WORK PLANS - Laserfiche WebLink

Home Browse Search

Work Plan for Groundwater Investigation and Groundwater Monitoring Well Installation Field Maintenance Shop #24 Stockton, California to well conditions based on well log information. The hydraulic conductivity can subsequently be estimated by dividing the transmissivity by the depth of the aquifer. 3.7 GROUNDWATER MONITORING WELL SAMPLING At least 48 hours after the monitoring wells have been developed, baseline groundwater samples will be collected from the three new groundwater monitoring wells. These groundwater samples, and samples collected from at least one additional well located outside the primary source area, will be submitted for laboratory analysis in support of providing baseline data for future performance monitoring, evaluating the potential suitability of ISCO as an interim remedial action at the site, and to serve as confirmation samples corroborating groundwater data collected during the MIP investigation. Prior to sampling, water levels will be gauged to ±0.01 foot for purposes of evaluating groundwater elevations. If SPH is suspected to be present based on findings during well installation, an electronic interface probe will be used to gauge one or more of the wells. After gauging, samples will be collected using a stainless steel monsoon pump to continuously pump water at a low -flow (250 - 500 milliliters/minute depending on well recharge). The sampling procedures will follow USEPA guidance for low stress (low -flow) purging and sampling for groundwater monitoring wells (USEPA, 1996). Low -flow purging minimizes turbidity in samples, thereby eliminating an objective for removal of a specified number of well volumes. As a result, this technique tends to minimize the volume of purge water that needs to be managed and disposed. The depth of the low -flow pump intake will be based on the expected site contaminants and the site-specific hydrostratigraphy identified during the monitoring well installation, and the rationale will be presented in the associated investigation letter report, as addressed in Section 4.0 below. Samples will be collected only after field -measured water quality parameters have stabilized indicating the presence of formation water. Water quality parameter stabilization will be documented separately for each well on a project -specific Monitoring Well Purge/Sample Log, which will be incorporated with reporting documentation as addressed below. Once water quality parameters have stabilized, groundwater samples will be collected in sterile, laboratory supplied containers, submitted to a California -certified laboratory under appropriate COC documentation, and analyzed for the following: • TPH-d using USEPA Method 8015 -Modified; • VOCs, including TPH-g, Naphthalene, BTEX, and Fuel Oxygenates using USEPA Method 82606; • Semi -Volatile Organic Compounds (SVOCs) using USEPA Method 8270C; • Dissolved Metals, including Total Iron and Sodium using USEPA 601013; • Total Dissolved Solids (TDS) using USEPA Method 160.1; • Total Organic Carbon (TOC) using USEPA Method 415.1; • Sulfate using USEPA Method 300.0; and • Hexavalent Chromium using USEPA Method 7196 or 7199. OTI E 14