Natural Source Zone Depletion Applications in LNAPL Site

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Natural Source Zone Depletion: Applications in LNAPL Site Management Morgan, D. *, Rousseau, M.

Natural Source Zone Depletion: Applications in LNAPL Site Management Morgan, D. *, Rousseau, M. ** & Smit, A. *** * GHD, 24 Honeysuckle Drive, Newcastle, NSW 2300, AUS * * GHD, 200 -1880 Assumption Street, Windsor, Ontario, N 8 Y 1 C 4, CAN * * * GHD, L 15, 133 Castlereagh Street, Sydney, NSW 2000, AUS Introduction In the continuing evolution of LNAPL site management toward more sustainable risk and science-based practices, the identification and quantification of LNAPL Natural Source Zone Depletion (NSZD) is increasingly playing a role in the long-term management and remediation of LNAPL sites. Setup for Dynamic Closed Chamber and CO 2 Trap Results Methodology NSZD Rates (gal LNAPL/acre/year) Max Avg Dynamic Closed Chamber – November 2016 21, 940 4, 126 CO 2 traps - November 2016 13, 424 7, 032 Dynamic Closed Chamber - December 2017^ 9, 215 1, 288 Source: API 4784 Fun facts 1. Greater than 90% of LNAPL biodegradation will be expressed in the vadose zone. Focus on groundwater parameters as the sole indicator of natural attenuation will miss most of it. 2. NSZD rates are commonly > 1, 000 gal LNAPL depleted/acre/year and can meet or exceed the LNAPL depletion/recovery rates achieved by engineered means without the remedial risk, emissions or overall environmental footprint (i. e. , more sustainable) ^ Undertaken around the LNAPL body fringe and edge of remediation well network Site information – Newcastle NSW 1. Bulk fuel terminal for > 60 years with a jet fuel release circa 2014. 2. Stable plume in shallow sandy aquifer. 3. Several potentially complete source-pathway-receptor linkages. 4. Primary driver for remediation is vapours (volatiles organic compounds and methane) below neighbouring building. 5. Active LNAPL remediation with monitoring well network has included: • Mobile multi-phase vacuum extraction (MPVE) • Manual LNAPL bailing • Active skimming • Stable plume in shallow sandy aquifer 6. In early 2017 an extraction well network and cap was installed with Actual LNAPL recovery vs. different potential NSZD rates extraction unit mobilised for remediation. Soil vapour extraction works are continuing, with MPVE planned. NSZD vs Active Remediation • NSZD-based metrics have been developed to track remedial benefit and support end-point demonstration • The confirmation of NSZD will eventually support the longterm management of the LNAPL in place • Whilst a cap has been installed over the LNAPL body, evidence of NSZD was still observed at the fringes during monitoring in December 2017 • Data collected to date suggests even low-end NSZD Methane concentrations through floor cracks above LNAPL body rate estimates have far outperformed historical and current active recovery combined • NSZD rates will need to be confirmed if adopted for longterm management under equilibrium conditions following active remediation • Strong evidence to support cessation of active remediation once remediation goals regards to vapour have been achieved. American Petroleum Institute (API) Publication #4784: Quantification of Vapor Phase-Related Natural Source Zone Depletion Processes (May 2017)