microsoft outlook - division of environmental quality (deq) · scs addendum responses to adeq doc....

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Blue, Karen

To: Pearson, JenniferSubject: RE: Addendum Response to ADEQ Comment Letter (Document ID: 73807) - Upper

SWRSWMD Class 1 Landfill Permit Mod Application Reports (HGI and GWSAP)

From: Watts, Rachel [mailto:[email protected]]Sent: Monday, September 24, 2018 2:26 PM To: Pearson, Jennifer Cc: McCullough, Daniel Subject: Addendum Response to ADEQ Comment Letter (Document ID: 73807) - Upper SWRSWMD Class 1 Landfill Permit Mod Application Reports (HGI and GWSAP)

Jennifer,

Please find attached the additional information you requested for the above referenced reports prepared for UpperSWRSWMD. Aside from a cover letter, the attachment includes the following documents/pages:

HGI Report, Rev. 2 – Text Only New FIGURES 1a and 1b Insertion page indicating that Figure 3 was removed A replacement cover page for Appendix C The 2018 well survey Stamped piezometer survey Revised Field Groundwater Sampling Record

If you need any additional modifications or information, please feel free to call myself or Dan a call. His direct number is501 503 4778.

Best regards,Rachel

Rachel A. WattsProject ProfessionalSCS Engineers11219 Richardson Dr.North Little Rock, AR 72113 USA501 503 4781 (W)501 943 2010 (C)[email protected]

Driven by Client Successwww.scsengineers.com

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Rec’d Digitally

AFIN:_________________________

PMT#:_________________________ SW

DOC ID#:______________________ MD

TO:___________________________

By Karen Blue at 10:54 am, Sep 26, 2018

31-00107

0265-S1-R1

74612

BS>FILE <KMB

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computer. SCS Engineers accepts no liability for the content of this email or for the consequences of any actions taken on the basis ofthe information provided. – SCS Engineers

11219 Richardson Drive, North Little Rock, AR 72113 | 501-812-4551

Environmental Consulting & Contracting

September 24, 2018 File Nos. 27216114.00 and 27218103.00 Ms. Jenny Pearson Arkansas Department of Environmental Quality 5301 Northshore Drive North Little Rock, AR 72118-5317 Subject: Upper Southwest Arkansas RSWMD Class 1 Landfill

ADDENDUM Responses to ADEQ Comment Letter (ADEQ Doc. ID: 73807) RE: Hydrogeologic and Geotechnical Investigation Report and the Groundwater Sampling & Analysis Plan within the Major Permit Modification Application AFIN: 31-00034; Permit No. 0265-S1-R1

Dear Ms. Pearson: On July 31, 2018, Stearns, Conrad, and Schmidt, Consulting Engineers, Inc. (dba SCS Engineers) responded to an ADEQ Comment Letter (ADEQ Doc. ID: 73807) regarding the facility’s Hydrogeologic and Geotechnical Investigation Report (HGI) and the Groundwater Sampling & Analysis Plan (GWSAP) included in a Major Permit Modification Application. The response included ADEQ-requested data and clarification, as well as revised reports. At the time of the July 2018 response, information was still being gathered by SCS and the facility regarding the current state of mined areas, seeps, springs and water wells within 0.5 miles of the landfill. Once this information was obtained, new site maps were generated to depict the current structural features, topography and land use(s) at and near the landfill. This letter and its enclosures provide the additional information and serve as an addendum to the July 31, 2018 submittal. HGI REPORT COMMENTS ADEQ Comment #1: There appears to have been extensive mining within one-half mile to the north and east of the proposed expansion area since 1991 and 1993. Also, the referenced Site Geologic Map from the 1991 Geotechnical and Groundwater Study has no scale, and the property boundary has changed considerably. Please investigate and update the mined areas on the geologic map, document whether or not new seeps or springs have been exposed in these areas, and revise the site geologic map to include a scale and the current property boundary as required by APC&EC Regulation 22.1102(c)(2).

SCS ADDENDUM Responses to ADEQ Doc. ID: 73869 Offices Nationwide AFIN: 29-00034; Permit No. 0226-S1-R2 www.scsengineers.com September 24, 2018 Page 2

11219 Richardson Drive, North Little Rock, AR 72113 | 501-812-4551

SCS Response Two new site maps are enclosed (Figure 1a and Figure 1b) that include a scale and updated property boundaries. Figure 1a depicts the current and proposed landfill boundaries on a geologic map. Figure 1b is a topographic map that depicts the mine areas within one half mile of the landfill boundaries. No new seeps or springs were identified in these areas. The HGI Report has been updated to reflect the new information.

ADEQ Comment #2: In Section 3.2 of the HGI Report, there is no indication a survey of surrounding residents for the identification of water wells was completed. In the conditional approval letter of the HGI Work Plan (Document ID 70640), ADEQ stated the following: “As part of the fulfilling the requirements of APC&EC Reg.22.1102(c)(2)(iv) and APC&EC Reg.22.303(c)(7), the facility needs to survey surrounding residents for identification of water wells. This survey needs to be performed within one-half mile of the landfill property boundary and can be performed using registered mail or other personal contact methods.” Please survey property owners as previously requested, include the results of the new survey in Section 3.2 of the HGI Report, and revise Section 3.7 of the Permit Modification Application to include discussion of the survey and its findings.

SCS Response SCS identified potential residential properties within 0.5 miles of the landfill property. These properties were visited in person by a facility representative (Mr. Jeff Barfield) in an attempt to identify water wells within this radius. The well survey (enclosed) identified no residential wells less than 0.5 miles from the boundaries of the landfill. The results of the well survey are enclosed and have been included in Section 3.2 of the HGI Report.

ADEQ Comment #14: The approved HGI Work Plan states all piezometers will be surveyed after completion and the survey will be conducted by an Arkansas Licensed Surveyor. There is no stamped survey included in the HGI Report. Please include a stamped survey within the report. If the existing piezometers were not part of the survey conducted under the HGI, please also include the 2015 stamped survey found within Document ID #67265 in the HGI Report.

SCS Response The piezometer survey was conducted by an Arkansas Licensed Surveyor. The stamped survey is enclosed.

GWSAP COMMENTS ADEQ Comment #46: The Field Groundwater Sampling Record found in Appendix A of the GWSAP needs a column added for recording the pumping rate or purge volume during the purging and sampling. Please revise the Field Groundwater Sampling Record form accordingly.

HYDROGEOLOGIC AND GEOTECHNICAL INVESTIGATION REPORT, REVISION 2

MAJOR PERMIT MODIF ICATION

Prepared For:

U p p e r S o u t h w e s t A r k a n s a s R e g i o n a l S o l i d W a s t e M a n a g e m e n t D i s t r i c t

319 Landfill Road, Nashville, Arkansas

Howard County, Arkansas

Permit No.: 265-S1-R1 AFIN No.: 31-00107

Presented by:

S C S E N G I N E E R S 11219 Richardson Drive

North Little Rock, AR 72113 (501) 812-4551

September 24, 2018

File No. 27216114.00

Offices Nationwide www.scsengineers.com

H y d r o g e o l o g i c a n d G e o t e c h n i c a l R e p o r t , R e v . 2

U P P E R S O U T H W E S T A R K A N S A S R E G I O N A L S O L I D W A S T E M A N A G E M E N T D I S T R I C T C L A S S 1 L A N D F I L L

H Y D R O G E O L O G I C A N D G E O T E C H N I C A L I N V E S T I G A T I O N R E P O R T R E V I S I O N 2

M A J O R P E R M I T M O D I F I C A T I O N

Presented To:

U p p e r S o u t h w e s t A r k a n s a s R e g i o n a l S o l i d W a s t e M a n a g e m e n t D i s t r i c t

Nashville, Howard County, Arkansas

Presented From:

S C S E N G I N E E R S 11219 Richardson Drive

North Little Rock, AR 72113 (501) 812-4551

September 24, 2018 File No. 27216114.00

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T a b l e o f C o n t e n t s Section Page

1.0 Introduction .............................................................................................................................................. 1 1.1 Site Background ........................................................................................................................... 1 1.2 Site Location .................................................................................................................................. 1 1.3 Surrounding Land Use ................................................................................................................. 2

2.0 Regional Characterization ................................................................................................................... 2 3.0 Site Characterization ............................................................................................................................ 3

3.1 Aerial Photography Analysis (Reg. 22.102(c)(1)) ................................................................. 4 3.2 Surface Geologic Mapping (Reg. 22.1102(c)(2)) ................................................................. 4 3.3 Surface Geophysical Survey (Reg. 22.1102(c)(3)) ............................................................... 5 3.4 Subsurface Exploration Programs(Reg. 22.1102(c)(4)) ........................................................... 6

3.4.1 Site Boring Program(Reg. 22.1102(c)(4)) .................................................................... 6 3.4.2 Borehole Geophysical Logs (Reg. 22.1102(c)(4)(vi)) ................................................ 7 3.4.3 Geologic Cross Sections (Reg. 22.1102(d)(7) ............................................................ 8

3.5 Geotechnical Testing(Reg. 22.1102(c)(6)) .............................................................................. 9 3.5.1 Sieve Analysis Summary .................................................................................................. 9 3.5.2 Aterberg Limits/Moisture Content Summary ............................................................. 10 3.5.3 Standard Proctor Density Summary/Moisture Density Relationships ................... 10 3.5.4 Hydraulic Conductivity Summary ............................................................................... 11 3.5.5 Soil Classification Summary ......................................................................................... 11 3.5.6 Standard Penetration Test Summary .......................................................................... 11 3.5.7 Suitability For Landfill Uses .......................................................................................... 12

4.0 Hydrogeologic Characterization ...................................................................................................... 13 4.1 Potentiometric surface and Flow Direction (Reg.22.1102(c)(5)(i),(ii)) ............................. 13 4.2 Hydraulic Aquifer Testing(Reg.22.1102(c)(5)(iii)) .............................................................. 14 4.3 Groundwater Flow Velocity (Reg.22.1102(c)(5)(vi)) ......................................................... 16 4.4 Groundwater Chemistry (Reg.22.1102(c)(5)(vii) ................................................................ 16

5.0 Conceptual Hydrogeologic Model (Reg 22.1102(b)(1) and Reg 22.1102(d) ....................... 18 6.0 Proposed Groundwater Monitoring System (Reg 22.1102(b)(3) and Reg 22.1102(d) ...... 19

6.1 Groundwater Protection Program ............................................................................................. 19 6.2 Groundwater Monitoring Program ........................................................................................... 19

7.0 References ............................................................................................................................................. 22

L I S T O F F I G U R E S

F I G U R E 1 a S i t e L o c a t i o n M a p ( G e o l o g i c M a p ) F I G U R E 1 b S i t e L o c a t i o n M a p ( T o p o g r a p h i c M a p ) F I G U R E 2 L a n d f i l l L a y o u t F I G U R E 3 R e g i o n a l G e o l o g i c M a p ( R E M O V E D ) F I G U R E 4 R e g i o n a l T o p o g r a p h y M a p F I G U R E 5 A e r i a l P h o t o g r a p h i c M a p F I G U R E 5 A 1 9 9 0 A e r i a l P h o t o g r a p h i c M a p F I G U R E 5 B 1 9 5 5 A e r i a l P h o t o g r a p h i c M a p F I G U R E 6 S u r f a c e G e o p h y s i c s H o r i z o n t a l D i p o l e F I G U R E 7 S u r f a c e G e o p h y s i c s V e r t i c a l D i p o l e F I G U R E 8 B o r i n g L o c a t i o n ( e x p a n s i o n a r e a ) F I G U R E 9 B o r i n g L o c a t i o n ( S i t e ) F I G U R E 1 0 G e o l o g i c C r o s s S e c t i o n L a y o u t F I G U R E 1 0 a G e o l o g i c C r o s s S e c t i o n A – A ’ F I G U R E 1 0 b G e o l o g i c C r o s s S e c t i o n B - B ’ F I G U R E 1 0 c G e o l o g i c C r o s s S e c t i o n C - C ’ F I G U R E 1 0 d G e o l o g i c C r o s s S e c t i o n D - D ’ F I G U R E 1 1 P o t e n t i o m e t r i c F l o w M a p – F e b r u a r y 2 0 1 7 F I G U R E 1 2 O b s e r v e d W a t e r L e v e l s D u r i n g D r i l l i n g F I G U R E 1 3 C u r r e n t G r o u n d w a t e r M o n i t o r i n g S y s t e m F I G U R E 1 4 P r o p o s e d G r o u n d w a t e r M o n i t o r i n g S y s t e m

L I S T O F A P P E N D I C E S

A P P E N D I X A S u r f a c e G e o p h y s i c a l D a t a A P P E N D I X B P a s t I n v e s t i g a t i o n s a n d B o r i n g L o g s A P P E N D I X C C u r r e n t I n v e s t i g a t i o n a n d B o r i n g L o g s A P P E N D I X D D o w n h o l e G e o p h y s i c a l L o g s A P P E N D I X E O r i g i n a l S i t e C r o s s S e c t i o n s A P P E N D I X F G e o t e c h n i c a l L a b o r a t o r y R e s u l t s A P P E N D I X G A q t e s o l v A n a l y s i s R e s u l t s A P P E N D I X H G r o u n d w a t e r A n a l y t i c a l R e s u l t s

L I S T O F T A B L E S

T A B L E 1 G e o t e c h n i c a l R e s u l t s T A B L E 2 B o r e h o l e W e l l D a t a T A B L E 3 G r o u n d w a t e r E l e v a t i o n s ( F e b r u a r y & J u n e 2 0 1 7 ) T A B L E 4 H i s t o r i c G r o u n d w a t e r E l e v a t i o n s T A B L E 5 A q u i f e r T e s t i n g R e s u l t s T A B L E 6 C a l c u l a t e d H o r i z o n t a l G r a d i e n t s T A B L E 7 G r o u n d w a t e r Q u a l i t y R e s u l t s T A B L E 8 P r o p o s e d G r o u n d w a t e r M o n i t o r i n g S y s t e m


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1 .0 INTRODUCT ION

This hydrogeological and geotechnical report documents the investigation conducted for the proposed Upper Southwest Arkansas Regional Solid Waste Management District (USWSWMD) Class 1 Landfill Major Permit Modification Application. This investigation was designed to meet the requirements of the Arkansas Pollution Control & Ecology Commission (APC&EC) Regulation 22 (Reg. 22), Chapter 11, “Geotechnical and Hydrogeological Investigations.” The investigation also followed the Arkansas Department of Environmental Quality (ADEQ) approved work plan as revised August 2015 (Document ID 70576) and approved by ADEQ on November 22, 2016 (document ID 70640). Specific references to APC&EC Regulation 22 are included within applicable subsection titles of this report.

1 . 1 S I T E B A C K GR OU ND

The USWSWMD owns and operates a Class 1 landfill (Landfill) under ADEQ Solid Waste Permit 0265-S1-R1. The Landfill was permitted under Solid Waste Disposal Permit 265-S1-R1 on August 27, 1993. The original landfill included a total of 305 acres of which 40 acres were designed for a Class 1 landfill. The Annual Engineering and Inspection Report for 2016 prepared by Civil Engineering Associates, LLC indicates that all permitted cells have been constructed. Anticipating the need for additional disposal capacity in the near future, the USWSWMD has prepared a Major Permit Modification Application to expand their Class 1 disposal area and capacity. The proposed expansion will incorporate approximately 43.5 acres located adjacent to the existing operation. Approximately 27 acres of the 43.5-acre expansion will be designed for additional landfill capacity. See Section 1.2 for the location of the existing Landfill and the proposed expansion.

1 . 2 S I T E L OC A T I ON

The USWSWMD is submitting this report for a hydrogeologic and geotechnical characterization associated with an approximate 43.5-acre tract that is located in the south half of the southwest quarter of Section 12 and the north half of Section 13, Township 8 South, Range 27 West, Howard County, Arkansas. The delineation of the proposed expansion tract is shown on FIGURE 1a and FIGURE 1b. It should be noted that of the 43.5-acre tract of land, 27-acres will be utilized for waste disposal. The layout of the existing landfill and the proposed expansion are shown on FIGURE 2.


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1 . 3 S U R R OU N D I N G L A ND U S E

The original permitted area consists of 305 acres. The proposed expansion consists of an adjacent 43.5-acre area. The entire 343.5 acres were previously associated with surface mining of gypsum. The surrounding land use is primarily the continuation of gypsum surface mining and the manufacturing of gypsum related products such as gypsum wall board. Other land uses in the vicinity include private and public land utilized for tree farming. The general layout of the proposed expansion tract is shown on FIGURE 2. Additional details of the surrounding land use, dwellings, and water supplies are provided in other sections of the application for the major modification of the Landfill permit.

2 .0 REGIONAL CHARACTER IZAT ION

Regional and site specific characterization of the original 305-acre permit were provided in the original solid waste permit application material dated April 27, 1993. That original application material included reports from Grubbs, Garner & Hoskyn, Inc. dated August 1990 (Doc. ID 41184) and May 1991 (Doc. ID 41185) as provided in APPENDIX B. Regional geologic, soils, and groundwater information are provided in those reports as summarized below. As discussed in Section 1.0, the proposed site was previously associated with gypsum mining. As such, the area in and around the existing and proposed landfill site drains generally to the north and northwest and is interrupted by mining or existing landfill operations. The gypsum surface mine pits in the vicinity extend from 80 to 100 feet below the original surface contours. The proposed Site is located within the Lower Cretaceous aged Trinity Group. The Trinity Group typically consists of clay, sand, gravel, limestone, gypsum, and celestite. The limestone typically occurs in two beds as follows:

1) The Dierks limestone member near the base and, 2) The DeQueen limestone member near the middle of the formation.

The gravel within the Trinity Group also occurs as two beds: 1) The Pike Gravel member at the base and, 2) The Ultima Thule gravel member (locally absent) above the Dierks limestone. These limestone and gravel members are interbedded with clay and some sand. The three geologic units of significance at the Site are the Paluxy, the DeQueen Limestone, and the Holy Creek (all members of the Trinity Group). The Paluxy consists of variegated clays, cross-bedded sands and gravel. The DeQueen consists of interbedded limestone and dark gray shaley clay with gypsum beds near the base. The underlying Holly Creek consist of clays, cross-bedded sands and some gravel. The regional geologic map obtained from the Arkansas


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Geologic Commission that includes the existing and proposed expansion is provided as FIGURE 3. The Trinity group deposits exposed to the south of the city of DeQueen apparently represent the overlying Paluxy unit. The upper portions of the mined areas are within the lower portion of the Paluxy, and the main body of the mine is within the DeQueen Limestone member. Since the gypsum units are present near the base of the DeQueen Limestone member, the existing gypsum mines extend in depth to just above the Holly Creek deposits. The gypsum beds within the DeQueen Limestone member dip approximately 1.5 degrees to the south. The areas utilized for landfill operations are generally located within excavations remaining after the removal of the gypsum. The DeQueen Limestone member of the Trinity Group generally does not yield substantial water to wells. The underlying predominantly clays of the Holly Creek also do not yield water to wells, unless areas of more permeable sand and gravel are penetrated. The fine-grained sands of the overlying Paluxy member yield moderate supplies to wells in Howard and Sevier Counties. The limited number of residential wells reported in the January 22, 1991 Grubbs, Garner, & Hoskyn, Inc. investigation (Doc. ID 41185) are shallow wells that penetrate sands of the Paluxy member and may not be considered reliable water producers. Deeper wells extended into the underlying Dequeen and Holly Creek members also may not increase water production significantly. The early investigations revealed that soils within the upper Paluxy unit are generally sandy and silty clays (unified soil classification of CL and CH). Soil conditions within the DeQueen Formation consist of interbedded gray clay, gray limestone, and gypsum. Underlying deposits generally consist of basically hard light gray and reddish brown clay with limestone, silt, and clay interbedding. Since the existing and proposed landfill sites are located generally in the mined areas near the base of the DeQueen Limestone member of the Trinity Group where the gypsum occurred, regional geologic conditions restrict the significant occurrences and movement of groundwater.

3 .0 S I TE CHARACTER IZAT ION

The following sections are intended to address the site characterization requirements found in Reg. 22.1102(c). The investigation also followed the ADEQ-approved work plan as revised August 2015 (Document ID 70576). Specific references to APC&EC Regulation 22 are included within applicable subsection titles of this report.


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3 . 1 A ER I A L P H O T O GR A P H Y A NA LY S I S ( R E G . 2 2 . 1 1 0 2 ( C ) ( 1 ) )

In accordance with Section 22.1102(c)(1), aerial photographs of the study area were reviewed to determine fracture traces and orientation, lineaments, sedimentary features, and depositional features. Pre-landfill aerial photographs from 1990 and1955 were utilized for the associated analysis. The 1955 aerial photograph is depicted on FIGURE 5B and the 1990 aerial photograph can be seen on FIGURE 5A. FIGURE 5 provides a more current aerial photograph (2014) of the proposed landfill expansion. During the aerial photograph analysis of the study area, no additional lineaments, fracture traces, sedimentary or depositional features were observed within the expansion area. The 1950 aerial photograph shows that, prior to landfilling and mining activates, the site was undeveloped wooded land.

3 . 2 S U R FA C E G E OLO GI C MA P P I N G ( R E G . 2 2 . 1 1 0 2 ( C ) ( 2 ) )

In accordance with Section 22.1102(c)(2), surface geologic mapping that includes surface stratigraphy, structural features, locations of springs and seeps, and domestic, agricultural, and municipal water wells was performed within a one-half mile radius of the proposed Landfill expansion as part of the original permit application. Previous reports discussing these features are provided in APPENDIX B. Updated surface geologic mapping including the above-listed features was also performed as part of the permit modification application. The current investigation included researching records from the Arkansas Water Well Commission, reviewing aerial photographs, and interviewing property owners within one-half mile of the landfill property boundary and the proposed expansion area boundary. A door-to-door well survey was also performed, which identified no water wells within 0.5 miles of the landfill property (current and proposed boundaries). Information obtained during the current investigation is depicted in Figure 1a and Figure 1b and provided in APPENDIX C. As discussed previously, the proposed expansion is located in the DeQueen Limestone member of the Trinity Group of Lower Cretaceous Age. The existing Landfill and the proposed expansion are generally located in areas where gypsum was previously removed, leaving an excavation extending to the base of the DeQueen Limestone member. The upper portions of the mined areas are within the lower portion of the Paluxy member, and the main body of the mine is within the DeQueen Limestone member of the Trinity Group. Since the gypsum units are present near the base of the DeQueen Limestone, the existing gypsum mines extended in depth to just above the Holly Creek deposits. The geologic map obtained from the Arkansas Geologic Commission that depicts the existing Landfill and the proposed expansion is included as FIGURE 1a and FIGURE 3. More detailed surface mapping on the applicable geologic worksheets are provided in earlier geologic investigations (see APPENDIX B).


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3 . 3 S U R FA C E G E OP H Y S I C A L S U R V EY ( R E G . 2 2 . 1 1 0 2 ( C ) ( 3 ) )

Under section 22.1102(c)(3) of APC&EC Regulation 22, a surface geophysical study must be conducted across the proposed expansion area utilizing at least one of the methods identified in the regulations. In order to fulfill the geophysical requirements outlined in the regulation, SCS conducted an Electromagnetic (EM) Induction geophysical survey on the approximately 27 acres of the 43.5-acre expansion area that are to be utilized for actual waste disposal. The Geonics EM-31 instrument was utilized for the required surface geophysical investigation. The EM-31 consists of a transmitter coil mounted at one end and a receiver coil mounted at the other end of a 3.7 meter long plastic boom. The transmitting coil outputs a primary electromagnetic field, which induces a secondary field in the ground. The receiving coil measures the magnitude of the secondary field (quadrature component) and the ratio between primary and secondary fields (in-phase component). Electrical conductivity [in millisiemens per meter (mS/m)], and in-phase field strength [in-phase ratio of the secondary to primary magnetic field, in parts per thousand (ppt)] are measured and stored along with line and station numbers in a digital data logger. Electromagnetic surface geophysical techniques provide information about the materials, such as clay, and or saturated conditions in the subsurface. Low conductivity readings can be the result of limestone, chert, or possible subsurface voids. The horizontal and vertical dipole readings were between 40 to 70 and 50 to 90 millisiems per meter (mS/M) with only one reading outside this range for both orientations (106.70 HD, 107.45 VD). There are several higher or lower single point readings that vary by 10 to 20 mS/M from the surrounding points. These would be considered to be anomalies caused by cultural interference or variations in the mine spoil material such as boulders, or perched water to name a few. The vertical dipole readings are believed to be higher than the horizontal dipole since the depth of measurement is greater were saturated conditions exist. When combined with additional geohydrologic data, such as data obtained from test borings, this method provides a possible means for defining possible subsurface conditions such as:

• Vertical and horizontal extent of clay and/or sand layers; • The depth of the overburden bedrock interface; • Possible “anomalies” in the subsurface.

The objective of the surface conductivity investigation is to determine a correlation between different soil and rock combinations and their associated conductivity values. Once this correlation is made, subsurface conditions can be more thoroughly characterized because the spacing of data points is closer in the surface geophysical survey than in the drilling program. In addition, the boring locations can be focused to areas that reported anomalous conductivity readings in order to characterize the conditions at these anomalies.


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During the surface conductivity survey, readings were taken at approximately every 100 feet across the 27-acre area (see FIGURE 6, FIGURE 7, and APPENDIX A). The spacing yielded a total of 118 nodes or locations to obtain conductivity readings. All surface geophysical data points were located utilizing a hand-held Global Positioning System (GPS). This provided more exact feature location information that will be accurately applied to the landfill design and future boring locations. A conductivity measurement was taken in both the horizontal dipole position (FIGURE 6) and the vertical dipole position (FIGURE 7) at each of the grid points. The EM-31 data is collected at an intercoil spacing of 3.7 meters in both the vertical and the horizontal dipole configurations. The effective penetration depths of the intercoil spacing are 6 meters in the HD configuration and 3 meters in the VD configurations. The EM-31 instrument is most responsive to the near-surface conditions in the HD configuration and to conditions at one-half the coil separation in the VD configuration. The data obtained from the survey was then placed in a computer contouring program (Surfer for Windows from Golden Systems, Inc.) and terrain conductivity maps were generated for the selected coil spacing. The data is included in APPENDIX A. Terrain conductivity maps for horizontal and vertical dipole positions are provided in FIGURE 6 and FIGURE 7. Surface Conductivity Observations The recorded data at each measurement point for each of the dipoles (VD and HD) are presented in APPENDIX A. No unusual geophysical anomalies that could not be attributed to previous mining activities were identified during the surface geophysical analysis.

3 . 4 S U B S U R FA C E EX P L OR A T I O N P R O GR A MS ( R E G . 2 2 . 1 1 0 2 ( C ) ( 4 ) )

Reg 22.1102(c)(4) requires a subsurface exploration program utilizing borings and test pits. The minimum required spacing for borings is one boring per five acres. The intrusive portion of the site characterization was performed by utilizing borings. The locations of these borings are depicted on FIGURE 8. Geologic and hydrogeologic data that has previously been collected from the USWSWMD Landfill site will be utilized to supplement the existing conceptual hydrogeologic model of the landfill as required by Reg22.1102 (b)(1). Lithologic logs and geotechnical results from previous borings and/or test pits are provided in APPENDIX B. 3 . 4 . 1 S i t e B o r i n g P r o g r a m ( R e g . 2 2 . 1 1 0 2 ( c ) ( 4 ) )

Reg. 22.1102 (c)(4) requires a minimum spacing of one (1) boring per five (5) acres of landfill expansion. The proposed lateral expansion area covers approximately 43.5 acres resulting in a requirement of at least nine (9) exploratory borings to satisfy the Regulation 22 spacing requirement. There are currently three (3) existing piezometers (B-4, B-5, and B-6R) located


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within the 43.5-acre expansion area, therefore, only six (6) additional borings are needed to satisfy the Regulation 22 spacing requirement. However, ten (10) additional borings (PZ-1 through PZ-6, NPZ-1 and NPZ-2, and SB-1 and SB-2) were advanced as part of this investigation. FIGURE 9 provides current and past boring and monitoring well locations for the entire site. TABLE 2 provides additional information concerning on-site borings. The drilling contractor for the current subsurface portion of the investigation was Anderson Engineering of Little Rock, Arkansas. A buggy mounted CME-55 drill rig was utilized to advance the borings. A SCS geologist logged the borings and directed piezometer installation. As depicted in FIGURE 8, the 27-acre expansion was divided into a 250 foot by 250-foot grid. The borings were equally spaced across the 43.5-acre expansion area, with the exception of two (2) temporary piezometers. These two (2) piezometers (NPZ-1 and NPZ-2) were advanced as nested piezometers and utilized in aquifer testing. NPZ-1 was located approximately 50 feet west of PZ-3, and NPZ-2 was located approximately 100 feet west of PZ-3. These wells were screened within different zones of the formation. It should be noted that all existing onsite piezometers were utilized in the determination of groundwater flow direction. During the drilling of the borings, the information required by Reg. 22.1102(c)(4)(i)-(v) was obtained and is provided on the boring logs in APPENDIX C. Standard Penetration Tests (SPT) were performed at 5-foot intervals to a minimum depth of 20 feet as per Reg. 22.1102(c)(6)(i). Continuous soil coring was performed to the top of bedrock or auger refusal. An attempt to determine depth to bedrock was made as per Reg. 22.102(c)(4)(ii) and the approved workplan at PZ-3 during this investigation. Auger refusal during the advancement of PZ-3 was at 64 feet below ground surface (bgs). TABLE 2 depicts the well depth information. Piezometers were installed in all boreholes. The piezometer construction consisted of a 2-inch diameter Schedule 40 PVC solid riser and ten feet of 0.010 inch slotted screen (with the exception of a 30 foot screen in PZ-3 and a 5 foot screen in PZ-1). The sand filter pack extends to two feet above the screened interval. A three foot bentonite pellet seal was placed immediately above the filter pack. After placement of the bentonite seal, the pellets were allowed to hydrate prior to the placement of the remaining bentonite seal to the surface. The depth of sand or bentonite was measured with a cloth tape as the material was added to the borehole to insure that bridging did not occur within any portion of the borehole. All piezometers were surveyed after completion. See APPENDIX C for actual boring logs and piezometer construction details. 3 . 4 . 2 B o r e h o l e G e o p h y s i c a l L o g s ( R e g . 2 2 . 1 1 0 2 ( c ) ( 4 ) ( v i ) )

In accordance with Reg. 22.1102(c)(4)(vi), borehole geophysical logging was performed within select boreholes on site. More specifically, downhole geophysical logs obtained from the


8

boreholes included natural gamma and induced resistivity, and conductivity. Because the majority of boreholes were not saturated, the type of geophysical logging that is possible is limited. These logging methods were also selected for their ability to be utilized in cased boreholes. Previous investigations at the site have found that these type of geophysical logs will provide information to be utilized in the interpretation of the subsurface conditions. Each piezometer was completed and the borehole logs were performed within the constructed 2 inch PVC casing to avoid logging in an open borehole. Borehole geophysical logs were conducted in borings PZ-1 through PZ-6 and NPZ-1 and NPZ-2. The hydrologic objectives of borehole geophysical logging include:

• correlation and definition of aquifer or other lithologic (or soil) units, • estimation of aquifer properties such as porosity and permeability, and • an assessment of physical properties associated with the materials surrounding the

borehole Natural gamma logs are records of the amount of natural gamma radiation that is emitted from all soils and rocks. The main use of this method in the current study is for the identification of lithology and stratigraphic correlation in cased, liquid filled, holes. The main gamma emitting isotope normally found in sediments and rocks is potassium-40. Potassium, which contains about 0.012 percent potassium-40, is abundant in feldspars and micas which decompose readily to clay. Probably the most important application in groundwater hydrology is in the identification of clay or shale bearing sediments. The second type of borehole geophysics used in this investigation was a combination borehole conductivity/resistivity. This instrument records the conductivity/resistivity of the sediments surrounding the borehole in both the saturated and vadose zones. The basic principle is that the higher the conductivity, the higher the clay and water content. This log also assists the interpretation of the natural gamma logs. The results of the borehole geophysical logs are presented in APPENDIX D. 3 . 4 . 3 G e o l o g i c C r o s s S e c t i o n s ( R e g . 2 2 . 1 1 0 2 ( d ) ( 7 ) )

During the previous investigations at the site, one generalized cross section was created for the originally permitted Landfill site. (See APPENDIX E for previous investigation cross section). In addition to the historical cross section, SCS produced four (4) additional cross sections across the proposed site expansion (see FIGURE 10a, FIGURE 10b, FIGURE 10c, and FIGURE 10d). Cross Section A-A’ (FIGURE 10a) traverses the proposed expansion area from north to south. Cross Section B-B’ (FIGURE 10b) traverses the proposed expansion area from west to east. Cross Section C-C’ (FIGURE 10c) traverses the proposed expansion area from northeast to southeast. Cross Section D-D’ (FIGURE 10d) traverses the east portion of the proposed


9

expansion area from South to north. FIGURE 10 depicts the cross section layout from this investigation. As required by Reg. 22.1102(d)(7)(i)-(vii) the following information is included on the Geologic Cross Sections:

• Site stratigraphy • Maximum proposed depth of excavation for the landfill expansion • Water table and/or potentiometric surface • Lithologic logs with physical properties test results • Geophysical logs of boreholes • Screened intervals • Aquifer test results

The uppermost aquifer across the proposed expansion area was found to be under confined groundwater conditions. The static water levels observed in the borings and piezometers were (in some cases) above the top of the uppermost aquifer. The depth that groundwater was first observed during drilling is depicted on FIGURES 10a, 10b, 10c, and 10d. Groundwater levels for February 2017 are also shown on the cross sections. The maximum depth of excavation as shown on the cross sections is greater than 5 feet above the bedrock and the groundwater table at all locations as required by Reg. 22.431(c)&(d).

3 . 5 G E O T EC H N I C A L T E S T I N G ( R EG . 2 2 . 1 1 0 2 ( C ) ( 6 ) )

In order to characterize the proposed expansion area in terms of geotechnical properties, samples were collected from the boreholes drilled during this investigation. Anderson Engineering was contracted to analyze the material in the lab to gain information on the engineering properties within the proposed expansion area. The purpose of the geotechnical study was to evaluate subsurface conditions in general accordance with the geotechnical criteria described in Regulation 22 Chapter 11. The results of the current geotechnical investigation for the proposed Class 1 Landfill Expansion are included in APPENDIX F. TABLE 1 of this report summarizes key results from the current geotechnical investigation. Past geotechnical investigations are provided in APPENDIX B.

3 . 5 . 1 S i e v e A n a l y s i s S u m m a r y

Particle size analyses were conducted on various soils at various locations and depths for the purpose of analyzing grain size distribution and classification associated with soils native to the area (as per ASTM D- 1140 &d-422). The results of these tests are included in APPENDIX F of this document. Past sieve analysis results from previous studies are provided in APPENDIX B.


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In the sieve analysis, a series of sieves (screens) having different sized openings are stacked with the larger sizes over the smaller. The soil sample being tested is dried, clumps are broken, and the sample is passed through the series of sieves by shaking. Larger particles are caught on the upper sieves, and the smaller particles filter through to be caught on one of the smaller underlying sieves. The weight of material retained on each sieve is conventionally presented as a grain or particle size distribution curve plotted as semilog coordinates. A hydrometer analysis is used to characterize the fines in a sample or that fraction smaller than a #200 sieve. The appearance of the particle size distribution plot depends on the range and amounts of various sizes of particles in the soil sample. These in turn have been affected by the soil's origin or the method of deposition. Well graded soils (a distribution of particles over a relatively large range of sizes) produce a long straight curve. A uniform soil will plot showing most of the particles of approximately similar size. The grain size plots can provide an indication of a soils history. See APPENDIX F for the current investigation grain size plots. 3 . 5 . 2 A t t e r b e r g L i m i t s / M o i s t u r e C o n t e n t S u m m a r y

In the remolded state, the consistency of clay soil varies in proportion to the water content. At higher water content, the soil-water mixture possesses the properties of a liquid. At lesser water contents a soil-water mixture possesses properties that resemble a plastic. At still lesser water contents, soil-water mixtures approach a solid or semi-solid state. The water content indicating the division between the liquid and plastic state has been designated as the Liquid Limit. The division between the plastic and semi-solid state is referred to as the Plastic Limit. The numerical difference between the Liquid Limit and the Plastic Limit is identified as the Plasticity Index. These values are often referred to as Atterberg Limits. The Atterberg Limits test (ASTM D-4318) is used to obtain basic index information on soils and is used to estimate strength, settlement, and workability characteristics. It is the primary form of classification for cohesive soils properties commonly used in the construction of landfill liner systems. In general, on-site clays determined to have Plasticity Indices greater than 10 can be considered for use in the construction of clay liner systems. The Atterberg Limits results are presented in APPENDIX F. Past Atterberg Limits analysis are presented in APPENDIX B. 3 . 5 . 3 S t a n d a r d P r o c t o r D e n s i t y S u m m a r y / M o i s t u r e D e n s i t y R e l a t i o n s h i p s

Standard Proctor density tests were performed on samples taken during the investigation in order to better classify the geotechnical properties of the soils on-site. Samples were obtained from soils within the study area to determine their suitability in the construction of the clay liner system. Samples were obtained and analyzed by Anderson Engineering Consultants, Inc. for determining the moisture-density relationship as defined in ASTM D698 and D1557. Based on Standard Proctor analyses taken from composite samples at a depth of 3 foot to 10 foot, it is


1 1

anticipated that the optimum moisture content will be approximately 16.4% with a maximum dry density of approximately 109.8 pounds per cubic foot (pcf). Based on Standard Proctor analysis taken from composite samples from depths of 16 feet to 20 feet, it is anticipated that the optimum moisture content will be approximately 18.8% with a maximum dry density of approximately 103.4 pounds per cubic foot (pcf). Standard proctor results are presented in APPENDIX F.

3 . 5 . 4 H y d r a u l i c C o n d u c t i v i t y S u m m a r y

Hydraulic conductivity of in-situ soils was evaluated by a total of six (6) permeability tests on representative soil samples from on-site borings. Results of these samples are presented in APPENDIX F. All tests were completed using flexible wall parameter methods in accordance with ASTM D-5084. The values from the tests ranged from 1.12X10-5 to 2.2X10-9. See TABLE 1 and APPENDIX F). 3 . 5 . 5 S o i l C l a s s i f i c a t i o n S u m m a r y

The Unified Soil Classification System is widely used in engineering and construction applications. Classifications are on the basis of coarse and fine grained soils and are categorized based on laboratory tests, including the grain size distribution analysis and Atterberg Limits. In general, the following soil classifications were identified on site in the vicinity of the proposed expansion area. CL: Inorganic clays of low to medium plasticity (lean clays); In general, the onsite soils were classified as CL clays. The CL clayey soils were identified in both samples to a depth of 20 ft. The clays were identified as light grayish brown, brown and to reddish brown clays with some sand at depth. See APPENDIX F for current soil classification information and APPENDIX B for past soil classification information.

3 . 5 . 6 S t a n d a r d P e n e t r a t i o n T e s t S u m m a r y

Standard penetration tests were conducted on overburden soils in the borings drilled within the proposed expansion area. The boring logs are located in APPENDIX C, note the “field” blow counts associated with the standard penetration test analyses in the “blows per ft” column of the logs.


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3 . 5 . 7 S U I T A B I L I T Y F O R L A N D F I L L U S E S

There are liner quality soils that meet the requirements of Regulation §22.428 (b) located on the site. The results of all current geotechnical testing is provided in APPENDIX F.


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4 .0 HYDROGEOLOGIC CHARACTER IZAT ION

Reg. 22.1102(c)(5) requires the hydrogeology of the proposed expansion to be explored through the installation of piezometers. The required information to be obtained is presented in the following sections.

4 . 1 P OT E NT I O M ETR I C S U R FA C E A N D F L OW D I R EC T I O N ( R E G . 2 2 . 1 1 0 2 ( C ) ( 5 ) ( I ) , ( I I ) )

The current groundwater monitoring system consists of sampling the underdrain for groundwater monitoring, however, there are fifteen (15) piezometers that are located around the landfill area and are utilized for groundwater elevations (See FIGURE 13). The underdrain is currently sampled on a semi-annual basis, therefore groundwater elevations at the piezometers are obtained twice a year. In addition, a potentiometric flow map is produced upon completion of each semi-annual groundwater sampling event. During the current investigation, piezometers were installed within eight new borings to allow the gathering of additional information relative to the groundwater flow in the proposed landfill expansion area. All of the piezometers were screened within the uppermost saturated zone. Attributes for each of these piezometers are listed in TABLE 2. The current well construction diagrams are presented in APPENDIX C. Each of these piezometers have two-inch diameter PVC casings. Groundwater levels were measured in all the wells at the USWSWMD Landfill in February 2017. Groundwater level elevations from February are listed in TABLE 3. A groundwater flow map of the site (FIGURE 11) was constructed utilizing the February 2017 groundwater levels. FIGURE 11 also shows the potentiometric surface within the expansion area utilizing the February 2017 water levels. Previous studies by Grubbs, Garner, & Hoskyn, Inc., have indicated that water is not considered to be naturally occurring groundwater, but is related to rainfall saturation of the mining fill material. It is believed that groundwater flow within the fill is located at varying depths and thicknesses across the expansion area and that the majority of groundwater flow is within the fill material. Based upon the data collected during the investigation, groundwater flow is primarily from the southeast to the northwest. According to APC&EC Reg. 22.431(c), a minimum separation of 5 feet must be maintained between the top of the landfill liner system and the seasonal high water table surface. As previously discussed in Sections 3.6.1.2 and 3.6.3, the uppermost aquifer across the proposed expansion area was found to be under confined groundwater conditions. The static water levels observed in the borings and piezometers were (in some cases) above the top of the uppermost


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aquifer. The five foot separation distance was measured from the top of saturation (first observance of wet samples), not the static water level. For example, boring PZ-2 was advanced to 22 feet bgs before it was described as wet. However, a static water level of 13.39 feet bgs was recorded on February 21, 2017. In this particular location, ADEQ advanced a test pit (TP-2) to 14 feet which remained dry after remaining open for an hour. Therefore, in this location, an excavation can be advanced to 17 feet bgs (5 feet above the top of saturation) and not encounter groundwater, assuming that the five foot of clay above the aquifer has sufficient density to overcome potentiometric pressure of the aquifer. TABLE 4 provides historic groundwater elevations taken semi-annually from the on-site piezometers installed prior to the current investigation. 4 . 2 H Y D R A U L I C A QU I F ER T ES T I NG ( R EG . 2 2 . 1 1 0 2 ( C ) ( 5 ) ( I I I ) )

Aquifer testing was performed during the current investigation as required by regulation §22.1102(c) to determine:

• Hydraulic conductivity as required by Reg. 22.1102(c)(5)(iii ) • Vertical and Horizontal Gradients as required by Reg. 22.1102(c)(5)(iv) • Hydraulic communications as required by Reg. 22.1102(c)(5)(v)

Slug tests were performed in the newly-installed 8 piezometers (PZ-1 through PZ-6, and NPZ-1 and NPZ-2) and 3 existing wells (B-4, B-5, and B-6R) located within the proposed expansion area. The falling head tests were performed by lowering a slug into the well and measuring the initial rise in water level followed by the gradual fall in water level to pre-slug conditions. The rising head tests were performed by removing the slug and measuring the initial fall in water level followed by the gradual rise in water level to pre-slug conditions. The slug test data were analyzed using the Bouwer-Rice method for unconfined aquifers. Data analysis was performed using the computer program AQTESOLV. Analysis graphs are included in APPENDIX G. Of the 8 piezometers where slug tests were performed, all were screened within clay mine spoils or fill. Since borings B-4, B-5 and B-6R are located in naturally-occurring stratigraphy and not mine spoils or fill material, hydraulic conductivity in these borings is not compared with that of the piezometers or included in the calculation of the average groundwater velocity. As presented on TABLE 5, the hydraulic conductivity (K values) in the piezometers ranged from 1.859X10-5 ft/min (9.443X10-6 cm/sec) to 1.03X10-2 ft/min (6.116X10-3 cm/sec). As described above, a falling head (slug-in) and raising head (slug out) test was performed at each of the piezometers locations. The difference in the calculated K values between the slug in and slug out tests varied from piezometer to piezometer. The mean K value between the two tests (slug in/slug out) at each location is presented in TABLE 5.


1 5

An aquifer pumping test with observation wells was performed on May 10, 2017 within the proposed expansion area. A step drawdown test on the pumping well was utilized to determine the appropriate pumping rate for the pumping test. The drawdown test required a constant pumping of the pumping well for an approximate 24-hour period. The drawdown was recorded in the pumping well during the test in order to determine the appropriate pumping rate to be utilized during the pumping test. During the test, piezometer PZ-3 was pumped for 5 hours at an average flow rate of approximately 2.5 gallons per minute (gpm). Groundwater levels were monitored in two wells surrounding PZ-3 (NPZ-1 and NPZ-2). PZ-3 contained a pressure transducer with data logger while the remaining piezometers were monitored manually with an electronic water level tape. The amount of drawdown measured in the well closest to PZ-3 at the end of the pumping period was 7.60 ft. It should be noted that the pumping of PZ-3 negligibly impacted groundwater levels within NPZ-2. Field boring logs with well construction information for all of the monitored wells are presented in APPENDIX C. Groundwater Pump Test drawdown curves for piezometers NPZ-1 and NPZ-2 were analyzed using the Theis method for confined aquifers. Assuming an aquifer thickness of 45 feet (approximate depth of PZ-3 below groundwater surface) the results of the analyses determined a calculated transmissivity of 3.5X10-3 ft2/min. The calculated hydraulic conductivity was 3.921X10-5 ft/min. The calculated hydraulic conductivity based on the slug test was 2.858X10-3 ft/min for PZ-3. Therefore, there is greater than an order of magnitude difference between pumping test results (which are considered more accurate) and the slug test results described previously. Aquifer test calculations are presented in APPENDIX G. Groundwater elevations, as shown in TABLE 3 measured in February 2017 were used to calculate horizontal gradients across the proposed Landfill expansion. The horizontal hydraulic gradient beneath the expansion area was calculated by taking the hydraulic head difference between PZ-4 and PZ-2 (31.69 feet) and dividing by the distance between the wells perpendicular to the groundwater elevation contour lines (845 feet). This calculation indicates a hydraulic gradient of 0.038 for the expansion area. TABLE 6 shows the calculated horizontal gradients for the expansion area. The vertical gradient was determined between nested piezometers PZ-3 and NPZ-2 by dividing the hydraulic head difference between the piezometers (2.17 feet) by the vertical distance between the median depth of PZ-3 and NPZ-2 (18.78). The vertical gradient was determined to be 0.116 in an upward direction.


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4 . 3 G R OU ND W A T ER F L OW V E L OC I TY ( R E G . 2 2 . 1 1 0 2 ( C ) ( 5 ) ( V I ) )

It should be noted that groundwater was encountered within the previously mined fill and spoil areas. Previous studies by Grubbs, Garner, & Hoskyn, Inc., have indicated that water is not considered to be naturally occurring groundwater, but is related to rainfall saturation of this fill related material. The uppermost aquifer, encountered at a depth of approximately 4.9 feet below ground surface to 22.08 feet b e l o w g r o u n d s u r f a c e at its maximum thickness, flows in a sou theas t to northwesterly direction. The average hydraulic gradient was calculated to be 0.0103. Based on a hydraulic conductivity range from 20.88 to 0.027 ft/day and an effective porosity of 0.20, the calculated average flow rate is between 1.08 and 1.39x10-3 ft/day. Based on the hydraulic conductivity determined from the pumping test (0.11 ft/day) and an effective porosity of 0.20, the calculated flow rate is 5.7x10-3 ft/day. These calculations are based on an assumed effective porosity that is a default value obtained from the Data Collection Handbook to Support Modeling the Impacts of Radioactive Material in Soil by C. Yu, C. Loureiro,* J.-J. Cheng, L.G. Jones, Y.Y. Wang, Y.P. Chia,* and E. Faillace, April 1993. The actual effective porosity may vary.

4 . 4 G R OU ND W A T ER C H E M I S TR Y ( R EG . 2 2 . 1 1 0 2 ( C ) ( 5 ) ( V I I ) )

Prior to this investigation there were fifteen (15) piezometers surrounding the landfill that were utilized for water level measurements only. In accordance with the current facility permit, the underdrains are currently the only sampling points utilized for groundwater quality monitoring. These underdrains are designated as N-UD for the north under drain and S-UD for the south underdrain. The location of each sampling point is depicted on FIGURE 13. Groundwater monitoring for the underdrains is performed semi-annually each June and December. For a detailed discussion of groundwater quality from these underdrains, refer to the semi-annual groundwater monitoring reports. The most recent groundwater sampling report “Second Half 2016 Groundwater Monitoring Report” (Terracon 2016) documents sampling conducted December 13, 2016. In accordance with the ADEQ request in document no. 69665, and since previous groundwater monitoring at the facility primarily included sampling only the underdrain at the landfill, the newly installed piezometers were sampled to determine the ambient groundwater chemistry in the proposed expansion area as required by Reg22.1102(c)(5)(vii). It should be noted that a strong sulfur odor was noted within the majority of the piezometers. The chemical decomposition of gypsum can result in production of free sulfur. TABLE 7 depicts the groundwater monitoring quality results within the newly installed piezometers. Laboratory analysis was conducted by Environmental Science Corporation in Mt. Juliet, Tennessee. The laboratory analytical results and a copy of the Chain-of-Custody are included in APPENDIX H.


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The Primary Drinking Water Standard-MCLs were exceeded for Arsenic at PZ-5 during the sampling of the newly installed piezometers. It should be noted that Arsenic is a common laboratory contaminate. None of the Regulation 22 Appendix 1 Volatile Organic Compounds (VOCs) were detected during the sampling of the newly installed piezometers.


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5 .0 CONCEPTUAL HYDROGEOLOGIC MODEL (REG. 22 .1102(B ) (1 ) AND REG. 22 .1102(D) )

Regulation 22.1102(b)(1) requires all individual studies to be integrated into a comprehensive hydrogeologic model and summarized in the written report. The recommended groundwater monitoring points must be proposed and the locations based upon the site hydrogeologic model and the facility design. SECTIONS 1.0 through 4.0 of this document constitute the details of the current individual studies conducted in support of the proposed landfill expansion at the USWSWMD Landfill. SECTION 6.0 of this document provides the details of the proposed groundwater monitoring system for the USWSWMD Landfill expansion. The findings of this investigation and previous investigations confirm the presence of the Paluxy, the DeQueen Limestone, and the Holy Creek members of the Trinity Group. The Paluxy member consists of variegated clays, cross-bedded sands and gravel. The DeQueen Limestone member consists of interbedded limestone and dark gray shaley clay with gypsum beds near the base. The underlying Holly Creek member consist of clays, cross-bedded sands and some gravel. As previously stated, the majority of the landfill expansion area lies within the mine spoils from the previously mined DeQueen Limestone member of the Trinity Group. The current conceptual hydrogeological model is based on the most current information as presented on the cross sections FIGURES 10a-10d. The westernmost area of the proposed landfill expansion (where piezometers PZ-1 through PZ-6 and NPZ-1 and NPZ-2 are located) have been mined-out leaving only a thin layer of DeQueen Limestone member deposits below the lowest gypsum bed. Below the base of the DeQueen Limestone are the Holly Creek deposits. The mine spoil consists of light gray and dark gray clay to gravel to boulder size limestone and gypsum fragments. This mine spoil makes up the majority of the geologic material present in the hydrogeologic model. Based on field observation, groundwater was typically found within the mine spoils. This groundwater is not believed to be naturally occurring groundwater, but is considered to be rainfall saturation of the mining spoil material. It should be noted that during aquifer testing, the piezometers were pumped continuously and did not go dry, indicating a large saturated area. The easternmost area to the south runs along the high wall of the old mine area. SB-1 and SB-2 were advanced within this area which is considered to be outside of the old mining spoil influences. These borings consisted of clays and silty clays from the Paluxy member of the Trinity Group. This area will primarily be utilized as borrow material.


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6 .0 PROPOSED GROUNDWATER MONITOR ING SYSTEM

(REG 22 .1102(B ) (3 ) AND REG 22 .1102(D)

The required elements of a detection monitoring program are detailed in APC&EC Regulation 22 (Chapter 12). A properly installed and maintained groundwater monitoring system can provide a high level of confidence as to the performance of the landfill liner system integrity. However, a groundwater-monitoring network represents the “fail-safes” built into a solid waste landfill designed to meet Regulation 22 standards with protection of the environment as a primary goal. The primary means of groundwater protection is the engineered control and operational systems included in the permit documents and implemented in the field. Upon closure, an engineered final cover prevents direct contact to the waste and inhibits infiltration of precipitation.

6 . 1 GR O U ND WA T ER P R O T EC T I O N P R OGR A M

The landfill liner system serves as the primary groundwater protection program and will be constructed with various components which work together to provide a level of groundwater protection to meet the requirements of Regulation 22. The groundwater monitoring program proposed in the following sections insures that any release from the Landfill will be detected and addressed before potential groundwater receptors are impacted.

6 . 2 GR O U ND WA T ER M ON I T OR I N G P R OGR A M

As provided in APC&EC Reg. 22.1201(a) and (d), a groundwater monitoring system must be installed that consists of a sufficient number of wells, installed at appropriate locations and depths, to yield groundwater samples from the uppermost aquifer that: 1) represent the quality of background groundwater that has not been affected by leakage from a unit and 2) represent the quality of groundwater passing the relevant point of compliance. As previously discussed, the current groundwater monitoring system for the USWSWMD Landfill consists of fifteen (15) piezometers surrounding the landfill that were utilized for water level measurements only. The underdrains are currently the only sampling points utilized for groundwater quality monitoring. Groundwater monitoring from the underdrains is performed semi-annually each June and December. These underdrains are designated as N-UD for the north under drain and S-UD for the south underdrain. The location of each sampling point is depicted on FIGURE 13. It should be noted that under the current Permit (0265-S1-R1) the facility must maintain a positive inward gradient and if the groundwater underdrain system does not function as it is designed, the ADEQ may require revision of the system or an alternative monitoring system. A letter from ADEQ dated March 3, 2016 (Doc. 69007) stated that “the facility has submitted groundwater


2 0

elevations with potentiometric surface maps from four (4) groundwater monitoring events. Each of the submittals shows that the facility is not maintaining a positive inward hydraulic gradient.” The proposed groundwater monitoring system to be utilized for both the existing landfill and the proposed lateral expansion will consist of a series of existing and new groundwater monitoring wells designed to address the current site comprehensive hydrogeologic model. Specific details of the proposed groundwater monitoring system were designed to monitor the proposed expansion area and to add to the site-wide monitoring program. The proposed site wide monitoring program is shown on FIGURE 14 and described as follows:

1. The existing underdrains (N-UD and S-UD) will continue to be monitored. 2. Existing piezometers B-5, B-6R, B-9R, B-11, B-12, and B-13 will be utilized as

groundwater sampling points.

3. As stated in the workplan submitted to ADEQ (doc. 71635), B-7 and B-8 are located just west of the property boundary in a low lying area that frequently floods. These piezometers are to be plugged and abandoned because they are a potential avenue to impact groundwater. Existing Boring B-8 will be replaced (B-8R) and utilized as a groundwater sampling point. The location for proposed replacement boring B-8R is approximately 500 feet due south of its current location.

4. B-15 is proposed as a groundwater sampling point located due south of the existing

location of B-7. The location of B-15 is in response to ADEQ document number 71635 dated May 1, 2017.

5. The downgradient point of compliance in a northeasterly direction will be expanded by

adding four (4) additional wells to the monitoring system designated MW-1, MW-2, MW-3, and MW-4.

The proposed monitoring system would therefore consist of N-UD, S-UD, B-5, B-6R, B-8R, B-9R, B-11, B-12, B-13, B-15, MW-1, MW-2, MW-3, MW-4 and the monitoring of leachate. B-1, B-2, B-3, B-4, B-10R, B-14, and C-1R will be utilized for water level determination only. Monitoring wells MW-1, MW-3, MW-4, B-8R, and B-9R are considered up-gradient wells. MW-2, MW-3, MW-4, B-8R, B-12, B-13, and B-15, are downgradient monitoring wells. See TABLE 8 for a listing of the proposed monitoring points and FIGURE 14 for the location of monitoring points.


2 1

The groundwater samples will be collected according to the approved Groundwater Sampling and Analysis Plan (GWSAP) for the facility. A proposed GWSAP for the new monitoring system will be submitted to ADEQ for approval once the final permit has been issued. The permanent groundwater monitoring wells will be subject to the strict sampling, testing and reporting requirements of Regulation 22 and the final permit. Four rounds of background data will be collected for Appendix I parameters in accordance with Reg. 22 22.1203 (e). Additional sampling events may be required prior to the first statistical evaluation. As previously stated, a GWSAP will be submitted to ADEQ for approval once the final permit has been issued. The GWSAP will include the requirements for detection monitoring and any required reporting for verified SSI’s and subsequent testing programs. The monitoring program will include semi-annual sampling of Appendix 1 parameters. The groundwater monitoring system will follow all aspects of Regulation 22 and be certified by an Arkansas Registered Professional Geologist experienced with the installation of groundwater monitoring systems at Arkansas landfills. The certification will be placed in the facility permanent operating record and notification provided to the Director of the ADEQ as specified in ADEQ Reg. 22. 22.1202(e).


2 2

7 .0 REFERENCES

ASTM D4044-96. Standard Test Method (Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining Hydraulic Properties of Aquifers. ASTM D4050-96. Standard Test Method (Field Procedure) for Withdrawal and Injection Well Tests for Determining Hydraulic Properties of Aquifer Systems. ASTM D5092-90. Standard Practice for Design and Installation of Groundwater Monitoring Wells in Aquifers. Bureau of Reclamation, 1995. Ground Water Manual, 2nd Edition. A Water Resources Technical Publication, U.S. Department of the Interior, United States Government Printing Office, Washington, DC. Dugan, J.T., and J.M. Peckenpaugh. 1986. The Effects of Climate on Consumptive Water Use and Ground-Water Recharge in parts of Arkansas, Colorado, Kansas, Missouri, Nebraska, Oklahoma, South Dakota, and Texas. U.S. Geological Survey Water-Resources Investigations Report 85-4326, 78 pp. Kruseman, G.P. and N.A. De Ridder. 1983. Analysis and Evaluation of Pumping Test Data (2nd edn.), International Institute for Land Reclamation and Improvement. Publication 47, Wageningen, the Netherlands. 377 pp. U.S. Environmental Protection Agency, 1993. Subsurface Characterization and Monitoring Techniques: A Desk Reference Guide. EPA 625-R-93-003, 448 pp.

FIGURES

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SCS ENGINEERS

FIGURE 1b - SITE LOCATION MAPHYDROGEOLOGIC & GEOTECHNICAL REPORT

UPPER SW REGIONAL SOLID WASTE MANAGEMENT DISTRICTNASHVILLE, ARKANSAS

11219 Richardson DriveNorth Little Rock, Arkansas 72113

PH. (501) 821-4551 WEB: www.scsengineers.com

FIGURE 3 HAS BEEN REMOVED AND NOT REPLACED.

APPENDIX C – CURRENT INVESTIGATION AND BORING LOGS

AREA WELL SURVEY 2018 (Within 0.5 miles of the landfill boundaries)

Upper SW RSWMD Well Survey Inquiry

Potentially-Identified Properties Within ½ Mile of Landfill Boundaries

Upper SW RSWMDWell Survey Inquiry Locations

Location # Latitude Longitude Direction Relative to Landfill1Approximate distance from nearest landfill boundary2

(miles)

1 34.060558° -93.834603° Due S of expansion area <0.1



4 34.058492° -93.834872° Due S of expansion area 0.15

5 34.057418° -93.835190° Due S of expansion area 0.19

6 34.065859° -93.846739° Directly N of the western side of the existing landfill <0.1

7 34.066149° -93.846895° Directly N of the western side of the existing landfill <0.11 For convenience, the most straightforward direction from a particular area of the landfill property is provided.

2 Distance was measured either from the location of an offsite structure (or near the center of a cluster of offsite structures) to the nearest landfill property boundary.

Revised 9/2016

Field Groundwater Sampling Record

Date Time Volume (gallons)

Pumping Rate

(gal/min)

pH (SU)

Temp (oC)

D.O. (mg/L)

ORP (mV)

S.C (μSm)

Turbidity (NTU)

Sampling Date & Time

Notes_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Well No Date Facility .

Sampling Personnel

Locked? Casing Diameter Condition of well

DTW (from TOC) Volume H2O in well Well Depth

Other Information

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