Title: Introduction Text: As the Navy's Environmental Restoration Program matures, a growing proportion of funds will be allocated to Long Term Management (LTMgt). A significant part of these funds will be needed for Long Term Monitoring (LTM) efforts. The use of direct push (DP) technology could significantly reduce the installation and sampling costs associated with LTM wells. However, there are regulatory barriers limiting DP installations for long-term use. Naval Facilities Engineering Command (NAVFAC) has conducted demonstration studies at several sites across the country to validate the use of DP wells for LTM and to promote regulatory acceptance of this approach. This Web tool provides Navy Remedial Project Managers (RPMs) with information about DP well installation and sampling considerations, as well as performance data from NAVFAC's comparative groundwater monitoring studies.

Title: Direct Push Technology Text: Direct push technology (DPT) can be used for collecting subsurface soil, groundwater, or soil-gas samples. The technology uses hydraulic pressure and static force to advance steel rods into the subsurface, creating a borehole typically of 2 inches or smaller. This borehole can be used to construct a groundwater monitoring well, which typically in the past was used only for short term monitoring (e.g. less than one year). These wells can be installed at least two times faster than conventionally drilled wells. Also DP technology can be used to obtain continuous soil cores or discrete soil samples to determine subsurface geology. A conductivity sensor probe can be used with DP rigs to map subsurface lithology. The information can be used by a field geologist for soil logging. Unlike conventional drilling techniques, DPT generates little or no soil cuttings or drilling mud for disposal. For more information regarding the operation of specific direct push platforms, please refer to the USEPA CLU-IN web site: Direct Push Platforms.

Title: Soil Logging Text: As a monitoring well or soil boring is advanced, geological and contaminant content information should be logged for the different depth intervals until the bottom of the boring is reached. The soil should be classified by a field geologist and recorded on a well log form. A well log is created for each monitoring well or soil boring and contains the following information: Well ID, site ID and location, method of installation, date of installation, geologist logging information, driller, soil classifications and field contaminant screening levels at the different intervals, depth of natural groundwater table, and the boring depth.

Title: Direct Push Monitoring Wells Text: The wells installed using DPT are referred to as direct push (DP) wells. This diagram illustrates three different types of well installations including conventional hollow stem auger (HSA) installation, a "protected" screen DP installation, and an "exposed" screen DP installation. The main difference between conventional wells and DP wells is the size of the borehole. The borehole diameter created from a conventional drill rig is larger. The larger borehole provides more annular space, which allows more room for a thicker filter pack and larger annular seal. A larger annular seal helps to ensure that formation particles do not enter the monitoring well.

Title: Construction Details (1 of 2) Text: There are two methods for installing DP wells including the "exposed" screen installation and the "protected" screen installation. Both methods involve using metal drive rods and an expendable drive point. The well casing for the “exposed” screen installation is on the exterior of the drive rod, while that of the “protected” screen installation is inserted from within the drive. There are two American Society for Testing and Materials (ASTM) standards for installation of DP wells as follows: ASTM Designation D6724-04 Standard Guide for Installation of Direct Push Groundwater Monitoring Wells ASTM Designation D6725-01 Standard Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers

Title: Construction Details (2 of 2) Text: The exposed screen installation technique places the well casing and screen around the drive rods or uses the well casing as the drive rod. Upon installation, the well screen is directly exposed to the formation materials and no additional backfill is required. With this method, proper well development is especially important to ensure that any silt or clay that may smear during installation is removed. When compared to other direct push installation methods, exposed screen installation is faster and less expensive. However, there are several limitations that may make it less desirable. The protected screen installation involves either advancement of the casing and screen inside the drive rod or lowering of the casing into the drive rod after the target depth is reached. The protected installation shown here is comparable to conventional drilling techniques because of the presence of a filter pack and annular seal. The filter pack prevents clogging of the well screen. Contamination is also prevented from being pushed to different zones during installation. Click here to see an example of a direct push installed well construction diagram.

Title: Well Materials Text: Typical DP well materials are as follows: Casing Materials. The most common casing is usually made of ¾, 1, or 2-inch Schedule 40 or 80 polyvinyl chloride (PVC) piping. Casing sections are assembled with threaded or flush jointed connections. Screens and Filter Packs. Screens are made of PVC, nylon mesh, or stainless steel with the slot size based on soil conditions and filter pack. The “protected” screen DP wells also have filter packs installed around the screen prior to insertion. The filter pack, with appropriate sized sand material inside, is intended to increase hydraulic conductivity and minimize turbidity. Grout. Grout seals, used to prevent vertical water movement, can be pre-packed or tremmied in from above. Some DP wells also have a grout barrier above the filter pack to prevent grout seal from penetrating into filter.

Title: Well Design Specification (WDS) Text: Well Design Specifications (WDS) software has been developed by the Bureau of Reclamation, the Navy, and ASTM. This rapid monitoring well design software uses cone penetrometer (CPT) derived soil type classifications to determine the appropriate filter pack gradation and slot size for monitoring wells. Using WDS allows characterization and well installation to be combined into one site mobilization. Additional soil samples do not need to be collected. When CPT data is entered into the WDS software, the output allows the user to select different depth ranges and determine the appropriate filter pack and slot sizes. An example output from this software is shown. A copy of the program can be requested from the T2 contact listed at the end of this tool.

Title: Limitations of Exposed Screen Installation Text: For the exposed screen method of direct push, the riser and screen are used as the drive rod or placed around the drive rod during installation. Contamination could be “dragged” down with the screen while the well is being installed. The protected screen installation does not allow the riser and screen to pass through potentially contaminated zones during installation, which decreases the risk of spreading. The exposed screen may become clogged with silt or clay, which may also require additional purging and reduced effectiveness of the well for future sampling Lack of an annular seal, which is a regulatory requirement

Title: Well Development Text: Well development is an important step to ensure the quality and representativeness of groundwater samples that will be collected from a monitoring well. Proper development removes fines and silt and clay that may have been smeared on the walls of the borehole during well installation. Removal of these particles is essential in ensuring that there is a hydraulic connection between a monitoring well and its surrounding area. Proper development also decreases the turbidity which can increase the quality of groundwater sample results. Proper well development can be achieved by mechanical surging, over pumping, air lifting, or well jetting. It is imperative that the well has been fully developed. One common pitfall is that drillers may only purge the new well until the water becomes clear, but do not complete proper development.

Title: Groundwater Sampling (1 of 2) Text: DP wells have been used extensively during the site characterization phase as temporary groundwater monitoring points. However, historically, DP wells have not been used for LTM. NAVFAC has performed comparative studies to validate the use of DP wells for long-term groundwater monitoring in place of conventional drilled wells. The demonstration results can help RPMs to develop a rationale for their use and to work with state regulators to accept this new approach. Regulatory issues and case study results are discussed in more detail later in this tool.

Title: Groundwater Sampling (2 of 2) Text: Methods for collecting groundwater samples from direct push installed wells are not significantly different from sampling conventionally drilled wells. Three commonly used methods are purge and sample, low flow sampling, and no purge sampling. There are several different types of pumps that may be utilized to purge and collect a sample. The no purge sampling method removes no water from within the well prior to sample collection. Instead, samples are collected using passive diffusion bags or snap-samplers.

Title: Pumps Text: Centrifugal and bladder pumps are recommended for purging monitoring wells. Peristaltic or submersible pumps may also be used. Sample collection may also be accomplished using a bladder, centrifugal, submersible, or peristaltic pump. However, it is not recommended and sometimes not allowable by regulators to use a peristaltic pump for collecting samples for VOCs, SVOCs, or petroleum hydrocarbon analyses. Other factors such as well diameter and depth to groundwater may also limit the type of pump that can be utilized to collect groundwater samples (San Diego County, 2004).

Title: Hydraulic Conductivity Measurement Text: NAVFAC performed a study in March 2003 to compare hydraulic conductivity values collected from DP wells with values collected from conventional HSA installed wells. The study also compared different types of DP well designs including varying prepack design, well radius, and induced head. There was no statistical difference between the pushed, no pack wells and the drilled wells. However, there was a statistical difference between the drilled wells and the prepack wells. The variance associated with hydraulic conductivity tests in individual wells was many times smaller than the variance computed using the average hydraulic conductivity values from wells of the same type. This implies that the differences in K values observed amongst the wells is largely due to formation spatial heterogeneity rather than differences in well construction, installation, or test method.

Title: Installation Cost Comparison Text: DP wells may provide a large cost savings. They require less time to install, which contributes to the overall cost savings. Cost savings are also achieved because the installation of DP wells greatly decreases the generation of liquid and solid wastes. The graph to the left shows the cost savings for installing DP wells and is based on information collected at the Naval Base Ventura County (NBVC) in Port Hueneme, California. As shown, the savings ranged from 44% to 65% for 3/4" monitoring wells and 24% to 49% for 2" monitoring wells. Additionally, DP wells produce less purge water during groundwater sampling and are easier to abandon, both of which may cause an additional project cost savings.

Title: Regulatory Acceptance Text: Requirements for monitoring wells differ from state to state and may include different considerations for the use of DP wells versus conventional wells. Permitting procedures typically specify how a well is sealed and the size of the filter pack. Most states require a minimum 4" annular space surrounding the monitoring well casing. Prepacked DP wells typically have a thinner filter pack. Most states allow use of DP wells with less than 4" of annular space for groundwater monitoring on a temporary basis without a written proposal for variance. Some states have approved use of DP wells for long-term groundwater monitoring (see map). Most states will allow their use with a written request for a variance allowing less than 4" annular spacing. Although legacy regulations exist, these variances are often granted.

Title: Advantages Text: The following is a list of advantages associated with the use of direct push monitoring wells over conventional drilling techniques: Minimizes the volume of soil cuttings for disposal and the potential for exposure to contaminants in the soil cuttings Minimizes the volume of well development purge water for disposal due to a smaller bore hole diameter Faster installation at 2 to 5 times the rate of conventional techniques Less expensive to install, replace, and abandon Allows for more sample locations for a given amount of time and money, resulting in higher data density, therefore more representative data Less disturbance to the site due to lighter equipment and a shorter installation period

Title: Limitations Text: There are also a few limitations associated with direct push monitoring wells including: DP wells generally cannot be used in consolidated formations, or in formations with gravels or "tight" sands. Site-specific geologic conditions will dictate whether DP wells can successfully be installed to target depths. May also be limited in heterogeneous geological conditions which may contain gravel or cobbles Some state regulators will not allow use for long-term monitoring Well diameters are limited to 2 inches Some environmental professionals believe that the potential for cross contamination of aquifers is more likely to occur when using the direct push technology

Title: Case Studies Text: NAVFAC has performed a series demonstration projects to validate the use of DP wells for long-term groundwater monitoring. Each case study compares sample results collected from conventionally installed wells to DP wells. The following case studies are discussed: Case Study 1: Naval Facilities Engineering Service Center (NFESC) Study: Demonstration performed at Naval Base Ventura County (NBVC), Port Hueneme, California. Case Study 2: Environmental Security Technology Certification Program (ESTCP) Demonstration including 5 test sites; Phase I of the study has been completed and Phase II of the study will be completed later in 2007 with publishing of the final reports.

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Title: Case Study 1 - NFESC Study Text: The study performed at NBVC Port Hueneme included a comparison of groundwater monitoring results from DP wells of varying designs to HSA-installed conventional wells. The criteria that were evaluated for the different types of well installations included the following: Sample representativeness (chemical) Hydrogeologic observations (groundwater table) Monitoring costs A statistical analysis of results was conducted to compare the performance of each type of monitoring well.

Title: Site Description Text: The study was performed at the leading edge of the methyl tert-butyl ether (MTBE) plume at NBVC Port Hueneme. The large MTBE plume at NBVC Port Hueneme is a result of a 1984 gasoline release from underground storage tanks (USTs) and fuel distribution lines at the Naval Exchange fuel service station. Two test cells (Cell A and B) were installed for the performance evaluation. Test Cell A was installed downgradient of plume migration and Test Cell B was installed inside the MTBE plume between a retail car lot and Building 401. Click on the figure to view the location of these test cells.

Title: Study Description (1 of 2) - Installations Text: Twelve monitoring wells were installed in Cell A, divided into four clusters. Each cluster contained 3 different types of wells including 3/4" and 2" diameter DP wells and a 2" diameter drilled well, all installed using ASTM standards. Twenty monitoring wells were installed in Cell B, divided into four clusters. Each cluster contained 5 different well installations including a 3/4" diameter DP well installed using ASTM standards, 2" diameter DP well installed using ASTM standards, 2" diameter drilled well installed using ASTM standards, a 3/4" diameter DP well with no filter pack, and a 3/4" DP well installed using conventional techniques. A standard nomenclature was established to easily identify the well cluster and type of installation for each well. The well clusters were also identified by having either 2-ft or 5-ft screens and either deep or shallow screened intervals.

Title: Study Description (2 of 2) Text: Low-flow sampling techniques were utilized for collecting groundwater samples. Four rounds of groundwater sampling were performed. Geochemical parameters were measured in the field for each well including dissolved oxygen (DO), pH, specific conductance, temperature, and turbidity. For Rounds 1, 2, and 4, a field laboratory was used for MTBE analysis. For Round 3, an analytical laboratory was used for MTBE analysis. Generally, triplicate samples were collected for MTBE analysis from each monitoring well. A statistical analysis was then performed on MTBE results.

Title: Study Results Text: Analysis of variance (ANOVA) statistical analysis was chosen as the best method for comparing the data, which consisted of categorical factor predictors and a continuously varying response variable. Box plots of MTBE concentrations by well type for Cell A and Cell B are shown to the left. The results indicated that the direct push sampling performance was not significantly different than the drilled well performance. Click here to view the ANOVA summary table for each cell, which includes categorical factors and contributions of each to the total variance. This statistical data demonstrates that the temporal and spatial variability outweigh variability due to specific well type. In addition, the water level monitoring data indicated that there was no significant difference in the water table elevations recorded for the different well designs. DP wells were also found to provide a more cost-effective means of sampling groundwater. This study demonstrated that performance of DP wells was comparable to drilled wells, which is a step to further gaining acceptance from state regulators.

Title: Text: ANOVA SUMMARY TABLES FOR CELL A AND CELL B ANOVA Results for Cell A Main Effects Model with Combined Four-Level Screen Depth Range Factor Source Sum of Squares DF Mean Square F Value Prob(F) Total 16.237 143 0.114     Well Type 0.386 2 0.193 3.799 0.025 Sample Date 1.971 3 0.657 12.907 0.000 Depth Range 7.009 3 2.336 45.901 0.000 Error 6.872 135 0.051     ANOVA Results for Cell B Main Effects Model with Combined Four-Level Screen Depth Range Factor Source Sum of Squares DF Mean Square F Value Prob(F) Total 602,673.5 237 2,542.93     Well Type 3,156.3 4 789.09 0.736 0.568 Sample Date 166,775.4 3 55,591.82 51.873 0.000 Depth Range 189,466.5 3 63,155.51 58.930 0.000 Error 243,275.1 227 1,071.70

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Title: Case Study 2 - ESTCP Text: As part of an ESTCP-funded project, NAVFAC is performing an ongoing study of direct push monitoring wells at 5 different site locations across the United States. The purpose of the study is to further compare the performance of DP wells versus conventional drilled wells for long-term monitoring. The conventional drilled wells are considered the baseline for the study. Phase I of the ESTCP study has been completed and Phase II has been partially completed with the draft final reports under review as of January 2007.

Title: Test Site Descriptions Text: Five test sites were chosen for the study that contained differing geological conditions and were located in different Environmental Protection Agency (EPA) regions across the United States. DP wells were installed at each site adjacent to existing drilled wells. The total depth and screened interval of DP wells were the same as for the drilled wells. The five test sites included: U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CCREL) located in Hanover, New Hampshire Dover National Test Site (DNTS) at Dover Air Force Base (AFB), Delaware NBVC Port Hueneme, California Tyndall Air Force Base (AFB), Florida Hanscomb AFB, Massachusetts

Title: Phase I Study Text: Four of the five site locations were utilized for Phase I of the study. The table shown to the left contains a summary of critical information about each site including the depth to groundwater, number of well clusters, number of monitoring wells per cluster, and contaminants present. The well selection criteria are also summarized. The NBVC Port Hueneme site has been divided into two test locations (Cell A and Cell B) that coincide with the locations discussed in the previous case study. Five quarterly sampling rounds were performed at each test site. Low-flow purge and sampling techniques were used to collect groundwater samples. Contaminants of concern at all sites were volatile organic compounds (VOCs). Water quality field parameters were also measured.

Title: Phase I Findings (1 of 3) Text: Statistical analyses were performed on the results obtained from groundwater sampling events for each contaminant of concern. Standard parametric tests were utilized to determine any significant differences in the data from the different monitoring well types. Non-parametric tests were used for any data that could not be analyzed using a parametric test. The types of statistical analyses used to review the study results are summarized here. Roll over the graphic for more information.

Title: Paired t-test Text: The t-test is a parametric matched sample analysis used to determine if significant difference exists between two sample population means. This method assumes that the paired population differences are normally distributed.

Title: Wilcoxon Signed Rank Test Text: If paired population differences are not normally distributed, Wilcoxon Signed Rank may be used to compare the relationship between two data sets. This nonparametric analysis alternative compares the effectiveness of two population methods.

Title: One-way RM ANOVA Text: ANOVA is a statistical method used to test for equality of the means of two different populations.

Title: Tukey Test Text: The Tukey Test is a statistical test used to determine which mean value from a group of mean values may significantly differ from the rest.

Title: Phase I Findings (2 of 3) Text: The first table shows typical well cluster results from a single well pair at Dover AFB. The results shown are mean values from the 5 sampling events during Phase I of the study. Geological variability was eliminated by comparing closely-spaced monitoring wells. No statistically significant difference was observed between the DP well and conventional well data sets for field parameters, inorganic, or organic results. The second table shows mean concentration data from Port Hueneme well cluster B. The data from the 2-inch HSA well was compared to data from several DP wells. Please note that two of the DP wells were installed to the ASTM standard, meaning soil cores were taken, grain-size analysis done, and slots and pre-pack filters were designed accordingly. The highlighted values in this table indicate that the mean value of that particular cell is greater than +/- 2 standard deviations (SD) from the mean value of the HSA well. Mean values that are two standard deviations apart are considered to have a “significant" statistical difference. In large data sets, such as the ESTCP study, instances of significant statistical differences between well types are expected due to preferential pathways and large spatial heterogeneities of contaminant concentrations in the groundwater. Therefore, it is most important to consider the entire data set and observe the overall trend of these differences.

Title: Phase I Findings (3 of 3) Text: The Phase I results from statistical analyses determined that no significant difference in contaminant concentrations and field parameters exists for the different well types for the majority of the test sites that contain sand or sandy/silt soils. In the few instances where statistical analyses determined significant differences existed, the relative magnitude of the differences were small. There were also no consistent trends with one type of monitoring well always yielding a higher/lower concentration. Management decisions regarding plume delineation or the remediation footprint would not differ if direct push monitoring wells were used instead of HSA monitoring wells.

Title: Phase II - Ongoing/Future Activities Text: Phase II of the study is still being performed. Eight additional rounds of groundwater sampling are planned for Phase II at all sites except the Hanscomb AFB site, which is not part of the Phase II study. As part of the Phase II effort, additional drilled and direct push monitoring wells were installed in several locations directly next to and with the same construction details as the existing drilled and direct push monitoring wells. The new wells will be used to determine the variability of identical wells within a cluster. The Phase II results will be analyzed and summarized in a final report which will be completed in 2007.

Title: References/Links Text: ASTM. 2002. Designation D6724-01, Standard Guide for Installation of Direct Push Ground Water Monitoring Wells. January. ASTM. 2002. Designation D6725-01, Standard Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers. January. EPA's CLU-IN Web site: Direct Push Platforms. ESTCP. 2000. Technology Demonstration Plan, Demonstration/Validation of Long-Term Monitoring Using Wells Installed by Direct Push Technologies. November. ITRC. 2006. Technical and Regulatory Guidance Document, Direct Push Well Technology for Long Term Environmental Monitoring in Groundwater. March. Kram, M., Lorenzana, D., Michaelsen, Dr. J., Lory, E. 2001. Performance Comparison: Direct Push Wells Versus Drilled Wells, NFESC Technical Report TR-2120-ENV. January. NAVFAC. 2006. Direct Push Wells for Long Term Monitoring. Remediation Innovation Technology Seminar (RITS) Fall. San Diego County. 2004. Site Assessment and Mitigation (SAM) Manual. February 18.

Title: Contact Text: For more information about direct push monitoring wells, please contact: NFESC POC (805) 982-1656 PRTH_NFESCT2@navy.mil