ARCHIVED REPORTS_XR0006937 - Laserfiche WebLink

Home Browse Search

ERT 227903 R02 Former Unocal Service Station 5098 Stockton,California July 30, 1999 On March 10 and 11, and June 7, 1999, an ERI representative developed the nine newly-installed groundwater monitoring wells using surging and pumping techniques A California-licensed land surveyor surveyed the locations and top of casing elevations of the wells on June 21, 1999 Purge water generated during well development was stored in 55-gallon drums and left on site pending ' appropriate disposal by Unocal Groundwater monitoring and sampling of newly-installed wells MW 10A, MW 14A, MW 1 S, MW 195, ' MW19D, MW21S, MW21D, MW22S, and MW22D, was scheduled with Unocal to coincide with the third quarter 1999 groundwater monitoring and sampling event for the site Results of groundwater monitoring and sampling are provided in Attachment E ' Analytical Methods-Soil Samples Soil samples collected from the borings were submitted under Chain of Custody record to Sequoia Analytical Laboratories, Inc (Sequoia) for laboratory analyses The laboratory analysis reports and Chain of Custody records are provided in Attachment F Select soil samples were analyzed for TPPHg, benzene, toluene, ethylbenzene,and total xylenes (BTEX), ethanol,methanol,t-butanol,MTBE, di- isopropyl ether(RIPE),ethyl tertiary butyl ether(ETBE),and tertiary amyl methyl ether(TAME) using the methods listed in Tables 1 and 2 ' The composite soil sample collected from the drill cutting stockpile was submitted under Chain of Custody record to Sequoia for laboratory analysis for TPPHg,BTEX, MTBE, and total lead using the methods listed in Table 1 RESULTS OF INVESTIGATION Site Geology ' Sediments encountered in the borings consisted of layers of silt, clay, mixtures of silt and clay, fine- grained to medium-grained sand, and silty or clayey sand Groundwater was encountered between approximately 33 and 40 feet bgs in the borings During second quarter 1999, groundwater flow ' direction from and in the vicinity of the site was south and west toward the Delta College well at a calculated gradient of 0 O1(Gettler-Ryan, Inc , July 6, 1999 - Attachment E) Soil Conditions 1 Results of laboratory analyses of soil samples are summarized in Tables i and 2 A total of 27 soil samples, collected from depths ranging from approximately 30 to 80 feet bgs,were selected for laboratory analyses Copies of laboratory reports are included in Attachment F Groundwater Conditions Results of laboratory analyses of grab groundwater samples are summarized in Table 3 Three discrete groundwater samples, collected from approximately 34, 45, and 63 feet bgs in boring HPI, were submitted for laboratory analyses Copies of the laboratory reports are included in Attachment F 4