January 6, 2021

Mr. Erik Makus This email address is being protected from spambots. You need JavaScript enabled to view it.

RE: Proposed Permit for Denver Federal Center, General Services Administration (GSA) Dewatering and Statement of Basis

Dear Mr. Makus: Environmental Review, Inc. has reviewed the Proposed Permit for Denver Federal Center GSA Dewatering (Permit) and the Statement of Basis (SOB), and has the following comments:

1) According to Section 5.1, item 2 of the Permit, the Permittee is: “to promptly take all reasonable measures necessary to immediately reduce toxicity” if acute toxicity occurs in a laboratory test. The test results appear to lag behind the discharge of treated water. By the time the Permittee is made aware of an exceedance of acute toxicity, water has been discharged. In the event of a toxicity exceedance, what mitigation efforts can be done to correct what has already been discharged? Also, what “reasonable measures” are foreseen that will reduce toxicity? The term “reasonable” is subjective.

2) Section 2 of the SOB indicates that a flow limit has been added to this Permit. Considering this is a new requirement and that the treatment system is a mobile unit, will multiple discharge pipes be needed (with unique flow meters) in order to adequately monitor the flows from different construction sites? Furthermore, is there an accuracy requirement for instrumentation (such as a flow meter)?

Please direct your response to: This email address is being protected from spambots. You need JavaScript enabled to view it..

Sincerely,

Barb Johnson, Associate in Minnesota

Senior Reviewer

Environmental Review, Inc. a 501(c)(3) Nonprofit Public Benefit Corporation

1792 Rogers Avenue, San Jose, CA 95112, http://www.envreview.org/