What are ISV’s?

许多房地产调查和再开发项目的一个重要环境驱动因素是空气和土壤孔隙中存在污染蒸汽，也称为土壤气体。这些蒸汽来自受污染的土壤或地下水，可能从污染源传播数百英尺。州和联邦监管机构已确定，如果建筑物附近或下方存在高浓度的污染蒸汽，这些污染蒸汽可能通过建筑物楼板上的裂缝或小开口进入建筑物，并与室内空气混合。

As a result, the明尼苏达州Pollution Control Agency（MPCA）已经发布了普通空气污染物可接受水平的筛选值；官方称为入侵筛选值（ISV）。MPCA根据美国环境保护署提供的研究和计算，不断审查ISV。多个ISV可用于确定土壤气体中的污染物是否具有入侵风险。

What has changed?

MPCA最近宣布了几个isv的临时变更。特别是，乙苯（汽油的一种常见成分）的ISV变得更加严格。少数其他挥发性有机化合物（VOCs）的ISV略有增加，或变得不那么严格。ISV较高的挥发性有机化合物包括苯（汽油的另一种常见成分）、四氯乙烯（一种常见的干洗溶剂）和三氯乙烯（一种常见的工业脱脂剂）。虽然这些变化影响了少量的挥发性有机化合物，但这些挥发性有机化合物在污染场地的土壤气体中经常遇到。

Changes in ISVs can affect the necessary response, and expense, for a property owner or developer. The MPCA has increasingly recommended the installation of vapor intrusion mitigation systems in both new and existing buildings with observed concentrations of contaminants in the soil gas. Those mitigation systems range from vapor barriers beneath new buildings to electrically-powered fan systems that produce a vacuum below the floor slab intended to collect and exhaust vapors to the atmosphere above the building. The selection of the mitigation approach depends on the concentrations of contaminants, the regulatory requirements, and the owner’s risk tolerance.

So, what’s next?

The MPCA plans to release updated guidelines for responding to elevated concentrations of contaminants in soil vapor in the year. We believe those guidelines will further clarify the required actions for property owners and developers at sites with VOCs in soil gas.

Braun Intertec works with dozens of clients to address the presence of contaminated soil gas vapors on properties with new and existing buildings. We constantly interact with MPCA officials to understand their guidelines and develop best approaches to threats of vapor intrusion. Contact Bruce Schaepe for more information.