WORK PLANS - Laserfiche WebLink

Home Browse Search

' • .NVIRONMENTAL.INC. February 24, 2012 Page 2 of 3 ' Based on existing onsite monitoring wells and hydrogeology beneath the site, the screened intervals will extend from approximately: ' 45 to 65 feet bgs for the A-zone • 95 to 110 feet bgs for the B-zone The wells will be installed using rotary sonic drilling technology. Telescopic conductor casing will be used during the drilling of B-zone wells to minimize communication between the water- bearing zones. The conductor casing will be advanced to the total depth of drilling (approximately 110 feet bgs) and removed in stages as the well is constructed. Neat cement will be placed in the well annulus as the conductor casing is removed during installation of the wells ' to maintain a seal between the water bearing zones. Each monitoring well will be constructed of 2-inch diameter schedule 40 PVC blank casing with ' 0.010-inch slotted screen. The annular space between the borehole wall and well screen will be back-filled with a silica sand filter pack to approximately two feet above the screen. A two-foot thick bentonite seal will be completed above the filter pack. The annular space above the bentonite seal will be sealed with neat cement to approximately two feet bgs. The wells will be completed with a traffic-rated metal well vault and a concrete pad installed flush to the surrounding surface. Wells not in vehicle traffic areas will be completed with a five-foot steel riser with locking lid installed approximately two feet bgs and secured in a concrete pad. Well design details are presented in Figure 2. ' Development, Purging and Sampling ' The wells will be developed by a combination of surging and bailing or pumping at least 48 hours after placing the annular seal. Development will continue until a minimum of five casing volumes of water have been removed and water quality parameters have stabilized. The water quality parameters will include oxidation-reduction potential, temperature, electrical conductivity, dissolved oxygen and pH. The newly installed monitoring wells will be gauged and sampled approximately 48 hours after development. The depth to water and total well depth will be ' gauged and low flow methodology will be used to purge and sample the wells. The water quality parameters will also be monitored and recorded during purging at a frequency of five minute intervals or greater during purging. Purging will continue until the field parameters have ' stabilized. Stabilization is considered to be achieved when three consecutive readings are within the following limits: t Parameter Stability Limit Dissolved Oxygen no greater than 20% saturation or t 10% Turbidity < 20 NTU or t 10% ' Temperature: t 0.2 °C pH: t 0.2 Standard Units Specific Conductance: t 10% of reading Once readings above have stabilized, samples will be collected using the peristaltic pump and tubing. Samples will be collected in individual sample containers provided by Calscience Environmental Laboratories (Calscience) of Garden Grove, California labeled, logged onto a