[Table of Contents]

This addendum to the Sampling and Analysis Plan (SAP) describes activities in support of the installation of twelve monitoring wells. This document is an amendment to the existing work plan for the installation of the monitoring wells. The purpose of this addendum is to identify the changes and additional field activities for RL83 and to verify that the activities are explained in either the SAP or addenda.

Changes to Field Activities

Changes to field activities to be completed under RL83 include:

1. The wells will be drilled in a manner that maximizes equipment efficiency and availability and minimizes stand-by time.

2. In the vicinity of Building 90, perched groundwater samples will be collected when present. Informed decisions regarding the completion of a well cluster will be based upon those results.

3. Uncontaminated drilling fluids (e.g., water) may be released to the surface if waste stream sampling indicates that no VOCs are present in the hydrologic zone.

4. QuickFoam^� may be used to aid in the recovery of drill cuttings during reaming of large diameter boreholes with prior approval from the AFCEE Team Chief.

5. The monitoring wells will be constructed with 4.5-inch outside diameter schedule 80 PVC riser instead of 304 stainless steel riser.

6. An 8/16-mesh sand will be utilized as the filter pack for the well intake.

Drilling Locations, Equipment, and Procedures

Each cluster may not be drilled in its entirety before proceeding to the next cluster. The order of drilling will depend on equipment availability and drill site logistics. At any given time, multiple rigs may be performing the coring and well installations at a cluster location.

Perched Groundwater

The initial drilling effort in a background location (MW9) has demonstrated that perched water is present, at least after significant precipitation in the North Pasture. It is likely that the same phenomenon will be encountered at other drilling locations. Therefore, an important consideration in drilling the coreholes is determining whether perched groundwater zones are present and, if so, to determine whether contaminants are harbored within that zone. As necessary, the perched groundwater will be kept isolated to prevent cross-connection or cross-contamination between water-bearing units. The following procedure will be used to meet these goals.

From the surface, coring will proceed as described in the work plan. During coring, the air returns and retrieved core will be inspected for indications of water. This procedure can be difficult since water is continuously being introduced during the �misting� process, which gets core significantly moist. In the vicinity of Building 90, drilling within the vadose zone will be completed without the use of �misting� to aid in the detection of isolated or perched water-bearing zones.

If perched groundwater in the corehole is indicated, a sample will be obtained by CSSA for 24-hour analysis at an offsite laboratory. If the analytical data indicates contamination at that depth, a single-cased groundwater well may be installed to monitor that zone. The implications of a contaminated perched zone may preclude the completion of the well cluster at that location if there are sufficient concerns regarding cross-contamination between hydrostratigraphic units. Those issues will be reviewed and addressed on a case-by-case basis with CSSA, AFCEE, and the EPA.

However, if the initial sampling of perched water does not indicate the presence of contaminants, the corehole will be continued unless field screening with the PID, visual, or olfactory evidence indicates that significant contamination has been encountered. At that time, the coring will be suspended and a single-cased well may be installed to monitor the affected zone. Otherwise, the well cluster will be completed in accordance with the work plan.

Currently, there are no provisions for installing additional permanent casing across perched zones. A quadruple-cased Cow Creek well would require the use of a foundation pier rig to attain the necessary diameter required to install a 4-inch well. This is well beyond the current SOW, and therefore will not be addressed in this amendment.

Investigation-Derived Waste

All IDW generated during the coring phase of a well cluster will be contained within roll-off boxes at each site. Once a corehole has achieved the target depth at which surface casing will be installed (e.g., Lower Glen Rose/Bexar Shale contact) a groundwater grab sample will be obtained and submitted for quick turnaround VOC analysis by a CSSA-contracted laboratory. The results will be used in the determination if groundwater generated during the reaming phase of the same hydrologic interval can be discharged to the surface. When possible, uncontaminated fluids will be discharged to the surface to minimize the storage and transport of copious amounts of uncontaminated water. Otherwise, contaminated fluids will be containerized for eventual treatment and disposal. Each hydrologic zone will be addressed in the same manner at each drilling location.

Products to Aid Drill Cuttings Removal

Drilling equipment that uses compressed air to remove drill cuttings is sometimes unable to properly clean boreholes. This is based on factors such as boring diameter, amount of water that the formation is producing, composition of the formation, pressure of compressed air, and volume of compressed air. Products are available to aid the recovery of drill cuttings. One of these products, QuickFoam�, will be available for use if deemed necessary. Isopropanol and ethanol are the primary active ingredients in the foaming agent that is commonly used in water well drilling. The decision to use QuickFoam� will be made only after approval has been given by CSSA, AFCEE, and the EPA. At present, the foaming agent will only be used as a last resort to flush out cuttings from large diameter boreholes. A fingerprint chemical analysis has been included in Appendix A.

Monitor Well Construction Material

For monitoring well construction, 4.5-inch OD (3.75-inch ID) Schedule 80 PVC casing will substituted for the stainless steel well casing included in the original work plan. The well screen will remain as 4-inch ID 304 stainless steel as described in the SAP. The net effect of changing the well casing material provides for significant cost savings for the installation project. However, the slightly smaller ID of the schedule 80 PVC casing will not accommodate standard well pump typically used in wells with a nominal diameter of 4 inches. A smaller pump that will fit within a 3.75-inch well and sufficiently sized to pump groundwater at that depth will be available for well development.

In lieu of the 4/10-mesh or 6/9-mesh sand specified in the original workplans, alternative 8/16-mesh sand will be utilized. The mesh sizes specified in the original workplans are not readily available, and can only be obtained at a significantly greater cost than the proposed alternative size. The proposed sand size is normally-stocked materials by the manufacturers, whereas the 6/9-mesh or 4/10-mesh would require the production of a specialized batch by the manufacturer at a significantly greater cost. Since the primary purpose of the filter pack in a limestone aquifer is to support the emplacement of the annular seals (bentonite and grout), the necessity of a specialized filter pack material is not warranted.

According to the manufacturers grain-size analyses of their product, less than four percent of the 8/16-mesh sand products would pass through a wire-wrapped screen with 0.050-inch slot apertures. The sieve analysis from the product manufacturer is included in Appendix B. According to Groundwater and Wells (Driscoll, 1986), at least 90 percent of the filter pack should be retained by the slot openings of the well screen. Therefore, the alternative sand size will be suitable for the construction of the proposed wells.