API PUBL 4760 VOL 1-2007

The American Petroleum Institute (API) Publication Number 4682, Free-Product Recovery of Petroleum Hydrocarbon Liquids (Charbeneau et al., 1999), provides an overview of recovery technologies for petroleum hydrocarbon liquids that are released to the subsurface environment and accumulate near the water table. The primary recovery technologies include skimmer wells that produce hydrocarbon liquids and single- and dual-pump wells that produce both water and hydrocarbon liquids. Hydrocarbon liquid recovery rates may also be enhanced by applying a vacuum pressure to the well to increase the gradient towards the well within the hydrocarbon layer. API 4682 describes two (Excel spreadsheet) models that may be used to characterize the subsurface distribution of liquid hydrocarbon (lighter-than-water nonaqueous phase liquids, LNAPL) in a single homogenous soil layer and to calculate the potential recovery rate and time using single- and dual-pump wells, and vacuum-enhanced wells.

API Publication Number 4729, Models for Design of Free-Product Recovery Systems for Petroleum Hydrocarbon Liquids (Charbeneau, 2003) describes scenario-based models for LNAPL liquid recovery using skimmer wells, water and vacuum enhanced recovery wells, and trenches. Soil capillary pressure characteristics are described using the van Genuchten (1980) capillary pressure model (soil characteristics and LNAPL distribution are described in API 4682 using the Brooks and Corey (1964) capillary pressure model). Implementation of the models through use of four separate spreadsheets is presented, based on single or two-layer heterogeneity, and on selection of relative permeability model (Burdine, 1953, or Mualem, 1976).

The present documentation supports release of the LNAPL Distribution and Recovery Model (LDRM) by API which supersedes API 4682 and API 4729 through development of a more general modeling framework with up to three soil layers. The objective of the present manuscript (Volume 1) is to provide necessary background information to support modeling assumptions and development of scenario-based models describing LNAPL liquid recovery. The scope of the material presented documents the quantitative framework on which the LNAPL distribution and recovery model is based. A more general discussion of LNAPL topics is presented in the API Interactive LNAPL Guide (2004). Huntley and Beckett (2002) discuss the effects of LNAPL recovery on dissolved plumes. Model implementation through a single executable program and model testing are described in a companion document (Volume 2).