W912DR18R0055_-_Attachment_N_-_OU7_biowalls.pptx

OU7 Biowalls

March 8, 2018

© Arcadis 2017 Biowall Location

Biowall 1 Biowall 2 Biowall 3 Biowall 4

FTA 2

FTA 1

Biowall Construction Details (2007) Pit 1 Biowalls 43% by volume mulch 5% leaf and grass clippings 52% sand 750 mg/kg dolomite and gypsum Pit 2 Biowalls 40% by volume mulch 5% leaf and grass clippings 3% poultry litter 52% sand 750 mg/kg dolomite and gypsum

Biowall Cross Sections

Cross sections from 2012 GW data in each section from February 2012 LWBU hydraulic conductivity testing indicates 10-4 to 10-2 cm/sec FTA Pit 2 Area FTA Pit 1 Area

Factors Limiting Biowall Effectiveness

As walls biodegrade and consolidate, permeability is lost Less TOC available to sustain ISB

Biowall Performance Review FTA Pit 1 Comparison of wells upgradient and downgradient of biowalls Upgradient Downgradient

Biowall Performance Review FTA Pit 2 Comparison of wells upgradient and downgradient of biowalls Upgradient Downgradient

Optimized Barrier Remedy

Proposed Biowall Replenishment Injection Well – Installed 2017 by ACE Proposed Injection Well – Remedy Optimization

Optimized Remedy FTA Pit 2 Area FTA Pit 1 Area

Monitoring Well Network Optimization 09 August 2018

TCE 2017

Gaps exist in source area well network New MWs to fill gaps and capture remedy performance 34 MW/CMT in LWBU 0.75-inch or smaller Consider replacing key wells with 2-inch diameter wells (e.g. MW-41, MW-48, and MW-57) Optimized network provides better data for remediation decisions

Optimized Remedy Optimized remedy complies with the current ROD.

Remedy is ISB not specifically a Biowall Significant declines in source area concentrations since 2007 Biowalls have provided remedial benefit, but are past the expected life Land surface subsidence above the walls reflects biodegradation of wall materials and the need for wall replenishment Biowall replenishment via horizontal pipe at bottom of wall likely not feasible given wall construction and surrounding geology Downgradient concentrations in FTA 1 area suggest the need for continued treatment in the shallow interval Optimize monitoring well network to enhance characterization and performance monitoring and inform remediation decisions Most feasible option to replenish biowall is DPT injections directly downgradient

Benefits of Optimized ISB Approach Focus on source area remediation will reduce remedial timeframes Optimized approach allowing remediation where needed through existing or new infrastructure More effective sources of TOC available to achieve complete dechlorination (semi-soluble or soluble donors) Increased depth and thickness of biowall will enhance restoration image2.emf image5.png image6.png image7.jpeg image8.jpeg image9.jpeg image10.jpeg image11.png image12.png image13.png image14.png image15.png image16.png image17.jpeg image18.png image1.jpeg image4.png