SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Well Monitoring Program -4- 11 September 1992 DDRW, Tracy 3. The recommendations on the frequency of monitoring were proposed for a quarterly, semi-annual or annual basis. However, the Draft Report did not specify which quarter the semi-annual and annual monitoring would occur. Recommendations for semi-annual and annual monitoring should be based in part, on the hydraulics of the system. Semi-annual monitoring may be best performed at the height of the wet and dry seasons. Annual monitoring may best be performed during the wet season when ground water pumping would be anticipated to be at a minimum and therefore, representing the most quiescent hydraulic conditions. However, annual monitoring during the peak of ground water withdrawals (usually during the summer quarter) , could provide a worst-case scenario for the extent of the ground water plumes. The issue of when to perform the semi-annual and annual monitoring should be discussed at a Project Manager's Meeting. 4. The recommendations for on-going monitoring do not agree with the all of the required monitoring under Waste Discharge Requirements (WDRs) No. 90-275. The WDRs require, at a minimum, quarterly monitoring of the extraction and injection systems for the Interim Remedial Measure (IRM) and for background. The following wells have required monitoring in these WDRs. Wells Purpose of Monitoring Frequency LM-15, LM-28, LM-29, LM-30, LM-49, Extraction performance Quarterly LM-50, LM-53, LM-62 LM-4, LM-27A, LM-71, LM-79 Injection performance Every 2 months LM-11, LM-12, LM-63 Background Quarterly The monitoring recommendations included the quarterly requirements for all of the extraction performance monitoring wells. However, the Draft Report recommended annual monitoring for the injection performance and background monitor wells. The monitoring frequencies for these wells should be revised to be consistent with the monitoring requirements in the WDRs. As previously discussed with DDRW, Tracy, we plan to revise the WDRs and changes in the monitoring frequencies for the IRM can be negotiated at a future date. The specific requirements for an on-going monitoring program should be discussed at the next Project Manager's Meeting. The monitoring objectives and requirements should be agreed upon by the Project Managers so that Tracy may implement the changes as soon as possible. Delaying changes in the monitoring program until after the Final Report is not favored. Background Concentrations. The Report summarizes the results for each of the quarters for volatile organic constituents (VOCs) , semi-volatile organics, pesticides and metals. Background concentrations for VOCs, semi-VOCs and pesticides are generally considered to be non-detect because these organics are not naturally occurring. However, because DDRW, Tracy is in an agricultural area, pesticides may occur sporadically in low concentrations on a regional basis. With respect to metals and minerals, establishing background concentrations may not be as easy as for the organic constituents. Of particular concern, is that two of