 and NGVD29 for position and elevation. The survey data are presented in Table 1 . The surveyor' s report is included in Appendix C. 19 2_4 _Groundwater Sampling and Analyses I I The depth to water was measured in MWl through MW10, MW11R, MW12 through MW16, MW18, and MW19 (Figure 3) on March 6, 2008 . Monitoring wells MW7, MW10, MW11R, i MW13 , MW14, and MW15 are sampled annually and were not sampled as part of the first quarter 2008 sampling event. Prior to collection of groundwater samples from MWl through MW6, MW8, MW9, MW12, MW16, MW18, and MW19, the depth to water, pH, electrical conductivity, and temperature were measured in groundwater purged from these monitoring J wells and recorded. Turbidity was visually observed and recorded. Approximately three well casing volumes were purged from each monitoring well prior to sampling. The wells were I � S:\Enviromental)28349heports\lnv rpt 2008.doc 4 ATC Associates Inc.