31 December 2000
J & L CONSULTING SERVICES
Environmental Assessments
Mitigation Plans and Permits
Site Evaluation and Analysis
Wetlands Mapping
Mr. John W. Gillespie
Chairman, Planning Commission
Dexter Township
6880 Dexter-Pinckney Road
Dexter, MI 48130
Re: Review of Proposed Bentomat SS Liner in Place of Natural Clay Liner, Proposed Salamey Gasoline Station, Conditional Use Permit, Parcels A-1 and A-3, Section I3, Dexter Township.
Dear Mr. Gillespie:
In response to your Letter, which was dated 11-29-00, the following report concerning the proposed Bentomat SS liner as an alternative to a natural clay layer is hereby submitted. J & L Consulting prepared this review report as an agent for Dexter Township.
The main issue to be addressed is: Will the proposed Bentomat SS liner adequately substitute, in terms of groundwater protection for a natural clay layer, which is not present in the subsurface, i.e., under the three proposed underground storage tanks (USTs)?
The current site plan for the proposed Salamey gasoline filing station is presented in Figure 1. This proposed project is located in the southwest intersection of Dexter-Pinckney Road and North Territorial Road. More specifically, the project location is in the SW 1/4 or section 13 of Dexter Township of Washtenaw County, MI. This station is to consist of three 10,000 gallon USTs, 7 or 8 fueling pumps, and will sell both gasoline and diesel fuel.
At the 9-25-00 meeting of Dexter Township, the Planning Commission indicated that the conditional use permit for the proposed filing station will require a natural clay layer under the proposed USTs. Confident of the presence of this natural clay layer, Innovative Environmental Solutions, Inc., prepared cross section A-A’ on behalf of Mr. Bill Salamey (Figure 2).
However, the two soil borings, which were advanced on 10-9-00 and on 10-11-00 by Innovative Environmental Solutions to demonstrate the presence of the subsurface clay layer(s), revealed that Clay was not encountered during the completion of the soil boring(s). Thus, Cross Section A-A’ in figure 2 is in error, as no clay was encountered in either the 60-foot or 90-foot deep soil boring.
Moreover, the gamma ray analysis (as required by Dexter Township), which highlights clay layers in particular, also did not indicate the presence of any clay layers in the two soil borings.
At the Planning Commission meeting of Dexter Township on 11-28-00, Strata Environmental Services, Inc., on behalf of Mr. Bill Salamey, proposed the substitution of a Bentomat SS liner in place of a natural clay layer or layers in the subsurface under the USTs of the proposed gasoline filing station.
The planimetric drawing by Atwell-Hicks, Inc., shows the horizontal extent of the proposed Bentomat SS liner (Figure 3). Note that the forebay of the detention basin (not retention basin) and the area under the oil/grit separator are not proposed to be lined. Figure 4, which was prepared by Strata Environmental Services, is a cross section which shows the presence of the Bentomat liner and the proposed monitoring well in the sump area of the containment area of the three 10,000 gallon USTs.
At the end of the 11-28-00 meeting at the Planning Commission of Dexter Township, action on the conditional use permit for the proposed gasoline filing station (of Mr. Bill Salamey), which was to include the Bentomat SS liner as a substitute for the natural clay layer, was delayed until 1-23-01. However, the following new conditions for approval of the conditional use permit in regard to the Salamey filing station were as follows:
That the bentonite clay liner be extended to include the areas under the forebay (of the detention basin) and under the oil-grit separator, in addition to the entire fueling area and under the vault of the three USTs of the proposed Salamey filing station.
That the bentonite clay liner be two feet in thickness and have a hydraulic conductivity of l.0E-7 centimeters per second.
As a substitute for a natural clay layer or layers, the Bentomat SS liner is a synthetic liner that is less than 1 inch in thickness. See figure 5 for cross sectional diagrams of some bentonite liners. After careful installation, and the hydration of the Bentomat liner with-water (usually via the sand layer above), this liner can swell up to 5/8s of an inch or more.
The bentonite clay layers are referred to geosynthetic liners, and are abbreviated GCLs. In comparison, natural clay layers have been utilized as landfill liners (i.e., in the bottom of landfill cells), but are compacted to ensure a hydraulic conductivity of 1.0E-7 cm/sec or less with regard to water movement through the clay layer. Compacted clay lines are abbreviated CCLs. At that rate, water could move 1.4 inches/year through the clay layer.
If J & L consulting is not mistaken, in this project, according to Planning Commission wishes, the two-foot thick bentonite clay laver is to be put down, then the Bentomat SS liner is to be installed above that 2-foot bentonite clay layer. With regard to hazardous waste landfills (i.e., Type I landfills), a compacted clay layer 5 to 10 feet thick is usually put down, followed by a HDPE (high density polyethylene) plastic liner installed directly above the compacted clay (CCL). In Type II landfills, i.e., municipal landfills, usually there is a 2-foot clay layer (geomembrane) with a HDPE plastic liner installed directly atop the clay layer.
The undersigned behaves that either the Bentomat SS liner (less than one inch thick) or the two feet of bentonite clay should be considered sufficient for this project. Requiring both may simply be too redundant. Further, it is believed that the cross section in Figure 4 refers to just the Bentomat SS liner, and not the 2-feet of bentonite clay as directed by the Planning Commission.
Bentonite clay is a shrink-swell clay, or montmorillonite type clay. Montmorillonite clay, when hydrated (water added) will swell and seal itself from water passing through it. If any standing water or liquid solutes are removed from atop the bentonite clay, then the probability of water passing through a thick bentonite clay layer is basically eliminated.
Natural clay can contain a variety of clay minerals, including montmorillonite type clays. However, in southeast Michigan we have less naturally-occurring montmorillonite type clays, and more kaolinite clays. Kaolinite clays, in contrast, are not of the shrink-swell or self-sealing type.
An important diagram, which was appended to the Letter from Mr. Edward E. Everett, Strata Environmental services, Inc., entitled "Technical Data for the Bentomat Liner", to Mr. Bill Salamey, which was dated 12-11-00, shows that gasoline does not alter the permeability (in cm/sec) of a sample of Bentomat SS liner. See Figure 6. This GCL (geosynthetic liner) did not show any increase in permeability after 44 days of the introduction of gasoline, diesel fuel, or jet fuel atop the Bentomat SS liner.
However, these data are relatively old, i.e., the test was conducted in 1992. Moreover the source document for this test was not made available to Dexter Township. Generally, important data as this would be published in an engineering journal. Moreover, I visited the web site (i.e., www.cetco.com) for CETCO (Colloidal Technologies Company), and found many publications. Most, however, were published between 1992 and 1997. I found no publications more recent than 1997. Why more current publications were not put on the web site, or articles dealing with filing station use of GCLs, is of concern to the undersigned.
In Koerner & Daniel (l993), these authors state regarding GCLs versus CCLs on p. 256, and I quote:
"Importantly, one should not think of a GCL as being totally equivalent to a CCL. Indeed there is no possibility that a 10 mm layer of bentonite could possibly be equivalent to a 300 to 900 mm thick layer of compacted clay in all respects. The critical issue is whether substituting an alternative material such as a GCL for the more traditional CCL will meet or exceed the performance objectives of the site specific situation. If the GCL will meet or exceed the performance objectives, then it should be considered that equivalence has been established."
Table 1, which was also taken from Koerner & Daniel (1993) provides a comparison of Bentonite (GCL) liners with that of compacted clay liners (CCLs). Note that in many performance areas, CCLs are superior to GCLs. However, this second column from the right in Table 1 suggests that compacted clay liners (CCLs) can out-perform GCLs in a few specific areas.
J & L consulting has reviewed some of the available literature pertaining to synthetic bentonite liners, and found that that published data are relatively old, and that the test data in Figure 6 was not referenced to a source document which could be checked for validity. Thus, unless the source document for Figure 6 is identified, and the purported results therein are validated, then additional technical data concerning the effectiveness of bentonite (GCL) liners must still be forthcoming to Dexter Township.
In a recent Letter to Mr. John Gillespie, which was dated 11-28-00, Mr. Bruce Pindzia, P.E., of Construction Engineers of Michigan, reviewed the current proposition of Strata Environmental services to substitute the bentonite clay layer for the natural clay layer. J & L Consulting agrees with the "Issues to consider" as outlined by Mr. Pindzia in his Letter to Mr. Gillespie of Dexter Township.
The two soil borings which were taken by Innovative Environmental Solutions, Inc., on October 9 and 11, 2000, contained groundwater level data (bgs - below ground surface) as well as grain size data of the sediments encountered in the 60-foot and 90-foot deep soil borings. The groundwater levels in the two soil borings, which were extracted next to each other, and at an approximate ground elevation of 870 feet above MSL, were at 847.5 feet. However, the groundwater level in Monitoring Well # 1 (MW1), as reported by Atwell-Hicks Inc., was at about 851 feet. See Figure 7.
The point is, with the additional groundwater level data provided by the deeper soil borings extracted by Innovative Environmental Services on 9 and 10 October 2000, the groundwater level and flow map of Atwell-Hicks should be updated. In addition, with the new grain size data obtained from these two soil borings, hydraulic conductivity estimates, and hence travel time of the groundwater flow toward the residence at 6900 Dexter-Pinckney Road, could have and should have been determined. The house at 6900 Dexter-Pinckney Road is only 390 feet from the three USTs of the proposed filing station. Verbal opinions expressed by groundwater experts at Planning Commission meetings are simply not acceptable in regard to this project.
According to Zoller (1994, p. 41), the physical processes which affect groundwater flow, and any dissolved liquids therein, through porous sediments (as those found on the Salamey property) are advection, diffusion, and hydrodynamic dispersion. Advection, which is the process by which the solutes such as gasoline) are moved by the bulk flow of the groundwater, is largely affected by the hydraulic gradient of the groundwater surface. Hence, through a more careful study of the hydraulic gradient in the subject filing station area, and using all of the available data, more useful data could be provided to Dexter Township. The hydraulic gradient probably increases sharply in spring, and declines in late winter with the frozen ground and snow cover.
More importantly, the conditional use applicant should provide sufficient groundwater flow data to Dexter Township. The map by Atwell-Hicks i.e., see enclosed Figure 7, is not adequate, nor is the cross section in Figure 2. A pump test should have been conducted when the 4 monitoring wells were installed by Atwell-Hicks on 5-3l-00. (Be informed that all four of the soil borings for the monitoring wells were carried out in one day!). No pump tests were performed at that time which could have provided significant groundwater information, such as transmissivity, hydraulic gradient, and travel time. Software such as the 'Aquifer Parameter Estimator' is readily available from the National Ground Water Association.
a. Though it appears as though gasoline, diesel fuel, and jet fuel do not pass through the bentonite liners (GCLs) over a 44-day time period (Figure 6), more up-to-date test data, as reported in an engineering Journal, should be made available to Dexter Township as a condition for the conditional use permit. No journal reference was made available to J & L consulting so that the test data in Figure 6 could be adequately reviewed and evaluated.
b. Whereas it appears as though a bentonite clay liner may substitute for a natural clay liner (of 10 feet or more), such a GCL (geosynthetic clay liner) should be of the Bentomat ST or of the appropriate type. For example, the Bentomat ST liner is a needle-punched, reinforced GCL liner which has high internal shear strength and capacity are will require low permeability. Fuel tanks of 10,000 gallon capacity are very heavy when full, and slopes about the tank vault liner will require a specific steep-slope type bentonite liner.
(This conclusion is under dispute).
c. If Dexter Township should concur that a GCL (geosynthetic clay liner) can substitute for a natural clay layer or layers as regards this project, the bentonite clay liner (GCL) extend beneath the forebay of the detention basin and under the oil/grit separator in addition to being installed under the entire fueling area and under the tank vault (where the 3 USTs are to be placed). See Letter from Bruce Pindzia dated 11-28-00.
d. The requirement for the monitoring well in the sump of the tank vault, as shown on enclosed Figure 4, is a most important monitoring measure. (See monitoring well located to the right of the 3 USTs in Figure 4). This monitoring well should be of the vapor sensing type, and must be included in any GCL installation.
e. If this filing station is truly state-of-the-art, i.e., contains all the US EPA UST recommendations (Figure 8), as the applicant has proposed, then the relatively thin Bentomat SS (or the appropriate bentonite GCL liner) alone should suffice, i.e., the additional 2-foot bentonite clay layer (geomembrane) beneath the bentonite GCL is not absolutely needed as a groundwater protection measure.
(This conclusion is under dispute).
f. At least one groundwater monitoring well (MW) should be installed directly downgradient of the UST tank vault; another MW installed directly downgradient of the fueling area; and, at least three monitoring wells should be installed along the west margin of Dexter-Pinckney Road, i.e., in addition to the GCL (geosynthetic clay liner), the vapor monitoring well in the tank vault, and the other state-of-the-art measures of a modern filing station.
g. If the proposed groundwater protection measures are installed and properly inspected, the remaining risk factors of this filing station would be the stormwater detention basin. A subsurface natural clay layer appears to be absent in this area of the project site. Therefore, water from this basin will infiltrate downward into the subsurface unconfined groundwater aquifer, and hence this basin is clearly a detention basin, and not a retention basin. Furthermore, liquids such as gasoline, diesel fuel, and their additives, could move downward and downgradient in the groundwater. The potential for this groundwater pollution from fuel spills was admitted in the Strata report dated 8-14-00 (Everett, 8-14-00, p. 5).
h. Because of great citizen concern, the hydraulic gradient, transmissivity, and travel time at the groundwater from the proposed filing station site downslope to the residences and Township Hall along Dexter-Pinckney Road should also be provided to Dexter Township as a condition for the subject conditional use permit. In short Figures 2 and 7 are rather inadequate as regards groundwater information for the people of Dexter Township.
i. The water supply well for this filing station is currently located at the southwest edge of the proposed convenience store. See enclosed figures 1 and 3. As water from this well is utilized by the filing station and convenience store, a drawdown (or cone of depression) will occur. Since the distance from this well to the fueling pumps and the tank vault would be approximately 210 feet and 230 feet horizontal feet, respectively, this proximity could allow the cone of depression of that water well to intersect potential fuel spills and/or fuel leaks. This matter should be of considerab1e concern to Mr. Bill Salamey as well as to the Environmental Services Division of Washtenaw County.
j. Since the color of the sands beneath the water level, as indicated on the two soil boring logs by Innovative Environmental Solutions that were extracted on 9 and 11 October 2000, are brown in color, that color suggests that some groundwater infiltration (i.e., recharge) is occurring on the subject property of the proposed filing station. See color of the fine to coarse sands at depths of 22 to 46 feet. The gray color, in contrast, is a reduced (non-oxidized) color, and suggests that the groundwater in the gray-color zone was underground for a much longer time period and derived from a more distant recharge area.
Everett, Edward E. 8-14-00. "Environmental Impact Assessment, Proposed Marathon Gas Station and Convenience Store". Strata Environmental Services, Mason, MI. 6 pp, plus Appendices.
Everett, Edward E. 22-11-00. "Letter entitled Technical Data for the Bentomat Liner". Strata Environmental Services, Inc. Mason, MI. 1 pp, plus Appendices.
Innovative Environmental Solutions, Inc. 10 & 13 October 2000. Reports to Mr. Nabil Salamey, "Findings Report, Completion of Soil Borings, with Gamma Ray Logging". Brighton, MI.
Koetner, R. M. & D. E. Daniel. 1993. "Technical Equivalency Assessment of GCLs to CCLs". Technical Resource Document 210. Geosynthetic Research Institute, Drexel University, and University of Texas at Austin, Tx. Pp. 255-275.
Pindzia, Bruce. 11-28-00. "Letter regarding Proposed Salamey Gas Station/Convenience Store", To Dexter Township. 5277 Jackson Road Ann Arbor, MI. 2 pp.
Zoller, Uri. 1994. Groundwater Contamination and Control. Marcel Dekker, Inc. New York, N. Y. 712 pp.
If you have any questions concerning this report, please contact Mr. John Gillespie, Chairman, Planning Commission, Dexter Township.
Sincerely,
Eugene Jaworski, PhD
Principal
J & L Consulting Services
We have not included any of these enclosures on this web site.
Figure 1 - Site Map, Proposed Salamey Filing Station
Figure 2 -Cross Section A-A', NW to SE, Filing Station
Figure 3 -Area of Bentomat Coverage, Filing Station
Figure 4 -Cross Section showing Bentomat coverage
Figure 5 -Vertical Sections of some Bentonite GCLs
Figure 6 -Permeability Test of Bentomat SS, with Gasoline Introduced atop the CCL
Figure 7 -Groundwater Contour Map, by Atwell-Hicks
Figure 8 -Leak Detection and Overfill Protection Measures, US EPA, office of USTs
Table 1 - Generalized Technical Equivalency or GCLs versus CCLs, Keorner & Daniel, 1993
A critique of this report written by George Kunkle.
If you have comments about this issue, send email to NoGasStation@aol.com