Direct push technology is a cost-effective alternative to conventional drilling for rapid site characterization of unconsolidated formations. 

Advanced Site Characterization Tools(ASCT-1)
Section 3 (Direct Sensing)
This section gives a firm overview with the rest of section 3 links to more specifics on different tools used with direct push to assist with site characterization and investigation.

Dense, Nonaqueous-Phase Liquids (DNAPLs-3)
Section 3.3.2 (Direct Push Technology and Cone Penetrometer Testing)
Good overview of DPT and CPT techniques and why they are useful in the beginnings of site characterization.

Dense, Nonaqueous-Phase Liquids (DNAPLs-4)
Section 5.2 (Characterizing DNAPLs in Unconsolidated Materials), starting page 21
Describes pros and cons of using direct push and discusses characterization in the vadose and saturated zones.

Petroleum Vapor Intrusion (PVI-1)
Appendix G. Investigation Method and Analysis Toolbox, Section G.2.3, page 183 – first bullet
Describes how to get the best results for groundwater vapor intrusion.

Petroleum Vapor Intrusion (PVI-1)
Section G.2.7 and Table G-1
Gives Groundwater sampling methods for vapor intrusion investigations.