Site Selection and Preliminary Design of a Landfill

Site Selection and Preliminary Design of a Landfill Requiring Post-Construction Stormwater ManagementW

Gregory Wilhelm1, Alfred M. Yates2, Paul White3, Matthew J. Gordon4, and Mark A. Radcliffe5

1Walter B. Satterthwaite Associates, Inc., 720 Old Fern Hill Road, West Chester, PA 19380; PH (610) 692-5770; FAX (610) 692-8650; email: [email protected]





On behalf of the Southeastern Chester County Refuse Authority (SECCRA), Walter B. Satterthwaite Associates, Inc. (Satterthwaite Associates) prepared a preliminary design of an expansion to the existing landfill facility located in southern Chester County Pennsylvania. In addition to the site selection and solid waste management criteria, the site evaluation and design included a multi-disciplined approach to data collection, groundwater and surface run-off modeling, site testing, and examination of various types of infiltration features. The goal of these activities is to protect an adjacent stream and to maintain the site’s hydrologic balance. The requirements essential to these processes are the collection and infiltration of surface runoff for two reasons. First, the need to maintain base flow in an existing stream adjacent to the proposed expansion area, and second, to meet the current trend in practice to infiltrate the difference in pre- to post-construction stormwater runoff resulting from the 2-year, 24-hour storm event. Since infiltration structures are subject to silt clogging which reduces their effectiveness, design alternatives, namely pre-conditioning structures, were examined to address this historical problem. The objectives of the design team are to prepare a sustainable design while minimizing the financial impact on the construction and operation of the proposed landfill cell. This paper presents an evaluation of previously deployed technologies, the options available to SECCRA for choosing a methodology, the evaluation and design criteria chosen for post-construction stormwater management, the hydrologic modeling of the site, and the engineering design processes that led to the selected stormwater management system. The purpose of this paper is to demonstrate the design team’s logic in analyzing the problem and selecting a solution as well as the impressions of the impacted parties with respect to the chosen stormwater management method and its ability to meet the design criteria. Overview and Purpose The SECCRA Community Landfill is planning and permitting a 39 ac landfill expansion to provide municipal solid waste disposal capacity for its 24 member municipalities. The expansion is estimated to provide this additional disposal capacity for 9 years or 1.8 million tons

2

of solid waste. As part of the overall permitting and approval process for the expansion, there are certain criteria, both objective and subjective, that must be achieved in order to demonstrate compliance with regulations and to minimize impacts related to environmental degradation. The Pennsylvania Department of Environmental Protection (PADEP) regulates the permitting and operation of municipal solid waste facilities within the Commonwealth. The Township of London Grove, located in southern Chester County, regulates land use within its boundaries. The PADEP requirements for stormwater infiltration are not scripted in regulations, but embedded in requirements for the permittee (SECCRA) to minimize and mitigate any known or anticipated environmental harm. In the case of this landfill expansion application, the stormwater efforts are directed at maintaining the baseflow in a stream adjacent to the proposed cell. The London Grove land use ordinances are prescriptive in their requirements to infiltrate the pre-development to post-development difference in the 2-year, 24-hour storm event. This essentially means that regardless of the need to balance hydrology at the site, the specified quantity of water must be infiltrated in order for the project to meet the threshold for acceptance. London Grove’s requirements are no t much different than those of many municipalities in the Commonwealth and those which the PADEP would like all municipalities to adopt as part of a statewide initiative to preserve groundwater resources. SECCRA’s, and consequently the authors’, challenge is to satisfy the prescriptive requirements while demonstrating that the impact to the baseflow of the stream by constructing the landfill cell is mitigated. Evaluation of Previously Deployed Technologies In the effort to develop the engineering design criteria to satisfy the criteria and in the absence of formal guidance for best management practices (BMPs) within the Commonwealth, the authors reviewed traditional methods used on other similar projects, the latest practices recommended or required by adjacent states, as well as technologies recently examined in technical literature. The authors have experience in designing water infiltration systems related to stormwater and wastewater effluent. In addition to the forced infiltration techniques previously utilized, we have also studied natural infiltration and the hydrologic balance in many different watersheds. These methods are not described in detail, but are incorporated in the references cited in this paper. We examined the stormwater infiltration BMP’s recommended or required by states surrounding Pennsylvania. Maryland, New Jersey, Delaware and New York have recommendations and requirements for the successful infiltration of stormwater resulting from land development. The manuals provided by these states represent the state-of-practice for the design, construction and operation of stormwater infiltration features which have been implemented, with varying degrees of success, for several years. Based somewhat in part on the successes and failures of the BMPs utilized in the states listed above, recent literature has attempted to dissect the reasons for success or failure in an effort to promote changes in the BMP manuals. As part of the evaluation and preliminary design of this

3

project, we screened these techniques to determine which one, or ones, would be most appropriate. The most appropriate structural BMPs are subsurface infiltration galleries, infiltration ponds and constructed wetlands (bio-retention facilities). Design and Evaluation Criteria Given the existing knowledge base and the information reviewed above, the team formulated a plan for guiding the field investigative phase of the design. Based upon the results of the field investigation, the team would determine the potential infiltration rates, area(s) available for infiltration facilities, and then determine the type of structural features to be utilized to accomplish the project’s goals. The required infiltration field techniques are defined in the London Grove stormwater ordinance. The ordinance defers to techniques required by the Chester County Health Department (Health Department) for the evaluation of soils for on- lot sewage treatment, or septic, systems. Given our experience in performing these tests and implementing system designs based upon the results, we decided that the prescribed techniques are appropriate for preliminary field screening and design given the site conditions and the goal of the final system. The Health Department’s criteria are based upon a soil’s ability to rapidly absorb water in order to maintain air migration to the subsurface. The specific evaluation procedures are summarized below:

• Excavation and observation of site soils and their horizons to identify potential limiting zones. A limiting zone is defined in the procedures as a horizon or condition of the soil or underlying strata which includes:

o A seasonal high water table, whether perched or regional, determined by direct observation of the water table or soil mottling;

o Rock with open joints, fractures or solution channels, masses of loose rock fragments including gravel, with insufficient fine soil to fill the voids between the fragments; and

o Rock formation, other stratum, or soil condition which is so slowly permeable that it effectively limits the downward passage of effluent.

• Percolation testing which consists of excavating a borehole to the required depth, preparation of the excavation sidewalls and bottom to remove smeared soil, an initial pre-soak to be conducted 8 to 24 hours prior to testing, a final pre-soak which is the first 60 minutes of the percolation test, the measurement phase which is conducted with dedicated measuring devices, measuring the percolation rate by recording the change in water level per the required time interval (either 30 minutes if water remains in the hole, or 10 minutes if the hole is dry). After 8 measurements are taken, or the hole stabilizes with a constant rate of fall over four consecutive readings, the test is stopped and the percolation rate in minutes per inch is calculated.

• Utilizing the results from the test holes in minutes per inch, an absorption rate in gallons per day was determined.

Hydrologic Model of the Site During the time that the authors were screening evaluation techniques, a quantitative model of the hydrogeologic flow system that contributes baseflow to the Stream was

4

developed. This model was utilized to predict the changes to baseflow that could occur as a result of the construction of the proposed landfill expansion, and to evaluate the range of feasibility of using surface water infiltration galleries at select locations around the perimeter of the landfill. Field observations of groundwater elevations and measured hydraulic conductivities were utilized to calibrate the model to approximately match the existing hydraulic head conditions. With this data and the anticipated total quantity of water to be infiltrated, the model produced estimates for the changes in the piezometric surface and the baseflow of the stream. Existing baseflow conditions were evaluated by developing a site-specific quantitative groundwater flow model utilizing the USGS MODFLOW groundwater modeling software (McDonald, 1988). The numerical finite-difference model input parameters and boundary conditions for use in predictive modeling were selected and further calibrated to correspond to local and regional hydrogeologic conditions for the site, which were determined through hydrogeologic investigation. Figure 1 illustrates the study area and shows existing topography, the Stream, the boundaries of the 84-acre surface water drainage area, and the approximate boundaries of the permit expansion.

The model was constructed by dividing the surface water drainage area into 890 individual “cells”, each one with an average area of 0.09 acres. Data was then input into each cell. Published groundwater recharge values for the Wissahickon Schist formation were input, along with site specific data, including hydraulic conductivity (k) values determined by slug and pump tests conducted on existing piezometers and monitoring wells, aquifer thickness determined from site geologic logs, and surface elevations from existing site topography. The values initially input into the model are summarized in the paragraph below

The hydraulic conductivity of the shallow overburden/fractured bedrock aquifer was determined from a pumping test to be equal to 3.26 ft/day, which is within the typical range for this type of lithology, which varies widely depending on the relative clay content and degree of the development of secondary porosity (Freeze, 1979; Fetter, 1988). Recharge to the aquifer was assumed to come exclusively from rainfall. Average rainfall in Chester County is 46 ipy. Recharge to the schist and gneiss in the Red Clay Creek Basin was reported at an average of 10.8 ipy (USGS, 1996) It should be noted that USGS has not reported recharge values for the White Clay Creek Basin. However, for the purpose of the study, values presented for the Red Clay Creek Basin were presumed to be equivalent based on the similar nature of the underlying geology.

After inputting the initial data, the software generated a predicted groundwater surface map. This was compared to an actual groundwater surface map prepared based on the mean of static water levels collected monthly for the year February 1999 through January 2000 prior to the model calibration at eight monitoring wells and six piezometers located at the site. These monthly water levels provide the most representative and unbiased data for calculation of average water level elevations. Long-term stream flow data to estimate baseflow were not available prior to modeling, but will be collected via a weir on a high frequency basis for at least a full year. As these data become available, SECCRA will further calibrate the hydrologic model to known

5

6

Stream baseflow presented herein for a more accurate prediction of the effects of stormwater infiltration to the Stream’s baseflow.

Model calibration was initiated by systematically altering the input values and regenerating computed groundwater surface maps until the model closely matched the observed conditions. The calibration of the south tributary model was achieved primarily by adding groundwater inflow to cells located along the upslope perimeter of the drainage basin, where the model was predicting lower static water levels than were observed in the site specific measurements. Sixteen cells were assigned groundwater inflow values ranging from 0.10 to 1.5 gpm. Additional changes made during calibration included adjusting recharge values based on site-specific topography and cover. For example, recharge on wooded hillsides and slopes were reduced, while recharge in open land with mild slopes was increased with final recharge values within model cells ranging from 0.004 to 26 ipy.

Figure 2 illustrates the calibrated model cells. Non-colored cells represent areas where recharge is occurring. Yellow cell markers represent areas where groundwater inflow derived from outside the surface water drainage basin was added to the model during calibration. Green cell markers illustrate the locations where groundwater is predicted to discharge at the surface as baseflow to the south tributary. Figure 3 illustrates the groundwater surface map generated by the calibrated model and the observed annual average groundwater surface developed from the site SWL measurements.

Figure 4 is a graph illustrating the computed SWL elevations in the site monitoring wells and piezometers on the x-axis and the observed SWL elevations on the y-axis. The degree to which the plotted points fall on the straight line indicating a one- to-one correspondence between observed and computed SWL elevations is a measure of the accuracy of the calibrated model. As shown, the computed versus observed SWL elevations define a nearly coincident straight line with the line indicating a perfect match, confirming the construction of an accurate and reliable model. The minor variat ions from the perfect match line indicate that the model error is on the conservative side, slightly over-predicting the SWL elevation.

Once the model is calibrated, the software calculates the volume of baseflow being contributed to the Stream in those cells where the groundwater surface intersects the ground surface. The sum of the volume of baseflow in each of these cells, which are referred to as “drain cells”, is equal to the total baseflow to the south tributary. In this case, the model predicted a total baseflow at the downstream end of the Stream of 0.077 cfs, which equates to 49,872 gpd or 34.6 gpm. As mentioned previously, a weir has been installed in the Stream to collect and record flow measurements multiple times daily over the course of at least one year. As this data becomes available, it will be used to further calibrate the base model to match existing conditions.

To determine the change in groundwater baseflow predicted by the installation of the impermeable liner, the recharge values within model cells located within the area of the future impervious liner (approximately 39 acres) were assigned recharge values of zero.

7

8

9

10

This reduces the total recharge to the model by 1,148 cfd, or 8,588 gpd. The model was then rerun to determine the impact to the baseflow. Figure 5 illustrates the model conditions without mitigation, with the area of the proposed lined disposal area shaded in yellow. Figure 6 illustrates the comp uted groundwater surface under these conditions. As illustrated, installation of the liner results in a lower groundwater surface elevation upgradient of the lined area since additional groundwater migrates from upgradient locations to replace the reduced recharge beneath the liner. During this portion of the modeling, the area was selected by the authors and SECCRA after a collaborative effort to select the most beneficial area for recharge.

The overall water balance is also affected. Without mitigation under post-development conditions, the sum of the volume of baseflow contributed to the Stream from the drain cells is reduced from 6,667 cfd (49,872 gpd) to 5,544 cfd (41,472 gpd). This equates to a total reduction in baseflow to the Stream of approximately 1,123 cfd (8,400 gpd), or 17% of the pre-development baseflow. However, even in this unmitigated state, no portion of the perennial stream is denied baseflow. As such, the model demonstrates that, absent any mitigation, no portion of the perennial stream will be eliminated or destroyed as a result of the location of the landfill.

The goal of the infiltration gallery design is to mitigate for the loss of groundwater recharge by providing for infiltration in a pattern that will result in a post-development groundwater surface consistent with pre-development site conditions, and that will also result in a baseflow to the south tributary of approximately 50,000 gpd. A preliminary design layout with an infiltration gallery along the south side of the landfill expansion area was factored into the model to meet this goal. This infiltration gallery serves a dual purpose of stormwater control and mitigation of baseflow recharge reduction. To accomplish the goals of stormwater control as required by township ordinance, a gallery along the southern edge of the landfill was designed to provide average infiltration of 16,000 gpd. This infiltration rate was distributed unevenly along the length of the gallery to allow 67% of the total infiltration to be accomplished along the upper (northwest) 56% of the gallery length. The distribution of this water was determined based on the results of infiltration testing carried out in accordance with township guidelines.

The infiltration gallery size was fixed by township ordinance as the difference between the pre-construction vs. post-construction predicted stormwater flow based on a 2-year return period storm. This resulted in an infiltration requirement of 1.5 ac-ft. In order to estimate the effect this infiltration structure would have on stream baseflow, a calculation was conducted based the method discussed in the Pennsylvania Handbook for Stormwater (PADEP, 2000). The gallery will receive runoff from a 15-acre drainage area of the capped landfill. Using the method of storm frequency analysis outlined in the BMP manual, as well as the NRCS Curve Number Method of estimating runoff, it was determined that if the galleries were designed to collect and infiltrate the runoff from all storms 1.62 in deep or less (storms of this size or less account for 80% of the annual precipitation depth in Chester county), and assuming that 55% of annual rainfall is lost to evapotranspiration, it would be possible to infiltrate 548,000 cf per year of water that would otherwise be lost as direct surface water runoff from the landfill.

11

12

13

This corresponds to an average of approximately 16,000 gpd. It is this flow that is returned to the aquifer in the groundwater model.

Figure 7 illustrates the addition of 16,000 gpd as recharge to cells located in the position of the proposed infiltration gallery (shown in blue). Figure 8 compares the computer generated groundwater surface map after infiltration gallery construction against the groundwater surface map generated from the predevelopment SWL measurements collected throughout 1999. The two maps are similar, indicating that the infiltration gallery design will mitigate changes to the groundwater flow system.

To provide a detailed analysis of changes in baseflow, the South Tributary was divided into three reaches, as shown in Figure 8. The cumulative baseflow to each reach calculated by the model, both before construction of the landfill and after mitigation, is summarized below:

Location

Computed Existing

Baseflow (gpd)

Computed Post-

Mitigation Baseflow

Springs/Headwaters 3,004 4,631 Midpoint 27,358 33,134 Immediately Upstream of Confluence with Chatham Run

49,872 56,336

As detailed above, the model predicts relatively minor changes to baseflow of the South Tributary as a result of landfill construction with mitigative measures. Baseflow to the headwaters of the South Tributary are predicted to increase by 54% as a result of mitigation. At the midpoint of the Stream length, baseflow will increase slightly (21%) as a result of landfill construction and mitigation. Cumulative baseflow to the South Tributary, at its confluence with Chatham Run, is predicted to be to 56,336 gpd, which represents an increase over predevelopment baseflow conditions of approximately 6,464 gpd, or 13%. This difference is within the accuracy of the modeling techniques and assumptions used to generate the two parameters being compared, and therefore is not significant.

The following results have been developed from the quantitative hydrogeologic modeling of the south tributary drainage basin:

• The predicted pre-development baseflow to the south tributary is equal to approximately 50,000 gpd.

• Without mitigation, the model predicts that the baseflow to the south tributary would be reduced to 83.0% of the pre-development baseflow, but not eliminated.

14

15

16

The utilization of infiltration galleries in the chosen locations as a BMP for surface water runoff from the proposed landfill can effectively restore the baseflow to predevelopment levels, distributing the baseflow in a pattern comparable to pre-development conditions.

Preliminary Engineering Design Design Criteria The infiltrat ion structures are being designed, utilizing the modeling and field data, to perform the following functions:

• Infiltrate the required quantity of water to maintain the site’s pre-existing hydrologic balance.

• Infiltrate the minimum quantity of water as required by the local ordinances.

• Provide a system that is sustainable with minimum maintenance.

As stated earlier, during the hydrologic modeling phase of the project, the authors and SECCRA considered several alternative designs capable of infiltrating the required quantity of stormwater at the site: infiltration galleries; infiltration ponds and constructed wetlands. All of these structures are capable of infiltrating the required volumes of stormwater runoff. However, due to potential regulatory limitations and reduced land availability, one structural feature was chosen over the remaining two. Surface structures, such as ponds and constructed wetlands, are both area intensive and allow the water time to heat up prior to infiltration, thus having a potential for causing some water quality concerns. Also, landfills have minimum setback criteria from wetlands, making permitting constructed wetlands adjacent to a landfill potentially problematic. Because infiltration galleries are constructed below grade, they have little impact on surface operations, with the exception of the appurtenant sediment pretreatment basins. Infiltration galleries with sediment pretreatment basins were selected based upon their capability to effect a minor surface area, promote water quality and reduce impacts on future site operations. Location In order to mitigate baseflow to the perennial stream, it is advantageous to locate the infiltration galleries as close to the upstream section of the perennial stream as feasible. Locating the infiltration galleries adjacent to the stream was considered, but rejected because it would violate minimum regulatory setbacks from the stream. Locating the infiltration galleries beneath the landfill was also considered and rejected because of concerns that the infiltration galleries could acts as a conduit for groundwater contamination in the event of liner leakage and because of regulatory criteria mandating a minimum 8 ft of separation between the landfill liner system and the top of seasonal high groundwater. The preliminary design specifies that the infiltration galleries will be located beneath the southern perimeter access road and portions of the vegetated berm, located between the proposed landfill expansion and SR 41. This locat ion allows

17

the infiltration galleries to mitigate baseflow reduction to the stream, caused by the proposed landfill expansion, while providing minimal impacts to site operations. Previous test pit excavation results were used to screen potential areas, within the pre-determined infiltration area, for percolation testing. Percolation testing was carried out in accordance with township guidelines to verify the suitability of these locations for infiltration galleries. Stormwater infiltration will be distributed unevenly across the infiltration galleries based upon the results of the percolation testing. Thus, more water will be infiltrated within those galleries observed to have higher percolation rates. Meeting Groundwater Recharge Requirements The infiltration galleries were sized to infiltrate the difference in the pre-development and post-development 2-year, 24-hour-storm. TR-55, version 2.10 (USDA, 1996) , was used to calculate the pre-construction vs. post-construction predicted stormwater flows based on the 24-hour, 2-year return period storm. This resulted in a minimum infiltration requirement of 1.5 ac-ft for the site. Stormwater runoff will enter the sediment pretreatment basins prior to being conveyed by gravity to the subsurface infiltratio ns galleries. In addition to improving water quality, the sediment pretreatment basins will provide additional runoff storage capacity. The storage capacity within the infiltration galleries and the sediment pretreatment basins will be capable of storing the required 1.5 ac-ft of stormwater. It will not be necessary to oversize the infiltration basins to provide this storage capacity, because the sediment pretreatment basins will provide the majority of this water storage capacity. Maintaining Baseflow to Perennial Stream In order to estimate the effect this infiltration structure would have on the perennial stream baseflow, a calculation was conducted based on the method discussed in Appendix F of the Pennsylvania BMP Handbook for Stormwater. Using the method of storm frequency analysis outlined in the BMP manual, as well as the NRCS Curve Number Method of estimating runoff, it was determined that if the galleries were designed to collect and infiltrate the runoff from all storms 1.62 in deep or less (storms of this size or less account for 80% of the annual precipitation depth in Chester county), and assuming that 55% of annual rainfall is lost to evapotranspiration, it would be possible to infiltrate 548,000 cf of water per year that would otherwise be lost as direct surface water runoff from the landfill. This corresponds to an average of approximately 16,000 gpd. It is this flow that is returned to the aquifer in the groundwater model. As detailed above, the groundwater model predicts relatively minor changes to the baseflow of the perennial stream as a result of the proposed landfill expansion with mitigative measures. Baseflow to the headwaters of the perennial stream are predicted to increase by 54% as a result of mitigation. At the midpoint of the stream length, baseflow will increase slightly (21%) as a result of landfill construction and mitigation. Cumulative baseflow to the perennial stream, at its confluence with Chatham Run, is predicted to be to 56,336 gpd, which represents an increase over predevelopment

18

baseflow conditions of approximately 6,464 gpd, or 13%. This difference created by the accuracy of the modeling techniques in comparison to the assumptions used to generate the two parameters being compared, and therefore it is not significant. Physical Design The preliminary design calls for the infiltration galleries to be located approximately four to six ft below the proposed perimeter access road and portions of a vegetated berm used to visual screen the landfill from the adjacent SR 41. Only stormwater runoff from the landfill cover, which has not touched the trash, will be infiltrated into the galleries. Runoff from the adjacent SR 41 will be conveyed to sediment basins on the site for surface discharge to minimize the potential that road wash and oil are transported to the groundwater through the infiltration galleries. The final design may include the use of piezometers in the infiltration galleries to measure water level and detect whether the galleries are becoming silted. Conclusions Utilizing a groundwater modeling, site testing and accepted engineering principles, the infiltration system is being designed to not only meet the applicable recharge standards, but to infiltrate the groundwater in such a manner that the natural stream baseflow quality and quantity will be maintained. The utilization of infiltration galleries with sediment pretreatment basins as a best management practice for surface water runoff from the proposed landfill can effectively restore the baseflow to predevelopment levels, distributing the baseflow in a pattern comparable to pre-development conditions. Therefore, no portion of the adjacent perennial stream should be adversely impacted as a result of this landfill expansion. Acknowledgements The authors wish to thank and acknowledge the Southeastern Chester County Refuse Authority and Walter B. Satterthwaite Associates, Inc. for the use of the application information and their support for the preparation of this paper. Nomenclature ac-ft Acre-feet, volume equivalent to 325,829 gallons BMP Best management practice(s) cf Cubic foot, cubic feet cfd Cubic feet per day cfs Cubic feet per second ft Feet gpd Gallons per day gpm Gallons (US) per minute in Inch, inches ipy Inches per year NRCS Natural Resources Conservation Service, formerly SCS or Soil Conservation Service TR-55 USDA/NRCS Technical Release 55 SR Pennsylvania State Route (Highway) SWL Static water level, ft

19

USDA United States Department of Agriculture USGS Unites States Geological Survey % Percent or per hundred References C. Fetter, Applied Hydrogeology, Macmillan College Publishing Company, New York,

1988. Chester County Health Department, Bureau of Environmental Health Protection, Site

Preparation Requirements, Procedures for Site Testing, and Absorption Area Requirements for Individual Lots, Revised 2001.

M. McDonald and A. Harbaugh, Techniques of Water Resources Investigations 06-A1A, Modular three-dimensional finite difference groundwater flow model , USGS, 1988.

PA Department of Environmental Resources, Bureau of Water Quality Protection, Erosion and Sediment Pollution Control Program Manual, March 2000.

R. Freeze and J. Cherry, Groundwater , Prentice-Hall, Englewood Cliffs, New Jersey, 1979.

Senior, L.A., Ground-Water, Its Relation to Hydrogeology, Land Use and Surface-Water Quality in the Red Clay Creek Basin, Piedmont Physiographic Province, Pennsylvania and Delaware, Water Resource Investigation Report 96-4288, USGS 1996.

US Department of Agriculture, National Resources Conservation Service (formerly the Soil Conservation Service), Urban Hydrology for Small Watersheds, Technical Release 55 (TR-55), Version 2.10, 1986.

Walter B. Satterthwaite Associates Inc., Major Permit Modification – SECCRA Community Landfill, July, 2003.

Documents

Site Selection and Preliminary Design of a Landfill