ARCHIVED REPORTS XR0011746 - Laserfiche WebLink

Home Browse Search

Report: Groundwater-quality Monitoring—flpril 15,2003: 7500 West Eleventh Street, Tracy, CA. Page 8 2.2 Purging of Monitoring Wells After the depths to groundwater were measured, a small-diameter, submersible pump was used to purge each groundwater-quality monitoring well of stagnant water. The pumped water was discharged into 5-gallon pails, each of which was, in turn, discharged into an open-topped, 55-gallon drum for temporary storage at the well-head. a During the purging procedure, the temperature and electrical conductivity of the stream } of purge water were monitored by checking those parameters periodically using a multi- function electronic meter. Purging continued until both parameters stabilized (i.e., r. 1 variations between measurements were less than 10%), or, in the case of wells screened above the water table, until a minimum of 15 gallons of groundwater had been removed, whichever was greater. The array of parametric results for each well was recorded in field i=-j notes. (See Field Notes, Appendix A). SJC's standard sampling procedure for the 7500 West Eleventh Street site includes =g monitoring the purge water for pH. Unfortunately, in the case of the April 15, 2003 sampling round, the pH element of the multi-parameter meter did not function properly and it could not be repaired in the field. Consequently, the pH values listed in the Field Notes reproduced in Appendix A are not accurate. Inspection of the temperature and conductivity data in the field notes shows that both parameters stabilized to within plus or minus 10% after the first few measurements were made on the purge water discharged from each well. This parametric stability is sufficient to demonstrate adequate well purging according to criteria suggested by the SJ`CEHD rj (San Joaquin County Public Health Services 2000). However, it is SJC's standard practice when purging shallow monitoring wells that have casings slotted in the zone above the water table at sites where groundwater is affected by analytes of concern that are lighter than water, regardless of the temperature, conductivity and pH data obtained, to purge a minimum quantity of groundwater equal to the casing volume plus the void space in the annular filter pack between the casing and the borehole wall. That volume (in { this case 15 gallons) is much g } ' greater than the three to five casing volumes that is often erroneously considered to be sufficient to purge adequately a well of that type and it is almost always greater than the volume that would be permissible based on the physical vj properties of the purge water alone. 2.2.1 Disposal of Pure Water Purge water temporarily held in the 55-gallon drum used to manage it at the well locations was pumped into a 1,000-gal. storage tank located on the 7500 West Eleventh .. , Street property. That water will be shipped to a permitted recycling facility for disposal when sufficient quantity has accumulated for that to be done economically following future rounds of groundwater sampling and analysis. sic _l