To: Honorable Mayor and Members of Town Council
From: Kristin Zagurski, Senior Management Analyst
Title
Resolution Approving a Variance Pursuant to Chapter 9.16.070.E of the Castle Rock Municipal Code for Soil and Groundwater Remediation at Town Hall
Body
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Executive Summary
Town Hall is located on the site of a former gas station. Though underground storage tanks were removed from the site decades ago, a 1994 environmental assessment revealed soil and groundwater hydrocarbon contamination.
The Town actively monitors the situation in accordance with Colorado Department of Labor and Employment Division of Oil and Public Safety requirements, with assistance from geotechnical and environmental consultants A.G. Wassenaar Inc. (AGW). Due to the elevated presence of petroleum compounds, AGW has recommended injecting a remediation agent into the soils and groundwater at the site this summer. Similar injections completed in 2014 were successful in significantly decreasing contamination; the hope is that this second round of injections will ultimately enable the Town to bring the issue to closure with the State.
The compounds are concentrated under the sidewalk west of Town Hall and under Wilcox Street, immediately west of the building. In order to complete the injections, a contractor must drill into the concrete sidewalk and street. Because Wilcox Street is a main thoroughfare for Downtown Castle Rock, the best time to complete this work is during non-peak traffic hours of 9 p.m. to 6 a.m. However, the Town’s noise ordinance does not typically allow such work to occur during those hours. Therefore, staff and AGW are seeking Council’s approval of a variance to the noise ordinance to allow these activities to occur at night.
Discussion
Town Hall is located on the site of a former gas station that closed in the 1970s. One 1,000-gallon and two 6,000-gallon underground storage tanks were removed from the site around 1980. A 1994 environmental assessment revealed soil and groundwater hydrocarbon contamination.
Since 2011, the Town has worked with AGW to determine the exact area and level of the contamination. Generally, the area spans from the west end of the building toward the west, across the full width of Wilcox Street (Attachment B). Recent soil and groundwater sampling has indicated a continued elevated presence of petroleum compounds - especially benzene.
To address that issue, AGW in July 2014 completed injections of BOS 200 - a combination of activated carbon, microbes, micronutrients and sulfate-reduction compounds - into the soils and groundwater in the impacted area. The compound treats hydrocarbons by trapping contaminants in an absorbent material and then treating them through bacterial activity.
The proposed work this summer is very similar to the previous work. One difference is that with this year’s work, the injections will also include gypsum, which will add sulfate to help the benzene-eating bacteria thrive. AGW will also vary the depths and locations of this year’s injections to offset them from the previous injections completed in 2014.
AGW will work with a subcontractor to bore up to 72 holes into the concrete, at depths ranging from 16 to 25 feet, to accomplish the injections. Work is anticipated to begin July 17, and to take about two weeks to complete. Due to the high traffic on Wilcox Street, AGW has proposed working hours from 9 p.m. to 6 a.m.
Town Code prohibits construction noise from occurring within residential areas between 7 p.m. and 7 a.m. weekdays and between 6 p.m. and 8 a.m. weekends. Staff is seeking a variance to the noise ordinance, to allow the work described herein to occur during otherwise restricted hours. The nearest residences to the boring area are several blocks away. Noise related to the boring is expected to be brief in duration, as the holes only will be 2 inches in diameter. No noise-related issues were experienced during the 2014 work.
The full street will not be closed at any point during the work; lane closures only will be used. Staff will communicate these work activities to the public as appropriate.
Financial Impact
The contract with AGW for the injection and monitoring work in 2016 is $187,000.
Staff Recommendation
Staff recommends approval of the proposed motion.
Proposed Motion
“I move to approve Resolution No. 2016-XX, Approving a Variance Pursuant to
Chapter 9.16.070.E of the Castle Rock Municipal Code for Soil and Groundwater Remediation at Town Hall.”
Attachments
Attachment A: Resolution
Attachment B: Map of Work Area