Well Installation Report - Wells CS-MW3 through CS-MW10, August 2003

Section 3 - Well Installation Summary

To simplify presentation of the MW installations, which varied from well to well, the MW construction will be presented in chronological order, with appropriate mention of deviations from the relevant Work Plan or Work Plan addenda. Further details on the Work Plans or their amendments may be found in the Environmental Encyclopedia (RL83 Work Plan, RL83 Amendment 1 to the Work Plan, RL83 Amendment 2 to the Work Plan, and RL83 Amendment 3 to the Work Plan). A summary of pertinent information for the well installations is provided in Table 3.1 (ft bgs) and Table 3.2 (ft MSL).

Drilling was performed by GeoProjects, and was supervised by Parsons geologists. Twelve wells were installed under the AMC RL83 task order, and three wells were completed under the AFCEE DO23 delivery order. GeoProjects utilized two crews during the field event. The primary crew mobilized on November 15, 1999, and was equipped with a Gardner-Denver 1500 drilling rig, a 3,000-gallon water truck, a 3,000-gallon vacuum truck, a Smeal winch truck, and various support vehicles and well installation equipment. A secondary crew mobilized on January 19, 2001 consisting of a Central Mine Equipment (CME) 75 drilling rig, mobile air compressor, and support vehicles.

The CME 75 rig provided additional coring capability, but reaming and well installations were left to the larger Gardner-Denver 1500 rig. One or more Parsons personnel supervised each rig. Waste management support was by provided by Eagle.

3.1 - CS-MW9 Cluster Wells

Three wells, CS-MW9-CC, CS-MW9-BS, and CS-MW9�LGR, were installed in the North Pasture at CSSA (Figure 1.1) under RL83. Drilling at this cluster began on November 17, 2000 and was completed on January 23, 2001.

3.1.1   CS-MW9-CC

Parsons and GPI mobilized personnel and equipment to CSSA on November 15, 2000 and readied the site for long-term fieldwork. The drilling commenced at CS-MW9-CC on November 17, 2000 and was completed by January 16, 2001. CS-MW9-CC was cored to 331 feet bgs, which was 5 feet below the LGR/BS contact. Three soil/rock samples were submitted for VOC and metals analysis from the LGR portion of this well. Based on analysis of the gamma, SP, and resistivity logs, the intervals for injection packer tests were selected and two tests were performed.

Following the packer tests, the corehole was then reamed to its final diameter of 17¹/₂-inches to accommodate 12-inch diameter surface casing. Because of difficulties associated with the return of drill cuttings, the use of QuickFoam as a drilling additive during the installation program was approved by AFCEE and the EPA. After the target depth of 331 feet bgs was achieved, the LGR portion of the well was cased off with 12.75-inch carbon steel casing. Individual casing joints were 40 feet in length, and were welded together onsite by the GPI crew. The lead casing joint was fitted with �Halliburton-style� drillable concrete float shoe that was molded with a grout injection hole. All casing was carefully lowered into the borehole without complication. Three �guides� were welded to the lead �drill-string sub� to facilitate seating the drill string into the Halliburton shoe.

Approximately 1,500 gallons of grout were mixed on site then added to the annular space between the borehole and the steel casing. The grout was pumped though the 5-inch OD drill string using the mud pump on the rig. Upon completion of the grout injection, the drill crew experienced difficulty removing the drill string from the casing. After drawing it up 20 feet with extreme difficulty, the drill string was able to move freely and was removed from CS-MW9-CC. The three steel �guides� had been sheared off the lead drill string sub. By using this Halliburton-style cementation, it was expected that approximately 15 to 20 feet of cement held within the drill string would drain to the bottom of the casing and would be drilled out after a 24-hour curing period.

After allowing 24 hours for the grout to set, the drillers re-entered the hole with a 12-inch bit to drill out the grout bottom and shoe. The bit encountered an obstruction at 311 feet and was unable to advance more than 4 inches into the obstruction. The following day, the 12-inch bit was replaced with a 6-inch bit, which was only able to advance to 311.5 feet until refusal. The obstruction was still not cleared, and appeared to be impassible.

Three scenarios were suggested, including collapse of the steel casing at mid-point of the lower 40-foot joint, casing collapse induced by excessive pressures during grout injection, and collapse of the geologic formation, which may have crushed the pipe.

A downhole camera survey was then performed by GeoCam on December 11, 2000. The casing interior was dried by air-lifting to provide an optimal view. The camera survey indicated that at 309 to 310 feet bgs, the casing appeared to be slightly oblique. Starting at 305 feet bgs, there is evidence of scraping on the steel casing, presumably due to the 12-inch bit placed in the hole the day after the grout was emplaced. In particular, at 308 feet, the marks on the casing appear uneven, suggesting the casing may have been out-of-round at this depth. At 311 feet bgs, the casing protruded inward, but details in this area were poor due to cloudiness of 2 feet of water remaining in the casing.

It appeared the casing had collapsed at 311 feet, therefore further drilling in this hole would be impossible. With concurrence from CSSA and AFCEE, it was decided the hole would be plugged with grout and abandoned, and a new well would be set in the immediate area. However, the LGR would not be re-cored in the replacement well. The well collapse was attributed to off-specification casing, and was therefore re-drilled at the expense of GPI and Parsons.

On December 12, 2000, a replacement boring for CS-MW9-CC was initiated. The 16³/₈-inch boring terminated at its final total depth of 332 feet. A 2.2-foot drillable shoe was welded to 12.75-inch diameter casing, and the casing was set in the same method used in the first well. Centralizers were welded to the bottom of the casing, and every 50 feet thereafter.

Grout was emplaced using the tremie pipe method of cementing on the outside of the steel casing. Additional grout was added over the next several days until the cement was set to ground surface level.

On December 20, 2000, coring of the BS began at CS-MW9-CC. One rock sample was submitted for VOC and metals analysis. The top of the CC Limestone was encountered at 386 feet bgs, and coring ceased at a total depth of 400 feet. Soon after, geophysical logging was performed over the 330 to 400 feet bgs interval. Two packer tests were conducted in the BS and one packer test was conducted at the top of the CC Limestone.

Based on analysis of the geophysical logs, the depth of 390 feet bgs was selected to set the casing for the bottom of the BS. CS-MW9-CC was then reamed to a 12-inch diameter down to 390 feet bgs, and 8-inch carbon steel casing was set in the well from 390 feet bgs to ground surface, and grout was emplaced in the annulus between the 8-inch and 12-inch casings via tremie pipe and the mud pump. The grout was allowed to set overnight between batch emplacements.

Once the grout was in place, CS-MW9-CC was cored through the CC Limestone into the Hammett Shale to a total depth of 480 feet bgs. GeoCam obtained a geophysical log of the 390 feet to 480 feet bgs interval. Two packer test intervals were selected based on the logs. The interval of 425 feet to 450 feet bgs was selected for the screen in the CC Limestone. Representatives of AFCEE and CSSA agreed to the screening interval. The corehole was reamed to its final diameter of 7⁷/₈ inches using a tri-cone rolling bit. The well was completed as described in Section 2.4 on January 16, 2001.

3.1.2   CS-MW9-BS

Drilling of CS-MW9-BS commenced on January 16, 2001 and was completed on January 21, 2001. CS-MW9-BS was installed 27 feet north of CS-MW9-CC. This well was not cored or geophysically logged since the BS section had been investigated during construction of CS-MW9-CC. The hole was advanced to 333 feet with a 12-inch diameter tri-cone roller bit. Likewise, 333 feet of 8-inch diameter steel casing, with a drillable shoe was installed into CS-MW9-BS at the LGR/BS contact. The annular space was plugged with grout in batches, allowing time for the grout to set.

The hole was advanced to 378 feet bgs with a 7⁷/₈-inch diameter tri-cone roller bit. The bottom foot was backfilled with bentonite and the screen was inserted from 352 to 377 feet bgs. The well was completed as described in Section 2.4 on January 21, 2001.

3.1.3   CS-MW9-LGR

CS-MW9-LGR was installed approximately 20 feet from CS-MW9-BS. Drilling of the 7⁷/₈-inch diameter hole was initiated on January 22, 2001. This well was not cored or geophysically logged since the LGR section had been investigated during construction of CS-MW9-CC. The total depth of 323 feet bgs was achieved on January 23, 2001, and the 25-foot screen intake was placed in the 296 to 321 feet bgs interval. The well was completed as described in Section 2.4 on January 23, 2001.

3.2 - CS-MW3-LGR

Under the DO23 delivery order, CS-MW3-LGR was constructed near the intersection of the Inner Cantonment and the North and East Pastures (Figure 1.1). Drilling at this well began on January 19, 2001 and was completed on February 13, 2001. The boring was cored using the CME 75 drilling rig, and the well was reamed and installed using the Gardner-Denver 1500 drilling rig.

Coring of CS-MW3-LGR began on January 19, 2001. The CME 75 used NX core pipe, which is a smaller diameter than the HX core pipe used by the Gardner-Denver 1500 drilling rig. CS-MW3-LGR was cored to 438.5 feet bgs on February 1, 2001. The LGR/BS contact was encountered at 427.6 feet bgs. Three soil/rock samples were submitted for VOC and metals analysis from the LGR portion of this well.

Geophysical logging of CS-MW3-LGR occurred on February 2, 2001, and packer tests were performed on February 4, 2001. Based on analysis of the gamma, SP, and resistivity logs, the intervals for packer tests were selected and three packer tests were attempted. Only one of the three packer tests resulted in a measurable amount of permeability based on the inherent coarseness of the field test.

Using the Gardner-Denver 1500 drilling rig, the corehole was reamed to an 8-inch ID using a 7⁷/₈-inch bit. Problems were encountered early when the deviation surveys conducted with a �TOTCO� controlled vertical drift indicator found that the original NX corehole was neither straight nor plumb. By 80 feet bgs the borehole had exceeded the work plan 2˚ plumbness requirement. Rather than struggling with a crooked corehole, it was decided by Parsons and GPI to abandon the hole and relocate to a new position. The remainder of the corehole was cleaned out by reaming with a 6-inch bit, and then plugged with grout and abandoned on February 7, 2001.

The replacement hole was advanced to 427.6 feet bgs with a 7⁷/₈-inch diameter tri-cone roller bit. The TOTCO surveys, collected every 50 feet, were all within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 402 to 427 feet bgs. The well was completed as described in Section 2.4 on February 13, 2001.

3.3 - CS-MW5-LGR

Also under the DO23 delivery order, CS-MW5-LGR was drilled near the north end of East Outer Road within the Inner Cantonment (Figure 1.1). Drilling at this well began on January 29, 2001 and was completed on February 5, 2001. The boring was cored and reamed using the Gardner-Denver 1500 drilling rig.

Coring of CS-MW5-LGR began on January 29, 2001. CS-MW5-LGR was cored to 462 feet bgs on February 1, 2001. The LGR/BS contact was encountered at 448 feet bgs. Three soil/rock samples were submitted for VOC and metals analysis from the LGR portion of this well. Geophysical logging of CS-MW5-LGR occurred on February 2, 2001, and packer tests were performed on February 4, 2001. Based on analysis of the gamma, SP, and resistivity logs, the intervals for packer tests were selected and two packer tests were attempted. Results from only one packer tests showed a measurable amount of permeability based upon the inherent coarseness of the field test.

On the following day, the corehole was reamed to an 8-inch ID using a 7⁷/₈-inch bit. The hole was advanced to 450 feet bgs with a 7⁷/₈-inch diameter tri-cone roller bit. The TOTCO surveys, collected every 50 feet, were all within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 420 to 445 feet bgs. The bottom 4 feet of the boring was plugged with bentonite. The well was completed as described in Section 2.4 on February 5, 2001.

3.4 - CS-MW4-LGR

Under the DO23 delivery order, CS-MW4-LGR was constructed within the Inner Cantonment, east of Salado Creek (Figure 1.1). Drilling at this well began on January 19, 2001 and was completed on February 2, 2001. The boring was cored using the CME 75 drilling rig, and the well was reamed and installed using the Gardner-Denver 1500 drilling rig.

Coring of CS-MW4-LGR began on February 2, 2001 using the CME 75 and NX core pipe. Because of a void encountered from 15 to 16 feet bgs, temporary surface casing was inserted into the boring. Coring resumed, and the total depth cored was 336.5 feet bgs by February 6, 2001. The LGR/BS contact was encountered at 325 feet bgs. Three soil/rock samples were submitted for VOC and metals analysis from the LGR portion of this well.

Geophysical logging of CS-MW4-LGR occurred on February 7, 2001, and packer tests were performed on the same day. Based on analysis of the gamma, SP, and resistivity logs, the intervals for two packer tests were selected, and the tests were performed.

Using the Gardner-Denver 1500 drilling rig, the borehole was first reamed to a 6‑inch ID to be sure the NX corehole was straight and plumb. The 6-inch pass barely stayed within Work Plan tolerances of 2˚, but was acceptable. On the following day the borehole was reamed to its final diameter using a 7⁷/₈-inch tri-cone roller bit. The hole was advanced to 325.1 feet bgs. The final TOTCO surveys, collected every 50 feet, were all well within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 299 to 324 feet bgs. The well was completed as described in Section 2.4 on February 16, 2001.

3.5 - CS-MW7 Cluster Wells

Two wells, CS-MW7-LGR and CS-MW7�CC, were installed at the southwestern portion of the facility, east of Building W92 (Figure 1.1) under the RL83 delivery order. Drilling at this cluster began on February 12, 2001 and was completed on July 16, 2001.

3.5.1   CS-MW7-CC

Coring of CS-MW7-CC began on February 2, 2001 using the CME 75 and NX core pipe. Coring continued to 372 feet bgs, after the LGR/BS contact had been encountered at 352 feet bgs. A bailer sample of groundwater collected on February 14, 2001 indicated 3.17 micrograms per liter (μg/L) PCE in the corehole. Rock samples from both the LGR and BS portions of this well were submitted for VOC and metals analyses.

Geophysical logging of CS-MW7-CC occurred on February 18, 2001, the same day the corehole was completed to the BS. Based on analysis of the gamma, SP, and resistivity logs, the intervals for two packer tests were selected, and the tests were performed on February 19, 2001. Since PCE had been detected in the groundwater, and the Gardner-Denver drilling rig was not yet prepared to ream the corehole, CS-MW7-CC was plugged with grout to the surface. The formation was quite permeable at this location, and 60 bags of cement were used when only 20 bags were expected to be needed.

The Gardner-Denver 1500 drilling rig resumed work at CS-MW7-CC on June 12, 2001 after completing the CS-MW6 and CS-MW8 well clusters. The wellbore was reamed next to the abandoned corehole. The corehole was first reamed with a 6‑inch diameter bit so a single packer sampling system could be used to collect discrete interval groundwater samples at depth. A total of two discrete interval samples (125 to 135 feet bgs and 285 to 295 feet bgs) were collected from the LGR portion of the aquifer. The boring was then reamed with a 12-inch diameter tri-cone roller bit to a depth of 372 feet bgs. The final TOTCO surveys, collected every 50 feet, were all well within the specifications required by the Work Plan. Eight-inch diameter carbon steel casing was installed and cemented via tremie pipe to 372 feet on June 20, 2001.

Once the grout cured, GeoProjects resumed coring on June 25, 2002. CS-MW7-CC was cored from 372 feet to 503 feet bgs, where the Hammett Shale was encountered at 497 feet bgs on June 26, 2001. On the same day, geophysical logging of CS-MW7-CC was performed. Based on analysis of the gamma, SP, and resistivity logs, the intervals for two packer tests were selected, and the tests were completed. Two discrete interval groundwater samples were collected from 420 to 432 feet bgs and 440 to 452 feet bgs on June 28, 2001. Two injection packer tests were also conducted on that same day.

On the following day the borehole was reamed to its final diameter using a 7⁷/₈-inch tri-cone roller bit. The hole was advanced to from 372 to 455 feet bgs. The final TOTCO surveys, collected every 50 feet, were all well within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 430 to 455 feet bgs. The well was completed as described in Section 2.4 on June 29, 2001.

3.5.2   CS-MW7-LGR

Drilling of CS-MW7-LGR began on July 10, 2001 using the Gardner-Denver 1500 and a 6-inch tri-cone roller bit. One bailer sample (when total depth was 90 feet bgs) and one discrete interval sample were collected from the LGR (209 to 220 feet bgs) on July 11, 2001. Two discrete interval samples were collected from the LGR (245 to 260 feet bgs and 285 to 295 feet bgs) on July 12, 2001. Drilling with a 6-inch diameter bit continued to 295 feet bgs. The hole was then reamed with an 8-inch diameter tri-cone roller bit to 352.5 feet bgs, and subsequently backplugged with bentonite to 348 feet bgs. The screened interval selected by Parsons and CSSA was from 322 to 347 feet bgs. The well was completed as described in Section 2.4 on July 16, 2001.

3.6 - CS-MW6 Cluster Wells

Under the RL83 delivery order, the CS-MW6 well cluster was drilled near the north end of Building 90, and south of Gate 2 (Figure 1.1). The sequence of drilling the CS-MW6 cluster wells was modified from the previous well installation sequences due to limited accessibility at this location. Each well was cored, logged, tested, and completed separately, thereby creating a composite lithologic log for the entire cluster. The LGR well was constructed first, followed by the BS, then CC wells. This modification of the Work Plan was approved by representatives from AFCEE (Rene Hefner) and CSSA (Brian Murphy).

3.6.1   CS-MW6-LGR

Drilling at this well began on February 18, 2001 and was completed on March 2, 2001. The boring was cored and reamed using the Gardner-Denver 1500 drilling rig.

Coring of CS-MW5-LGR began on February 18, 2001, and was cored to its total depth of 382 feet bgs on February 20, 2001. The LGR/BS contact was encountered at 368 feet bgs. Two rock samples from the LGR portion of this well were submitted for VOC and metals analyses. Geophysical logging of CS-MW6-LGR occurred on February 21, 2001, and packer tests were performed on the same day. Based on analysis of the gamma, SP, and resistivity logs, two intervals for packer tests were selected. Only one of the packer tests resulted with a measurable amount of permeability based on the inherent coarseness of the field test.

On the following day, the corehole was reamed to an 8-inch ID using a 7⁷/₈-inch bit. The hole was advanced to 365 feet bgs with a 7⁷/₈-inch diameter tri-cone roller bit. The TOTCO surveys, collected every 50 feet, were all within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 340 to 365 feet bgs. The bottom 15 feet of the corehole had been with plugged with bentonite prior to reaming. The well was completed as described in Section 2.4 on March 2, 2001.

3.6.2   CS-MW6-BS

Drilling of CS-MW6-BS commenced on March 2, 2001 and was completed on March 16, 2001. The hole was advanced to 368 feet with a 12-inch tri-cone roller bit on March 7, 2001. Likewise, 368 feet of 8-inch diameter steel casing, with a drillable shoe was installed into CS-MW6-BS at the LGR/BS contact. The annular space was plugged with grout in batches, allowing time for the grout to set.

Coring of the BS segment began and finished on March 13, 2001. The CC contact was encountered at 427.5 feet bgs. Two rock samples were collected and submitted for analysis. The corehole was geophysically logged on March 14, 2001. Three injection packer tests were attempted, but none found measurable permeability. The corehole was plugged back with bentonite to 422 feet bgs, then reamed to 422 feet bgs with a 7⁷/₈-inch diameter tri-cone roller bit. The screen was inserted from 397 to 422 feet bgs. The well was completed as described in Section 2.4 on March 16, 2001.

3.6.3   CS-MW6-CC

Reaming of the LGR portion of CS-MW6-CC began on March 17, 2001 with a 16³/₈-inch diameter tri-cone roller bit. A total of 368 feet of 12-inch steel casing was installed to the LGR/BS contact on March 29, 2001. Reaming of the BS portion of the well with a 12-inch tri-cone roller bit ensued on April 3, 2001 and was completed on April 4, 2001. Likewise, 432 feet of 8-inch steel casing was installed in the well through the BS.

Coring of the CC portion of the well began on April 6, 2001 and was completed the following day. Coring continued to 522 feet bgs, after the CC/Hammett Shale contact had been encountered at 505 feet bgs. One rock sample from the CC portion of this well was submitted for VOC and metals analyses. Geophysical logging of CS-MW6-CC occurred on April 8, 2001. Based on analysis of the gamma, SP, and resistivity logs, the intervals for two packer tests were selected, and the tests were performed on April 8, 2001. After testing was completed, the bottom portion of the corehole was plugged with bentonite from 475 to 522 feet bgs.

On the following day the borehole was reamed to its final diameter using a 7⁷/₈-inch tri-cone roller bit. The hole was advanced from 432 to 476 feet bgs. The final TOTCO surveys, collected every 50 feet, were all well within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 451 to 476 feet bgs. The well was completed as described in Section 2.4 on April 9, 2001.

3.7 - CS-MW8 Cluster Wells

Two wells, CS-MW8-LGR and CS-MW8�CC, were installed at the southwestern portion of the post, west of Building W92 (Figure 1.1) under the RL83 delivery order. Drilling at this cluster began on April 11, 2001 and was completed on June 6, 2001.

Drilling at CS-MW8

3.7.1   CS-MW8-LGR

Drilling of CS-MW8-LGR began on April 11, 2001 using the Gardner Denver 1500 and HX core pipe. This drilling location was approached with caution due to its proximity to the Plume 2 source area and recent detections of contaminants in near-surface perched wells installed during investigations at AOC-65. A plan was developed and implemented for monitoring for perched water at this cluster. This plan included obtaining groundwater samples as perched layers were encountered and the use of a pumpable straddle packer system.

Perched water accumulated in the corehole at 53 feet bgs and again at 83 feet bgs. Both times a grab groundwater sample was submitted for VOC analysis. The 53-foot interval was found to contain 50 �g/L acetone and 15 �g/L 2-butanone (methyl ethyl ketone [MEK]). Coring continued to 173 feet bgs, where another grab sample indicated 14 �g/L PCE. At this point the discrete interval groundwater sampling program was devised and implemented. Four discrete interval samples were collected from the LGR on April 18, 2001 (87.5 to 98 feet bgs, 105.5 to 116 feet bgs, 131.5 to 142 feet bgs, and 155.8 to 165.5 feet bgs) and were found to contain detectable amounts of PCE and TCE above the MCLs. The hole was geophysically logged on April 19, 2001.

On April 20, 2001, the hole was reamed to an 8-inch diameter to a depth of 173 feet bgs. To prevent potential cross contamination, a 4.5-inch diameter, temporary steel casing was installed to seal off the upper zones that contained VOCs from entering deeper potentially non contaminated zones. Bentonite was added to the annular space to 105 feet bgs to form an adequate seal. Coring resumed on April 21, 2001 and proceeded to a depth of 272 feet bgs. The hole was then geophysically logged from 173 to 272 feet bgs and a discrete interval sample was collected (223.5 to 234 feet bgs) on April 22, 2001. Two more discrete interval samples were collected (188.5 to 199 feet bgs and 222.5 to 223 feet bgs) on April 23, 2001. These samples were also found to have concentrations of PCE and TCE above the MCLs.

To prevent potential cross-contamination before entering the main LGR production zone, the corehole was plugged with bentonite from 272 to 173 feet bgs on April 25, 2001. The temporary casing was then removed and reaming to a 12-inch diameter to a depth of 273 feet bgs commenced on April 26, 2001. On May 3, 2001, 8-inch steel casing was installed. Coring was then resumed on May 4, 2001, and the total depth of 373 feet bgs was reached on May 6, 2001. The BS was encountered at 357 feet bgs. Two samples were obtained and submitted for chemical analysis from the LGS.

The hole was then geophysically logged from 273 to 373 feet bgs. Four more discrete interval samples were taken from 346.5 o 357 feet bgs, 324.5 to 335 feet bgs, 305.5 to 316 feet bgs, and 290 to 300.5 feet bgs. Below 300 feet bgs, no VOC contamination was detected above the MDLs. Injection packer tests were performed on May 7, 2001 at the intervals between 346.5 and 357 feet bgs, and between 305.5 and 316 feet bgs.

Finally, the hole was reamed to an 8-inch ID to a total depth of 357 feet bgs. The screened interval selected by Parsons and CSSA was from 332 to 357 feet bgs. The well was completed as described in Section 2.4 on May 8, 2001.

3.7.2   CS-MW8-CC

Drilling of CS-MW8-CC began on May 17, 2001 using the Garner Denver 1500 and a 6-inch tri-cone roller bit. Discrete interval samples were to be collected at similar depths obtained at CS-MW8-LGR for comparison. A VOC grab sample was obtained between the 89 foot bgs water table and a depth of 116 feet bgs on May 18, 2001. On the same day, a discrete interval sample was obtained from 132 to 142 feet bgs. Both samples resulted with PCE and TCE concentrations above the MCLs. On May 19, 2001, drilling continued until discrete interval samples were obtained at 190 to 200 feet bgs and 224 to 234 feet bgs. Once again, both samples resulted with TCE and PCE concentrations in excess of the MCLs. Drilling continued on May 20, 2001 until a depth of 300 feet bgs was reached and sampled. This sample yielded similar results to the CS-MW8-LGR well, with PCE and TCE both exceeding the MCLs. Since the trend had been established, it was assumed that VOC contaminant concentrations would attenuate below 300 feet bgs. Therefore, 12-inch surface casing was installed within a 16³/₈-inch borehole to a depth of 304 feet bgs. This activity was completed on May 24, 2001.

The boring progressed deeper into the LGR to a depth of 325 feet bgs. A discrete interval groundwater sample was collected from 311 to 317 feet bgs, and no contamination was detected. The hole was then drilled to 367 feet bgs with a 12-inch tri-cone roller bit, and 8-inch steel casing was set on May 31, 2001.

Coring using HX core pipe was then resumed at 370 feet bgs in the BS and continued to a depth of 503 feet bgs on May 29, 2001. The CC Limestone was encountered at 423 feet bgs, and the Hammett Shale was penetrated at 496 feet bgs. Two rock samples from the CC Limestone were collected for analyses during coring.

On June 5, 2001, two discrete interval samples were collected (440 to 450 feet bgs and 460 to 470 feet bgs) and two injection packer tests were performed (435 to 445 feet bgs and 450 to 460 feet bgs). Lastly, the hole was reamed from 4-inches to 8 inches diameter starting at 426 feet bgs to the total depth of 465 feet bgs.

The final TOTCO surveys, collected every 50 feet, were all well within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 436.5 bgs to 464.5 feet bgs. The well was completed as described in Section 2.4 on June 6, 2001.

3.8 - CS-MW10 Cluster Wells

Two wells, CS-MW10-LGR and CS-MW10�CC, were installed at the far southwestern portion of the post (Figure 1.1) under the RL83 delivery order. Drilling at this cluster began on August 15, 2001 and was completed on September 24, 2001.

3.8.  1 CS-MW10-CC

Coring of CS-MW10-CC began on August 15, 2001 using the Gardner-Denver 1500 and HX core pipe. Coring continued to 191 feet bgs and a bailer sample was collected on August 17, 2001. That open hole groundwater sample yielded a PCE concentration of 0.83 �g/L. The LGR/BS contact was reached at 394.5 feet bgs on August 21, 2001, and a rock sample was also collected from the 394 to 394.5 feet bgs interval. Coring continued to a depth of 411 feet bgs.

On August 23 and 24, 2001, five discrete interval groundwater samples were collected and four injection packer tests were performed. The hole was also geophysically logged. Reaming of the hole to 12-inch ID then commenced on August 27, 2001 and ended on September 6, 2001 at a total depth of 406 feet bgs, where 8-inch steel casing was installed to the same depth.

Coring continued on September 10, 2001 and ended on September 12, 2001 at a depth of 541 feet bgs. The CC Limestone was encountered at 455 feet bgs, and the Hammett Shale was penetrated at 528 feet bgs. The hole was then geophysically logged on September 12, 2001. Three discrete interval groundwater samples were collected and five injection packer tests were conducted on September 13, 2001.

The corehole was backplugged with bentonite from 495 to 541 feet bgs prior to reaming the well to its final diameter. The hole was then reamed to an 8-inch ID to a depth of 495 feet bgs on September 14, 2001. The final TOTCO surveys, collected every 50 feet, were all well within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 470 to 495 feet bgs. The well was completed as described in Section 2.4 on September 14, 2001.

3.8.2   CS-MW10-LGR

Drilling of CS-MW10-LGR began on September 17, 2001 using the Gardner-Denver 1500 and an 8-inch tri-cone roller bit. The boring was advanced to 405 feet bgs and geophysically logged on September 19, 2001. The final TOTCO surveys, collected every 50 feet, were all well within the specifications required by the Work Plan. The screened interval selected by Parsons and CSSA was from 370 to 395 feet bgs. The boring was backfilled with bentonite from 396 to 405 feet bgs. The well was completed as described in Section 2.4 on September 19, 2001.

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