Regional Long-Term Remediation Strategy

Regulatory emphasis has recently focused on the following issues  

Certainly, if protection of the Silverado aquifer is the primary objective, and the water table aquifers (i.e., Gage, Old Dune Sand, or Semi-perched aquifers) are essentially a write-off, then the intervening aquifer(s), although not used for water supply, may serve the purpose of guardian aquifers. 

Two of the larger LNAPL hydrocarbon occurrences, site No. 1 and 4 (see Ligure 12.23), formerly reinjected coproduced groundwater into generally the same hydros-tratigraphic zone from which it is withdrawn site No. 1 reinjected without treatment into the Gage aquifer, whereas site No. 4 reinjected into the Old Dune Sand aquifer. Because of the presence of dissolved hydrocarbons, notably benzene, in the coproduced water that is typically returned to the aquifer during LNAPL recovery operations, immediate application of the EPA toxicity characteristic rule may result in classification of the reinjected water as disposal of a hazardous waste. This, in turn, would terminate use of UIC Class V wells (which many of these operations currently 

Petroleum-affected soil and groundwater primarily reflect historic releases although present contributions also exist at some sites. Source elimination programs are thus currently being developed on a site-specific basis. The objectives of this program are to assure that the majority of releases are historical in nature, and to identify current releases. This program in general will include  

Cleanup strategies for hydrocarbon-affected soil will most likely be the last issue to be mandated from a regulatory perspective and certainly the most difficult technically to address. This difficulty reflects the large, deep-seated volumes of residual hydrocarbon present, and the current lack of efficient, cost-effective methodologies for in situ remediation of residual hydrocarbons in low-permeability, fine-grained soils. 

---

A case study is presented that demonstrates the importance of evaluating lithofacies distribution, or lateral and vertical heterogeneities, and depositional environment as a control on LNAPL occurrence and migration, and implementation of an effective and efficient remediation strategy. This is followed by a case history on the development of a long-term remedial strategy for LNAPL recovery and aquifer restoration from a regional perspective. 

---