Memorandum To: Coinpany: From: File number: Date: Subject: [ SDMS DocID 2091421 Kelley Chase EPA Region III i§r and Derek Tomli: 0057238.0007 30 November 2006 Bedrock Data Gaps Proposed Locations of Monitoring Wells Environmental Resources Management 350 Eagleview Boulevard Suite 200 Exton, PA 19341 (610) 524-3500 (610) 524-7335 (fax) ERM. Per your request during the 10 August 2006 project team meeting and follow-up technical discussions on 20 September 2006, this memorandum shows the proposed locations of the bedrock monitoring wells to be installed. The goal of these new monitoring wells is to better define the bedrock structure and hydrogeologic conditions at the former Stabilus facility. • Based on borings and well installations completed by others, cross- sections of the facility were completed. Figure 1 provides the location of these three cross-sections and Figure 2, 3, and 4 present the cross-sections. The location of the cross-sections were selected as follows: • Cross-section A-A' is completed rbiighly parallel to bedrock strike, • Cross-section B-B' is completed along the potential down gradient direction based on ERM's modeling, • Cross-section C-C is completed along the potential down gradient direction based on USGS modeling. Please note that only the boring logs for the Rl-series of wells was available for creation of these logs, as well as the geophysical logging completed by the USGS for other select wells. ERM recently completed a detailed review of files in the possession of Pennsylvania Department of Environmental Protection (PADEP) to garner the logging information for the RW-series, A-series and W-series of wells. However, no boring logs or well construction logs were present within the reports in the PADEP files. Based on the information available, the facility is underlain by an overburden material comprised of red-brown to brown silt or silty sand with trace rock fragments which overlays the Brunswick Formation. The AR304740
Transcript
Memorandum
To:
Coinpany:
From:
File number:
Date:
Subject:
[ SDMS DocID 2091421
Kelley Chase
EPA Region III
i§r and Derek Tomli:
0057238.0007
30 November 2006
Bedrock Data Gaps Proposed Locations of Monitoring Wells
Environmental Resources Management
350 Eagleview Boulevard Suite 200 Exton, PA 19341 (610) 524-3500 (610) 524-7335 (fax)
ERM.
Per your request during the 10 August 2006 project team meeting and follow-up technical discussions on 20 September 2006, this memorandum shows the proposed locations of the bedrock monitoring wells to be installed. The goal of these new monitoring wells is to better define the bedrock structure and hydrogeologic conditions at the former Stabilus facility. •
Based on borings and well installations completed by others, cross-sections of the facility were completed. Figure 1 provides the location of these three cross-sections and Figure 2, 3, and 4 present the cross-sections. The location of the cross-sections were selected as follows:
• Cross-section A-A' is completed rbiighly parallel to bedrock strike,
• Cross-section B-B' is completed along the potential down gradient direction based on ERM's modeling,
• Cross-section C-C is completed along the potential down gradient direction based on USGS modeling.
Please note that only the boring logs for the Rl-series of wells was available for creation of these logs, as well as the geophysical logging completed by the USGS for other select wells. ERM recently completed a detailed review of files in the possession of Pennsylvania Department of Environmental Protection (PADEP) to garner the logging information for the RW-series, A-series and W-series of wells. However, no boring logs or well construction logs were present within the reports in the PADEP files.
Based on the information available, the facility is underlain by an overburden material comprised of red-brown to brown silt or silty sand with trace rock fragments which overlays the Brunswick Formation. The
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majority of the bedrock appears, based on information from the lithologic logs, to be more representative of the Brunswick Formation. Lithologic indicators of the Lockatong Formation (dark gray to black color, harder texture, etc.) were not evident on any of the logs that were reviewed.
Based on televiewer-accoustic logs completed by the USGS the strike is generally North 62° East dipping 31° Northwest beneath the facility. The apparent dip of the bedding within the Brunswick Formation is shown on Figures 3 and 4. The apparent dip accounts for the orientation between the section line and the orientation of the maximum dip angle (i.e., the dip angle will appear less than maximum when not viewed parallel to the direction of dip).
Ground water is present within the overburden in the area of the Stabilus facility. The saturated thickness of the overburden is generally 8 to 12 feet, based on the static water elevations in both overburden and bedrock wells. At certain locations west and southwest of the Stabilus facility, the static ground water level within bedrock wells was observed to be below the soil/bedrock interface. The presence of water within the overburden in these areas was less well defined.
Based on the current installed wells, bedrock data gaps may exist at the former Stabilus facility in the potential down-gradient direction and in areas northeast and southeast of the former Stabilus facility. ERM proposes to install the monitoring wells shown on Figure 5, with potential screened intervals as shown on Figures 3 and. The proposed new wells to be installed are RI-27I, RI-33S, RI-33I, RI-34S, RI-34I, RI-35I, and RI-36S:
• RI-33S and RI-33I
o These two wells will be completed in the direction of ground water flow predicted by USGS near the topographic low observed in the bedrock surface.
o The shallow well (i.e., RI-33S) will be completed similar to the other shallow bedrock wells just below the bedrock and overburden interface (approximately 40 to 50 feet bgs).
o The intermediate well (i.e., RI-33I) will be completed at approximately 100 to 120 feet below ground surface (bgs), which corresponds to the estimated depth that a bedding plane would intersect this location.
RI-27I
This well is proposed to be completed at a depth that will aid in i.mderstanding the potential plume migration
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direction further to the west along the axis predicted by USGS. The two existing wells (i.e., RI-27S and RI-27D) are either too shallow (RI-27S completed from 40 to 55) or too deep (RI-27D completed from 305 to 308 feet bgs) to intersect the bedding planes connected to the potential source area.
o This well is proposed to be completed at approximately 90 to 180 feet bgs. This is the anticipated depth at which the bedding planes would intersect this location.
RI-34S and RI-34I
o These two wells will be completed in the anticipated direction of the ground water flow as modeled by ERM.
o The shallow well (i.e., RI-34S) will be completed similarly to the other shallow bedrock wells just below the bedrock and overburden interface (approximately 25 to 40 feet bgs).
o The intermediate well (i.e., RI-34I) will be completed approximately 50 to 70 feet bgs which corresponds to the estimated depth that a bedding plane at the potential source area would intersect this location.
• RI-35I
o This well will be completed further to the west in the anticipated direction of the ground water flow based on the modeling completed by ERM.
o This intermediate well (i.e., RI-35I) will be completed approximately 100 to 120 feet bgs to complement the shallow W-5 well in this area. This depth range corresponds to the estimated depth that a bedding plane at the potential source area would intersect this location.
• RI-36S
o This well is proposed to be completed along the bedrock strike direction as determined by USGS within the shallow bedrock.
o The well will be completed similarly to the other shallow bedrock wells just bellow the bedrock and overburden interface (approximately 40 to 50 feet bgs).
Upon drilling of each bedrock well, the boreholes will be left open in order to facilitate geophysical testing. Four downhole geophysical tests will be completed at each well location. These tests will include caliper.
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fluid resistivity, fluid temperature, and heat pulse flowmeter. The caliper tests will serve to physically identify fractures and possible water bearing openings through continuous measurement of the borehole diameter. Fluid resistivity and fluid temperature logs are used to determine ground water producing and water receiving zones, and intervals of vertical borehole flow. Lastly, the heat pulse flow meter is used to estimate the direction and rate of vertical ground water movement within the borehole.
The interval to be screened in each well may be modified based on the results of the geophysical testing. In general, the shallow bedrock wells will be set to monitor the uppermost water bearing zone within the bedrock, and the deeper wells will be set to monitor the depth at which a bedding plane in the potential source area on the former Stabilus facility could intersect the well location. The geophysical results will be reviewed to modify these intervals if necessary, to monitor fractures or flow zones of interest, and/or to adjust the anticipated screened intervals if active water bearing fractures are evident within the targeted zones of monitoring.
Prior to installing the inner well casing and screen, select wells will be evaluated for the presence of dense non-aqueous phase liquid (DNAPL) using the FLuTe system. The initial wells where this will be conducted are RI-33S/I and RI-34S/I, since these are closest to the potential source area. Should indications of DNAPL be present in these wells, additional testing using the FLuTe system could be conducted in wells RI-27I and RI-35I, which would monitor the same bedrock structural zone further down dip from RI-33I and RI-34L
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CROSS-SECTION LOCATIONS NORTH PENN AREA 5 SITE COLMAR, PENNSYLVANIA
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