WORK PLANS_CASE 2 - Laserfiche WebLink

Home Browse Search

in the vicinity of the former USTs comprises mostly fine- to very fine-grained sand and silty sand to a depth of about 17 feet bgs, with silt and clay predominant from about 17 to 28 feet bgs, the maximum depth explored at the site. Soils encountered near the former dispenser area(borings B5- 4 and B5-5) comprise mostly clay. A to 2-foot thick bed of sand occurs beneath the former dispenser area at about 17 feet bgs. Data from nearby studies indicate that the current depth to groundwater in the vicinity ranges from about 5 to 10 feet bgs(SPDC, 1998, and EMCON, 1998). Seasonal fluctuations in the water table _ appear to range from about 3 to 5 feet,with some as much as 6 to 9 feet. Tank removal inspection records for this and other Port sites (dating back to 1987) indicate that no groundwater was encountered during excavation of tanks or soil resampling to a depth of as much as 16 feet bgs. Water levels in this area have risen as much as 8 feet since 1994, 2 to 3 feet of which appear to be attributable to the heavy and prolonged EI Nino rainfall events of last winter. The static water level in the borings emplaced near the former USTs(borings B5-1 to -3)was about 9 feet bgs on August 5,while water levels in the borings emplaced near the former dispenser area(borings B54 and -5) were about 11 feet bgs. Based on nearby studies (SPDC, 1998, and EMCON, 1998) groundwater flow directions in the vicinity appear to be variable, ranging from west northwest to east southeast. Flow direction changes may be due to tidal influences produced by the deep water channel to the north and the San Joaquin River to the west and southwest of the Port complex. 3.0 PROPOSED SCOPE OF WORK The proposed scope of work includes advancing three borings, one in the vicinity of the USTs, one in the vicinity of the dispenser, and one in the northwest corner of the site, using the hollow-stem auger method. Each of these borings will be completed as a monitoring well and the wells will be developed and subsequently sampled on a quarterly basis for analysis of PHCs and determination of groundwater gradient. In addition, a supply well survey will be conducted in the vicinity of the site to evaluate the effects of potential migration of PHCs from the site. A Technical Report will be prepared including documentation of field work, results of the initial groundwater sampling, and a summary of findings from the supply well survey. This work plan will be carried out under the supervision of a California registered geologist. The procedures for completing the scope of work are summarized in the following subsections. 3.1. INSTALLATION OF MONITORING WELLS Prior to initiating any field work, an application for"Permit to Construct Monitoring Wells and/or Soil Borings for the Purpose of Subsurface Investigation," will be submitted to and approval s,edin.cwpn 4 PHILIP P. ROSS, R.G.