03-20585. Los Alamos Site Office; Floodplain/Wetlands Statement of Findings for Two Monitoring Wells at Los Alamos National Laboratory, Los Alamos, NM

AGENCY:

National Nuclear Security Administration, Los Alamos Site Office, DOE.

ACTION:

Floodplain/Wetlands statement of findings.

SUMMARY:

This floodplain/wetlands statement of findings is for the installation and operation of two groundwater monitoring wells within two separate canyon floodplain locations at Los Alamos National Laboratory (LANL), Los Alamos, New Mexico. Monitoring well CdV-16-1 (i) would be located within LANL in Canon de Valle, and monitoring well R-2 would be located near the LANL boundary within the Incorporated County of Los Alamos in Pueblo Canyon. The installation process for the wells would include the placement of small cement pads around the wells, along with a gravel-covered area, and road improvements, culverts and erosion control materials and mechanisms as needed. The wells would be operated and monitored periodically after installation was completed. In accordance with 10 CFR part 1022, the Department of Energy (DOE), National Nuclear Security Administration (NNSA) Office of Los Alamos Site Operations has prepared a floodplain/wetland assessment and would perform this proposed action in a manner so as to avoid or minimize potential harm to or within the affected floodplain.

FOR FURTHER INFORMATION CONTACT:

Elizabeth Withers, U.S. Department of Energy, National Nuclear Security Administration, Los Alamos Site Office, 528 35th Street, Los Alamos, NM 87544. Telephone [phone], of facsimile [phone]; or electronic address: [e-mail].

For Further Information on General DOE Floodplain Environmental Review Requirements, contact: Carol M. Borgstrom, Director, Office of NEPA Policy and Compliance, EH-42, Department of Energy, 100 Independence Avenue, SW., Washington, DC 20585-0119. Telephone [phone] or [phone], facsimile [phone].

SUPPLEMENTARY INFORMATION:

In accordance with DOE regulations for compliance with floodplain and wetlands environmental review requirements (10 CFR part 1022), NNSA prepared a floodplain/wetland assessment for this action. The NNSA published a Notice of Floodplain and Wetlands Involvement (Volume 68, Number 139). This Notice announced that the floodplain/wetlands assessment document was available for a 15-day review period and that copies of the document could be obtained by contacting Ms. Withers at the above address or were available for review at two public DOE reading rooms in Los Alamos and Albuquerque, New Mexico. No comments were received from the Federal Register notice on the proposed floodplain action.

Project Description: The DOE is installing a network of monitoring wells around and within LANL to characterize the hydrogeological setting of the Pajarito Plateau. These monitoring wells will be installed at varying depths and used to provide information on the groundwater aquifers present and to monitor various characteristics of the aquifers over time. The two subject monitoring wells would be installed in canyon-bottom settings chosen by the New Mexico Environment Department, which is the local regulator for water quality appointed by the Environmental Protection Agency.

Alternatives: Alternative locations for the wells were not considered for this project due to the focused scope of the hydrogeological characterization of groundwater impacts from past LANL activities. The placement of wells R-2 and CdV-16-1 (i) has been mandated by the New Mexico Environment Department, hence alternate well sites were not deemed feasible. However, the proposed drilling activities would be conducted outside the stream channel and the short-term adverse construction impacts to the floodplains of Cañon de Valle and Pueblo Canyon would be mitigated to the extent practicable.

Floodplain/Wetlands Impacts: Well CdV-16-1 (i) in Cañon de Valle would be located above the top bank of the stream and would not directly impact wetlands. Erosion and sediment control best management practices (BMPs) would be installed to prevent material from entering the stream channel. Short-term, direct impacts to the floodplain above the top bank of the Cañon de Valle stream channel would occur from the construction of the well, the concrete pad, and the graveled area around the pad.

There would be short-term indirect impacts from discharge of well development water to the ground.

Wetlands are not present at well location R-2 or along the existing access road to the construction site in Pueblo Canyon. Short-term direct impacts to the stream channel would result from improving the access road stream crossings. A culvert would be installed of sufficient size to pass normal flows and would be removed at the completion of the project. In addition, direct impacts to the floodplain would occur above the top bank of the Pueblo Canyon stream channel due to construction of the well, concrete pad, and graveled area. As with the well in Cañon de Valle, there would be short-term indirect impacts from discharge of well development water to the ground.

The proposed action of installing and operating two monitoring wells does conform to applicable State or local floodplain protection standards. The pertinent Los Alamos County Code Ordinance is: 85-70 “An Ordinance Repealing Chapter 15.16 of the Los Alamos County Code Adopting a New Chapter 17.70 Pertaining to Flood Damage Prevention.”

Floodplain Mitigation: Placement of BMPs (such as silt fences, straw bales or wattles, or wooden or rock structures to slow down water runoff and run-on at cleared sites) at the construction area and post-construction reseeding and revegetation of the disturbed ground around the well pads would minimize soil disturbance and reduce or prevent the potential for soil erosion. The road design would include an appropriately designed culvert so that downstream flow and function of the floodplain will not be impeded. Indirect impacts from discharge of well development water to the ground would be minimized. The water would be sampled and the analytical results would be sent to the New Mexico Environment Department for their approval prior to discharge. Discharge would be through sprinklers or via a water truck along the access roads. No debris would be left at the work site. No vehicle maintenance or fueling within 100 feet of the floodplain would occur. Any sediment movement from the site would be short term and temporary.

Issued in Los Alamos, NM, on August 5, 2003.

Ralph E. Erickson,

Manager, Department of Energy, National Nuclear Security Administration, Los Alamos Site Office.