HomeMy WebLinkAbout20- Revision 1 to TO - Tetra Tech - 202022021 Groundwater and Perimeter Methane Monitoring Assessment of System Performance and Effectiveness for Bozeman LandfillOTETRA TECH
REVISION 1 EVALUATION OF HYDROGEOLOGY AND REFUSE DISTRIBUTION IN
SOUTHEAST CORNER OF LANDFILL
TO TASK ORDER
2020 - 2021 GROUNDWATER AND PERIMETER METHANE MONITORING
ASSESSMENT OF SYSTEM PERFORMANCE AND EFFECTIVENESS
FOR
BOZEMAN LANDFILL
September 22, 2020
CLIENT: CONSULTANT:
The City of Bozeman Tetra Tech, Inc.
P.O. Box 1230 851 Bridger Drive, Ste 6
Bozeman, Montana 5971 1-1 230 Bozeman, MT 59718
Attention: Mr. Shawn Kohtz, PE
INTRODUCTION
Attention: Mr. Kirk A. Miller
The purpose of this task order revision is to evaluate the persistence of volatile organic
compounds in the southeast corner of the Story Mill landfill. These activities will be conducted
between September 2020 and June 30, 2021 and are directed at meeting DEQ Solid Waste
rules and the requirements of DEQ's June 6, 2014 letter requiring the City of Bozeman to
conduct a Corrective Measures Assessment and implement remedial measures. This Task
Order revises our May 26, 2020 Task Order that was approved by the City Commission in June
2020.
Based upon recommendations from the 2018/2019 Remediation System Evaluation report
(March 11, 2020), we propose to conduct a more detailed investigation of the hydrogeology in
the southeast corner of the landfill and the distribution of refuse in the area to better understand
the recent increase in volatile organic compounds in that area. This information will be used to
identify revisions to the existing landfill gas extraction and/or soil vapor extraction systems.
SCOPE OF SERVICES
This task order includes Task 500 -Evaluate hydrogeology and refuse distribution in southeast
corner of landfill. The scope of work for this task is outlined below.
Task 500 Evaluate hydrogeology and refuse distribution in southeast corner of landfill
The 2018/2019 Remedial System Evaluation Report (dated March 11, 2020) identified increases
in VOC concentrations in groundwater in well MW -17, including the appearance of methylene
chloride above Montana groundwater protection standards for the first time since a single
occurrence in 2015. This indicates the need to improve landfill gas capture in the southeast corner
of the landfill. This task will entail a brief evaluation into whether increasing air flow from nearby
LFGES wells and/or installing one or two additional landfill gas extraction wells in that area will
Tetra Tech
851 Bridger Drive, Suite 6; Bozeman, MT 59715
Tel 406.582.8780 Fax 406.582.8790 tetratech.com
Revision 1 to Task Order — 2020 to 2021 Groundwater and Methane Monitoring and Assessment
Bozeman Landfill, Bozeman, Montana
September 22, 2020
reduce VOC concentrations in groundwater in the southeast corner of the landfill. It will also
evaluate the distribution of VOC impacted groundwater in the area in order to better understand
the source of the VOC in MW -17.
Tetra Tech will evaluate the source and distribution of the VOCs with particular focus on
methylene chloride. We see two possible scenarios: landfill gasses are not being fully captured by
the LFGES (GW -20 was removed from the system to accommodate the convenience site), or
landfill gasses are migrating offsite along the eastern property boundary, contacting groundwater
which allows phase transfer of VOCs, which subsequently migrate back onto the landfill site.
Our analysis will include investigating the potential to adjust flows in nearby LFGES wells to affect
a vacuum across a larger portion of the southeast corner of the property. This analysis will be
based on the extent and thickness of refuse in the area. The possibility of installing a horizontal
LFG well in the thin areas of refuse will also be evaluated. To evaluate the possibility that VOCs
are reaching groundwater upgradient of well MW -17, an offsite, a new upgradient monitoring well
will be evaluated.
Tetra Tech will evaluate well logs from the following locations: SVE 8, -9, and -16, MW -5 and -17,
BSV-9, and -13, BLG-1 and -2 and GW -10, -15, -19, -20 and -26 to identify interbeds, changes in
lithology or other indications for preferential pathways for either landfill gas or groundwater.
Based on this analysis, Tetra Tech will identify LFG, SVE, groundwater monitoring and methane
monitoring wells where landfill gas/soil gas can be collected to map the distribution of evaluate
potential offsite migration of LFG along eastern boundary of landfill. Following sample collection
and laboratory analysis we will compile this new data with existing methylene chloride data from
SVE or LFG gas samples. Typical sources of methylene chloride in landfills will also be
researched and compared to historical information on past landfill disposal practices in this area of
the landfill and possible degradation
The data collected by this program will be used to identify if more groundwater monitoring wells
are needed in the area to better understand the source of the VOCs observed in MW -17, if flow
from existing LFG wells can be adjusted to increase the capture zone without pulling oxygen into
the cell, and if new LFG wells are needed. The use of horizontal wells in areas of thin refuse will
also be evaluated. Our recommendations will be submitted to the City, then based upon approval
from the City, we will develop a scope of work for our recommendations. This might include
developing specifications for drilling a monitoring well, modifying existing wells to act as LFG wells
or installation of additional LFG wells. Tetra Tech will assist the City with contractor management,
oversight and construction QC as needed.
7 �1:QZ91229:1Me];]T1F-1101[97:�
Tetra Tech's anticipated schedule to complete the above described activities will be the
following: Technical memorandum presenting findings and recommendations for new well
locations by January 31, 2021, final report and recommendations for remediation system
operations by June 2021.
Page 2 of 3
TETRA TECH
Revision 1 to Task Order — 2020 to 2021 Groundwater and Methane Monitoring and Assessment
Bozeman Landfill, Bozeman, Montana
September 22, 2020
COSTS
Estimated costs to complete the foregoing scope of services are $62,100. This includes the costs
for laboratory analysis and for a drilling contractor to install several new wells. Our costs will be
on a time and materials basis. A detailed cost estimate can be provided upon request.
SPECIAL CONDITIONS: Execution of this Task Order constitutes acceptance of all terms and
conditions contained in Tetra Tech's Professional Services Agreement with the City of Bozeman,
dated April 15, 2014.
CLIENT:
Citv of Bozeman
Its: �, i -y llilar�..cT
Date:
CONSULTMT:
.LM
Printed Name: Kirk A. Miller
Its: Senior Project Manager
Date: =4Z
NOTICE OF CONFIDENTIALITY This Task Order (including attachments) contains information confidential to Tetra
Tech, Inc., its subsidiaries, and subcontractors. It is intended only for City of Bozeman to consider Tetra Tech
providing professional services at the Bozeman Landfill. Any other use is prohibited, without the prior written consent
of Tetra Tech.
Page 3 of 3
TETRA TECH