Appendix C3 Final_Focused Technical Review_CC-CC_North WTP.pdf

Office of Land and Emergency Management Office of Superfund Remediation and

Technology Innovation

SUMMARY OF FINDINGS AND RECOMMENDATIONS

FOCUSED TECHNICAL REVIEW

NORTH CLEAR CREEK WATER TREATMENT PLANT

CENTRAL CITY, CLEAR CREEK SUPERFUND SITE

GILPIN AND CLEAR CREEK COUNTY, COLORADO

TECHNICAL MEMORANDUM

February 11, 2024

EPA Region 5 START V Contract Document Tracking Number 2689 www.clu-in.org/optimization | www.epa.gov/superfund/cleanup/postconstruction/optimize.htm www.epa.gov/aboutepa/about-office-land-and-emergency-management

Central City/Clear Creek Superfund Site Summary of Findings and Recommendations Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

1.0 INTRODUCTION

This document provides findings and recommendations derived from the focused technical review of historical site documents and data for the North Clear Creek Water Treatment Plant, Central City, Clear Creek Superfund Site, located in Gilpin and Clear Creek County, Colorado.

This information is provided at the direction of the U.S. Environmental Protection Agency (EPA) Office of Superfund Remediation and Technology Innovation (OSRTI) in response to a request from Region 8.

Work described herein was performed by Tetra Tech, Inc. (Tetra Tech) for EPA OSRTI under the Region 5 Superfund Technical Assessment and Response Team (START) V (contract number 68HE0519D0005, under Task Order 68HE0520F0031, Task Order Line Item Number 0001BD001). Tetra Tech performed this review as part of the National Strategy to Expand Superfund Optimization Practices from Site Assessment to Site Completion implemented by OSRTI1. The OSRTI project contact is Mr. Kirby Biggs, OSRTI’s National Optimization Program Manager.

Detailed consideration of EPA policy was not part of the scope of work for this review. This document does not impose legally binding requirements, confer legal rights, impose legal obligations, implement any statutory or regulatory provisions, or change or substitute for any statutory or regulatory provisions. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

The findings and recommendations provided in this document Table represent the technical views of the technical review team, based on the evaluation of site documents and data, meetings and discussions among EPA, the technical review team, and site team representatives.

The findings and recommendations are intended to help the site team identify opportunities for improvements in the current site remediation strategy. Recommendations do not constitute requirements for future action; rather, they are provided for consideration by EPA and other site stakeholders including the Colorado Department of Public Health and Environment

(CDPHE).

While certain recommendations may provide specific details to consider during implementation, these recommendations are not meant to supersede other, more comprehensive, planning documents such as work plans, sampling plans, and quality assurance project plans (QAPPs) nor are they intended to override applicable or relevant and appropriate requirements (ARARs). Further analysis of recommendations, including review of EPA policy, may be needed prior to implementation.

1 EPA. 2012. Memorandum: Transmittal of the National Strategy to Expand Superfund Optimization Practices from Site Assessment to Site Completion. From: James. E. Woolford, Director Office of Superfund Remediation and Technology Innovation (OSRTI). To: Superfund National Policy Managers (Regions 1 – 10). Office of Solid Waste and Emergency Response (OSWER) 9200.3-75. September 28.

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

2.0 OVERVIEW OF FOCUSED TECHNICAL REVIEW EFFORT

EPA Region 8 requested this focused technical review of the North Clear Creek Water Treatment Plant (WTP) at the Central City, Clear Creek Superfund Site. Figure 1 shows the site location and vicinity.

Figure 1: Central City/Clear Creek Superfund Site

Source: US Environmental Protection Agency (EPA) 2024. Sixth Five-Year Review Report for Central City Clear Creek Superfund Site. May 13.

EPA Region 8 requested that the review focus on:

• Potential improvements to WTP operation performance

• Cost-effectiveness of WTP operation

The technical review team (Table 1) included independent, third-party technical personnel from Tetra Tech who collaborated with representatives of EPA Headquarters, Office of Land and Emergency Management (OLEM), OSRTI, EPA Region 8, Colorado Department of Public Health and the Environment (CDPHE), and WSP, the WTP operations contractor to CDPHE.

North Clear Creek Water Treatment Plant

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

Table 1: Technical Review Team

Name Organization Title

Kirby Biggs EPA OLEM OSRTI TIFSD National Optimization Program Manager

Amanda Van Epps EPA OLEM OSRTI ARD CPCMB Environmental Engineer Matthew Spencer EPA OLEM OSRTI ARD CPCMB Physical Scientist Ashley Miller EPA OLEM OSRTI ARD CPCMB Environmental Engineer

Jody Edwards, P.G. Tetra Tech, Inc. Program Manager; Principal Hydrogeologist

Peter Rich, P.E. Tetra Tech, Inc. Environmental Engineer Rangesh Srinivasan PhD, P.E. Tetra Tech, Inc. Environmental Engineer

Jen Johnson Tetra Tech, Inc. Project Administrator / Logistics Coordinator

Notes: EPA = U.S. Environmental Protection Agency; OLEM = Office of Land and Emergency Management; OSRTI = Office of Superfund Remediation Technology Innovation; TIFSD = Technology Innovation and Field Services Division; ARD = Assessment and Remediation Division; CPCMB = Construction and Post-Construction Management Branch; P.G. = Professional Geologist, P.E.

Professional Engineer

On November 18, 2024, EPA, CDPHE, WSP, and Tetra Tech representatives completed a project Kick-Off Call to discuss site background and focused technical review goals. Table 2 lists the regulatory agency and site stakeholder personnel who contributed to the focused technical review.

Table 2: Technical Review Contributors

Name Organization Title Angela Fowler EPA Region 8 Remedial Project Manager Ian Bowan EPA Region 8 Regional Optimization Liaison Nathan Smith EPA Region 8 Hydrogeologist Mary Boardman CDPHE Unit Leader Sarah Graves, P.E. CDPHE Project Manager (Water Treatment) Kyle Sandor CDPHE Project Manager (Site) Victor Wirick, P.E WSP Project Manager Michael (Vincent) Stock WSP On Site Coordinator

Notes: EPA = U.S. Environmental Protection Agency, CDPHE= Colorado Department of Public Health and the Environment; P.E.

Professional Engineer.

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

3.0 FINDINGS AND RECOMMENDATIONS

The general observations of the focused technical review include the following:

• The WTP operation is generally effective.

• The WTP met effluent limits except for silver in one month over the past year of operations and passed whole effluent toxicity (WET) tests.

• The WTP typically treats approximately 180 gallons per minute (gpm) and has over 99 percent uptime.

• Actual flow rates are at the low end of the system design range.

• WTP operating and maintenance (O&M) costs, especially labor, are relatively high:

o The total costs not including power and water were approximately $1,169,000 in 2023 and $907,000 in 2022.

o Six full-time staff operate the WTP – four operators, one maintenance person, and one project manager. The staff generally work 10-hour shifts x 7 days per week, with 2-4 staff typically on-site each day.

o Labor costs (at approximately 75 percent of total costs not including power and water) and non-routine maintenance (at approximately 15 percent) are the largest components of total O&M costs.

o The O&M cost breakdown for Fiscal Year 22-23 was approximately:

Operator Labor - $689,000 Office Labor - $99,000 Non-routine maintenance - $185,000 Chemicals (lime, polymer, carbon dioxide [CO2]) - $56,000 Sludge disposal - $34,000 Laboratory analysis - 26,000 On-site laboratory supplies - $5,000 Subcontract maintenance - $29,000 Maintenance supplies - $29,000 Subcontract (non-maintenance) - $10,000

Table 3 provides a summary of the technical review team’s findings and recommendations.

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

Table 3:

Summary of Findings and Recommendations

Item # Findings Recommendations

1 For a WTP that started operation in 2017, it has many significant non-routine maintenance requirements. Recent examples include:

• Sludge pumping problems, including a pump replacement costing approximately $15,000.

• A major sand filter rehabilitation costing approximately $71,000, to address lime plugging, line jetting, and control issues.

The site team is adding a variable frequency drive (VFD) to the aeration blower to support lower power use.

The sand filter rehabilitation included removing and replacing media and adding new airlift modules. Operations seem to have improved since the rehabilitation effort.

The operational issues with the sand filters were associated with plant startup and the issues seem to have been resolved with the rehabilitation effort. No action is required or recommended here in the short-term.

If operational issues recur, the technical review team recommends considering replacement of the sand filter with simpler, multimedia filter vessels. This would require significant capital expenditure; hence a cost evaluation would be necessary to compare the O&M costs of the current system with the new system prior to implementation.

2 The plant currently runs unmanned at nights, with a provision to call operators in case of alarms/shutdown.

However, six full-time staff are currently used in the day shift, including weekends, to support operations – primarily for rounds, monitoring, maintenance, on-site laboratory analysis, and management. This is high for a WTP treating less than 200 gallons per minute (gpm) average flow and only two main unit operations (chemical precipitation and filtration).

The technical review team recommends:

• Potentially reducing hours by approximately 20 percent with consistent operations.

• Cutting down on sample frequency for on-site laboratory analysis since influent flow and water quality are relatively consistent.

3 Costs associated with jetting lines and cleaning tanks have been significant.

The technical review team recommends that the site team consider procuring new jetting equipment so smaller flushing activities can be performed by operations/maintenance personnel, thereby limiting

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

Item # Findings Recommendations contractor effort for off-site jetting of source lines and for tanks/equipment requiring confined space entry.

This would help lower the non-routine maintenance costs associated with contractor jetting/flushing.

For long-term operations, the technical review team recommends a review of the existing collection system infrastructure to identify potential capital upgrades for implementation to improve operations and reduce O&M costs. The upgrades would include improved access and modifications to prevent or reduce potential for plugging in the collection system.

4 Chemical costs for 2023 were relatively high, including approximately:

• $47,000 for lime

• $5,000 for polymer

• $3,000 for carbon dioxide (CO2)

The influent iron concentrations have dropped from 120 milligrams per liter (mg/L) in 2023 to 60 mg/L in 2024.

Manganese concentrations dropped from 26 mg/L in 2023 to 2.7 to 14 mg/L in 2024.

The reaction tank pH averaged approximately 10.0 standard units in 2023. The effluent water quality has been maintained consistently. For almost all metals, the effluent concentrations were nearly an order of magnitude below the discharge limit.

The technical review team recommends that the site team consider operating the high-density sludge system (HDS) at a pH setpoint of 9.0, which is acceptable for this water chemistry. Given the buffer in the effluent water quality generated by the system and improved influent chemistry, operating at a lower pH may be feasible. This could be validated with bench-testing before implementation. This change could potentially reduce the chemical costs and solids disposal costs by up to 20 percent. Per the plant operations team, replacing the existing mix tank with a smaller and more appropriately sized unit is likely required for better pH control to allow operations at this lower pH setpoint. As an alternative, the technical review team recommends reviewing the pH control loop and potentially making adjustments to reduce pH fluctuations.

5 The WTP frequently experiences issues with the lime feed system, especially the dry feeder on the silo. Lime plugs

The technical review team recommends that the site team consider switching to a delivered high density (35 percent)

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

Item # Findings Recommendations have occurred on an almost monthly basis causing the system to stop operating and requiring the operator to clear out the plug.

lime slurry given the lower plant flow rate. At the current flow, average lime slurry us would be approximately 200 gallons per day. Two 3,000-gallon tanks could provide lime slurry storage for 2 weeks each.

At approximately $400 per ton delivered, lime slurry costs would be approximately $52,000 at the current usage rate.

This option becomes especially feasible if the pH setpoint is dropped close to 9.0; this adjustment also would prevent issues such as lime plugs in the silo.

Per the plant operations team:

1 – Replacing the existing mix tank with a smaller and more appropriately sized unit is likely required for better pH control and to allow switching to a lime slurry feed system.

As an alternative, the technical review team recommends reviewing the pH control loop and potentially making adjustments to reduce pH fluctuations.

2 – An isolation valve is recommended to be installed above the mix tank.

6 The WTP experiences challenges with sludge recirculation and filter press feed line; these lines frequently plug up and have to be cleaned out and flushed. The equipment throughout the process is currently oversized and should be able to meet the required effluent water quality with the modified process.

The technical review team recommends that the site team consider switching to conventional lime neutralization with sludge recirculation in lieu of HDS if these issues persist. The clarifier underflow would be sent directly to the reaction tank to mix with the lime and influent water. On-site or off-site bench-testing could confirm the feasibility of this alternative.

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

Item # Findings Recommendations

The change to conventional lime neutralization would likely increase the sludge disposal costs marginally; however, it would potentially address most operational challenges resulting from plugging of lines and equipment. A cost evaluation is recommended to compare O&M costs for the two options at the increased treatment rates expected in the future.

Gilpin and Clear Creek County, Colorado EPA Region 5 START V Contract: Document Tracking Number 2689a

4.0 KEY DOCUMENTS REVIEWED

The following documents were the most pertinent to this focused technical review, based on the technical review team’s evaluation of the documents and data provided.

• Colorado Department of Public Health and Environment (CDPHE). 2010. Central City/Clear Creek Superfund Site, Amendment to the Operable Unit 4 Record of Decision for the Active Treatment of the National Tunnel, Gregory Incline and Gregory Gulch. April 29.

• Golder. 2018. North Clear Creek Water Treatment Plant Operations and Maintenance Plan. June 25.

• US Environmental Protection Agency (EPA). 2024. Sixth Five-Year Review Report for Central City Clear Creek Superfund Site. May 13.

• EPA. 2024. NCCWTP Optimization- Background (Presentation). May 6.

• EPA. 2017. Fifth Five-Year Review Report for Central City Clear Creek Superfund Site.

November 3.

• EPA. 2009. Fourth Five-Year Review Report for Central City Clear Creek Superfund Site.

September 29.

• EPA and CDPHE. 2004. Record of Decision Central City/Clear Creek Superfund Site Operable Unit 4. September 29.

• WSP. 2024. Annual Report- December 22, 2022 – December 21, 2023, North Clear Creek Water Treatment Plant Operations and Maintenance. June 17.

• WSP 2023-2024. Monthly Reports (January 2023 to July 2024), North Clear Creek Water Treatment Plant Operations and Maintenance. Various.