ARCHIVED REPORTS_XR0002255 - Laserfiche WebLink

Home Browse Search

Jonas & Associates Inc ' screened portion of the well was then backfilled with filter pack As the filter pack was placed, the augers were withdrawn from the hole so the sand would flow out of the augers and fill the annular space of the borehole The filter pack extended to approximately 1 foot above the top of the well screen A I-foot seal of bentonite pellets was placed in the annular space above the filter pack Since the bentonite seal was above the water table, approximately 3 gallons of potable water were added ' to allow swelling of the bentonite After sufficient time had passed for the bentonite to swell (at least 1 hour), the remaining annular space was backfilled to the surface ' with a cement-bentonite grout Representatives of the San Joaquin County Environmental Health Department were onsite to inspect and approve the grouting of each well (PG&E, 1988) ' Each well was finished with a tamper-resistant, watertight street box set into concrete The street boxes were set slightly above the existing ground surface to provide additional protection against infiltration of surface water A threaded water- tight cap with a cork liner (2-inch wells) or rubber clamp-on cap (4-inch wells) was placed over the end of each well casing inside the street box (PG&E, 1988) ' Each well was developed by surging with a surge block and pumping with a centrifugal pump Due to the fine texture of the soil material surrounding the wells, none of the wells produced clear water, even after extensive developing However, turbidity was reduced significantly in all wells With the exception of well OW-2, all wells produced water continuously throughout the development process Well OW-2 t was pumped dry twice during development Development water from each well was retained in labeled drums pending chemical analysis and appropriate disposal (PG&E, 1988) ' Wells were located a sufficient distance from one another to allow determination of the groundwater gradient and flow direction through analysis of water level data ' collected from these wells The top of casing of each well was surveyed to the nearest 0 01 foot to allow comparison of water elevations The depth to water from the top of the well casing was measured with an electronic emersion probe The ' water elevation in each well was computed by subtracting the depth to water from the elevation at the top of the well casing This procedure was repeated on several occasions from January 1988 to November 1995, in an effort to observe any fluctuations in groundwater flow direction and gradient (PG&E, 1988) 2 3 2 Groundwater Sampling Methodology ' Prior to purging and sampling each well, the depth to water was measured and recorded An acrylic bailer was then used to collect a sample from the water surface 5 t