Was Mission Valley stadium site damaged by farming?

POSTED ON FEBRUARY 21, 2018 IN OUR CITY SAN DIEGO

By Chris Spengler

As San Diego debates what should be done with the former Chargers’ stadium and the lawyers debate the current status of the remediation of the of petroleum plume from the Mission Valley terminal tank farm with regulators and responsible parties, there are potentially other environmental issues that shouldn’t be overlooked.

While the site doesn’t have much in the way of historical industrial land uses, it does have a history of large-scale commercial agriculture. This agriculture was the primary use of the land prior to the current stadium being built in 1965/67.

Many people think of farms as a benign land use, the truth is far different. There are numerous sources of environmental contamination on farms, especially at the commercial scale. Such operations often had their own gasoline and diesel storage tanks (either above or below ground) to fuel their trucks and equipment. Then there’s the use of organochlorine pesticides like DDT starting in the 1940s and at least through the 1960s when the existing stadium was construction. Additionally, as we look back further in time, the burning of refuse was common practice resulting in burn pits filled with ash containing heavy metals, carcinogens and dioxins.

When the current stadium was constructed, the amount of grading at the site was significant. The southern half of the site had three stream channels of the San Diego River running through it. Soil from the northern (upper) half, where the agriculture dominated, was cut and placed into the southern (lower) half to fill-in the stream channels to provide a somewhat level site. Which means that if there were pesticides used in the former fields, they were likely placed in the former riverbed during the grading process.

Since such pesticides are persistent and insoluble in water, they are likely still there. DDT is highly toxic to fish, insects, and most aquatic fauna. In their current state, buried beneath a stadium and parking lot, they likely aren’t posing a threat to humans or the environment. However, that could change with the redevelopment of the site.

Both of the currently proposed plans, SoccerCity and the San Diego State University (SDSU) plan, both include extensive park land along the San Diego River. At least one of the plans, the SDSU plan, envisions lowering the grade in the southern portion of the site and using the soil to raise the grade on the northern half. This provides for greater protections from severe floods in the river valley and generates soil for raising the grade where the Aztec stadium and student housing are proposed. Both of these ideas are good ones. However, if the soil in the southern half contains significant concentrations of pesticides or other contaminants, then it may result in those contaminants being exposed to the environment including the river and to the public.

There are three major issues with such contaminants that must be addressed: 1) Do they pose a health risk to humans at the property, 2) Do they pose a risk to the environment, 3) Proper handling, management, and disposal of contaminated soil and/or groundwater.

1) Human Health Risk

Human health risk involves a potentially toxic contaminant, a pathway to exposure to a person, and duration of exposure (or “dose”). If one of these is eliminated, the risk is eliminated. While the petroleum plume from the tank farm has been largely remediated, the potential risk from residual contaminants in the groundwater and potentially from residual vapors in the soil.

Based on available public records, it appears that soil vapor studies for health risk have yet to be undertaken at the site. Regardless of the results of such studies, engineering controls are readily available to protect future users of the site. However, with regard the soil contaminants, whether they are pesticides, metals, burn ash by-products or something else, the reuse of that soil will need careful consideration in terms of where it is used relative to the ground surface (open space, parks, greenways) so that the public and maintenance workers are not exposed to the contaminants if their concentrations exceed appropriate risk criteria.

2) Risk to the Environment

The creation of acres of open space and parks with in the flood zone creates a need to pay particular attention to the potential for these contaminants to be present. The location of any soil placed or exposed in this area relative to the river will be important. Once the soil no longer capped by the parking lot, rain and irrigation water can mobilize the contaminants, if present, toward the river.

3) Proper Handling, Management, and Disposal/Reuse of Contaminated Soil and/or Groundwater

It’s been said that the SDSU plan will keep all the excavated soil on the site which is a smart way to save money. However, if significant concentrations of contaminants are wide-spread from the historical land uses, careful planning and management of how the soil is handled and where it is reused will be very important. Soil with concentrations of contaminants above certain levels will not be allowed for use as fill soil and will require disposal off-site at the appropriate disposal or treatment facility. Due to the petroleum plume, if dewatering is required for any part of the project, the groundwater extracted will likely require treatment prior to discharge.

A site-wide evaluation of these issues with potential contaminants and how it all fits in with the proposed grading and construction plans should be undertaken. This is the approach that was successfully implemented when I managed the assessment and remediation of the 19 city blocks of the Petco Park and East Village Redevelopment project. It began with a thorough assessment of the site and an integration of the construction plans which supported efficient and effective mitigation plans that successfully protected human health and the environment while keeping the construction on schedule.

Everyone plans for the obvious issues; the trick is to understand the hidden ones and how to best handle the unknowns. Too many times developers choose to limit the effort they put into the assessments up front. On projects of this scale, that can have a disastrous outcome to the projects budget and schedule. With a solid assessment and a well thought out plan, remediation costs can be minimized and schedules can be protected.

Below are photos of the site, both in 1964 and 1966, after grading. Photos were provided by www.historicalaerials.com

Chris Spengler of C. Spengler Strategies is an environmental professional with 26 years of remediation of brownfields and specializes in combining remediation and grading to benefit the client and the construction process. He has assessed/remediated over 2 million square feet of urban properties. With extensive experience is managing earthwork, remediation and grading, Spengler also lends his construction management expertise to owners and general contractors for sites that need remediation.

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2018-03-05T02:22:18+00:00