WORK PLANS - Laserfiche WebLink

Home Browse Search

Ms Lori Duncan Page 2 An additional subsurface investigation was conducted on January 12, 2001 pursuant to a PHS/EHD directive dated January 2, 2001 to determine if groundwater had been impacted. Non detectable levels of targeted analytes were found in the soil; however, analysis of groundwater indicated that low levels of chlorinated solvents and MTBE were present. The location of boring SB1A is shown on Figure 2. Soil and groundwater analytical results are summarized in Tables 2 and 4, respectively. On March 27, 2001, a meeting was held at the request of PHS/EHD to discuss options for further investigation of groundwater contamination at the subject site. At the conclusion of the meeting, it was agreed that one monitoring well would be installed at the subject site with the understanding that additional monitoring wells may prove necessary in the future. Hydrogeological Setting The site is situated in the Lodi South quadrangle, Section 8, T2N, R6E, San Joaquin County, California. Regionally, the property is located in the San Joaquin Valley physiographic province. The valley is a topographic and structural basin bounded on the east by the Sierra Nevada and on the west by the Coast Ranges. Locally the topography slopes gently toward the southwest at approximately six feet per mile. Significant surface water bodies in proximity to the site are Five Mile Creek, Mosher Slough, and the Calaveras River. Mosher Slough and Five We Creek,are located approximately 800 feet and 1 mile south of the site, respectively. These two waterways flow in a westerly direction. The southwest flowing Calaveras River is located approximately 4 miles west southwest of the site and is a tributary of the San Joaquin River. The Calaveras River generally exhibits moderate stream flow losses over portions of the year,which contributes to groundwater recharge(USGS Professional Paper 1401-D, 1989). Regional groundwater flow in the site area is generally in an easterly direction toward a regional groundwater depression centered approximately 4 miles east of Stockton (San Joaquin County Flood Control and Water Conservation District, Fall 1998). Drinking water wells in the region are generally completed at depths greater than 100 feet below ground surface (bgs) due to the relatively poor quality of near-surface groundwater. Current depth to first groundwater at the site is approximately 32 feet below grade,and is expected to flow in a northeasterly direction (San Joaquin County PHS/EHD Corresp, 9/6/00). Historical data from the San Joaquin County Flood Control and Water Conservation District suggests that water levels are currently at or near a historical high. Historical low water levels are expected to have been between 45 and 50 feet bgs. PROPOSED SCOPE OF WORK To further evaluate the nature and extent of groundwater impact on the property the following workscope is proposed: Drilling,Well Construction and Soil Sampling One monitoring well (MWl)will be installed at the site at the approximate location shown on Figure 3. A C-57 licensed drilling contractor will advance one eight-inch diameter hollow stem auger boring for conversion into a groundwater monitoring well. The well will be completed to depth of approximately 47 feet below ground surface or 15 feet below the finding of first groundwater. Well construction will consist of 2-inch diameter,Schedule 40 PVC casing,and 0.020"slotted screen. The screened interval will extend from F:\Datm\GROUNDZE\NSAUrO\REPORTS\WORYPLAN—IhfW.doe