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April 2001

Hamilton Groundwater Flushed With Toxics

By Elena Belsky

Following the underground water table can be a challenge. Amazingly, not everyone realizes that there is more water than what surfaces in creeks, wetlands, and ponds, and that these surface waters are only a small fraction of the water table. Where and how underground water flows, depends primarily on types of bedrock, soils, sand channels, mud and the multitude of interactions of these various layers. Movement of water can be horizontal and vertical depending on the above conditions, storm water runoff, and gradient of the land. The combination of water and time are the most powerful, corrosive elements on the Earth. Together they move mountains.

When a hazardous waste landfill is placed in a marsh area with high ground water that fluctuates within the landfill, it is only a matter of time before the toxins enter the water table.

Landfill 26 on Hamilton Air Force Base (HAFB) is known to contain toxic materials such as the pesticide DDT, Polychloride biphenyls (PCBs), volatile organic chemicals (benzene, toluene, etc., aka VOCs), petroleum hydrocarbons (diesel fuel, motor oils). These are only a partial list of the many previously identified hazardous compounds in landfill 26. Mixed soils, including a number of sand channels within the landfill, can provide for easy movement of groundwater and toxic compounds. The vertical rise and fall of the water within the landfill can cause mixing of the various toxins, then the horizontal movement (the water flow is to the north-east) can transport the toxins through the groundwater table into neighboring wetlands, Pacheco Pond, Bel Marin Keys 5 property, and onto the runway area slated for wetland restoration. Ultimately, all water and runoff on Hamilton Air Force Base flows naturally, or is pumped mechanically, into San Pablo Bay.

Official documents show that there are at least five unidentified, "suspected" landfills in the marsh and wetlands areas in the northern portions of the property, around Ammo Hill, Landfill 26 and the north end of the runway (wetlands project). These have not been categorized, nor thoroughly investigated to determine potential hazardous materials. A few of these suspected landfills appear to be actually in the wetlands, which are currently swamped with water.

Toxics on Hamilton may also be unusually mobile, due to the presence of methane gas. The fluctuation of groundwater in the landfill is causing degradation of garbage, as is normal for any landfill, which in turn is producing methane gas, which again, is normal. What is not normal, or standard for a toxic landfill, is the fact that it was not designed with a venting system for methane gas production. This error is forcing the methane into the groundwater and soils, and out the sides of the landfill. Methane is more soluble in water than other toxics, and can allow other chemicals to "hitch a ride," delivering them to water that would not be otherwise accessible.

On its own, methane gas is extremely explosive even at small concentrations (5% methane is considered an explosive hazard). As it is odorless and colorless, it can therefore be a very dangerous public health and safety problem. The most recent US Army tests show concentrations of 100% in a surprising number of monitoring wells and in-ground sensor units in and around the perimeter of Landfill 26. These levels were detected within the landfill, as well as on the edge of the 150 foot buffer zone, within close proximity of the Shea Home subdivision. The Army, who are owners of the landfill site in perpetuity, must monitor for methane in a 1000 foot buffer zone around Landfill 26, which includes homes already built and sold on the neighboring development. Shea Homes has recently installed their own perimeter methane detection system; building in this area has been aborted until the Army remediates the landfill's methane problem.

Unfortunately, two migrating plumes of MTBE and benzene from the Navy's gas station site upstream, have crossed under the subdivision, through Pacheco Creek (also being diverted through sub-surface storm drains discharging into the creek), into Landfill 26, and appear to be continuing north, following the water flow. Recent maps of MTBE, benzene and methane plumes show that they have intersected paths in the landfill's south-west quadrant and perimeter area.

The Regional Water Quality Control Board mandated in a letter dated February 7, 2001, that the Army perform an immediate study on the possibility that the methane could act as a transport for the VOCs (MTBE and benzene) out of the landfill and into the groundwater. The report is due the end of March. This scenario could increase the amount of toxic substances entering the groundwater.

It seems that only the south and east areas of the landfill were tested for methane problems (the Shea Homes subdivision side). It is unknown as to what danger the north and west portions of landfill 26 pose regarding methane concentrations and contaminant migration. Water quality testing in the northern areas of the landfill, in Pacheco Pond, and in the wetlands is sparse and inconsistent at best, and completely absent at worst.

Local environmental advocates have repeatedly called for increased testing in these areas since last year. To date, they have received no response from the US Army, Navy, Army Corps of Engineers, Regional Board, EPA or the Department of Toxic Substances Control, the lead government agency.

Because of the high groundwater table and proximity to sensitive habitat surrounding HAFB, whatever toxins contaminate the site have a phenomenal potential to migrate into the adjacent wetlands, ponds, creeks and San Pablo Bay. All due diligence should be used in determining the danger to the ground and surface water quality, and immediate action should be forthcoming to correct the problems.

The sale and redevelopment of Hamilton Air Force Base has been on a "fast track" for many years. It is time for the remediation of adverse environmental impacts on water quality to be fast tracked as well.

 

 

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