A small water district in the Central Coast Mountains, received a letter of noncompliance from Santa Cruz County Department of Health because of concerns with the surface water treatment system and disinfection system. We provided internal and external support to the water district, including meeting with the oversight agency representative to address the concerns. To the extent possible, we enabled the district, thereby limiting their cost for compliance. As part of our services, we developed a compliance plan, identified equipment vendors, developed engineering estimates, and helped the district in decision-making. In another case, we designed a slow sand water treatment system to provide drinking water for a small number of connections. The water supply emanated from a water diversion on a small creek. Design of a slow sand filter was proposed because it could operate remotely without electrical power and is an approved filtration technology according to Title 22 of the California Code of Regulations.
A gasoline release from an underground storage tank (UST) at a rural corner store/service station in Santa Cruz County, California resulted in impacted groundwater. Of major concern was a dissolved plume of methyl tertiary butyl ether (MtBE). The MtBE plume extended over 1,200 feet and impacted a domestic supply well that provided water to several households. The MtBE plume was delineated using groundwater sampling via temporary Geoprobes and diffusive sampling. With an understanding of the impact plume, a closed-loop groundwater extraction and sparge barrier system was designed, constructed, and operated. Additionally, drinking water was temporarily supplied to households whose water supply was impacted, while a replacement water supply well was located and constructed, the distribution system was replaced, and the newly installed water supply system was activated.
Two underground storage tanks (USTs) containing diesel and gasoline were used to supply vehicles and trucks for a small agricultural hauling company in Aromas, California. Investigation at the time of tank removal revealed gasoline-impacted soil and groundwater. Using a turnkey approach, impacted soil was excavated to the extent possible and biosparging (air injected into groundwater) was implemented to initiate groundwater restoration. Semiannual groundwater monitoring and sampling was also implemented as requested by the oversight agency. Importantly, it was shown that sparging could be accomplished without vacuum extraction of soil gas due to the enhanced capacity of the unsaturated zone to degrade gasoline concentrations, thus limiting cost. Since activation of the biosparging system, gasoline and benzene concentrations in groundwater have decreased by 88 percent and 96 percent, respectively. The Central Coast Regional Water Quality Control Board is in the process of closing the environmental case.
An underground storage tank was removed from a farmhouse property in Watsonville, California. The tank was used to store gasoline. Gasoline-impacted soil and groundwater were discovered during the tank removal, and investigation commenced. Gasoline components including methyl tertiary butyl ether (MtBE) were identified in soil and groundwater samples. Investigation was completed to discern the magnitude and extent of impact; and a cleanup plan was implemented. Since MtBE-affected groundwater was a primary concern, groundwater extraction with ozone treatment was deployed for cleanup. Groundwater was extracted from the MtBE plume using an array of wells specified through groundwater modeling. Extracted groundwater was treated using ozone, and the treated mixture of groundwater, ozone, and dissolved oxygen was re-injected into a well situated within the core of the MtBE plume. After a period of operation and verification monitoring that included soil and soil gas analyses, the Central Coast Regional Water Quality Control Board closed the site.
Soil and groundwater at a residence in Woodside, California were impacted by fuel oil. The source of fuel oil was a fuel oil-fired boiler that was located in the basement of the house. Investigation was completed to discern the composition, magnitude, and extent of impact; and a cleanup plan was implemented. Soil vapor extraction was used to reduce impact concentrations in soil and groundwater, and concrete from the former location of the boiler was removed. A concrete vault that contained the remains of the boiler was discovered beneath the concrete slab. The vault also contained fuel oil that had leaked from the preheater tank. Work was done to remove the fuel oil and boiler from the basement and replace the concrete slab. A case closure letter was issued by the County regulatory agency upon completion of work.