Solving Complex Environmental Problems #17 – Forensic Assessment Through Groundwater Dating Negates Remediation

BSTI was hired to assist with a former gas station which has been an open LUST site since the 1980s.  Benzene impacts were present in groundwater and in the Site’s potable well. The client’s scope of work included additional soil and groundwater characterization to be followed by remedial pilot testing and ultimately full-scale remediation. However, BSTIs evaluation of historic and new site characterization data indicated that an adjacent gas station was the probable source of the groundwater impacts. Consequently, BSTI recommended a shift in the scope of work to routine groundwater monitoring along with forensic assessment of on and offsite data to further document the offsite nature of the source.

Forensic assessment of groundwater data included fate and transport modeling as well as evaluation of petroleum constituent ratios. The origin of the potable well impacts was evaluated through the use of groundwater dating. Tracer dating of potable water using chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) indicated that potable water was a mixture of older water (pre-1945) and water which recharged around 1980.  This eliminated shallow groundwater in the vicinity of the potable well and rapid short circuiting of the potable well casing as a source of the petroleum compounds in the potable well and was further supportive of an offsite source. Monitoring subsequently documented a rapid (time scale of months) decrease in on site benzene concentrations in response to the first round of in-situ remediation conducted at the adjacent gas station.  This confirmed that petroleum impacts in groundwater at the site originated from this off-site source and that no active remediation to our client’s site was required.

For further information or to talk to BSTI’s Project Manager, contact Tripp Fischer at

Twelve Best Practices to Avoid Pipeline Construction Shutdowns and Fines by Tony Finding, BSTI’s VP and Chief Operating Officer

Tony Finding, BSTI’s VP and Chief Operating Officer authored the article “The Twelve Best Practices to Avoid Pipeline Construction Shutdowns and Fines” which was featured in the NASTT publication Trenchless for Gas Infrastructure.

In this article, Tony identifies some of the more common causes of environmental, regulatory and permit violations that can result in work delays. Please click the link below to read the entire article.

BSTI’s Green Remedy Helps Client Save Money and Avoid Permit Violations at a Wastewater Treatment Plant Spray Irrigation Field

Early Spray Field

BSTI was asked by the operator of a wastewater treatment plant to explore options that would mitigate the diminishing capacity of an existing spray irrigation field. Over time, the diminishing capacity of the spray irrigation field was creating operational issues and exposing the operator to potential violations of their Water Quality Management Permit.

The spray field is an upland deciduous forest with an area covering approximately 12 acres. Infiltration testing carried out by BSTI along with the observance of excess surface runoff indicated that hydraulic loading to the spray field had exceeded its infiltration capacity. Further, a significant population of mature trees within the spray fields died as a result of intolerance of spray field conditions; thereby exacerbating the problem. Because the logistics to simply transfer the excess wastewater to another location was problematic and cost prohibitive, BSTI focused on helping the existing spray field become more effective.

The Solution

BSTI determined that establishing additional vegetation would increase the evapotranspiration rate of the area and improve spray field hydrology.  Several species of shrub willow were identified and selected for further study due to their rapid growth, disease resistance, high yield of leaves and adaptability to a wide range of soil and moisture conditions.

An in-field pilot study indicated that the tested shrub willow species were indeed well suited for the water and soil chemistry conditions that exist in the spray field, and when established have potential average transpiration rates of approximately one inch per week, similar in magnitude to the permitted hydraulic loading rate for the spray field (1 to 3.4 inches per week). BSTI also determined that the survival of any future willow plantings would require the temporary installation of a deer fence enclosure. The enclosure will ensure that the willows planted in the spray field had time to grow to a size resistant to browsing, expected in three to five years, at which time the fence can be removed if desired.

Based on testing conducted by BSTI, gypsum demand across used portions of the spray field varied from 9 to 140 pounds per 1,000 square feet. Given these variable conditions, BSTI conducted a single application of gypsum at 40 pounds per 1,000 square feet prior to planting. This moderate dosing, in line with typical agricultural practices, will improve calcium to sodium ratios, reduce the potential for negative impacts on vegetation from sodium while minimizing the potential for excessive leaching of metals from soil, and potentially improve soil infiltration rates by improving soil structure. 

The full-scale planting of 28,000 willow “stakes” was comprised of the four shrub willow species that exhibited the greatest tolerance to spray field conditions during the pilot study. The four shrub willow species were intermixed throughout the planting zones to avoid monocultures that are more susceptible to disease and pest predation. The target willow planting density was achieved using 9 high density rows of varying lengths (6,000 stems/acre), one willow stake per 7 square feet, with open corridors around spray heads to provide clearance for spray operation and maintenance access. When fully mature these willow species will reach heights ranging between 18 to 25 feet with 2 to 3-inch calipers.

Immediately following the shrub willow planting, BSTI began monitoring willow growth and the integrity of the deer fencing on a bimonthly basis. BSTI is also monitoring spray field hydrology through three soil moisture monitoring stations to establish a baseline of current conditions for comparison to conditions once willows are fully established. 

The Benefit

The high-density willow planting was completed in the spring of 2020 and has returned early positive results. BSTI’s solution to this complex environmental problem has allowed our client to continue to provide wastewater services without fear of permit violation or the high cost of engineered alternatives. Moreover, the once-decaying vegetation in the area will be augmented with a vibrant green landscape.

To learn more about this project, contact Shaun Quinlan at or at (610) 593-5500.  Visit for more information on our capabilities.