Addendum No 3.pdf

IFB NO. 500640-FY27-02

SOLIDS PROCESSING IMPROVEMENTS (PHASE 1)

ADDENDUM NO. 3

August 31, 2026

ITEM NO. 1: BIDS DUE

The Bids Due date/time of the IFB is revised to: Tuesday, September 29, 2026 at 2:00 pm (local time).

ITEM NO. 2: INSTRUCTIONS TO BIDDERS

On page 20/44 in the Instructions to Bidders, under the heading “Use of Brand Names/Substitutions (VPPA 2.2-4315”, ADD the following sentence to the end of the paragraph:

“To be considered as a substitute, bidders and materials and equipment suppliers shall provide all information required under the Specifications to clearly show that the item meets all requirements of the Specifications.”

ITEM NO. 3: GENERAL NOTE

Several manufacturers and equipment suppliers have requested that their products be named in the Specifications as substitutes now. The Town (and its engineer) are reviewing these as received.

Substitutes can be considered during the construction phase as well--Bidders are referred to General Condition 4.6.2 regarding substitutes.

ITEM NO. 4: QUESTION(S) AND RESPONSE(S)

In response to questions from Bidders, the Town provides the responses and changes below.

1. In addendum #1, Attachment B Project Manual was reissued. However, the updated table of contents lists the following sections, but I could not find the actual sections within the project manual:

• Section 23 31 16 - Nonmetal Ducts and Duct Accessories

• Section 40 71 79.13 - Flow Switches

RESPONSE: The specification sections indicated are not needed.

CHANGE: DELETE Specification Section 23 31 16 and 40 71 79.13 from the Table of Contents in the Project Manual.

2. Reference Spec 01 14 00; paragraph 1.06 A.3.b.2). This paragraph mentions "Demolition of liquid sludge loading facility." but we find no reference in the bid document drawings. Please clarify.

RESPONSE: Demolition of the components of this facility is indicated but not called out on sheet C014. A descriptive screenshot is provided below.

CHANGE: ADD the supplemental information above to Sheet C014.

3. Reviewing the bid spec: 46 76 33 for the thickening centrifuge at Leesburg. GEA would like to be added through addendum as an or equal.

RESPONSE: The design team evaluated the proposed submission and determined that the information provided was insufficient; additional details are required to verify full compliance with the specification. Please submit a full product submittal, demonstrating conformance with the requirements in the specifications within three (3) business days of the issuance of this Addendum in order to be considered for acceptance.

4. For the crystalline waterproofing, sheet S200 shows an option to use either surface applied waterproofing or addition of a waterproofing admixture into the concrete mix. Sheet S201 only shows the option of using a waterproofing admixture. Please confirm whether waterproofing admixture is the only allowed option where called out on S201.

RESPONSE: Crystalline waterproofing admixture is the only acceptable option for the TSPS concrete slab at elevation 268.17 as stated in Note 1 on Drawing S201.

5. Drawing M101 shows the new Primary Scum line that connects to the existing 4" PSM on one end, and to the Scum Pit A on the other end. Please clarify how the line connects to the Scum Pit, as it currently shows to simply stop at the wall.

RESPONSE: Drawing M101 is hereby modified to accurately indicate the removal and replacement of the existing 4-inch PSM and dresser coupling on the suction piping serving Primary Scum Pump No. 1, leaving approximately 1’ of existing pipe cast into the scum pit wall.

CHANGE: MODIFY the PLAN on Drawing M101 per the figure below.

6. Drawing M101 calls for a ball valve (TYP) for the 2" V PVC/CPVC piping. What is the material and properties to follow for this type of ball valve?

RESPONSE: Refer to 40 05 68.13, Section 2.02.

7. Specification Section 40 05 59 requires the supply and installation of stop plates and stop logs.

Please provide stop plates schedule as there is no data in the specs and Drawings.

RESPONSE: Section 1.01 C in Specification 40 05 59 directs the Contractor to the stop plates schedule in Section 40 06 20 - Process Pipe, Valve and Gate Schedules.

8. Specification Section 40 05 59.23 requires the supply and installation of Stainless Steel Weir Gate

(Slide Gate). Please provide SST Weir Gate schedule as there is no data in the specs and Drawings

RESPONSE: Refer to section 40 06 20 for the fabricated Stainless Steel Weir Gate (Slide Gate) schedule.

9. Drawing M151 shows two 6" Knife Gate Valves before the Primary Sludge Pumps. However, on drawing I150 the instrumentation of the Primary sludge pumping station 2 does not call for knife gate valves. Please confirm if it is required to provide knife gate valves or the plug valves shown on the instrumentation drawings.

RESPONSE: Knife gate valves are required due to lay space constraints. I150 hereby modified to reflect this.

CHANGE: On Drawing I150, CHANGE the symbol for the plug valves (upstream of the diaphragm seal) to the symbol used for knife gate valves. See figure below.

10. Specification 42 22 00, Please confirm that only 1 gantry crane is required in the project (DIGESTED

SLUDGE MIXING BUILDING)

RESPONSE: Confirmed, only one gantry crane is required in the project, which will serve both the Digester Building and the Digested Sludge Mixing Building.

11. Drawing I100 shows an extra plug valve next to the existing flowmeter to be used, that is not shown on the drawings. Please confirm if we require 4 plug valves as shown on this drawing. If so, what is the diameter of the plug valve between the existing flow meter and combination vacuum and pressure relief valve.

RESPONSE: The plug valve shown on Drawing I100 immediately upstream of the flow meter is not needed.

CHANGE: DELETE the plug valve shown immediately upstream of the flow meter.

12. Plumbing Drawing P101 points out a detail at the sump pit referred to as "P-22-0219". There are no details "P-22-0219", please provide this detail.

RESPONSE: Referenced detail number is misprinted - Correct detail is included within the set.

Reference is hereby changed on sheet P101.

CHANGE: REPLACE “P-22-0219” with “P-22-0913” on drawing P101.

13. Drawing No. C-202 (Attachment E), "Typical Wall Section," depicts a concrete dome and references Specification 03500. This specification section is missing from the provided package.

Please provide Specification 03500 for our review.

RESPONSE: Revised the detail to show the corresponding specification section. Refer to Item No.

5 (Revised Drawing) below.

CHANGE: REPLACE Drawing C-202 with new Drawing C-202 dated 8/20/26.

14. Drawing S204 shows the beam length of the monorail crane (TSPS) as 44'-09", and specification

41 22 00 shows the monorail beam length as 24'. Please confirm which of these values is the correct one

RESPONSE: Monorail beam length shall be 44'-9" as shown on the Drawings. The Project Manual is hereby modified to reflect the following:

CHANGE: DELETE Specification Section 41 22 00-1.03 Crane and Hoist Schedule, TSPS Monorail Span of 24 ft.

INSERT Specification Section 41 22 00-1.03 Crane and Hoist Schedule, TSPS Monorail Span of

44.75 ft (attached hereto, red text added for emphasis)

15. DWGs S251/S252 sections A, B and C show the splitter box top of foundation slab at elevation

264.17 and when scaling the document, it indicated a 1' vertical discrepancy between the sectional drawings of A and B against sectional drawing C. Sectional drawings A and B show the flowable fill dimension at 13.5' deep while section C show a 12.5' deep. Please confirm the correct elevation of subgrade under the splitter box

RESPONSE: The bottom of concrete elevation of the TSPS foundation varies at the drawing sections indicated. For a basis of bid, the lower elevations shown in Section A on Drawing S251 and Section B on Drawing S252 shall be used for determining extents of excavation and required flowable fill.

16. Topic: Process. Reference Spec/Drawing: Spec 0114 00 Dwg M101. Reference Spec 01 14 00;

paragraph 3.03 B. Shutdown #2 "Installation of bypass fitting on PSPS1 and Dwg M101 - Primary

Sludge Pumping Station No. 1 Mechanical Plan & Sections. The bypass fittings are not shown on the drawings. Please clarify the Owner/Engineer's intended bypass configuration.

RESPONSE: The Owner/Engineer's intended bypass configuration is to discharge from newly replaced Primary Sludge Pump A through temporary piping to a connection in Primary Sludge Pump Station 2, as indicated on drawing M151.

CHANGE: ADD the following note to Drawing M101: CONTRACTOR SHALL ADD A TEE AND VALVE

WHICH SHALL SERVE AS A TEMPORARY BYPASS CONNECTION POINT. CONTRACTOR SHALL

PROVIDE TEMPORARY PIPING FROM NEW SLUDGE PUMP A TO PSPS 2 WHILE PSPS 1 IS BEING

REFURBISHED.

17. Topic: General. Is the unit price schedule in the bid form the anticipated internal structural repairs in the Digesters?

RESPONSE: The unit prices in items 3-6 of the Bid Form are the estimated structural repairs necessary for Anaerobic Digesters A-D in addition to other structures on site.

18. Topic: Process. Reference Spec/Drawing: Dwg M001 & M002. Reference Dwg. M002 - Solids

Process Flow Diagram - Proposed. A dark line is shown between the Sludge Transfer Pumps ahead of the Digested Sludge Storage Tanks, then to a new Sludge Blending Tanks with dark lines from each of the Digested Sludge Storage Tanks and finally a dark line from the Sludge Blending Tanks to "BFP". These are not shown on Dwg M001 - Solids Process Flow Diagram - Existing. Neither the Process Mechanical drawings nor the P &IDs support this additional work. Please clarify.

RESPONSE: The proposed Solids Process Flow diagram on drawing M002 will be revised in the contract package to reflect no new work associated with the sludge blending tanks or piping to and from them.

CHANGE: REPLACE the portion of Drawing M002 with snip below:

19. Topic: Process. Reference Spec/Drawing: IFB p27 of 4 4 Spec 0114 00; Table 01 14 00-8 Dwg 1501 & 1601. Reference IFB p27 of 4 4; Table 0114 00-8; and Dwg 1501& 1600. The 60-day max duration for Shutdown No. 8 is in conflict with the Milestone #1 and #2 durations. Was the 60-day duration only intended for the installation of the new MOVs? Please clarify.

RESPONSE: The referenced shutdown is for DSSTs being out of service only, for installation of and connection to process piping.

20. Topic: Civil. Reference Spec/Drawing: Spec 40 05 00-3.01 Dwg CD3. Specification 40 05 00-3.01S states all pipe shall have Type A bedding. Per Detail SD-5 and WD-2 on Drawing CD3, Class A bedding is a concrete cradle. Please clarify the bedding detail to be used for underground pipe.

RESPONSE: The Town of Leesburg Design and Construction Standard details are provided on sheet CD3 for water and sewer bedding and trenching. The typical trenching detail C-01-0106 on CD1 is for non-sewer and water installations.

21. Topic: Process. Reference Spec/Drawing: Spec 40 05 19 Spec 40 06 20. 40 05 19 Specs Epoxy Lined and Glass Lined DI Pipe. 40 06 20 Pipe Schedule shows Primary Scum PSM to be glass lined DI Pipe. Are any other pipelines epoxy lined or glass lined?

RESPONSE: Bidders shall refer to lining specifications in both specification books attached to the IFB for lining requirements.

22. Topic: Civil. Is there a geotechnical report available?

RESPONSE: Geotechnical reports have been uploaded to the bid posting site with this addendum.

Refer to Item No. 6 below.

23. Topic: Process. Reference Spec/Drawing: Spec 40 05 19. 40 05 19-2.0 488 Specifies - A307 Carbon

Steel Hex Head Bolts for DI pipe flanged joints. Are Stainless Steel bolts needed for wetted or submerged locations? If so, what grade?

RESPONSE: Stainless steel hardware will be required for submerged and wetted locations for joining ductile iron pipe flanged joints. The project manual hereby updated as follows:

CHANGE: ADD the following as section 40 05 19-2.04.B.9:

"Bolts used for flanged joints in submerged applications shall be Type 316 stainless steel and installed with dielectric isolation flange kits and anti-seize."

24. Topic: Process. Reference Spec/Drawing: Drawing M514. Note 1 on drawing M514 states that the replacement digester roof (assume cover) shall be furnished by the original manufacturer and installed by contractor. Spec section 46 73 11 2.01A states that the digester cover shall by manufactured by Ovivo, Wes Tech or approved equal. We assume the replacement covers are not limited to the initial manufacturer but can be manufactured as identified in the specifications?

RESPONSE: Correct.

CHANGE: REPLACE Note 1 on Sheet M514 in its entirety with the following:

"REPLACEMENT DIGESTER COVER SHALL BE FURNISHED AND INSTALLED IN ACCORDANCE WITH

SPECIFICATION 46 73 11.”

25. We respectfully request that Nefco be added to the list of acceptable manufacturers in Section

06 51 00 for the Fiberglass Weirs and Baffles. Attached are Nefco’s standard physical property specs to compare with what is specified.

RESPONSE: Concur.

CHANGE: In Section 06 51 00, paragraph 2.02.G, ADD NEFCO as an acceptable manufacturer.

26. We respectfully request that Westech be added to the list of acceptable manufacturers in Section 46 43 21.23 for the Circular Gravity Thickener Equipment. Westech’s drive mechanism requirements are spec’d in this section, but they are not named in 2.01 as an approved manufacturer.

RESPONSE: Concur.

CHANGE: In Section 46 43 21.23, paragraph 2.01.B, ADD Westech as an acceptable manufacturer.

27. We respectfully request that Swaby Lobeline be added to the list of acceptable manufacturers in Section 43 23 58 for the Rotary Lobe Pumps. Please note, it appears the sizing of the rotary lobe pumps could have been done using “clean water”, resulting in a lower max break horsepower for each pump. When sized with the specified % solids, viscosity, and accounting for drive losses it should require a higher break HP. Pump selection data sheets, with calculations, can be provided.

RESPONSE: The design team evaluated the proposed substitution for Swaby Lobeline pumps for section 43 23 58 and deemed the information submitted to be insufficient to determine acceptability. Please submit a full product submittal, demonstrating conformance with or exceptions take to the requirements specifications and drawings within three (3) business days of the issuance of this Addendum in order to be considered for acceptance. Also include seal water requirements. Should acceptance not be possible at this time, substitutions may be made during construction phase as stipulated in section 01 25 00. Be advised that larger footprints of Swaby Lobeline pumps may be grounds for rejection due to space constraints in the Primary Sludge Pump Stations. Rotary lobe pumps were not sized using clean water.

28. Referencing specification section 40 05 97, paragraph 2.01A, pipe bands are required every 30-inches. This spacing is unusually small. Is the offset interval intended to be 30-feet?

RESPONSE: The project manual hereby revised as follows:

CHANGE: REMOVE Specification section 40 05 97, paragraph 2.01.A, second sentence and REPLACE with the following:

"Such bands shall be 6-inches wide, neatly made by masking, and spaced at intervals of 30-feet on centers regardless of the diameter of the pipe being painted."

29. Referencing specification section 40 05 97, paragraph 2.02.B, “Identification lettering shall be located midway between color coding bands where possible”. Paragraph 2.01A requires 30-inch spacing for bands (error?), which means identification lettering is to occur every 15-inches. Paragraph 2.02.B also states lettering to be located at 15-feet intervals. Please confirm required spacing and unit of measurement for spacing (ex. feet, inches, etc.)

RESPONSE: Per the response to the previous question, no further revisions to this Specification are required as a result of this question.

30. Referencing specification section 33 24 00, paragraph 2.02, there are unusual requirements for

PVC roof drains. Please confirm asphaltic coating and cement mortar lining are erroneous and do not apply to roof drains under this project. We assume uncoated and unlined PVC roof drains to be acceptable. Please confirm.

RESPONSE: Confirmed.

CHANGE: In Specification 332400, DELETE paragraph C.

31. Referencing the Odorous Air Profile on Drawing Number C036, at the far right, between the 8”x4” reducer (STA 2+90) and 2” tapping saddle (STA 2+97) there is a callout on the pipeline stating 6” OA. Please confirm reference to 6” diameter is erroneous, or provide additional clarification.

RESPONSE: On sheet C036 the 6" diameter callout at station 2+93 should reference the 4" odorous air (OA) line. There is no 6" OA line at station 2+93. Drawings hereby updated to reflect the correct OA line diameter.

CHANGE: INCORPORATE the drawing snip below onto Drawing C036, which revises the drawing to effect the change.

32. Conflicting information is provided on the drawings and specs for yard hydrants supplied by W3 (non-potable water). Drawing Number C-033 calls for 2” pipe and references detail on Drawing Number CD4. The detail on CD4 states Type K soft copper pipe. The pipe schedule in specification section 40 06 20, states Schedule 80 PVC for diameters less than 4-inches. Specification section 40 05 81 states yard hydrants to have 4” MJ inlet. Please confirm material type and diameter for W3 line servicing the yard hydrants.

RESPONSE: The W3 line serving the yard hydrants will remain at 2", and the pipe schedule will remain the same. Detail C-33-0641 will be revised to reflect PVC pipe and fittings.

CHANGE: DELETE the first sentence of section 40 05 81-2.01.B and REPLACE it with: "The inlet shall be 2” mechanical joint and outlet shall be 1 ½” NST."

33. Referencing Drawing Number C033, the W3 line located near the southeast corner of the

Thickened Sludge Pumping Station states 1-inch. This conflicts with Drawing Number M201 that states 2-inch diameter. Please confirm W3 pipe diameter.

CHANGE: On Drawing C033, CHANGE the diameter callout of the W3 line entering the building from 1” to 2".

34. Referencing Drawing Number C033, there is a 4” SD pipeline between the Thickened Sludge Pumping Station and the manhole, PD MH F. This is also shown on Drawing Number M201, but noted as “D” pipeline type. This conflicts with information shown on the profile on Drawing Number C035, which states 6-inch pipe is the smallest diameter penetrating this manhole. Please confirm pipe diameter.

RESPONSE: The pipe diameters shown on sheet C033 for PD MH F are correct. The SD pipe entering the NW corner of PD MH F is 4". The callouts in the Plant Drain Profile on C035 have been revised to reflect the pipe designation rather than materials.

CHANGE: INCORPORATE the redlined changes in the figures below to effect the necessary changes to Drawings C033 and C035.

35. Referencing Drawing Numbers C033 and C035, inconsistent information is provided for manhole, PD MH F. Drawing Number C033 shows (3) new pipelines intersecting this manhole, in addition to (3) existing “D” pipelines. Drawing Number C035 shows a total of (5) pipes penetrating this manhole. Please clarify and reissue a corrected drawing(s).

RESPONSE: The existing pipe connection shown to the north of PD MH F is a singular 12" drain pipe. There is a total of 5 penetrations on PD MH F. Refer to the figure below.

36. Globally, throughout the yard pipe and mechanical drawings, there is inconsistent references to drain piping. Please confirm Drain, small diameter SD (likely intended as “sanitary drain” in most cases), D, and PDG are all synonymous – with the exception of the obvious stormwater RCP, which is also noted as “SD” in the pipe schedule spec section. If this is not true, please review your drawings and reissue a corrected drawing set.

RESPONSE: Please reference the Piping Designations on sheet G003. The piping designations on the Yard Piping plans have been reviewed. Civil drawings are revised per the below figure.

37. Referencing Drawing Number C032, there is a new 1” NG pipeline located at the southwest corner of the Gas Flare Station. This pipeline connects to the Digester Building, between Digesters B and D. There does not appear to be any information on where this 1” NG pipeline ties into the building. I expected to see more information on Section K of M522, but there are no references to a 1” pipe. Please clarify which drawing(s) show the continuation of the 1” NG pipeline inside the Digester Building.

RESPONSE: The 1" NG line serving the new Waste Gas Flare will be tapped from natural gas piping exterior to the digester building, downstream of the gas utility meter. Such a connection will be underground and that line will not extend inside the building. This connection is considered a “means and methods” detail and the Contractor is to make this connection in accordance with all applicable plumbing codes.

CHANGE: ADD the following callout to Drawing C032.

ITEM NO. 5: REVISED DRAWING

Attachment E – Drawing No. C-202 is hereby replaced in its entirety with the attached Drawing C-202.

ITEM NO. 6: ADDITIONAL IFB ATTACHMENTS

The following additional documents (copies attached) are hereby incorporated into IFB as additional Attachments and are provided for informational purposes only.

• Attachment F – Revised Geotechnical Report prepared by ECS Mid-Atlantic, LLC dated February 25, 2026

• Attachment G – Test Hole Inventory Report prepared by Accumark

• Attachment H – Leesburg WPCF Digester B Inspection Photographs (2011)

Bidders must take due notice and be governed accordingly. This addendum must be acknowledged as indicated in the Invitation for Bid or your bid may not be considered.

For the Town of Leesburg, David A. Christianson, CPPB, VCA Deputy Procurement Officer Town of Leesburg, Virginia Email: BidQuestions@leesburgva.gov Bid Board: http://www.leesburgva.gov/bidboard

END OF ADDENDUM NO. 3

mailto:BidQuestions@leesburgva.gov http://www.leesburgva.gov/bidboard

MAY 2026

110270036

TOWN OF LEESBURG WPCF

DIGESTER SLUDGE STORAGE TANK B REPLACEMENT

No. Revisions By Date

CJH

PGS

VS

WALL, LADDER, AND ACCESS HATCH DETAILS C-202

100%

PROGRESS

SUBMITTAL

VEL. SUBRAMANIAN

Lic. No. 047552

VEL. SUBRAMANIAN

Lic. No. 047552

VELMURUGAN

SUBRAMANIAN

5/15/2026

ECS Mid-Atlantic, LLC Revised Geotechnical Engineering Report Leesburg WPCF Solids Process Improvements

1385 Russel Branch Parkway SE Leesburg, Loudoun County, Virginia

ECS Project Number 01:33121-A

February 25, 2026

Attachment F

May 14, 2025 Revised February 25, 2026

Mr. Jeremy Hise, PE Associate Vice President Hazen and Sawyer, D.P.C.

4035 Ridge Top Road, Suite 400 Fairfax, VA 22030

Cc: Mr. Mark Mazzochete, PE; Hazen and Sawyer, D.P.C.

ECS Project No. 01:33121-A

Reference: Revised Geotechnical Engineering Report Leesburg WPCF Gravity Thickeners Russel Branch Parkway SE, Leesburg, Loudoun County, Virginia

Dear Mr. Hise:

ECS Mid-Atlantic, LLC (ECS) has completed the subsurface exploration and geotechnical engineering analyses for the above-referenced project. Our services were performed in general accordance with Proposal No. 01:71214-GP dated November 13, 2024, and the Subcontract Agreement for Professional Services 31111-098 dated March 5, 2025, and Change Order No. 1 dated August 21, 2025, and authorized on September 15, 2025. This report has been revised to include additional recommendations pertaining to the stormwater management pond and the digested sludge mixing building and presents our understanding of the geotechnical aspects of the project along with the results of the field exploration and our design and construction recommendations.

It has been our pleasure to be of service to you during the design phase of this project. We would appreciate the opportunity to remain involved during the continuation of the design phase, and we would like to provide our services during construction phase operations as well to verify the assumptions of subsurface conditions made for this report. Should you have any questions concerning the information contained in this report, or if we can be of further assistance to you, please contact us.

Respectfully submitted, ECS Mid-Atlantic, LLC

Nick C. Bass, P.G., P.E. Oscar Merida, P.E.

Senior Engineering Geologist Principal Engineer nbass@ecslimited.com omerida@ecslimited.com

Https://ecslimited365-my.sharepoint.com/personal/nbass_ecslimited_com/Documents/Desktop/Leesburg Gravity Thickeners/33121_Leesburg WPCF Gravity Thickeners.docx

2/25/2026 mailto:nbass@ecslimited.com mailto:omerida@ecslimited.com Oscar Merida

VA

Leesburg WPCF Solids Process Improvements February 25, 2026 ECS Project No. 01:33121-A Page i

TABLE OF CONTENTS

EXECUTIVE SUMMARY

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 Project Location

2.2 Proposed Construction

2.3 Regional/Site Geology

3.0 FIELD EXPLORATION AND LABORATORY TESTING

3.1 Soil Survey Mapping

3.2 Subsurface Characterization

3.3 Groundwater Observations

3.4 Laboratory Testing

4.0 DESIGN RECOMMENDATIONS

4.1 Design

4.1.1 Foundations (Pump Station and Electrical Building)

4.1.2 Mat Foundation (Gravity Thickeners)

4.2 Slabs On Grade

4.3 Below Grade Walls

4.4 Seismic Design Considerations

4.5 Stormwater Management Pond

5.0 SITE CONSTRUCTION RECOMMENDATIONS

5.1 Subgrade Preparation

5.1.1 Demolition, Stripping, And Grubbing

5.1.2 Proofrolling

5.1.3 Construction Groundwater Control

5.2 Earthwork Operations

5.2.1 Existing Man-Placed Fill

5.2.2 High Plasticity Soils

5.2.3 Weathered Rock And Rock Excavation

5.2.4 Structural Fill And Placement

5.3 Foundation And Slab Observations

5.4 Utility Installations

6.0 CLOSING

ECS Project No. 01:33121-A Page ii

APPENDICES

Appendix A – Drawings & Reports

• Site Location Diagram

• Boring Location Diagram

• Geology Mapping Diagram

• Soils Mapping Diagram

Appendix B – Field Operations

• Subsurface Exploration Procedures

• Reference Notes for Boring Logs

• Boring Logs B-01 through B-05, and SWM-01 through SWM-03

Appendix C – Laboratory Testing

• Laboratory Test Results Summary

• Plasticity Charts

• Grain Size Analysis

Appendix D – Supplemental Report Documents and Calculations

• French Drain Installation Procedure

• Zone of Influence Diagram

• Simplified Granite Weathering Profile

• Typical Dam Cross Section and Drainage Detail

ECS Project No. 01:33121-A Page 1

EXECUTIVE SUMMARY

The following summarizes the main findings of the exploration, particularly those that may have a cost impact on the planned development. Further, our principal foundation and pavement recommendations are summarized. Information gleaned from the executive summary should not be utilized in lieu of reading the entire geotechnical report.

• The recent geotechnical exploration performed for the planned development included drilling a total of eight (8) soil borings referenced as Boring B-01 through B-05 and SWM- 01 through SWM-03. The borings that did not meet their planned termination depth were advanced to auger refusal. Auger refusal was encountered at depths ranging from 12.6± feet to 23± feet below existing ground surface.

• Groundwater was not encountered during the drilling operations. The soil samples recovered from the borings advanced in the area of the stormwater management facility were evaluated for the presence of redoximorphic features indicative of a seasonal high-water table (SHWT). SHWT indicators were not observed in the recovered soil samples.

Perched groundwater may be encountered during earthwork operations at the existing fill and natural soils boundary, as well as the natural soils and weathered rock boundary.

• Existing undocumented fill material consisting of stiff Sandy Lean CLAY (CL), and loose to very dense Clayey SAND (SC) was encountered in all eight (8) borings to depths up to approximately 8.5± feet below the existing ground surface. We anticipate these fills are associated with the demolition and backfill of the roughening filters that used to occupy the area of the site.

• Although highly plastic soils are not anticipated to be a significant issue; these soils are typically encountered within areas underlain by diabase geology and can also be found within the surficial soils within areas where prolonged seasonal high-water tables are present, especially in low lying areas where water can pond for long durations. These types of soils can develop significant shrink/swell problems with variations in moisture content.

• The planned gravity thickener tank structures can be supported by mat foundations bearing on newly placed structural fill, natural soils (Stratum II) or weathered diabase rock (Stratum III). We recommend that the mat foundation be designed for a net contact stress of up to 2,500 psf.

• The planned digested sludge mixing building, thickened sludge pumping station, and electrical building can be supported on conventional shallow foundations bearing on suitable engineered fill, or natural residual soils. Based on the information obtained, an allowable bearing pressure of 3,000 pounds per square foot (psf) is recommended for design of spread footings. If higher bearing pressures are required, an allowable bearing pressure of 10,000 psf is recommended for foundations bearing on weathered rock.

In general, the site appears suitable for construction of the proposed gravity thickener tanks, pumping station, mixing building, pumping station and electrical building. The primary factors that could affect the proposed development are potential for difficult excavation through the weathered diabase rock stratum, the presence of high shrink-swell soils and existing fill material, and the potential for perched and seasonal groundwater.

ECS Project No. 01:33121-A Page 2

1.0 INTRODUCTION

The purpose of this study was to provide geotechnical information for the design of the proposed underground gravity thickener tanks, a thickened sludge pumping station, and the solids electrical building at the Leesburg Water Pollution Control Facility (WPCF). Additionally, recommendations have been provided for the proposed stormwater management pond and site pavements. The recommendations developed for this report are based on project information provided by Hazen and Sawyer, the lead design engineer. This report contains the procedures and results of our subsurface exploration and laboratory testing programs, review of existing site conditions, engineering analyses, and recommendations for the design and construction of the project.

Our services were performed in general accordance with Proposal No. 01:71214-GP dated November 13, 2024, change order no. 1 dated August 21, 2025, the Subcontract Agreement for Professional Services 31111-098 dated March 5, 2025, as well as the Subcontract Agreement Amendment No. 1 dated September 15, 2025.

The report dated January 22, 2026, has been revised herein based on review comments and various conversations with your office.

The report includes the following items.

• A brief review and description of our field and laboratory test procedures and the results of the testing conducted.

• A review of surface topographic features and site conditions.

• A review of area and site geologic conditions.

• A review of subsurface soil/rock stratigraphy with pertinent physical properties.

• Final soil exploration test boring logs as well as applicable subsurface data collected by ECS.

• Recommendations for site preparation and construction of compacted fills, including an evaluation of on-site soils for use as compacted fills and identification of potentially unsuitable soils and/or soils exhibiting excessive moisture at the time of sampling.

• Recommended foundation type(s) and pertinent design recommendations.

• Recommendations for preparation of slab subgrades during construction.

• Recommendations for seismic site classification and ground motion parameters in accordance with the Virginia Construction Code (VCC-2021) and Chapter 20 of ASCE-7-22.

• Recommendations for design and construction of drainage structures and stormwater management facilities.

• Evaluation and recommendations relative to groundwater control.

• Recommendations for design and construction of below grade walls, including lateral earth pressures, sliding resistance coefficients, and allowable bearing pressures.

• An evaluation of soil and rock excavation issues.

• Recommendations for additional studies, if warranted.

ECS Project No. 01:33121-A Page 3

2.0 PROJECT INFORMATION

2.1 PROJECT LOCATION

The project site is located at the Leesburg WPCF at 1385 Russel Branch Parkway SE in Leesburg, Loudoun County, Virginia. The site is bound by Russel Branch Parkway, to the south by Tuscarora Creek, to the east by Keystone Drive, and to the west by Battlefield Parkway. Below is a Site Location figure depicting the general location of the project based on the description above for reference.

A Site Location Diagram is provided in the appendix of this report that is “to scale” to meet Loudoun County Facilities Standards Manual (FSM) requirements.

Figure 2.1.1 Site Location

The site consists of an open grassy area. Based on our conversations with you, and a review of historic aerial imagery, the area of the proposed construction was once developed with water treatment roughening filters. The roughening filters appear to have been demolished sometime between 1995 and 2002. Since that time, numerous expansion projects have taken place at the water treatment facility, and the area appears to have been predominantly used as a laydown area for construction equipment, or had temporary storage units and vehicles in the now open space.

The site slopes toward Tuscarora Creek to the south with existing grades within the vicinity of the proposed gravity thickeners, sludge pumping station, and electrical building range from EL. 268± feet to EL. 258± feet.

NOT TO SCALE

SITE

ECS Project No. 01:33121-A Page 4

2.2 PROPOSED CONSTRUCTION

Based on the 60-percent design drawings provided by Hazen and Sawyer, dated October 2025, we understand that the proposed construction will include the construction of three (3) partially buried wastewater gravity thickener tanks, a thickened sludge pumping station, an electrical building, as well as a digested sludge mixing building. Additionally, site construction will include the construction of a stormwater management facility south of the proposed tanks and pumping station, as well as site roadways, and needed utilities.

Figure 2.2.1 Excerpt of the Overall Plan from 60-percent civil drawings (Sheet C010)

Approximate Electrical Building Location

ECS Project No. 01:33121-A Page 5

Figure 2.2.2 Excerpt of the Overall Plan from 30-percent design drawings (Sheet M200)

Figure 2.2.3 Gravity Thickener Section from 30-percent design drawings (Sheet M253)

ECS Project No. 01:33121-A Page 6

The following information details our understanding of the project and design assumptions.

Gravity Thickener Design Values

SUBJECT DESIGN INFORMATION /

EXPECTATIONS

Tank Diameter Approx. 27± feet Tank Depth Approx. 15± feet Approximate Bottom of Tank Subgrade Elevation EL. 256± Usage Wastewater Treatment Construction Cast in place concrete with stone base

Load (thickener tank filled to capacity) Up to 587± kips, Contact pressure of 1,300± psf

Thickened Sludge Pumping Station Design Values

EXPECTATIONS

Building Footprint Approx. 2,250± square feet # of Stories 1-story Usage Water treatment pump station Framing Cast in place concrete walls

Loads Column Loads of 80± kips Wall Loads of 5± kips per linear foot

Finished Floor Elevation EL. 254 feet

Solids Electrical Building Design Values

EXPECTATIONS

Building Footprint Approx. 1,200± square feet # of Stories 1-story Usage Mechanical building Framing Masonry Walls and wood framing

Loads Column Loads of 30± kips Wall Loads of 3± kips per linear foot

Finished Floor Elevation EL. 266± feet

Digested Sludge Mixing Building Design Values

EXPECTATIONS

Building Footprint Approx. 1,000± square feet # of Stories 1-story Usage Mechanical mixing building Framing Masonry Walls and wood framing Loads Wall Loads of 3± kips per linear foot Finished Floor Elevation EL. 260.83± feet

ECS Project No. 01:33121-A Page 7

Stormwater Management Pond

EXPECTATIONS

Bottom of Pond Elevation EL. 254± ft.

Top of Embankment Elevation EL. 261± ft.

Usage Extended detention pond

Outfall

Riser structure outlet to reinforced concrete pipe through embankment to existing storm sewer manhole structure.

A retaining wall is proposed at the southeast corner of the proposed stormwater management pond. The proposed wall is expected to be a cast in place concrete wall with a maximum exposed height ranging from 2 to 6 feet.

If any of the information is inaccurate, either due to misunderstanding or due to design changes that may occur later, we recommend that we be contacted to provide additional or alternate recommendations that may be required.

2.3 REGIONAL/SITE GEOLOGY

The site is located within the central portion of the Culpeper Triassic Basin which extends from the Rapidan River near Madison, Virginia to just west of Frederick, Maryland. The Culpeper Basin is a structural trough, or half-graben, which formed as a result of tensional tectonic activity during the Triassic Geologic Period (±250 million years ago). The tensional tectonic activity that formed the Culpeper Basin ultimately continued to form the current Atlantic Ocean. In the down dropped portion of the basin, a playa lake formed which was subsequently filled by erosional deposits primarily from the Blue Ridge to the west and, to a lesser extent, from the Piedmont to the east.

During sedimentation of the basin, the western border fault periodically reactivated which has led to the shallow (20˚ to 40˚) westward dip of local strata observed today. After sedimentation of the basin, border fault reactivation resulted in cyclic layers of basalt and sandstone rock along the western margin of the basin. Late in the formation of the basin, local tectonic activity occurred which caused the basin sediments to be intruded by igneous magma forming dikes, sills, and lopoliths of diabase granite bedrock.

The Geologic Map of Loudoun County, Virginia indicates that the is underlain by diabase dikes and sheets (Jdh). The residual soils that develop above diabase bedrock generally have high plasticity and high shrink-swell potential. The residual sand soils that form above the diabase bedrock generally have low plasticity and medium shrink/swell potential.

Areas underlain by diabase bedrock often form a thickened residuum or weathering profile which contains weathered diabase float boulders and a greater depth to bedrock. Diabase bedrock has the potential for spheroidal weathering which produces rounded to subrounded weathered diabase boulders within a medium dense to dense residual soil horizon overlying weathered rock and ultimately bedrock. The presence of boulders in the subsurface can give a false indication of bedrock in soil borings. Additionally, these boulders can be problematic during construction if encountered at, or near, planned subgrade elevations.

ECS Project No. 01:33121-A Page 8

3.0 FIELD EXPLORATION AND LABORATORY TESTING

Our scope of services included drilling a total of eight (8) soil borings referenced as borings B-01 through B-05, and SWM-01 through SWM-03. The borings were identified in the field by ECS personnel using a handheld Global Navigation Satellite System (GNSS) unit. The GNSS system utilized for boring stake-out is capable of providing locations to sub-meter accuracy. The approximate locations of our borings are shown on the Boring Location Diagram in Appendix A and are expected to be within 3± feet of their actual locations. Ground surface elevations noted on our recent boring logs were interpolated from the site plan prepared by Hazen and Sawyer that presents topography at a 2-foot interval.

3.1 SOIL SURVEY MAPPING

The natural soils which have resulted from the in-place physical and chemical weathering of the underlying diabase bedrock are composed primarily of residual clay and sand soils with increasing amounts of gravel with depth. The granular nature of the residual soils encountered generally increases with depth as does the percentage of rock fragments. These layers are termed weathered rock due to their rocklike structure but exhibit characteristics which qualify them as soil. The weathered rock strata often abruptly transition into relatively unweathered rock in diabase lithologies. In some instances, the profile transitions from soil to relatively unweathered rock with very little, if any, weathered rock materials. The presence of diabase boulders within the residual soil profile can give a false indication of bedrock.

In addition, we have also reviewed the available Loudoun County Natural Resource and Conservation Service (NRCS) Soils Mapping. The table below briefly presents the pertinent characteristics of the soil types mapped at this site.

According to the Loudoun County Soils Mapping, the site is generally in an area mapped with Class IV soils, corresponding to very poor potential for general site development. Engineering recommendations addressing the possible presence of soils with wetness and perched water tables are addressed in the Groundwater Observations and Construction Groundwater Control sections.

High plasticity soils are discussed in the High Plasticity Soils section.

Mapping Unit

Soil Group

Typical Terrain

Parent Rock

Problems/Limit ing Factors

Depth to Seasonal

High Water Table

(SHWT)

pH (determined to a depth of 10 ft.)

Soil Class

67B Jackland and Haymarket soils

Convex ridgetops and side slopes

Diabase and some basalt

High shrink-swell clays and seasonal perched water table

10 to 20 inches 5.9 IV

ECS Project No. 01:33121-A Page 9

3.2 SUBSURFACE CHARACTERIZATION

The soils identified in the attached boring logs are relatively consistent with the regional geology and soils mapping. The predominant soil profile appears to have been derived from the in-place physical and chemical weathering of underlying diabase bedrock materials. For the purposes of this report, weathered rock is any residual soil material having an SPT blow count of 60 blows per foot (bpf) or greater.

The table below provides generalized characterizations of the soil and rock strata encountered during our subsurface exploration. For subsurface information at a specific location, refer to the Boring Logs in Appendix B.

Subsurface Stratigraphy

Approximate Depth Range (ft) Stratum Description Ranges of

SPT(1) N-values (bpf)

0.3 feet (Surface cover) n/a up to 4± inches of topsoil N/A

0.3-8.5 feet

I Existing undocumented FILL consisting of stiff Sandy Lean CLAY (CL), and loose to very dense Clayey SAND (SC)

9 to 50/6-inches

2.0-13.5 feet II Natural Residual Soils consisting of loose to dense Clayey SAND (SC), and very stiff Sandy Lean CLAY (CL)

6 to 48

8.5- End of Boring III Very Dense Weathered Diabase Rock ≥60

Notes: (1) Standard Penetration Test

Existing fill was encountered in all eight (8) borings performed to depths ranging from 1.0± feet to 8.5± feet below existing ground surface elevations. These fill soils are assumed to be associated with the demolition of the previously constructed roughening filter in the project area. Auger refusal on assumed bedrock was encountered within all five (5) structure borings at depths ranging from 12.6± feet to 23± feet below the existing ground surface. All of the stormwater management borings were extended to their planned termination depth of 12± feet below existing ground surface elevations. Rock coring was not performed as part of our field explorations.

ECS Project No. 01:33121-A Page 10

3.3 GROUNDWATER OBSERVATIONS

Groundwater was not encountered while drilling or after removing the augers in all eight (8) soil borings. Following completion of the soil borings, temporary, machine slotted, 1.25-inch diameter, PVC pipes were installed in each location to monitor the stabilized groundwater level. Following drilling operations, the stabilized groundwater levels were measured at borings B-01 through B-04 and were all dry. Once the 24-hour water levels were measured, the temporary standpipes were removed from each location and the holes were backfilled with the drilling spoils. Stabilized water level measurements were not included in the scope for borings B-05, and SWM-01 through SWM- 03.

Although groundwater was not encountered during this exploration, the site is conducive to the presence of perched water tables, especially at the soil to bedrock interface. Perched water occurs as precipitation that enters the site, either directly or from overland flow from adjacent properties, begins to percolate through the near surface soils. Once the water percolation reaches the bedrock, which is virtually impermeable, it begins to flow at the intersection of the rock and the soil and on top of less permeable soil layers. This ground water flow continues down gradient with the water table occasionally surfacing to form springs and intermittent streams. Only in the lowest lying areas and adjacent to existing creeks is a shallow groundwater table in a continuous condition.

Otherwise, it is related to precipitation, although springs may exist in the lower lying areas for extended periods of time without recharge from precipitation. Therefore, the ground water conditions at this site are expected to be significantly influenced by surface water runoff and precipitation.

The soil samples recovered from the borings advanced in the area of the stormwater management facility were evaluated by ECS Senior Engineering Geologist, Mr. Nick Bass, for the presence of redoximorphic features indicative of a seasonal high-water table (SHWT). SHWT indicators were not observed in the recovered soil samples.

Because of the perched nature of the groundwater at this site, long term groundwater conditions can be deceptive. Although the true groundwater table can exist several hundred feet below the existing ground surface, groundwater located in streams and creeks, as a result of perched overland flow, creates the presence of an effective near surface groundwater table. Because the water is perched and flows at the interface between the soil and bedrock, water exiting fracture channels and cracks is common. Therefore, although all building excavations may appear dry at the time of completion, it is very common for fracture patterns in the rock, as a result of natural conditions or blasting to become natural pathways for ground water flow.

The highest groundwater observations are normally encountered in the late winter and early spring. Variations in the location of the long-term water table may occur as a result of changes in precipitation, evapo-transpiration, surface water runoff, and other factors not immediately apparent at the time of this exploration. The site may also be subject to severe desiccation during extended dry periods. Therefore, earthwork operations, especially in the winter and spring months, are more likely to encounter difficulties with perched conditions than those operations undertaken in the summer or fall.

ECS Project No. 01:33121-A Page 11

3.4 LABORATORY TESTING

The laboratory testing performed by ECS for this project consisted of selected tests performed on samples obtained during our field exploration operations. The following paragraphs briefly discuss the results of the completed laboratory testing program. Classification and index property tests were performed on representative soil samples obtained from the test borings in order to aid in classifying soils according to the Unified Soil Classification System and to quantify and correlate engineering properties.

An experienced geotechnical engineer visually classified each soil sample from the test borings on the basis of texture and plasticity in accordance with the Unified Soil Classification System (USCS) and ASTM D-2488 (Description and Identification of Soils-Visual/Manual Procedures). After classification, the geotechnical engineer/engineering geologist grouped the various soil types into the major zones noted on the boring logs in the Appendix. The group symbols for each soil type are indicated in parentheses preceding the soil descriptions on the boring logs. The stratification lines designating the interfaces between earth materials on the boring logs are approximate; in situ, the transitions may be gradual.

The soil samples will be retained in our laboratory for a period of 60 days, after which they will be discarded unless other instructions are received as to their disposition.

ECS Project No. 01:33121-A Page 12

4.0 DESIGN RECOMMENDATIONS

4.1 DESIGN

The following sections provide geotechnical recommendations regarding the design of the proposed gravity thickener tanks, the digested sludge mixing building, the thickened sludge pump station, and the electrical building. These include recommendations with regard to foundations, lateral earth pressures, earthwork, construction dewatering, and seismic design parameters.

4.1.1 Foundations (Pump Station, Electrical Building)

As outlined previously, the thickened sludge pump station, electrical building, and the digested sludge mixing building will be constructed with a finished floor elevations of EL. 254 feet, EL. 266 feet, and EL. 260.83 feet, respectively. This will require cuts on the order 5± feet or less to reach planned grades. Based on the structural loading information provided by Hazen and Sawyer, the project engineer, maximum column loads on the order 80± kips, and maximum wall loads of 5± kips per linear foot, should be anticipated. ECS recommends that the building be supported on a foundation system consisting of shallow spread footings.

Shallow Spread Foundations

Provided subgrades and structural fills are prepared as discussed herein, the proposed structure can be supported by conventional shallow foundations: individual column footings and continuous wall footings. The design of the foundation shall utilize the following parameters:

Table 4.1.1.1 Foundation Design

Design Parameter Column Footing Wall Footing Net Allowable Bearing Pressure (Stratum II Soil/Structural Fill) 1 3,000 psf 3,000 psf

Net Allowable Bearing Pressure (Stratum III)1 10,000 psf 10,000 psf

Minimum Width 24 inches 24 inches

Minimum Footing Embedment Depth (below slab or finished grade) 24…