SITE HISTORY - Laserfiche WebLink

Home Browse Search

1 S '• Mr. Chuck Carmel U l June 26, 1992 i Page 2 i of 13 feet, where groundwater was encountered. Borehole logs are provided 'in Attachment A. Soil samples were collected for laboratory analysis from HP-1 at depths of 4.5 to 5 feet and 6 to 6.5 feet and from HP-2 at depths of 7 to 7.5 feet and 8.5 to 9 feet.r Groundwater samples were collected by driving a hydropunch sampler approximately 1 foot into groundwater. The boreholes were then backfilled with a bentonite-cement grout pumped through a tremie pipe. Groundwater samples were also collected from the on-site wells. Samples from AL-1 and AL-4 were collected on March 19, 1992. A sample from AL-2 could not be collected on March 19 because the well christie box could not be opened. The christie box'was replaced, and AL-2 was sampled on April 14, 1992. Results and Discussion Borehole HP-1 was drilled through the backfilled area where the waste oil tankwas previously located. Pea gravel was encountered from beneath the asphalt to a depth of 3.5 feet. Below the pea gravel, silty sand and sand were encountered to the total depth of the borehole. HP-2 was drilled through native soil located adjacent to the south margin of the former tank area. The soil consisted of silty sand and sand to a depth of 13 feet. The soil sample analytical results from this and previous investigations are summarized in Table 1. BETX and TPH as diesel were not detected in any of the soil samples collected from the boreholes drilled during this investigation. The laboratory report and chain-of- custody documentation for all analytical results are enclosed as Attachment B'' BETX and TPH-as diesel have not been detected in any of the past or current groundwater n`p samples, as summarized in Table 2. However, the laboratory reported that low levels of � hydrocarbons were detected in HP-2 but were noted as not being diesel fuel. '+ Water-level elevations and the general groundwater flow direction for April 27, 1992, are shown on Figure 1. The general groundwater flow direction is to the east-northeast under a hydraulic gradient of approximately O.WO3. Water-level data are summarized in Table 3, and historical groundwater flow directions and hydraulic gradients are shown in Table 4. As indicated by the data presented in Table 4, the hydraulic gradient is very low, and the groundwater flow direction is widely variable. Based on the results of this and previous investigations, further work is not warranted at this site: It is requested that this site be "closed" and removed from San Joaquin County's list of E environmental-impacted sites. i Brown and Caldwell i Consultants t6�I-".L.2