Jacobs Engineering Group Inc.

Transcription

1 -:] j TECHNICAL MEMORANDUM SM-lA WASTE PIPELINE DILUTION WELL SUMMARY FORT GREELY, ALASKA JANUARY 1999 Jacobs Engineering Group Inc. ' I J In affiliation with: Anderson Alaska, Inc. Philip Services Corporation Radian International, LLC Shannon & Wilson, Inc. Wilder Construction Company Alaska District Total Environmental Restoration Contract : j,.. FILE COPY

2 TECHNICAL MEMORANDUM SM-lA WASTE PIPELINE DILUTION WELL SUMMARY FORT GREELY, ALASKA JANUARY 1999 Prepared for: U.S. Army Corps of Engineers P.O. Box898 Anchorage, Alaska Prepared by: Jacobs Engineering Group Inc B Street, Suite 600 Anchorage, Alaska Total Environmental Restoration Contract Contract No. DACA D-0018 Task Order No.lO FILE COPY

3 TABLE OF CONTENTS SECTION PAGE ACRONYMS AND ABBREVIATIONS... ii 1.0 INTRODUCTION OBJECTIVES WATER ACTIVITY LEVEL ANALYSIS REGULATORY ANALYSIS SITE-SPECIFIC ANALYSIS SURF ACE CONTAMINATION ANALYSIS SUMMARY OF ALASKA ADMINISTRATIVE CODE APPLICABILITY TO THE FORT GREELY DILUTION WELL AAC 80 Drinking Water AAC 70 Water Quality CONCLUSIONS/ALTERNATIVES/RECOMMENDATION EVALUATION OF DILUTION WELL CONTAMINATION CONCLUSIONS ACTION ALTERNATIVES RECOMMENDATION APPENDICES Appendix A Synopsis of Dilution Well Field Activities Appendix B Dilution Well Photo...,..., I:\FfGREELY\05m31003\wp\Dilution Well Summary.doc 01/07/99 1 AKT M

4 ACRONYMS AND ABBREVIATIONS '~ :~ ~ -~~ BRAC CFR cpm Cs-137 DOE EPA Base Realignment and Closure 95 Commission Code of Federal Regulations counts per minute Cesium-137 Department of Energy Environmental Protection Agency --:, -- ~ H-3 tritium MCL MDA mrem mrem/yr NRC pci!l Sr-90 TEDE maximum contaminant level minimum detectable activity millirem millirem per year Nuclear Regulatory Commission picocuries per liter strontium-90 total effective dose equivalent :.., I:\FTGREELY\05m31003\wp\Dilution Well Summary.doc 01107/99 11 AKT M

5 1.0 INTRODUCTION The Fort Greely SM-1A waste pipeline dilution well was sampled after the well pump was removed in October Laboratory results revealed the presence of strontium-90 (Sr-90), a beta emitting radioactive isotope. This summary presents the results, regulatory analysis and considerations, conclusions, and recommendations for closure of the well. A synopsis of the field activities is included as Appendix A, and a photograph of the dilution well is found in Appendix B. 1.1 OBJECTIVES 1. Present and analyze the Ft. Greely dilution well groundwater sample results; 2. Evaluate the source and extent of well contaminants; and 3. Recommend a future course of action for the dilution well based on applicable considerations. 2.0 WATER ACTIVITY LEVEL ANALYSIS Two groundwater samples consisting of a bailer sample and a low volume purge sample were drawn from the Ft. Greely SM-1A waste pipeline dilution well. Each sample was analyzed for isotopic strontium (E905.0), gamma spectrometry (E901.1), and tritium (E906). All analyses, with the exception of the gamma spectrometry analysis for the low volume purge sample, were performed by Quanterra Environmental Services. DataChem Laboratories, Inc. analyzed the low voluine purge sample for gamma spectrometry. The choice of analyses was based on three radionuclides of concern that had potential pathways to the dilution well groundwater: Sr-90, cesium-137 (Cs-137), and tritium (H-3). Sr-90 and Cs-137 were the primary contaminants found along the SM-1A waste pipeline corridor and were analyzed by the isotopic strontium and gamma spectrometry analyses, respectively. H-3, evaluated by the associated tritium analysis, would have existed in the former SM-1A reactor's primary coolant which had a potential path to the well via the waste pipeline. I:\FfGREELY\05m3!003\wp\Dilution Well Summary.doc 01107/99 1 AKT -J07-05M3l

6 Results are summarized below: Laboratory Results (pci/l) Total Sr Gamma Spectrometry Bailer Sample 49.9 <MDA Low Volume 24.1 All results <MDA with the Purge Sample exception of Lead-212 result of 11 with an MDA of Confirmed with laboratory as a likely erroneous hit. Notes: MDA = minimum detectable activity -- < = less than Tritium <MDA <MDA REGULATORY ANALYSIS The Environmental Protection Agency (EPA), Department of Energy (DOE), and Nuclear Regulatory Commission (NRC) each have agency-specific limits for Sr-90 water concentration. The EPA has set a limit for Sr-90 in community drinking water systems at 8 picocuries per liter (pci/l) while DOE and NRC have set less conservative industrial limits for Sr-90 in water at 1,000 and 500 pci/l respectively. Although the DOE and NRC limits apply to industrial effluent levels and should not be interpreted as drinking water levels, they are provided to aid in the evaluation of the Sr-90 water concentration. Environmental Protection Agency The EPA has set_ a maximum contaminant level (MCL) in 40 Code of Federal Regulations (CFR) for Sr-90 in community drinking water systems of 8 pci/l. This is based on a 4 millirem per year (mrem/yr) dose equivalent to an internal organ (i.e., the bone marrow in the case of Sr-90), which is much more stringent than a 4 millirem (mrem) total effective dose equivalent (TEDE) for whole body exposure. i ;; ' Department of Energy DOE Order lists the most conservative Sr-90 ingested water limit as 1,000 pci/l. A TEDE of 100 mrem will be received by drinking 730 liters of water at a concentration of 1,000 pci/l. (2L/day x 365 days= 730 L). I:\FfGREELY\05m3!003\wp\Dilution Well Summary.doc 01/07/99 2 AKT M

7 Nuclear.Regulatory Commission 10 CFR 20 documents effluent activity concentration limits for Sr-90 in water as 500 pci!l based on a TEDE of 50 mrem/yr received from drinking 730 liters. This relationship between waterborne activity and TEDE is analogous to the one above from DOE Order (and is in contrast to the EPA's drinking water MCL of 8 pci!l based on a 4 mrem/yr dose equivalent). A summary of the regulatory limits based on assumed consumption of 730 liters per year is presented in the following table. Regulat~ry Sr-90 Water Concentration Sr-90 Water Concentration Agency Limit and Basis to Dose Relationship EPA 8 pci/l based on a 4 Drinking 730 liters of water at 500 mrem/yr critical organ dose pci/l results in a critical organ dose to the bone marrow of 250 mrem DOE 1000 pci/l based on a Drinking 730 liters of water at 500 TEDE of 100 mrem/yr pci/l results in a TEDE of 50 mrem NRC 500 pci/l based on a TEDE Drinking 730 liters of water at 500 of 50 mrem/yr pci/l results in a TEDE of 50 mrem 2.2 SITE-SPECIFIC ANALYSIS The project standard of 15 mrem/yr TEDE above naturally occurring background on an assumed farm would result in an allowable drinking water activity concentration limit for Sr-90 of 150 pci!l. This standard is based on the previously discussed DOE and NRC Sr-90 water concentration to TEDE relationships. This comparison assumes a 15 mrem/yr TEDE above background exclusively from drinking the dilution well water and does not consider the whole body dose received from any other radioactivity along the pipeline corridor. A project specific standard for a bone marrow organ dose was not established. As discussed, the EPA Sr-90 water concentration to critical organ dose relationship would be expected to yield a much lower allowable water activity concentration limit than the 150 pci!l limit presented in the previous paragraph. I:\FfGREELY\05m31003\wp\Dilution Well Summary.doc 01/07/99 3 AKT -J07-05M31 O-J

8 As a final consideration, if the groundwater from the dilution well is not ingested and simply remains below grade in the well casing, it would not provide a whole body or critical organ radiation dose to persons living on the assumed farm. 2.3 SURFACE CONTAMINATION ANALYSIS Based on the results from the dilution well, objects (i.e., pumps, hoses, or other items placed down the well casing) that come into contact with the water would not receive surface radioactive contamination above or even near applicable limits. The removable surface contamination regulatory limit for Sr-90 is 200 disintegrations per minute (dpm) per 100 cm 2 This corresponds to 90 pci/1 00 cm 2 Assuming that 1 cubic centimeter ( cc) of water spreads over an area of 100 cm 2, contamination levels of roughly.05 pci/100 cm 2 result when water at 49.9 pci!l Sr-90 (the highest Sr level of the dilution well samples) is spread over surfaces. This is roughly l/2,000th of the surface contamination limit and does not pose a surface contamination problem. 2.4 SUMMARY OF ALASKA ADMINISTRATIVE CODE APPLICABILITY TO THE FORT GREELY DILUTION WELL AAC 80 Drinking Water 18 AAC Source Protection: The Ft. Greely dilution well construction does not meet the minimum requirements for a water well serving a public water system. 18 AAC Maximum Contaminant Levels: The MCLs are specified for a public water system with a Sr-90 radioactive contaminant limit of 8 mg/l listed. This is assumed to be a mistake and units are likely in pci!l, consistent with the CFRs. 18 AAC MCL Compliance: Compliance with the MCLs for radioactive contaminants occurs if the average of the analysis of the four most recent consecutive quarterly samples (or a four-quarter composite sample) does not exceed the MCL. I:\FfGREELY\05m31003\wp\Dilution Well Summary.doc 01107/99 4 AKT -J07-05M

9 18 AAC Definitions, Abbreviations, and Symbols: This section defines public water system, classes of drinking water systems, and private water source. The Ft. Greely dilution well does not meet the definition of a public or private water source AAC 70 Water Quality 18 AAC Antidegradation Policy: Reducing water quality will not result in water quality that is inadequate to fully protect existing uses of the water. 18 AAC Protected Water Use Classes and Subclasses; Water Quality Criteria; Water Quality Standards Table: This section specifies different subclasses for fresh water to be used in applying water quality standards. The fresh water subclass which remotely applies in this case is water supply. Under this subclass, a further division occurs among drinking water, agriculture, aquaculture, and industrial. In the water quality criteria table, drinking water standards apply for agriculture applications (watering crops intended for human consumption). 18 AAC Procedure for Applying Water Quality Criteria: This section states that at the boundary between waters protected for different use classes, the water quality for the more stringent use class will apply. 18 AAC Mixing Zones: These sections discuss m1xmg zone criteria, requirements, and the associated application process. This section is not believed to apply in the case of the Ft. Greely dilution well. 3.0 CONCLUSIONS/ALTERNATIVES/RECOMMENDATION 3.1 EVALUATION OF DILUTION WELL CONTAMINATION In determining regulatory applicability and future action recommendations, consideration must first be given in characterizing the well contamination profile. This consideration must include the development of possible contamination sources as well as their possible impact. I:\FfGREELY\05m31003\wp\Dilution Well Summary.doc 01/07/99 5 AKT M

10 Although detectable Sr-90 levels exist in the water within the well casing, this contamination must be evaluated in terms of its migration potential and overall possible impact to the aquifer. A review of dilution station construction and past remedial actions on the dilution well reveals three possible means by which contaminants may have entered the dilution well: 1. The dilution station was designed to prevent the back flow of contaminated water down into the well. During normal system operation, the discharge flow of the well pump would prevent the contaminated water from going into the well. Additionally, a system swing check valve would act as a barrier if water was inadvertently pumped to the dilution station without the well pump running. Although the system was designed to prevent back flow, some system failures may have occurred which could have caused back flow of contaminated water down the well. During 1998 remedial actions, it was discovered that the drain culvert from the dilution station was likely blocked during portions of the pipeline's history (hence the outfall contamination hotspot). If contaminated water was pumped to the dilution station without the well pump running during such a period, it is likely that some leakage could occur past the swing check valve (generally designed to prevent gross back flow and not as a primary pressure barrier) and send contaminated water into the well. Although this scenario is possible, it is considered the most unlikely source of dilution well contamination based on a) its reliance on multiple system failures; b) the absence of contamination on the dilution well inner riser; and c) the fact that if such a release occurred during the operational period of the dilution station, the contaminated water would most likely be pumped up and out of the well during a later operational cycle. 2. As verified during 1998 remedial actions, at some point in time the dilution station had a significant leakage of radioactively-contaminated water into the dilution station concrete shell. This was proven by elevated radioactivity levels on the station concrete inner walls and along the dilution station drain line. These elevated activity levels would not be present unless the closed piping system of the dilution station experienced some form of rupture or major leakage. During such an event or during the subsequent repair efforts, radioactively-contaminated material may have been released down the well casing. 3. During the original dilution station abandonment process, the dilution well pump upper piping section inside the dilution station was left open (without an exclusion plug) and the dilution station concrete structure was filled with radioactively-contaminated soil. This was observed during 1998 remedial actions when the contaminated soil was removed from the concrete structure and the open upper. piping section was found with a direct path down the well (see photo in Appendix B). There is a high probability that some contaminated soils from inside the dilution station fell down the open piping into the well (see photo in Appendix B). Based on the multiple order of magnitude differences between soil activity limits and waterborne activity limits (for project specific Sr-90, the soil limit of 4 picocuries per gram (pcilg) can be compared to the water limit of 8 pci/l with one liter of water having a mass of 1 OOOg), it can be shown that it does not take a large amount of I:\FfGREELY\05m31003\wp\Dilution Well Summary.doc 01/07/99 6 AKT -J07-05M

11 contaminated soil to result in significant waterborne activity in a finite volume (such as the volume ofthe dilution well casing). Additionally, removal ofthe dilution well's outer 18" construction casing during the 1998 field season may have resulted in a small quantity of soil falling down into the well. Although this soil was field screened and sampled with non-detectable activity levels for both beta and gamma, activity levels below detection limits may have existed in the soil and contributed to elevated activity levels in the water volume ofthe well casing. There are no known historical records that document a large-scale introduction of radioactivity into the dilution well. Although a combination of the above described events probably resulted in a radioactivity introduction into the well, none of the events represent a source likely to result in large-scale radioactive contamination outside of the localized water volume inside the well casing. The most likely presented scenario is one in which soil falling down the well casing is the original source of well contamination. Based on the presented possible sources, field observations, laboratory data, and known Ft. Greely groundwater hydraulic gradient, the assumption is made that the radioactive contamination in the. dilution well is a finite amount that is likely confined within the well casing water volume. The contamination is likely associated with soil present at the bottom of the well casing and the associated suspended fines in the water. Agitation of the soil at the bottom of the well casing occurred prior to sampling as a result of the poly removal from the well (see Appendix A for timeline and details.) This process likely resulted in suspended fines that resulted in the detectable Sr-90 in laboratory samples. Over time and without further agitation, these fines would be expected to re-settle at the bottom of the casing. With the general Ft. Greely hydraulic gradient of.001 to.004 foot per linear foot, significant migration of the fines from the well to the surrounding groundwater is not expected. One unanswered question is the apparent absence of Cs-13 7 in both of the analyzed samples. Although the two radionuclides do not have a direct corresponding relationship, it is expected, as seen during the SM-1A radioactive waste pipeline remediation, that a contamination source likely to introduce Sr-90 would also introduce Cs Both of these radionuclides existed in the pipeline radioactive wastewater and were the remaining contaminants of concern along the SM-lA pipeline corridor. Although the two radionuclides have different migration profiles I:\FTGREEL Y\05m31003\wp\Dilution Well Swnmary.doc 01/07/99 7 AKT -J07-0SM3l

12 (Sr-90 being more soluble in water), the absence of Cs-137 may be attributable to an electrostatic interaction between specific radionuclides and suspended fines in the water. 3.2 CONCLUSIONS Based on the results from the bailer and low volume purge samples, the samples do not meet drinking water quality standards but are well within NRC and DOE industrial effluent discharge limits. Because the well was not significantly purged during the sampling process, these results are believed indicative of the well casing water volume and are not representative of the groundwater and associated aquifer characteristics. During the history of the well, an event or combination of events caused an introduction of radioactivity into the dilution well. Based on existing knowledge of the well's history, this introduction can be assumed to be finite and limited. The activity is likely confined to the immediate volume within the well casing with the likely source being low level radioactively-contaminated soil that has fallen down the well casing and settled at the bottom. Sr-90 waterborne activity regulatory limits differ and their considerations vary, as discussed in Section 2.1. Applicability of water quality standards for the Ft. Greely dilution well needs to be considered by the Base Realignment and Closure 95 Commission (BRAC) Cleanup Team. Further action or characterization may be required prior to well abandonment. Abandonment of the dilution well based on the existing sample data could invite concern over the unlikely groundwater contamination from the well. 3.3 ACTION ALTERNATIVES Based on the above discussions, the following alternative courses of action are presented. Option #1: Abandon the Well Using Existing Data The Ft. Greely dilution well is not a source of drinking water. Although the drawn samples indicate Sr-90 levels above EPA primary drinking water standards, this is a localized, finite concentration that, based on possible introduction sources and groundwater gradient, likely does not pose a threat to the aquifer. Water sample results from the nearest existing well (skeet range well) document Sr levels below minimum detectable activity (MDA). Characterization of the well water has been completed and the well may be abandoned in accordance with the 1998 Work Plan Addendum. As a consideration, radionuclide analyses I:\FfGREELY\05m31003\wp\Dilution Well Summary.doc 01/07/99 8 AKT M

13 could be included in the post-wide groundwater monitoring program to eliminate any future concerns of possible contaminant migration in the aquifer. Option #2: Abandon the Well Following Additional Characterization The first step of this process is to take another bailer sample from the well at the beginning of the 1999 field season and prior to additional further action. This sample will provide well characterization after fmes in the well have had several months to settle. Care is to be taken in this process to draw a sample without disturbing the casing bottom sediment and inducing suspension of fines. Results less than MDA for the radionuclides of concern are likely to come from this sample, based on the assumed soil source and the amount of well settling time. Although this sample alone is not meant to provide closure for the well, it provides a strong data point that supports a limited-introduction source likely associated with ~oil at the bottom of the well casing and associated suspended fines. The second step of this process is to remove a limited amount of the settled soil from the bottom of the well casing and thus eliminate the assumed source of well contamination. This is to be performed using a sand bailer. As an option, a large split spoon or a driller's sand pump may be used if the silt proved to be too dense or difficult to extract with the sand bailer. The sand pump is the least preferred option based on 1) higher costs of such a unit and 2) difficulties that would be encountered in radiological release of such a unit. During this process, a limited and finite amount of material is to be removed based on measurements of settled soil depth vs. the known total casing length. Total settled soil depth is not expected to be greater than 3 feet. This would require less than 3 cubic feet of material removal. The removed material is to be collected, field screened, analytically sampled, and disposed of accordingly. Immediately following the silt removal process, further sampling of the well is to be conducted using a high volume purge process. Such a process involves an initial well casing volume sample followed by subsequent purge samples. The primary purpose of the well flush is to provide adequate characterization samples for the well. Additionally, the flush I:\FfGREELY\0Sm31003\wp\Dilution Well Summary.doc 01107/99 9 AKT -J07-05M

14 (immediately following settled soil removal) removes any suspended fines caused by the removal process. Based on the expected limited extent of well radioactive contamination, a flush of five times the well volume should result in the removal of the waterborne contamination. An analysis of samples collected following each volume flush should demonstrate the lowering levels as the flush volume is increased. Water is to be purged directly into 500-gallon bladders. Assuming a well casing volume of 400 gallons, five 500-gallon bladders will be sequentially filled to 400 gallons during the purge process (for a total volume of 2,000 gallons of purge water). During this process, samples will be drawn and archived in gallon purge increments. These samples will be labeled and stored for possible future use. Additionally, a water sample will be taken immediately following the filling of each bladder. These five samples will be analyzed for gamma spectrometry, isotopic strontium, and tritium. Results of the samples will determine the disposition of the water in each of ~e bladders. Water meeting release requirements for the Ft. Greely wastewater treatment system will be drained from the associated bladder into the system. Water in bladders not meeting release requirements will be filtered onsite using a portable means of mechanical filtration and/or ion exchange treatment and will be resampled for release into the Ft. Greely wastewater treatment system. Following use, bladders will be smear-sampled, decontaminated (if necessary), and disposed of if necessary. Associated used filter or resin media is to be disposed of at an appropriate radioactive waste disposal facility. The expected results and goals of this process are to: 1) remove the possible soil source for well contamination; 2) purge the well until a sample is obtained with results below community drinking water standards for radionuclides; 3) demonstrate that well contamination is localized to the well casing volume and does not extend into the aquifer; and 4) provide adequate characterization data upon which well closure could be based without further concern over groundwater impact. 1:\FfGREEL Y\05m31003\wp\Dilution Well Summary.doc 01/07/99 10 AKT -J07-05M

15 If waterborne activity unexpectedly remains constant or above community drinking water standards following the well purge, many of the previously discussed assumptions would be proven incorrect. The well contamination may not be limited in lateral extent; and questions may be raised regarding the quantity/extent of contamination as well as the source. In this case, at least limited groundwater contamination would be determined to exist and the following steps and ascending levels of effort would be followed as necessary: Level 1 - Analysis, as necessary, of archived purge samples in order to resolve any remaining analytical sample data gaps or remaining questions from the purge process. As part of this level, a statistical analysis of archived sample results may be performed to assist in contaminant characterization. Level 2 - Possible additional purge samples to support contaminant characterization or contaminant removal (if levels were observed to drop but were not yet below drinking water standards). Level 3 - Hydraulic modeling of contaminated groundwater to determine the effect on the aquifer using existing historical, analytical and aquifer data. Such a level would not require additional data acquisition. Level 4 - Inclusion of radionuclide analysis in the post-wide groundwater monitoring program using existing wells. The analysis suite would be based on characterization data obtained from purge samples. No additional wells would be installed. Level 5 - Additional soil and groundwater data acquisition as necessary to support hydraulic modeling. This would be considered the ultimate level of action. The installation of monitoring wells and sampling to characterize the soil would be required in order to provide additional data to support hydraulic modeling. 3.4 RECOMMENDATION Based on a review of the existing data and applicable regulations, the recommended future action is to abandon the dilution well following additional characterization. The main requirement for future action lies with the existing sample results. Although likely misrepresentative, the current data suggests groundwater exists in the dilution station well with Sr-90 levels above the EPA's community drinking water standards. Future concerns over the well's condition would likely be avoided by carrying out the recommended course of action during the 1999 field season. 1:\FTGREEL Y\05m31003\wp\Dilution Well Summary.doc 01/07/99 11 AKT -J07-05M3l

16 As provided in this discussion, the well contamination source is likely a localized amount of low-level radioactivity associated with soils at the bottom of the well casing. Waterborne contamination is probably limited to within the well casing volume. Sampling and purging following a limited removal of settled soil from the bottom of the well casing will result in the following expected outcomes: 1. The dilution well will be adequately characterized. ""l 2. The localized nature and removal of the well contamination will be documented. 3. Well closure will occur with water samples documenting radioactivity levels below applicable limits. 4. The addition of radionuclide analyses to the basewide groundwater monitoring program will not be necessary. 1:\FfGREEL Y\05m31003\wp\Dilution Well Summary.doc 01/07/99 12 AKT M

17 APPENDIX A Synopsis of Dilution Well Field Activities

18 SYNOPSIS OF DILUTION WELL FIELD ACTIVITIES The 1998 field activities to remove the SM-1A dilution station well pump and casing is summarized as follows: 1017/98---Dilution well pump assembly was pulled using a boom truck. Aside from known fixed contamination on the upper manifold assemby (and associated 8" casing section), no radioactive contamination was discovered on either the inner 8" casing section or the pump assembly extending into the well. 10/8/98---Removed pump assembly is cut apart to allow for radiological survey and release of casing/shafting. Again, aside from the upper manifold assembly and localized 8" casing section, radioactive contamination was not found on the casing inner surface of the pump shafting. The released casing and shafting was delivered to Ft. Greely DPW Roads and Grounds. Per client direction, the well pump was not cut apart for radiological survey. Although there was no indication of contamination on the outside pump surface, the pump remains stored in a connex in the Ft. Greely laydown yard due to the inability to survey inaccessible surfaces. 10/10/98---Dilution well casing concrete base (upon which the manifold assembly sat) was removed. Prior to removal, a large section of poly was placed in the well casing to prevent foreign material from entering the well. After the concrete base removal, a 18" outer casing was found which surrounded the 14" dilution well casing. The annular space between the two casings appeared to contain soil. The outer casing was determined to be contaminated by direct frisk with readings up to 1,500 counts per minute (cpm) (14-15 times the contamination limit). Contamination on the 18" casing appeared to be fixed as smears taken off the casing did not show detectable activity. Soils surrounding the 18" casing were surveyed and found to be without radioactive contamination. The 18" casing was removed using the excavator and found to be 10' long. During the removal process, soils from the annulus fell into the well casing and forced the poly down into the well. With the 18" casing removed, direct frisk readings of the 14" well casing revealed

19 . surface contamination up to 300 cpm at depths up to 10' below ground surface. Again, the contamination appeared to be fixed as determined by smears taken off the casing surface. 10/12/98---A detailed contamination survey of the 14" casing was performed. The casing surface appeared to have four localized hot spots with counts ranging from cpm above background. Decontamination on the casing was first attempted using wet rags and subsequently attempted using wire brushes and small files. The files yielded moderate success as hot spots were lowered to cpm above background. Efforts to decontaminate the casing were stopped when further decontamination resulted in no cpm reduction in the hot spots. The casing was wrapped with poly and taped prior to backfilling of the former dilution station area.. ~ 10/15/98---The poly was retrieved from the dilution well and frisked out with no indicated contamination. Approximately two hours after removing the poly, a dilution well bailer sample was drawn. Results of the sample showed detectable levels of Sr at 49.9 pci/l. Activity levels for gamma spectrometry, and tritium were below minimum detectable levels. 10/16/98---A detailed radiological contamination survey was performed on the removed 18" casing section. The outer surface of the casing section had direct frisk contamination levels ranging from 140-1,800 cpm. Direct ~sk readings on accessible portions of the casing inner side did not indicate radioactive contamination above limits (although only a fraction of the entire inner surface was able to be surveyed). 10/17/98---The dilution well was sampled using the low flow purge procedure. Direct frisk readings and surveys throughout the sampling procedure did not reveal activity levels above background. During the purge period; the visible turbidity of the sample increased while purge monitoring parameters remained stable. Sample results showed detectable levels of Sr at 24.1 pci/l. Tritium results were below minimum detectable levels. Results of the gamma spectrometry analysis showed Pb-212 at 11.0 pci/l Gust above the minimum detectable activity of 10.6 pci/l). A conversation with the laboratory indicated that the Pb-212 activity slightly above the detection limit was likely an erroneous hit.

20 APPENDIXB Dilution Well Photo

21 Opening in upper pipe section where backfilled soil may have entered the well casing