CAVE CREEK IGA MEMO.PDF

Maricopa County
Risk Management
Thomas P. Liddy TO: Maricopa County Board of Supervisors
Director
222 N. Central Avenue FROM: Rita Neill, Environmental Program Manager
Suite 1110
Phoenix, Arizona 85004 DATE: August 30, 2016
Phone: (602) 506-7888
FAN: (602) 506-5939
liddyt@maiImaricopa.gov SUBJECT: Cave Creek Landfill IGA
The County is under a Consent Order from ADEQ to characterize and remediate
volatile organic compounds (VOC) groundwater contamination at the Cave Creek
Landfill.
We have finished characterizing the problem and are moving into the mandated
remediation phase. We have had the mandatory public meeting and have completed
the remedial action plan (RAP), all except for the location of the recharge well. We
have already started a full scale soil vapor extraction system. We are required by
ADEQ to pump and treat the contaminated water. We have just completed installing
the groundwater extraction well on Cave Creek Landfill property. We will next have
to have a way to get rid of the treated groundwater. We are pumping a large amount
of water and the only viable way to get rid of it is to reinject it into the ground. We
have looked at placing the well at the north end of the landfill property, upgradient
of the contamination and our modelling showed that this would work. However, the
City of Phoenix (COP) in their comments to the RAP was concerned that this
location could potentially cause the contamination plume to split and would not be
protective of the downgradient COP drinking water wells.
The COP approached us with the plan for the well proposed in the IGA. This
location is better both for treatment of groundwater and for protection of the COP
drinking water because it will create a hydraulic barrier downgradient of the
landfill. Estimated costs for both the onsite and the offsite recharge well are similar,
offsite is slightly higher. The long term benefits are better for the offsite well,
because if the plume split, we would incur significant additional costs to protect the
COP drinking water wells. The costs of this investigation and cleanup are being
covered by the Risk Trust as this is an environmental claim. The estimated
groundwater cleanup is $8 to $8.5 million over a period of 15 to 30 years (depending
upon results of pump tests of the new extraction well).
The COP has yet to acquire the property in question, but has identified a site. One of
the benefits of working with COP is that a large reinjection well would require
backwashing on a regular basis. We do not have sewer access on our property and
would need to connect to a COP sewer line. The COP location will have a sewer
discharge and the COP will waive discharge costs, this may actually make the offsite
location less expensive for the life of the remediation.
1

Cave Creek Landfill IGA
August 30, 2016
Page 2
In summary, we have been working with the City of Phoenix on the IGA that will
involve the City purchasing a downgradient parcel of land and the County installing
an injection well to City specifications. This will be so that the City can use the well
for injecting (banking) water credits in the future. Any additional costs to the meet
City requirements will be paid by the City. The City will also allow us to discharge
to the City sanitary sewer system for no cost when the well is
backwashed. Placement of the reinjection well downgradient of contaminant plume
retards the movement of the plume allowing easier clean up and is more protective
of City downgradient drinking water wells.